Temporal variations in sun photometer measured precipitable water in near IR band and its comparison with model estimates at a tropical Indian station

Multi-channel sun photometer observations of precipitable water content (PWC) in the near-infrared band over a tropical Indian station, Pune, during the period May 1998-May 2006 have been used to investigate temporal and seasonal variations. Precipitable water estimated from surface meteorological parameters (temperature and relative humidity) and that obtained from MODIS satellite for the same station have been compared with those observations made by the sun photometer. There exists a well defined seasonal variation in precipitable water content with maximum during Southwest monsoon months (June-September) and minimum during the month of March. Variability in PWC is higher during post-monsoon and winter months (October to February) and smaller during pre-monsoon and monsoon months (March to September). The overall mean PWC measured by Sun photometer at Pune is 13.27 mm. Precipitable water estimated from Surface meteorological parameters and that obtained from satellite retrieval are higher in magnitude compared to that from the ground-based sun photometer measurements. However, the temporal variations on all time scales agree very well and are in-phase. A well calibrated portable Sun photometer operated at the near infrared wavelengths would give very good temporal observations of precipitable water at any location.