Departures from the local inverse barometer model observed in altimeter and tide gauge data and in a global barotropic numerical model

Abstract

Sea level data from the TOPEX/Poseidon altimeter satellite and from subsets of the global tide gauge and bottom pressure recorder networks have been employed to study the worldwide distribution of departures from the simple local inverse barometer (LIB) model. From a combination of measurement techniques the LIB model was found to provide a reasonable representation of the data (within 5–10%) outside of the tropics for timescales from several days to several weeks for most locations. However, several parts of the Southern Ocean and other higher‐latitude areas were seen from the altimetry to contain significant departures across the range of timescales accessible for study by the technique. Within the tropics the response of sea level to air pressure forcing was observed to be typically 50% of that of the LIB model at timescales of several days, with considerable spatial variation, and to approximate the LIB model more closely at timescales of several weeks. A coarse‐grid global barotropic numerical model was found to reproduce qualitatively the global average response as a function of frequency, to simulate many of the characteristics of the spatial variation of the response, and to demonstrate the relative importance of air pressure and wind forcing at different timescales. Data sets from the Permanent Service for Mean Sea Level and U.K. Meteorological Office were used to investigate LIB departures at intraseasonal and longer timescales along continental coastlines and at ocean islands. Increasingly large departures were observed along many parts of the world coastline as timescales increased from months to seasons.