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(Question #1) When atmospheric scientists describe the "weather" at a particular time and
place or the "climate" of a particular region, they describe the same sort of characteristics:
air temperature, type and amount of cloudiness, type and amount of precipitation, air
pressure, and wind speed and direction. Weather is the current atmospheric conditions
that include temperature, rainfall, wind, and humidity at any given place. If you stand
outside, you can tell how hot it is by taking a temperature reading or feel if it is raining or
windy, sunny or cloudy. All of these factors make up what we think of as weather.
Weather is what is happening right now or likely to happen tomorrow or in the very near
future.
Climate, on the other hand, is the general weather conditions. For example, in the winter,
we expect it to often be rainy in Portland, Oregon, sunny and mild in Phoenix, Arizona,
and very cold and snowy in Buffalo, New York. But it would not be particularly startling
to hear of an occasional January day with mild temperatures in Buffalo, rain in Phoenix,
or snow in Portland. Meteorologists often point out that "climate is what you expect and
weather is what you get. Climate is sometimes referred to as "average" weather for a
given area. The National Weather Service uses values such as temperature highs and lows
and precipitation measures for the past thirty years to compile "average" weather for any
given area. However, some atmospheric scientists consider "average" weather to be an
inadequate definition. To more accurately portray the climatic character of an area,
variations, patterns, and extremes must also be included. Thus, climate is the sum of all
statistical weather information that helps describe a place or region. Climate can be
applied more generally to large-scale weather patterns in time or space (for example, an
Ice Age climate or a tropical climate).
To investigate how climate may be changing due to human influences, scientists use
weather data from as far back as the historical record goes, as long as the data are
accurate. Detailed daily weather data are collected at surface meteorological stations
(weather stations) throughout the world. However, several factors can limit the accuracy
of the data. For example,
1.)Many stations are in or near urban areas, which often experience warmer temperatures
than the surrounding rural land. This is due to the heat absorbing properties of concrete
and asphalt and the lack of shade and evaporative cooling from vegetation. This
phenomenon is known as the "heat island effect."
2.)Many weather stations have been moved from rural locations to airports, making it
difficult to interpret and compare measurements over time.
(Question #2) Clouds look different depending on what they are made of. Water droplet
clouds tend to have sharp, well-defined edges. If the cloud is very thick, it may look gray,
or even black. This is because the sunlight is unable to pass through. Ice crystal clouds
tend to have fuzzy, less distinct edges. They also look whiter.
There are three basic cloud forms. Stratus clouds form in blanket like layers. Cumulus
clouds are puffy clouds that appear to rise up from a flat bottom. Cirrus clouds form at
very high altitudes out of ice crystals and have a wispy, featherlike shape. If rain or snow
falls from a cloud, the term nimbo -for "rain"- is added to the cloud's name.
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.
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.
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.
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.
A contrail, also known as a condensation trail, is a cirrus-like trail of condensed water
vapor often resembling the tail of a kite. Contrails are produced at high altitudes where
extremely cold temperatures freeze water droplets in a matter of seconds before they can
evaporate.
Billow clouds are created from instability associated with air flows having marked
vertical shear and weak thermal stratification. The common name for this instability is
Kelvin-Helmholtz instability. These instabilities are often visualized as a row of
horizontal eddies aligned within this layer of vertical shear.
Mammatus are pouch-like cloud structures and a rare example of clouds in sinking air.
Sometimes very ominous in appearance, mammatus clouds are harmless and do not mean
that a tornado is about to form; a commonly held misconception. In fact, mammatus are
usually seen after the worst of a thunderstorm has passed.
Orographic clouds are clouds that develop in response to the forced lifting of air by the
earth's topography (mountains for example).
Pileus (Latin for "skullcap") is a smooth cloud found attached to either a mountain top or
growing cumulus tower.
(Question #3) Air masses are large bodies of air which have temperature and moisture
characteristics nearly the same in the horizontal. The characteristics of an air mass derive
from the region over which the air mass forms, called its source region. The source
region is generally a region of light surface winds which allows the air to remain in
contact with the surface long enough for the air to take on the temperature and moisture
characterizes of the region over which the air is lying.
As the air mass moves out of its source region, directed by the upper air flow, they may
move across the location where you live bringing the temperature and moisture
characteristics of the source region to you and they may encounter other air masses with
different characteristics such as:
1.)Continental Arctic (cA): This air mass is characterized by extremely cold temperatures
and contains very little moisture. These air masses form north of (or very near) the Arctic
Circle and pole ward and usually affect the United States primarily in the wintertime. As
shown by the image, they typically enter the United States from across Canada into the
northern states and then move southeastward affecting the central and eastern part of the
country. These air masses can move into Texas bringing clear, but cold conditions, the
"Texas or Blue Norther." They bring bitterly cold temperatures and dry air to the affected
areas. Continental Arctic air masses affect the continental United States usually in winter
and rarely affect any of the states during the summer.
