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In this study, global (501S-501N) distribution of water vapor is investigated using COSMIC GPS RO measurements. Detailed comparisons have been made between COSMIC and high resolution GPS radiosonde measurements across 13 tropical stations and model outputs (ERA-Interim, NCEP, and JRA-25 reanalyses data sets). In comparison with independent techniques like radiosonde (Väisälä), it is found that COSMIC GPS RO wet profiles are accurate up to 7-8 km (assuming radiosonde as standard technique). In general, comparisons with corresponding seasonal means of model outputs are qualitatively in good agreement, although they differ quantitatively especially over convective regions of South America, Africa, and Indonesia. In tropical latitudes, the COSMIC specific humidity values are higher than the model outputs. Among various model outputs, ERA-Interim data set show near realistic features to that observed by COSMIC GPS RO measurements. Large asymmetry in the specific humidity distribution is observed between northern and southern hemispheres.

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Understanding the structure and dynamics of the Martian thermosphere (100-220 km) is extremely important as this region, in particular the upper thermosphere, acts as a buffer zone between the reservoir of atmospheric species down below and the exosphere above from where the gaseous escape happens (e.g., Bougher, Cravens, et al., 2015). From this view point, the exobase acts as a lid on top of the thermosphere and the gaseous escape is regulated by the amount of energy, particles, and fields (both electric and magnetic) that reach the upper thermosphere. Thermospheric neutral densities, in general, decrease exponentially with an increase in altitude. Superimposed on this, there are perturbations of various scales that are due to forcings from above and below. Forcings from below include the planetary waves, thermal tides, and gravity

[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,

Sixteen-year (1998Sixteen-year ( -2013 climatology of cirrus clouds and their macrophysical (base height, top height and geometrical thickness) and optical properties (cloud optical thickness) observed using a ground-based lidar over Gadanki (13.5 • N, 79.2 • E), India, is presented. The climatology obtained from the ground-based lidar is compared with the climatology obtained from 7 and a half years (June 2006-December 2013) of Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. A very good agreement is found between the two climatologies in spite of their opposite viewing geometries and the differences in sampling frequencies. Nearly 50-55 % of cirrus clouds were found to possess geometrical thickness less than 2 km. Ground-based lidar is found to detect a higher number of sub-visible clouds than CALIOP which has implications for global warming studies as sub-visible cirrus clouds have significant positive radiative forcing. Cirrus clouds with mid-cloud temperatures between −50 to −70 • C have a mean geometrical thickness greater than 2 km in contrast to the earlier reported value of 1.7 km. Trend analyses reveal a statistically significant increase in the altitude of sub-visible cirrus clouds which is consistent with the recent climate model simulations. The mid-cloud altitude of sub-visible cirrus clouds is found to be increasing at the rate of 41 ± 21 m year −1 . Statistically significant decrease in optical thickness of sub-visible and thick cirrus clouds is observed. Also, the fraction of sub-visible cirrus cloud is found to have increased by 9 % in the last 16 years (1998 to 2013). This increase is mainly compensated by a 7 % decrease in thin cirrus cloud fraction. This has implications for the temperature and water vapour budget in the tropical tropopause layer.Published by Copernicus Publications on behalf of the European Geosciences Union.

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