Heat storage and advection in the North Pacific Ocean

Abstract

We analyzed the process maintaining the seasonal heat storage in the 0–250 meter surface layer of the North Pacific Ocean by using 140,000 bathythermograph observations. Horizontal mixing contributes less than 10% to the local monthly change in heat storage throughout the North Pacific except in the areas east of Japan, west of Vancouver Island and south of the Aleutian Islands. In these areas mixing contributes up to 38% of the local monthly change in heat storage. Horizontal advection of heat is calculated from the heat conservation equation by using estimates for net surface heat exchange. Advection is equal or greater in importance than the net surface heat exchange in determining the local thermal structure. Advection also leads the net surface heat exchange by an average of 2 months. A numerical model of the seasonal change in heat storage is developed by using the heat conservation equation to further examine the influence of horizontal mixing and advection on the seasonal changes in the local heat storage. The results show that a horizontal circulation of 42 million m3 sec−1 is required in the large subtropical anticyclonic gyre in the central Pacific. In addition, an eastern Pacific gyre southeast of the Hawaiian Islands of 12 million m3 sec−1 is required. By using the numerical model, we also examined the behavior of heat storage anomalies in the North Pacific Ocean. The results show that the heat storage in the areas east of Japan and in the western and eastern tropical Pacific are primarily affected by changes in the circulation.