The maxima in northerly wind speeds and wave heights over the Arabian Sea, the Arabian/Persian Gulf and the Red Sea deri
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The maxima in northerly wind speeds and wave heights over the Arabian Sea, the Arabian/Persian Gulf and the Red Sea derived from 40 years of ERA5 data V. M. Aboobacker1 · P. R. Shanas2 · Ebrahim M. A. S. Al‑Ansari1 · V. Sanil Kumar2 · P. Vethamony1 Received: 13 April 2020 / Accepted: 28 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Recent studies point out the importance of northerly winds and waves in the Arabian Sea, especially those due to shamal and makran events in addition to the northeast monsoon system. We have analyzed climatology and trends of northerly maximum wind speed and significant wave height ( Hs) in the Arabian Sea and the connected marginal seas, Arabian/Persian Gulf and the Red Sea, during non-monsoon season derived from 40 years of ERA5 wind and wave data, and estimated monthly, annual and decadal extreme climate and their trends. The study brings out an increasing trend in the northerly maximum wind speed (0.8–1.2 cm/s/year) and Hs (0.42–0.88 cm/year) in the southern and central Arabian Sea, which is consistent with the global trend in extreme wind speed and Hs. The northern Arabian Sea including the Sea of Oman exhibits significant decreasing trend in northerly maximum wind speed (− 1.4 cm/s/year) and H s (− 0.67 cm/year), while the Gulf and the Red Sea exhibit sectorial contrasting trend, indicating the dominance of localized effects in modifying the regional climate. Distinct features identified in the climate and trends of northerly winds and waves are further discussed. Keywords ERA5 · Shamal swells · Makran waves · Climatology · Arabian Sea · Arabian/Persian Gulf
1 Introduction Wind climate in the Arabian Sea (Fig. 1a) varies according to particular seasons (southwest monsoon, SWM: June–September; northeast monsoon, NEM: October–January; premonsoon, PM: February–May), unlike other oceans or seas. The NEM is also referred to as post-monsoon, since “monsoon” is generally attributed to SWM (Aboobacker et al. 2011a). The low-level jets (LLJ) associated with each season are characterized by their uniqueness in direction, frequency and magnitude. Figure 2 shows the snapshots of the northerly wind systems—NEM, shamal and makran winds—prevailing during non-monsoon seasons, derived from ERA5 reanalysis winds (Hersbach et al. 2019). NEM is the reversal of the SWM, and during this season, wind blows in the NE * V. M. Aboobacker [email protected] 1
Environmental Science Center, Qatar University, P.O. Box 2713, Doha, Qatar
CSIR-National Institute of Oceanography, Dona Paula, Goa 403 004, India
2
direction due to high pressure over the cold Asian regions and low pressure over the Indian Ocean. The northwesterly shamal wind blows over Iraq and Arabian Peninsula with higher wind speeds, both in summer and winter. Its impact is more significant in the Arabian/Persian Gulf (hereafter, the Gulf) (Senafi and Anis 2015), however, often extends up to the west coast of India with a decreasing order of magnitude (Aboobacker et al. 2011b; Vinod Kumar
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