Download Meteorology

Meteorology
Study of the changes in temperature, air pressure, humidity, and wind
direction in the troposphere.
Energy Flow In The Earth System:
Scientists are concerned about global warming due to changes in the flows of
energy through the Earth system. The ocean plays an important role in
determining and moderating the effects of an energy imbalance. The physical
properties, large-scale movements and global distribution of the ocean make
it a key indicator of changes in Earth's temperature and energy balance. The
ocean is not a passive thermometer. Instead it manages and distributes stored
solar energy to all regions of the planet. It is essential that scientists look for
evidence of stability, change and variability not only in ocean surface
temperatures but also in the major currents that redistribute the energy. Small
changes in ocean surface temperature can indicate large exchanges of energy
with the atmosphere.
To learn more about the water cycle also known as the hydrologic cycle use
website : http://ga.water.usgs.gov/edu/watercycle.html
What Do You Know?
Before beginning this lesson it is helpful to learn how much information you
already know about the patterns of energy flow in the ocean. A simple
preconceptions survey has been created for you to assess your prior
knowledge.
Determine if the following statements are true or false
Earth is always in energy balance: energy received (primarily from the Sun) equals
energy emitted.
Our climate determines the energy balance of Earth.
The average temperature of Earth has been constant over time.
The higher the temperature of an object or substance, the greater the
intensity of radiation it emits.
Water vapor in the atmosphere cools Earth.
In July, Earth is closest to the Sun.
Sea surface temperature and currents are used to make forecasts of fishing
conditions in the ocean.
Satellites in space measure the temperature of ocean water by its color: light
blue is warm and dark blue is cool.
Earth’s energy balance:
1. Input - Sun's Energy reaches Earth
2. Solar energy passes through the atmosphere, is reflected or
absorbed
o Ozone layer absorbs a fraction of the incoming radiation
o Clouds reflect a portion of the radiation
o Atmospheric "window" allows some radiation in. Some
gases are transparent to Visible, UV, and IR; others absorb
the radiation.
3. Energy reaches Earth where it is reflected or absorbed by Earth's
surface. Absorbed energy is transformed from one wavelength to
another, creating sensible heat and driving Earth's systems, such as
the water cycle.
o Evaporation - latent heat creates clouds and weather
o Heat absorbed into land surfaces and oceans - sensible
heat warms matter
o Sensible heat, creates thermals and convection
4. Energy is transferred from Earth to the atmosphere
o Energy is used / transformed heating surfaces and driving
processes
o Energy is absorbed by clouds and atmospheric gases
o Energy is back radiated to Earth
5. Output – Infrared and Visible Energy is emitted back to space
Energy In = Energy Out
How can a model of the human body be used to better understand energy in the Earth
system?
Energy balance is a familiar topic to most people
because it relates directly to their health. Your body
maintains an energy balance:
Energy In = Energy Out + Energy Stored
The above formula illustrates energy conservation—all
the energy has to “go” somewhere. It cannot just
disappear. Humans eat food that provides energy for
biochemical processes necessary for life and for heat
that the body sheds through various processes
(radiation, conduction, convection and evaporation).
The unit of energy found on food package labels is the Calorie (1 Calorie = 1000
calories = 4186 Joules). The body regulates blood flow to increase or decrease
body heat. If too many calories are consumed, the body stores the excess energy as
fat.
6. In the chart below, complete the following analogies that compare the energy
balance of the body to that of the Earth.
Energy
Primary energy source
Human Body
Atmosphere/Ocean
Food
Exercise, work,
Ways the energy is
internal body
expended
functions
Fat accumulation,
Ways the energy is stored
chemical energy
Evaporation (sweat),
conduction,
convection (blood
Ways to transfer energy circulation-The blood
is pumped through
the body, carrying
heat), radiation
Factors that affect climate and weather:
Temperature: It is a measure of the average kinetic energy associated with the
motion of atoms and molecules. The flow of heat is from a high temperature region
toward a lower temperature region. It is easy to demonstrate that when two
objects of the same material are placed together (physicists say when they are put
in thermal contact), the object with the higher temperature cools while the cooler
object becomes warmer until a point is reached after which no more change
occurs, and to our senses, they feel the same. When the thermal changes have
stopped, we say that the two objects (physicists define them more rigorously as
systems) are in thermal equilibrium.
