Relative role of Tibetan Plateau, Asian Monsoon and the tropics in moistening of the global stratosphere

during summer season

Rong FuRong FuJackson School of Geosciences Jackson School of Geosciences

The University of Texas at Austin, USAThe University of Texas at Austin, USAJonathon WrightJonathon Wright

Department of Applied Mathematics and Theoretical PhysicsDepartment of Applied Mathematics and Theoretical Physics

University of Cambridge, UKUniversity of Cambridge, UK

International Workshop on ASM-STE

Lhasa, China, July 21-23, 2010

What control water vapor in the stratosphere?

Sources of water vapor in the stratosphere:– From the troposphere-to-stratosphere transport in the

tropics– From methane oxidation

The “tropical pipe” 70hPa

What control water vapor transport into the stratosphere?

• Whether moistening of the stratosphere during summer season is solely controlled by the tropical tropopause temperature is still debatable.

Mote et al. 1995, 1996: The “tape recorder”

Role of Asian Monsoon/Tibetan Plateau:

Importance of the Asian monsoon/Tibetan Plateau:• Chen 1995; Dunkerton 1995; Rosenlof et al. 1997: • Jackson et al. 1998, Randel et al. 2001; Read et al. 2004• Gettelman et al. 2004: contribute to ~75% of the global cross-

tropopause water vapor flux in summer

Rosenlof 1995

JulyJan

winter summer

Randel et al. 2001

• How is water vapor transported to the How is water vapor transported to the tropopause layer in the Asian monsoon/TP tropopause layer in the Asian monsoon/TP region?region?– Monsoon convection vs. convection over TP

• Could water vapor in the troppause layer Could water vapor in the troppause layer over the Asian monsoon/TP region enter the over the Asian monsoon/TP region enter the “tropical pipe”?“tropical pipe”?

By convection over the S. Asian Monsoon region:• Dethof et al. 1999: transported by monsoon convection, then

advected to the extratropical LS.

However,• Randel & Park 2006: trapped by monsoon anticyclonic

circulation.

How is water vapor transported to the tropopause layer over the Asia Monsoon/TP region?

Randel and Park, 2006: Isentropic mixing is weak

By convection over the East Asia monsoon By convection over the East Asia monsoon region:region:

• Dessler and Sherwood 2004: Water vapor is transported by extratropical convection in the East Asian monsoon region, then transported by northeasterly to the monsoon region.

• However, cannot explain the location of the moist center in the tropopaus layer.

By convection over the TPBy convection over the TP:• Fu et al. (2006): Moist air is mainly

transported by convection over TP because convection is deeper and the tropopause layer is warmer and less saturated over the TP than over the monsoon region.

• However, whether deep convection occurs frequent enough is still an open question.

CLAUS data: cloud top

TRMM PR rainrate (mm/h), JJA, 1998-2000

Fu et al. 2006,GRL

TP SLP MON

380K 203K

+7K

199K

+2K

197K

360K 212K

+12K

208K

8 K

200K

Aura MLS clear-sky temperatures:

Could moist air in the tropopause layer over the Asian monsoon/Tibetan region enter

the “tropical pipe”?

Holton et al. 1995: Source: Pan et al. 2006, UCAR TIIMES

?

Data Sets and the Model:Data Sets and the Model:

• Aura MLS, water vapor, – Water vapor: 215 hPa, 147 hPa, 100 hPa, 68 hPa, ~ 3 km vertical

interval, accuracy ~10% at 100 hPa– Temperature: accuracy: 0.5-1K

• The Goddard Fast Trajectory model: (Schoeberl and Sparling, 1995) driven by (UKMO, NCEP, MERRA) reanalysis data:– UKMO: updated daily at 12 UTC, 2.5º×3.75º lat/lon grid.– NCEP: updated 6 hrs, 2.5º lat/lon grid.– GMAO MERRA: updated 6 hrs, 1.25º lat/lon grid

What determines water vapor transport?

– Air mass transport– Water vapor loading, the dry point (the

coldest temperature)

• Start back-trajectories at annual maximum of WV at based of BDC in the tropics (68 hPa)

• ;

Identify the source regions for the stratospheric moistening?

Density distribution of back-trajectory (air mass) enter convective detrainment zone at 215 hPa is highest over

the Asian monsoon/Tibetan Plateau.

At 68 mb, MLS H2O >3.6 ppmv, Oct-Dec, 12˚S-12˚N.

40 days ago

80 days ago 120 days ago, July-Sept.

Mostly from the Asian monsoon region!

UKMOreanaysis

NCEP/NCAR GMAO/MERRA

Density distribution of back-trajectory (air mass) enter convective detrainment zone at 215 hPa is highest over the Tibetan Plateau and S. China Sea.

• Tibetan Plateau is an importance source region of the air mass that enters the global stratosphere.

Density distribution of back-trajectory (air mass) encounter deep convection (CLAUS, < 240 K) is highest over the Tibetan Plateau and S. China Sea.

NCEP MERRA

What is the relative contribution among different source regions to the air mass that enters the “tropical pipe”.

CAMTIB

MOMSCS

NCEP reanalysis:• About 25-30% of the air mass that enters the “tropical

pipe” comes from Tibetan Plateau and South China Sea, respectively.

SCS

TIB

TRP MON

MERRA reanalysis:• About 25-30% of the air mass that enters the “tropical pipe” comes

from tropics and South China Sea, respectively.

• Only 10% comes from the Tibetan Plateau..

What about water vapor loading?

• The “dry point” for air originated from Tibetan Plateau is wetter than any other regions for fast transport (120 days) in both reanalysis products.

TIB

TIB

TRP

Water vapor transport from each regions:

• Air from Tibetan Plateau carries the highest concentration of water vapor,

• Air from the tropical UT is the driest.

Unrealistically low q*

• Why is more air mass at the base of the “tropical pipe” originated from Tibetan than from the monsoon and tropical region?

Why?• Radiative driven upward motion

peaks at 30˚N in summer. • Strong tropical-extropical

exchange below 420K-450K, ~40-50% air in tropics comes from extratropics: Rosenlof 1995; Tunk et al. 1997; Mote et al. 1997

Bannister et al. 2004

Rosenlof 1995

Conclusions:

• 10% to 25% of the air at the base of the “tropical pipe” can be traced back to the upper troposphere over the Tibetan Plateau; • 10-40% from the tropics• 10% or less from the monsoon region

• Transport from TIB exhibits greater moisture loading, whereas transport from the tropics exhibits the lowest moisture loading, relative to other source regions.

• 10% to 25% of the air at the base of the “tropical pipe” can be traced back to the upper troposphere over the Tibetan Plateau; • 10-40% from the tropics• 10% or less from the monsoon region

• Transport from TIB exhibits greater moisture loading, whereas transport from the tropics exhibits the lowest moisture loading, relative to other source regions.

Final Remark:

• Convection and warm tropopause temperature over the Tibetan Plateau appear to play an as important role in moistening the global stratosphere as the tropics during boreal summer.

• The relative role between the tropics and the Tibetan Plateau in determining water vapor change in the stratosphere needs to be further clarified.