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Absolute Vorticity
A measure of the total spin in the atmosphere. It is the sum of the spin due to the Earth’s rotation (the Coriolis force) and the relative vorticity.

Adiabatic Process
A process in which no heat is added or removed from an air parcel. The temperature change is due solely to expansion or contraction of the air parcel.

Advection
The horizontal transport of some property of the atmosphere (e.g., temperature, vorticity, moisture) by the wind.

Curvature vorticity
Rotation due to curvature of the wind flow (curvature in the contour lines or streamlines).

Dine’s Compensation Rule
The condition in which upperlevel convergence (divergence) is approximately balanced by lowlevel divergence (convergence)

Equivalent Potential Temperature (Θe):
The temperature of an air parcel if it is lifted pseudoadiabatically until all moisture is condensed, then lowered dry adiabatically to 1000 MB.

Geopotential Height
A measure of the height given in geopotential meters rather than true meters (2998m=3000gpm at 45ºN).

Geostrophic Wind
The “hypothetical” wind generated by the balance between the pressure gradient force and the Coriolis effect. The geostrophic wind flows with high pressure (heights) to the right. The geostrophic wind is a good approximation for the actual wind for straightline flow without friction.

Isentrope
A line of constant potential temperature.

Positive Vorticity Advection (PVA)
The horizontal transport of decreasing vorticity (anticyclonic spin) to some location.

Potential Temperature (q)
The temperature a parcel of air would have if it were moved dry adibataically to 1000 MB.

Relative Vorticity (ζ)
A measure of the local spin in the atmosphere. It does not include the vorticity due to the Earth’s rotation (the Coriolis force).

Solenoids
Boxes formed by the intersection of geopotential height contours and isopleths of some atmospheric property. The size of the solenoids represents the amount of advection (smaller boxes means greater advection).

Specific Heat
The amount of energy it takes to raise the temperature of 1g of water by 1 ºC.

Synoptic Scale
The size of migratory high and low pressure systems in the lower troposphere that cover a horizontal area of several hundred miles or more.

Thermal Wind
A component of the wind generated by temperature differences in the atmosphere. The thermal wind blows with warm air to the right. Also defined as the vector difference of the upperlevel geostrophic wind minus the lowerlevel geostrophic wind.

Thickness
The difference in geopotential height between two pressure levels (commonly 500 and 1000mb). According to Poisson’s equation, the thickness is directly proportional to the mean virtual temperature of the layer defined by the two pressure levels.

Vorticity
A measure of “spin” in the atmosphere. Positive vorticity is a cyclonic spin (counterclockwise in the Northern Hemisphere); negative vorticity is an anticyclonic spin (clockwise in the Northern Hemisphere).

Warm Air Advection (WAA)
The horizontal transport of warm air to some location, associated with increasing temperatures.


Temperature
measure of internal (thermal) kinetic energy of a system.

Heat
thermal energy transferred between systems at different temperatures.

Heat Capacity
Ratio of the amount of energy absorbed by the substance to the temperature rise that occurs in the substance.

Diabatic Process
Loss or gain of energy or heat from a system

Adiabatic process
No exchange of heat with the surroundings.
 – Lifting and lowering of unsaturated air is an adiabatic process.
 – Temp change due to expansion and contraction without loss or gain of heat

Dry adiabat
A line of constant potential temperature used in a vertical profile of the atmosphere.

Theta surface or isentropic surface
A surface of constant potential temperature, as opposed to a constant elevation or constant pressure surface.
– Often used on cross sections

Ideal Gas Law
Pressure = Density * Constant * Temperature
pV = ρRT
  p = pressure (Pa)
  V = volume (m3)
  ρ = mass or density (kg)
  R = gas constant (J K1 kg1)
  T = temperature (K)

dryair gas constant
R = 287 J K1 kg1

If we hold temperature Constant...
 pV = ρRT
 Pressure ~ Density
 At the same temperature, air at a higher pressure is more dense than air at a lower pressure.

If we hold pressure constant...
 P = ρRT
 (constant P) * 1/R = T*ρ
 At a given atmospheric pressure, air that is cold is more dense than air that is warm.

Virtual Temperature
The temperature dry air would need to attain in order to have the same density as moist air at the same pressure.

geopotential
Is the amount of work necessary to raise the mass of air to some height (or pressure!)

Planetary boundary layer
is a viscous sublayer that has profound consequences for atmospheric flow.

Omega Equation
for which f is the Coriolis parameter, σ is the static stability, vg is the geostrophic velocity vector, ζg is the geostrophic relative vorticity, φ is the geopotential, ∇H2 is the horizontal Laplacian operator, and ∇H is the horizontal del operator.The righthand side of the omega equation can also be expressed in terms of the divergence of the Q vector.