° F = 1.8° C + 32
° K = ° C + 273
Conduction, Convection, Radiation: Heat can be transferred from one place to
another by three methods: conduction in solids, convection of fluids (liquids or
gases), and radiation through anything that will allow radiation to pass. The
method used to transfer heat is usually the one that is the most efficient. If there is
a temperature difference in a system, heat will always move from higher to lower
temperatures.
CONDUCTION:
Conduction occurs when two object at different temperatures are in contact with
each other. Heat flows from the warmer to the cooler object until they are both at
the same temperature. Conduction is the movement of heat through a substance by
the collision of molecules. At the place where the two object touch, the fastermoving molecules of the warmer object collide with the slower moving molecules
of the cooler object. As they collide, the faster molecules give up some of their
energy to the slower molecules. The slower molecules gain more thermal energy
and collide with other molecules in the cooler object. This process continues until
heat energy from the warmer object spreads throughout the cooler object. Some
substances conduct heat more easily than others. Solids are better conductor than
liquids and liquids are better conductor than gases. Metals are very good
conductors of heat, while air is very poor conductor of heat. You experience heat
transfer by conduction whenever you touch something that is hotter or colder than
your skin e.g. when you wash your hands in warm or cold water.
CONVECTION:
In liquids and gases, convection is usually the most efficient way to transfer heat.
Convection occurs when warmer areas of a liquid or gas rise to cooler areas in the
liquid or gas. As this happens, cooler liquid or gas takes the place of the warmer
areas which have risen higher. This cycle results in a continuous circulation
pattern and heat is transferred to cooler areas. You see convection when you boil
water in a pan. The bubbles of water that rise are the hotter parts of the water
rising to the cooler area of water at the top of the pan. You have probably heard the
expression "Hot air rises and cool air falls to take its place" - this is a description of
convection in our atmosphere. Heat energy is transferred by the circulation of the
air
RADIATION:
Both conduction and convection require matter to transfer heat. Radiation is a
method of heat transfer that does not rely upon any contact between the heat
source and the heated object. For example, we feel heat from the sun even though
we are not touching it. Heat can be transmitted though empty space by thermal
radiation. Thermal radiation (often called infrared radiation) is a
type electromagnetic radiation (or light). Radiation is a form of energy transport
consisting of electromagnetic waves traveling at the speed of light. No mass is
exchanged and no medium is required.
Objects emit radiation when high energy electrons in a higher atomic level fall
down to lower energy levels. The energy lost is emitted as light or electromagnetic
radiation. Energy that is absorbed by an atom causes its electrons to "jump" up to
higher energy levels. All objects absorb and emit radiation. When the absorption of
energy balances the emission of energy, the temperature of an object stays
constant. If the absorption of energy is greater than the emission of energy, the
temperature of an object rises. If the absorption of energy is less than the emission
of energy, the temperature of an object falls.
Air Temperature Investigations:
What do data reveal about daily energy cycles in the Earth system?
To investigate energy cycles, begin by examining air temperature data collected
in Washington, DC on July 4–5, 2005 – a calm, clear summer day in the nation’s
capital. On July 3, the Earth is farthest from the sun—94,500,000 miles (in the first
week of January, Earth is closest—91,400,00 miles). Many of the details that you
will learn about this daily energy cycle will apply to the yearly cycle of ocean
surface temperatures as well. The daily cycle occurs because Earth rotates once on
its axis every 24 hours. The yearly seasonal cycle occurs because the Earth’s axis is
tilted 23o relative to the plane of its orbit. As Earth orbits the Sun, this tilt remains
constant, so the United States experiences winter when the Northern Hemisphere
tilts away from the Sun and summer when it tilts towards the Sun.
