On Earth, most weather occurs within the first ten to fifteen
kilometers of the atmosphere. In fact, 99% of the gases in the atmosphere are
around thirty kilometers above the Earth’s surface. Most of the atmosphere
contains nitrogen and oxygen with trace amounts of water vapor and a miniscule
amount of CO2. Clouds are not made up gas, but are condensed vapor
in liquid droplet form. Recently, carbon dioxide, methane and nitrogen oxides
have increased in the atmosphere. CO2, specifically, has
risen more than 18% from 54 years ago. Many scientists are blaming fossil fuels
for this dramatic increase. Aerosols and pollutants can lead to the greenhouse
effect as well and are caused by both human and natural activities, from
factory emissions and volcanoes. Examples of aerosols include sea spray,
volcanic ash and pollutants from factories.
Gravity is the main ingredient to
air pressure. Air pressure is the amount of force exerted over an area.
Likewise, air density is the number of air molecules in a given volume.
Atmospheric pressure decreases with altitude. Lapse rate is the rate where air
temperature decreases with height. The average lapse rate in the atmosphere is
about 6.5 degrees Celsius per one kilometer, or 3.6 per 1,000 feet. Air
pressure can also be explained through opposite air temperatures and their
effects. Warm air, or expanding or rising air, leaves behind low pressure where
as cold air, or sinking air, leaves an area of high pressure.
Sunlight can go through the
atmosphere and do two things on Earth: it can either be absorbed or reflected,
depending on the albedo, or the fraction of solar radiation reflected back into
space, or absorption, the fraction of solar radiation not reflected into space.
The absorption of sunlight in urban areas leads to the urban heat island effect
which is caused primarily by modification of land surfaces in developments that
use materials that retain heat.
Another key member of the atmosphere
is the cloud. Generally speaking, clouds can be classified according to their
altitudes: low level clouds are stratus clouds and use the prefix, “strato”, mid-level
clouds have the prefix, “alto” and higher level clouds have the prefix, “cirro”
or are plainly called cirrus clouds. Not only does altitude identify clouds,
but their shapes do as well.
What is wind? Seemingly complicated,
the explanation is, however, sensible. Due to the uneven heating of Earth’s
surface, different temperatures have to be moved around to balance the planet’s
temperature. Warm weather at the Equator is moved to other parts of the world
to cool them down or heat them up. Similar to temperature, winds blow from high
pressure areas to low areas of pressure. The pressure also describes the
tendency of the air to rise or sink at any given place or time.
Finally, humidity is also very
important to discuss in regards to the atmosphere. Humidity is the amount of
water vapor stuck in between molecules in the air. The air’s ability to hold
water also depends on the air temperature. Relative humidity is often measured
for humidity, and it measures the amount of water vapor compared to the amount
of air it can hold through percantages. For example, air is saturated at 100%.
