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Wave-critical layer interactions observed using GPS data

Wave-critical layer interactions observed using GPS data. Bill Randel, NCAR. Overview. GPS radio occultation temperature measurements GPS observations of tropical temperatures large and small-scale waves coupling to convection and background flow. Occulting GPS. 20 msec. data. (LINK 1).

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Wave-critical layer interactions observed using GPS data

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  1. Wave-critical layer interactionsobserved 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. Occulting GPS 20 msec data (LINK 1) Ionosphere Neutral atmosphere Occulting LEO Earth GPS Radio Occultation 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 convectionfrom OLRmeasurements 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 maximum in tropics (see Alexander et al.,JAS,2002) Tsuda et al., JGR, 2000

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

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

  20. Gravity waves interacting with a critical level

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

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

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

  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

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

  27. Gravity waves interacting with a critical level critical level

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

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