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

Abstract. The study examines the observed storm-generated sea-level oscillations (June 2007 and November 2009) along with the Sumatra geophysical tsunami (September 2007), indicating similarities in the sea-level response in the Mandovi estuary of Goa in the eastern Arabian Sea. Sea-level and surface meteorological measurements collected 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 ~12 mb, the wind direction stabilized to ~249° with peak wind speed up to 16 m s−1 and the positive sea-level surge swelled up by ~40 cm. Also, the water temperature cooled down by ~4.5 °C. Approximately 3 days prior to the 12 September 2007 Sumatra earthquake, the water temperature at Verem station started exhibiting a distinctly stronger semidiurnal oscillation (with a relatively larger variance of ~17.9 °C2 in contrast to a lesser variance of ~12 °C2 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.