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RADIOSONDE OBSERVATIONS

The investigative team has requested the deployment of the National Center for Atmospheric Research (NCAR) mobile GPS/Loran Atmospheric Sounding System (GLASS) in Southwest Australia during the two intensive field campaigns.  There are two proposed field campaigns: one during the growing season in August-September and the other after the harvest in December.  High temporal resolution (4 launches/ day) radiosonde launches will be used to examine the boundary layer evolution and vertical wind profiles over selected study areas.  Two GLASS systems have been requested to be deployed over the selected study areas.  These study areas are selected to sample distinctly different types and scales of spatial heterogeneities.  For an extended period the pair of GLASS systems will be deployed on the two sides of the bunny fence, coincident with the already existing surface energy flux measurement sites that are acquiring Bowen Ratio and other measurements. The observations from this pair will be used to sample conditions simultaneously on the two sides of the fence and to examine the mesoscale circulations generated by large scale heterogeneity in the vicinity of the bunny fence.

Another set of GLASS system deployments will take place in the adjacent native vegetation/ agricultural areas close to the coast for part of the field campaign. These measurements will be used to examine the effect of land use on sea breeze circulations.  Finally, the GLASS systems will be moved to the isolated natural vegetation preserve in the middle of the agricultural area and to a complementary site.  Observations from this set of measurements will be used to study the “island effect” associated with a relatively small stand of native vegetation in the midst of a vast areas of agriculture.

The radiosonde observations will be used for multiple applications.  In conjunction with surface energy flux measurements and satellite observations of cloudiness, the radiosonde observations will be used to examine the influence of land use on cloudiness.  Specifically, the interplay of surface energy flux patterns and atmospheric stability on suppression or enhancement of cloudiness will be explored using statistical techniques.   The radiosonde observations will be directly used for detecting the existence of mesoscale circulations.  We will utilize a technique similar to that of Souza et al. (2000) for this purpose.  From a time series of radiosonde observations it is possible to identify mesoscale circulations as perturbations over a large scale flow.  The orthogonal components of the wind u,v can be decomposed into mean (U,V) and perturbation (u’, v’) parts by using averaging.  Vertical profiles of u’ and v’ can be used to examine the existence of mesoscale circulations.  Finally, the radiosonde observations will be utilized for initializing the RAMS numerical model, and along with satellite data they will be used for identifying case study days.

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