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Impact of the large-scale wind and mesoscale shallow flows on the development of

cumulonimbus clouds over Istria

Karmen Babić, Marko Kvakić & Maja Telišman Prtenjak

Department of Geophysics

http://www.gfz.hr/

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CONTENTS:

1. Introduction, aim & motivation

2. WRF model

3. Numerical simulations

4. Summary and conclusions

Department of Geophysics

http://www.gfz.hr/

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Introduction

Department of Geophysics

http://www.gfz.hr/

• The role of the SB circulation, including SB front in triggering convection has long been recognized

•Convection initiation often takes place when 2 or more features (fronts and /or rolls, thunderstorm outflows) collide or merge.

•Locations of the very extensive Cb and SB research, e.g: Florida (e.g. Pielke, 1974; Yuter and Houze, 1995; ) Australia & Indonesian archipelago (MCTEX; e.g. Saito et al., 2001) Japan, Kanto plain (e.g. Sano and Tsuboki, 2006) Spain (e.g. Azorín-Molina et al., 2009) ……

Holland and McBride (1989)

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Department of Geophysics

http://www.gfz.hr/

Italy

CroatiaAlps

Istria: an area with the highest frequency of thunder in Croatia

The mean annual number of days withthunderstorms (1948-1966); Penzar et al. (2001)

Perod: 2006-2009

0

10

20

30

40

50

60

IV V VI VII VIII IX X

months

num

ber

of d

ays

wit

h lig

htni

ng

East Croatia

CentralCroatiamountainousCroatiaNorth Adriatic

CentralAdriaticSouth Adriatic

Lightning data from LINET network

the analysis of some spatial and temporal characteristics of lightning in 4-years warm period (2006-2009)

Arbitrary choiceConvective day = a day with more than

10 strokes of the total discharge data (CG+IC) detected per hour

across limited area

402 convective days

Mikuš et al. (2012)

Climatology of convection in Croatia

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Department of Geophysics

http://www.gfz.hr/

Above northeastern Adriatic

the most common summer weather types during convective days:

non-gradient (NG) pressure conditions & low pressure pattern (C, T)

the peak in daytime convective activity during NG weather type in July

in 82% of overall days with convective activity 3 dominant large-scale windregimes SW, NE, NW

Mikuš et al. (2012)

01020304050607080

IV V VI VII VIII IX Xrela

tiv

e f

req

ue

nc

y (

%)

NG C T A

0

10

20

30

40

50

60

IV V VI VII VIII IX Xrela

tiv

e f

req

ue

nc

y (

%)

SW NW NE W

weather types

wind regimes

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Department of Geophysics

http://www.gfz.hr/

SB climatology over Istria (1997–2006)

∆T → prime peak in August, → secondary max in Junedue to dominance of daytime

convection

SLB frequency→ max in August up to65%of all summer days(June-September)

Pula-airport

1

2

3

4

5

6

7

8

9

10

11

12

VI VII VIII IXmonths

DT

(°C

)

15

25

35

45

55

65

75

SL

B f

req

ue

nc

y (%

)

Pazin

13

16

19

lE

10

l7224

N

1

W

u (m s-1)

v (

m s

-1)

-1

0

1

2

-3 -2 -1 0 1 2

S

hodograph

0

1

2

3

4

5

1 4 7 10 13 16 19 22

t (CET)

Mea

n w

ind

sp

eed

(m s

-1)

0

10

20

30

40

50

60

70

80

90

100

ste

ad

ine

ss

(%

)

Pula-airport

CW rotation of wind vectors

mean SB speed about 3.5 m/s

mean LB speed about 2 m/s

low steadiness of SB between 10-13 CET

In average during summerAt least every second day with SB

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Department of Geophysics

http://www.gfz.hr/

QUESTION:

Sea breeze + large-scale wind

Convective activity?????

Cb development????

QUESTION:

Sea breeze + large-scale wind

Convective activity?????

Cb development????

