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SUMMARY:Polar low formation: ambient environments and the role of moisture
  - Annick Terpstra\, University of East Anglia
DTSTART:20180501T130000Z
DTEND:20180501T140000Z
UID:TALK102742@talks.cam.ac.uk
CONTACT:Dr Gillian Young
DESCRIPTION:Polar lows are maritime meso-scale cyclones occurring during c
 old air outbreaks at high latitudes. Previous studies have shown that wind
  shear\, baroclinicity\, latent heat release\, and surface fluxes are impo
 rtant factors during formation and intensification\, yet their relative co
 ntributions and importance are still not fully understood.\n \nWe identify
  the characteristics of ambient pre-polar low environments to gain insight
  in the underlying dynamical mechanisms for intensification and formation 
 of polar lows. Classification of these environments is based on the direct
 ion between the thermal wind and the mean flow in the lower troposphere\, 
 where environments are classified as ‘reverse shear’ if the thermal wi
 nd and mean flow are in opposing directions and ‘forward shear’ if the
 y are in the same direction. The two types of pre-polar low environments e
 xhibit distinctly different features in terms of synoptic scale patterns\,
  baroclinicity\, configuration of the sea-surface temperature\, as well as
  depth and stratification of the troposphere. These clear-cut differences 
 hint at different dynamical pathways for the formation and intensification
  of polar lows for different shear environments.\n\nIn addition\, we explo
 re the role of latent heating during polar low formation utilizing an idea
 lised baroclinic channel model. The experimental design resembles a typica
 l forward-shear moist-baroclinic environment at high-latitudes. Cyclogenes
 is is triggered by a weak\, low-level thermal perturbation in hydrostatic 
 and geostrophic balance. Our experiments show that significant disturbance
  growth is possible in absence of upper level forcing\, surface fluxes\, a
 nd radiation. The relative importance of diabatic versus baroclinic proces
 ses for the generation of eddy available potential energy is used to diffe
 rentiate between the dynamical processes contributing to disturbance growt
 h. The experiments indicate that sufficient latent heat release in the nor
 th-eastern quadrant of the cyclone is crucial for rapid disturbance intens
 ification\, where environmental relative humidity\, baroclinicity\, and st
 atic stability modulate the relative importance of latent heat release. Fu
 rthermore\, the relative shallowness of the perturbation at high-latitudes
  increases the effectiveness of latent heat release on cyclone amplificati
 on. 
LOCATION:British Antarctic Survey\, Innovation Centre\, Seminar Room 2
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