PGF V grd V grd Co NH North Ce Co Ce R T If we assume a constant horizontal pressure gradient force PGF in the ridge and trough along with a similar curvature in the ridge solid line and trough dashed line we see that in a balanced flow condition horizontal forces are ID: 257089
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If we assume a constant horizontal pressure gradient force (PGF) in the ridge and trough, along with a similar curvature in the ridge (solid line) and trough (dashed line), we see that in a “balanced flow” condition (horizontal forces are in balance); the flow must be relatively fast for air parcels moving about a ridge since the PGF and the “force of spinning” {Ce, what we experience as we squish our partner sitting on the outer half of a spinning carnival ride} both counteract the Coriolis Force (Co). The latter, by definition, is proportional to the speed of the air parcel (and latitude, although we assume that latitude isn’t varying much in this wave) and so a parcel is accelerated as it approaches a ridge until its Co is large enough to balance the net of PGF and Ce.the flow must be relatively slow for air parcels moving about a trough since the PGF alone is counteracting both the Ce and Co. As an air parcel approaches a trough, the air parcel is decelerated until its Co is small enough, when summed with Ce, to balance the PGF.Slide3
Examination of streamlines in actual weather waves show that flow approaching a; ridgeline generally has a component directed across the geopotential height (Z) contours upstream of the ridge, toward lower heights, in order to accelerate the flow (so it is supergeostrophic) by the time the air is at the ridgeline, andtroughline generally has a component directed across the geopotential height (Z) contours upstream of the trough, toward higher heights, in order to decelerate the flow (so it is subgeostrophic) by the time the air is at the
troughline.