Download Background Attempt 1

Chapter_ONE_001.doc
In this document I’m trying to merge info from the multiple documents and get the ideas into the
proper sequence:
 MoreThinking.doc
 MoreSection1Stuff.txt
 AtmosphericPaper….doc (the big document)
 ChapterV0p5…doc (a previous attempt at chapter 1)
 _____others
Into one to produce the first chapter’s content for my paper.
- -- - -- - -- - --- -- - -- - -- - --- -- - -- - -- - --- -- - -- - -- - --- -- - -- - -- - --- -- - -- - -- - -Outline of presentation order for chapter 1:
MoreThinking.doc
Section 1
importance of water in the atmosphere: mention highlights.
Need to understand the atmosphere:
Hadley cell is the biggest (especially since it extends around the near the equator) circulation
region. (If there is to be any first mention of sea surface temperatures, it should be here,
especially if the Hadley cell convection persists over the night phase of each day.)(Also
important to mention the solar equator, point where most sunshine.) Transport of air and water
vapor upward in the troposphere, temperature upward is cooler towards the tropopause (by
definition) and the warm moist air expands (cooling) as it rises. the air parcel responds to
sufficient cooling by condensation of water in it (here the relative humidity vs absolute
humidity). (Condensation is a heating process--the water vapor releases latent heat to the cooler
air, or more precisely, to the hydro(hygro)scopic aerosol particles in the air (are there
hydrophobic aerosols?). Probably follows naturally from thermodynamics and the equipartition
of energy principle.)
The condensation is on the somewhat ubiquitous cloud condensation nuclei. (aside on cloud
condensation nuclei, or more later). The air has a hard time penetrating into the stratosphere
because of the thermal profile, so it turns poleward.
Sunlight energy reflected/absorbed/transmitted by clouds, so effectively enables more heating on
sunny side, allows cooling on shady/shielded side. Clouds are not water vapor--liquid or ice, but
obviously we have water vapor saturation where there are clouds. (dew point, jet vapor shroud
condenses with pressure wave).
Between the Hadley and polar cells is the Ferrell cell, which is called a secondary feature (I think
because it is) primarily dependent upon the previously described circulation (modes) and is not
driven directly.
This pretty much covers tropospheric circulation, so the next part of circulation is above the
tropopause. Now go into the Polar vortex. and of course, we'll have to go into the effects of the
earth's axis tilt. Seasonal upwelling/ downwelling and middle-atmospheric flow. (something
has to connect the two. Fill in the gaps describe Brewer-Dobson circulation (illustration?) and
re-iterate the solar equator, e.g. latitude where the Hadley cell upwelling is. (This will be useful
for looking at the HALOE monthly contours.) Just because we 'stop' here with the details does
not mean that there isn't any circulation above this layer. There is some circulation in the lower
thermosphere. At some point, the air density and circulation is overwhelmed by or dominated by
the gravitation layering effect of gases by mass and that is where the heterosphere begins. There
is also longitudinal flow, (I missed the jet stream and the biennial oscillation thing.) but I'm
looking more at variation by latitude.
Circulation from summer pole to winter pole is like part of a cell. The circulation 'return path' is
not so clearly defined as in the troposphere cells--also, air is expandable/compressible so summer
expansion/winter compression reduces the need for a return path. (Toy Slinky coils move back
and forth without going through an entire closed cycle.)
Returning to the polar vortex, (or maybe go back and insert there)
we can talk about PMCs--can we talk about PMCs without the chemistry? need chemistry for
the recombination. PMCs are a rather direct result of circulation. (PMCs are dependent upon
phase change of water from vapor to ice--tells us at what altitude temp reaches the frost point
(frost point easily verifiable from lab experiments). (Notice the thermal profile for the
mesosphere has decreasing temp with increasing altitude like the troposphere does.) Also, PMCs
as noctilucent clouds can reflect some small amount of light back down to the earth, but I
imagine the contribution to atmospheric heating would be negligible.
[[digression: (Normal PMCs are probably 'good', but thick PMCs might be scary--esp if they
block light and heat, allowing more cooling region in mesosphere and affecting the thermal
profile that we like so much. If the cooling effect is under the thick PMC clouds... maybe it
would reduce the summer upwelling and bring less water vapor to the cloud layer--a negative
feedback, which would reduce PMC growth and be good. Thomas 1991 cites gravity waves
originating from the surface as being responsible for the summer polar upwelling /winter polar
downwelling, so it isn't something easy to guess-timate...]]
Following PMCs at the summer pole, so there are PSCs at the winter pole.
(Thomas p 560 shows contours of temperature found by rocket-grenade measurements at
Barrow, AK over a year.)
This pretty much completes the circulation part of the H2O budget and brinds us closer to
looking at the H2O in the mesosphere. Next: chemistry.
--miscellaneous:
(influx of cometary water, evaporation into thermosphere and out?--water heavier than
hydrogen.)
Somewhere it would be good to mention the triple point altitude for water: about 34 km, where
pressure is about 0.006 atm.
what can we say about 34 (or 35 km?) On the HALOE temperature plots, it is the bottom of the
red zone, e.g. about 240 K (that's according to markings on the scale...
On the CH4 plots, it iw roughly where the CH4 concentration has a steeper gradient--hence
reaction, but higher near the equator and sometimes lower near the poles. Similarly for the H2O
contours .
The bottom of the NO contours is pretty well aligned with 35 km--relatively level through
equatorial latitudes and a little lower, 30 km nearer to the poles. (Hmm, PSC's and nitric acid?)
Of course, a gas has greater surface area for reaction than its liquid counterpart...
Chemistry.
chemistry and photochemistry help explain the thermal profile of the atmosphere.
There's chemistry due to the atmospheric composition (and circulation), but there are also inputs
to drive the chemistry, particularly insolation.
Heating by absorption, absorption of photochemistry within the atmosphere (absorption by
aerosols?--seems like it would be very small, but need to remember to mention aerosols as
reaction platforms.)
ozone layer and CH4 oxidation both contribute to stratospheric heating (NO too? probably
many other reactions as well that I wasn't looking for but probably many people have studied.)
Since the tropopause lets only about 3 ppmv water through to the stratosphere, there is a limit on
the amount of heat contributed to the stratosphere by condensation. (It would be useful to put in
something for relative humidity and dew point in the troposphere range--how many ppmv is a
relative humidity of 50% or 100% at STP, at the typical temp at the tropopause?
(The stratopause is where the temperature profile changes again.)
How do the ozone reactions and CH4 oxidation affect the concentration of water (CH4 oxidized
into water. Ozone reactions may bias water reactions by affecting reactant-product
concentrations. ('lots' of ozone ~20-60 km (50 is about stratopause), max about 30-35 km and
center 'follows' the sun, peak CH4 ... more CH4 equatorial... (in HALOE contours, upper parts
may conform to Brewer-Dobson circulation, but need to save that for the HALOE section.)
--need to lead into (back to) the question about the amount of water in the mesosphere.
(Meteor dust contribution of water by recombination has also been put forward as an explanation
for the amount of water in the mesosphere.)
--and lead to satellites
measurement of water in mesosphere by soundings, lidar, ... satellite ... lead to HALOE.
Atmosphere
Density profile,
Gases layer by density,
More Section 1 stuff.txt
Earth's climate depends on a complex interaction of the atmosphere's composition and processes
that can affect its composition (sources and sinks: chemistry, ...) and distribution (*both* where
they are and how they move) of its constituent components (e.g. circulation... also injection).
[Focus on water vapor in the mesosphere.]
Water vapor in the mesosphere, an upper level of the atmosphere that can be measured
(observed) directly by rocket probes and remotely by lidar and satellites (unreachable by balloon
or aircraft verify!]), is of interest to us as an indicator of the state of (that portion of) the
atmosphere and as a part of understanding Earth's climate.