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Setup of the model: two-way nesting Lambert conformal projection

3 domains : x = 13.5 km, 4.5 km, 1.5 km 81 vertical levels (terrain- following)

Initial and boundary data from ECMWF

Schemes: MYJ scheme for the PBL; RRTM for the longwave radiation; Dudhia scheme for the shortwave

radiation; Lin microphysics scheme; Eta surface layer scheme; five-layer thermal diffusion scheme for the

soil temperature; Betts-Miller-Janjic cumulus

parameterization two outer domain

WRF-ARW model

mzkmztop 10)(,20 min D

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In the finest model domain

date Dominantlarge-scale

wind

Cb durationonset – end

(CET)

SB durationonset – end

(CET)

Max SB speed

Case A 09 July 2006 NE 10:50 – 16:00 9- 19 5.1

Case B 08 June 2003 SW 12:40 - 16:30 9- 20 3.6

Case C 08 August 2006 NW 11:10 – 16:30 9- 13 4.1

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For Case A sensitivity test: without microphysics

Three selected cases simulated by WRF

Similarities the Cb cloud over Istria weather type: almost non-gradient pressure conditions SB at the Pula-airport site (tip of the Istria peninsula).

The main dissimilarity wind regimes

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Department of Geophysics

http://www.gfz.hr/

LINET (CG+IC) data between 14-15 CET

MAX ECHO (DBZ) at 13 CET CASE A = large scale wind NE

-11 CET – formation of convergence zone ( 15 km inland, 75 km long )

- 12 CET – cloudiness and precipitatation 5 mm – 15 mm over Istria

Convective activity

- 13 CET – formation of Cb (Pazin)- 14 – 16 CET – disipation of Cb (moved to south) along convergence zone

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WRF 10-m surface wind at 14 CET

Department of Geophysics

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Measured surface wind field

statistical indices at 14 CET

Wspeed (m/s)

Wdirection

(°)

Temp

(°C)

MAE 1.20 45.45 4.08

RMSE 1.54 64.31 3.39

IOA 0.66 0.89 0.65

20 km

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Department of Geophysics

http://www.gfz.hr/ Results

- large-scale NE wind enhanced the SB at the southeastern Istrian coast

- prevented deeper penetration of the dominant western SB over the peninsula - convergence zone is not moved to east too much

- indication for the superposition between SB front and outflow below Cb along convegence zone

- Sb weaker after the storm; - Cb act destrucive on the air-sea temp. diff.

17 CET

17 CET

Comparison between control A run and sensitivity test

CASE A = large scale wind NE

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WRF 10-m surface wind at 14 CET

11 CET – formation of convergence zone ( 30 km inland, 75 km long )

11 – 12 CET – cloudiness and precipitation 10 mm – 15 mm

Convective activity

Department of Geophysics

http://www.gfz.hr/

CASE B = large scale wind SWMeasured surface wind field

30 km

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deeper penetration of SB inland

convergence zone is moved to east

Department of Geophysics

http://www.gfz.hr/

MAX ECHO (DBZ) at 13:50 CET

CG lightning data at 13:50 CET

13 CET – formation of Cb ( north part of Istria )14 – 16 CET – disipation of Cb

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WRF 10-m surface wind at 14 CET

Department of Geophysics

http://www.gfz.hr/

CASE C = large scale wind NWMeasured surface wind field

30 km -10 CET – formation of convergence zone (30 km, 50 km long – highly curved in space)

- 11 CET – penetration of SB deeper over land (in the central part of peninsula )

-12 – cloudiness and precipitation 5 – 25 mm

convective activity

30 km

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13 CET – Cb moved southward of Istria, Rijeka and Cres (cloudiness and 45 mm precipitation) large-scale NW wind is superimposed on the western SB producing larger inland penetration and amplifying the magnitude of the SB speed 14 – 17 CET – dissipation of Cb

Department of Geophysics

http://www.gfz.hr/

CASE C = large scale wind NWMAX ECHO (DBZ) at 13:50 CET

LINET (CG+IC) data between 14-15 CET

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Summary

-The large-scale winds (LSW) influence the SB development and evolution, therefore creating the zone of convergence

-The interaction SB - LSW reinforces the convergence of the flow field in the boundary layer and consequently the intensity of SB fronts and its updrafts

- The certain amount of cloudiness and precipitation has been developed in the zone of the convergence between 12 CET and 13 CET

- The ZC, cloudiness and percipitation depended on the type of the LSW

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THANK YOU FOR YOUR ATTENTION !!!!!!!!!!!!