A Study of Mean Winter Circulation Characteristics and Energetics over Southeastern Asia

Abstract

A mean climatology is studied to examine atmospheric circulation characteristics to assess the wintertime (December, January, February and March -DJFM) synoptic weather system affecting northern India. The main objective is to study the mean circulation and mean energetics distribution pertaining to the winter season, which are embedded with an eastward moving synoptic weather system in westerlies, called Western Disturbances (WDs). Forty years of uninitialized daily re-analysis data of the National Center for Environmental Prediction -National Center for Atmospheric Research (NCEP-NCAR, henceafter NCEP), U.S. has been considered for this study. Winter circulations are considered over the domain 15°S-45°N and 30°E-120°E. This domain is considered particularly to illustrate the impact of wintertime synoptic weather system Western Disturbances (WDs), which travel towards the east over the western Himalayas during winter and yield an enormous amount of precipitation in the form of snow. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture budget terms are analyzed. The main findings of the study show that strong rising motion in the extratropical region brings a significant amount of precipitation over the region of study. Also, horizontal flux of kinetic energy converges in the tropical region and diverges over the extratropical region. It is seen that both the zonal and meridional component of kinetic energy contributes to the production of kinetic energy in the upper troposphere. Vorticity budget shows that wintertime circulation over the western Himalayas is characterized by a negative generation of vorticity. The relative and planetary vorticity advection contributes to the horizontal transport of vorticity. The moisture flux transported into the region shows that in the middle tropospheric levels moisture undergoes phase transformation due to turbulent exchange and hence releases latent heat.

Wintertime climatic trends in the western Himalayas

“…Large scale energetic associated with excess and deficit year of precipitation is studied (Dimri 2007a, b). The normalized precipitation anomaly trends at different stations are not homogeneous which indicates variability in precipitation amount over the western Himalayas due to various thermodynamical and orographic processes (Dimri 2004(Dimri , 2007a. Though there are significant decreasing trends in precipitation across the WH, but careful scrutiny of dry and wet phases shows that these phases do not occur in the same year among the stations considered in this study.…”

Prediction of winter precipitation over northwest India using ocean heat fluxes

“…2a-c. Notable modifications are observed in the wind field at lower levels due to orographic barrier and upper level westerly jet (Dimri 2007). The composite mean of normal years shows that the winds are easterly or northeasterly over the equatorial Pacific and Indian Ocean at 850 hPa pressure level.…”

Study of seasonal climatology and interannual variability over India and its subregions using a regional climate model (RegCM3)

“…Dimri and Ganju (2007) used a regional climate model (RCM) to study the climatology and intraseasonal variability over the western Himalayas during winter. Dimri (2007) studied the mean circulation and energetic distribution during winter over the south-east Asia. ISM is primarily caused by the differential heating of landmass and ocean (Cadet 1979).…”