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Georg Pistotnik , Thomas Haiden, Christoph Wittmann

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Georg Pistotnik , Thomas Haiden, Christoph Wittmann

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

  2. Overview CSIP & COPS Meeting 2009, Cambridge • Contents: • What is INCA, ALADIN, AROME? • Previous work on convective initiation (INCA / ALADIN framework) • Future work on convective initiation (INCA / AROME framework) – a test case • Conclusions and expectations

  3. What is … INCA? CSIP & COPS Meeting 2009, Cambridge Integrated Nowcasting through Comprehensive Analysis (INCA): radar and satellite data station measurements NWP model data INCA high resolution analyses and (short range) forecasts (Δx = 1 km, Δt = 15min or 60 min) high resolution topographic data http://www.zamg.ac.at/fix/INCA_system.pdf

  4. What is … ALADIN, AROME? CSIP & COPS Meeting 2009, Cambridge Limited area NWP models ALADIN and AROME:

  5. Previous work CSIP & COPS Meeting 2009, Cambridge • 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

  6. Previous work (2) CSIP & COPS Meeting 2009, Cambridge • 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“!

  7. Previous work (3) CSIP & COPS Meeting 2009, Cambridge For each `convective‘ gridpoint (i.e., with CAPE > 0 J/kg): • Initiation? • Intensification? • Weakening? • 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

  8. Previous work (4) CSIP & COPS Meeting 2009, Cambridge Precipitation analysis t = t0 [mm/15min]

  9. Previous work (5) CSIP & COPS Meeting 2009, Cambridge Precipitation analysis t = t0+60min [mm/15min] Initiation!

  10. Previous work (6) CSIP & COPS Meeting 2009, Cambridge CAPE analysis t = t0 [J/kg] Initiation area

  11. Previous work (6) CSIP & COPS Meeting 2009, Cambridge MOCON analysis [10-9/s] Initiation area

  12. Previous work (7) CSIP & COPS Meeting 2009, Cambridge VIS signal analysis [ ] Initiation area

  13. Previous work (8) CSIP & COPS Meeting 2009, Cambridge convective nowcast of precipitation [mm/h] Initiation area

  14. Previous work -> future work CSIP & COPS Meeting 2009, Cambridge • 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?

  15. Future work – a test case (1) CSIP & COPS Meeting 2009, Cambridge July 09th, 2009 – INCA analyses 07-19 UTC

  16. Future work – a test case (2) CSIP & COPS Meeting 2009, Cambridge July 09th, 2009 – AROME forecasts 07-19 UTC – – –

  17. Future work – a test case (3) CSIP & COPS Meeting 2009, Cambridge July 09th 2009, 11 UTC: AROME forecast (left); INCA analysis (below) – – – primary convection

  18. Future work – a test case (4) CSIP & COPS Meeting 2009, Cambridge July 09th 2009, 14 UTC: AROME forecast (left); INCA analysis (below) – – – transition from primary to secondary convection

  19. Future work – a test case (5) CSIP & COPS Meeting 2009, Cambridge July 09th 2009, 17 UTC: AROME forecast (left); INCA analysis (below) – – – secondary convection

  20. Conclusions and expectations CSIP & COPS Meeting 2009, Cambridge • (Subjective) percipience of AROME: • Primary convection: • Convective initiation too early and too widespread; • Good skill in predicting wind field • 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

  21. Conclusions and expectations (2) CSIP & COPS Meeting 2009, Cambridge • 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)