by ZAMG
> 0 | Divergence |
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< 0 | Convergence |
Divergence is a property of the flow field.
There is a connection to vertical motion through the Richardson equation:
A very simple model describing an ideal situation leads to the following considerations: If there is the assumption of convergence existing at the surface level, upward motion results in the levels above up to the tropopause; at this barrier air cannot rise further and consequently has to diverge there. Therefore a circulation cell is created and cloudiness may develop in the upward motion.
11 February 1997/06.00 UTC - Meteosat IR image; SatRep overlay: names of conceptual models
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11 February 1997/06.00 UTC - Meteosat IR image; green solid: divergence 1000 hPa, green dashed: convergence 1000 hPa
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11 February 1997/06.00 UTC - Meteosat IR image; yellow solid: divergence 300 hPa, yellow dashed: convergence 300 hPa
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11 February 1997/06.00 UTC - Meteosat IR image; blue dashed: vertical motion (omega) - upward motion 700 hPa, blue solid: vertical
motion (omega) - downward motion 700 hPa
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There are several big convergence areas at the surface level representing the lower boundary of the circulation cell; they are connected with the following cloud systems (left image top):
Compared to the divergence field at 300 hPa (left image bottom) representing the upper level of the circulation cell the following results can be summarized:
All the cloud systems just mentioned are accompanied by divergence at this high level. So in the frontal areas as well as in the area of the EC, convergence occurs at low levels and divergence at high levels.
The vertical motion field (lower image) completes the ideas of a circulation cell in these areas:
Looking again at the surface level (right image top) several big areas are accompanied by divergence indicated by the solid lines; they are connected with the following cloud systems (left image top):
Compared to the 300 hPa level (left image bottom) nearly all areas just mentioned are areas of convergence at high and divergence at low levels. This can be interpreted as a reverse circulation cell with downward motion in the troposphere between these two boundaries.
The vertical motion image (low panel) supports this idea with the solid lines representing downward motion.
11 February 1997/12.00 UTC - Meteosat IR image
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11 February 1997/18.00 UTC - Meteosat IR image
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