Presented here is
-background information about atmosphere
(composiiton, state (thermal layers) chemistry, circulation,
other processes)
about satellite detection
-HALOE: satellite info, algorithm, visualization
-SOFIE: satellite info, algorithm, visualization
Background information:
composition and structure of Earth's atmosphere
overall the atmosphere is composed of ...
but it is not homogenously distributed.
Air circulation, due to rotation of the surface and other driving influences
(like insolation, evaporation, ), works to mix the atmospheric gases.
Mixing dominates in the first approximately 100 km of altitude, and though
it is not perfectly homogenous throughout, that region is called the
homosphere. Above that, gases tend to settle and layer according
to density due to gravity in the region called the heterosphere.
(continuing with the structure)
The atmosphere responds to incoming solar radiation (insolation), heat transfer due to chemical
reactions and phases changes of water, and heating from sunshine absorbed at the surface or on
aerosol particles suspended within the atmosphere. The resultant temperature variation, when
averaged over longitude and latitude, yields a vertical profile of the atmosphere's temperature
with respect to altitude. This profile allows us to distinguish layers of the atmosphere according
to altitude ranges where the temperature generally decreases and other rangese where it generally
increases.
[diagram, more details]
(why are the layers important?) Air behaves differently in layers where the temperature
decreases with altitude than where the temperature increases. In particular, it is the behavior of
humid air that is a key factor in the weather (and climate).
[We're in the one-dimensional vertical description, and we're getting into circulation.]
Warm air is less dense than cold air of the same composition at the same pressure (This is
readily described in the ideal gas law: PV=nRT), so it is naturally buoyed up by surrounding
cooler air. A hot air balloon flies because the heated air inside the balloon is less dense and
therefore lighter than the air outside--enough so to lift the weight of the balloon, gondola and
passengers too.
(Is water vapor a factor in hot air balloon flight?)
When a parcel of air rises, it experiences lower pressure at higher altitude and expands. By
expanding, the air cools adiabatically.
In the troposphere, the layer nearest the earth's surface, the temperature profile decreases with
height and a rising air parcel remains warmer than surrounding air 'longer' simply because it
continually moves into cooler surroundings at higher altitudes. Of course, the bouyancy would
stop when the air has cooled to the temperature of its surroundings, and if the air cools even
more, it will descend.
(air would leak out of a hot air balloon. A weather balloon would expand, but a weather balloon
would probably have lighter-than-air gases inside rather than warmed air.)
If the temperature increased with altitude instead, the warm air would have to compete against
warmer surroundings at higher altitude, so it could not be buoyed up until its own temperature is
increased somehow.
(Without additional heat from the pilot's burner the hot air balloon would then stop rising)
Discuss density of humid air vs. dry air(at 10 g/mole vs __ g/mole of 80% N2 + 20% O2 ),
buoyancy,
is buoyed up
in them
Paper Notes
The laws of physics are in effect (active) everywhere, but some phenomena are more dominant
than others at certain places and times. As scientists, we want to know what those processes are
and the response of the system (e.g. the earth’s atmosphere) to various influences.
So, the introduction starts with the basic ideas and works towards the more detailed and complex
ideas.
[Maybe outline the introduction here!]
(Geometry) The atmosphere is a gaseous envelope around the earth. The air pressure and density
are greatest nearest the earth’s surface and less at higher altitudes: If we were to pick a point at
any altitude in the atmosphere, then the pressure is caused by the weight (due to gravity) of all of
the air in a column above that altitude. Any point in the atmosphere below our first point would
have a higher pressure due to the weight of air already mentioned plus the weight of the partial
air column between the first and lower altitudes. Since the pressure is higher lower in the
atmosphere, the air is more dense and volume of the denser air, say a cubic meter, will weigh
more simply because it is denser.
Variation according to location, particularly with respect to the altitude (for atmospheric
science), is called a profile. The atmosphere’s air pressure profile basically decreases with
respect to altitude (an exponential decay).
So, our basic conceptual model of the earth and atmosphere is a sphere with an atmosphere of a
gas called ‘air’ that has pressure and density profiles that decrease exponentially with altitude.
The earth is actually more of an oblate spheroid, bigger around the equator and somewhat
flattened at the poles, and its surface is textured with mountains and valleys and so forth. Of
course, we also know from weather reports that the pressure varies from place to place at the
surface, so we know this model lacks the finer details.
I could say what an ideal model would be:
An ideal model would do more: it would describe in as much detail as we desire the state of the
air (composition and motion) at each point of interest (altitude, latitude and longitude), and
describe the system of influences and processes, and it would predict the response of the system
and how the state develops (changes) over time.
This is starting to go in the wrong direction. The natural thing to do next is to talk about the cost
of modeling pertaining to resources of memory, processing, & time and then to talk about
reduction of the model complexity and resolution detail to just those parts of interest…
I do want to talk about the state of the air, e.g. the composition and motion, maybe not in the
finest detail of altitude, latitude and longitude, but in regions of altitude and latitude ranges…
… and I want to talk about the system of influences and processes. As for the response, I want to
present the satellite measurements as an example of the system’s response. I’m not sure if I have
enough to anticipate how the state will develop over time.
[For fluid dynamics, the state of the air was given by pressure or density, velocity and energy (I
think)].
ATMOSPHERE: STATE AND SYSTEM
The state of the air in the atmosphere: condition: density, energy(temperature), composition;
location: altitude, latitude, and longitude; and motion in each direction.
WHY: Two reasons to describe the general circulation: first, it provides the transport portion of
how quantities (of gases) are replenished or ‘change’ in particular locations. Secondly, it will
help us understand what we see in the contour plots of H2O, etc. (Caution: don’t mistake the
gradient of any quantity for the direction of airflow, because various processes of source and sink
, e.g. production and consumption/destruction also play a part in the gradient of concentration of
air component (e.g. gas or aerosol).)
The system of influences and processes: gravity (buoyancy, tides), rotation (Coriolis Effect),
insolation (heating, photochemistry, reflection & shielding (greenhouse effect); affected by solar
cycle, orbit virtually circular, though summer at south pole at aphelion?), tilt (affects insolation,
tides), injection (of aerosols and gases from erosion and evaporation, volcanism (and release
from reservoirs like carbon dioxide dissolved in a lake upset by earthquake), and influx of
meteoric and cometary material). [Neglected: electrical phenomena such as due to friction,
lightning, sprites and elves, auroras, solar wind and radiation, and any other phenomena not
mentioned.]
Some processes dominate due to conditions or influences that affect the rate of the process. For
example, _____. The processes that occur in the atmosphere are basically the same that can be
made to occur in a lab, provided that expansive volume is not necessary—absorption, reflection,
transmission, etc. … What can be done in a lab? What cannot be done in a lab?
Biosphere influences: cattle methane, swamp gas, photosynthesis, decay processes.
Industrial and man-made influences: manufacturing and transportation emissions (injection),
commercial and residential energy usage, farming (cattle methane, burn-harvesting of sugar
cane), recycling and green efforts. Secondary effects, water usage, runoff, land clearing and use.
Influences by a single person alone may not be significant, but when multiplied by a significant
chunk of the 6.7 billion people on the planet through the inventions of mass production and
standards (mode of operation), daily human influences can really add up. (Hence the need for
good stewardship.) The US population about 300 million (http://www.census.gov/) is about 5%
of the world population. Example: automobiles and CO2 emissions in industrialized countries.