The graph below represents outside air temperatures for July 4–5, 2005 in
Washington, D.C. For this investigation, we have selected a calm, clear day with no
precipitation or significant movement of air masses. Examine the graph and
answer the following three questions.
7. Determine the maximum temperature
and the time and date it occurred.
Max Temp:
Time:
Date:
8. Determine the minimum temperature and the time and date it occurred.
Min Temp:
Time:
Date:
9. What is the temperature range shown in the graph?
During the entire 24-hour interval, the Kelvin (absolute) air temperature
was relatively constant:
30.2oC (max temp) = 30.2 + 273.15 = 303.35oK
21.9oC (min temp) = 21.9 + 273.15 = 295.05oK.
Measured on this scale, the Kelvin temperature of the air changed by less than 3%
over
24 hours:
The energy radiated by a substance or object depends directly on its Kelvin
temperature. Objects with a higher temperature radiate more. Assuming that the
nearby ground surfaces have temperatures similar to the air temperatures, it can
be concluded that during the 24-hour period, the electromagnetic energy radiated
around the site of this Washington, D.C. weather station site was fairly constant.
Gathering And Manipulating Data :
Basic Data Gathering and Processing
When studying the ocean, scientists use automated instruments such as buoys and
satellites to collect data. These measuring tools are very accurate and stable, but
they also can be as prone to error and uncertainty as the thermometer you hang
outside your window.
Scientists realize they can never make perfect measurements. Instead they try to
be as accurate as possible within the limitations of their measuring instruments
and their protocols (i.e., the set of procedures scientists follow for every
measurement). They consider a measurement that is close to the true value an
accurate measurement. Random uncertainties can cause these measurements
either to be too high or too low. Such uncertainties must not be systematic. In other
words, the measurements should not be consistently higher or lower than the true
values. Scientists therefore must constantly reevaluate the uncertainties that affect
their measurements and the conditions under which the measurements are made.
Following measurement protocols insures as much accuracy and reproducibility as
possible.
1. Use a thermometer to measure the temperature of water in a cup or
deep bowl. Each student (or team of students) should record their
name(s), the temperatures they measure and any comments they may
have about their measurements (scientists call these
comments metadata) on a board or poster for all to see.
Copy the results of the measurements along with any student comments in the
table below:
Name
TemperatureValue Comments/Metadata
2. Compare the measurements of the water temperature. Are all the measurements
the same or nearly the same?
3. List some of the factors that might cause the temperature measurements to
differ?
4. Create a protocol (or procedure) to measure the temperature of water in a
nearby pond, lake or ocean. The protocol should have enough detail so that any
student following the protocol will measure the same (or very nearly the same)
value.
Joyful Data Graphing And Finding The Mean
Assume that 15 water temperatures were collected with a calibrated thermometer.
Each of the following five processing steps may help you to better understand
characteristics of the data collected.
Graph the Data: The temperature data points make a pattern that seems to be level
– not slanted up or down. If the points showed a systematic trend rising or falling
from left to right, it would suggest that the “true” value being measured was
systematically changing during the measurements. In this case, the measurement
protocol should be re-examined and revised.
Expand the Graph Scale: To see the variations in the data more clearly, expand
(magnify) the data scale. The data points look different but correspond to the same
values.
Compute the Mean: Add all temperature measurements and divide by the number
of points (15) to compute the mean value of the data. The red line in the figure
shows the mean value. Its value is just above 21o. The mean value line does not
exactly intersect any of the temperature data points but it lies in the middle of the
data points (7 above the line, 8 below).
Compute the Differences from the Mean: Compute the difference between each
data point and the mean value. This will be used to estimate the variation in this
set of measurements.
