Systematic errors in the medium range prediction of the Asian summer monsoon circulation |
| |
Authors: | U C Mohanty K J Ramesh |
| |
Institution: | (1) Centre for Atmospheric Sciences, Indian Institute of Technology, Hauz Khas, 110016 New Delhi, India;(2) National Centre for Medium Range Weather Forecasting (NCMRWF), INSAT Building, Mausam Bhavan Complex, Lodi Road, 110003 New Delhi, India |
| |
Abstract: | The present study describes an analysis of Asian summer monsoon forecasts with an operational general circulation model (GCM)
of the European Centre for Medium Range Weather Forecasts (ECMWF), U.K. An attempt is made to examine the influence of improved
treatment of physical processes on the reduction of systematic errors. As some of the major changes in the parameterization
of physical processes, such as modification to the infrared radiation scheme, deep cumulus convection scheme, introduction
of the shallow convection scheme etc., were introduced during 1985–88, a thorough systematic error analysis of the ECMWF monsoon
forecasts is carried out for a period prior to the incorporation of such changes i.e. summer monsoon season (June–August)
of 1984, and for the corresponding period after relevant changes were implemented (summer monsoon season of 1988).
Monsoon forecasts of the ECMWF demonstrate an increasing trend of forecast skill after the implementation of the major changes
in parameterizations of radiation, convection and land-surface processes. Further, the upper level flow is found to be more
predictable than that of the lower level and wind forecasts display a better skill than temperature. Apart from this, a notable
increase in the magnitudes of persistence error statistics indicates that the monsoon circulation in the analysed fields became
more intense with the introduction of changes in the operational forecasting system.
Although, considerable reduction in systematic errors of the Asian summer monsoon forecasts is observed (up to day-5) with
the introduction of major changes in the treatment of physical processes, the nature of errors remain unchanged (by day-10).
The forecast errors of temperature and moisture in the middle troposphere are also reduced due to the changes in treatment
of longwave radiation. Moreover, the introduction of shallow convection helped it further by enhancing the vertical transports
of heat and moisture from the lower troposphere. Though, the hydrological cycle in the operational forecasts appears to have
enhanced with the major modifications and improvements to the physical parameterization schemes, certain regional peculiarities
have developed in the simulated rainfall distribution over the monsoon region. Hence, this study suggests further attempts
to improve the formulations of physical processes for further reduction of systematic forecast errors. |
| |
Keywords: | Summer monsoon parameterization of physical processes systematic errors general circulation model forecast skill |
本文献已被 SpringerLink 等数据库收录! |
|