* Metastable conditions, or why did it rain on my picnic?
Fovell, 1995-2011
Below, the curve labeled "Env" shows how the environmental air temperature varies with height. These data are collected by
launching an instrumented weather balloon. Note the tro

Some routes to saturation
AOS 101 Winter, 2013 Fovell
Denition of terms and the Stuve diagram
The mixing ratio expresses the ratio of the water vapor mass to the dry air mass in an air parcel.
The saturation mixing ratio , rs , represents the maximum amou

Gravity waves
derivation
A&OS C110/C227 - Spring, 2013
Introduction
Gravity waves describe how environment
responds to disturbances, such as by
oscillating parcels
Goal: derive dispersion relation that
relates wave characteristics (wavelength,
period) t

Gravity waves
AS 101 Fall, 2002 Fovell
Previously, we examined the oscillatory behavior of a displaced air parcel within a stable
environment. We obtained a pendulum-like equation in which the frequency was proportional to the vertical gradient of potenti

1
Total Derivative
Suppose
. The differential of this is
.
If we divide this expression by the dt we obtain
where
=total derivative (Lagrangian method of describing the motion); for changes in
following the parcel,
=local derivative (Eulerian method of de

A&OS C110/C227 Vorticity and circulation
Winter, 2011 Fovell
Vorticity
Vorticity is a measure of rotation, represented by the curl of the 3D vector velocity eld, namely
Vorticity = =
V =
w v
u w
v
u
i+
j+
k.
y
z
z
x
x y
Note that the th (x-direction)

1
Momentum Equation
The vector momentum equation can be written as
dV
1
= p 2 V + g + FR
dt
where
dV
1
dt =relative acceleration, p =pressure gradient force, 2 V =Coriolis force
g =gravity, and FR =friction.
It is useful to break the above equation into c

1
Quasi-Geostrophic -Equation
For large-scale ow in the atmosphere, we have learned about two very important characteristics:
1. The atmosphere is approximately hydrostatic.
2. The atmosphere is approximately geostrophic.
These two features are what we me

13 February 2006 case
NAM 12Z model run
Forecast hour 00
500 mb heights, winds
Add 500 mb abs. vort.
See PVA region.
850 mb heights, winds.
See PVA (much) smaller.
See cold advection.
Add 500 mb thickness
Add 500 mb thermal wind
vectors
500 mb thermal win

A&OS C110/C227 Potential vorticity and lee-side troughs
Winter, 2012 Fovell
Potential vorticity
On an isentropic surface, even in a baroclinic atmosphere, there are no pressure-density solenoids
and thus absolute circulation Ca is conserved. That is,
dp
=

Radar Meteorology
AOS C110/C227
Fovell
Spring 2013
Goals
Gain apprecia?on of uses and limita?ons of radar
informa?on
Summarize materials available through Comet
Program
Create free account at hFps:/www.meted.ucar.edu