Compute the Standard Deviation: Use all the differences to compute the standard
deviation (σ) of the data set. The red lines show the limits of the [mean + σ] and
[mean – σ]. Note that 10 data points lie between these limits and 5 lie outside:
Within limits: 10/15 = 2/3 = 67% of the data set
Outside limits: 5/15 = 1/3 = 33% of the data set
Standard Deviation For The Courageous
Level 2, More Challenging
Here is an exercise where you will practice calculating the mean and standard
deviation of data values. Imagine that you have measured the following
temperatures 27.4oC, 26.5oC, 28.1oC, 27.6oC, 26.9oC and you wish to compute the
mean and standard deviation of your data. Organize the data into a table (Column
A) and perform calculations as discussed in the steps below. Follow the flow and
method of this example and then you will practice the calculations yourself:
1
2
3
4
5
Column A
Column B
Column C
Data
XI
27.4
26.5
28.1
27.6
26.9
Sum of Data
Difference
Squared Difference
XI-XM
(XI-XM)2
(27.4-27.3)=0.1 (0.1)2=0.01
(26.5-27.3)=-0.8 (-0.8)2=0.64
(28.1-27.3)=0.8 (0.8)2=0.64
(27.6-27.3)=0.3 (0.3)2=0.09
(26.9-27.3)=-0.4 (-0.4)2=0.16
Sum of Squares
Mean Value
Standard Deviation
SUM
MSD
• List the data as in Column A
• Add all the data values and record the sum in the SUM row of Column A.
• Compute the mean by dividing the sum (from Step 2) by the number of
measurements (N=5). Record this result in the MSD (Mean
and Standard Deviation) row of Column A.
• Subtract the mean value (Step 3) from each data value as shown in Column B.
• Compute the square of each difference value from Column B and record it in
Column C.
• Add all the squared differences from Column C (Step 5) and record the sum in the
SUM row of Column C.
• Compute the standard deviation by taking the square root of the sum of the
squared differences (Step 6) divided by one less that the number of measurements
(N-1 = 5-1 = 4). Record this result in the MSD row of Column C.
The mean and the standard deviation are related in a very important way. For a
given data set, the mean is the single value that minimizes the standard deviation of
the data. Choosing any value other than the mean for calculating the standard
deviation yields a larger standard deviation. If, for example, you replace the mean
value 27.3 with 28.0 everywhere in the above calculation, you will find that the
standard deviation increases. In this sense, choosing the mean value as the best
value to represent a dataset is justified by the fact that it
deviates (differs) least from the other numbers in the dataset.
5. Your Turn: The following is a new dataset. Practice the calculation of mean and
standard deviation values:
Column A
1
2
3
4
5
6
7
SUM
Column B Column C
Data
Difference Squared Difference
XI
XI-XM
(XI-XM)2
4.73
4.65
4.82
4.70
4.69
4.83
4.77
Sum of Squares
Sum of Data
Air Pressure:
Air pressure is the force exerted on you by the weight of tiny particles of air
(air molecules). Although air molecules are invisible, they still have weight and
take up space. Since there's a lot of "empty" space between air molecules, air can
be compressed to fit in a smaller volume.
When it's compressed, air is said to be "under high pressure". Air at sea level is
what we're used to; in fact, we're so used to it that we forget we're actually feeling
air pressure all the time!
Weather forecasters measure air pressure with a barometer. Barometers are used
to measure the current air pressure at a particular location in "inches of mercury"
or in "millibars" (mb). A measurement of 29.92 inches of mercury is equivalent to
1013.25 millibars.
.
Standard Atmospheric Pressure (atm) is used as a reference for gas densities
and volumes. The Standard Atmospheric Pressure is defined at sea-level at 273oK
(0oC) and is 1.01325 bar or 101325 Pa (absolute). The temperature of 293oK
(20oC)is also used.
In imperial units the Standard Atmospheric Pressure is 14.696 psi.
1 atm = 1.01325 bar = 101.3 kPa = 14.696 psi (lbf/in2)= 760 mmHg =10.33
mH2O = 760 torr = 29.92 inHg = 1013 mbar = 1.0332 kgf/cm2 = 33.90 ftH2O
1 bar - 100,000 Pa
1 millibar - 100 Pa
1 atmosphere - 101,325 Pa
1 mm Hg - 133 Pa
1 inch Hg - 3,386 Pa
A torr (torr) is named after Torricelli and is the pressure produced by a column of
mercury 1 mm high - equals to 1 / 760th of an atmosphere.
