[1] In this study, long-term (2.5 years) observations of a high vertical resolution radiosonde are used for the first time to identify the atmospheric boundary layer (ABL) height over a tropical station, Gadanki (13.5°N, 79.2°E). An alternative method of detecting ABL height from refractivity (N) profiles is proposed, which includes both temperature and water vapor information, and several advantages were found. The identified height using N is compared with that detected by traditional methods like potential, virtual potential temperature, and mixing ratio during different background meteorological conditions. Very good correlations in all weather conditions indicate that N can also be used as an indicator for detecting the ABL height. The ABL height thus obtained is compared with independent measurements of N from the Constellation Observing System for Meteorology Ionosphere and Climate GPS radio occultation (RO), and very good correlation is found between the two. ABL height is found to be higher during premonsoon, followed by monsoon and postmonsoon, and is minimum in winter. In addition, radiosondes launched four times a day during different seasons have been used to study the diurnal variation. These results were compared with GPS RO data collected during different times in a day for a given season, and very strong diurnal variation was found. For studying the global distribution of ABL height from GPS RO data, it is suggested that one considers the GPS RO data for a fixed time or range of time (as RO data are very sparse in tropical regions) and the profiles reaching down to 0.5 km, particularly during nighttime.Citation: Basha, G., and M. V. Ratnam (2009), Identification of atmospheric boundary layer height over a tropical station using highresolution radiosonde refractivity profiles: Comparison with GPS radio occultation measurements,

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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.

Surface Temperature (ST) over India has increased by ~0.055 K/decade during 1860–2005 and follows the global warming trend. Here, the natural and external forcings (e.g., natural and anthropogenic) responsible for ST variability are studied from Coupled Model Inter-comparison phase 5 (CMIP5) models during the 20th century and projections during the 21st century along with seasonal variability. Greenhouse Gases (GHG) and Land Use (LU) are the major factors that gave rise to warming during the 20th century. Anthropogenic Aerosols (AA) have slowed down the warming rate. The CMIP5 projection over India shows a sharp increase in ST under Representative Concentration Pathways (RCP) 8.5 where it reaches a maximum of 5 K by the end of the 21st century. Under RCP2.6 emission scenarios, ST increases up to the year 2050 and decreases afterwards. The seasonal variability of ST during the 21st century shows significant increase during summer. Analysis of rare heat and cold events for 2080–2099 relative to a base period of 1986–2006 under RCP8.5 scenarios reveals that both are likely to increase substantially. However, by controlling the regional AA and LU change in India, a reduction in further warming over India region might be achieved.