Equatorial Waves in the Lower Stratosphere Observed by the High Resolution Dynamics Limb Sounder

Previous studies have shown Kelvin waves detected in radiosonde and GPS profiles modulate the climatological tropopause temperature structure. Temperature fluctuations caused by equatorial waves of all scales are also important components in determining the observed frequency and geographical distribution of tropical cirrus cloud formation. The High Resolution Dynamics Limb Sounder (HIRDLS) provides observations of wave-induced temperature fluctuations over a broad range of horizontal and vertical scales. Zonal modes with wavenumbers 1- 8 and small-scale gravity waves with 200 km along-track wavelengths are resolved by HIRDLS with fine 1.2 km vertical resolution. HIRDLS is an infrared limb-scanning instrument that can observe wave structures in the middle atmosphere down to cloud-top altitudes. The resolution is higher than previous satellite limb scanning techniques with the exception of GPS. HIRDLS and GPS have very different horizontal sampling characteristics: HIRDLS has 1-degree meridional resolution near the equator with 24-degree spacing between orbits and typically 650 profiles per day in the 10S-10N latitude band. GPS in comparison samples randomly, and the previously analyzed combined SAC-C and CHAMP data sets in 2001-2002 gave 20-30 profiles per day between 10S-10N latitudes. We will report on the properties of equatorial waves observed by HIRDLS in the lower stratosphere, with special emphasis on Kelvin waves and the annual cycle.