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Nowcasting down- valley winds in prealpine shallow valleys

Nowcasting down- valley winds in prealpine shallow valleys. Gert-Jan Duine 1,2 Pierre Durand 1 Thierry Hedde 2 Pierre Roubin 2. 1: Laboratoire d’Aérologie, Université de Toulouse 2: LMTE, CEA Cadarache. Ateliers de Modélisation de l’Atmosphère , Météo France, 18 January 2016.

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Nowcasting down- valley winds in prealpine shallow valleys

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  1. Nowcasting down-valleywinds in prealpineshallowvalleys Gert-Jan Duine1,2 Pierre Durand1 Thierry Hedde2 Pierre Roubin2 1: Laboratoire d’Aérologie, Université de Toulouse 2: LMTE, CEA Cadarache Ateliers de Modélisation de l’Atmosphère, Météo France, 18 January2016

  2. Why study down-valley winds? • Knowledge of down-valley winds essential because: • Modification of general wind pattern • Transport of aerosols or tracer gases • More than 25 % of Earth’s surface is on mountaineous terrain (Barry, 2013) • Knowledge can improve, both on local and regional scale: • Modeling purposes • Impact studies • Risk management • Knowledge is critical for: • Sanitary impact assessment • Atmospheric dispersion of pollutants

  3. Atmospheric dispersion… … in the atmospheric boundary layer Depends on the atmospheric stability in the vertical profile Nighttime: Daytime: Unstable • Relatively high dilution • Low concentration of pollutants Stable • Relatively low dilution • High concentration of pollutants the most penalizing • Thermallydriven wind systems develop

  4. Thermally driven wind systems in complex terrain • Turntwice a day • Horizontal temperature gradients  thermallydrivenwinds • Lowlevel jets • Strongestwithweaksynoptic forcing and clear skies • Affected by along-valleywind system, weather, changingtopography… • Several types, here: thermallydriven down-valleywinds Whiteman (2000)

  5. Study Area N Alps Rhône valley KASCADE campaign Mediteranean Sea KASCADE: KAtabaticwinds and Stability over CAdarache for the Dispersion of Effluents Cadarache: Nuclear research center of Commissariat à l’Energie Atomique (CEA)

  6. Cadarache Valley • Shallow: 100 – 200 m deep • Narrow: 1-2 kmwide • Weakslopeanglealongthevalleybottom: 1.2° • Modifieslocal wind andconsequentlythedispersion: ThermallydrivenCadarache down-valley wind  CDV wind N 125°  Southeasterly directed 1-2 km 5km

  7. La Verrerie (VER) 15 m T,RH,U • Field experiment winter 2013 tocharacterizestability-relatedprocesses in complex terrain • 3-month durationcontinuousobservationsand 23 IOPs • Micro-meteorological instrumentation, sodar, radiosoundings, tetheredballoon • - GBA: Permanentlyinstalled • - M30: Campaigndurationonly • Focus on twodistinctvalleys: • DuranceValley • CadaracheValley GBA 110m T,U N Tethered balloon TB (0 – 300m) p,RH,T,wdir,wspd M30 VER SODAR GBA SODAR (100 – 500m) 30m TB/RS/M30 RS 0-5 km Fluxes 3 levels Radiation 2 levels T,RH 2 levels • Thermally driven down-valley wind in Cadarache Valleyobserved

  8. In the vertical B Tethered balloon A 125° Before sunrise: IOP 15 at 05:00 UTC Wind direction [°] Residual layer Height Stable boundary layer SBL: 250m B 125° A 100m Cadarache down-valley wind Temperature [°C] Wind speed [m/s] • 1 - 4 m/s • Restricted to valley depth

  9. Thermally driven CDV wind GBA: ∆T M30: wind • Dominant wind during winter of 2013 • Stability driven • No permanent observations available in the domain of the wind • Knowledge important for local risk management of Cadarache research center • GBA-tower permanently installed: • Wind at 110 m • Temperature at 2 and 110 m • M30 3-month dataset of wind at 30, 10 and 2 m GBA U110m 110m M30 30 m ∆θ ∆θ =θ110m – θ2m Relate observations of dislocated GBA to temporary wind observations M30 Can we nowcast and maybe predict?

