Oscillation responses to tropical Cyclone Gonu in northern Arabian Sea from a moored observing system

In June 2007, tropical Cyclone Gonu passed over an ocean observing system consisting of a deep autonomous mooring system in the northern Arabian Sea and a shallow cabled mooring system in the Sea of Oman. Gonu was the largest cyclone known to have occurred in the Arabian Sea and to strike the Arabian Peninsula. The instruments on the moorings continuously recorded water velocities, temperature, conductivity, pressure, dissolved oxygen (DO) and turbidity at multiple depths and at hourly intervals during the storm. nertial oscillations at all moorings from thermocline to seafloor are coincident with the arrival of Gonu. Sub-inertial oscillations with periods of 2–10 day are recorded at the post-storm relaxation stage of Gonu, primarily in the thermocline of the deep array and at the onshore regions of the shallow array. These oscillations consist of warm, saline water masses, likely originating from the Persian Gulf. Prominent 12.7-day sub-inertial waves, measured at a station ∼300 km offshore, are bottom-intensified and have characteristics of baroclinic topographically trapped waves. Theoretical results from a topographically trapped wave model are in a good agreement with the observed 12.7-day waves at Murray Ridge. The wavelength of the 12.7-day waves is about 590 km calculated from the dispersion relationship. Further analysis suggests that a resonant standing wave is responsible for trapping the 12.7-day wave energy inside the Sea of Oman basin. The observational results reported here are the first measurements of deepwater responses to a tropical cyclone in the Sea of Oman/Arabian Sea. Our study demonstrates the utility of sustained monitoring for studying the impact of extreme weather events on the ocean.