Five Basic
Laws Used by Meteorologists to Understand
the Evolution
of Atmospheric Flow Patterns
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1. Ideal Gas Law (Equation of State) --
expresses the relationship of the pressure a gas exerts to the volume it
occupies and its temperature. (The product of the pressure a gas exerts and the
volume the gas occupies is directly proportional to the temperature of the
gas).
Heating the atmosphere causes it to expand
(special application of the gas law)
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2. Newton's Second Law of Motion (Equation
of Horizontal Motion) -- states that the acceleration experienced by an object
is due to the sum of the forces acting on the object . (An object at rest will be accelerated
in proportion to the forces that act on the object). (F = ma)
How Wind
Develops: -- air
motion can be understood on the basis of the forces that cause air to
move. In the absence of all other
forces, at a given elevation (say, sealevel or at
18000 feet), air tends to be accelerated horizontally from regions of higher
pressure to regions of lower pressure.
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3. Hydrostatic Law (Obtained from the
Equation of Vertical Motion) -- the upwards directed pressure gradient force
acting on an air parcel (explained in class) is balanced by the weight of the
air parcel.
How Vertical Winds Can Develop [special case
of (2)]
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4. First Law of Thermodynamics -- the
temperature changes experienced by an air parcel can be put into two general
categories: i. those related
to direct heating or chilling of the air parcel (termed sensible or diabatic heating or cooling; and, ii. those
related to non-direct heating or chilling associated with expansion or
contraction of the air parcel (termed adiabatic
heating or cooling).
How temperature changes
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5. Conservation of Mass Applied to the
Atmosphere (Equation of Continuity ) -- with
respect to the sealevel weather map, pressure changes
occur because of net accumulation
or net deficit of air in the air column above. (In simplified form, this
is termed Dine's Compensation by synoptic meteorologists -- which
states the result of this principle on atmospheric flow -- upper level
divergence tends to be balanced by lower level convergence and vice versa).
How pressure
changes at a given level develop--creation of high and low
pressure area. Also, upper tropospheric
divergence tends to be larger than the compensating lower level
convergence: hence, surface low pressure areas develop under regions of upper tropospheric divergence.