Forecasting convective initiation over Alpine terrain by means of automatic nowcasting and a high-resolution NWP model Georg Pistotnik, Thomas Haiden,

Forecasting convective initiation over Alpine terrain by means of automatic nowcasting and a high-resolution

NWP model

Georg Pistotnik, Thomas Haiden, Christoph Wittmann

2009-10-27

CSIP & COPS Meeting 2009, Cambridge

Overview

Contents:

1. What is INCA, ALADIN, AROME?

2. Previous work on convective initiation (INCA / ALADIN framework)

3. Future work on convective initiation (INCA / AROME framework) – a test case

4. Conclusions and expectations

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What is … INCA?

high resolution analyses and (short range) forecasts

(Δx = 1 km, Δt = 15min or 60 min)

station measurementsradar and satellite data

high resolution topographic data

INCA

NWP model data

Integrated Nowcasting through Comprehensive Analysis (INCA):

http://www.zamg.ac.at/fix/INCA_system.pdf

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What is … ALADIN, AROME?

Limited area NWP models ALADIN and AROME:

ALADIN AROME

update frequency: 6 hours 24 hours

domain: Central Europe Austria (plus near surroundings)

forecast range: 72 hours 30 hours

horizontal resolution: 9.6 km 2.5 km

vertical resolution: 60 levels 60 levels

treatment of convection: parameterization explicit simulation

status: operational testbed

use in INCA: background fields no

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Previous work

INCA precipitation (2D):• Analysis generated by optimized combination of station

measurements and radar data• Pure nowcast (extrapolation of analysis) from t0 to t0+2h• NWP forecast (optimized combination of ALADIN and ECMWF)

beyond t0+6h• Linear transition in-between

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Previous work (2)

INCA temperature and humidity analysis (3D):• ALADIN forecast interpolated onto INCA grid• 3D correction by observations• Physical assumptions to allow boundary layer effects=> Input for analysis of convective indices (CAPE, CIN, …)

INCA wind analysis (3D):• ALADIN forecast interpolated onto INCA grid• 3D correction by observations• Relaxation algorithm to ensure mass-consistency=> Input for analysis of moisture flux convergence

Replace conventional nowcasting by „convective nowcasting“!

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For each `convective‘ gridpoint(i.e., with CAPE > 0 J/kg):

Initiation?

Intensification?

Weakening?

Previous work (3)

Predicted if:CAPE > CAPEstart (100 J/kg)MOCON > MOCONstart (2*10-

7 /s)VIS > VISstart (0.5)| CIN | < | CINstart | (200 J/kg)ΔTtrig > ΔTtrigstart (-2 K)

Predicted if:CAPE > CAPEint (50 J/kg)MOCON > MOCONint (2*10-

7 /s)RR > RRint (0.2 mm/h)| CIN | < | CINint | (200 J/kg)ΔTtrig > ΔTtrigint (-2 K)

Predicted if:CAPE < CAPEweak (50 J/kg)MOCON < MOCONweak (0 /s)RR > RRweak (0.0 mm/h)| CIN | > | CINweak | (200 J/kg)ΔTtrig < ΔTtrigweak (-4 K)

RRmax = RRmax (CAPE, q);RR (t, RRmax) assumed to show Gaussian variation in time

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CSIP & COPS Meeting 2009, Cambridge Precipitation

analysist = t0

[mm/15min]

Previous work (4)

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Initiation!

Precipitation analysis

t = t0+60min [mm/15min]

Previous work (5)

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Initiation area

CAPE analysis

t = t0 [J/kg]

Previous work (6)

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Initiation area

MOCON analysis

[10-9/s]

Previous work (6)

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Initiation area

Previous work (7)

VIS signal analysis

[ ]

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Initiation area

Previous work (8)

convective nowcast of

precipitation [mm/h]

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Previous work -> future work

Verification of convective nowcast:

• Minor improvement in Alpine catchments• Essentially neutral results in non-Alpine catchments• No operational implementation yet (due to risk of false alarms)• But: encouragement to resume research again

=> Conclusion: knowledge of near-surface wind field is limiting factor

=> Question: Can we gain any profit by using the new high-resolution AROME model?

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Future work – a test case (1)

July 09th, 2009 – INCA analyses 07-19 UTC

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July 09th, 2009 – AROME forecasts 07-19 UTC

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July 09th 2009, 11 UTC:AROME forecast (left);INCA analysis (below)

primary convection

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transition from primary to secondary convection

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secondary convection

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Conclusions and expectations

(Subjective) percipience of AROME:

1. Primary convection:

Convective initiation too early and too widespread;Good skill in predicting wind field

2. Secondary convection:

Usually over-estimation of convective precipitation;Wind field gets increasingly disturbed by exaggerated „model gust fronts“

=> Pre-convective wind field may prove helpful in automatized detection of convection-prone areas

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Conclusions and expectations (2)

Goals:

• To improve nowcasting by adding ability to simulate initiation and life cycle of convective cells

• Comparison between advanced nowcasting methods and high-resolution NWP model

• Validation of strengths and weaknesses of a high-resolution NWP model (both important for forecasters and model developers)

• Systematic analysis of predictability of Alpine convective initiation on a 10-20 km scale

(=> Towards replacing ALADIN by AROME as an input in INCA)

Documents

Forecasting convective initiation over Alpine terrain by means of automatic nowcasting and a high-resolution NWP model Georg Pistotnik, Thomas Haiden,