Kelvin waves near the tropical tropopause observed in GPS data
                                                                                                                              

Kelvin waves are eastward traveling, planetary scale waves trapped near the
equator, evident in atmospheric temperature, pressure and wind fields (and also
in the ocean).  They contribute a substantial component of temperature variability
near the tropical tropopause.  Kelvin waves are important for influencing the
dehydration of air entering the stratosphere, and also for the formation of tropical
cirrus clouds.  We have used high vertical resolution GPS radio occultation
temperature measurements to study the detailed structure and variability of
Kelvin waves.

      
This plot shows a longitude-time section of temperature anomalies at 17 km
during April - September 2002, derived from CHAMP and SAC-C GPS
temperature measurements.  Contours are +/- 0.5, 1.5, 2.5, ...K.  The
eastward traveling features in May and August-September are planetary-scale
Kelvin waves.

      
Here's an example of a large-amplitude Kelvin wave on Jan. 28, 2002.
Contours (+/- 0.5, 1.5, 2.5, ...K) show temperature anomalies (deviations from zonal
average) of equatorial (10 N - 10 S) temperatures.  The eastward phase tilt with height
is characteristic of an upward propagating Kelvin wave (with a vertical wavelength
of ~8 km for this case).  The heavy line is the cold point tropopause.  This Kelvin
wave event was observed in association with enhanced deep convection occurring
over Indonesia, as derived from outgoing longwave radiation (OLR) observations
(indicated by the schematic clouds).   The vertical arrow denotes the Kelvin wave
group velocity.


Correlations with OLR data show that the Kelvin waves are forced by variations
in deep convection.  The upper time series shows the tropical temperature
variance at 17 km, with peaks corresponding to large amplitude Kelvin waves
(the large peak in January corresponds to the event in the previous figure).
The lower time series is OLR over the Indonesian region; peaks correspond to
enhanced deep convection (note the inverted scale).  The arrows highlight
maxima in Kelvin waves that are correlated with variations in convection.

For more details on the links with deep convection, plus coupling of the Kelvin
waves with the stratospheric wind field (in particular, the QBO), see our paper:

Randel, W.J., and F. Wu, 2005: Kelvin wave variability near the equatorial
tropopause observed in GPS radio occultation measurements. J. Geophys. Res.,
Vol. 110, No. D3, D03102, doi10.1029/2004JD005006. Here's a pdf reprint.

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