Long-range forecast of the break and active summer monsoons
CADET, DANIEL L.
- Publisher: Co-Action Publishing
(issn: 1600-0870, eissn: 0280-6495)
Ship observations along the major shipping route from Sri Lanka to Sumatra have been processed over a 23-year period from January 1954 to December 1976. Daily time series of the zonal and meridional components of the wind, pressure, cloudiness, air temperature and SST have been constructed over the southern Bay of Bengal. The zonal wind component, the pressure and the cloudiness exhibit a well-defined 30- to 50-day mode. The fluctuations of these parameters are physically consistent. The period of the low-frequency mode varies over the 23-year period, but does not show a seasonal or annual cycle. The low-frequency variations of the surface parameters can be associated with the break and active cycle of the Indian summer monsoon. The low-frequency relationship established between the surface meteorological parameters over the southern Bay of Bengal and the activity of the summer monsoon (rainfall at stations in India) is used to forecast the occurrence of the active and inactive periods. The forecast is based on the fitting of an auto-regressive moving average process over a 4-month period of the time series to extrapolate it over 30, 40 or 50 days. During years when the 30- to 50-day mode is well-defined, high-quality forecasts can be obtained. The forecasts fail during years when the phase of the low-frequency mode varies rapidly during spring and summer. On the average, the dates of the peak of the active/inactive monsoons can be predicted with an accuracy of about a week. This study offers new perspectives for the long-range forecast of fluctuations of the activity of the summer monsoon.DOI: 10.1111/j.1600-0870.1988.tb00412.x