the seasonal heat budget of the North Pacific: Net heat flux and heat storage rates (1950-1990)

Abstract

A new estimate of the heat budget for the North Pacific Ocean is presented in this paper. The seasonal net heat flux and heat storage rates were calculated for the North Pacific Ocean from 1950 to 1990 on a spatial resolution of 5° × 5°. Temperature profiles from the National Ocean Data Center were used to calculate the heat storage rates. Satellite remotely sensed solar irradiance and ship marine weather reports from the Comprehensive Ocean - Atmosphere Data Set were used to calculate the net surface heat flux. Heat storage rates were calculated as the time rate of change of the heat content integrated from the surface down to the isotherm that was 1°C less than the coldest locally observed wintertime sea surface temperature, which was defined as the locally observed wintertime ventilation isotherm. The monthly climatology of the 5° × 5° resolution net heat flux was balanced by the heat storage rate for most regions of the North Pacific. To achieve this balance the net heat flux was calculated using the Liu et al. formulations for latent and sensible heat exchange and a modified version of the Reed cloud correction for solar insolation. The root-mean-square error in the difference between the net heat flux and heat storage rate climatologies was calculated at 40 W m-2. When the individual temperature profiles from the northeastern portion of the basin were normalized to the local 300-m mean temperature, thereby removing some of the potential local changes caused by barotropic variability of water motion, the root-mean-square error in this region was further reduced to 20 W m-2 and the large-scale semiannual periodicity in the difference observed in the subtropics was removed. This normalization process may have removed some of the basin-scale variability in the horizontal heat advection. An estimate of the northward heat transport was calculated by integrating the annual mean net heat flux over the North Pacific. The resulting heat transport values were closer to actual northward heat transport estimates made at 10°, 24°, 35°, and 47°N, than previous ocean heat flux estimates. The bias in the data was estimated to be less than 7% by comparing the demeaned seasonal cycle of the net heat flux with that of the heat storage rates. The annual mean net heat flux was then used with the 7% bias and the 20 W m-2 uncertainty to calculate a more constrained error envelope for the annual mean northward heat transport in the North Pacific.