A study of meteorologically and seismically induced water level and water temperature oscillations in an estuary located on the west coast of India (Arabian Sea)

Abstract

The study examines the observed storm-generated sea-level oscillations (June 2007 and November 2009) during the Sumatra geophysical tsunami (September 2007), indicating similarities in the sea-level response in the Mandovi estuary, Goa. Sea-level and surface meteorological measurements carried out during storms exhibit strong synoptic disturbances leading to the coherent oscillations in the estuary with significant energy bands centred at periods of 24, 45, and 80 min. In particular, during the sporadic atmospheric event of June 2007, the atmospheric pressure dipped by approx. 12 mb, the wind direction stabilized to approx. 249 degrees with peak wind speed up to 16 m s sup(−1) and the positive sea-level surge swelled up by approx. 40 cm. Also, the water temperature cooled down by approx. 4.5 degrees C. Approximately 3 days prior to the 12 September 2007 Sumatra earthquake, the water temperature at Verem station, in Mandovi estuary started exhibiting a distinctly stronger semidiurnal oscillation (with a relatively larger variance of approx. 17.9 degrees C sup(2) in contrast to a lesser variance of approx. 12 degrees C sup(2) during the preceding normal days) and these well-defined oscillations continued to manifest for a week after the earthquake. The pre-earthquake enhanced seawater temperature oscillations observed at this tropical estuary provides an indication that routine monitoring of seawater temperature from tropical estuaries with fine temporal resolution may provide early information about impending coastal earthquakes.