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Title and Authors
On Convective Severe Weather Forecasts.
Empirical Relations vs the Theoretical
Approach
by(1)Gallai I., (1,2)Giaiotti D. B., (3,4)Gladich I., (1,2)Stel F.
(1)ARPA FVG - OSMER - Visco (UD) - ITALY
(2)ESSL - Wessling - GERMANY
(3)University of Trieste - Trieste - ITALY
(4)ICTP - Trieste - ITALY
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
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Outline of the presentation
• Common aspects of the atmospheric hazards related to convective severe weather events.
• Expected improvements of convective severe weather events forecasts.
• Brief review and discussion of the most used empirical forecasting rules.
• Important aspects connected with the empirical rules used for severe convection forecasts.
• A strategy for forecasts improvement.
• Interdisciplinary studies stimulated by the specific problem.
• Conclusions.
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
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Common aspects of convective severe weather events
Convective Severe Weather Events
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Large Hail Flash FloodsIntense
Donwndrafts Tornadoes
Intense Electrical
Activity
Intense Vertical Vortex
(Mesocyclones, Tornadoes)
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Expected improvements of convective severe weather events forecasts.
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Improvement of convection ignition
forecast
Improvement of boundary conditions
forecast
Improvement of instability forecastNumerical Models
LAMs
Empirical Rules
Theory of Severe
Convection
Atmospheric Convection
Severe Atmospheric Convection Tools for Improvement
LAMs Outputs
quality
Severe Convection
Forecast qualityNot sufficient,
but necessary condition
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Theoretical basis of empirical rules for intense vertical vortex forecast
•How to generate intense vertical vortexes at the mesoscale?
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
The basic idea is to tilt the horizontal environmental vorticityand then stretch the vorticity along the vertical
Lagrangian
differential
approach
since Davies-Jones
Klemp & Rotunno
Weisman & Klemp
works in 1980’s
This consideration leads to the study (and as a consequence to forecast)
the environment where vortexes form: wind shear, thermal-moisture
boundaries and buoyancy.
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The most used empirical rules for intense vertical vortex forecast
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Rasmussen and Blanchard
Wea. Forecasting 1998
Brooks et al
Wea. Forecasting 1994
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The most used empirical rules for intense vertical vortex forecast (cont’d)
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Bulk Richardson Number
Vorticity Generation Parameter
VGP = S (CAPE)1/2
Rasmussen and Blanchard
Wea. Forecasting 1998
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Discussion on the most used empirical forecasting rules.
The empirical rules in use have been calibrated on specific data sets
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
NSSL - Brooks H., courtesy
Weakening of the
empirical rule
Missing alarms are frequent
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Discussion on the most used empirical forecasting rules (cont’d)
The functions used as forecasting rules have high sensitivity to the variables
uncertainty in those regions of the domain where we are mostly interested in.
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
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Important aspects connected with deep severe convection forecasts.
The empirical rules come from integral (global) properties of the environment,
even if they have been inspired by differential considerations.
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
DisadvantagesRelevant small scale and time fluctuations may be smoothed out
AdvantagesEasy to apply
• from routine measurements
• from numerical model outputs
• for climate change downscaling
Expected due to
climate change
Actual climatology
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A strategy for forecasts improvement (both weather and climate change).
• Increase spatial resolution. Boundary
Layer (LES Moeng C.H. 2007 EMS meeting)
• Physics of the model (microphysics)
(WRF community)
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Numerical Models
LAMs
Empirical Rules
Theory of Severe
Convection
Areas of the Improvement
• Integral approach to the vertical
vorticity generation (Gladich, Giaiotti, Stel)
• Bifurcations of small scale fluctuations
(Gladich, Giaiotti, Stel)
• Extend the statistics to all areas
(ESWD, Pucillo, Gladich, Giaiotti, Stel)
• Interdisciplinary experiments
(Sommer A. P.)New forecast tools
+
+
=
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Interdisciplinary studies stimulated by the specific problem
The understanding of reality sometimes pass through the the study of analogies among very different phenomena.
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Evaporation of a water drop containing polystyrene nanospheres, in particular experimental conditions. The distribution of the spheres reveals the presence of intense vertical vortexes in the drop during the evaporation process. Experiment made by Sommer A. P. Ulm University; Germany (Picture taken form Cryst. Growth Des. March 2007, courtesy by Sommer A. P.)
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Interdisciplinary studies stimulated by the specific problem (cont’t)
Bifurcations in the trajectory of the representative point on the
empirical rules diagrams
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
Bifurcation point
Vortex occurrence
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Conclusions
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007
• Nowadays, the operational forecasts of convective severe weather events are based on two relevant elements:
- High resolution numerical model forecasts- Empirical rules
• Improvements in the convective severe weather forecast should come from:
- Improvement of high resolution numerical model forecasts- Theory of intense vertical vortex formation at mesoscale- Adaptation of the empirical rules to new data sets
• New insights into the empirical rules could come from fields not strictly related to the atmosphere physics (interdisciplinarity)
•There are attractive perspectives in the application of the empirical rules to speculate projections on the future convectivesevere storms climatology from climate change scenarios
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Title of slide
Regional Agency for Environmental Protection
of
Work part-financed by the European Union Community Initiative INTERREG III B Alpine Space - project FORALPS
7th EMS Annual Meeting/ 8th ECAM - El Escorial, Spain, 01-05 October 2007