Synoptic Situation
The synoptic situation on 20 and 21 June 2007 was characterized by an upper air trough over West Europe and a ridge over Middle Europe. Both systems moved slowly to the East. The potential unstable air was lifted partly severe convection developed. Precipiation amounts of up to 70 mm/h (06 UTC on 21st June, Langen, near Frankfurt) were measured. Gusts up to beaufort 11 (mountains beaufort 12) over Switzerland were registered.The IR 10.8 (Enhanced) satellite images below show for the afternoon of the 20th June the development of a squall line which moved during the next hours slowly to the East and dissolved till the end of the day. From 20th June (evening) to 21st June (noon) several super cells crossed the southern parts of Germany. During the night a mesoscale convective complex (MCC) moved from Southwest Germany to the North-Northeast.
In this chapter we will deeply investigate convective structures and how they can be diagnosed in the different products (satellite and radar data). We will point the strongnesses and weaknesses by comparing of the different data categories. For completition measurements and observations will be mentioned. The derived parameters (e.g., PV-anomalies) do not reveal instructive results. Therefore, neither overlays of derived parameters nor cross sections and interactive overlays will be considered.
20 June 2007, 12.00 UTC - Meteosat-8 IR 10.8 Enhanced
|
|
Satellite Overview
Meteosat-8 IR10.8 Enhanced time sequence [30min]
We will consider the development seen with infrared imagery. An animation of the IR10.8 channel is presented with enhanced colours. This enhancement enables us to study the different cloud top temperatures more in detail.
For instructive cases, a comparison with corresponding composites "Convective storms" and the highly resolved (1x1 km) composite radar data will be carried out. Advantages and disadvantages of the different data sources will be investigated.
Significant weather observations and measurements will be mentioned, too, however, without images.
Summary
Satellite data enable us to study both the large-scale situation and the regional thunderstorm situation by the interpretation of cloud structures, cloud top temperatures (CTT) and channel combinations in various RGB composites. Important criteria, like character and intensity of the thunderstorm development become apparent in satellite images.
The development of multi cells and super cells and MCC can described using Enhanced IR imagery. However, these data are only covering the cloud tops and reveal a horizontal resolution of about 5 km (Middle Europe). Radar data are important for investigations of structures below the resolution of Meteosat-images in Europe. The radar data we considered in this case exhibit a horizontal resolution of 1 km. Additionally to satellite images, radar data give an overview of precipitation amount, precipitation type can be obtained. More information about the inner structures and conclusions about the most likely development of convective complexes can be taken. Because sections of radar data for individual cells are not yet available at the DWD the composite "Convective Storms" gives the best information about the strongest updrafts and best indication of cell intensification or weakening.
The Nowcasting-SAF-Product "Global Instability Indices" (GII) is only available in cloud free areas. It leads to valuable hints about regions of potential instability for nowcasting. However, the GII should be used in combination with other information about convection's triggering, e.g., dyncamical forcings. Investigations of (only) 3 days in the diploma thesis (Linda Noel, 2007: "Praktischer Nutzen der Instabilitätsindizes und des Gesamtwassergehaltes aus Meteosat-Daten der zweiten Generation") yielded a better quality of 12h-forecasts from the ECMWF compared to the corresponding satellite data. A big advantage of model results is its availability also in cloudy areas. One conclusion of his Diploma thesis was that GII-values from satellite data are useful for nowcasting purposes and as long as the newest model results are not available. Later on ECMWF-data should be considered.