1. GPS tropical tropopause temperatures and stratospheric water vapor William Randel 1 and Aurélien Podglajen 2 1 NCAR Atmospheric Chemistry Division 2 Pierre and Marie Curie University - Paris

2. QJRMS, 1949 The stratosphere is extremely dry because air is dehydrated passing the cold tropical tropopause

3. QJRMS, 1949 17.5 km Large annual cycle in tropical tropopause temp.

4. QJRMS, 1949 global climatology

5. Objective: study correlated behavior of stratospheric H 2 O and GPS cold point tropopause temps on daily to annual time scales Can we understand the large-scale behavior of H 2 O in a simple way from accurate temperatures? When and where does dehydration occur? Empirical complement to trajectory studies

6. Data: GPS radio occultation temps: Daily data from CHAMP, COSMIC, others ~3000 obs/day for middle 2006-present High vertical resolution (~ 1 km), well-resolved cold point Saturation mixing ratios Q sat (RH=1.0) MLS water vapor: daily gridded fields at 100, 83, 68, … hPa; late 2004 – 2012

7. GPS measurements gridded GPS temps Daily gridded data set 5 o x 20 o x 0.2 km 2006 - 2012

8. Large-scale variability at the tropical tropopause (10 o N-S) 0180360 longitude time

9. GPS Temperature spectra at 17 km Mixed Rossby gravity waves 2 5 10 30 3 Antisymmetric Kelvin waves MJO Symmetric 2 5 10 30 3 Period (days) Zonal wavenumber westwardeastwardwestwardeastward

10. Temperature spectra at 23 km Kelvin waves Symmetric 2 5 10 30 3 Period (days) Zonal wavenumber Mixed Rossby gravity waves Antisymmetric Zonal wavenumber 2 5 10 30 3 westwardeastwardwestwardeastward

11. MLS orbital data gridded MLS H 2 O 100 hPa ~ 16 km

12. Temps H2OH2O

13. 20052006 200720082009 20102011 2012 Tropical tape recorder observed by MLS 2004-2012 cold point tropopause Cold phase of tropopause annual cycle

14. 100 hPa H2O GPS tropopause temperature Boreal Winter 15 o N-S 2009-2010 time

15. GPS saturation mixing ratio Boreal Winter 15 o N-S 2009-2010 time 100 hPa H2O

16. Boreal Winter 15 o N-S 2009-2010 time GPS saturation mixing ratio

17. 100 hPa H2O Boreal Winter 15 o N-S 2010-2011 time GPS saturation mixing ratio

18. Fractional area of RH>1 for 20 o N-S and 100 and 83 hPa Max during boreal winter fraction.30 0.15 2007 2008 20092010 2011

19. Winter (DJF) Summer (JJA) Fraction of RH > 1.0 at 100 hPa locations where dehydration may occur 0.45 0.25 longitude latitude longitude Dehydration mainly over ~20 o N-S 40 N 40 S

20. Fraction of RH > 1.0 at 100 hPa Schoeberl and Dessler 2011 Dehydration locations derived from Lagrangian trajectories Winter (DJF) longitude 40 N 40 S

21. Summer (JJA) Schoeberl and Dessler 2011 Trajectory dehydration location longitude Fraction of RH > 1.0 at 100 hPa 40 N 40 S

22. Winter (DJF) longitude 40 N 40 S Distribution of relative humidity in western Pacific 100%140% frequency

23. Key points: MLS and GPS data sets provide opportunity to understand H 2 O – T coupling on daily to interannual time scales * links to clouds, dynamics of the TTL Dehydration regions (RH > 1.0) occur mainly during boreal winter. Summertime behavior is less-well understood. Observed dehydration patterns compare well with trajectory calculations. Where are the differences?

24. Thank you

25. Africa Lidar cloud observations from CALIPSO

26. 100 hPa H 2 O 83 hPa H 2 O Q sat at the cold point Q sat 15% driest area Zonal averages 15 o N-S ppmv

27. 100 hPa H 2 O 15 o N-S GPS saturation mixing ratio at locations where RH > 1.0 H 2 O vs. Q sat