  10. Methodology GBA M30 Threshold optimization procedure Dichotomous forecast verification principle (Wilks, 2000) GBA 110m M30 30 m a: Hit b: False alarm c: Miss d: Correct rejection 3 criterions: ∆θ = θ110m – θ2m U110m RiB Proportion Correct (PC)

  11. 3 candidates examined For 10 m wind GBA U110m [m/s] ∆θ[K] RiB [-] ∆θ : 0.90 at 2.6K U110m: 0.72 at 4 m s-1 RiB: 0.86 at 0.8 Flaws RiB: - Measurement availability non-optimal - Large bulk - Hysteresis behavior

  12. Vertical temperature difference Very stable (∆θ> 2.6 K )  Thermally driven CDV wind Stable to unstable (∆θ < 2.6 K)  No thermally driven CDV wind GBA 110m • High score (0.91) • Other parameters RiB and U110m showed less high scores ∆θ< 2.6 K Stable to unstable ∆T ∆θ > 2.6 K Very stable 2m ∆θ[K] Duine et al. 2015, submitted to JAMC

  13. CDV wind nowcast with ΔT White background: good classification Grey background: wrong classification Very stable (∆θ> 2.6 K ) CDV wind nowcast Stable to unstable (∆θ < 2.6 K) No CDV wind nowcast Valley wind direction - Confirms that CDV wind is thermally driven - Methodology could be eventually used to statistically predict the CDV wind from a 1-km resolution simulation Duine et al. 2015, submitted to JAMC

  14. Generally applicable? Different heights and seasons: No information above 30 meter agl Complementary measurements at 2 m since 2014, which allows further testing the method

  15. Application: Reconstruction CDV wind - 5 years of ∆θ - Exists throughout the year - Strongly related to nighttime duration Duine et al. 2015, submitted to JAMC

  16. Conclusions • Methodology to infer down-valley winds in minimally-instrumented shallow valleys • Data from KASCADE winter field campaign 2013 • Vertical temperature difference can be used to nowcast thermally driven down-valley winds with remote measurements (0.91)  very simple criterion • Defeats wind speed and bulk Richardson number • Threshold Δθ found is valid for different heights and seasons • Work submitted to Journal of Applied Meteorology and Climatology, under revision GBA 110m ∆T 2m

  17. Perspectives • Climatology could be reconstructed • Practical importance for local risk management and impact assessment • Forecasting purpose: • Winds on these scales (=< 1km) not seen by operational and research forecasting models  a combination of dynamical and statistical downscaling Feel free to visit http://kascade.sedoo.fr Data website wit background and documents (PhD-thesis) (…partly under construction)

  18. Merci pour votre attention! Questions? Diurnal wind pattern at Cadarache http://kascade.sedoo.fr gert-jan.duine@aero.obs-mip.fr

  19. Background slides…

  20. Dominant wind during the campaign M30 Cadarache down-valley (CDV) wind Wind direction at 30 m height M30 30 m night day night day sunrise sunset M30: Wind observations at 2, 10 and 30 m Full KASCADE climatology: Data from 13/12/2012 to 18/03/2013

  21. Details on approach Outside SE: b: False alarm d: Correct rejection Inside SE: a: Hit c: Miss Exclude the SE-quadrant --> mixture of synoptical events

  22. 1. Introduction Study area: the Provence • Large variety in orography and land use • Influences of different synoptical and local meteorological events Southern Alps Rhône Valley Durance Valley Mistral Localvalleywinds in stableconditions in theDurancevalley: KASCADE 2013 Cadarache Cloudy / rainy / thunderstorm episodes Sea breezes (spring and summer) 10km Mediterranean Sea

  23. 3. Results - observations (Based on ensemble of 22 IOPs of KASCADE) Valley wind phenomenologyunder weak synoptic forcing and clear skies Diurnal wind pattern at Cadarache Southeasterly wind: GBA 110m Northwesterly wind: ∆T 2m GBA Duine et al. 2015, submitted to QJRMS • Dominant down-valley winds, related to stability • Consequences for pollutant dispersion • Knowledge can be used for numerical modeling validation • High variability below 110 m

