ALBERT

Description: Vertical wind variations in the Upper Troposphere and Lower Stratosphere (UTLS) measured by the Equatorial Atmosphere Radar (EAR) at Kototabang, Sumatra, between 2003 and 2005 but mainly in 2004, have been statistically analyzed to study the characteristics of wind variances associated with convective activity, which is related to gravity wave generation and propagation. The analyses are intended to characterize relatively short period disturbances of less than 12 hours and an energy propagation direction of a relatively high elevation angle, and to relate vertical wind variations to convective activity close to the EAR. Correlation analyses between vertical wind variations and rainfall show that the wind variances have a clear diurnal variation indicating probable effects of tropospheric convection. They also show some intraseasonal variation. However, there are no significant correlations with the Out-going Long-wave Radiation (OLR) anomaly. The correlations between variances at UT and LS suggest that the UTLS coupling of vertical wind variation through upward propagation of gravity wave is similarly evident in the afternoon during both the active and the inactive phase of OLR that is a proxy of large-scale convective activity.

Description: Using stratospheric temperature profiles derived from GPS radio occultation (RO) measurements made by the German CHAMP satellite from June 2001 to May 2006, we studied the climatological behavior of atmospheric wave activity in the tropics. The wave potential energy, E p, is calculated from temperature fluctuations with vertical scales shorter than 7 km in a longitude and latitude cell of 20° × 10° at 19–26 km. E p is then averaged every 3 months (June–July–August (JJA), September–October–November (SON), December–January–February (DJF), March–April–May (MAM)), and the averages are compared with the cloud top temperature from outgoing long-wave radiation (OLR) and the convective rain rate from the TRMM precipitation radar (PR). E p at 19–26 km in the western Pacific to Indian Ocean is found to show a clear seasonal variation, with a large E p during DJF and MAM and a considerably enhanced E p in SON; it becomes minimum during JJA near the equator, when the center of the enhanced E p region appears over north India and the Indochina peninsula. Localized enhancement of E p seems to be mainly due to atmospheric gravity waves. In addition, the longitudinally elongated portion of E p is partially affected by Kelvin wave-like disturbances with short horizontal scales. In DJF and MAM, the convective clouds are located over the western Pacific and around Indonesia, at which time the Kelvin wavelike disturbances are effectively generated. The spatial and seasonal variations of E p are closely related to the distribution of clouds, implying that convective wave generation is very important in the tropics. However, wave-mean flow interactions due to the wind shear of the QBO become important in the lower stratosphere, which considerably modifies our analysis of the E p distribution at 19–26 km. Therefore, both wave generation and propagation characteristics must be taken into account in describing the climatological behavior of atmospheric wave activity in the equatorial stratosphere.