Armengot-Serrano, Rafael (GPV de Valencia, INM)
Abellan-Andres, Juan Jose (Dep. Estadistica, Univ. de Valencia)
The Valencian Region is located at the eastern edge of the Iberian Peninsula. It registers a high incidence of heavy rainfall; during the period 1976-90, 129 days reached 100 mm of rain somewhere in this territory, 25 of those measured 200 mm or more, and rose to figures even higher than 800 mm/day.
These episodes usually happen in autumn, in the context of a still warm sea surface temperature (SST), together with phases of low zonal index in the mid-and-upper troposphere circulation. But, with less frequency, intensity and extension, they happen all year.
All these cases can be classified in different synoptic populations, but share some essencial elements in their basic contexts: the existence of a centre of action in the mid-and-upper troposphere (generally a cut-off low, located in ther southwest of the area) inducing cyclogenesis on the Balear and Algerian Mediterranean sea, and a maritime advection at low levels on the analysed territory.
The present study analyses thoroughly these synoptic contexts for the period 1976-90, whether produced heavy rain in the area or not. During the 15 years, 603 days exhibited the basic synoptic conditions either with reference to the location of the centre of action in upper-mid levels and/or a defined easterly advection in low levels; these include the 129 cases of heavy rain considered. For all these days, in 5 levels from the surface up to 300 hpa, parameters were obtained on the position and motion of centres of action, thermal and hydrometric characteristics, and gradient of the implied advective flows.
Hence, research is done on the key elements that reinforce or inhibit the heavy rain episodes, paying special attention to their location related to the main orographic axes. The role of the vorticity advection linked to the movement of the mid-upper low, induced cyclogenesis in low levels and recent history of the advected air mass are highlighted.