UPPER LEVEL LOW - KEY PARAMETERS
by ZAMG and FMI
- Height contours 500 hPa:
During the initial stage the absolute topography at 500 hPa shows an upper level trough. During the different stages of development the trough forms an inverse omega field which leads to a closed cyclonic circulation in the southern part of the trough (see Cloud structure in satellite image and Meteorological physical background ). - Height contours 1000 hPa:
Within this field no distinct low level features can be observed. The gradient of the height contours generally is weak. During the later phases of a cut-off some weak cyclonic circulation may appear, initiated by the circulation from above. - Equivalent thickness:
This field is characterized by a thickness ridge in front of the low and a trough or a distinct minimum behind or in the centre of the low. - Thermal front parameter:
There are two baroclinic zones:- In front of the low, which is connected with a frontal-like cloud band.
- Behind the low, connected with a Baroclinic Boundary (see Baroclinic Boundary ).
- Temperature at 500 hPa:
The air within the Upper Level Low is colder than in the surroundings. The temperature field shows a life cycle similar to that of the upper height field. - Potential vorticity:
Within the Upper Level Low there is colder air with lower tropopause than in its surroundings. Consequently, in the area of the low there is a local maximum of PV.
Height contours 1000 and 500 hPa
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24 January 1998/00.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, cyan: height contours 500
hPa
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24 January 1998/06.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, cyan: height contours 500
hPa
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24 January 1998/12.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, cyan: height contours 500
hPa
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Equivalent Thickness and Thermal Front Parameter
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24 January 1998/12.00 UTC - Meteosat IR image; blue: thermal front parameter 500/850 hPa, green: equivalent
thickness 500/850 hPa
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Temperature 500 hPa
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06 May 2001/00.00 UTC - Meteosat IR image; cyan: height contours 500 hPa, dark green: temperature 500 hPa
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08 May 2001/12.00 UTC - Meteosat IR image; cyan: height contours 500 hPa, dark green: temperature 500 hPa
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10 May 2001/00.00 UTC - Meteosat IR image; cyan: height contours 500 hPa, dark green: temperature 500 hPa
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Potential Vorticity
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06 May 2001/12.00 UTC - Meteosat IR image; magenta: height of PV = 1 unit
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