Atms 4320 / 7320 Convergent / Divergent regions associated with jet streaks: Forecasting Applications.

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Presentation transcript:

Atms 4320 / 7320 Convergent / Divergent regions associated with jet streaks: Forecasting Applications.

 We have talked about Jet streaks, in terms of convergence / patterns associated with the streak.  We’ve examined how these patterns evolve via the process of geostrophic adjustment.  We have also examined secondary circulations associated with these streaks.

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  We have mentioned the intimate connection between convergence / divergence patterns, height tendencies, vorticity, tendencies, and omega.  We also know that there are certain synoptic considerations associated with jet maxima, in term of development.

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  We can superpose the convergent regions of the low - level jets with upper level jets. This allows us to forecast severe weather in the spring.

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  Off the east coast of North America, it is not infrequent to have a poleward, downstream jet maximum (equatorward entrance region) couple with an upstream equatorward jet maximum (poleward exit region)  Rogers and Bosart (1991) shows that this enhances cyclone development as the two divergent regions overlap!

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  This frequently is associated with rapidly developing cyclones. A similar scenario can be described for east coast South American cyclogenesis (Lupo et al., 2001?)

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  See Fig!

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  Jet Streak coupling with lower-level fronts (Shapiro, 1982)  Jet streaks can enhance and couple with low-level frontal circulations.  When the exit region becomes coupled with the low- level frontal circulations (which are thermally direct in the vertical), this can suppress the development of precipitation.

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  When the entrance region becomes superposed over the front, both circulations are thermally direct. The atmosphere becomes de-stabilized which enhances the development of precipitation.  Finally, when jet maxima superpose with low-level forcing that causes similar motions, they can enhance eachother. (Low-level warm advection, under left exit region of the jet (PVA).

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  Picture (S. plains scenario)

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  The picture superposes low-level Warm Air Advection which contributes to upward motion, as well as upper level CVA, which contributes to upward motion as well.

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.  The End

Convergent / Divergent regions associated with jet streaks: Forecasting Applications.