Observed Associations Among Storm Tracks, Jet Streams and Midlatitude Oceanic Fronts

Abstract

An association is discussed among a midlatitude storm track, a westerly polar-front jet stream and an underlying oceanic frontal zone. Their close association is observed when a subtropical jet stream is weak, as in the Southern Hemisphere summer or in the North Atlantic. Along a near-surface baroclinic zone that tends to be anchored around a frontal zone, storm track activity is enhanced within a well-defined polarfront jet with modest core velocity. This eddy-driven jet exhibits a deep structure with the strong surface westerlies maintained mainly through a poleward eddy heat flux. The westerly wind stress exerted along the frontal zone acts to maintain it by driving the oceanic current system, suggestive of a feedback loop via midlatitude atmosphere-ocean interaction. It is argued that the context of this feedback must be included in interpreting the tropospheric general circulation and its variability. In fact, decadalscale sea-surface temperature anomalies observed in the North Pacific subarctic frontal zone controlled the anomalous heat release to the atmosphere. Seemingly, the local storm track responded consistently to the decadal-scale shift of the frontal axis, acting to reinforce basin-scale flow anomalies. Over the North and South Pacific, the association is disturbed in winter by an intensified subtropical jet that traps eddy activity into its sharp core. The trapping impairs baroclinic interaction of upper-level eddies with the surface baroclinicity along a midlatitude oceanic front, leading to the suppression of eddy activity as observed in midwinter over the North Pacific.

How well do state-of-the-art atmosphere-ocean general circulation models reproduce atmospheric teleconnection patterns?

“…This is confirmed for the North Pacific winter jet (e.g. Nakamura et al, 2004), whereas over the North Atlantic in winter, the subtropical and eddy-driven jets are generally separated (e.g. Li and Wettstein, 2012).…”

Cyclone Activities in Heavy Rainfall Episodes in Japan during Spring Season

“…Finally, this study highlights atmospheric circulation fields, but spatial and temporal variations of the oceanic frontal zone are not considered. As noted in Nakamura et al (2004), the storm track axis of the western North Pacific in spring is anchored on the oceanic frontal zone, in contrast to that in winter. Information regarding the responses of cyclone activities to variations of surface baroclinicity over the ocean will enhance our understanding of the mid-latitude air-sea interaction over the western North Pacific.…”

The atmospheric frontal response to SST perturbations in the Gulf Stream region

“…These wintertime fluxes are remarkably variable on a daily timescale and are highly correlated with overlying synoptic atmospheric activity [Shaman et al, 2010;Zolina and Gulev, 2003]. Locally, these strong oceanic fronts are known to increase the height of the marine atmospheric boundary layer [Nakamura et al, 2004], affect cyclogenesis through differential heating [Persson et al, 2008;Giordani and Caniaux, 2001], and anchor the low-level baroclinicity [Nakamura et al, 2008]. Despite this, first-order observations appear to suggest that it is the atmosphere that forces the ocean, and the extent to which extratropical air-sea interactions, in particular ocean-to-atmosphere feedback, affect climate variability is still a contentious issue.…”