Abstract
Abstract. Temporal variations in wind speed and significant wave height (SWH) at a location in the eastern Arabian Sea are studied using ERA-Interim reanalysis data from 1979 to 2012. A shallow water location is selected for the study since measured buoy data are available close to the location for comparison with the reanalysis data. The annual mean wind speed shows a statistically significant decreasing trend of 1.5 cm s−1 year−1, whereas a statistically insignificant increasing trend of 3.6 cm s−1 year−1 is observed for annual maximum wind speed due to the local events that altered the trend in annual maximum wind speed. Weakening of SWH during one of the peak monsoon months (August) is identified from the monthly analysis of SWH, which shows a higher upward trend in SWH during the southwest monsoon period, with an exception during August. The annual mean SWH shows a slight upward trend (0.012 cm year−1), whereas a larger upward trend (1.4 cm year−1) is observed for annual maximum SWH. Both identified trends are statistically insignificant. The influence of tropical cyclone activity is also studied and it is found that the maximum SWH and wind speed during 1996 are directly related to the cyclonic event.
Highlights
Knowledge of the wind and wave climate is required for engineering design and the shipping industry (Krogstad and Barstow, 1999; Tucker and Pitt, 2001)
As a part of the global study, Caires and Swail (2004) examined the long-term trend in significant wave height (SWH) in the Arabian Sea (AS) based on voluntary observing ship (VOS) data, but the long-term changes and decadal variation in wave climate in the eastern AS are not known at present
We studied monthly variation in parameters by creating monthly data from the 6-hourly data and taking the mean of those months over a period of 34 years
Summary
Knowledge of the wind and wave climate is required for engineering design (e.g., ships and offshore platforms) and the shipping industry (Krogstad and Barstow, 1999; Tucker and Pitt, 2001). As a part of the global study, Caires and Swail (2004) examined the long-term trend in SWH in the AS based on VOS data, but the long-term changes and decadal variation in wave climate in the eastern AS are not known at present. ERA-Interim is the first re-analysis using adaptive and fully automated bias correcrived from the zonal and meridional components of winds at 10 m a.s.l. We studied monthly variation in parameters (wind speed and SWH) by creating monthly data from the 6-hourly data and taking the mean of those months over a period of 34 years. The nearest available ERA-Interim SWH data to the measured in situ buoy data at Honnavar during 2011 and 2012 are used for the comparison. The scattering index (SI) value is 0.23, with a positive bias of 0.2 m during 2011, whereas a slightly reduced SI and bias are observed during 2012 (Fig. 2)
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