Global analyses of gravity wave (GW) activity in the stratosphere are presented using radio occultation data from the Challenging Minisatellite Payload (CHAMP) satellite. Temperature profiles obtained from CHAMP/ GPS radio occultations are first compared with ground-based instruments. In general, good agreement is found between these different techniques. Monthly mean values of potential energy Ep, being a measure of GW activity, which is estimated with radiosonde observations, are compared with CHAMP/GPS data and it is found that radiosonde-observed Ep values are slightly higher than those estimated with radio occultations. Strong diurnal variation of GW activity has been found. From the global morphology of GW activity, large Ep values are noticed, besides at tropical latitudes, even at midlatitudes during winter, but not during equinoxes. This suggests that wave activity at stratospheric heights is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variatio... Abstract Global analyses of gravity wave (GW) activity in the stratosphere are presented using radio occultation data from the Challenging Minisatellite Payload (CHAMP) satellite. Temperature profiles obtained from CHAMP/ GPS radio occultations are first compared with ground-based instruments. In general, good agreement is found between these different techniques. Monthly mean values of potential energy Ep, being a measure of GW activity, which is estimated with radiosonde observations, are compared with CHAMP/GPS data and it is found that radiosonde-observed Ep values are slightly higher than those estimated with radio occultations. Strong diurnal variation of GW activity has been found. From the global morphology of GW activity, large Ep values are noticed, besides at tropical latitudes, even at midlatitudes during winter, but not during equinoxes. This suggests that wave activity at stratospheric heights is not only modulated due to orography (mountain/lee waves) but mainly depends on seasonal variatio...

The state of Kerala, located on the west coast of India, experienced a record 100‐year flood that resulted in major landslides from unprecedented prolonged and extremely heavy rainfall (50–480 mm·day⁻¹) during August 1–19, 2018, causing extensive damage and about 500 causalities. Rainfall observations indicate that the heavy rainfall occurred over two spells (August 7–10 and 14–18) in association with an offshore trough, and a depression over the Bay of Bengal (BOB). High‐resolution 38‐year climatology data (5 km) and the ERA‐Interim reanalysis dataset show a strong low‐level jet over the Arabian Sea and a depression over the BOB with a southwestward tilt during the heavy rainfall. Very high‐resolution (2‐km) mesoscale model simulations suggest that this high convective instability due to the strong westerly jet along with the formation of offshore vortex, the transport of mid‐tropospheric moisture under the presence of conducive vertical shear of horizontal wind, and transport of mid‐tropospheric moisture from the BOB are the major factors (as shown in the schematic diagram) behind the extreme heavy rainfall over Kerala.

The diurnal variation of atmospheric boundary layer (ABL) height is studied using high-resolution radiosonde observations available at 3 h intervals for 3 days continuously from 34 intensive campaigns conducted during the period December 2010–March 2014 over a tropical station Gadanki (13.5° N, 79.2° E; 375 m), in the Indian monsoon region. The heights of the ABL during the different stages of its diurnal evolution, namely, the convective boundary layer (CBL), the stable boundary layer (SBL), and the residual layer (RL) are obtained to study the diurnal variabilities. A clear diurnal variation is observed in 9 campaigns out of the 34 campaigns. In 7 campaigns the SBL did not form in the entire day and in the remaining 18 campaigns the SBL formed intermittently. The SBL forms for 33–55 % of the time during nighttime and 9 and 25 % during the evening and morning hours, respectively. The mean SBL height is within 0.3 km above the surface which increases slightly just after midnight (02:00 IST) and remains almost constant until the morning. The mean CBL height is within 3.0 km above the surface, which generally increases from morning to evening. The mean RL height is within 2 km above the surface which generally decreases slowly as the night progresses. The diurnal variation of the ABL height over the Indian region is stronger during the pre-monsoon and weaker during winter season. The CBL is higher during the summer monsoon and lower during the winter season while the RL is higher during the winter season and lower during the summer season. During all the seasons, the ABL height peaks during the afternoon (∼ 14:00 IST) and remains elevated until evening (∼ 17:00 IST). The ABL suddenly collapses at 20:00 IST and increases slightly in the night. Interestingly, it is found that the low level clouds have an effect on the ABL height variability, but the deep convective clouds do not. The lifting condensation level (LCL) is generally found to occur below the ABL for the majority of the database and they are randomly related.