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Equatorial waves in High Resolution Dynamics Limb Sounder (HIRDLS) data

Summary: Equatorial waves in High Resolution Dynamics Limb
Sounder (HIRDLS) data
M. J. Alexander1
and D. A. Ortland2
Received 19 July 2010; revised 21 September 2010; accepted 29 September 2010; published 23 December 2010.
[1] We examine equatorial wave structure in temperature measurements from the High
Resolution Dynamics Limb Sounder (HIRDLS) on the Aura satellite. Waves with periods
longer than 1 day and zonal wave numbers up to 8 (depending on frequency) are derived
from an asynoptic Fourier transform analysis. HIRDLS measurement sampling and
resolution afford unprecedented views of the latitudeheight structure of equatorial Rossby
wave, mixed Rossbygravity wave, and Kelvin wave modes at altitudes above cloud tops
in the tropical upper troposphere and stratosphere. Wave modes with vertical wavelength as
short as 4 km can be clearly seen in the data. Kelvin waves comprise a dominant signal
throughout the 3 years of HIRDLS measurements, and we further examine time, height, and
longitude variations observed in the Kelvin waves. An annual cycle of Kelvin wave
temperature amplitudes near the tropopause is observed that may have implications for
annual variations in wavecirrus formation in the tropics. This annual variation can
be largely explained by effects of the background wind and stability on Kelvin wave
propagation and potential energy in the tropical tropopause layer. At altitudes 20 km and
above, the annual cycle gives way to an interannual cycle in Kelvin wave amplitudes that is


Source: Alexander, M. Joan - Colorado Research Associates Division, Northwest Research Associates, Inc.


Collections: Geosciences