Impact of NOAA/TOVS derived moisture profile over the ocean on global data assimilation and medium range weather forecasting

Abstract

A realistic three-dimensional distribution of moisture in the initial condition is essential for successful numerical weather prediction. The moisture profile serves as direct input to any forecast model. Since the ocean surrounding the Indian sub-continent is one of the enormous data sparse regions in the tropics, the remotely sensed data is an important source of meteorological information, used at various operational numerical weather prediction centers for preparing initial conditions. The temperature and moisture sounding data from the Television and Infrared Observation Satellite (TIROS) and the Operational Vertical Center (TOVS) onboard the National Oceanographic Atmospheric Administration (NOAA) polar orbiting satellite is being routinely received at National Centre for Medium Range Weather Forecasting (NCMRWF) through the Global Telecommunication System (GTS). Moisture information is available at three broad layers. In the present study an attempt has been made to derive a humidity profile from the NOAA polar orbiting satellite by the variable scale height algorithm. These profiles derived at standard pressure levels are validated with coinciding radiosonde observations, other humidity estimations, and analysis. The validation indicates that the percentage of root mean square (r.m.s) error is less than 10. The impact of these moisture profiles is examined in the NCMRWF analysis and forecast system for the June 1997 period. A positive impact of this TOVS derived moisture in the forecast of onset of monsoon-97 is noticed. Some of the results during the monsoon lows and depression arc also presented for the same period. In particular the rainfall forecast for 20th June, 1997 has improved.