Diagnosing convection during selected MAP-IOP cases

The better understanding of the Alpine hydrological cycle is an important scientific target of the Mesoscale Alpine Programme (MAP). This issue will be addressed by evaluating gridscale and sub-gridscale atmospheric moisture and heat budgets components on the meso-alpha scale. The basic concept of evaluating sub-gridscale quantities indirectly from gridscale atmospheric energy budgets goes back to Yanai et al. in the early seventies. The presented approach goes beyond Yanai’s concept in the sense that the vertical eddy flux of equivalent temperature is also calculated from the budget components. This quantity is a measure of the strength of the atmospheric convection and referred to as the convective flux. The proposed method is rather sensitive to input data quality. It is demonstrated with a thermodynamic diagnostic model that the convective flux can be diagnosed from routine gridscale analyses with tolerable error.

Input data are the gridscale initialized fields from the ECMWF data archive, further the surface values of latent and sensible heat flux from a SVAT-model. Surface precipitation is analysed by an objective interpolation method from SYNOP-reports.

Case studies will be concentrated on heavy precipitation events in the Alpine area and surroundings during the MAP Special Observing Period (SOP) from early September to mid of November in 1999. Characteristic vertical profiles of the budget components and of the convective flux will be presented.

However, the proposed method may suffer from systematic errors in the assimilating forecast model which can be comparatively large over mountainous terrain. Further, some information is lost due to interpolation onto the regular model grid. An alternative approach for calculating moisture budgets is proposed in the paper Haimberger et. al which will also be presented at the conference.