1 atm = 760 torr = 14.696 psi
Pounds per square inch (psi) was common in U.K. but has now been replaced in
almost every country except in the U.S. by the SI units. Since atmospheric pressure
is 14.696 psi - a column of air on a area of one square inch area from the Earth's
surface to the space - weights 14.696 pounds.
The bar (bar) is common in the industry. One bar is 100,000 Pa, and for most
practical purposes can be approximated to one atmosphere even if
1 Bar = 0.9869 atm
There are 1,000 millibar (mbar) in one bar, a unit common in meteorology.
1 millibar = 0.001 bar = 0.750 torr = 100 Pa
Humidity:
When thinking of humidity always think in terms of energy and there is only so much
energy to go around and not all of it is available to do the work of evaporation. The
remainder goes to the other molecules in the air - each gas in the mechanical mixture
gets its fair share.
There is a connection between humidity and air temperature, but the connection has
nothing to do with warm air "holding" more water vapor. Think of air as a kinetic
energy delivery system. Warmer air moving into a region has more thermal energy
than the air it is replacing. At the molecular level we say the average kinetic energy of
the molecules is greater in the warmer air and the thermal energy of the warmer air is
transferred to water molecules as the faster moving air molecules collide with the
slower molecules in the water. The faster moving air molecules lose energy and the
slower moving water molecules gain energy and begin to move faster and collide with
each other more violently. Some of the water molecules will gain enough kinetic
energy (or speed or thermal energy - all three are the same) to escape the liquid and
become a free moving gas molecule. If the newly arriving air is colder the opposite
occurs.
A molecule evaporates when sufficient kinetic energy is gained through collisions with
its neighbors for it to overcome the attractive forces between the liquid molecules.
These forces include hydrogen bonds and Van der Waals force. As the molecule
escapes it takes with it kinetic energy, leaving the water surface with a diminished total
kinetic energy.
A molecule condenses when it is moving slowly enough and is pulled back to the water
surface by the attractive forces, i.e. its velocity is insufficient to resist the pull of the
various forces of attraction. The molecule plunges into the water, transferring energy
to the molecules near where it hit the surface and is once again liquid.
It is easy to see why evaporation cools a surface and condensation warms it - when
you THINK ENERGY
Dew point temperature is a measure of humidity. If air is cooled eventually enough
energy will be removed for water vapor to begin to condense. When we say condense
it just means some of the molecules slow enough so that the attractive forces between
liquid molecules are strong enough to make the molecules stick together. Remember
the water vapor was originally liquid water and to get it to evaporate you had to add
energy. As long as a molecule is moving fast enough (faster = warmer) it will remain
vapor, but as a molecule cools (cooler = slower) at some point it will slow enough so it
will stick to other water molecules. When that happens scientists say the molecule
condensed.
The temperature where condensation first begins is the dew point temperature.
Winds affecting global weather
As equatorial areas are heated most, the air above them warms and rises as it
becomes lighter than the surrounding air, causing an area of low pressure. In
cooler areas, the air sinks because it is heavier and results in an area of high
pressure. Winds will blow as air is squashed out by the sinking cold air and drawn
in under the rising warm air. Any difference in temperature like this will always
cause a difference in air pressure – and therefore winds will blow. A good
expression to remember is that:
"winds blow from high to low" (ie: from high pressure to low pressure).
These movements result in a global wind pattern, with air moving between
different areas around the world and also at different heights in the atmosphere.
Colder air from the poles tends to sink and move towards the equator closer to the
surface of the Earth. In contrast, warm air from the equator rises and moves
towards the poles high in the atmosphere because it is lighter.
