COMPLEX PROPERTIES OF THE BORA WIND I. Stiperski 1 , B. Ivan čan-Picek 1, V. Grubiši ć 2 and A. Baji ć 1 1Meteorological and Hydrological Service, Croatia 2University of Vienna, Vienna, Austria HyMeX, 8-10 June 2010, Bologna Outline Overview Aim and motivation Data and model Complex Bora flow Air-sea interaction Conclusions HyMeX, 8-10 June 2010, Bologna Overview NE Effects of Bora HyMeX, 8-10 June 2010, Bologna Overview - huge Bora variability MASLENICA BRIDGE 23. 12. 2003. form 04:10 UTC to 04:20 UTC Vse c V10min 60 58.6 m/s 50 40 30 20 wind speed (m/s) speed wind 10 13.9 m/s 0 04:101 61 04:12 121 181 04:14 241 30104:16 361 42104:18 481 541 - maximum Bora speed on the Adriatic coast – 69 m/s 7 0 3 6 0 V 10m in V m a x 6 0 3 1 5 D ire ctio n M ASLENICA BRIDG E 2 7 0 5 0 2 2 5 4 0 1 8 0 3 0 1 3 5 Wind direction (deg) direction Wind Wind speed (m/s) Wind speed 2 0 9 0 1 0 4 5 0 0 13. 12. 14. 12. 15. 12. 16. 12. 17. 12. 18. 12. 2001. HyMeX, 8-10 June 2010, Bologna Overview Major advances in the understanding of Bora flow : ALPEX and MAP Basic severe Bora dynamics: - presence of the upstream low-level critical level and/or upstream temperature inversion - 3-D structure (hydraulic jumps, mountain wave breaking, gap jets , wakes, rotors, pulsation) List of recent publications: Grubiši ć, 2004; Gohm and Mayr, 2005; Gohm et al. 2008; Belušić, 2007; Horvath et al., 2009; Grisogono and Beluši ć, 2009 HyMeX, 8-10 June 2010, Bologna Motivation and aim N V E L E B I T WE S 2005-2006 HyMeX, 8-10 June 2010, Bologna Motivation and aim - Most of the Bora studies of the past have focused on the northern part of the Dinaric Alps - Zadar area is highly vulnerable to weather conditions (tourism, transport and communication, natural environment, ...) - Special sodar measurements during the winter - spring 2004/5 season - Investigate small-scale characteristics and spatial variability of the strong Bora flow in the lee of Southern Velebit and identify reasons for weak winds in the city of Zadar HyMeX, 8-10 June 2010, Bologna Data and model - severe Bora event 20 December 2004 sea level pressure - COAMPS (non-hydrostatic, fully-compressible model with multiple nesting capability) ∆x = 1 km ∆x = 333 m HyMeX, 8-10 June 2010, Bologna Data and model 20 December 2004 – time series of measured (black) and modeled (orange) 10-minute wind speed, measured gusts (grey) and wind direction (dots) HyMeX, 8-10 June 2010, Bologna Data and model Sodar data Time-height diagrams wind speed (m/s) and wind vectors vertical velocity (m/s) HyMeX, 8-10 June 2010, Bologna Complex Bora flow Wake vorticies ZD HyMeX, 8-10 June 2010, Bologna Complex Bora flow Wind field retrieved by WiSAR from ASAR data 23 Jan 2008, 09 UTC Jets and wakes Courtesy by Alperts, Ivanov, Horstmann, 2009 Mon.Wea.Rev. HyMeX, 8-10 June 2010, Bologna Complex Bora flow Undular Hydraulic Jump Rotor ZD HyMeX, 8-10 June 2010, Bologna Air-sea interaction Modeling and observational studies of the Adriatic Sea: MAP, DOLCEVITA, EUROSTRATAFORM Daily averaged ALADIN 10m wind (blue) and station measurements (red) for 12 February 2003 (left); Model predicted sea level and transports for 13 February 00UTC (right). (Kuzmi ć et al., 2005) HyMeX, 8-10 June 2010, Bologna Air-sea interaction Bora induced gyre in northern Adriatic Sea shown are mean ocean surface currents, both in contours and vectors 14UTC 31 Jan to 06UTC 2 Feb 2003 Taken from Pullen et al. (2007) HyMeX, 8-10 June 2010, Bologna Conclusions • significant time/space variability of the wind speed and direction during the severe Bora • the Bora flow in the lee of southern Velebit is shown to be highly complex, characterized by hydraulic jumps, wakes, wake vorticies and rotors • the wake, responsible for the occurrence of lighter than average Bora winds in the Zadar area, is induced by the highest peaks of southern Velebit and forms downwind of a stong hydraulic jump • the wake is unstable and transitory • strong horizontal and vertical wind shear • Bora and Adriatic Sea interaction – with timescales of a few days or even less (oceanic gyre, sea surface temperature) • need for improvement our understanding of the air – sea processes using in-situ observations and high resolution modeling particularly short-duration feedback effects HyMeX, 8-10 June 2010, Bologna Thank you! HyMeX, 8-10 June 2010, Bologna.