Interannual variations in upper ocean heat content and heat transport convergence in the western North Atlantic.

摘要

The heat balance in the Gulf Stream region during the period November 1992 to December 1999 is studied using two methods: (1) a simple three-dimensional thermodynamic model, and (2) a subsurface temperature profile analysis. The goal of the analyses is to understand the relationship of observed large-scale fluctuations in heat storage to changes in surface heat fluxes (HF) and advection.; The model is forced by HF, with geostrophic surface velocity and Ekman transport specified from sea surface height measurements and wind stress, respectively. Interannual variations in the upper ocean heat content (HC) are dominated by the advection-diffusion term. Within the advection term itself, the largest variations are from the geostrophic advection anomaly. These ocean forced variations in HC appear to force HF. The changes in oceanic advection, HC, and HF are related to the state of the Gulf Stream: in an "elongated" state, the Gulf Stream transports more heat, more heat is stored in the region, and there is a net loss of heat to the atmosphere. The converse is true for the "contracted" state.; The second analysis uses temperature, objectively mapped to a uniform grid. Interannual variations in HC from the objective map agree well with those from the model. This data analysis reaches the same conclusion as the model study regarding the relationship between the oceanic advection, HC, and HR In addition, the subsurface data show good correspondence between HC and 18°C layer; there is less 18°C water and this layer has a deep depth during a high HC period. Interannual variations in the cold water (mainly 18°C water - mode water) volume are dominated by oceanic convergence, not by HF.; How much heat the atmosphere can extract from the ocean depends on the total amount of anomalous heat stored in the ocean. What matters in climate is the accumulated heat obtained by the atmosphere, not the instantaneous rate of flux at the air-sea interface. The relationship of HF to HC and the dominance of geostrophic advection in interannual variations of HC suggest that the ocean can play an important role in air-sea interaction on interannual time scales.