This creates cell-like patterns of wind around the world, as seen in the diagram
However, winds do not simply blow in straight lines from north to south. Instead,
they are bent by the spinning of the Earth: to the right north of the equator, and to
the left in the south. This is called the Coriolis Effect and it bends every wind on
Earth, resulting in a distinct pattern of winds around the world. In the midlatitudes (30-60º north and south of the equator) most winds are westerlies,
blowing from the west. Elsewhere they blow mainly from the east; for example the
steady winds blowing towards the equator from the subtropics. These are known
as trade winds because they were used by sailing ships carrying trading goods
around the world. They blow consistently from the NE north of the equator (north
easterlies) and from the SE south of the equator (south easterlies).
The Coriolis Effect experiment
With only very simple equipment, this activity can be used to demonstrate the
concept of the Coriolis Effect.
Materials
You will need:
a paper plate or round piece of cardboard
a marker pen
a record player turntable
scissors
Procedure
Carefully push a small hole through the centre of the paper plate with the
scissors.
Place the paper plate onto the turntable as you would a record.
Without starting the turntable, draw a straight line from the centre to the outside
of the plate.
Now spin the record player (or turn it on) and draw another straight line from
the centre to the outside of the plate.
Stop the record player and look at the two lines you have drawn.
You should notice that the second line was bent by the rotation of the record
player. This is what happens with winds on the Earth, and explains why they do
not simply blow in straight lines from north to south. Instead, they are bent by the
spinning of the Earth - to the right north of the equator andto the left in the south.
This is called the Coriolis Effect and it bends every wind on Earth, resulting in a
distinct pattern of winds around the world.
Having completed this activity, here are some questions to think about.
1.) Explain the difference between the two lines.
2.) What do the lines tell us about the rotation of the Earth?
Additional explanation and example of coriolis effect:
http://littleshop.physics.colostate.edu/docs/CMMAP/tenthings/Hurricanes.pdf
The global wind pattern is also known as the "general circulation" and the surface winds of
each hemisphere are divided into three wind belts:
Polar Easterlies: From 60-90 degrees latitude.
Prevailing Westerlies: From 30-60 degrees latitude (aka Westerlies).
Tropical Easterlies: From 0-30 degrees latitude (aka Trade Winds).
The easterly trade winds of both hemispheres converge at an area near the equator called
the "Intertropical Convergence Zone (ITCZ)", producing a narrow band of clouds and
thunderstorms that encircle portions of the globe.
The equator receives the Sun's direct rays. Here, air is heated and rises, leaving low
pressure areas behind. Moving to about thirty degrees north and south of the
equator, the warm air from the equator begins to cool and sink. Between thirty
degrees latitude and the equator, most of the cooling sinking air moves back to the
equator. The rest of the air flows toward the poles.
What are the trade winds?
The trade winds are just air movements toward the equator. They are warm,
steady breezes that blow almost continuously. The Coriolis Effect makes the trade
winds appear to be curving to the west, whether they are traveling to the equator
from the south or north.
What are the doldrums?
The doldrums is an area of calm weather. The trade winds coming from the south
and the north meet near the equator. These converging trade winds produce
general upward winds as they are heated, so there are no steady surface winds.
What are the prevailing westerlies?
Between thirty and sixty degrees latitude, the winds that move toward the poles
appear to curve to the east. Because winds are named from the direction in which
they originate, these winds are called prevailing westerlies. Prevailing westerlies
in the Northern Hemisphere are responsible for many of the weather movements
across the United States and Canada.
What are the polar easterlies?
At about sixty degrees latitude in both hemispheres, the prevailing westerlies join
with the polar easterlies to reduce upward motion. The polar easterlies form when
the atmosphere over the poles cools. This cool air then sinks and spreads over the
surface. As the air flows away from the poles, it is turned to the west by the Coriolis
effect. Again, because these winds begin in the east, they are called easterlies.
Ocean currents
Ocean waters are constantly on the move. How they move influences climate and
living conditions for plants and animals, even on land.
