Scale Dependence of Midlatitude Air–Sea Interaction

Abstract

It has traditionally been thought that midlatitude sea surface temperature (SST) variability is predominantly driven by variations in air–sea surface heat fluxes (SHFs) associated with synoptic weather variability. Here it is shown that in regions marked by the highest climatological SST gradients and SHF loss to the atmosphere, the variability in SST and SHF at monthly and longer time scales is driven by internal ocean processes, termed here “oceanic weather.” This is shown within the context of an energy balance model of coupled air–sea interaction that includes both stochastic forcing for the atmosphere and ocean. The functional form of the lagged correlation between SST and SHF allows us to discriminate between variability that is driven by atmospheric versus oceanic weather. Observations show that the lagged functional relationship of SST–SHF and SST tendency–SHF correlation is indicative of ocean-driven SST variability in the western boundary currents (WBCs) and the Antarctic Circumpolar Current (ACC). By applying spatial and temporal smoothing, thereby dampening the signature SST anomalies generated by eddy stirring, it is shown that the oceanic influence on SST variability increases with time scale but decreases with increasing spatial scale. The scale at which SST variability in the WBCs and the ACC transitions from ocean to atmosphere driven occurs at scales less than 500 km. This transition scale highlights the need to resolve mesoscale eddies in coupled climate models to adequately simulate the variability of air–sea interaction. Away from strong SST fronts the lagged functional relationships are indicative of the traditional paradigm of atmospherically driven SST variability.

An Assessment of Representation of Oceanic Mesoscale Eddy‐Atmosphere Interaction in the Current Generation of General Circulation Models and Reanalyses

“…A recent study by Ma et al () reveals that the oceanic mesoscale eddy‐atmosphere (OMEA) interaction is an important yet previously overlooked component in the mesoscale eddy dissipation. At mesoscales, sea surface temperature anomaly (SSTA) tends to be positively correlated with heat flux (HF; defined positive upward) anomaly (HFA) due to the dominance of HF induced by oceanic eddies to atmospheric forcing (Bishop et al, ; Ma et al, ). This leads to the destruction of eddy potential energy (EPE).…”

“…S. Smith, 2007), whereas their energy pathway to dissipation has not been completely understood (Ferrari & Wunsch, 2009;Wunsch & Ferrari, 2004). surface temperature anomaly (SSTA) tends to be positively correlated with heat flux (HF; defined positive upward) anomaly (HFA) due to the dominance of HF induced by oceanic eddies to atmospheric forcing (Bishop et al, 2017;Ma et al, 2016). This leads to the destruction of eddy potential energy (EPE).…”

A New Framework for Near‐Surface Wind Convergence Over the Kuroshio Extension and Gulf Stream in Wintertime: The Role of Atmospheric Fronts

“…Over the past few decades, there has been a steadily growing body of evidence suggesting that ocean mesoscale and frontal-scale features in the Kuroshio Extension (KE) and Gulf Stream (GS) regions are forcing the atmosphere (e.g., Chelton et al, 2004;Kuwano-Yoshida & Minobe, 2017;Ma et al, 2016;Piazza et al, 2016;Seo et al, 2017;Small et al, 2014;Xie, 2004). In particular, a positive correlation between sea surface temperature (SST) and near-surface wind speed over western boundary currents (WBCs) suggest an ocean-toatmosphere forcing through turbulent heat fluxes (Nonaka & Xie, 2003), whose variability on monthly and longer timescales is largely driven by internal ocean processes (Bishop et al, 2017). Studies considering the atmospheric impact of WBCs typically fall into one of two broad categories-the oceanic impact on the mean state (e.g., Shimada & Minobe, 2011) and on synoptic storms (e.g., Hirata et al, 2015Hirata et al, , 2018, with community efforts still very much ongoing (e.g., Nkwinkwa Njouodo et al, 2018;Small et al, 2018).…”

Impacts of mesoscale sea surface temperature anomalies on the meridional shift of North Pacific storm track

“…In the western boundary current and its extension, such as the Kuroshio Extension (KE), energetic ocean mesoscale eddies and fronts contribute greatly to mesoscale sea surface temperature (SST) variability (Chelton et al, 2004;Xie, 2004;Small et al, 2008;Bryan et al, 2010;Neill et al, 2012;Bishop et al, 2017). The mesoscale SST anomaly (SSTA) is tightly coupled with the atmosphere (Minobe et al, 2008;Ma et al, 2016b).…”

“…The mesoscale SST anomaly (SSTA) is tightly coupled with the atmosphere (Minobe et al, 2008;Ma et al, 2016b). Previous studies using high-resolution satellite observations and numerical models showed that it is the ocean that drives the atmosphere at the mesoscale (e.g., Bryan et al, 2010;Chelton and Xie, 2010;Frenger et al, 2013;Ma et al, 2016a;Bishop et al, 2017).…”