The Modulation of Gulf Stream Influence on the Troposphere by the Eddy-Driven Jet

Abstract

This study suggests that the Gulf Stream influence on the wintertime North Atlantic troposphere is most pronounced when the eddy-driven jet (EDJ) is farthest south and better collocated with the Gulf Stream. Using the reanalysis dataset NCEP-CFSR for December–February 1979–2009, the daily EDJ latitude is separated into three regimes (northern, central, and southern). It is found that the average trajectory of atmospheric fronts covaries with EDJ latitude. In the southern EDJ regime (~19% of the time), the frequency of near-surface atmospheric fronts that pass across the Gulf Stream is maximized. Analysis suggests that this leads to significant strengthening in near-surface atmospheric frontal convergence resulting from strong air–sea sensible heat flux gradients (due to strong temperature gradients in the atmosphere and ocean). In recent studies, it was shown that the pronounced band of time-mean near-surface wind convergence across the Gulf Stream is set by atmospheric fronts. Here, it is shown that an even smaller subset of atmospheric fronts—those associated with a southern EDJ—primarily sets the time mean, due to enhanced Gulf Stream air–sea interaction. Furthermore, statistically significant anomalies in vertical velocity extending well above the boundary layer are identified in association with changes in EDJ latitude. These anomalies are particularly strong for a southern EDJ and are spatially consistent with increases in near-surface atmospheric frontal convergence over the Gulf Stream. These results imply that much of the Gulf Stream influence on the time-mean atmosphere is modulated on synoptic time scales, and enhanced when the EDJ is farthest south.

Future Evolution of an Eddy Rich Ocean Associated with Enhanced East Atlantic Storminess in a Coupled Model Projection

“…However, we note that the SST changes in other basins are minor compared to the North Atlantic and the GS in particular (see Figure ). We also note that similar basin wide changes associated with the GS shifts have previously been found in both observed air‐sea fluxes (Joyce et al., 2009; Parfitt & Kwon, 2020, relative to the overlying jet) and atmosphere only model experiments of mid‐latitude Atlantic storms (Lee et al., 2018).…”

The role of atmospheric fronts in austral winter precipitation changes across Australia

“…Furthermore, Rudeva et al (2019) also highlighted to first order that significant correlations exist between the number of fronts in the low midlatitudes and the location and intensity of the subtropical ridge, and an equatorward‐shifted southern hemisphere wintertime subtropical jet has also been shown to be eddy driven and associated with the poleward displacement of the eddy‐driven jet (Gillett et al, 2021). In addition, Parfitt and Kwon (2020) demonstrated that the trajectory of atmospheric fronts covaries with the latitude of the eddy‐driven jet.…”

FluxSat: Measuring the Ocean–Atmosphere Turbulent Exchange of Heat and Moisture from Space

“…[39]), but errors in wind speed and SST inputs are also important [41]. Several recent studies have indicated that spatial gradients in heat fluxes are of primary importance in determining the influence of western boundary currents such as the Gulf Stream, not just on the local atmospheric frontal variability, but also on the basin-wide circulation and time-mean atmosphere [10,46]. The effect of spatial resolution on these heat flux gradients can be seen in Figure 4e,f, which shows the time-mean spatial gradients for latent and sensible heat fluxes estimated from the WRF output decimated to 0.5 • resolution (current measurement capability corresponds to about 0.5 • resolution).…”

“…For example, atmospheric fronts cause up to 90% of the precipitation in mid-latitudes [76]. They also set the time-mean wind convergence and vertical motion throughout the troposphere [46,77], critical for hemispheric circulation [78]. In other words, through atmospheric fronts, WBCs can potentially modulate the atmosphere on all timescales.…”