numerial simulations of convective events – the effect of propagating gust fronts
DESCRIPTION
Numerial Simulations of Convective Events – The Effect of Propagating Gust Fronts. Kaspar and Müller ([email protected]) Institute of Atmospheric Physics ASCR, Prague, CR. H – head height. Simpson (1972). H. gust front. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
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Numerial Simulations of Convective Events
– The Effect of Propagating Gust Fronts
Kaspar and Müller ([email protected])
Institute of Atmospheric Physics ASCR, Prague, CR
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- collision with other gust fronts and convergence lines (Wilson and Schreiber, 1986)
Interaction with environmental air – convection initiation - interaction with ambient vertical shear
(Thorpe et al., 1980; Rotunno, 1988; Moncrieff and Liu, 1999) - interaction with mesoscale oscillations
(Crook et al., 1990)
Gust front = an advancing surface boundary of the outflow of thunderstorm downdrafts cooled by evaporation.
Nowcasting, numerical and analytical studies.(Droegemeier and Wilhelmson, 1987; Liu and Moncrieff, 1996b)
H
H – head heightSimpson (1972)
gust front
Motivation
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Methodology (Kaspar, 2003)
LM COSMO thermodynamic data, 2.8km (Doms and Schättler, 1999)
Model for the Objective Analysis of Gust Fronts (OAGF)
LOCATION 3-dim. position (thermal def.)
head heightMORPHOLOGY
MOVEMENT speed vector
VERTICAL SHEAR regime of propagation (Liu and Moncrieff, 1996a)
STABILITY potential instability, LCL
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Propagating regimeUpshear movementDownshear movement
Steering-level (hs) regimeDownshear movement with an overturning updraft
Vertical shear conditions
Relative flow1
2
3
1
2
3
Convection initiation(a) PI and a low LCL
all regimes(b) PS and / or a high LCL
the steering-level and downshear prop. regime
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OA gust fronts + surface precipitation rates [mm/h]OA gust fronts + vertical velocities [m/s]OA gust fronts + potential temperature [K]
Case study 2.7.2000- validation tests
Radar SkalkyZmax
13UTC 14UTC 15UTC
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Case study 2.7.2000Height of OA gust heads + RSM [dBZ] (Haase and Crewell, 2000)
Downshear propagating regime
c0=7.1m/sH =1180m
PI + decreasing LCL
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Case study 22/23.7.1998- squall line (Salek, 2000)
01UTC 02UTC 03UTC
SkalkyZmax
OA gust fronts + surface precipitation rates [mm/h]
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Case study 22/23.7.1998OA gust heads + RSM [dBZ]
Steering-level regime
c0=5.1m/sH=1343m
Potential stability + increasing LCL
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Conclusions
The validation tests confirmed the applicability of the LM COSMO-OAGF chain in the case of both isolated and multicellular convection.
The propagating gust fronts had the potential for convection initiation in both presented case studies.- 2 July 2000:
favourable vertical shear, humidity and stability conditions- 22 / 23 July 1998:
favourable vertical shear conditions
- the both case studies are included in a paper accepted for Atmospheric Research (2006)
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The tuning and verification of the OAGF will continue.- radar data assimilation- locating procedures based on the analysis of wind field …
The products of the OAGF are assumed to be used in formulating decision criteria.- total index quantifying the potential of a gust front to trigger
new convection
Outlooks
Acknowledgement: GA ASCR B3042404, GACR 205/04/0114DWD (LM and RSM codes), CHMI (radar pictures)
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thank you for your attention
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