Thermal flows along the south-eastern Adriatic EGU 2009

Thermal flows along the south-eastern Adriatic EGU 2009 -1561 Maja Telišman Prtenjak & Sanda Đivanović Department of Geophysics, Faculty of Science, University of Zagreb, Croatia Email: telisman@irb. hr RESULTS Model vs. measurements CONCLUSIONS v Airports are located in the area which is under significant influence of the convergence zones (as the result of the merged thermal circulations) v considerably channeling of the surface wind occurred in sea passages as well over the Neretva river v. Formation of several mesoscale eddies (e. g. over the island of Šolta near Split-airport and in the lee the island of Vis) Table 1. Calculated statistic indices during 24 -25 April 2006: RMSE (root mean square error), d-index of agreement and MAE (mean absolute error) reflect the degree to which measurements are accurately estimated by the model. The calculations were made for wind speed, wind direction and temperature at 9 stations with 24 hour measurements. Wind direction and 2 -m temperature showed reasonable model performance, although somewhat poorer agreement was obtained for the wind speed (e. g. Split, Makarska, Komiza and Dubrovnik) wind direction wind speed 04: 00 LST 2 -m temperature AIM & MOTIVATION v. Klaić et al. (2009) examined sea/land breeze and etesian interaction along the Adriatic. v However, a spatial distribution of the small-scale features in the wind field during sea breeze event along the south-eastern Adriatic (SEA) is still unknown. v In SEA, the existed sea/land breeze knowledge is predominantly climatological. Only certain number of the forecast sites were analyzed (Lukšić, 2004; Pandžić and Likso, 2005). v. Since several airports (Split-airport, Brač-airport and Dubrovnikairport) are located in this area, the aim is to detect possible (sometimes very dangerous) convergence zone (and other wind forms). Daytime surface wind field 15: 00 LST Nighttime surface wind field Figure 2 Vertical comparison between. modeled (pink) and measured (blue) wind at Split – airport on 24 April 2006. Wind (a) speed and (b) direction at 04: 00 LST and wind (c) speed and (d) direction at 15: 00 LST during land/sea breeze event. Position of the measuring site is indicated in Fig 1. Vertical wind measurements were performed by Scintec MFAS sodar with the measurements range from 30 to 700 m. Averaging and output intervals were set to 10 minutes and space resolution is 20 m. The model results are in a good agreement with the sodar results. 03: 00 LST Modeled 10 -m wind field on 24 April 2006 (b) 14: 00 LST (c) 14: 00 LST (a) measurements During the nighttime , weak land breeze interacted with downslope wind reaching 3. 4 m s-1. The strongest channeling between Mosor and Biokovo mountains Šolta (d) 14: 00 LST Figure 1 (a) Configuration of nested model grids over the study area on the south-eastern Adriatic coast. Frames. indicate the coarse-grid (1), mid-frame (2) and fine-grid (3) WRF model domains, respectively. (b) The fine-grid domain with the positions of measuring sites; hourly meteorological measurements (green circles): 1 = Šibenik, 2 = Knin, 3 = Split, 4 = Makarska, 5 = Hvar, 6 = Komiža, 8 = Ploče and airport stations: Split-airport, Brač-airport and Dubrovnik-airport (red circles). Topography contours are given for every 100 m between at 0 and 2000 m. Abbreviations are SC = Split channel, BC = Brač channel, HC = Hvar channel, VC = Vis channel, KC = Korčula channel, NC = Neretva channel. MODEL & SIMULATION SPECIFICATIONS v WRF-ARW (version 2. 2) 3 D nonhydrostatic mesoscale model (e. g. Michalakes et al. , 2004); v a two-way nested configuration with grid spacing of 10. 8 km, 3. 6 km and 1. 2 km in model domains (on the Lambert conformal projection) (Fig. 1). v 80 terrain-following coordinate levels with the lowest level at about 25 m. v Initial and boundary conditions from ECMWF at the standard pressure levels every 6 h; v Simulations of 65 h were performed from 0700 h of 28 June 2004 until midnight of 30 June 2004. v WRF dynamic and physical options for all domains: § a Mellor-Yamada-Janjic scheme for the PBL; § a rapid radiative transfer model for the longwave radiation and a Dudhia scheme for shortwave radiation; § a single-moment 3 -class microphysics scheme with ice and snow processes; § the Eta surface layer scheme based on MO theory § a five-layer thermal diffusion scheme for the soil temperature. § the Betts-Miller-Janjic cumulus parameterization is only used on the coarse domain (e) 17: 00 LST Specific features in the surface wind field was: Ø the formation of the mesoscale eddy above the island of Šolta within SC and BC. This vortex with the offshore flow formed (relatively weak) nighttime convergence zone near Split-airport. ØAbove Brač-airport weak convergence zone was developed. Øatmospheric vortex the lee of in the island of Vis. Figure 4 Same as in Fig. 3. except for 03: 00 LST on 24 April 2006. Acknowledgements Figure 3 (a) 10 -m wind vectors (m s-1) from meteorological (Fig. 1) and climatological stations at 14: 00 LST for 24. April 2006; (b) modeled WRF wind field in the fine model domain at 14: 00 LST; (c) the modeled wind field above Neretva river at 14: 00 LST; (d) the modeled wind field above the island of Brač at (d) 14: 00 LST and (e) at 17: 00 LST. The wind vectors are given at a horizontal resolution of 3 km and the wind speed is depicted by filled areas (scale legend on the right) with a 1 m s-1 interval. During the day after 09: 00 LST, sea breeze developed as well as upslope wind over the , mountainous coastline v They superimposed with the strength up to 6 m s-1 at 14: 00 LST. v Specific features in the surface wind field were: Ø convergence zones e. g. near Split-airport (stronger) and above the island of Brač (weaker) close to the Brač-airport that moved eastward and southward, respectively. Vertical velocities were over 1 m s-1; Ø canalizing flows trough the mountainous gaps and sea channels (HC, BC, SC, NC) as well as above Neretva river (Fig. 3 c); Ø atmospheric vortex the lee of the island of Vis (Fig. 3 e). in This work has been supported by the Ministry of Science, Educational and Sport (BORA project No. 119 -1193086 -1311). References Klaić, Z. B. , Pasarić, Z. , Tudor, M. , 2009. On the interplay between sealand breezes and etesian winds over the central Adriatic. J. Marine Syst. (in press). Lukšić, I. , 2004. Neki odnosi između zmorca, etezija i atmosferskog poremećaja. Hrv. meteorol. časopis, 39: 121– 133. (in Croatian) Michalakes J, Dudhia J, Gill D, Henderson T, Klemp J, Skamarock W, Wang W. 2004. The Weather Research and Forecasting Model: software architecture and performance. In 11 th ECMWF Workshop on the use of High Performance Computing in Meteorology, edited by George Mozdzynski. Reading. U. K. Pandžić, K. , Likso, T. , 2005. Eastern Adriatic typical wind field patterns and large-scale atmospheric conditions. Int. J. Climatol. , 25: 81 -98.