2.)Continental Polar (cP): Continental Polar air masses are also cold to cool and dry, but
are not as cold as the Arctic air masses. Continental Polar air masses form farther south
over central and southern Canada. These air masses bring cold air during the winter and
cool, relatively clear, rather pleasant weather in the summer. As the continental Arctic
and continental Polar move south across the warmer land, the lower portion of the air
mass becomes warmer and may cause a few clouds to form.
3.)Maritime Polar (mP): Maritime Polar may be considered the cool, moist air mass
which affects the United States. The source region for these air masses is the northern
Pacific and the north-western Atlantic. Because they carry an abundance of moisture,
they usually produce clouds and precipitation as they move inland and are forced upward
by the rising land.
4.)Maritime Tropical (mT): Being from a source region in the Tropics and over water,
this air mass is characterized by hot, humid conditions. These air masses occur frequently
in all seasons across the south, southeastern and eastern United States. Cloudiness and
precipitation are associated with this type of air. As the air is moved northward across the
southern and eastern United States, it encounters rising land which forces the air upward
producing much cloudiness and precipitation.
5.)Continental Tropical: These are the hot, dry air masses which originate over northern
Mexico and the southwestern United States. This air mass enters the United States
through New Mexico and Arizona and frequently moves eastward to northeastward
bringing hot, dry air to western Texas. The leading edge of this air mass is often called
the dry line where it encounters the maritime tropical air mass moving northward from
the Gulf of Mexico. Frequently in the summer, rain showers and thunderstorms form
along this dry line bringing much needed precipitation to western Texas.
(Question #4) The Earth's surface spheres (atmosphere, hydrosphere, lithosphere, and
biosphere) interact and behave much like a living community. The interaction of these
spheres with solar energy and each other results in changing conditions which we refer to
as weather and climate. Before reaching the Earth's surface, solar radiation passes
through clouds and atmosphere, which reflect, scatter, absorb, and transmit various
amounts of energy. The Earth's surface reflects some of the incoming solar radiation and
absorbs the remainder. As the surface absorbs the energy, it heats and radiates the energy
back into space. When the rates of absorption and radiation are equal (radiative balance)
the Earth's temperature is stable. If the atmosphere did not exist, the Earth's surface
would reach radiative balance at 33° Celsius (60° Fahrenheit) colder than it is. However,
some gases in the atmosphere absorb some of the energy radiated from the surface. They
heat and re-radiate energy back to the surface. In this way, the atmosphere maintains a
higher surface temperature than the Earth would have without an atmosphere. This
process is called the greenhouse effect.
Much of the energy absorbed at the Earth's surface is radiated upward as infrared (IR)
thermal energy. Several gases that occur naturally in the atmosphere absorb this infrared
energy and re-radiate it back to the surface. Therefore, heat that would be lost to space is
trapped near the surface. The effect of the atmosphere and its heat-absorbing gases warms
the Earth's surface and the Earth's surface therefore reaches radiative balance at a higher
temperature than if there were no atmosphere, or an atmosphere without IR-trapping
gases. The term "greenhouse" is used to describe this phenomenon since these gases act
like the glass of a greenhouse to trap heat and maintain higher interior temperatures than
would normally occur. The atmospheric gases most responsible for this effect are water
vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone
(O3). This "greenhouse effect" occurs naturally in our atmosphere and is responsible for
the Earth's moderate surface temperature.
Water vapor and carbon dioxide are the largest contributors to the natural greenhouse
effect due to their overall abundance in the atmosphere. Methane, although at very low
atmospheric concentrations, is a much more efficient absorber of infrared radiation than
either H2O or CO2. Over a 100 year period, a molecule of methane can absorb about 25
times more IR energy than a molecule of carbon dioxide. A molecule of nitrous oxide can
absorb about 320 times more energy than one of CO2. Therefore, although methane and
nitrous oxide occur in very low concentrations, they exert a substantial influence because
they are potent absorbers.
Natural greenhouse gas concentrations have varied over time and shows variations in
CH4 and CO2 concentrations and temperature anomalies for the past 200,000 years as
derived from analysis of the Vostok ice cores from Antarctica. The major temperature
trends from warmer (140,000 yrs BP) to colder (20,000 yrs BP) are called the interglacial
(warmer) and glacial (colder) periods. CH4 varied from ~700 parts per billion by volume
(ppbv) to ~300 ppbv, CO2 varied from ~300 parts per million by volume (ppmv) to ~150
ppmv. Temperature anomalies varied about 4-5° C (Lorius and Oeschger, 1994).
