FOEHN - TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS

by ZAMG


The typical appearance in vertical cross sections is somewhat false, because of the fact that the effect of mountains is not treated realistically within cross sections, neither from radiosoundings nor from numerical models. Radisonde stations have too big a spatial resolution while numerical models usually do not contain the fine structure and real height of mountainous areas. Nevertheless some interesting features can be derived.

The example below, used to demonstrate general Foehn dynamics, is from the Alpine region. Therefore the following relation between vertical cross section, frontal cloud and mountains exists.

06 November 2000/12.00 UTC - Meteosat IR image

Equivalent potential temperature: vertical cross sections from radiosonde stations compared with the output from numerical models

06 November 2000/12.00 UTC - Vertical cross section; blue: moist adiabatic isentropes - radiosounding, black: moist adiabatic isentropes: ECMWF, orange thin: IR pixel values, orange thick: WV pixel values

Relative humidity: vertical cross section from radiosounding stations

06 November 2000/12.00 UTC - Vertical cross section; blue: relative humidity, black: isentropes (ThetaE), orange thin: IR pixel values, orange thick: WV pixel values

Convergence: vertical cross sections from numerical model

06 November 2000/12.00 UTC - Vertical cross section; magenta: divergence, black: isentropes (ThetaE), orange thin: IR pixel values, orange thick: WV pixel values

Vertical motion: vertical cross sections from numerical model

06 November 2000/12.00 UTC - Vertical cross section; cyan: vertical motion, black: isentropes (ThetaE), orange thin: IR pixel values, orange thick: WV pixel values


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