Estimating the influence of summertime deep convection over the Tibetan Plateau on water vapor transport into the tropical lower stratosphere

Transcription

1 Estimating the influence of summertime deep convection over the Tibetan Plateau on water vapor transport into the tropical lower stratosphere Jonathon S. Wright Tsinghua University Center for Earth System Science February 20, 2012

2 Introduction Stratospheric Water Vapor Stratospheric Water Vapor Water vapor is of central importance to chemical and radiative processes in the stratosphere. An increase of water vapor: 1 cools the stratosphere 2 warms the surface 3 enhances ozone destruction

3 Introduction Stratospheric Water Vapor The Stratospheric Tape Recorder Stratospheric water vapor is primarily controlled by temperatures at the tropical tropopause. The imprint of the seasonal cycle of tropical tropopause temperatures propagates upward over time.

4 Introduction Stratospheric Water Vapor The Tropical Pipe This upward propagation occurs in the tropical component of the stratospheric Brewer-Dobson Circulation: the tropical pipe.

5 Introduction The Potential Importance of Tibet Contributions From Deep Convection Over Tibet? Fu et al. (PNAS 2006) showed that deep convection over the Tibetan Plateau moistens the local lower stratosphere.

6 Introduction The Potential Importance of Tibet Contributions From Deep Convection Over Tibet? Does this water vapor reach the tropical pipe? What is its contribution relative to tropical convection?

7 Introduction The Potential Importance of Tibet Contributions From Deep Convection Over Tibet? Multiple studies indicate that transport from Southeast Asia is crucial. Some studies suggest that deep convection over Tibet makes important contributions to this flux (e.g., Lelieveld et al., ACP 2007); other studies disagree (e.g., Park et al., JGR 2007; James et al., ACP 2008).

8 Study Design Starting Points Hypothesis #1 Transport from convective events over the Tibetan Plateau and South Slope of the Himalayas is moister than transport from other convective events within Southeast Asia. Hypothesis #2 This transport makes a substantial contribution to the annual maximum of water vapor in the tropical lower stratosphere.

9 Study Design Trajectory Analysis Trajectory Analysis Lagrangian back trajectories from Aura MLS observations of water vapor in the tropical lower stratosphere (68 hpa) to identify the relative importance of different convective source regions.

10 Study Design Trajectory Analysis Focus on Annual Maximum Initialize trajectories at 68 hpa during OND, and trace backward in space and time to global convective sources.

11 Study Design Trajectory Analysis Trajectory Model Formulation Trajectories are driven using reanalysis winds and diabatic heating rates. Independent ensembles are constructed using three different reanalysis datasets to drive the trajectories: 1 NCEP/NCAR Reanalysis 1 2 GMAO MERRA (NASA) 3 ERA-Interim (ECMWF) The primary focus is on points of consistency. Determination of Convective Sources Convective source locations are identified by matching observations of cloud top pressure (derived from CLAUS 11µm brightness temperatures) with all trajectory locations.

12 Study Design Trajectory Analysis Simulations of Stratospheric Water Vapor Identify the transport of water vapor into the tropical lower stratosphere according to the advection-condensation paradigm.

13 Study Design Trajectory Analysis Simulations of Stratospheric Water Vapor Identify the transport of water vapor into the tropical lower stratosphere according to the advection-condensation paradigm.

14 Study Design Trajectory Analysis Simulations of Stratospheric Water Vapor Identify the transport of water vapor into the tropical lower stratosphere according to the advection-condensation paradigm. This paradigm works for stratospheric water vapor for the same reason that the tape recorder exists: stratospheric water vapor depends on tropical tropopause (dry point) temperatures.

15 Results Convective Sources in Southeast Asia Distribution of Convective Sources in Southeast Asia Summertime convective sources in Southeast Asia are concentrated in the South Asian and South China Sea monsoon regions.

16 Results Convective Sources in Southeast Asia Distribution of Convective Sources in Southeast Asia There are three geographically distinct convective source regions within Southeast Asia.

17 Results Convective Sources in Southeast Asia Distribution of Convective Sources in Southeast Asia Together and individually, these three regions account for a substantial fraction of summertime convective source events.

18 Results Water Vapor Transport Simulated Water Vapor The magnitude of simulated water vapor transport into the tropical lower stratosphere differs by convective source region. These regional differences are qualitatively consistent in all three trajectory ensembles.

19 Results Transport Characteristics Transport Pathways These differences in water vapor transport are related to systematic differences in preferred transport pathways.

20 Results Transport Characteristics Lagrangian Dry Points LDPs are shifted northward and westward for trajectories from TIB convection relative to those from MON convection.

21 Results Transport Characteristics Lagrangian Dry Points LDPs are shifted upward and northward for trajectories from TIB convection relative to those from MON convection.

22 Results Transport Characteristics Bypassing the Cold Trap Shifting of cold points northward, westward, and upward bypasses freeze-drying at the coldest temperatures.

23 Results Transport Characteristics Bypassing the Cold Trap Higher detrainment potential temperatures give TIB trajectories an extra isentropic boost.

24 Results Transport Characteristics Bypassing the Cold Trap Tighter confinement to the monsoon anticyclone gives TIB trajectories an additional diabatic boost.

25 Results Conclusions Hypothesis #1 Transport from convective events over the Tibetan Plateau and South Slope of the Himalayas is moister than transport from other convective events within Southeast Asia. Hypothesis #2 This transport makes a substantial contribution to the annual maximum of water vapor in the tropical lower stratosphere.

26 Results The Big Picture The Big Picture Artificially removing transport from each of the three source regions in Southeast Asia from the global water vapor flux indicates that transport from TIB convection has only a small impact on the annual maximum in tropical lower stratosphere water vapor.

27 Results Conclusions Hypothesis #1 Transport from convective events over the Tibetan Plateau and South Slope of the Himalayas is moister than transport from other convective events within Southeast Asia. Hypothesis #2 This transport makes a substantial contribution to the annual maximum of water vapor in the tropical lower stratosphere.

28 Results Conclusions Hypothesis #1 Transport from convective events over the Tibetan Plateau and South Slope of the Himalayas is moister than transport from other convective events within Southeast Asia. Hypothesis #2 This transport makes a substantial contribution to the annual maximum of water vapor in the tropical lower stratosphere. For More Details Wright, J. S., R. Fu, S. Fueglistaler, Y. S. Liu, and Y. Zhang (2011): The influence of summertime convection over Southeast Asia on water vapor in the tropical stratosphere. J. Geophys. Res. 116, doi: /2010jd