Role of the nocturnal coastal-front depth on cloud formation and precipitation in the Mediterranean basin
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Ten nocturnal coastal front events formed in the Mediterranean basin are simulated and analyzed, focusing on the coastal-front depth by using version 3.3 of the WRF-ARW mesoscale model. During the night the inland air cools faster than the air over the Mediterranean Sea. Consequently, this colder air may move offshore, forming a coastal front when interacting with the warmer and moister maritime air mass, which is lifted over the colder air. Then clouds and precipitation may occur. In this mechanism the depth of the cold air mass (H) plays an important role in theformation of clouds and precipitation. Stratiform clouds appear if H is higher than the lifting condensation level of the warm air mass. Moreover, if H is higher than the corresponding level of free convection convective clouds are formed. H is estimated from the mesoscale simulations at an hourly scale, as well as taking the average and maximum values during the whole night. Furthermore, several parameters related to trigger convection, the blockage effect that the cold air mass offers to the prevailing flow, the deceleration induced by cold front on the upstream maritime flow and the location of precipitation with respect to the front are estimated. Additionally, a forecasting cloud-band index is proposed in order to evaluate whether stratiform clouds are formed offshore in the ten simulated nocturnal coastal fronts.
CitationMazon, J.; Pino, D. Role of the nocturnal coastal-front depth on cloud formation and precipitation in the Mediterranean basin. "Atmospheric research", 01 Febrer 2015, vol. 153, p. 145-154.