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

Abstract

AbstractIn and around the Indian Ocean basin, historical records documenting observations of climatic variables such as rainfall, surface‐air and sea‐surface temperature, and atmospheric pressure can be found in various publications by the European colonial powers of the time. However, it is only the most accessible of these records from the mid‐to‐late 1800s that have been transferred into electronic form and used in any contemporary climatic studies. A longer‐term set of observations from the observatory at Madras (now Chennai), set up by the English East India Company, was found to have the potential to provide useful climatic data back to 1796.In this study, atmospheric pressure data recorded at the Madras Observatory, and at other climate stations in or near Madras, and in India, were recovered and examined for their quality and veracity. From the old observatory publications, pre‐1841 records (that is prior to those documented in standard data compilations) were quality controlled, and the full record from 1796 was then reduced to mean sea level, standard gravity and 24 h means to produce a 205 year set of monthly observations. This monthly mean sea‐level pressure (MSLP) record was correlated with monthly or seasonally stratified instrumental indices of the El Niño southern oscillation (ENSO) phenomenon and all‐India rainfall, and a seasonally stratified palaeoclimatic reconstruction of the southern oscillation index. In general, the Madras MSLP record is shown to be robust over time, and thus a useful long‐term measure of fluctuations in the ENSO phenomenon across the Indian Ocean basin and of the Indian summer monsoon. Copyright © 2002 Royal Meteorological Society.