(Why study the atmosphere and climate? We want to understand the atmosphere and how it
responds to various influences. Why? For one thing, we influence it by emissions of industry
and transportation. If we understand how the atmosphere works, we can observe it and interpret
what we see as indicators of stability or change. Knowing how the atmosphere ‘works’,
particularly how we influence it, allows us to make better decisions and plans on how we
perform our manufacturing processes and how we make our products work—how we do the
things that we do that can affect the atmosphere--stewardship. Stewardship: we want to
maintain goodness (depends upon how we define ‘good’—ecologically, economically, or
otherwise… ) or improve—at least protect from making things worse. Economy: maximize
return vs risk…?) Prediction & planning
Response: the behavior of the state of the atmosphere, which may be steady (no change) or
vary in some way according to changes in the state or influences.
When looking at the satellite data, we need to be able to trust the measurement (this requires
understanding what the measurement is and how the measurement is made (at least by
somebody!)
Patterns and regions in the atmosphere that share characteristics, e.g. circulation patterns, layers
of similar composition (e.g. ozone layer), seasonal variation (due to tilt and orbit),
Here are some ‘working definitions’:
Climate: a steadily repeating annual cycle of behavior of the weather (e.g. state of the
atmosphere, particularly the troposphere near the surface) in a particular geographical region of
the earth. Climate change is the departure from the ‘normal’ climate for a geographical region
(e.g. the recent historical climate) over periods of years or longer, and it is most likely caused by
changes in the influences to the system (e.g. changes in the forcings—and changes to the state
that alter the influences are feedback.) Recovery is the return of the climate to normal when the
influences have returned to normal, especially natural, behaviors. (The return of plants and
animals after Mt. St. Helen’s erupted is an example of recovery, though not of climate.)
More paper notes:
Thermal profile, vertical motion of air due to temp & density, vertical motion of air due to
composition & density—specifically the water vapor content (relate ppm to relative humidity)
Thermal profile derives from effects of heating and composition, and the composition is in turn
affected by insolation.
From here go on to general circulation.
Try to avoid repeating in the text info given in the diagrams (e.g. the ones borrowed from other
references). Do call the reader’s attention to features of the contour and profile plots.
Review the abstract.
Focus on H2O in the mesosphere.
Composition of the atmosphere.
ALGORITHM & DATA Processing
Tree ring display, automatic profile ‘outlier’ filter( based on sum of standard deviations at three
checkpoint altitudes), manual file entry to exclude events (for first versions).
Assumptions/Generalizations
HALOE: Only altitude vs latitude variations, suppresses longitudinal variation. Contours are
taken over 14 years at various latitude/longitude/time of year combinations—sparse.
Assumption: which year doesn’t matter.—actually the insolation is not constant but varies
according to the solar cycl., longitude variation assumed to average out, keep latitude and time of
year.
Ideal: CAT scan,
MISCELLANY
SOFIE: daily continuous profiles but latitude varies (one track). HALOE northernmost sample
over 14 years.
First-order circulation- atmosphere turns with the earth, ‘dragged’ along by the surface and the
‘outer parts’ of the atmosphere lag behind, being pulled along by lower layers. (Discussion with
Dr. Summers)
Troposphere & trand winds, vortex, Brewer-Dobson circulation (altitude vs. latitude), JetStream,
biennial oscillation
IDEA, SOURCE/Reference
Summer Polar simmer or boil, analogy of PMCs as condensed clouds over pot of boiling water.
(Confirmed by conversation with Dr. Summers.)
Biosphere: H2O, CO2, Sulphur, Chlorine from volcanic vents.
From a TV show:
White daisies and black daisies acts as a natural temperature control on ‘DaisyWorld’. Palam
Atoll islands, Flowerpot Islands.
Aerosols: smoke (from bombs) stop sunlight, affect climate, burning of forest near attack sites.
Firestorm: winds drive smoke miles into the atmosphere  nuclear winter scenario.
National Center for Atmospheric Research
Bikini Atoll, Hydrogen Bomb  US & Russia Nuclear Test Ban
Is a quantity increasing or decreasing, and if so, by how much
Variation along longitude like Jetstream & Biennial southern oscillation are not shown
Troposphere circulation, Brewer Dobson
Observe
Recall
Recognize
Analyze
Analogize
Understand
Influence
Control
Synthesize
(Recreate/reproduce something)
-- - --- OUTLINE:
What , why, when, where, how, who…
What? Focus is on water and vapor in the middle atmosphere. Presented is background
information and visualization of data from the HALOE and SOFIE satellites.
Why? (1) It is the dissertation research topic. (2) the desire for understanding of the
atmosphere, and (3) usefulness of the understanding in planning, manufacturing, etc. …
Why go into detail about the background? (1) Response of water in mesosphere depends on
transport from other parts and sources and sinks. (2) The details will help us understand what
we will see later in the plots.
Background Attempt 1
Let’s consider the atmosphere as a system. Each part of the atmosphere (small parcel) has a
state, and there is a system of influences and processes that work together to maintain or
change the state.
[Comment: It is important to understand how the influences and processes affect the state and
how they work together to produce larger scale regional features.]
We can learn a lot about the atmosphere by considering the small scale view as if we were doing
laboratory experiments—such as do not require the large expanse of the atmosphere itself. In the
following sections, we look at the state of a parcel of atmosphere and influences and processes
that occur in the atmosphere, first as lists and then described in detail. On the larger scale, the
atmosphere has developed a structure characterized by feature regions similar in certain aspects
of state (or with patterns) or where certain influences and processes are dominant, so we’ll
introduce structure ideas too.
[This structure is like a map of the state, and where in the atmosphere certain things (such as
concentrations of particular gases) are located affects the influences. The interconnection
between the state & structure and influences & processes makes it easier to discuss them together
than separately. That’s why I’m doing lists first.]
[This is probably a good place to introduce the concept of climate.]
The atmosphere maintains a relatively steady basic structure, but there are also regular seasonal
changes over the course of a year as the earth orbits the sun. The repeating annual pattern of
seasonal changes determines the climate.
[Comment: We naturally anticipate the climate in any particular region of the earth to remain the
same from year to year, by anticipating that the influences should remain the same unless
something occurs to change them—a case of ‘if all things are equal…’, e.g. if all things
(influences) going into a system and the processes are the same, then a particular input state
should produce a particular output state, the same each time’. In actuality, the influences are not
all steady but can vary: for example, the sun’s light output changes by a small fraction over it
11-year sunspot cycle. Human influences are the most controversial because we can control
them and so affect the atmosphere’s response (supposedly! U.S. population ~300 million, world
~6.7 billion [www.census.gov]).]
These concepts of state, influences & processes, structure and climate should help us in
understanding and interpreting the satellite information presented later.
List of variables describing the state of a parcel of the atmosphere.
Composition, pressure, volume, and temperature, coordinates of position (3) and velocity (3).
Add: (orientation and ) angular momentum
Let’s start with a description of what the atmosphere is—its composition: the atmosphere is
mainly nitrogen (<80%) and oxygen (<20%) with trace amounts of various other gases like,
carbon dioxide, … , which are measured in quantities like parts per million (ppm). Also present
in the atmosphere are aerosols, solid or liquid particles, such as sea spray salts/evaporates and
desert dust lofted from the sea surface or the ground, dust and smoke (and gases) injected by
volcanic activity, and material that has fallen from space like cometary dust and water or
meteoric particles that burn into smoke and vapor and recondense as dust. Water is also present
in the atmosphere in great quantities as vapor and as ice or liquid condensed onto the rather
ubiquitous aerosols that act as cloud condensation nuclei. (more about water later…relate
absolute & relative humidity to ppm)
Though the atmosphere is relatively well mixed by circulation below about 100 km altitude,
there is some variation in its composition from place to place. Though most of the atmosphere is
invisible to the eye, an obvious example is a cloud: a patch of clear sky may have invisible water
vapor in it, but a piece of cloud contains liquid water or ice too.
