Can someone clarify something: shortwaves and baroclinic cyclogenesis
Posted: Thu Dec 03, 2020 8:42 pm
I got my undergraduate degree in meteorology but never entered the field as a profession. I have been getting back into it as a hobby but want something to be re-clarified to me:
In the Quasi-geostrophic 2-layer and Eady models of baroclinic instability, the ideal wavelength of exponential growth is on the order of several thousand km (the exact number depends on static stability and differs between the Eady and 2 layer toy models). I can see that this is in line with the overall size of mid-latitude cyclones and their associated frontal structures. In Holton, it described how static stability prevents shortwaves from undergoing baroclinic growth (due to the steeper required vertical motion of air parcels).
But, in synoptic meteorology, I remember that shortwaves and jetstreaks often initiate cyclogenesis. So I am confused: why do synoptic texts mention shortwaves/jetstreaks being important for cyclogenesis, while dynamical texts about baroclinic instability emphasize that shortwaves are stabilized?
If my understanding is correct: the jetstreak at 250mb or so initiates a shortwave (visible at 500mb charts) due to strong upper level divergence. This shortwave then distorts the longer wave flow into becoming an amplifying baroclinic disturbance?
I'm feeling somewhat frustrated- like I don't understand the basics. Yet I haven't been able to find a text that explicitly talks about this (apparent?) discrepancy.
In the Quasi-geostrophic 2-layer and Eady models of baroclinic instability, the ideal wavelength of exponential growth is on the order of several thousand km (the exact number depends on static stability and differs between the Eady and 2 layer toy models). I can see that this is in line with the overall size of mid-latitude cyclones and their associated frontal structures. In Holton, it described how static stability prevents shortwaves from undergoing baroclinic growth (due to the steeper required vertical motion of air parcels).
But, in synoptic meteorology, I remember that shortwaves and jetstreaks often initiate cyclogenesis. So I am confused: why do synoptic texts mention shortwaves/jetstreaks being important for cyclogenesis, while dynamical texts about baroclinic instability emphasize that shortwaves are stabilized?
If my understanding is correct: the jetstreak at 250mb or so initiates a shortwave (visible at 500mb charts) due to strong upper level divergence. This shortwave then distorts the longer wave flow into becoming an amplifying baroclinic disturbance?
I'm feeling somewhat frustrated- like I don't understand the basics. Yet I haven't been able to find a text that explicitly talks about this (apparent?) discrepancy.