A Calculation of Ocean Heat Storage and Effective Ocean Surface Layer Depths for the Northern Hemisphere

Abstract

In the hierarchy of simple ocean formulations available for coupling to atmospheric GCMs, a scheme whereby ocean surface-layer depths vary geographically and seasonally is deemed better than a fixed depth layer at all locations and seasons, but still is less sophisticated than dynamic ocean models. Yet such simple ocean formulations are useful for basic sensitivity studies. Here, a calculation of varying surface layer depths is done by first performing an ocean heat storage calculation using gridded, long-term mean mixed-layer depths and sea surface temperatures with a parameterized temperature structure beneath the mixed layer derived from weather ship data. Heat storage values in the midlatitudes are larger in the Atlantic than in the Pacific, which is in qualitative agreement with the weather ship data. Variants of the basic calculation show that neither mixed layer data nor SST data alone are sufficient to compute heat storage adequately. Using the results from the parameterized heat storage calculations, effective ocean surface-layer depths are computed. These are found to be deeper in the Atlantic than in the Pacific, with a strong semiannual monsoon signal apparent in the Indian Ocean. Since these calculations exclude the effects of vertical and horizontal motion further analysis as to the viability of these calculations can be done with the specified depths coupled to an atmospheric GCM.