Intraseasonal variations of upper tropospheric water vapor

in Asian monsoon region

Intraseasonal variations of upper tropospheric water vapor

in Asian monsoon region

Jianping Li1, Ruifen Zhan2 and A. Gettelman3

1. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing;

2. Shanghai Typhoon Institute of China Meteorological Administration, Shanghai;

3. National Center for Atmospheric Research, Boulder, CO, USA

International Workshop on Asian Summer Monsoon and Its Role in Global Stratosphere-Troposphere Exchange (ASM-STE)

July 21-23, 2010, Lhasa, ChinaACPD, 2006

Introduction

Data and methodology

The UTWV distribution

UTWV characteristics associated with ISO in Asian monsoon region

Relationship with the Asian summer monsoon

Conclusions

OutlineOutline

IntroductionWhy concern intraseasonal oscillation (ISO) of upper troposphere water vapor (UTWV)?

UTWV is one of the key greenhouse gases UTWV is a major source of the hydroxyl radical UTWV is also a valuable tracer of atmospheric

motions and transports significant amounts of energy in the form of latent heat.

The ISO can affect not only the humidity field in the troposphere but also stratosphere-troposphere exchange.

The Asian monsoon region is believed as the main source of the UTWV between May and September (Dethof

et al. 1999; Gettelman et al., 2004; Randel and Park, 2005). About 75% of the total net upward WV flux at tropopause levels is contributed by the Asian monsoon circulation from July to September (Gettelman et al., 2004).

The Asian summer monsoon is well known for its prominent ISO. Since the summertime WV field in the upper troposphere often exhibits a monsoon signature, it seems significant to document UTWV seasonal variability associated with the ISO in the Asian monsoon region.

Why focus on the Asian summer monsoon region?

What are the seasonal characteristics of UTWV associated with ISO in Asian monsoon region?

What are the relationships between UTWV and Asian summer monsoon on the intraseasonal time scale?

QuestionsQuestions

Data & methodology

AIRS Water Vapor:

May-September in 2003 and 2004, 1°x1° grid, available on 12 standard pressure levels over 1000-100 hPa

NCEP/NCAR u, w and OLR:

May-September of 2004, 2.5° x2.5° grid

Continuous Spectrum Analysis

Butterworth Band-Pass Filter

Lag correlation

South Asia

Asian monsoon region

East Asia

EASMEASMSASMSASM

UTWV global distribution

Global distribution of water vapor (ppmv) from AIRS data at 200 hPa averaged in 15-30 August 2004. White solid lines indicate contours of tropopause pressure (150, 120 hPa).

UTWV distributionUTWV distribution

HovmÖller plot of daily AIRS WV at 200 hPa averaged over 2030N from May to September 2004. The black sold contours are 35 ppmv.

UTWV distributionUTWV distribution

Power spectra of the UTWV Power spectra of the UTWV

South Asia East Asia

Power spectra (thick solid line) for 5-day running mean 200 hPa WV from May to September 2004 based on AIRS.

30-60 day mode: 61%10-20 day mode: 13%

Total: ~74%

UTWV cUTWV characteristics associated with ISO in Asian monsoon region

30-60 day mode: 67%10-20 day mode: 14%

Total: ~81%

Longitude-time sections of the UTWV associated with the ISO

30-60d mode in 2003

Averaged over 15-25N

30-60d mode in 2004

0 3 6 9 0 3 6 9 12

Source of the UTWV(a) South Asia (b) East

Asia

South Asian pattern

East Asian pattern

Influence of monsoon sub-system is independent?

Time-longitude cross-section of lag correlations of 1025N 5-day running mean WV (without the band-pass filter) at 200 hPa with WV averaged over (a) 6575E and (b) 120130E based on AIRS. Positive lags correspond to WV averaged over 1025N leading.

Is the longitudinal 3060d oscillation of UTWV related to ISO of Asian monsoon deep convection?

If so, what is the relationship between monsoon convection and UTWV?

Relationship with the Asian summer monsoon

Source of monsoon convection

Like the UTWV, the convective fields also exhibit the pronounced regional reverse ISO patterns in two monsoon systems.

South Asia East Asia

Lag correlations of 1025N 5-day running mean OLR with OLR averaged over (a) 6575E and (b) 120130E.

Characteristics of UTWV associated with 30-60d oscillation in Asian monsoon region

SASMSASM EASMEASM

OLR

UTWV Longitude-pressure sections of 30-60d filtered WV (ppmv, shading) based on AIRS and vertical wind components (vectors) from Pentad 40 (15~19 Jul) to Pentad 48 (24~28 Aug) in 2004.

The longitudinal distribution of 30-60d filtered OLR for the same period. The red line represents the enhanced convection. All plots are for 15-25N.

Lag correlations between OLR and UTWV

Lag correlations between OLR and AIRS WV on 3060 day band in (a) South Asia (3597.5E, 522.5N) and (b) East Asia (110140E, 020N) during May-September 2004. Positive lags refer to OLR leading WV.

South Asia East Asia

The high UTWV lags the enhanced monsoon convection by about 1-2 pentads, suggesting that the upper troposphere is generally moistened following intense monsoon convection.

ConclusionsConclusions

The pronounced regionally propagating features of UTWV associated with an ISO in the Asian summer monsoon region with an emphasis on relationship to the Asian monsoon. The UTWV peak in summer lies not only in South Asia but also in East Asia.

The ISO of UTWV has two significant periods, a 30-60d mode and a 10-20d mode, respectively. The 30-60d mode is dominant in the intraseasonal variability of UTWV over the Asian monsoon region in summer. The mode exhibits two distinct patterns in the two monsoon sub-systems, defined as the South Asian pattern and East Asian pattern, respectively.

ConclusionsConclusions

Like the UTWV, the convection also exhibits the pronounced regional ISO patterns in two monsoon systems.

The lag correlation pattern between OLR and the UTWV on 30-60d band shows that the upper troposphere is moistened following the enhanced monsoon convection with lags about 5-10 days. The result shows that the Asian summer monsoon plays an important role in the intraseasonal variations of UTWV.

Thank you!Thank you!

AIRS global distributionAIRS global distribution

Global distribution of water vapor (ppmv) from AIRS data at 150 hPa averaged in 15-30 August 2004. White solid lines indicate contours of tropopause pressure (150, 120 hPa).

The peak (~18 ppmv) is a widely elongated belt stretching eastward from the Indian subcontinent to the East Asia, including China and south of Japan

(c) 10-20-day mode in 2003 (d) 10-20-day mode in 2004