Ocean models that neglect mass and momentum contributions from precipitation can have a systematic bias in sea surface height (SSH). Here, a new rainfall scheme is introduced into the Regional Ocean Modelling System (ROMS) to incorporate the effects of precipitation mass. When precipitation is added to the sea surface, it spreads out via surface gravity waves that increase in propagation speed with increasing water depth. Over several days, the SSH increase due to the precipitation mass added created a geostrophic adjustment, generating anti-cyclonic geostrophic currents around the SSH increase. The transfer of momentum from precipitation to the sea surface, or rain stress, can also be important. In the case study of a real tropical cyclone, Monica passing North Australia, the effect of incorporating precipitation mass is compared with other processes affecting the storm surge: surface wind, inverse barometer effect and rain stress. The maximum SSH response is 170.6 cm for the wind effect, 61.5 cm for the inverse barometer effect, 7.5 cm for the effect of rain stress and 6.4 cm for the effect of rain mass. Each process has been shown to have different spatial influences. The effect of rain mass has a strong remote influence compared to the inverse barometer effect and the effect of rain stress. This is particularly seen in semi-enclosed bays
Storm surges pose significant threats to coastal communities, yet negative surges are not as well understood as positive surges. In this study, idealized experiments of a tropical cyclone forcing a 3D ocean model are conducted to investigate the asymmetry of positive and negative surges. Negative surges are larger in magnitude and extend further across the coastline than positive surges. While positive surges are driven by wind blowing onshore, negative surges are largely dominated by alongshore winds, with horizontal divergence as the main mechanism. This asymmetry also increases with decreasing depth and increasing latitude.
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