Current Research Projects
The asymmetric response of the Atlantic and the Pacific storm track to stratospheric forcing
The stratosphere can have a substantial impact on surface weather in winter, in particular after sudden stratospheric warming (SSW) events. The tropospheric response tends to dominate in the North Atlantic basin, while a significantly weaker response is observed over the North Pacific. Several mechanisms have been suggested to explain the downward influence of SSW events, including sensitivity to the SSW type and the magnitude of the tropospheric background flow, however their role and relative importance for determining the zonal asymmetry of the response remains unclear. Through eddy - mean flow interaction, synoptic-scale eddy feedback may affect the variability of the downward influence of the stratosphere, and play a significant role is maintaining the observed response. Using ERA-Interim re-analysis data and idealized modelling, we investigate the dominant patterns of tropospheric response to SSW events, and in particular how stratospheric forcing affects the intensity, position and persistence of the midlatitude storm track.
Other Research projects
The jet stream (zonal wind) in climatology, averaged between December to February using ERA-Interim reanalysis.
Storm track seasonal cycle
In the midlatitudes, atmospheric variability is dominated by large-scale eddies, associated with momentum, heat and moisture transport. These eddies are generated by baroclinic processes and are concentrated in two preferred regions, over the Pacific and the Atlantic oceans, known as the storm tracks. Using reanalysis data, we studied the seasonal variations of the storm tracks over both basins and their relation to the jet strength and latitudinal position (Afargan and Kaspi, 2017, GRL; Yuval et. al, 2018).
The Pacific midwinter minimum (MWM)
Over the Pacific, transient eddy activity exhibits a distinct minimum during midwinter, relative to fall and spring, despite the relatively strong jet and high baroclinicity during this season. Motivated by this phenomenon, we examine the relation between the strength and location of the subtropical jet and the intensity of the storm track using an aquaplanet idealized general circulation model. We analyze both perpetual and seasonally-varying conditions, implemented by seasonally varying the radiative parameters of the model. We examine whether a midwinter minimum can be simulated in a zonally-symmetric configuration, without topography or land-sea contrasts. We focus on the relationship between the strength of the subtropical jet (and the Hadley circulation), and eddy energetics in the midlatitudes.