Wavecritical layer interactions observed using GPS data

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Wave-critical layer interactionsobserved using
GPS data
Bill Randel, NCAR
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Overview

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

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GPS Radio Occultation
Basic measurement principle Deduce atmospheric
properties based on precise measurement of phase
delay and amplitude.
high vertical resolution! 200 m
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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.
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Comparison of GPS with radiosondes
very good agreement for wave structures
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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
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Equatorial sampling of CHAMP and SAC-C
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Simple gridding procedure
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Kelvin waves near the tropopause
eastward traveling Kelvin waves
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Vertical structure
tropopause
eastward phase tilt with height characteristic
of Kelvin waves
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How are Kelvin waves linked to deep convection?
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Variations in tropical convectionfrom
OLRmeasurements
Nov
Dec
Jan
Feb
Mar
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Correlation of waves with convection (OLR)
wave variance at 16.5 km
OLR near Indonesia
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Global-scale Kelvin wave forced by convection
location and altitude of convection deduced from
OLR data
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Residual temperature variance (small scales)
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Sample of GPS tropical temperature profiles
note enhanced variability above 15 km
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Gravity waves observed by GPS/MET
maximum in tropics (see Alexander et al.,JAS,2002)
Tsuda et al., JGR, 2000
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Residual (small-scale) wave variance
maximum near tropopause
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Residual (small-scale) wave variance
QBO winds
maximum just below u0 line
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Gravity waves interacting with a critical level
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Model simulation of gravity waves forced by deep
convection
no critical level
critical level (Ugt0)
Alexander and Holton, 2000
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Residual (small-scale) wave variance
QBO winds
maximum just below u0 line
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QBO winds
extension to early 2006 using CHAMP
variance maxima only for descending westerlies
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Key points

• Over the equator, small-scale waves have variance
  maxima
• near the tropopause (why?)
• in lower stratosphere, just below U0 line
• (but only for descending westerlies)

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Future COSMIC EQUARS Soundings in a Day
COSMIC EQUARS Radiosondes
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(No Transcript)
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Model simulation of gravity waves forced by deep
convection
Alexander and Holton, 2000
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Gravity waves interacting with a critical level
critical level
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Quasi-biennial oscillation (QBO) in temperature
contours /- 0.5, 1.5, ...
cold point
result QBO influence of 0.5 K on tropical
tropopause