Evaluation of broad scale vertical circulation and thermal indices in relation to the onset of Indian summer monsoon

✍ Scribed by S. K. Roy Bhowmik

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 585 KB
• Volume: 22
• Category: Article
• ISSN: 0899-8418
• DOI: 10.1002/joc.742

✦ Synopsis

Abstract

The onset of the Indian summer monsoon over Kerala for an individual year of delayed (1997), early (1999) and normal onset (2000) was examined in relation to the intensity of vertical circulation and thermal indices during the pre‐monsoon months (April and May). The study showed that in the delayed monsoon onset year (1997) negative anomalies of vertical zonal index dominated over the north Indian Ocean during pre‐monsoon months, particularly in April. In contrast, in the early onset year (1999) the positive anomalies of this index over the north Indian Ocean during the pre‐monsoon months were considerably stronger (April and May). However, the meridional vertical index did not show any appreciable difference. The gradient of the vertical thermal index anomalies over the Tibetan Plateau in the month of April was prominently stronger during the years of early and normal onset (1999 and 2000). The anomalies of geopotential height at 200 hPa over the Tibetan Plateau in the pre‐monsoon months were significantly lower in the year of delayed onset (1997). The precipitable water content was found to be another major feature, which grew rapidly over the equatorial belt of the Indian Ocean extending up to the Arabian Sea and Bay of Bengal during the two weeks prior to onset. Most of these features were observed very distinctly in the month of April, well before the monsoon onset, and promise to provide important predictive signals for the onset over Kerala. Copyright © 2002 Royal Meteorological Society.