Tropical temperature variability over 10–30 km and associatedKelvin-wave activity are investigated using GPS radio occultation(RO) data from January 2002 to December 2014. RO data are apowerful tool for quantifying tropical temperature oscillations withshort vertical wavelengths due to their high vertical resolution andhigh accuracy and precision. Gridded temperatures from GPS RO showthe strongest variability in the tropical tropopause region (on average3 K). Large-scale zonal variability is dominated by transientsub-seasonal waves (2 K), and about half of sub-seasonalvariance is explained by eastward-traveling Kelvin waves withperiods of 4 to 30 days (1 K). Quasi-stationary wavesassociated with the annual cycle and interannual variabilitycontribute about a third (1 K) to total resolved zonalvariance. Sub-seasonal waves, including Kelvin waves, are highlytransient in time. Above 20 km, Kelvin waves are strongly modulatedby the quasi-biennial oscillation (QBO) in stratospheric zonalwinds, with enhanced wave activity during the westerly shear phaseof the QBO. In the tropical tropopause region, however, peaks ofKelvin-wave activity are irregularly distributed in time. Severalpeaks coincide with maxima of zonal variance in tropospheric deepconvection, but other episodes are not evidently related. Furtherinvestigations of convective forcing and atmospheric backgroundconditions are needed to better understand variability near thetropopause.
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