Low-level humidity boundary across Europe

Low-level humidity boundary across Europe

14 July 2006 00:00 UTC

Low-level humidity boundary across Europe
Low-level humidity boundary across Europe

Low-level humidity boundary across Europe.

Last Updated

21 October 2020

Published on

14 July 2006

by Jochen Kerkmann and HansPeter Roesli (EUMETSAT)

As discussed in the case study Monitoring airmass/moisture boundaries with MSG (4-5 October 2005) , the dust RGB product, besides monitoring dust storms and tracking thin, high-level clouds, can also be used for the detection of low-level humidity boundaries. An interesting case for this application is shown below.

The RGB product (upper left image) shows a mostly cloud-free situation over the UK, Northern Germany and the Benelux countries (with a pale blue to magenta colour) and a large area of convective clouds over Southern Europe (with a strong blue 'background' colour). The reason for this colour difference can be attributed to an airmass/moisture boundary that crosses Europe from west to east at about 49 degrees latitude North (see Interpretation ). North of this line (49°N) there is mainly dry air as a result of the earlier passage of a cold front (that can be seen over Eastern Poland), whereas south of this line moist air is present in the lower layers of the troposphere.

The existence of the moisture boundary is confimed by the ECMWF analysis fields (see e.g. Dust RGB with abs. humidity 850 hPa, ECMWF analysis ). Across the moisture boundary the relative humidity at 850 hPa drops from around 80% on the moist side to about 20% on the dry side of the boundary. In parallel, the brightness temperature difference IR10.8–IR12.0 drops from around +3 K to 0 K, which causes the change of the colour discussed above.

 

Met-8 Images

 
Met-8, 14 July 2006, 18:00 UTC
Met-8, 14 July 2006, 18:00 UTC
RGB Composite (Dust RGB)
IR12.0–IR10.8, IR10.8–IR8.7, IR10.8
Full Resolution
Interpretation
with abs. humidity 850 hPa
(ECMWF analysis)
Met-8, 14 July 2006, 18:00 UTC
Met-8, 14 July 2006, 18:00 UTC
Difference Image IR12.0–IR10.8
Range: -4 K (black) to + 2 K (white)
Full Resolution
with dew point temperature 850 hPa
(ECMWF analysis)
with rel. humidity 850 hPa
(ECMWF analysis)

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Met-8, 14 July 2006, 18:00 UTC
Met-8, 14 July 2006, 18:00 UTC
Channel 06 (WV7.3)
Full Resolution
with rel. humidity 850 hPa
(ECMWF analysis)
Met-8, 14 July 2006, 18:00 UTC
Met-8, 14 July 2006, 18:00 UTC
RGB Composite (Airmass RGB)
WV7.3–WV6.2, IR9.7–IR10.8, WV6.2
Full Resolution