Additional state variables that are used to describe a parcel of air are those in the ideal gas law,
pressure, volume, and temperature, and the coordinates of position (3) and velocity (3).
[This would naturally lead into discussion of the model exponentially decreasing pressure profile
vs. altitude, and then to the density profile and how volume of a given mass would change with
altitude. Temperature would lead to the thermal profile and named layers. I suppose that if we
push the analogy, we could continue by extending the ideas of position and velocity into regional
features (and structure) and circulation… of the atmosphere.]
List of influences and processes that occur in the atmosphere.
Gravity, tides,
chemistry (composition, recombination processes, evaporation/condensation, phases of water),
rotation, planetary and gravity wave motion, coriolis effect
insolation, (energy)
orbit & tilt,
injection,
circulation, … other?
Earth rotation, insolation, …
Example of state-influence-structure
First example of state-influence-structure: pressure & density (state) due to gravity (influence)
imposes an exponentially decreasing distristribution of pressure vs. altitude (structure). How?
[explain how with ‘the weight of the air above…’].
This is a simple one-dimensional model of a ‘column’ of atmosphere. To improve the model, we
would need to extend it to a sphere, and then also note that the earth is an oblate spheroid, bigger
around the equator and flatter near the poles. We must realize that each refinement or
adjustment would modify the model. The model is still very rough, and each time we include a
‘layer’(category) of influence and structure, we increase the complexity of the model and the
simpler model descriptions may also have to be modified. Specifically, the atmosphere’s density
profile roughly decreases exponentially with altitude, but effects of other influences make the
actual profile different. (For a better example, check for data from the model atmosphere
website
http://ccmc.gsfc.nasa.gov/modelweb/models/msis.html
http://modelweb.gsfc.nasa.gov/atmos/cospar1.html
http://ccmc.gsfc.nasa.gov/modelweb/
http://ccmc.gsfc.nasa.gov/modelweb/
MSISE-90 Model [info, ftp, RUN ]
http://ccmc.gsfc.nasa.gov/modelweb/models/msis.html
).
The state influences and processes are interconnected and produce, structural features of the
atmosphere, so now we look at first an example, density structure produced by gravity and then
Rotation, insolation, …
Attempt 1:
At this point it might be useful to imagine a stack of transparencies. I recall transparency overlay
pages in a textbook, where a basic structure is on an opaque printed page, the first transparency
overlay page shows a layer of additional (or modified) details, and subsequent transparency
pages add or modify the information further.
[The order of these items would be perfect if each item depended only on preceding items, but
the interconnected nature makes such a sequence difficult/impossible. Again, first presented is a
summary (overview) list followed by sections of detail. This list is subject to change because I
find that as I try to add information from my other files to the detail section, the
partitioning is not making as much sense!]
0. The base page would simply show the surface of the earth in profile, with altitude vs.
latitude.
1. The first transparency layer gives the air pressure and/or density profile vs altitude
 depends on gravity as the primary driving influence.
mention that there is not a clear-cut ‘top’ of the atmosphere.
2. second layer adds in the thermal profile density (temperature profile) and the named
layers
 depends on insolation, composition, chemistry & phase change of water (transfer of
latent heat).
Response to insolation & processes involving heating or heat transfer leads to thermal
profile, layers: Troposphere, stratosphere, mesosphere, thermosphere
3. the third layer shows the general circulation (the altitude vs. latitude cross-section)
 depends on rotation, wave motion, composition buoyancy (gravity), (insolation?,) as
drivers
Troposphere general circulation, Hadley cells, polar cells, Ferrel cell, trade winds; polar
planetary waves, gravity waves. Moving up in altitude polar vortex, Brewer-Dobson
circulation in stratosphere and mesosphere, mesospheric flow from summer pole to
winter pole. [Seasons affect this most, so I may have to incorporate the seasonal effects
section here or move this to near the end...]
4. aerosols & water, phase change
 distribution depends on circulation, thermal profile (for water) & precipitation,
water vapor releases latent heat upon condensation. Condensation process, triple-point
altitude, PMCs (PSCs)
5. chemistry and photochemistry
depends on composition, distribution of composition, insolation filtering (distribution
of composition)
Composition, regional composition—layering, like the ozone layer. [Other gases subject
to the same kinds of influences of photolysis and shielding would probably also tend to
form layers. I think the HALOE NO gas does this.]
-
* Where do I put the part about the insolation vs. latitude for various tilts? After
everything done without tilt!
6. Seasonal effects.  depends on where the earth is in its orbit—specifically its relative
tilt putting one hemisphere facing toward or away from the sun. (This would be the
place also to mention tides briefly, for completeness.)
All together, these produce the features in the atmosphere.
Now say how a gradient in any particular quantity (e.g. gas concentration) is not just from
circulation, but from chemistry and composition too.
Then move to satellite …
Details section
Section 0
0. The base page would simply show the surface of the earth in profile, with altitude vs.
latitude.
Section 1
1. The first transparency layer gives the air pressure and/or density profile vs altitude
 depends on gravity as the primary driving influence.
mention that there is not a clear-cut ‘top’ of the atmosphere.
Section 2: temperature profile
2. second layer adds in the thermal profile density (temperature profile) and the named
layers
 depends on insolation, composition, chemistry & phase change of water (transfer of
latent heat).
Response to insolation & processes involving heating or heat transfer leads to thermal
profile, layers: Troposphere, stratosphere, mesosphere, thermosphere
present the thermal layers model, a somewhat steady-state of the atmosphere. How does it come
to be like this? Factor in circulation and chemistry.
Section 3: circulation
3. the third layer shows the general circulation (the altitude vs. latitude cross-section)
 depends on rotation, wave motion, composition buoyancy (gravity), (insolation?,) as
drivers
Troposphere general circulation, Hadley cells, polar cells, Ferrel cell, trade winds; polar
planetary waves, gravity waves. Moving up in altitude polar vortex, Brewer-Dobson
circulation in stratosphere and mesosphere, mesospheric flow from summer pole to
winter pole. [Seasons affect this most, so I may have to incorporate the seasonal effects
section here or move this to near the end...]
[tendency for gases to layer by density (if there was no circulation...), but circulation mixes
them.]
[Starting with the rotation: equatorial easterlies, tropospheric part of the Polar vortex &
planetary waves, orography, gravity waves, coriolis effect. (Spinoff from the polar vortex of
cyclones and anticyclones (but can they also start from the equatorial region?), Hairy ball
theorem [http://en.wikipedia.org/wiki/Hairy_ball_theorem]--we might prefer that the polar
vortices be the only ....)]
Section 4: aerosols & water, phase change
4. aerosols & water, phase change
 distribution depends on circulation, thermal profile (for water) & precipitation,
water vapor releases latent heat upon condensation. Condensation process, triple-point
altitude, PMCs (PSCs)
. Water has a major role here. Insolation to the surface, evaporates water where present, and
that's pretty much everywhere on earth: 5/6 oceans, and water present in some quantity wherever
there is greenery--only deserts are extremely low in water, and even in deserts there is sometimes
water, even if rarely or in very low quantity (even cactus plants need some water). water vapor,
at 14 or 15? g/mol is lighter than dry air at 28? g/mol. and so is buoyed up by drier air. This leads
to convection. Water's latent heat of vaporization allows it also to carry energy when in vapor
phase, so the motion of water vapor also represents the transport of latent heat energy. (I heard
that water acts as a moderator of temperature--I think that was in the context of water around
islands and climate.) Of course, where there is more insolation, there can be more water
evaporated.
Section 5: chemistry and photochemistry
5. chemistry and photochemistry
depends on composition, distribution of composition, insolation filtering (distribution
of composition)
Composition, regional composition—layering, like the ozone layer. [Other gases subject
to the same kinds of influences of photolysis and shielding would probably also tend to
form layers. I think the HALOE NO gas does this.]
