Abstract
AbstractAir‐sea turbulent heat fluxes play a fundamental role in generating and dampening sea surface temperature (SST) anomalies. To date, the turbulent heat flux feedback (THFF) is well quantified at basin‐wide scales (20 ) but remains unknown at the oceanic mesoscale (10–100 km). Here, using an eddy‐tracking algorithm in three configurations of the coupled climate model HadGEM3‐GC3.1, the THFF over mesoscale eddies is estimated. The THFF magnitude is strongly dependent on the ocean‐to‐atmosphere regridding of SST, a common practice in coupled models for calculating air‐sea heat flux. Our best estimate shows that the mesoscale THFF ranges between 35 and 45 globally, across different eddy amplitudes. Increasing the ratio of atmosphere‐to‐ocean grid resolution can lead to an underestimation of the THFF, by as much as 80% for a 6:1 resolution ratio. Our results suggest that a large atmosphere‐to‐ocean grid ratio can result in an artificially weak dampening of mesoscale SST anomalies.
Highlights
The turbulent heat flux feedback (THFEF, in W m 2 K 1, denEoted hereafter) is a critical parameter, which measures the change in the net air-sea turbulent heat flux in response to a 1 K change in sea surface temperature (SST)
Our estimates (Figure 2a) implicitly account for (a) the full complexity of the bulk formulae implemented in HadGEM3-GC3.1, where the drag coefficient is function of atmospheric boundary layer (ABL) stability
For the highest ocean-atmosphere resolution available, the estimates of the turbulent heat flux feedback (THFF) over mesoscale eddies range from 35 Eto 45 W m 2 K 1 where values roughly increase with eddy amplitude
Summary
The turbulent heat flux feedback (THFEF, in W m 2 K 1 , denEoted hereafter) is a critical parameter, which measures the change in the net air-sea turbulent heat flux in response to a 1 K change in sea surface temperature (SST). It is a powerful tool to quantify the rate of dampening of SST anomalies. THFF can vary seasonally (largest in winter), geographically and with ocean spatial scale. Studies estimate THFF at E∼20 W m 2 K 1 for basin-scale mid-latitude SST anomalies, which, to first order, respond passively to atmospheric forcing (Bretherton, 1982; Frankignoul, 1985; Frankignoul et al, 1998, 2004; Small et al, 2020). More recent studies estimate that THFF increasesEto 40 W m 2 K 1 in the Gulf Stream, and decreases down Eto 10 W m 2 K 1 in the Antarctic Circumpolar Current (Hausmann & Czaja, 2012; Hausmann et al, 2017). While THFF is known to increase towards smaller scales, the smallest spatial scale used to quantify THFF is ∼100 km
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