Currents flow in complex patterns affected by wind, the water's salinity and heat
content, bottom topography, and the earth's rotation.
Upwelling brings cold, nutrient-rich water from the depths up to the surface.
Earth's rotation and strong seasonal winds push surface water away from some
western coasts, so water rises on the western edges of continents to replace it.
Marine life thrives in these nutrient-rich waters.
Deep water forms when sea water entering polar regions cools or freezes,
becoming saltier and denser. Colder or saltier water tends to sink.
A global "conveyor belt" set in motion when deep water forms in the North
Atlantic, sinks, moves south, and circulates around Antarctica, and then moves
northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years
for water from the North Atlantic to find its way into the North Pacific.
Warm surface currents invariably flow from the tropics to the higher latitudes,
driven mainly by atmospheric winds, as well as the earth's rotation.
Western boundary currents are good examples of warm surface currents: they are
warm and fast, and they move from tropical to temperate latitudes.
Cold surface currents come from polar and temperate latitudes, and they tend to
flow towards the equator. Like the warm surface currents, they are driven mainly
by atmospheric forces. Gyres form when the major ocean currents connect. Water
flows in a circular pattern--clockwise in the Northern Hemisphere, and
counterclockwise in the Southern Hemisphere.
The Gulf Stream surface current is a western boundary current, one of the
strongest--warm, deep, fast, and relatively salty. It separates open-ocean water
from coastal water.
The California current is an eastern boundary current. It's broad, slow, cool, and
shallow. Eastern boundary currents are often associated with upwelling.
Essential link:
http://www.windows2universe.org/earth/Water/ocean_currents.html
Synoptic Meteorology
Synoptic meteorology is the study and analysis of weather information obtained
simultaneously over a wide area. Observations are collected simultaneously in
order to obtain a comprehensive and nearly instantaneous picture of the state of
the atmosphere.
Synoptic weather observations are made periodically (usually at three-hourly and
six-hourly intervals as specified by the World Meteorological Organization).
Information collected about weather is shared worldwide via the Global
Telecommunications System (GTS).
A synoptic chart is a map presenting data and analyses that describe the state of
the atmosphere over a large area at a given moment in time. Synoptic-scale
weather is characterized by migrating storms, air masses, and fronts, such as those
highlighted on television and newspaper weather maps.
The objective of synoptic meteorology is to forecast weather. Forecasting the
weather is a complicated and expensive process, with forecasters requiring
extensive training to be able to make accurate predictions. Weather forecasters use
data about wind patterns, temperature, moisture, and pressure prevailing across
the globe to predict developing weather patterns. Computer-based numerical
models are used to create short-term (24 hour to 48 hour) forecasts and extended
range predictions for three days or more.
Cloud Types
common cloud classifications
Clouds are classified into a system that uses Latin words to describe the
appearance of clouds as seen by an observer on the ground. The table below
summarizes the four principal components of this classification system (Ahrens,
1994).
Latin Root
Translation
Example
cumulus
stratus
cirrus
nimbus
heap
layer
curl of hair
rain
fair weather cumulus
altostratus
cirrus
cumulonimbus
Further classification identifies clouds by height of cloud base. For example, cloud
names containing the prefix "cirr-", as in cirrus clouds, are located at high levels
while cloud names with the prefix "alto-", as in altostratus, are found at middle
levels. This module introduces several cloud groups. The first three groups are
identified based upon their height above the ground. The fourth group consists of
vertically developed clouds, while the final group consists of a collection of
miscellaneous cloud types.
High-Level Clouds
High-level clouds form above 20,000 feet (6,000 meters) and since
the temperatures are so cold at such high elevations, these clouds
are primarily composed of ice crystals. High-level clouds are typically
thin and white in appearance, but can appear in a magnificent array
of colors when the sun is low on the horizon.
Photograph by: Knupp
Mid-Level Clouds
The bases of mid-level clouds typically appear between 6,500 to
20,000 feet (2,000 to 6,000 meters). Because of their lower
altitudes, they are composed primarily of water droplets, however,
they can also be composed of ice crystals when temperatures are
cold enough.
