Non-orographic gravity waves in mesoscale simulations and from stratospheric balloon observations over the Southern Ocean

Joint GTP MMM Seminar

Riwal Plougonven
Laboratoire de Meteorologie Dynamique/IPSL
Ecole Polytechnique
Palaiseau, France

this talk will be webcast and recorded

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 role in the emission of the gravity waves.

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