Introduction
· Meteorology = the study of the atmosphere and the processes (such as
cloud formation, lightning and wind movement) that cause what we refer to as
the “weather”
· Weather is distinct from climate
in that the former deals with the short-term phenomena and the latter with the
characteristic long-term patterns.
The Atmosphere, Weather and Climate
· Atmosphere = a mixture of gas molecules, small suspended particles of
solid liquids, and falling precipitation.
· Climatology
o Relies on averages taken over a number of years in order to
gauge typical atmospheric conditions for locations across Earth’s surface.
o Also want to know about variability of the weather
elements.
o Frequencies of occurrences of weather events (such as
extreme heat, hail or lightning) are also aspects of climates.
o Concerned with changes in Earth’s climate and the factors
responsible for those changes.
Thickness of the Atmosphere
· How high is the sky?
o There is no definitive answer. However, because Earth’s
atmosphere becomes thinner at higher altitudes, even at heights of several
hundred kilometers above sea level, there is some air and, hence, an
atmosphere. But we have no way to establish its upper boundary because there is
no universally accepted definition of how much air in a given volume
constitutes the presence of an atmosphere.
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Horizontal Winds
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Vertical Winds
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Primary motion over
large areas
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Are typically
hundreds to thousands of times greater than vertical wind speeds
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Hardest to detect and
forecast
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Determine much of the
atmospheric behavior
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Composition of the Atmosphere
· The atmosphere is composed of a mixture of invisible gases
and a large number of suspended microscopic solid particles and water droplets.
· Molecules
o Molecules of gases can be exchanged between the atmosphere
and the Earth’s surface by physical
processes (i.e. volcanic eruptions) or by biological processes (i.e. plant and animal respiration).
o Can be produced and destroyed by purely internal processes (i.e. chemical
reactions between gases)
o Steady State /
Equilibrium Condition = input rate is equal
to the output rate
o Dynamic Equilibrium = molecules cycling in and out of the atmosphere
o Residence Time = average length of time that individual molecules of a
given substance remain in the atmosphere
· Homosphere
o The lowest 80 km (50 mi) of the atmosphere
o Vertical motions are more important than gravitational
settling thus processes (other than settling) under gravity must explain any
variations present.
o Reflects the homogenizing role of wind and other motions
o Gases are often categorized as being permeant or variable,
depending on whether or not their concentration is uniform.
§ Permanent Gases = found everywhere in nearly the same proportion.
§ Variable Gases = distribution is uneven in both time and space.
· Heterosphere = layer of the atmosphere (above the homosphere) where
gases segregate according to molecular weight
· Permanent Gases
o Make up more than 99% of the atmosphere
o Nitrogen (most abundant gas)
§ 78% of all permanent gasses volume or 75.5% of their mass
§ Largely unreactive
§ Occurs primarily as paired nitrogen atoms bonded together
to form single molecules denoted N2
§ Isotopes = variants of an element with different neutron counts
o Oxygen (second most abundant gas)
§ 21% of the volume of the atmosphere and 23% of its mass
§ Crucial to the existence of virtually all forms of life
§ Dynamic Oxygen = paired oxygen atoms
o Nitrogen + Oxygen = 99% of all permanent gases
· Variable Gases
o Water vapor (most abundant) is 1% of the total volume
§ Condenses to a liquid at relatively low levels in the
homosphere
§ Not uniformly distributed with altitude—at higher
altitudes, water vapor is even more rare
§ Hydrologic Cycle (water cycle)
§ Source of moisture to form clouds
§ Very effective absorber of energy emitted by the Earth’s
surface (radiant energy) thus making it one of the “greenhouse gases”
on constant pressure surfaces. However, the
slope of the isobaric surfaces and the speed of the geostrophic wind may vary
from level to level due to those thickness variations.
