High-level mountain wave cloud over Pyrenees

High-level mountain wave cloud over Pyrenees

02 July 2015 04:00–14:00 UTC

High-level mountain wave cloud over Pyrenees
High-level mountain wave cloud over Pyrenees

Pronounced high-level orographic cloud pattern appeared in the Severe Storm RGB behind the ridge of Pyrenees.

Last Updated

04 November 2020

Published on

02 July 2015

By Ivan Smiljanic (DHMZ)

The animation of the Severe Convection RGB imagery, 2 July  04:00–14:00 UTC shows the persistent high-level orographic wave cloud which developed on the lee-side of the Pyrenees mountains.

 Met-10, 02 July 2015, 12:00 UTC
Figure 1: Met-10 Severe Convection RGB with ECMWF Isotachs at 300hPa overlaid, 02 July 2015, 12:00 UTC (source: EUMeTrain). Full Resolution
 
 Met-10, 02 July 2015, 05:00 UTC
Figure 2: Met-10 High Resolution Visible (HRV), 02 July 2015, 05:00 UTC. Full Resolution

It is obvious from the synoptic view of the area (Figure 1) — especially looking at the position of high level jet (depicted by isotachs at 300hPa height) — that the formation of these clouds was connected to the strong high level flow. As is usual in such cases, the position of the cloud is to the right side of the jet axis.

On top of this large and long wave cloud (wavelength of hundreds of kilometres), which stretched almost perpendicular to the mountains, a formation of smaller orographic waves can also be seen. To depict these smaller patterns, images with better resolution are needed, such as the High Resolution Visible (HRV) (Figure 2).

 Meteosat-10 Severe Convection RGB, 2 July 08:30 UTC
Figure 3: Meteosat-10 Severe Convection RGB, 2 July 08:30 UTC. Full Resolution

Normally, Severe Convection RGB imagery is used for detection of convective systems, especially the most intensive cores or updrafts.

These cores are easily detected in this case because the most active parts of thunderstorms, especially the most intense cores/updrafts, have smaller ice particles at higher levels. However, in this case, no convective activity was present, only high level orographic clouds in the area of interest.

The typical yellow colour of these orographic clouds (also a typical colour of intense thunderstorm updrafts) comes from the small ice particles which form quickly at high levels.

These smaller particles reflect more sunlight back to the satellite than normal high-level ice clouds, at IR3.9. Therefore, in the RGB imagery (Figure 3) they appear as yellow shades not red.

 

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