Stratosphere and Troposphere Exchange (STE) Above the Tibetan Plateau

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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
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Background

• 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).

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STE contributes to Ozone Valley
Strong Concevtion
Asia summer monsoon
TP, average height 4 km ASL
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Ozone valley STE - Chemistry

• 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?

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What we have done

• Modelling study of STE over the TP using a CCM.
• Modeling of a Tropopause fold event using a
  meso-scale model (WRF).

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TOMS Total Column Ozone Over TP
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ERA-40 Thermal and Cold point Tropopause
Height over TP
Thermal tropopause height Is highest from July to
august
Thermal tropopause
Cold point tropopause
Cold point tropopause height is highest from Mar
March to May
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Deep Convective Systems from TRIM Satellite
Courtesy to Dr Tie Yuan
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Modeled O3 Profiles over TP
Ozone
Ozone
WP
TP
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.
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Modeled Geopotential Height over TP in the
Stratosphere
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Modelled O3 and CH4 on 380K Surface
CCM O3 (July and August mean)
CCM CH4 (July and August Mean)
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Modelled NOx and CO on 380K Surface
CCM NOx (July and August Mean)
CCM CO (July and August Mean)
Atmospheric chemistry may play a role.
Tian et al, 2008, TELLUS B
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A Tropopuase Fold Events
CALIPSO image
Pulse Radar Image
Surface zone concentratiosn
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A Tropopause Fold Event over TP
Zhang, Tian ,Chen, Lv , 2009, AAS
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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
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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
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AIRS Water Vapor at 100hPa over the TP
Tian et al, 2010, ASL
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AIRS Cloud Top Pressure over the TP
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Temperature and Potential Vorticity Distributions
on the 350K Surface
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Summary

• 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.

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Summary Continued

• 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.

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Thanks