Teleconnection between the North Indian Ocean high swell events and meteorological conditions over the Southern Indian Ocean

Abstract

The link between North Indian Ocean (NIO) high swell events and the meteorological conditions over the Southern Indian Ocean (SIO) is explored in this article, using a combination of in situ measurements and model simulations for the year 2005. High waves, without any sign in the local winds, sometimes cause severe flooding events along the south‐west coast of India, locally known as the Kallakkadal events and cause major societal problems along the coasts. In situ observations report 10 high swell events in NIO during 2005. Our study confirms that these events are caused by the swells propagating from south of 30°S. In all cases, 3–5 days prior to the high swell events in NIO, we observed a severe low pressure system, called the Cut‐Off Low (COL) in the Southern Ocean. These COLs are quasistationary in nature, providing strong (∼25 ms−1) and long duration (∼3 days) surface winds over a large fetch; essential conditions for the generation of long‐period swells. The intense equator ward winds associated with COLs in the SIO trigger the generation of high waves, which propagate to NIO as swells. Furthermore, these swells cause high wave activity and sometimes Kallakkadal events along the NIO coastal regions, depending on the local topography, angle of incidence, and tidal conditions. Our study shows that such natural hazards along the NIO coasts can be forecasted at least 2 days in advance if the meteorological conditions of the SIO are properly monitored.

Propagation Route and Speed of Swell in the Indian Ocean

“…Nayak et al () found that the low‐frequency swells from the Southern Ocean reach the southern tip of Indian mainland in about 4 days without much energy dissipation. Our results agreed well with those of Remya et al (). In addition, the propagation speed of swells in the Indian Ocean was fastest (required the shortest time) in May and August, followed by November.…”

“…Furthermore, these swells cause high wave activity and sometimes Kallakkadal events along the NIO coastal regions. The overall propagation characteristic of SIOW‐related swells in this study is agreed with Remya et al ().…”

“…And approximately 132–138 h are required for H s to propagate from the Roaring Forties to the tropical waters of the NIO. Based on the results from Remya et al () and Zheng and Li (), it means that the natural hazards along the NIO coasts can be forecasted at least 2 days in advance if the meteorological conditions of the SIO are properly monitored.…”

“…By using the observations, Remya et al (2016) found 10 high swell events in North Indian Ocean (NIO) (also named Kallakkadal events) during 2005, which are caused by the swells propagating from south of 308S. In all cases, 3-5 days prior to the high swell events in NIO, they observed a severe low pressure system, called were first highlighted and then connected with a single line, as shown in Figure 8a, where the red arrow represents the main propagation route.…”

“…Alves () noted that many southern Indian Ocean westerly (SIOW) swells freely propagate eastward into the tropical and subtropical latitudes of the Indian and Pacific Oceans. By monitoring the wave height and peak period, Remya et al () determined that swells propagated from the SIOW to northern Indian Ocean during 14–21 May 2005. By tracking the swell observations using SAR wave mode data, Jiang et al () found that swells generated by a storm in 58°S, 132°W could propagate to the coast of Mexico.…”