Articles | Volume 34, issue 10
https://doi.org/10.5194/angeo-34-871-2016
https://doi.org/10.5194/angeo-34-871-2016
Regular paper
 | 
18 Oct 2016
Regular paper |  | 18 Oct 2016

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

V. Sanil Kumar and Jesbin George

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 ( >  2.5 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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Short summary
Influence of monsoon variability on the surface waves using measured data covering 7 years and reanalysis data from 1979 to 2015 during the Indian summer monsoon in the eastern Arabian Sea is examined. A high positive correlation (r ~ 0.84) between average low-level jet for the block 0–15° N, 50–75° E and wave height of eastern Arabian Sea is observed in all months except August. The monsoon seasonal average wave height is found to be relatively low during the strong El Niño years.