Understanding significant precipitation in Madeira island using high-resolution numerical simulations of real cases

In order to advance the knowledge about precipitation development over Madeira island, four rainfall patterns are investigated based on high-resolution numerical simulations performed with the MESO-NH model. The main environmental conditions during these precipitation periods are examined, and important factors leading to significant accumulated precipitation in Madeira are shown. We found that the combination of orographic effect and atmospheric conditions is essential for the establishment of each situation. Under a moist and conditionally unstable atmosphere, convection over the island is triggered, and its location was determined mainly by variations of the ambient flow, which was also associated with different moist Froude numbers. Interestingly, our results showed some similarities with situations discussed in idealized studies. However, the real variations of the atmospheric configuration confirm the complexity of significant precipitation development in mountainous regions. In addition, precipitating systems initially formed over the ocean were simulated reaching the island. The four periods were characterised by different time durations, and the local terrain interacting with the mesoscale circulation was decisive in producing a large part of the precipitation, which concentrated in distinct regions of the island induced by the airflow dynamic.

Numerical simulations of significant orographic precipitation in Madeira island

High-resolution simulations of high precipitation events with the MESO-NHmodel are presented, and also used to verify that increasing horizontal resolution in zones of complex orography, such as in Madeira island, improve the simulation of the spatial distribution and total precipitation. The simulations succeeded in reproducing the general structure of the cloudy systems over the ocean in the four periods considered of significant accumulated precipitation. The accumulated precipitation over theMadeirawas better represented with the 0.5 km horizontal resolution and occurred under four distinct synoptic situations. Different spatial patterns of the rainfall distribution over the Madeira have been identified

Numerical Simulations of Fog Events in Southern Portugal

This work aims at improving the knowledge on fog formation and its evolution in the Alentejo region (Portugal). For this purpose, brief regional fog climatology, essentially based on information from the Beja Air Base meteorological station, was produced and several numerical high resolution simulations were performed using the Meso-NH. The ECOCLIMAP database used to generate the model physiography was improved to include the Alqueva reservoir (~250 km2), filled in 2003. The model results were compared with surface and satellite observations, showing good agreement in terms of fog occurrence and persistence. Various forcing mechanisms for formation, development, and dissipation of fog were identified, confirming the influence of two small mountains that block the moist air from the Atlantic Ocean, preventing the fog from reaching innermost regions. The introduction of the Alqueva large reservoir induces changes in the landscape and environment. The effects of the water vapour addition and of the changes in mass and energy surface fluxes on fog formation and evolution were studied. It was found that the reservoir may have a direct impact on fog formation over the lake and its vicinity. Depending on the large scale meteorological conditions, their influence can be both positive and negative, in terms of spatial coverage and temporal persistence.