Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

摘要

pstrongAbstract./strong Tropical temperature variability over 10a??30span class="thinspace"/spankm and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3span class="thinspace"/spanKsup2/sup). Large-scale zonal variability is dominated by transient sub-seasonal waves (2span class="thinspace"/spanKsup2/sup), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30??days (1span class="thinspace"/spanKsup2/sup). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1span class="thinspace"/spanKsup2/sup) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20span class="thinspace"/spankm, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause./p.