[GTP] GTP Seminar at NCAR- Riwal Plougonven

[Silvia Gentile]

Joint MMM GTP
Non-Orographic Gravity Waves in Mesoscale Simulations and
in Stratospheric Balloon Observations over the Southern Ocean
Riwal Plougonven
Laboratoire de Meteorologie Dynamique/IPSL
Ecole Polytechnique, Palaiseau, France

Thusday, 25 July 2013, 3:30PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 Small Seminar Room 1001


Gravity waves in the lower stratosphere above Antarctica and the 
Southern Ocean have been characterized from observations by 
superpressure balloons from the Vorcore campaign (Hertzog et al 2008). 
Mesoscale simulations with the WRF (Weather Research and Forecast Model) 
are carried out to analyze further the gravity-wave field, with an 
emphasis on non-orographic waves.
First, the realism of the simulated waves is assessed by comparison to 
the observations. A satisfactory overall agreement is found, but 
different behaviour is noted for orographic waves (overestimation in the 
simulations relative to the observations) and non-orographic waves 
(underestimation).
Second, the gravity-wave field is analyzed in more detail. It is 
necessary to quantify orographic and non-orographic waves separately. 
Orographic waves are larger and more intermittent, yet affect only a 
limited geographical region. Hence their overall contribution to 
momentum fluxes entering the stratosphere is comparable to that of 
non-orographic sources. A diagnostic for intermittency, the Gini 
coefficient, is proposed.
Third, in order to better identify non-orographic sources, case studies 
are carried out for episodes of intense momentum fluxes over the 
Southern Ocean, far from islands. The emitted gravity waves occur over 
intense and rapid cyclogenesis events (polar lows). It appears that, 
despite the high latitude, moist effects play a crucial rôle in the 
emission of the gravity waves.

-- 
Silvia Gentile
NCAR IMAGe
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