complex properties of the bora wind · conclusions hymex, 8-10 june 2010, bologna • significant...

COMPLEX PROPERTIES OFTHE BORA WIND

I. Stiperski 1 , B. Ivančan-Picek 1, V. Grubišić 2 and A. Bajić 1

1Meteorological and Hydrological Service, Croatia2University of Vienna, Vienna, Austria

HyMeX, 8-10 June 2010, Bologna

Overview

Aim and motivation

Data and model

Complex Bora flow

Air-sea interaction

Conclusions


Outline


Overview

Effects of BoraNE

- huge Bora variability

0

10

20

30

40

50

60

1 61 121 181 241 301 361 421 481 541

win

d sp

eed

(m/s

)Vsec V10min23. 12. 2003. form 04:10 UTC to 04:20 UTCMASLENICA BRIDGE

04:10 04:12 04:14 04:16 04:18

13.9 m/s

58.6 m/s

- maximum Bora speed on the Adriatic coast – 69 m/s

0

1 0

2 0

3 0

4 0

5 0

6 0

7 0

Win

d sp

eed

(m/s

)

0

4 5

9 0

1 3 5

1 8 0

2 2 5

2 7 0

3 1 5

3 6 0

Win

d di

rect

ion

(deg

)

V 1 0 m i n

V m a x

D i r e c t i o nM A S L E N IC A B R ID G E

1 3 . 1 2 . 1 4 . 1 2 . 1 5 . 1 2 . 1 6 . 1 2 . 1 7 . 1 2 . 1 8 . 1 2 . 2 0 0 1 .

Overview



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 u pstreamtemperature 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; Beluši ć, 2007; Horvath et al., 2009; Grisogono and Beluši ć, 2009

Motivation and aimN

W E

S

2005-2006

V E L E B I T


Motivation and aim

- Most of the Bora studies of the past have focused on the nort hernpart 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 variabi lity ofthe strong Bora flow in the lee of Southern Velebit and identif yreasons for weak winds in the city of Zadar


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

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)

Data and model


Sodar dataTime-height diagrams

wind speed (m/s) and wind vectors vertical velocity (m/s)

Complex Bora flow


Wake vorticies

ZD

Wind field retrieved byWiSAR from ASAR data

23 Jan 2008, 09 UTC

Courtesy byAlperts, Ivanov, Horstmann, 2009Mon.Wea.Rev.

Complex Bora flow


Jets and wakes

Complex Bora flow


Undular Hydraulic Jump Rotor

ZD

Air-sea interaction


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).(Kuzmić et al., 2005)

Modeling and observational studies of the Adriatic Sea: MAP, DOLCEVITA, EUROSTRATAFORM

Air-sea interaction


Taken from Pullen et al. (2007)

Bora induced gyre in northernAdriatic Sea

shown are mean ocean surfacecurrents, both in contours andvectors

14UTC 31 Jan to 06UTC 2 Feb 2003

Conclusions


• significant time/space variability of the wind speed and di rection during thesevere Bora

• the Bora flow in the lee of southern Velebit is shown to be h ighly complex, characterized by hydraulic jumps, wakes, wake vorticies and rotors

• the wake, responsible for the occurrence of lighter than av erage Bora winds in theZadar area, is induced by the highest peaks of southern Vel ebit and formsdownwind 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 fe w days or even less(oceanic gyre, sea surface temperature)

• need for improvement our understanding of the air – sea proce sses using in-situobservations and high resolution modeling particularly sh ort-duration feedbackeffects


Thank you!

complex properties of the bora wind · conclusions hymex, 8-10 june 2010, bologna • significant...

Documents