Since the beginning of the Industrial Revolution about 200 years ago, atmospheric
concentrations of greenhouse gases including CO2, CH4 and N2O have risen
substantially. These increases are a result of a variety of anthropogenic activities such as
the production and use of fossil fuels, as well as other industrial and agricultural
activities.
Naturally occurring CO2 undergoes a seasonal cycle. Atmospheric CO2 is taken up
through photosynthesis of plants during the growing season and released through
respiration throughout most of the year. These exchanges are about equal over the period
of one year. This biospheric cycle is the major cause of the large seasonal oscillations in
atmospheric concentrations of CO2. In addition, naturally occurring forest fires release
CO2 when the vegetation is burned. This disturbance in the cycle is followed by a longer
term uptake of CO2 by re-growth of vegetation lasting years to decades after the fire.
Anthropogenic activities perturb the natural carbon cycle. During the last ~200 years,
atmospheric concentrations of CO2 have increased about 25%. Because CO2 is not
chemically active, terrestrial emissions either accumulate in the atmosphere or are taken
up by the oceans or by the terrestrial biosphere (vegetation and/or soil). The largest single
source of atmospheric CO2 is the burning of fossil fuels which accounts for ~80% of the
annual emission from the Earth to the atmosphere (Matthews 1997). CO2 is also emitted
from vegetation and soils from tropical deforestation and from savanna fires. A portion of
the CO2 emitted from the Earth accumulates in the atmosphere while some is taken up by
the oceans and by the re-growth of northern forests following abandonment and fires.
Naturally occurring terrestrial N2O emissions are primarily due to microbial action in
soils especially in tropical regions. These processes are strongly controlled by the status
of oxygen, water, and nutrients in the soils.
Anthropogenic activities have contributed to a 10% growth in methane concentrations in
the atmosphere over the last ~200 years. Anthropogenic sources include land clearing,
biomass burning, fossil fuel combustion, and nitrogen fertilizer use. Unlike CO2, nitrous
oxide is chemically active; it is broken down in the stratosphere by sunlight (photolysis)
and other chemical reactions.
Naturally occurring terrestrial methane emissions are dominated by wetlands where
anaerobic decay of organic material results in production and release of methane. Other
natural methane sources include wild fires in both forests and grasslands, and wild
animals.
Atmospheric concentrations of methane have approximately doubled during the last two
centuries. Anthropogenic sources include rice cultivation, agricultural animals such as
cattle, animal waste, landfills, and the mining, processing, and distribution of fossil fuels.
The emission of methane by both natural and anthropogenic sources varies seasonally.
For example, methane is produced only when wetlands at high latitudes are warmed and
thawed or when rice fields are flooded. Since methane is chemically active, it is broken
down in the troposphere by hydroxyl (OH) radicals eventually forming carbon monoxide.
Venus, Earth, and Mars travel in neighboring orbits around the sun. All of them are rocky
planets, but only the earth has abundant life. Only the earth has conditions which support
the presence of liquid water.
The surface temperatures of these planets are governed by three factors:
1.)the amount of energy that they receive from the sun
2.)the composition of their atmospheres and
3.)their albedos.
Venus is closer to the sun than the earth is. It has a very thick, dense atmosphere, made
up mostly of carbon dioxide. The carbon dioxide acts like a blanket and keeps the sun's
heat is trapped on the surface of Venus. This is called the Greenhouse Effect. Scientists
tell us that the temperature on Venus is about 890 degrees Fahrenheit. This is 477 degrees
Centigrade (or Celsius). At this temperature lead and tin would be melted. Carbon-based
life forms would be vaporized. Water would boil away. It is difficult to discover what the
surface of Venus is like. Our earth probes do not survive long in the heat, and the dense
atmosphere makes it difficult to transmit information and signals.
Earth would be too cold for life if it had no atmosphere. The atmosphere holds enough of
the sun's heat to make life possible here. Temperatures on earth range from a high of
perhaps 130 degrees Fahrenheit to about -90 Fahrenheit. There are places on earth in
which it is challenging for us to stay alive. For example, the temperature on earth in Los
Angeles is about 70 degrees Fahrenheit, which is 21 degrees Centigrade. This is pleasant
for carbon-based life forms, though some with adaptations for cold might feel
uncomfortably warm.
Mars is the furthest rocky planet from the sun. It is a smaller planet than the earth, and
has lost much of its atmosphere. The weaker gravity of Mars allows more atmospheric
molecules to escape into space. As a result of Mars' very thin atmosphere, solar heat
escapes easily. The temperature on Mars can be as high as 50 degrees Fahrenheit (10 C)
at the equator and as low as -185 degrees Fahrenheit (-120 C) at the poles. Carbon-based
life forms could survive at the warmer temperatures (given oxygen and other necessities)
but the water in our cells freezes at 0 C, and maintaining our body heat would be
challenging in even the warmest areas. We would have to really focus on staying warm at
night and during the winters.
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