The diagnostic model DIAMOD has been developed in Parts l and II of this study. Its core is the convection equation for the vertical sub-gridscale flux of moist enthalpy, called total convective heat ...flux h. The convection equation is forced by the analyzed gridscale total heat budget. It has been implied in Part II that the size of h is controlled by the mean vertical derivative (the slope) of the budget, mainly in cases of strong convection. The slope of the budget, and consequently h, is quite sensitive to the numerical representation of the convection equation. The original implementation of DIAMOD in pressure coordinates (p-DIAMOD) suffers from the downward extrapolation of analysis data to standard pressure levels over high orography. This generates spurious values of the gridscale budget below the earth's surface which heavily affects the slope of the budget. The insufficient vertical resolution in the stratosphere also has a strong impact. Both problems are eliminated in the present implementation (η-DIAMOD) which is based on terrain following hybrid coordinates and discretized like the ECMWF forecast model. DIAMOD further yields an objective error estimate, the imbalance. While the vertical mean of the imbalance in the convection equation is a diagnosed quantity, its vertical profile has to be specified by an external error model. This profile is now chosen such that the impact upon h is minimized. The results obtained with the two model versions are compared for a rainstorm situation and contrasted with Yanai-type diagnostic studies. The h-profiles from η-DIAMOD in the free atmosphere are smaller than those from p-DIAMOD. However, they are better in accord with the meteorological situation.
Comparisons are made between the postsunrise breakup of temperature inversions in two similar closed basins in very different climate settings, one in the eastern Alps and one in the Rocky Mountains. ...The small, highaltitude, limestone sinkholes have both experienced extreme temperature minima below −50°C and both develop strong nighttime inversions. On undisturbed clear nights, temperature inversions reach to 120-m heights in both sinkholes but are much stronger in the drier Rocky Mountain basin (24 vs 13 K). Inversion destruction takes place 2.6–3 h after sunrise in these basins and is accomplished primarily by subsidence warming associated with the removal of air from the base of the inversion by the upslope flows that develop over heated sidewalls. A conceptual model of this destruction is presented, emphasizing the asymmetry of the boundary layer development around the basin and the effects of solar shading by the surrounding ridgeline. Differences in inversion strengths and postsunrise heating rates between the two basins are caused by differences in the surface energy budget, with drier soil and a higher sensible heat flux in the Rocky Mountain sinkhole. Inversions in the small basins break up more quickly following sunrise than for previously studied valleys. The pattern of inversion breakup in the non-snow-covered basins is the same as that reported in snow-covered Colorado valleys. The similar breakup patterns in valleys and basins suggest that along-valley wind systems play no role in the breakups, since the small basins have no along-valley wind system.
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BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This paper summarizes the findings of seven years of research on foehn conducted within the project lsquoFoehn in the Rhine Valley during MAPrsquo (FORM) of the Mesoscale Alpine Programme (MAP). It ...starts with a brief historical review of foehn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on foehn at a local scale and the processes driving foehn propagation in the Rhine Valley. The crucial importance of interactions between the foehn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of foehn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between foehn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation. Copyright 2007 Royal Meteorological Society
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
A new automatic tracking method for convective cells and cell complexes is introduced. The method uses a simple Gaussfilter and a selection procedure to define displacement vectors of the specific ...system. The change of the half width of the filter results in a separation of the system's scale. The proposed method is applied on two data sources: lightning density and RADAR reflectivity. They describe different properties of convective cells and cell complexes. A strong connection of the storm tracks to topography becomes also evident.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Mesoscale convective precipitation systems in the Alpine region are studied by analyzing radar and rain gauge data. The data from weather radars in Austria, France, Germany, and Switzerland are ...combined into a composite. Availability of radar data restricts the study mainly to the northern part of the Alpine region. Mesoscale convective systems (MCS) occur often in this region and are comparable to large systems observed in the USA. Seven precipitation events lasting one to six days from the years 1992-1996 are examined in detail. They all moved west to east and showed no diurnal preference in formation or dissipation. They reach sizes of 2-6 : 10 super(4) km super(2) . MCS with leading-line trailing-stratiform structure tended to be larger and more intense. A 25-year set of rain gauge data indicates that a giant MCS (covering more than 4 : 10 super(4) km super(2) with more than 30 mm/day) occurs every 6 years in the northern Alpine region. MCS occur more frequently in the southern Alpine region.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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