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MODELLING: SYNOPTIC SITUATION AND CLOUDINESS USING WRF . To explain the difference between the cumulus clouds development during August 3 and August 4, we analyze the meteorological situation by WRF model. Figures 3b shows the sea level (925hPa) pressure and temperature at 14:00 LT on August 3. A high pressure extends over the Western Mediterranean and Western Europe with a maximum over the Biscay Bay. The 1017 hPa isobar is aligned with the west coast of Calabria and the pressure field over the central Mediterranean is rather flat. These surface conditions lead to calm synoptic scale winds, which favor breezes development. At 500 hPa (figure 3c) a pronounced mid-tropospheric trough extends from Scandinavia to the Mediterranean while a ridge is well evident over western Africa and Europe. The trough is modified by the interaction of synoptic scale winds with Alps and deepens over northern Italy. This baric configuration determines winds from W over Calabria at 500hPa. An inspection of model output for 850hPa and 750hPa shows that the wind direction is from W-NW over Calabria. The following day, the maximum surface pressure moves from the Biscay Bay to central Europe (figure 4b). The pressure over the Central Mediterranean weakens and the 1015hPa contour is aligned with the Calabria west coast. A sea level pressure decrease of 2hPa between 3 and 4 August is also confirmed by measurements at the experimental site surface station own). The pressure gradient, however, is weak over the central Mediterranean and favors the development of TFMCs. At 500hPa (figure 4c) the trough evolved in a cold cut-off low over Eastern Europe while the ridge over Africa expands toward Northeast. Compared to the previous day, the winds over Central Mediterranean turn clockwise and advect colder and drier air masses over Calabria. This change in wind direction is very important for cumulus cloud formation. Indeed, an inspection of model output over Calabria shows that temperature decreases over the region. This is partially visible at 925hPa (figures 3b and 4b) and is confirmed by the model output for third grid and by surface station measurements. So, relative humidity increases between the two days and cumulus clouds develop on 4 August following a decrease in temperature. Figure 1. The Calabria region, is a mountainous peninsula located at the southern tip of the Italy, elongated 300km in the north-south direction in the Central Mediterranean Basin. The experimental site ISAC-CRATI is located at about 300 m from the coastline at the west end of the only sea-to-sea valley around 30 km wide (the narrowest part of the region along West-East direction. CASE STUDY. During six consecutive days (2-7 August 2007) where sea/land breeze circulation was well developed (Figure 2a), we studied the development of inland clouds for two days with different synoptic situation i.e. August 3 and 4 2007. Sea breeze days are selected by surface meteorological measurements and sea breeze vertical structure is analyzed by Sodar. Figure 2 b and c show the time evolution during the whole week of the vertical profiles of vertical velocity w and its standard deviation σw respectively both estimated by the sodar. Wind speeds U reaches values of 7 ms-1 during the central hours of the day and early afternoon while at night the winds are light (< 2ms-1). Figure 2a. U (red) and Dir (blue) at 10m. Figure 2b time evolution vertical profile of vertical velocity w (m/s) Figure 2c time evolution vertical profile of w standard deviation σw (m/s) SITE INSTRUMENTS • Ground meteorological station by ADCON TELEMETRY. (Rain T, q, U and Dir, Pyranometer, P, Soil Moisture). Figure 2a • In house ISAC-CNR Mini Sodar H up to 200 m. Figure 2 b and c • Wind Profiler / RASS VAISALA, model LAP-3000. Wind and T profiles 2 km range, Fig. 4 • Radiometric Station KIPP & ZONEN and VAISALA (pyranometer model CM11, an UV B radiometer, model UVS-B-T and a net radiometer, model CNR1 • Mini SoDAR METEK, model DSDPA.90-24. H range: 15-500 m • A sonic anemometer and a fast response Hygrometer will also be installed. These instruments will give the possibility to study coastal areas flow development for new parameterizations and testing model performances INTEGRATED STUDY OF CLOUDINESS DEVELOPMENT INLAND DURING SEA BREEZE FROM A COASTAL SITE USING MODELLING AND REMOTE SENSING De Leo L. 1,2 , Federico S. 1,2 , Sempreviva Anna M. 1 , Pasqualoni Loredana 2 , Avolio E. 1,2 , Bellecci C. 2,3 1) Institute of Atmospheric Sciences and Climate, ISAC-CNR, Lamezia Terme (CZ), 2) CRATI s.c.r.l., Lamezia Terme, Italy,3) Engeenering Dep., University of Rome - Tor Vergata, Italy We present the activity carried out at a coastal experimental site (see SITE INSTRUMENTS) in the Italian Calabria peninsula (figure1) located in the central Mediterranean. We address the development of inland cloudiness i.e. interaction between breezes and large scale circulation and their impact on cumulus cloud formation. This is a main issue in Calabria because the area is prone to episodes of heavy precipitation and severe weather. Moreover, data here collected are crucial to test model performances in