Assessment of quality and impact of full resolution TOVS temperature profile data on the operational global data assimilation forecast system of India

TOVS temperature profile data (SATEM) at its full resolution (85 km) has no w become available in India on experimental basis. An attempt is made in th is study to examine the quality and impact of this on the medium range fore casts over India and neighbourhood. For this purpose, a seven day period st arting from 15 March 1996 is chosen to study the impact of the data on the global analysis-forecasting system operational in India. Though one week da ta is utilized for the impact study, the complete data of March 1996 is use d for examining quality, representativeness and consistency of the retrieva ls. In the operational system of the National Centre for Medium Range Weath er Forecasting (NCMRWF), all types of data, including coarse resolution (50 0 km) global TOVS retrievals-coarse grid SATEM (CGS) data, received on GTS at hourly intervals are used in the assimilation cycle. For the present stu dy the assimilation cycle is repeated for the above period by including hig h resolution data over the geographical regions covered by the New Delhi's high resolution picture transmission (HRPT) station and simultaneously remo ving coarse resolution SATEM data. The analysis and forecast fields thus ge nerated are compared with the corresponding operational archives. The impac t of the data is examined in terms of various objective scores and through circulation characteristics. The study reveals that the quality of high resolution SATEM (HRS) data is s atisfactory and is such that it can be utilized in the global data assimila tion system on real-time basis. A general improvement in the RMSE and ACC s cores of the medium range forecasts is found over the data void equatorial sectors of the Indian Ocean after the incorporation of the HRS data fields in the assimilation cycle. With regard to a typical easterly wave activity of moderate intensity during the period of experimentation, a marginal modu lation in low level vorticity and divergence forecasts is found to be impro ving the precipitation magnitudes over the south peninsular India as well.