Fig 1 - uploaded by Joseph Egger
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Covariance C(T − o2 , p|τ ) of the negative 90 @BULLET E Alpine torque with pressure in hPa in fall at z=500 m at (a) τ =−1 day and (b) τ =2 days but with the sign reversed to obtain the " observed " pressure fields; topography dark; contour interval 0.5 hPa; negative values shaded.
Source publication
Typical events of torques exerted by the Alps are analysed by correlating flow observations in the Mediterranean with these torques. More specifically, events with positive torques with respect to the "rotation axis" at 90° E, 0° N in fall are selected. A trough forms above the western Mediterranean during such an event with a ridge in the west. A...
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Citations
... T 1,2 = F p s ∂h ∂ϕ cos ϕ − sin λ cos λ + ∂h ∂λ sin ϕ cos λ sin λ a 2 dλdϕ (2.3) (e.g. Egger et al., 2007 ...
The mountains surrounding the Mediterranean exert torques T during the passage of North Atlantic systems which affect the angular momentum of the airflow passing over and around the massifs. The Alps, the Atlas range and the
orographic block of Asia Minor are selected to investigate the typical flow conditions during torque events. These mountain ranges are small enough to justify a local angular momentum analysis. Both the zonal and the meridional components of a mountain’s torque (Tλ and Tϕ) are used as stratification parameters in a statistical investigation of the interaction of large-scale perturbations with this mountain. How are these flows affected by the obstacle? A simple scheme is tested which attempts to interpret results.
The torque analysis singles out eastward-moving large-scale systems. Their isobars are oriented from southwest (northwest) to northeast (southeast) near the mountain in zonal torque Tλ (Tϕ) cases. The massifs tend to generate a low-level distortion of the pressure field such that the angular momentum of the flow over the mountain is reduced. These results can be explained within the framework of the scheme. The influence of the mountains on the pressure field is seen only at heights ≤4000 m. The low-level distortions of the pressure field contribute positively to the total torque for lags τ ≤ 0 in the Alps and for all lags −2 ≤ τ ≤ 2 days in Asia Minor, where only Tλ is evaluated. The impact of the Atlas mountains is seen only at τ = 0.
