The Solar Influence on Tropical Cyclones Occurring over the Bay of Bengal and Arabian Sea

Abstract

During the last few decades, a prominent example of extreme weather events in the Indian Ocean region has been cyclonic storms. In this paper, annual variations of different categories of tropical cyclonic storms over the Bay of Bengal (BOB) and Arabian Sea (ARS) are analyzed. The analysis reveals that the total number of cyclones (TNC) has increased at a high rate (the gradient being + 1.67 per year) and that there are more CSs over the BOB than over the ARS. The rate of increase in CSs over the Arabian Sea is more than that over the Bay of Bengal. Furthermore, two interesting features were noted: (i) monsoons tend to prohibit the formation of CSs; (ii) cyclonic storms (CSs) increased with the increase in Global Sea Surface Temperature (GSST) during said period. An attempt was also made to find out the influence of solar activity on these extreme weather events. Keeping in mind that the sunspot number (SSN) is an indicator of the strength of solar effects, it was found that, most of the time, a high SSN value was associated with a small number of total cyclones (CSs). A high SSN (>90) and number of cyclones showed ahigh correlation coefficient (0.78). The significance was at the 99.99% level, while the correlation coefficient (CC) of cyclones with time was 0.53, and with SSN < 60, it was 0.095. Thus, it appears that although CS frequency is increasing with time, the influence of sunspots is such that it basically opposes the formation of cyclones provided the SSN exceeds a certain critical value (roughly 90).

Keywords

• Indian Ocean
• cyclone
• solar influence
• critical sunspot number