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1 Impact of the large-scale wind and mesoscale shallow flows on the development of cumulonimbus clouds over Istria Karmen Babić, Marko Kvakić & Maja Telišman.

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Presentation on theme: "1 Impact of the large-scale wind and mesoscale shallow flows on the development of cumulonimbus clouds over Istria Karmen Babić, Marko Kvakić & Maja Telišman."— Presentation transcript:

1 1 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

2 2 CONTENTS: 1.Introduction, aim & motivation 2.WRF model 3.Numerical simulations 4.Summary and conclusions Department of Geophysics

3 3 Introduction Department of Geophysics 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)

4 4 Department of Geophysics Italy Croatia Alps Istria: an area with the highest frequency of thunder in Croatia The mean annual number of days with thunderstorms ( ); Penzar et al. (2001) Lightning data from LINET network the analysis of some spatial and temporal characteristics of lightning in 4-years warm period ( ) Arbitrary choice Convective 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

5 5 Department of Geophysics 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 wind regimes  SW, NE, NW Mikuš et al. (2012) weather types wind regimes

6 6 Department of Geophysics SB climatology over Istria ( 1997–2006) ∆T → prime peak in August, → secondary max in June due to dominance of daytime convection SLB frequency → max in August up to 65%of all summer days (June-September) Pazin hodograph 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 CET In average during summer At least every second day with SB

7 7 Department of Geophysics QUESTION: Sea breeze + large-scale wind  Convective activity?????  Cb development???? QUESTION: Sea breeze + large-scale wind  Convective activity?????  Cb development????

8 8 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 Department of Geophysics

9 9 In the finest model domain dateDominant large-scale wind Cb duration onset – end (CET) SB duration onset – end (CET) Max SB speed Case A09 July 2006NE10:50 – 16: Case B08 June 2003SW12: : Case C08 August 2006NW11:10 – 16: Department of Geophysics 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

10 10 Department of Geophysics LINET (CG+IC) data between 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

11 11 WRF 10-m surface wind at 14 CET Department of Geophysics Measured surface wind field statistical indices at 14 CET Wspeed (m/s) Wdirection (°) Temp (°C) MAE RMSE IOA km

12 12 Department of Geophysics 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 Comparison between control A run and sensitivity test CASE A = large scale wind NE

13 13 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 CASE B = large scale wind SW Measured surface wind field 30 km

14 14  deeper penetration of SB inland  convergence zone is moved to east Department of Geophysics 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

15 15 WRF 10-m surface wind at 14 CET Department of Geophysics CASE C = large scale wind NW Measured 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

16 16  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 CASE C = large scale wind NW MAX ECHO (DBZ) at 13:50 CET LINET (CG+IC) data between CET

17 17 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

18 18 THANK YOU FOR YOUR ATTENTION !!!!!!!!!!!!


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