.
Section 6: Seasonal effects
6. * Where do I put the part about the insolation vs. latitude for various tilts? After
everything done without tilt!
Seasonal effects.  depends on where the earth is in its orbit—specifically its relative
tilt putting one hemisphere facing toward or away from the sun. (This would be the
place also to mention tides briefly, for completeness.)
.
Background Attempt 2:
List of variables describing the state of a parcel of the atmosphere(2).
Why present it this way? We are interested in structure. We want it easy to understand.
[I guess that if it sounds like a high-school textbook, that’s okay.]
State-influence(process)-structure
The amount of any particular substance in a parcel of air depends on the initial amount, plus
changes due to circulation of material (gas) in and out of the parcel and sources and sinks for
that particular material.
1st circulation in the vertical direction is driven by gravity & buoyancy due to the density of air in
relative to the surroundings, which is itself dependent on composition, pressure and temperature.
Also by airflow over surface mountains, friction.
(a)
(b)
(c)
(d)
(a) vertical motion primarily depends on gravity and buoyancy (affected by composition and
insolation)
(b) flow over surface features generates a vertical component
(c) zonal flow (along lines of latitude) mainly due to rotation
(d) meridional flow (along lines of longitude) due to …
Earth rotates, part of the vertical motion is due to flow over orography (surface features)
On the smaller scale, friction effects, as from wind on the sea generates ripples in the surface of
the water and also waves in the atmosphere which can propagate upward too. As gravity is the
restoring force for ripples in the water, so it is for this type of wave in the atmosphere and it is
called a gravity wave.
Add to state: angular momentum! Aerosol particle (size, type) distribution.
STATE of a parcel of the atmosphere.
There is a lot of air in the atmosphere so let’s take a small piece and look at it. Imagine a sample
volume of atmosphere (in the standard rectangular box shape). What can we say about this
parcel of air?
We want to be able to describe this piece of atmosphere as completely as possible, so let’s start
asking questions about and list the characteristics that describe this parcel of atmosphere. Start a
column list and give it the title ‘state’. The first thing to list is ‘volume’ because it should have
a particular volume (and it is given at the start).
Who, what, where, when, how, why…?
There’s not much to say about who, so let’s go to what. What exactly is inside this volume?
The composition of air is about __% nitrogen, __% oxygen and the remainder is a variety of
trace gases (Measurement in ppm or smaller parts). … It may also have liquid or solid particles
in it. Aerosols are particles of liquid or solid material that tend to stay suspended ‘in solution’ by
circulation in the air, but they also can clump together until they are too heavy and fall as
precipitation. If there is enough of an aerosol present in large enough particles, we can see it—
clouds are droplets of water or ice. We also can see smoke or dust clouds. Usually we can’t see
differences in the gas part of the atmosphere, but we can see different colors in the auroras and
use instruments that detect wavelengths of light we can’t see (more about this later in the section
about satellites). Usually, when we talk about composition we are referring to the gas portion of
air and we specifically mention aerosols when we want to talk about them.
Water is important because it can exists in all three phases in the atmosphere, gas, liquid and
solid. In fact, we have a special word for the water vapor content of the air—humidity (We don’t
have a special word for carbon-dioxide content…)
Temperature is another characteristic which is in our common experience, so we must add that
to our list. Perhaps thoughts about atmospheric pressure are less common to everyday life,
except in the context of weather or altitude; but, sounds that we hear are pressure waves.
The where and when questions can be answered by location and velocity (or momentum, also
angular momentum). Location can be described by altitude, latitude, and longitude, and the
velocity is how location changes over time—the wind is a good example of velocity.
Mainly we will look at the atmosphere as parcels at fixed locations, and on the larger scale, we
will be able to map out a structure particular features or regions where certain characteristics are
similar, but first let’s look at influences and processes.
Influences and processes, or the atmosphere as a (state-response) system
There are various influences and processes that work upon (within) the atmosphere to maintain
or to change its state. They are interrelated and also can be affected by the state of the
atmosphere. (This is the viewpoint that the atmosphere is a system and the state of a region is
maintained or changed as a response to influences and processes.)
Parcel viewpoint
We would expect that identical parcels of air undergoing identical influences and processes
would respond in identical ways and result in identical parcels afterwards. [This is the
fundamental concept of reproducibility in science.] We would like to be able to generalize and
say that similar parcels undergoing similar influences and processes will behave similarly, but
we must remain aware that small differences can accumulate and lead to large differences.
[Chaos theory & weather. (Maybe that pertains more to computation and prediction than to
actual phenomena?)]
In general, the state of a parcel of air at one location can differ from the state of another parcel at
a different location due to location differences in (or location dependencies of) in the various
influences and processes. A parcel of air may be changed as it moves from one location to
another.
Also, a parcel of air at a fixed location can change over time due to time variation in the various
influences and processes acting upon or within it. If the influences and processes remain steady,
then we would expect the parcel’s state to change steadily (consistently) over time or even be
maintained.
Likewise, we would expect that a single parcel that undergoes a certain series of influences and
processes and returns to its original state, will do so repeatedly under the exact same
circumstances, e.g. annual cycles of seasonal behavior.]
We can say that, for any parcel of air,
contents = initial contents + what is transported in – what is transport out + sources – sinks.
This describes how the composition characteristic changes in terms (of influences and
processes?) like circulation and chemistry, but we could write similar equations for other
characteristic state variables. (changing or being maintained due to the net effects of external
influences and internal processes
[I need to go to the big view and I need to introduce the influences and processes.]
If we were to list the major influences and ways they affect the atmosphere, our list would be
something like this:
Earth’s gravity & air buoyancy:
depends on  density & composition, particularly water vapor content
contributes to vertical motion & distribution.
Insolation → heating, affects temperature, circulation, water vapor content through
evaporation and air’s capacity for water vapor, Hadley Cell circulation, photochemistry:
spectroscopy & filtering, ozone layer
Chemistry → affects composition and distribution of gases—depends upon them too.
Earth’s rotation  airflow + airflow over surface features  circulation trade winds,
produces the polar vortex and planetary waves, airflow over the surface generates
disturbances that propagate as gravity waves through the body of the atmosphere,
Coriolis Effect.
tilt of Earth’s axis relative to the sun which changes as the earth orbits the sun.  annual
cyclic change of seasons and atmospheric structure.
Together the state and influences and processes produce regions of similar characteristics and
features that have developed into a structure of the atmosphere. Some of these features have
already been mentioned, like the ozone layer and the polar vortex. Now we will look at ways
how the atmospheric state, influences and processes work together to develop structure… and
details of the influences and processes. Also note that certain influences and processes may tend
to work against each other, but some may be more predominant than other under certain of
conditions.
[This should allow for a little flexibility in how to proceed.]
Go into the atmospheric density according to gravity.. thermal layering, etc.
We first look at a simple one-dimensional model of a ‘column’ of atmosphere over the earth. In
this model, the influence of gravity on the atmosphere in this model acts to produce a pressure
profile that decreases exponentially with increasing altitude (an exponential decay). (Variation
according to location, particularly with respect to altitude (for atmospheric science), is called a
profile.) How?
[copied from page 6 gray area above]
If we were to pick a point at any altitude in the atmosphere, then the pressure is caused by the
weight (due to gravity) of all of the air in a column above that altitude. Any point in the
atmosphere below our first point would have a higher pressure due to the weight of air already
mentioned plus the weight of the partial air column between the first and lower altitudes. Since
the pressure increases downward in the atmosphere, the air is more dense and a volume of the
denser air, say a cubic meter, will weigh more.
