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The difference in temperature between the poles and the equator is the main source of large-scale atmospheric motions around the globe and in particular the atmospheric mid latitude cyclogenesis. It is well known that, at these latitudes, the temperature gradient is maximum during winter and over land-ocean interfaces and is at the onset of upper-tropospheric atmospheric jet streams.

These jets are propitious to the forming of extra tropical cyclones that gather momentum from what is known as baroclinic interaction or baroclinic instability. Even though this mechanism responsible for cyclogenesis is well known, it is nonetheless true that other parameters can strongly modulate the properties of extra tropical cyclones. For example, latent heating processes may increase their amplitude but other phenomena such as the barotropic interaction related to horizontal wind shears may have the opposite effect. The impact of these phenomena on mid latitude cyclogenesis is still the subject of intense research.


5 latest articles

9 December 2009

Evolution of a low-level cyclone in a storm in the absence of an upper-level precursor

Before reaching the french coasts, the two European storms of Christmas 1999 were two low-level cyclones with moderate amplitude traveling across the Alantic. They have rapidly deepened during their interaction with the upper-level large-scale jet. For the second storm, this (...)
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7 December 2009

Daily PV inversion

This section aims at showing some aspects of the interaction of the main PV pattern at 00UTC every day over the Atlantic ocean and western Europe with its environment. PV is split in terms of synoptic scale (high-frequency) PV (...)
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4 December 2009

Upper-Level Coherent Structures and Deep Convection

The relative importance of the two upper-level troughs, of the mid- to upper-level humidity and in the development of the heavy precipitating event of September 2005 over southern France is investigated by considering their individual impacts using a hierarchy of numerical (...)
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2 December 2009

PV inversion as a tool for synoptic forecasting

Rationale: upper-level PV patterns or coherent structures are key patterns for mid-latitudes weather system baroclinic development. Satellite images in IR or WV channels and total ozone retrievals may be used to assess initial conditions or very short range forecast of (...)
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26 November 2009

Relationship between convection over Central America and the jet stream bearing on the 1999 December storms

At the end of December 1999, two very powerful and devastating extratropical cyclones hit Western Europe. These two storms were associated with an upper-level zonal jet, remarkable by its intensity and by its large extension over the Atlantic Ocean. The figure above (...)
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