[1] Several investigations of the dominant period gravity waves (GWs) were conducted earlier using Indian mesosphere-stratosphere-troposphere (MST) radar located at Gadanki (13.5°N, 79.2°E). However, these works had their own limitations of unavailability of continuous data, low SNR, and lack of reliable data at the stratospheric heights (in the case of MST radar) and low spatial resolution (for routine balloon data). For the present study, high-resolution GPS radiosonde data for more than 2 years (2006)(2007)(2008) has been used for the first time to characterize the dominant GWs and their associated source mechanisms. Particular attention is paid (1) to check the consistency in GW characteristics observed with MST radar, (2) to estimate potential energy, kinetic energy, and hence total energy, (3) to extend the analysis up to 25 km and check whether vertical wavelength is the same as that observed by MST radar in the lower stratosphere, and finally (4) to estimate the exact direction of propagation in horizontal, which was not possible from MST radar alone. Clear semiannual variation in GW energy, with maximum during monsoon and winter and minimum during premonsoon and postmonsoon in the troposphere, is noticed during 2006 but not clear in 2007. Annual variation is observed in the lower stratosphere with maximum during monsoon (winter enhancement is not significant) season. Strong eastward shear due to tropical easterly jet and orography is found to be responsible for generating the GWs during the monsoon and winter, respectively. Although several features are consistent with that observed earlier, a few new features have been observed by GPS radiosonde and are reported in the present study.Citation: Debashis Nath, M. Venkat Ratnam, V. V. M. Jagannadha Rao, B. V. Krishna Murthy, and S. Vijaya Bhaskara Rao (2009), Gravity wave characteristics observed over a tropical station using high-resolution GPS radiosonde soundings,

The influence of El Niño–Southern Oscillation (ENSO) on the East Asian–western Pacific (EAWP) climate in boreal winter is investigated in the phase 5 of the Coupled Model Intercomparison Project (CMIP5) model results and then compared to that in the phase 3 (CMIP3) results. In particular, the role played by the differences among models in ENSO properties, including the amplitude and longitudinal extension of ENSO’s sea surface temperature (SST) pattern, is analyzed. Results show that an eastward shrinking of ENSO’s SST pattern leads to quite weak circulation and climatic responses over the EAWP regions in the models. On the contrary, a westward expansion of the SST pattern shifts the anomalous Walker circulation too far west. The resultant precipitation anomalies and lower-tropospheric atmospheric Rossby wave responses both extend unrealistically into the Indian Ocean, and the hemispheric asymmetry of the Rossby wave response is missing. All these features lead to unrealistic climatic impacts of ENSO over the EAWP regions. In contrast to the above two cases, a reasonable longitudinal extension of ENSO’s SST pattern corresponds to better ENSO teleconnections over the EAWP regions. Nevertheless, the atmospheric responses over the western Pacific are still located farther west than observed, implying a common bias of CMIP5 models. In this case, a larger amplitude of ENSO variability to some extent helps to reduce model biases and facilitate better climatic responses to ENSO in the EAWP regions. Compared with CMIP3 models, CMIP5 models perform better in representing ENSO’s impacts on the East Asian winter climate.

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