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Mesoscale air transport at a midlatitude squall line in Europe – a numerical analysis
Author(s) -
Uebel M.,
Bott A.
Publication year - 2015
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.2610
Subject(s) - squall line , outflow , mesoscale meteorology , geology , thunderstorm , atmospheric sciences , convection , inflow , cold front , meteorology , troposphere , warm front , precipitation , mesoscale convective system , environmental science , convective available potential energy , climatology , physics
This study examines a fast‐propagating squall line over Western and Central Europe. A high‐resolution regional weather prediction model is used to analyze the three‐dimensional wind field and the corresponding air mass transport induced by the mesoscale convective system. The squall line can be divided into a bow‐shaped strong part with a continuous line of heavy convective precipitation, and a weaker part exhibiting several isolated multi‐cell storms. In the strong part, a deep and intense rear inflow jet occurs with relative wind speeds of 12–18 m s −1 . This part is also characterized by moderate to strong wind shear, in contrast to the weaker part of the squall line where a shallow cold pool surges under the potentially unstable presquall air. To investigate the air mass transport along the squall line, in the model simulations passive fluid tracers are initialized in several vertical layers with different thermodynamic conditions. At the strong part of the squall line a very efficient vertical tracer transport occurs. Potentially warm low‐level air is lifted from the lowermost 2 km to the upper troposphere where an organized horizontal outflow is observed. The potentially coldest presquall air descends just in front of the updraught region and partly penetrates the convective precipitation area. In the weaker part of the squall line, the potential instability is not significantly reduced because the vertical air mass transport is less effective there. Additionally, passive tracers are used to analyze the composition of the cold pool which turns out to be a very heterogeneous mixture of descending post‐frontal cold air and presquall air originating at different heights.