SECONDARY LOW CENTRES IN OCCLUSION CLOUD BANDS - KEY PARAMETERS
by FMI
- Height contours at 1000 hPa:
On the surface there is an elongated low pressure area connected to a long occluded front. The original low centre is separated from the occluded front, whereas the secondary centre develops within the frontal cloud band. - Equivalent thickness at 500-850 hPa:
There is the typical structure of an Occlusion, and usually the thermal structure of the Occlusion is neutral, see e.g. Occlusion: Warm Conveyor Belt Type (compare Occlusion: Warm Conveyor Belt Type ). In all types of Occlusions there is a thickness ridge along the occluded front. - Omega at 700 hPa:
There is ascending motion related to the whole frontal system, but also a distinct maximum over the deepening Secondary Low. - Shear and curvature vorticity at 300 hPa:
Over the Secondary Low there are maxima of both positive shear vorticity and curvature vorticity related to the jet and the upper trough. - 300 hPa Isotaches at 300 hPa:
The core of the jet stream crosses the occlusion point, and the strength of the jet streak is at least 50 m/s.
In the images below the Secondary Low is marked by a red arrow.
Height contours at 1000 hPa and equivalent thickness at 500 - 850 hPa
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07 February 2002/12.00 UTC - Meteosat IR image; magenta: height contours 1000 hPa, green: relative topography 500 - 850 hPa
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Omega at 700 hPa
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07 February 2002/12.00 UTC - Meteosat IR image; cyan: omega
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Isotachs at 300 hPa
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07 February 2002/12.00 UTC - Meteosat IR image; yellow: isotachs 300 hPa
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Shear and curvature vorticity at 300 hPa
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07 February 2002/12.00 UTC - Meteosat IR image; blue: shear vorticity, brown: curvature vorticity 300 hPa
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