Abstract
Abstract. Three offshore rainbands associated with nocturnal coastal fronts formed near the Israeli coastline, the Gulf of Genoa and on the northeastern coast of the Iberian Peninsula, are simulated using version 3.3 of the WRF-ARW mesoscale model in order to study the dynamics of the atmosphere in each case. The simulations show coastal fronts producing relatively high (in comparison with some other similar rainbands) 1 and 10 h accumulated precipitations that formed in the Mediterranean Basin. According to these simulations, the coastal fronts that formed near the Israeli coastline and over the Gulf of Genoa are quasi-stationary, while the one that formed on the northeastern coast of the Iberian Peninsula moves away from the coast. For the three events, we evaluate and intercompare some parameters related to convective triggering, deceleration induced by the cold pool in the upstream flow, and the blockage that the cold coastal front offers to the warmer maritime air mass.
Highlights
When drainage winds interact with a prevailing flow, nocturnal offshore rainbands can form close to the coastline
We numerically investigate three observed events of relatively intense precipitation associated with nocturnal cold coastal fronts that formed near the coast in some areas of the Mediterranean Basin, which were caused by the drainage of cold inland air interacting with a prevailing
The events detected by Tropical Radar Measurement Mission (TRMM) have been caused by nocturnal drainage winds or a land breeze interacting with a synoptic flow, the following conditions had to be fulfilled: (i) the nocturnal precipitation formed near the coastline; (ii) the precipitation spot either remained quasi-stationary offshore near the coast, or it moved slightly; (iii) it lasted no more than 6 consecutive hours, and disappeared a few hours after sunrise; and (iv) it extended no more than 500 km, being sometimes in clusters of several individual cells
Summary
When drainage winds interact with a prevailing flow, nocturnal offshore rainbands can form close to the coastline. The most iconic investigation of nocturnal coastal fronts in this basin was made by Neumann (1951) This author proposed a convergence between a prevailing synoptic wind and the land breeze to explain the observed offshore convection in south Israel. Mazon and Pino (2009) studied the increase in nocturnal precipitation at the mouth of the Llobregat River (close to Barcelona city), which is caused by the interaction between the relatively cold drainage winds and the warm and moist Mediterranean air mass, especially during late summer and early autumn. We numerically investigate three observed events of relatively intense precipitation associated with nocturnal cold coastal fronts that formed near the coast in some areas of the Mediterranean Basin, which were caused by the drainage of cold inland air interacting with a prevailing.
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