by FMI
When this happens, the cold pool can grow as large as 500-1000 km in diameter in the layer 2-6 km above the surface. This kind of event took place over the Northern Atlantic when Janika was deepening. It can be seen in the loop below seen in the spreading of cold advection at 700 hPa. According to several theories the expansion of the cold pool can lead to the formation of a very strong jet stream.
Behind the southern and eastern edges of the gust front related to a gravity wave, a compact region of latent heating near the tropopause is often enclosed. A similar feature was observed in Finland associated with the passage of Janika. In the vertical cross sections on 16 November 2001 at 00.00 UTC a local maximum in WA appears and could be a sign of such a feature.
16 November 2001/00.00 UTC - Meteosat IR image; position of vertical cross section indicated
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16 November 2001/00.00 UTC - Vertical cross section; black: isentropes (ThetaE), red: temperature advection, orange thin: IR pixel
values, orange thick: WV pixel values
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In water vapour imagery the waves can been seen as rapidly propagating, narrow 10-30 km and 500-1000 km long white arc lines. The absence of significant cloudiness makes them detectable primarily in the water vapour images.