Photograph by: Holle
Low-level Clouds
Low clouds are of mostly composed of water droplets since their bases generally lie below
6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may
also contain ice particles and snow.
Photograph by: Holle
Vertically Developed Clouds
Probably the most familiar of the classified clouds is the cumulus cloud. Generated most
commonly through either thermal convection or frontal lifting, these clouds can grow to
heights in excess of 39,000 feet (12,000 meters), releasing incredible amounts of energy
through the condensation of water vapor within the cloud itself.
Photograph by: Holle
Other Cloud Types
Finally, we will introduce a collection of miscellaneous cloud types which do not fit into
the previous four groups.
Classifications High-Level Clouds
Cloud types include: cirrus and cirrostratus.
Mid-Level Clouds
Cloud types include: altocumulus, altostratus.
Low-Level Clouds
Cloud types include: nimbostratus and stratocumulus.
Clouds with Vertical Development
Cloud types include: fair weather cumulus and cumulonimbus.
Other Cloud Types
Cloud types include: contrails, billow
clouds, mammatus, orographic and pileus clouds.
Weather Fronts:
When a front passes over an area, it means a change in the weather. Many fronts
cause weather events such as rain,thunderstorms, gusty winds, andtornadoes. At a
cold front passes there may there may be dramatic thunderstorms. At a warm front
there may be low stratus clouds. Usually the skies clear once the front has passed.
A weather front is a border between two different air masses at the Earth’s surface.
Each air mass has its own characteristics such as temperature and humidity.
Where two different air masses come in contact, the line between them is a front.
Often there is turbulence where those different air masses come together. The
turbulence can cause clouds and storms.
While many fronts cause storms andclouds, some fronts do not cause dramatic
weather events, just a change in the temperature. However, a few fronts start
Earth’s largest storms. Tropical waves, fronts that develop in the tropical Atlantic
Ocean off the coast of Africa, are able to develop into tropical storms
or hurricanes if conditions allow.
Fronts move over time as the air masses move. The direction that fronts move is
often guided by high winds such as Jet Streams. Landforms like mountains can also
change the path of a front.
There are 4 different types of fronts: cold fronts, warm fronts, stationary fronts,
and occluded fronts.
Weather in Urban Areas:
Heavy rainfall often occurs around cities. In fact, cities themselves can affect
the weather. Scientists have several different hypotheses that may explain how cities
impact rain.
One hypothesis is that the urban heat island effect, which causes
warmer temperatures in cities, creates unstable air which leads to rain. Air is unstable
when it is warmer than the air around it. The warm, unstable air starts to rise. The air
cools as it rises, which allows water vapor within it to condense and form clouds. If the
warm, rising air was carrying enough water vapor, those clouds can grow into
rainclouds.
Another hypothesis is that when wind hits the skyscrapers and other tall buildings in a
city, it is pushed up higher in the atmosphere. This makes unstable air. The unstable air
flows upward and cools, allowing water vapor to condense, forming clouds, which can
lead to rain.
Tall buildings might have another effect that causes clouds and rain.
As wind approaches the buildings, it may be divided with some of it blowing around
one side of the city and some of it blowing around the other side. Past the city, the
wind comes back together. It collides, flows upward, cools, and releases water vapor
forming clouds.
Air pollution in cities may also affect cloud formation and rain. Water vapor condenses
on tiny particles in the air pollution, forming the droplets that make a cloud.
Websites required for further research:
http://www.wunderground.com/
http://www.windows2universe.org/earth/Water/ocean_currents.html
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/home.rxml
YouTube videos explaining Coriolis effect and Global circulation
http://www.youtube.com/watch?v=__SlJtnpCD8&NR=1
http://www.youtube.com/watch?v=DHrapzHPCSA
DID YOU KNOW :
Compensation:
According to the U.S. Bureau of Labor Statistics, the average salary of
meteorologists and space scientists was $85,160 a year in 2009.