Dipole behaviour in maximum significant wave height over the Southern Indian Ocean

Abstract

ABSTRACTThe study reports on existence of a dipole pattern in maximum significant wave height (MSWH) as well in mean significant wave height over the Southern Indian Ocean (SIO) based on analysis using 24 years of satellite observations. Analysis using quality checked daily altimeter data from nine satellite missions for entire Indian Ocean region revealed the spatio‐temporal variability of observed dipole phenomena. Interestingly, the second empirical orthogonal function (EOF) mode (EOF2) in monthly and monthly anomaly MSWH data clearly shows the prevalence of dipole over the SIO having a period of 6 months for monthly dataset Principal Component (PC) leading to a 3 months oscillation. The EOF of monthly anomaly dataset analysis also exhibited a similar dipole pattern for the EOF2 mode having a period of 2.1 years. In addition, the study also considered seasonal EOF analysis for four austral seasons December–January–February (DJF), March–April–May (MAM), June–July–August (JJA), and September–October–November (SON). The EOF2 for all seasons exhibits a similar dipole pattern in SIO basin, except for the DJF months. Based on seasonal EOF analysis, the DJF and JJA EOF2s have similar dipole pattern that reverses its polarity because of wind variability for the MAM and SON EOF2s justifying 3 months dipole oscillation obtained for monthly datasets. The Radon transform is used to investigate the orientation of this dipole, and for the first time this method is used in the field of climatology to study orientation and the degree of polarity of a dipole pattern. Furthermore, the study investigated possible correlation of dipole with various proven climate indices establishing the fact that Southern Annular Mode Index (SAMI) showed a significant correlation. The other seasonal datasets also correlated well with SAMI, except DJF months that do not show the dipole pattern, and it had a good correlation with Nino3 index representing the El Nino Southern Oscillation Index.