coastal areas studies and develop suitable parameterizations. Calabria is particularly interesting for studying the development of such thermally induced meso-scale circulations (TMFCs). Owing to the specificity of the Mediterranean climate and to the topographic characteristics of the peninsula, i.e. the presence of high mountains parallel to the coast, intense local wind circulations can develop, mainly in fair weather conditions, which are common during summertime in the Mediterranean Basin. The high water vapor atmospheric content in summer, due to the sea evaporation, is reorganized by the TMFCs; because of the peculiar shape of the peninsula, the thermal gradient associated with the sea-land contrast and with the mountain peaks-free atmosphere merge together generating wide and intense local circulations. Humid marine air masses, which come from lower levels, are advected and lifted upward by breeze circulation and can determine the onset of cumulus clouds over the main peaks, with chances to trigger afternoon thunderstorms. A comprehensive study can only be conducted using spatial and temporal high resolution information by integrating experimental data and modeling. s.c.r.l. 25/05/08 00:00 25/05/08 24:00 Time (UTC) Tv (oC) 25/05 00:00 25/05 24.00 FIGURE 5. Example of evolution of vertical profiles of Virtual Temperature (left) and wind direction DIR and speed U (right) during May 25 2008 by the RASS CONCLUSIONS AND FUTURE WORK The pronounced thermally forced meso-sale circulations in Calabria is related to two basic features: first Calabria is located in the Central Mediterranean Basin where synoptic scale conditions are favorable to breezes development, second the peculiar shape of the peninsula induces strong sea/land breezes and mountain/valley flows which acts synergically. The water vapor is organized by local circulations and transported in the center of the peninsula where, owing to convergence is uplifted. This process can produce cumulus clouds and trigger rainfall in the afternoon if suitable conditions are met. Results are promising and show the capability of the methodology for studying thermally forced meso-scale circulations over Calabria. As next step, we are considering a whole year period where Sodar data are available to assess the impact of breezes on the Calabria climate. Future development includes the use of other remote sensing devices such as the Rass recently installed in the experimental field (Figure 5 a and b) and experimental tower with turbulence meausrements sensors (see next) Rass has been sponsored by the Calabria Region SEA BREEZE Wind direction is from west during the day and from east at the night, except between 2-3 August and 3-4 August, when the light wind is from S-SW. Considering the location of the experimental site, the measurements in figure 2 are typical of sea breeze development for the region. Figure 2b shows a positive w during the day and negative at night, noticeably for 2, 5 and 6 August. Diurnal values are larger than 1ms-1 above 100m and confirm the full convection development above the surface layer (about 100m). The sea breeze front overpass the coastal site between 06:00 and 09:00 am LT. As expected for TMFCs the absolute value of vertical velocity is higher during the day. This is also evident from figure 2c that shows σw ; values between 0.5 and 1 m2s-2 are measured for the central hours of the day while they are nearly zero at night. Figures 2a, 2b and 2c show a typical occurrence of rather intense breeze circulations over Calabria, as expected considering the peculiar shape of the peninsula and the characteristic of the Mediterranean climate in summer. CLOUDINESS. An interesting issue about breeze circulations is their ability to form inland cumulus cloud during the day producing afternoon thunderstorms. Thermally forced meso-sale circulations appear pronounced for Calabria where strong sea/land breezes and mountain/valley flows act synergically. Cloud development is analyzed by subjective inspection of METEOSAT MSG satellite images in the visible channel and two days were chosen i.e. August 3 (figure 3a) and August 4 (figure 4a). The WRF (Weather Research and Forecasting) meso-scale model is used to analyze the meteorological situation over the Calabria region during the two days . Figure 3 b and 3c show the synoptic situation for August 3. Figure 4b and 4c shows the synoptic situation on August 4 and in figure 4d, 4e, the WRF forecast for rain along the transect A-B . Figure 4f shows the precipitation measurements by the regional pluviometers network. Figure 5 shows the precipitation measurements by the regional pluviometers network on August 5. 40 Figure 5. (left) Precipitation measured during August 5. Comparing to figure 4f, we show that in Calabria the precipitation can be localized (red circle) and can vary daily Fig. 3a MSG image Fig. 3b and 3c synoptic situation T and P fields over Europe 950 hPa (left) 500 hPa (right). August 3 Fig. 4a MSG image Fig. 4b and 4c. synoptic situation T and P fields over Europe Fig. 4d, 4e: cloudiness by WRF over Calabria and along Fig. 4f measured 950 hPa (left) 500 hPa (right) A-B transect vertical section precipitation A B August 4
