gps tropical tropopause temperatures and stratospheric water vapor william randel 1 and aurélien...
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GPS tropical tropopause temperatures
and stratospheric water vapor
William Randel1 and Aurélien Podglajen2
1NCAR Atmospheric Chemistry Division2Pierre and Marie Curie University - Paris
QJRMS, 1949
The stratosphere isextremely dry because
air is dehydratedpassing the cold
tropical tropopause
QJRMS, 1949
17.5 km
Large annual cycle in tropical tropopause temp.
QJRMS, 1949
global climatology
Objective: study correlated behavior of stratospheric H2O and GPS cold point tropopause temps on daily to annual time scales
• Can we understand the large-scale behavior of H2O in a simple way from accurate temperatures?
• When and where does dehydration occur?
• Empirical complement to trajectory studies
Data:
GPS radio occultation temps:
• Daily data from CHAMP, COSMIC, others ~3000 obs/day for middle 2006-present
• High vertical resolution (~ 1 km), well-resolved cold point
• Saturation mixing ratios Qsat (RH=1.0)
MLS water vapor:
• daily gridded fields at 100, 83, 68, … hPa; late 2004 – 2012
GPSmeasurements
gridded
GPS temps
Daily griddeddata set
5o x 20o x 0.2 km2006 - 2012
Large-scale variability at the tropical tropopause (10o N-S)
0 180 360longitude
time
GPS Temperature spectra at 17 km
Mixed Rossby gravity waves
2
5
10
30
3
Antisymmetric
Kelvin waves
MJO
Symmetric 2
5
10
30
3
Perio
d (d
ays)
Zonal wavenumber Zonal wavenumber
westward eastward westward eastward
Temperature spectra at 23 km
Kelvin waves
Symmetric 2
5
10
30
3
Perio
d (d
ays)
Zonal wavenumber
Mixed Rossby gravity waves
Antisymmetric
Zonal wavenumber
2
5
10
30
3
westward eastward westward eastward
MLSorbitaldata
gridded
MLS H2O100 hPa~ 16 km
Temps
H2O
2005 2006 2007 2008 2009 2010 2011 2012
Tropical tape recorder observed by MLS 2004-2012
cold pointtropopause
Cold phase of tropopause annual cycle
100 hPa H2O GPS tropopause temperature Boreal Winter15o N-S
2009-2010
time
GPS saturation mixing ratioBoreal Winter15o N-S
2009-2010
time
100 hPa H2O
100 hPa H2OBoreal Winter15o N-S
2009-2010
time
GPS saturation mixing ratio
100 hPa H2OBoreal Winter15o N-S
2010-2011
time
GPS saturation mixing ratio
Fractional area of RH>1 for 20o N-S and 100 and 83 hPa
Max duringboreal winter
frac
tion
.30
0
.15
2007 2008 2009 2010 2011
Winter (DJF) Summer (JJA)
Fraction of RH > 1.0 at 100 hPa locations where dehydration may occur
0.45 0.25
longitude
latit
ude
longitude
Dehydration mainly over ~20o N-S
40 N
40 S
Fraction of RH > 1.0
at 100 hPa
Schoeberl and Dessler 2011
Dehydration locations derived fromLagrangian trajectories
Winter (DJF)
longitude
40 N
40 S
Summer (JJA)
Schoeberl and Dessler 2011
Trajectory dehydration location
longitude
Fraction of RH > 1.0
at 100 hPa
40 N
40 S
Winter (DJF)
longitude
40 N
40 S
Distribution of relative humidityin western Pacific
100% 140%
freq
uenc
y
Key points:
• MLS and GPS data sets provide opportunity to understand H2O – T coupling on daily to interannual time scales
* links to clouds, dynamics of the TTL
• Dehydration regions (RH > 1.0) occur mainly duringboreal winter. Summertime behavior is less-wellunderstood.
• Observed dehydration patterns compare well with trajectory calculations. Where are the differences?
Thank you
Africa
Lidar cloud observations from CALIPSO
100 hPa H2O
83 hPa H2O
Qsat at the cold point
Qsat 15% driest area
Zonal averages 15o N-Spp
mv
100 hPa H2O15o N-S
GPS saturation mixing ratio at locations where RH > 1.0
H2O vs. Qsat
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