GPS tropical tropopause temperaturesand 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

fracti

on

.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