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.