This pressure profile provides a basic model of the structure of pressure and density in the
atmosphere. Of course, this basic model is a simplification and only an approximation: a better
model would be the atmosphere as a three dimensional envelope of gas around a spherical earth,
but even that could be refined because the earth is more of an oblate spheroid (bigger around the
equator and flatter at the poles than a sphere).
[[found semilog plot http://en.wikipedia.org/wiki/Image:Atmosphere_model.png[[
[Added when I was trying to tie up the thermal profile and vertical things and go to latitudinal
variation: ]
Continuing, we look at some more things (influences & processes) that affect the vertical
structure of the atmosphere with regards to the thermal profile and its structure. (Maybe I
should introduces this as a where., a location influence.)
The next aspect of structure is given by the thermal profile. (See diagram.) It is an average
profile over the whole globe. (For example, the tropopause is lower near the poles and higher
near the equator. [Also, the atmosphere is fluid, so the tropopause isn’t a rigid ceiling.] ) This
profile shows the atmosphere’s response (temperature-wise) as the result of a variety of
influences and processes. The presence of a vertical temperature gradient also acts to influence
the behavior of the atmosphere.
Figure 1 standard temperature model with MSIS-E-90 local temperature
Model profile chart from ____
MSIS-E-90 overlay: data from http://ccmc.gsfc.nasa.gov/modelweb/ (choose MSISE-90 Model [info, ftp, RUN ] to
get to the menu at http://ccmc.gsfc.nasa.gov/modelweb/models/msis.html. Use the default parameters, except for
using stepsize=1: January 1, 2000, UT 1.5, geographic coordinate: 55 latitude, 45 longitude; height 100, start 0,
stop 1000, step 1; output {O, N2, O2, Total, Tn, T_exos}.
[[another chart of layer altitudes showing where familiar things are: airplane, weather balloon,
meteors, aurora. http://en.wikipedia.org/wiki/Earth%27s_atmosphere]]
The temperature gradient in the troposphere is mainly due to solar heating of the earth’s
surface. The sun shines into and through the atmosphere onto the earth: some is absorbed in the
atmosphere and heats it, and a lot is absorbed by the surface, heating it a lot. In turn, the hot
surface warms the air nearest it. (Heat energy travels through a volume by convection of
material, conduction through material, and radiation from one location to another.)
Warmed air is less dense than cool air at the same pressure (the volume increases by
heating approximately according to the ideal gas law PV=nRT), so it tends to be buoyed up by
cooler denser air which will descend according to the same principle. There is, however, another
major factor (at least one for now: water vapor, maybe more later: gravity waves) that
contributes to the upwelling: and that is water vapor content. Why?
Water’s atomic mass is 18 g/mol (2 H @ 1 g/mol + 1 O @ 16 g/mol) whereas the atomic mass of
dry air is approximately 29 g/mol ( 80% * 2 N @ 14 g/mol + 20% * 2 O @ 16 g/mol). When
water vapor mixes into a volume of air, the water vapor molecules displace about as many dry air
molecules resulting in a lighter-than-(dry)air mix. (This is supported by the standard molar
volume…at room temperature and standard pressure a mole of an ideal gas occupies 24.5 liters.)
Additionally, warmer air has a greater capacity for water vapor, so warmth enhances the
buoyancy even more. So warmed moist air will rise, and cooler drier air will descend.
As the air parcel rises, the volume expands because the air pressure is less at higher altitudes.
Without (much, if any) heat energy added, the heat energy is spread out over the larger volume,
resulting in lower temperature.
As the air cools, it becomes more likely that water vapor will condense. As the ambient air
pressure decreases for the rising parcel so too does the partial pressure of water. The decrease in
temperature decreases the saturation vapor pressure—the level of maximum water vapor the air
can hold at that temperature. When the two pressures are equal, water changes phase: from gas
to liquid or solid while cooling, and the other direction if warming.
[By noting that water’s triple point pressure is about 0.006 atmospheres(kPa) and that the
atmosphere’s pressure profile decreases with altitude, we can estimate a ‘ceiling’ at
approximately 34 km (for the liquid phase of water) above which water will be present only as
vapor or ice.]
Condensation reduces the portion of water vapor in the parcel and so acts to reduce the total
volume of the parcel. Of course, it also reduces the parcel’s buoyancy. The cyclic process due
to buoyancy is completed as the parcel we have been following becomes part of the cooler
denser air that descends towards the surface again.
[The process just described is the major process in Hadley Cell circulation, a main feature of the
general atmospheric circulation pattern. (When I get to the point of ‘mapping out’ circulation
features, I should be able to just say the Hadley cell is driven by solar heating and buoyancy and
describe the location features of the Hadley cell.)]
[Continue upwards along with the thermal profile and layers. The other option is to remain in
the troposphere and discuss circulation.]
The tropopause is at the top of the troposphere where the temperature profile stops (pauses)
decreasing. It is the thin named boundary between the troposphere where the temperature profile
decreases and the stratosphere where the temperature profile increases with altitude.
Though the previous discussion was about buoyancy in the troposphere, buoyancy is still an
influence in higher levels in the atmosphere. However, in the stratosphere, a parcel of air has to
compete against the warmer air that is higher; so, it cannot rise as easily as it did in the
troposphere. Therefore buoyancy processes are not as dominant in the stratosphere as they are in
the troposphere.
So, what causes the temperature gradient in the stratosphere? (Already mentioned latent heat
transport by circulation of water vapor and phase change.) We look to chemistry (, insolation,
and) photochemistry for examples of their contributions. Again, these processes work
throughout the atmosphere, but are more or less dominant depending upon conditions at different
altitudes or locations.
Methane oxidizes in the atmosphere producing water vapor and heat and carbon dioxide, with
the exothermic chemical equation.
CH4 + 2 O2 → 2 H2O + CO2 + heat (amount?)
Methane is generated naturally by vegetative decomposition and cattle digestion and is present in
concentrations of about 2 ppmv in ‘clean dry air’ at sea level (Houghton p 226). In comparison,
a humidity of 50% at sea level and 20 or 25 °C (68 or 77°F) corresponds to __ ppmv water
vapor.
Most water vapor is trapped in the troposphere, and only a small portion passes into the
stratosphere, about 3 ppmv. (Other atmospheric gases and aerosols pass through the tropopause
too, upwards or downwards as they are driven, but gases behave differently—especially in terms
of phase change.) A majority of methane, about 1.6 ppmv, passes the tropopause into the
stratosphere.
The rate of this reaction, and thus it heating contribution depends upon the relative
concentrations of the reactants and products—the composition in the parcel of air.
(The general circulation is upward in the tropics, so the methane ‘burns hottest’ in the tropical
stratosphere.)
Where heat energy is available endothermic reactions can also proceed.
A photochemical reaction is triggered by, or its rate of reaction is increased by the absorption
of light by the reactants, specifically light of wavelengths characteristic to the reactant’s
absorption/emission spectrum. A particularly important reaction is the photolysis of ozone
which absorbs biologically harmful ultraviolet rays and splits into smaller parts:
[ozone photolysis equation ]
Ozone molecules are readily(?) rebuilt by [[process]], which occurs readily due to the abundance
of O2 in the atmosphere.
When a particular wavelength is absorbed from a beam of light, that wavelength is attenuated: if
the beam encounters enough of a particular absorbent gas along its path, that wavelength can be
filtered out completely. In that case, the gas has acted to shield parts of the atmosphere farther
along the beam path. A sunbeam that comes from directly overhead passes through a minimum
thickness of atmosphere before reaching the earth’s surface. A sunbeam that passes through the
atmosphere at an angle is attenuated more when it reaches the earth’s surface and any sunbathers
on the surface—that is why it is important to be mindful of sun exposure moreso during midday
hours than early morning or late afternoon.
