Influence of Indian summer monsoon variability on the surface waves in the coastal regions of eastern Arabian Sea

Abstract

We assess the influence of monsoon variability on the surface waves using measured wave data covering 7 years and reanalysis data from 1979 to 2015 during the Indian summer monsoon (JJAS) in the eastern Arabian Sea. The inter-annual comparison shows that the percentage of higher wave heights (>2.5m) is higher (~26%) in 2014 than in other years due to the higher monsoon wind speed (average speed ~7.3ms^-1) in 2014. Due to the delayed monsoon, monthly average significant wave height (H_m0) of June was lowest (~1.5m) in 2009. The spectral peak shifted to lower frequencies in September due to the reduction of wind seas as a result of decrease in monsoon intensity. The study shows high positive correlation (r~0.84) between average low-level jet (LLJ) for the block 0-15°N, 50-75°E and H_m0 of eastern Arabian Sea in all the months except in August (r~0.66). The time series data on wave height shows oscillations with periods 5 to 20 days. Wavelet coherence analysis indicates that the LLJ and Hm0 are in-phase related (phase angle 0°) almost all the time and LLJ leads Hm0. The monsoon seasonal anomaly of H_m0 is found to have a negative relationship with the Oceanic Nino Index indicating that the monsoon average H_m0 is relatively low during the strong El Nino years