Typical Appearance In Vertical Cross Sections

Isentropes of equivalent potential temperature show a Cold Front-like gradient zone, which can often be separated into two parts: a surface and an upper level Cold Front. The surface front generally is more pronounced in the cross section than the upper level front.

The field of vorticity advection is characterized by small values of NVA within the area of the surface front up to about 700 hPa. Above 700 hPa, and within the whole frontal area, PVA can be found. The values of PVA are continuously increasing from approximately 700 hPa up to the jet level, which is situated at approximately 300 hPa. The maximum of PVA can be found between 350 and 250 hPa in front of the gradient zone of the isentropes, which is above the surface Cold Front.

In the ideal case the maximum isotachs should be found upstream from the PVA maximum, but according to the position of the cross section and the stage of development it can also be close to the PVA maximum.

The satellite image shows, in the area of Front Intensification in the VIS, IR and WV images, high pixel values indicating multilevel cloudiness (see Cloud structure in satellite image ). The difference in the grey shades between the area of Front Intensification by Jet Crossing and surrounding areas is much more pronounced in the IR image than in the WV image.

12 August 2005/12.00 UTC - Meteosat 8 IR10.8 image; position of vertical cross section indicated
12 August 2005/12.00 UTC - Vertical cross section; black: isentropes (ThetaE), green thick: vorticity advection - PVA, green thin: vorticity advection - NVA, orange thin: IR pixel values, orange thick: WV pixel values
12 August 2005/12.00 UTC UTC - Vertical cross section; black: isentropes (ThetaE), yellow: isotachs, orange thin: IR pixel values, orange thick: WV pixel values

Looking at the satellite image, see where the cross section appears in the image. Equivalent potential temperature plots show a frontal zone which is well developed in upper levels. Top: The PVA maximum and highest IR and WV signals coincide perfectly around 54N/10W. Bottom: The isotach maximum is situated upstream of the PVA maximum above the gradient zone of the equivalent potential temperature, around 57N/18W.