Satellite images and derived numerical parameters
Basic parameters like surface pressure (height of 1000 hPa) do not reveal the whole physical background of a situation and can therefore not explain neither the details seen in the cloud features of satellite images nor the different conceptual models.
Parameters and parameter combinations which can be helpful in the diagnosis of front intensification by jet crossing are:
- Positive vorticity advection (PVA) in upper levels and especially at jet level;
- Thermal front parameter(TFP);
- Isotachs and zero line of shear vorticity at 300 hPa.
Theoretical apects of the mentioned parameters can be found in the
Manual of Synoptic Satellite Meteorology in the chapter BASICS.
In the following chapters you can see the process of the front intensification by jet crossing as seen in the satellite images overlayed by the meteorological parameter fields:
Isotachs and Positive Vorticity Advection at 300 hPa
Isotachs at 300 hPa show the distribution of the wind speed and the location of the jet streak, zero line of shear vorticity indicates the jet axis while PVA in the same level is an indication for areas where it becomes more cyclonic and where there is additional upward motion. The typical configuration is a maximum of PVA at the left exit region of the jet streak.
Isotachs and vorticity advection at 300 hPa are displayed and described in a 6-hourly sequence.
Thermal Front Parameter and Isotachs at 300 hPa
Isotachs at 300 hPa show the distribution of the wind speed and the location of the jet streak while TFP is indicating the frontal zone.
Isotachs, TFP and zero line of shear vorticity at 300 hPa are displayed and described in a 6-hourly sequence.
Summary of the investigations in this chapter
The most interesting features in this case study, the intensification of the cloudiness in the left exit region of the jet streak is shown by satellite images in the IR channels overlayed by the different meteorological parameter fields.
The frontal cloud band is moving from the north-west to the south-east with several intesification on the left exit region of the jet streak. The jet streak is almost all the time very dominant which can be seen in the isotach field. The field of the PVA shows good agreement of PVA maxima with cloud intensification. The Thermal Frontal Parameter indicates the cold front. The frontal character of the cloud band is recognized through TFP maximas which are usually in the area of the cloud enhancement.