Transcript AGU Fire Poster - University of Utah

The coupled stratosphere-troposphere response
to impulsive forcing from the troposphere
Princeton University
Thomas Reichler1, Paul J. Kushner2, Lorenzo M. Polvani3
1GFDL/Princeton
University (NJ), 2University of Toronto (CA), 3Columbia University (NY)
SPARC 2004, Victoria, British Columbia, Canada
1. Objectives
4. Classification
6. Independent test
Investigate the life cycle of stratospheretroposphere interaction in a simple GCM
by stimulating a wave activity pulse from
the lower troposphere.
First, we exclude cases with abs(AM)t=0 >
2/3 and remain with 201 out of 403 cases.
Based on the timing of the tropospheric
return signal, we then classify the
experiments
into
EARLY,
INTERMEDIATE and LATE cases.
R-REM
R
From the control run we select 6
independent additional
ICs,
which most
Z’
u’
strongly satisfy the LATE criteria, and
make perturbation experiments.
2. Experimental design
We use a relatively simple model of the
stratosphere-troposphere system (Polvani
and Kushner 2002) and perturb the lower
boundary for 10 days. Then, we run out to
day 100 and observe the response. This
experiment is repeated 403 times using
independent ICs
R experiments
R control
3
z
t
2
4
i
stratosphere
1
t0
5
troposphere
t0+ t
t0+
5. Composite ICs
R
EARLY
100
0
50
100
LATE
Initial states that strongly satisfy the LATE
criteria respond in the expected way.
Rindividual
 ( p, t )
50
meridional structure at t=0
3. Mean response

0
Z’
sctl (  )( p)
7. Dynamical interpretation
• The initial weak upper stratospheric
vortex causes more wave activity to be
absorbed at higher levels, which delays
the tropospheric response.
REM
u’
• The initial EP-flux signature indicates
that wave activity just propagated out of
the lower into the upper stratosphere,
which helps to precondition the polar
vortex.
z
F’
The mean response REM does not show a
distinct downward propagating signal.
This is because the individual outcomes
are highly variable. Therefore, we have to
objectively classify the response types to
understand their variability.
t
stratosphere
LATE cases are favored by a weak and
poleward shifted polar vortex and by
decreased lower stratospheric wave drag.
troposphere
t0
t0+  1
t0+  2