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| Titel |
Impacts of mesoscale SST anomalies on atmospheric mid-latitude storms |
| VerfasserIn |
Riwal Plougonven, Guillaume Lapeyre, Xavier Perrot |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250110445
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| Publikation (Nr.) |
 EGU/EGU2015-10441.pdf |
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| Zusammenfassung |
| Idealized simulations of a mid-latitude storm track are investigated to quantify the
atmospheric response (heat and moisture fluxes, surface winds) to mesoscale SST
anomalies.
Analysis of satellite observations have revealed, in the past decade, that surface winds
over the ocean exhibit spatial variations that are strongly correlated to underlying SST
anomalies. Two different mechanisms have been proposed to explain how the SST influences
the Marine Atmospheric Boundary Layer: the momentum mixing mechanism (emphasizing
cross-wind SST gradients), and the pressure adjustment mechanism (emphasizing the
Laplacian of the SST, and hence smaller scales). Complementary work (Perrot et al) shows
that the atmospheric response transitions from the latter response in the case of weak winds to
the former in the case of stronger winds.
In the present study we investigate the impacts of the SST anomalies on a mid-latitude
storm-track. Specific questions include the mechanisms for atmospheric response in
different regions of the flow, and the depth of the influence of the SST anomalies :
how much does the spatial organisation of the SST anomalies constrain the fluxes
from the ocean to the atmosphere?
how are the spatial patterns of surface winds correlated to those of the SST
anomalies, in regions of strong winds and in regions of weak winds?
does the influence of the SST anomalies reach beyond the Boundary Layer,
ie is their impact visible in the free troposphere? Can they influence (at least
sporadically) developping storms?
Simulations of an idealized storm track in aquaplanet configuration are carried out with
the Weather Research and Forecast Model, in a zonally periodic channel with two different
underlying SST spatial organisation. A reference simulation consists in a zonally uniform
SST field with a smooth meridional gradient whereas an "eddying" version additionally
includes typical mesoscale (200km) SST anomalies.
It is found that mesoscale SST anomalies organize much of the lower level flow, in
particular the sensible and latent heat surface fluxes. They also influence the amplitude of
precipitations and part of the tropospheric flow, such as the Eliasen-Palm fluxes. Sensitivity to
choices of parameterizations, in particular for moist processes, and to resolution will be
discussed. |
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