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The seasonal net heat flux and heat storage rates were calculated for the North Pacific from 1950 to 1990 at a spatial resolution of 5° longitude by 5° latitude. Over 1.2 million assorted XBT and CTD profiles from the National Ocean Data Center (NODC) were used to calculate the net heat storage rates. Satellite remotely sensed solar radiation estimates and ship marine weather reports from the Comprehensive Ocean Atmosphere Data Set (COADS) 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 which was 1°C colder than the coldest local observed wintertime sea surface temperature, which we defined as the coldest local observed wintertime ventilation isotherm. Using these chosen isotherms, the heat storage rates were much less sensitive to changes in isotherm than that of heat storage rates calculated to either a fixed depth or an isotherm which did not vary with region. At the horizontal scale used, for most regions of the North Pacific the monthly climatology of the net heat flux was balanced by the local heat storage rate. In order to achieve this balance we were required to choose the Liu et al. (1981) formulations for latent and sensible heat exchange and to modify Reed's (Reed, 1977) cloud correction for solar insolation. The root mean square error in the difference between the net heat flux and heat storage rates climatologies was calculated at 40 W m-2. When the individual temperature profiles from the northeastern portion of the basin were normalized to the 300 m local temperature mean, thereby removing some of the potential local seasonal variability due to 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 semi-annual periodicity in the difference observed in the subtropics was removed. This normalization process may have served to remove some of the basin scale seasonal 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. By comparing the seasonal cycle of the net heat flux with that of the heat storage rates, the bias in the data was estimated to be less than 10 percent. This 10 percent bias was then used with the annual mean net heat flux and the calculated less than 20 W m-2 uncertainty in the difference between the seasonal net heat flux and heat storage rates to calculate a more constrained error envelope for the annual mean northward heat transport in the North Pacific.
by Peter Niiler and John Moisan
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