1. Wave-critical layer interactions observed using GPS data Bill Randel, NCAR

2. Overview GPS radio occultation temperature measurements GPS observations of tropical temperatures –large and small-scale waves –coupling to convection and background flow

3. GPS Radio Occultation Occulting LEO Occulting GPS 20 msec data Ionosphere Neutral atmosphere Earth (LINK 1) Basic measurement principle: Deduce atmospheric properties based on precise measurement of phase delay and amplitude. * high vertical resolution! ~200 m

4. Sample of GPS tropical temperature profiles Temperature profiles are characterized by high variability (planetary waves, gravity waves), closely linked to convection. GPS data offer a new tool to understand this variability.

5. Comparison of GPS with radiosondes very good agreement for wave structures

6. Space-time variability on daily time scales using CHAMP + SAC-C data Kelvin waves –identification –forcing by tropical deep convection Small scales (gravity waves) –coupling with background winds Randel and Wu, JRG, 2005

7. Equatorial sampling of CHAMP and SAC-C

8. Simple gridding procedure

9. Kelvin waves near the tropopause eastward traveling Kelvin waves

10. Vertical structure tropopause eastward phase tilt with height characteristic of Kelvin waves

11. How are Kelvin waves linked to deep convection?

12. Variations in tropical convection from OLR measurements Nov Dec Jan Feb Mar

13. Correlation of waves with convection (OLR) wave variance at 16.5 km OLR near Indonesia

14. Global-scale Kelvin wave forced by convection location and altitude of convection deduced from OLR data

15. Residual temperature variance (small scales)

16. Sample of GPS tropical temperature profiles note enhanced variability above ~15 km

17. Gravity waves observed by GPS/MET Tsuda et al., JGR, 2000 maximum in tropics (see Alexander et al.,JAS,2002)

18. Residual (small-scale) wave variance maximum near tropopause

19. Residual (small-scale) wave variance maximum just below u=0 line QBO winds

20. Gravity waves interacting with a critical level

21. Model simulation of gravity waves forced by deep convection Alexander and Holton, 2000 no critical level critical level (U>0)

22. Residual (small-scale) wave variance maximum just below u=0 line QBO winds

23. extension to early 2006 using CHAMP variance maxima only for descending westerlies QBO winds

24. Key points: Over the equator, small-scale waves have variance maxima –near the tropopause (why?) –in lower stratosphere, just below U=0 line (but only for descending westerlies)

25. Future: COSMIC + EQUARS Soundings in a Day COSMIC EQUARS Radiosondes

27. Model simulation of gravity waves forced by deep convection Alexander and Holton, 2000

28. Gravity waves interacting with a critical level critical level

29. Quasi-biennial oscillation (QBO) in temperature contours: +/- 0.5, 1.5,... cold point result: QBO influence of ~ 0.5 K on tropical tropopause