Guidance How to Use SatManu - An Example

Appearance in satellite images

Figure 1: Occlusion front

The schematic shows and describes features typical for occlusion cloud bands in the basic satellite channels. These are to be compared with an actual case:

Meteorological-physical background

Figure 2a & 2b

For the CM "occlusion" the meteorological physical background has to describe the development. A well-developed occlusion cloud band is often the end stage of the classical polar front theory.

This can and should be checked with a sequence of images showing each stage of development from wave to occlusion.

Key parameters

For the CM "Occlusion" six key parameters have been derived which have a special relation to the cloud band and show special configurations:

An example for height contours:

14 July 2016 / 18 UTC
Developed WCB Occlusion

Upper image:
Height contours 1000 hPa

Lower image:
Height contours 500 hPa

Fully developed low centre from surface to upper levels

Figures 3a-3c: Height contours

Another schematic indicates a jet axis spiralling around the cloud spiral, a jet streak on the rear side of the cold front cloud band and a maximum of cyclonic vorticity advection in the left exit region of the jet streak, which is the center of the cloud spiral.

14 July 2016 / 18 UTC
Developed WCB Occlusion

Upper image:
Relative Vorticity 300 hPa
Orange/black: zero line - jet axis at 300 hPa
Red: cyclonic vorticity
Blue: anticyclonic vorticity

Lower image:
Isotachs 300 hPa; jet streak

Jet streaks are along the rear edge of the CF and the Occlusion cloud band; jet axis extends from the inner cloud edge of the occlusion to the outer one

Figure 4: Jet stream

Chapter 4: Appearance in Vertical Cross Sections

For the CM "Occlusion" there are seven key parameters which are indicative and show special features in vertical cross sections:

An example for isentropes:

Figure 5: Vertical cross section of relative humidity

The schematic shows a trough over the spiral cloud band, indicating the presence of warm air in middle and upper levels.

Another schematic indicates a large area of warm air advection on the leading frontal side and within the isentropic trough and a thick layer with cold air advection to the rear of the isentropic trough.

Figure 6: Vertical cross section of temperature advection

Weather Events

Parameter Description
  • Broad precipitation lines (5-50 km wide) are found within and ahead of the surface front. Maximum precipitation close to the Occlusion point(in contrast to Occlusion: Cold Conveyor Belt Type)
  • At the rear part of the cloud spiral showers and thunder, even hail.
  • Seasonal dependance; rising temperature in wintertime, cool conditions in the summer.
Wind (incl. gusts)
  • Moderate to strong winds. The most instense wind on the outer edge of the cloud spiral.
Other relevant information
  • Generally, Occlusions are connected with multi-level cloudiness. Therefore the weather activities are highly variable.

Figure 7: Weather types in Warm Conveyor Belt Occlusion

Weather and radar observation are basic parameters for cloud and precipitation conditions.

Figure 8a & 8b: Synoptic observations (left), synoptic observations + Opera Radar (right)

For more detailed cloud information, satellite evaluations such as from the Nowcasting SAF are supplementary information sources.

Figure 9: Additional cloud information