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Fernando Martín
,
Sylvia N. Crespí
, and
Magdalena Palacios

Abstract

The Topography Vorticity-Mode Mesoscale (TVM) model has been evaluated for four different cases of thermal low pressure systems over the Iberian Peninsula. These conditions are considered to be representative of the range of summer thermal low pressure conditions in this region. Simulation results have been compared with observations obtained in two intensive experimental campaigns carried out in the Greater Madrid Area in the summer of 1992. The wind fields are qualitatively well simulated by the model. Detailed comparisons of the time series of simulations and observations have been carried out at several meteorological stations. For wind speed and direction, TVM results are reasonably good, although an underprediction of the daily thermal oscillation has been detected. The model reproduces the observed decoupled flow in the nighttime and early morning along with the evolution of mixing layer flow during the day. In addition, the model has simulated specific features of the observed circulations such as low-level jets and drainage, downslope, upslope, and upvalley flows. The model also simulates the formation of hydrostatic mountain waves in the nighttime in some cases.

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Fernando Martín
,
Magdalena Palacios
, and
Sylvia N. Crespí

Abstract

This paper discusses the variability of air-parcel transport under similar summer thermal low pressure conditions over the Iberian Peninsula. Three-dimensional trajectories were estimated by means of the Topography Vorticity-Mode Mesoscale model. Four cases of the 1992 summer thermal low pressure system have been considered, covering most of the variability of this synoptic meteorological situation.

Transport patterns were very different among the four studied cases. Results indicate that synoptic wind forcing can influence trajectories under thermal low conditions. It was found that a remarkable difference exists between the transport of air parcels released at low levels, which are affected by thermally driven flows, and those released at higher levels, which are more influenced by the synoptic wind. Moreover, potentially polluted air parcels (released in the daytime) travel farther than the potentially nonpolluted ones (released at night) in the case of lower-level releases. In addition, important differences between the transport patterns of polluted morning air parcels and polluted afternoon air parcels are detected and discussed.

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