Longest instrumental regional and all-India summer monsoon rainfall series using optimum observations: reconstruction and update

Abstract

Long period June-to-September total rainfall series are vital for the study of summer monsoon/climatic variability over the Indian region. Owing to high spatial variability in rainfall, the representativeness of the summer monsoon rainfall series for the entire country is limited. In order to develop an effective system for monsoon rainfall studies, the country has been divided into six zones, named as North West India (NWI), North Central India (NCI), North East India (NEI), West Peninsular India (WPI), East Peninsular India (EPI) and South Peninsular India (SPI). Fluctuation, empirical orthogonal function (EOF) and cluster analyses of the summer monsoon rainfall of the period AD 1871-1984 of 306 raingauges are carried out for this classification. Updating the different zonal rainfall series on a real-time basis from all the gauges is a difficult task. In the present study, an objective technique is applied to select a subset of gauges whose mean showed the highest correlation with the all-gauges mean series; a total of 116 raingauge stations (19 for NWI, 27 for NCI, 15 for NEI, 18 for WPI, 14 for EPI and 23 for SPI) maintained by the India Meteorological Department (IMD) have been identified for updating the different zonal series. The different zonal series are extended as far as possible backward (prior to AD 1871) by applying an objective technique to the available gauges. The NEI and the EPI series are extended back to 1848, the NWI to 1844, the NCI to 1842, the WPI to 1817 and the SPI to 1813. Though of limited practical value, the all-India series is widely used in studies of long-range monsoon forecasting, teleconnections and large-scale climate dynamics. The all-India monsoon rainfall series from AD 1871 onwards is therefore calculated from the area-weighted mean of the six zones. The series is also extended back to AD 1813 by applying the objective technique on the available gauges. The different reconstructed series for the longest instrumental period are reported.

A reconstruction of Madras (Chennai) mean sea‐level pressure using instrumental records from the late 18th and early 19th centuries

“…Patterns of correlation between monthly Madras MSLP and various ENSO indices can only be explored using instrumental data after the 1860-70s period. Examinations of the full monthly Madras MSLP record are possible against long proxy ENSO indices (Stahle et al, 1998), or since 1813 with regard to all-India June to September (JJAS) monsoon rainfall (Sontakke and Singh, 1996). All of these various indices are correlated for the full period of overlap, and for 21-year epochs.…”

“…Two sets of all-India rainfall series for the summer monsoon season of JJAS are examined. One is from 1813 to 1992 (Sontakke and Singh, 1996) and the other from 1871 to 1996 (http://tao.atmos.washington.edu/data sets/india/parthasarathy.html). These rainfall data provide important regional indicators against which to assess most of the Madras MSLP record.…”

“…Shaded bars highlight correlations that are significant at the 95% and 99% confidence limits. Correlations that explain >50% of the variance between the data are also highlighted; see the key these two rainfall data sets is that Sontakke and Singh (1996) compile their data using a maximum of 36 rainfall stations after 1870, whereas the other set uses specifically district rainfall aggregations. In Figure 11(a) and (b), the strongest, temporally stable and coherent correlations between monthly Madras MSLP and JJAS all-India rainfall are found in the September to October period.…”

“…These data were finally all converted to 24 h means (see Appendix C) using the traces of diurnal variations of atmospheric pressure for each month at Madras given by the graphs in Eliot (1902), and post-1841 monthly Madras corrections in Meteorological Office (1917). (Sontakke and Singh, 1996), (b) monthly Madras MSLP and all-India JJAS from 1871 to 1996 (http://tao.atmos.washington.edu/data sets/india/parthasarathy. html), and (c) a tree-ring reconstruction of the DJF SOI (Stahle et al, 1998) for each month during the year.…”

Variation in the orographic extreme rain events over the Meghalaya Hills in northeast India in the two halves of the twentieth century

“…Northeast India, where the Meghalaya Hills are located, can be treated as a relatively separate region, with summer monsoon rainfall weakly correlated or out of phase with that of peninsular India (Mooley and Shukla 1987;Parthasarathy et al 1987;Sontakee and Singh 1996;Guhathakurta and Rajeevan 2008;Guhathakurta et al 2011). The area receives high rainfall (the annual mean approximately 2,066 mm with a coefficient of variation of 8.6 %), but its large spatiotemporal variation, related to multiscale interaction with topography, results in difficulties in the detection of trends in extreme rain events (Parthasarathy et al 1995;Goswami et al 2010).…”