Obviously, this process depends upon the amount of the photosensitive gas, i.e. the composition
of the atmosphere, and it depends upon the distribution because of the shielding effect. Of
course, it affects the amount and distribution of that gas and contributes to the heating in
atmosphere. The end result in the earth’s atmosphere is an ozone layer with maximum
concentration centered at an approximately __-__ km altitude. Other gases undergo
photochemical reactions too, and, may form layers in the atmosphere at other altitudes depending
on their concentrations and distributions.
Molecular photolysis is not the only interaction between light and the atmosphere.
[[Does light ever promote combination of molecules in the atmosphere—a kind of photosynthesis?]]
Photons of the appropriate wavelengths can free electrons from a gas (photoionization) or
aerosol particles (photoelectric effect), affecting (gas and gas-aerosol) reaction rates and aerosol
coagulation (clumping) rates. Additionally, some gases and aerosols can scatter light and some
gases can absorb and re-emit photons without reacting chemically or being ionized. Of course,
clouds reflect a lot of light back to space as well as scattering and diffusing it.
Greenhouse gases are so named is because they absorb infrared wavelengths of heat radiated
from the earth’s surface and re-emit the infrared photons both upwards and downwards: since
part of the energy is returned towards the surface, the gas helps the earth retain warmth, like a
greenhouse.
The major greenhouse gases are water vapor, carbon dioxide, methane, ozone
[http://en.wikipedia.org/wiki/Greenhouse_gas, illustration:
http://en.wikipedia.org/wiki/Image:Atmospheric_Transmission.png])
[[It seems that there are a lot of articles with atmospheric information in Wikipedia that have
been improving a lot recently!]]
However, the same greenhouse gases can absorb and re-emit incoming solar radiation as well,
and in that case the net effect is to partly shield the surface (and lower regions of the atmosphere)
because part of the energy is emitted upwards. The upward-directed energy might participate in
some processes in higher parts of the atmosphere or be radiated out to space, which is a cooling
process. How much and where the atmosphere is heated by chemistry or light processes depends
on how and where the gases are distributed in altitude, and this helps explain the contribution of
these processes to the thermal profile of the atmosphere.
[Houghton has a heating rate profile for CO2 on page 75 showing a peak near 80 km and a
positive heating rate between about 70-90 km.]
The thermal gradient in the mesosphere decreases with altitude, so we might expect buoyancy
effects be more dominant again in there as they were in the troposphere. [[The exam question
about stable and unstable thermal gradients with respect to the adiabatic lapse rate makes me
wonder if that is correct.]] Of course, pressure and density are much lower in the mesosphere.
Then in the thermosphere… what? Atmosphere so rarefied above 100 km or so, the vertical
circulation processes are no longer dominant and dissipation processes preside.
[[have to tie up the thermal profile and move to circulation… Alternatively, go back and
restate its start to make the thermal profile only a guide to processes & influences…?]]
This has covered gravity & buoyancy, insolation, chemistry & photochemistry with regards to
how they work in the atmosphere in the vertical direction.
The scope of this paper extends to the mesosphere, and this discussion has covered most of the
processes that act in the vertical direction within that scope. Continuing on, let’s look at a
different direction.
The earth’s rotation gives us references: points at the poles, which don’t move, the equator
between them, and a direction of rotation. (Rotation is mainly what makes the earth oblate in
shape rather than spherical.) This provides a basis for defining latitude in the geographical
coordinate system. We can choose an origin for longitude by selecting some point on the globe,
preferably at some landmark and not at a pole, e.g. the Royal Observatory in Greenwich,
England.
Meridians are great half-circles of constant longitude that extend from pole to pole across all
latitudes. A zone is defined as a region around the globe defined between parallels of constant
latitude.
Before, we looked at how a quantity varies with altitude in a vertical profile (as if there was only
dependence on altitude). The vertical profile model is a reduction to one dimension from the full
three-dimensional model with variation by altitude, latitude, and longitude. The data presented
later is reduced to a basis of altitude and latitude, with the variation by longitude suppressed by
some method, like sample averaging.
The earth’s shape and the location of a place on the surface have a bearing on the influences and
processes that occur near that place. For example, chemical processes do not depend upon
geographic location (rather they depend on concentrations), but photochemical processes do
depend on location because the amount of insolation varies from place to place over the earth’s
surface. The sun’s rays are more perpendicular near the equator and oblique near the poles,
varying with the seasons according to the earth’s tilt and orbital position.
At equinox the sun is directly over the equator at noon, and a one square meter sunbeam lights
one square meter of the earth’s surface. However, a one square meter of sunbeam reaching the
earth’s surface at a higher latitude at the same time is spread over more area because the beam
hits the surface at an angle. Also, the sunbeam at an angle had traveled a longer path through the
atmosphere and so had more chance to lose energy by reflection, scattering or absorption in the
atmosphere. Through the combination of just these effects, the sunshine that reaches the earth
surface (and lowest levels of atmosphere) is strongest at near equator and weaker towards the
poles.
(If we want to be more precise, we could also think about the oblateness of the atmosphere due
to rotation, the greater thickness of atmosphere due to solar driven upwelling in the tropics and
tidal influences by the sun and by the moon.)
The earth’s spin axis is tilted with respect to its orbit, so while the earth orbits the sun, its
orientation with respect to the sun changes. The solar zenith point, where the sunshine is most
direct and strongest, moves northward and then southward according to the time of year. At the
same time, the corresponding polar region experiences greater insolation during its summer (and
the other pole is dark).
Remarkably, the north pole point during summer receives as more sunlight during its 24-hour
day than sunny Mexico does during its 12-hour day, and about 30% more accumulated sunshine
than a point on the equator (Equador). (This is a simple approximation that ignores the
reflection, absorption and scattering effects of the atmosphere, that is—I don’t know whether it
would still be true if atmospheric shielding is considered).
[[Place here the diagrams (a) showing 100 km thickness of atmosphere on a circle profile of the
earth, and (b) the diagram showing insolation vs latitude at various tilt angles and the ‘cold
zone’.) Include in caption: At midsummer when the relative tilt exceeds about 21 degrees, the
summer pole would receive more sunlight per day than any other latitude, neglecting shielding
effects of the atmosphere. The chart represents insolation on a sphere, by zonal total in a latitude
for the entire zone or equivalently, for a single location in the zone over a full rotation.]]
[[I want to move on to the general circulation and describe the general regions of the tropical
Hadley Cell, and the Polar Cell and the Ferrell cell. Then while talking about the Polar cell,
PMCs. (and PSCs)]]
There is a tremendous difference in insolation in the polar regions between the summer
maximum and winter zero, and we will see it has an important effect on (part of) the general
circulation.
The general circulation.
We have already mentioned some of the driving influences for the general circulation: gravity
and buoyancy due to heating (insolation & chemical) and due to water content (composition) and
variation of the insolation with respect to location (altitude and latitude) and season.
The earth’s rotation is the grand-daddy of influences. (…and generates a variety of effects.)
(A) The earth rotates against the air and drags air near the surface with it, so this tends to make
the wind come from the east. Higher layers of the atmosphere rotate with the earth too, but they
lag farther behind lower layers. There is a centrifugal effect that tends to push air outward (and
equatorward) along the surface in the polar regions, and outward (upward) at the equator.
(B) There are three main (latitudinal) zones that have developed in the troposphere, defined by
how air flows along meridian planes and varies with respect to altitude and latitude:
(1) The Hadley Cell region is driven by buoyancy mainly and is centered near the heat equator,
where the sunshine is strongest and most direct (intense). As described above, warmed moist air
rises towards the tropopause and flows generally poleward. The air cools and becomes less
humid. Denser and heavier, it descends again around 30º, mixing with air from higher latitudes.
