Air‐sea and oceanic heat flux contributions to the heat budget of the northern Gulf of Alaska shelf

Abstract

[1] We constructed annual cycles of National Centers for Environmental Prediction air-sea fluxes and temporal oceanic heat content change from Seward Line hydrographic surveys to quantify the different contributions to the oceanic heat budget within the Alaska Coastal Current (ACC) on the northern Gulf of Alaska shelf. The deficit between air-sea fluxes and the temporal change in oceanic heat content throughout the cooling season (October-April) varies from~40 to 110 W m À2 and is balanced by ocean heat flux convergence. Cross-shelf heat flux convergence is insignificant on annual average, and the nearshore heat budget is likely entirely balanced by the ACC, which resupplies~15%-50% of the heat removed by air-sea fluxes during the cooling season. Furthermore, we estimated spatial heat flux gradients and conclude that air-sea fluxes increase from east to west and from offshore to onshore. The cross-shore gradients are governed by wind speed gradients, likely due to ageostrophic nearshore wind events during the cooling season, while the along-shelf heat flux gradients are governed by the occurrence of low-pressure systems in the northern GOA that result in cold northerly winds over the northwestern GOA. These results underline the ACC's role as the dominant oceanic heat source to the northern GOA shelf and further imply an increased cooling rate of the ACC west of the Seward Line. Furthermore, our analysis showed that nearshore regions, particularly waters in the ACC, are subjected to stronger winter cooling than the middle and outer shelves.Citation: Janout, M. A., T. J. Weingartner, and P. J. Stabeno (2013), Air-sea and oceanic heat flux contributions to the heat budget of the northern Gulf of Alaska shelf,

Flow variability within the Alaska Coastal Current in winter

“…In winter, these storms produce a large amount of precipitation along the coast. The solar radiation influx is very small (∼10 W m −2 ), and air temperatures are also at the minimum and typically <4°C in the northern Gulf between December and March, resulting in heat losses that can be as high as ∼250 W m −2 [ Janout et al ., ].…”

“…This flux spanned between −236.4 and 165.6 W m −2 with the deployment‐period mean of −30.3 W m −2 and RMSE of 6.1 W m −2 . All listed values are within the range of those reported by other researchers [ Wilson and Overland , ; Weingartner , ; Janout et al ., ].…”

“…In winter, these storms produce a large amount of precipitation along the coast. The solar radiation influx is very small (10 W m 22 ), and air temperatures are also at the minimum and typically <48C in the northern Gulf between December and March, resulting in heat losses that can be as high as 250 W m 22 [Janout et al, 2013]. Figure 2 displays time series of downwelling solar irradiance, net short-wave radiation, net long-wave radiation, sensible and latent heat fluxes, net heat flux, air temperature, atmospheric pressure, wind stress magnitude, and wind components that span over the deployment period.…”

“…Figure 2 displays time series of downwelling solar irradiance, net short-wave radiation, net long-wave radiation, sensible and latent heat fluxes, net heat flux, air temperature, atmospheric pressure, wind stress magnitude, and wind components that span over the deployment period. The measured downwelling solar irradiance and estimated net short-wave radiation flux exhibited higher values at the beginning (October 2012) and at the end (March 2013) of the experiment (Figure 2a [Wilson and Overland, 1986;Weingartner, 2007;Janout et al, 2013].…”

“…Precipitation is usually at the minimum in June, July, and August, while the influx of solar radiation (∼225 W m −2 ) and air temperatures are at the maximum (>8°C) from June to September. As a result, the Gulf gains heat in summer and the net heat gain is ∼150 W m −2 [ Janout et al ., ]. From October to April (winter season), the Aleutian Low Pressure System dominates over the Gulf.…”