A 19th century daily surface pressure series for the Southwestern Cape region of South Africa: 1834–1899

Abstract

The first daily mean sea‐level pressure (MSLP) series for the Southwestern Cape region of South Africa is presented for the 19th century, and is one of the longest and oldest for the Southern Hemisphere. Sub‐daily barometer readings from the South African Astronomical Observatory were digitized, together with temperature readings, and extend over the period 1834–1899. Pressure readings were recorded using mercury barometers and so needed to be corrected and reduced to standard conditions. Overall, austral winter (June, July, August) has the highest mean monthly MSLP values, symptomatic of the ridging anticyclones during this season. The year 1862 stands out with particularly low MSLP values and has 27 days during austral winter that were below the 10th percentile. This most likely indicates that the winter of 1862 experienced the highest number of passing cold fronts throughout the 66‐year study period.