Stratosphere and Troposphere Exchange (STE) Above the Tibetan Plateau Wenshou Tian, Min Zhang, Hongying Tian Lanzhou University, Lanzhou, China Martyn Chipperfild Univeristy of Leeds, Leeds, UK Prepared for 2010 ASM-STE, Lhasa, July 21-23, China

Background Chinese Scientists first found the ‘ozone valley’ over Tibetan Plateau (TP) from observations (e.g., Zhou et al., 1995). Chinese Scientists first found the ‘ozone valley’ over Tibetan Plateau (TP) from observations (e.g., Zhou 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 TP and Asia The recent studies showed that TP and 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 TP using a CCM. Modelling study of STE over the 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 Tropopause Height over TP ERA-40 Thermal and Cold point Tropopause Height over TP Thermal tropopause height Is 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 Satellite Courtesy to Dr Tie Yuan

TP WP Modeled Modeled O 3 Profiles over TP Ozone 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 O 3 (July and August mean) CCM CH 4 (July and August Mean) Modelled O 3 and CH 4 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 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