Air accumulates warmth and water vapor as it returns toward the equator along the surface, and
the cycle repeats.
“[The Hadley cell] is a closed circulation loop, which begins at the equator with warm, moist air lifted aloft
in equatorial low pressure areas to the tropopause and carried poleward. At about 30°N/S latitude, it descends in a
high pressure area. Some of the descending air travels equatorially along the surface, closing the loop of the Hadley
cell and creating the Trade Winds.” [http://en.wikipedia.org/wiki/Atmospheric_circulation#Hadley_cell]
(2) In the Polar Cell regions, air tends to flow along the surface away from the pole and to rise
on the outer part of the polar cells.
“Though cool and dry relative to equatorial air, air masses at the 60th parallel are still sufficiently warm
and moist to undergo convection and drive a thermal loop. Air circulates within the troposphere, limited vertically
by the tropopause at about 8 km. Warm air rises at lower latitudes and moves poleward through the upper
troposphere at both the north and south poles. When the air reaches the polar areas, it has cooled considerably, and
descends as a cold, dry high pressure area, moving away from the pole along the surface but twisting westward as a
result of the Coriolis effect to produce the Polar easterlies.”
[http://en.wikipedia.org/wiki/Atmospheric_circulation#Hadley_cell]
(3) The Ferrell Cells are a secondary circulation feature, driven by the circulation in the Hadley
and Polar cells rather than directly by buoyancy and rotation influences. They are located in the
mid latitudes at about 30-60° on each side of the equator.
Prevailing winds patterns are from the east to west where the circulation is along the surface,
where it air flows away from the poles and towards the (heat) equator, as it is in the lower parts
of the Hadley and Polar cells. Surface winds generally flow from the west in the Ferrell cell and
are calm in the doldrums and horse latitudes.
The surface of the earth is textured with mountains and valleys, so airflow over the surface
features (orography) generates disturbances. For example, air that flows against a mountain and
is pushed up by it into less dense air will tend to fall back to earth simply due to gravity,
initiating disturbances that propagate upward through the atmosphere and past the mountain as
gravity waves. Air against land is not the only source of disturbances, air against air, like warm
air flowing against the ‘soft’ mountain range of a cooler air mass (cold front) will also be
directed upwards, but the effects would likely be much weaker.
[[this would be a good transition into Brewer-Dobson circulation, but really needs the polar
summer upwelling. ]]
It is not clear from the following diagrams what exactly are the prevailing east/west directions
for the higher tropospheric winds. However, they generally agree on the circulation in meridian
planes.
The same influences mentioned already are present in varying degrees throughout the
atmosphere
Still to cover are the polar vortex and planetary waves and surface (and tropospheric)
disturbances and gravity waves… the jet stream and the quasi-biennial oscillation, which could
make the directions of the upper troposphere airflow vary between east and west.
The tropopause isn’t solid. We can extend the meridional cross section to higher layers
to see the Brewer-Dobson circulation patterns (subsequent figure) which is also affected by
season due to insolation.
Figure 2
General circulation (left) Atmospheric Physics class handout. [[sic: I think the southern 30-60° range should have
been labeled ‘westerlies’. I can edit the picture to correct it…]]
(right) Wikipedia [http://en.wikipedia.org/wiki/Atmospheric_circulation#Hadley_cell]
(bottom) Wayne, Chemistry of Atmospheres, p. 68.
[[The left picture suggests mixing near the 60° zone, whereas the right picture suggests a front. The right picture
also suggests a transition of surface winds from east to west within the polar cells.
All three disagree in east-west direction at the top of the Ferrell cell and top and/or bottom of the Hadley cell.
All three appear to have some internal inconsistency: (left) ‘prevailing easterlies’ should be ‘wasterlies’.
(right) The color for the surface winds in the Hadley Cell region don’t match the surface part of the vertical loop.
(bottom) the polar region arrows point towards the pole, but the vertical loop points away from the pole.
I think I saw somewhere on Wikipedia another circulation image that shows a helical circulation pattern where the
rising air moves poleward, rotates slower or faster than the surface, and descends at a different longitude. ]
[[Let’s suppose that problem is worked out… pressing on:]]
(C)
(D) Circulation above the troposphere
Longitudinal or zonal flow.
Polar vortex
Planetary waves
Most direct are the equatorial trade winds and the polar vortex.
[[Now go into the map-able regions and the circu
Brewer-Dobson circulation, see Houghton p 70,79,159 (as Dobson-Brewer)
If I include that diagram of the general circulation (note differences between troposphere and
higher),
BrewerDobson picture at
http://www.atmosphere.mpg.de/enid/28d8624d35e713e8e10a17fa6a8becdf,0/1__Dynamics___A
viation/-_Dynamics_205.html
Circulation:
Meridional flow:
Hadley Cell (solar driven),
Polar Cell, Ferrell Cell, Brewer-Dobson Circulation, mesospheric summer pole-to-winter pole
cell
Rotation:
Zonal flow: Jet Stream, Southern Quasi-Bienniel Oscillation,
trade winds, esp at equator, flow over surface orography → gravity waves, rotation in polar
regions → polar vortices, planetary waves, cyclones
Coriolis effects,
This is all background for the main as yet unanswered question, which is if 3 ppmv H2O [[where
does this number come from?]] originates from flow upwards from the troposphere and 3.2
ppmv H2O comes from methane oxidation[[where does 1.6 ppmv CH4 come from?]], how is it
that we measure more water vapor O(10 ppmv) in the mesosphere?
[[Comment. The presence of 3 ppmv at the level of the troposphere doesn’t tell us the
throughput at that level. It would help to know airflow velocity there, it would help, but then we
also have to account for volume changes… ]]
BOOKMARK
Photon Scattering
Raman: inelastic, some energy goes into internal energy of a scattering molecule
[http://en.wikipedia.org/wiki/Raman_scattering]
Rayleigh: elastic,
Excess energy goes into the excited state of the product(s) and is given off as photons of lower
energy (and longer wavelength) or the kinetic energy of the products (e.g. temperature).
[[I suppose it is also possible for gases to absorb sunlight of a certain wavelength and then emit
energy at the same or lower energies (longer wavelength) without reacting chemically, in a way
similar to the way a laser works. ]]
This may also be a good point to introduce how greenhouse gases work: ‘intercepting’ light and
the re-emitting its energy, acting as an infrared light source—and if it radiates isotropically (as
through a randomization of the incident photon momenta by the motion of the molecules, then
where a greenhouse gas is higher in the atmosphere, its will filter out the characteristic
wavelengths from the light beam, reducing or even blocking those wavelengths from reaching
lower parts of the atmosphere or the surface.
very cold and well below water’s freezing temperature.
, and it acts like a trap for water vapor.
to trap
(retain, conserve, fence in, ) nearly all of the water vapor that reaches it in the troposphere.
[My goodness! I was looking at Martin Chaplin’s water phase diagram with the thermal profile
and the at a copy of one of the HALOE water contours… of course, there is more water vapor
between about 40-60 km—that’s where the thermal profile shows the temperature is in the water
vapor region of the phase diagram! I suppose then the question is why is there vapor above 60
km? It’s not a case of all vapor/no ice or all ice/no vapor.]
[[Note: half of all the atmosphere is below ___ km altitude.]]
Since any ideal gas
, so, hence the sloped line in the profile. and heats the atmosphere some, and the surface a lot.
Some sunshine is reflected and passes upward into and through the atmosphere again. The
For example,
[gravity, buoyancy and vertical circulation]
+- - -- --- - -- ---Okay, after all that, we need to lead in to information about satellites, orbits and detection.
HALOE and SOFIE are separate chapters.