WARM FRONT BAND - TYPICAL APPEARANCE IN VERTICAL CROSS SECTIONS

by ZAMG


The isentropes of the equivalent potential temperature across the Warm Front Band show a crowding zone through the whole troposphere which, looking downstream, is inclined from low to high levels. The colder air can be found in front of, and below, the warmer air in front of and above the crowding zone. (see Meteorological physical background).

The field of humidity shows high values immediately behind and above the frontal surface of the Warm Front. Low values can be found below the crowding zone of the equivalent potential temperature.

Like the distribution of the humidity, the field of temperature advection can also be separated into two parts. Therefore WA exists above and within the crowding zone of the Warm Front. The maximum of the WA can be found within the crowding zone in the mid-levels of the troposphere at approximately 500 hPa. On the other hand CA can be found below and in front of the crowding zone.

At the leading part above the frontal surface, at approximately 300 hPa, the atmosphere is characterized by a pronounced isotach maximum.

Well developed fronts are accompanied by a zone of distinct convergence within and divergence above the frontal zone. Consequently, upward vertical motion can be found above the frontal zone, responsible for cloud development.

The satellite images across the Warm Front in the ideal case are characterized by typical distributions. While the IR image shows across the frontal area continuously increasing values of grey shades from the rear to the leading edge, the distribution of the grey shades in the VIS image is inverse (see Cloud structure in satellite image). In contrast to this the WV image shows high pixel values within the frontal cloudiness and a pronounced minimum connected with the dry air.

22 November 1995/06.00 UTC - Meteosat IR image; position of vertical cross section indicated
The first cross section shows the crowding zones of the equivalent potential temperature of a surface and upper level warm front with intense WA within the whole troposphere. In the IR signal the sharp leading edge can be clearly discriminated. This decrease coincides with the decrease of the relative humidity field in the second cross section, while values higher than 80% accompany the frontal zones. The third cross section shows a zone of convergence within the lower level front, followed by intense upward motion within and above it. The fourth cross section finally shows the jet streak around 250 hPa connected with the pronounced decrease of WV pixel values.
22 November 1995/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), red thick: temperature advection - WA, red thin: temperature advection - CA, orange thin: IR pixel values, orange thick: WV pixel values
22 November 1995/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), blue: relative humidity, orange thin: IR pixel values, orange thick: WV pixel values
22 November 1995/06.00 UTC - Vertical cross section; magenta thin: divergence, magenta thick: convergence, cyan thick: vertical motion (omega) - upward motion, cyan thin: vertical motion (omega) - downward motion, orange thin: IR pixel values, orange thick: WV pixel values
22 November 1995/06.00 UTC - Vertical cross section; black: isentropes (ThetaE), yellow: isotachs, orange thin: IR pixel values, orange thick: WV pixel values

SUB-MENU OF WARM FRONT BAND
KEY PARAMETERS
WEATHER EVENTS