Evaluation of daily and diurnal signals of total precipitable water (TPW) over the Indian Ocean based on TMI retrieved 3‐day composite estimates and radiosonde data

Abstract Tropical rainfall measuring mission (TRMM) TRMM microwave imager (TMI) retrieved total precipitable water (TPW) has been shown in previous studies to be useful for characterizing energy transport and rainfall variability over water bodies. In this study, 3‐day composite TPW values during the monsoon months of June–September in 1999 and 2003 were evaluated against radiosonde derived TPW over the coastal regions of Indian Ocean. The radiosonde measurements were from coastal locations, island stations and ship‐based observations made during the 1999 Bay of Bengal Monsoon Experiment (BOBMEX). Our study is one of the first attempts to compare TMI‐derived TPW with the BOBMEX data. Root mean square (RMS) error of 8.1 mm and a bias of −0.76 mm were obtained for TMI 3‐day composite TPW data with respect to the radiosonde data over the Indian coastal regions. TMI overestimated (underestimated) radiosonde measurements under dry (wet) atmospheric conditions. Daily TMI‐derived TPW was also validated with radiosonde measurements from the BOBMEX data for the period 21 July–28 August 1999. Diurnal signals of TPW over Bay of Bengal were found to be comparable to the in situ measurements during the same period. Copyright © 2006 Royal Meteorological Society