These MLS averages are made inside the polar vortex on the 440-K isentropic surface
(~18 km or 65 h Pa), (c) Temperature on the 440-K isentropic surface
over Antarctica (60[degrees]-90[degrees]S) from MERRA-2 (Gelaro et al.
Index Diagnosis of Pollution Transport at the Isentropic Surface
. As it is known, both updraft and subsidence of dry or wet air are usually the most common and frequent air motions in the atmosphere.
It moves slowly up or down as it travels to conserve potential temperature; in other words, it clings to its "potential temperature surface" or isentropic surface
(assuming heat isn't being added or removed).
Viewing this quantity on the 355-K isentropic surface
, we found that during their intensification stage, each of the four storms had an unusually symmetric "doughnut" structure to the PV field.
We calculated the mean vortex edge from 450 K to 650 K and found that the mean edge is closest to the edge on 550 K isentropic surface
. Therefore, we use the criterion PV contour (-28.8 PVU) on550K isentropic surface
to calculate the averaged total column zone within the polar vortex.
A useful quantity for this purpose is potential vorticity (PV) on the [theta] = 315-K isentropic surface
. We will estimate the growth rate by calculating tendencies in the ensemble standard deviation [[sigma].sub.PV] in the 12-h background (first guess) forecasts of the EDA (25 members).
Screenshot of instructor's lecture video annotations on map of pressure contours on 300-K isentropic surface
. [Map from Rauber et al.
PV cutoffs Structures of stratospheric air Wernli and ([absolute value of PV] > 2 PVU) Sprenger that are detached from the main (2007) stratospheric body on a specific isentropic surface
. PV streamers Filaments of stratospheric air on Wernli and an isentropic surface
, where the Sprenger surrounding [+ or -] 2-PVU contour (2007) fulfills certain geometric criteria.
While not discussed in the abovementioned tropospheric vortex studies, the edge of the tropospheric vortex can (as in the stratosphere) be defined from potential vorticity contours on an isentropic surface
or (equivalently) potential temperature on a surface of constant potential vorticity (Hoskins et al.
We then derived the zonally integrated meridional mass flux above a specific isentropic surface
[[THETA].sub.n] at latitude [phi] on day t as
Haynes and McIntrye  showed that potential vorticity can be diluted or concentrated only by flow across isentropes and it cannot be created or destroyed within a layer bounded by isentropic surfaces
. Thus, Choi and Zhang  described in detail the dust transportation route, using relative vorticity and depicting shade area in Figure 11(b) with the big magnitudes of potential vorticity near the ground surface of downwind side area and the shade area implied the accumulation of air masses inside a strong stable atmospheric layer.