the impact of convergence zones on the initiation of deep convection

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7th COPS WorkshopCollège Doctoral Européen

Strasbourg, France, 27 - 29 October 2008

The impact of convergence zones on the initiationof deep convection

Bianca Adler

The impact of convergence zones on the Initiation of Deep Convection

B. Adler*, N. Kalthoff, Ch. Barthlott, U. Corsmeier, S. Khodayar, Ch. Kottmeier, K. Träumner, S. Mobbs, S. Crewell, V. Smith

* Institut für Meteorologie und Klimaforschung, IMKKarlsruhe Institute of Technology, KIT

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Bianca Adler

• 1500 UTC: deep convection southeast of Freudenstadt with rain rate of roughly 21-35 mm h-1

• Question: Why did deep convection develop and why only over the Black Forest area?

1500 UTC

• 1115 UTC: first cumulus clouds over Black Forest

• 1230 UTC: cumulus clouds over Vosges; two weak north-south oriented cloud bands east of Black Forest crest

1230 UTC1430 UTC

• 1400 UTC: both cloud bands intensified

• 1430 UTC: isolated deep convective cells with rain rates of roughly 5-8 mm h-1

IOP 8b (15 July 2007)

1. Evolution of deep convection

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Bianca Adler

• COPS area was in the transition zone between an eastern Atlantic trough and an eastern European ridge

• Surface low in the west (south-westerly wind) and surface high in the east (easterly wind), convergence in between

• No significant upper level lifting in the COPS area

2. Synoptic conditions

1200 UTC

1800 UTC

hPa h-1

1200 UTC

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Bianca Adler

Achern, 1100 UTC

2. Convective conditions

30223260783611129Heselbach

25793577327901059Achern

243836762534831100Burnhaupt

279732291474081100FZK

CCL(m asl)

LFC(m asl)

CIN(J kg-1)

CAPE(J kg-1)UTC

Achern (Rhine valley): low CAPE, high CIN

Heselbach (Black Forest): moderate CAPE, lower CIN

• Conditions not too favourable for deep convection

• If trigger mechanism present, convection most likely in Black Forest area

Heselbach, 1100 UTC

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Bianca Adler

• 0700 to 0800 UTC: Onset of up-slope winds resulting in convergence over the mountain crest

3.1 PBL processes relevant for triggering of convection

western slope eastern slope

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Bianca Adler

3.2 Evolution of a convergence zone between the surface low and high

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Bianca Adler


Meistratzheim

• change from SE to SW wind finished at 1000 UTC in lowest 2 km

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Bianca Adler

Achern

• change from SE to NW wind finished at 1030 UTC


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Bianca Adler

Hornisgrinde: • 1100 UTC change from SE to W wind • convergence zone SUPERIMPOSES on the stationary slope-wind generated one • updrafts of 2 m s-1 extend up to 3100 m asl penetrate capping inversion and nearly reach LFC• 15 min after the convergence zone passed the Black Forest crest first clouds formed


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Bianca Adler


Barongartenhütte

• change from SE to NW wind finished at 1330 UTC

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Bianca Adler

Heselbach

• change in wind direction from SE to SW in lowest 2 km finished at 1400 UTC

• base of deep convection at 2.5 km agl (3 km asl)

• at the same time increase of humidity


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Bianca Adler


Igelsberg

• change from SE to SW wind finished at 1400 UTC

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Bianca Adler


DO 128: 1217 – 1328 UTC, flight level: 1500 m asl

• near Barongartenhütte vertical updrafts up to 3.5 m s-1 (DO 128)

• over Murg valley updrafts up to 5 m s-1 (BA 146; flight level: 1900 m asl)

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Bianca Adler

• 15 July 2007 deep convection developed over the Black Forest area

• Conditions were not too favourable for convection, because

– high CIN and moderate CAPE

– no significant upper air lifting

– If a trigger mechanism was present, the Black Forest area would be slightly favourable to the evolution of deep convection

• The reason for development of convection was an optimal superposition of different convergence zones over the Black Forest resulting in vertical updrafts of about 2 m s-1 which penetrated the lids and triggered convection

• East of the Black Forest crest the convergence zone intensified, strong updrafts of up to 5 m s-1 below convective cells were measured

Summary

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Bianca Adler

Thanks for your attention!

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Bianca Adler

• 0748-0900 UTC: Dornier 128 flight at level 1500 m asl SW wind in the whole COPS domain• along Black Forest crest vertical velocity up to 0.5 m s-1 • 1217-1328 UTC: SW wind in most parts

the impact of convergence zones on the initiation of deep convection

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