Observation of Nonseismic Sea level Oscillations at TsunamiTimescales (T < 2 hours) along the Indian Subcontinent

Sea-level observations provide information on various processes occurring over different spatio-temporal scales prone to coastal flooding hazards. However, the research on sea-level extremes is often limited to hourly or daily datasets, which prevent the quantification and analyses of shorter-period processes, like seiches, meteotsunamis, infragravity, and coastal waves, which may even dominate in low tidal basins. This study examines for the first time the intensity, frequency and spatio-temporal distribution of nonseismic (< 3 h) sea level variations along the Indian subcontinent using a 13-year sea level record with a sampling rate of 1 to 6 mins along 50 tide gauge stations in the east and west coast of the Indian Subcontinent. A meticulous two-stage quality control (QC) has been carried out for the data reduction of outliers, stuck values, datum shifts, spikes, and clock errors. A buddy checking has also been carried out if the tide gauge has multiple sensors and the sensor having the least data loss is taken for the analysis. Finally, we implemented a visual inspection interactive tool to eliminate spurious erroneous data to ensure data accuracy and reliability and, each data point is assigned a quality control flag on a scale from 0 to 6, indicating research-grade data following each QC level. The QC flags and interactive Python-based QC module will be open to the research community. Preliminary analysis shows the existence of nonseismic sea level oscillations (<2 hours) along the entire Indian subcontinent. The range of these oscillations is comparable with the climatological storm surge height on the west coast of India. Finally, an overview of all the existing major frequencies and its temporal and spatial distribution is described across the east and west coast of the Indian subcontinent. Our findings emphasize the relevance of high-frequency sea level variability for regional sea level forecasting and flood risk management.