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

Kumar, V. Sanil; George, Jesbin

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 ( >  2.5 m) is higher ( ∼  26%) in 2014 than in other years due to the higher monsoon wind speed (average speed ∼ 7.3 m s −1) in 2014. Due to the delayed monsoon, monthly average significant wave height ( Hm0) of June was lowest (∼ 1.5 m) 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 Hm0 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 Hm0 is found to have a negative relationship with the Oceanic Niño Index indicating that the monsoon average Hm0 is relatively low during the strong El Niño years.

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Kumar, V. Sanil / George, Jesbin: Influence of Indian summer monsoon variability on the surface waves in the coastal regions of eastern Arabian Sea. 2016. Copernicus Publications.

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