VARIABILITY OF THE GLOBAL PRECIPITABLE WATER WITH A TIMESCALE OF 90-150 DAYS

A 90-150 day signal is identified in the global precipitable water fie ld generated by the Global Data Assimilation Systems (GDAS) of the God dard Laboratory for Atmospheres (GLA), National Meteorological Center, and European Centre for Medium-Range Weather Forecasts. The finding o f this intraseasonal signal in global precipitable water is significan t for two reasons: (1) it suggests that there is 90-150 day intraseaso nal variability in the atmospheric branch of the global hydrological c ycle and (2) it provides a useful parameter to test the sensitivity of the GDAS-generated hydrological data. This newly identified intraseas onal signal in the global precipitable water was verified with Special Sensor Microwave/Imager precipitable water data over oceans and stati on-mixing ratio data over the continental United States. Based upon so me simple statistical analyses and global and regional composite chart s, it was found that the 90-150 day low-frequency oscillations contain ed in different GDAS data sets are more coherent with each other in re gions with good data coverage but are poorly correlated over the data- sparse areas. Furthermore, the GLA GDAS provides the most realistic re presentation of this intraseasonal global precipitable water signal.