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

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

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.

Comparison of GPS with radiosondes very good agreement for wave structures

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

Equatorial sampling of CHAMP and SAC-C

Simple gridding procedure

Kelvin waves near the tropopause eastward traveling Kelvin waves

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

How are Kelvin waves linked to deep convection?

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

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

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

Residual temperature variance (small scales)

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

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

Residual (small-scale) wave variance maximum near tropopause

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

Gravity waves interacting with a critical level

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

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

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

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)

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

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

Gravity waves interacting with a critical level critical level

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