Evaluation of AIRS precipitable water vapor against ground-based GPS measurements over the Tibetan plateau and its surroundings

The atmospheric infrared sounder (airs) on board the aqua satellite provides the estimate of precipitable water vapor (pwv),which can be assimilated into numerical prediction models to improve precipitation forecasts. in this study,the airs retrieval of pwv is evaluated against ground-based gps measurements at 24 stations over the tibetan plateau (tp) and its surroundings. first,the pwv estimates from the gps delay signals at these stations are improved by applying a new scheme for computing the water-vapor-weighted mean atmosphere temperature,a key parameter in the gps pwv retrieval. compared with a traditional retrieval,this revision can improve the pwd estimate by up to 6% in some cases. second,the newly retrieved pwv data are used to evaluate the airs product. prior to the evaluation,an elevation correction is made to these gps pwv data to account for the elevation difference between the gps stations and the corresponding airs footprints. this correction effectively removed false negative biases in the airs product. nevertheless,an average negative bias of 2 mm still exists in the airs product. a further analysis suggests that the negative bias may be attributed to the cloudclearing algorithm in the airs retrieval scheme. © 2012,meteorological society of japan.