Stratosphere and Troposphere Exchange (STE)

Above the Tibetan Plateau

Wenshou Tian, Min Zhang, Hongying Tian

Lanzhou University, Lanzhou, China

Martyn ChipperfildUniveristy of Leeds, Leeds, UK

兰 州 大 学 大 气 科 学 学 院College of Atmospheric Sciences, Lanzhou University http://atmos.lzu.edu.cn

Prepared for 2010 ASM-STE, Lhasa, July 21-23, China

BackgroundBackground

Chinese Scientists first found the Chinese Scientists first found the ‘‘ozone valleyozone valley’ over Tibetan Plateau ’ over Tibetan Plateau (TP) from observations (e.g., Zhou (TP) from observations (e.g., Zhou et al., 1995).et al., 1995).

The absence of about 4 km air column itself can lead to a reduction of TCO by around 2.5%, but this is not enough to account for all the observed decrease of column ozone over the TP in summer, which may reach 11% in May (Ye and Xu, 2003, Coldewey-Egbers et al., 2006).

Ozone valley vs Strong STE?

Westerly winds

STE contributes to Ozone Valley

Asia summer monsoon

Strong Concevtion

TP, average height 4 km ASL

The recent studies showed that The recent studies showed that TPTP and and Asia Asia monsoon circulation provide an effective pathway for pollution from Asia to enter the global stratosphere (e.g., Fu et al ., 2006; Randel et al., 2010).

What are the main STE processes over the TP? Where is the favorable location for STE over the TP? What is the contribution of atmospheric chemistry processes to the ozone valley over the TP?

‘ Ozone valley’ – STE - Chemistry

Modelling study of STE over the Modelling study of STE over the TP using a CCM.TP using a CCM.

Modeling of a Tropopause fold event using a meso-scale model (WRF).

What we have done

TOMS Total Column Ozone Over TP

ERA-40 Thermal and Cold point TropERA-40 Thermal and Cold point Tropopause Height over TPopause Height over TP

Thermal tropopause heightIs highest from July to august

Cold point tropopause height is highest from Mar March to May

Thermal tropopause

Cold point tropopause

Deep Convective Systems from TRIM SatelliteDeep Convective Systems from TRIM Satellite

Courtesy to Dr Tie Yuan

TPWP

ModeledModeled O3 Profiles over TP

OzoneOzone

Compared to the annual mean ozone profile, the summer (JJA) ozone profile over the TP is shifted upward, and the winter (DJF) ozone profile is shifted down (12-22 km).

Over the western TP, this shift is relative small and confined bellow 17 km.

Modeled Modeled Geopotential Height over TP in the Stratosphere

CCM O3

(July and August mean)

CCM CH4

(July and August Mean)

Modelled O3 and CH4 on 380K Surface

CCM NOx

(July and August Mean)

CCM CO

(July and August Mean)

Tian et al, 2008, TELLUS B

Modelled NOx and CO on 380K Surface

Atmospheric chemistry may play a role.

A Tropopuase Fold EventsA Tropopuase Fold Events

CALIPSO image

Pulse Radar Image

Surface zone concentratiosn

A Tropopause Fold Event over TP

Zhang, Tian ,Chen, Lv , 2009, AAS

Orographic Effects on the Tropopause Fold

With the real topography

With the real terrain height higher than 1.5 km decreased by 10%

With the real terrain height higher than 1.5 km decreased by 20%

Continuous STE over the Slope of the Northern TP

When cold air from the north push towards the northern slope of the TP, forced lifting together with cold fronts can inject tropospheric air directly into stratosphere

AIRS Water Vapor at 100hPa over the TP

Tian et al, 2010, ASL

AIRS Cloud Top Pressure over the TP

Temperature and Potential Vorticity Distributions on the 350K Surface

1. The variation of tropopause height over the TP is accompanied by large-scale uplift of isentropic surfaces in summer This leads to upward and downward shifts of tracer vertical profiles of several kilometers.

2. It is also found that the monsoon anticyclone circulation causes an isentropic transport of trace gases from the higher latitudes towards over the TP.

• Chemistry processes may also play a role.

Summary

1. The slope of the northern TP is also a favorable location for the STE.

2.Changing of the terrain height has no significant effects on the morphology of folds but can change its propagation speed.

3.The quantitative contribution of meso scale processes on the STE over the TP worth further investigation.

Summary Continued

兰 州 大 学 大 气 科 学 学 院College of Atmospheric Sciences, Lanzhou University http://atmos.lzu.edu.cn