Conditional symmetric instability: Difference between revisions

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An air particle at a certain altitude will be stable if its adiabatically modified temperature during an ascent is equal to or cooler than the environment. Similarly, it is stable if its temperature is equal or warmer during a descent. In the case where the temperature is equal, the particle will remain at the new altitude, while in the other cases, it will return to its initial level4.

In the diagram on the right, the yellow line represents a raised particle whose temperature remains at first under that of the environment (stable air) which entails no convection. Then in the animation, there is warming surface warming and the raised particle remains warmer than the environment (unstable air). A measure of hydrostatic stability is to record the variation with the vertical of the [[equivalent potential temperature]] (<math>\theta_e</math>):<ref name="Doswell">{{cite web |url= http://www.cimms.ou.edu/~doswell/csidisc/CSI.html |archiveurl=https://web.archive.org/web/20150227203926/http://www.cimms.ou.edu/~doswell/csidisc/CSI.html|archivedate=February 27, 2015| title= CSI Physical Discussion | website = www.cimms.ou.edu | author1= [[Charles A. Doswell III]] | publisher= [[Cooperative Institute for Mesoscale Meteorological Studies|CIMMS]] | accessdate= August 23, 2019|author1-link=Charles A. Doswell III}}

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<math>\eta</math> can be positive, null or negative depending on the conditions in which the move is made. As the absolute vortex is almost always positive on the [[synoptic scale]], one can consider that the atmosphere is generally stable for lateral movement. Inertial stability is low only when <math>\eta</math> is close to zero. Since <math>f</math> is always positive, <math>\eta \le 0 </math> can be satisfied only on the anticyclonic side of a strong maximum of [[jet stream]] or in a [[Ridge (meteorology)|barometric ridge]] at altitude, where the derivative velocities in the direction of displacement in the equation give a significant negative value.<ref name="Moore" />

The variation of the [[angular momentum]] indicate the stability:<ref name="Doswell"/><ref name="Moore">{{cite web | language= en | format= ppt | url= http://www.comet.ucar.edu/class/rfc_hydromet/03-1/docs/Moore/Mesoinstab/Meso-proc.ppt | author= James T. Moore | title= Mesoscale Processes | publisher= [[University Corporation for Atmospheric Research|UCAR]] | accessdate= August 23, 2019 | date= 2001 | pages= 10–53 | archive-url= https://web.archive.org/web/20141221040317/http://www.comet.ucar.edu/class/rfc_hydromet/03-1/docs/Moore/Mesoinstab/Meso-proc.ppt | archive-date= December 21, 2014 | url-status= dead }}</ref><ref name=Schultz>{{cite journal | language = en | format= pdf | url = http://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281999%29127%3C2709%3ATUAMOC%3E2.0.CO%3B2 | title= The Use and Misuse of Conditional Symmetric Instability | first1= David M. | last1 = Schultz | first2= Philip N. | last2= Schumacher | journal = [[Monthly Weather Review]] | volume = 127 | issue = 12 | pages = 2709 | date = December 1999 | doi = 10.1175/1520-0493(1999)127<2709:TUAMOC>2.0.CO;2| publisher= [[American Meteorological Society|AMS]] | accessdate=August 23, 2019 | issn = 1520-0493}}</ref>

*<math>\Delta M_g = 0 </math>, the particle then remains at the new position because its momentum has not changed

*<math>\Delta M_g > 0 </math>, the particle returns to its original position because its momentum is greater than that of the environment