  24. Other heights: graph

  25. Stable boundary layer processes Steeneveld, G.J. (2014)

  26. 2. Methodology SODAR IOP during KASCADE (z,t) Height (m) GBA 5000 M30/TB/RS Radio-sounding #3 500 Radio-sounding #1 Radio-sounding #2 TB #1 TB #2 SODAR 300 GBA 100 30 Mast 30 m 10 2 Surface 12:00 00:00 12:00 18:00 06:00 Time (UTC) From 14 January 2013 to 02 March 2013: - 23 IOPs in total, focus around sunset- and sunrise transitions - 760 TB soundings, 61 radio-soundings

  27. La Verrerie (VER) 15 m T,RH,U KASCADE winter of 2013 KAtabaticwinds and Stability over CAdarache for the Dispersion of Effluents Continuousobservations (Dec. 2012 – Mar. 2013): • 3 meteorological stations (GBA, VER, M30) • Sodar Intensive observationperiods (IOPs): • Tethered balloon sessions • Radio-soundings GBA 110m T,RH,U Tethered balloon TB (0 – 300m) p,RH,T,wdir,wspd SODAR M30 VER Goals: • Neededtodescribeprocessesrelatedtostability: • Characterizeatmosphericstability over Cadarache • Characterizewinds in CadaracheandDurancevalleys • Improveprognosticmodeling SODAR GBA SODAR (100 – 500m) 30m TB/RS/M30 RS 0-5 km Fluxes 3 levels Radiation 2 levels T,RH 2 levels • Focus on twodistinctvalleys: • CadaracheValley • DuranceValley

  28. 3. Results - observations A night during KASCADE unstable Temperature: Typically a stable layer starts forming 1 hr before sunset. 30° 30m stable WNW Cadarache valley M30 M30 2m 135° sunset Wind direction: 1. Before sunset: westerly winds 2. After sunset: wind orients in down-valley direction 3. Maintains until sunrise 4. Thermally driven Cadarache down-valley wind 5. In the middle of the night Durance down-valley wind appears 135° 30° sunset

  29. After sunrise: cold pools persist within valleys - Delay in down-valley wind cessation - Pollutants may be trapped under inversion longer than nighttime only Whiteman (1982)

  30. 1. Introduction The atmospheric boundary layer “The atmospheric boundary layer is that layer of the atmosphere which acts directly on processes occurring at or close to the surface.” (Stull, 1988) Mixed layer: Turbulence is dominant process Stable boundary layer: Complex interplayof processes at smaller scales ~1-2 km ~300 m • This picture holds for horizontal, homogeneous and flat terrain • This thesis: focus on stable boundary layer processes over complex terrain

  31. CDV wind forecast: statistical downscaling Based on 23 IOPs  biased to stable conditions

  32. On stability Full campaign (from 13/12/2012 to 18/03/2013) Temperature Sensible heat flux z/L Friction velocity

  33. SBL-formation and local winds NW IOP-12 Sunset 1702 UTC Sunrise 0640 UTC 0630 UTC 135° Wind direction [°] Residual layer hSBL Stable boundary layer 50m Temperature [°C] Wind speed [m/s] - 100m – 500m height: Flow into CV (no blocking hill) - CV drainage flow is formed - CV-flow reaches height of 50m (instead of 100m) - Height of CV-flow important for dispersion • SBL-height = 150m  75m lower

  34. Details on approach thresholding Outside SE: b: False alarm d: Correct rejection Inside SE: a: Hit c: Miss Exclude the SE-quadrant --> mixture of synoptical events

  35. 1. Introduction Valley direction Valley wind relationships Downward momentum transport Thermally driven flow Narrow valleys, Weak synoptic forcing Wide valleys, strong coupling Wide & shallow valleys, lightly to moderate stable conditions Narrow valleys, Unstable/neutral conditions Forced channeling Pressure-driven channeling Adapted from Whiteman and Doran (1993)

  36. Energie Défense Sciences de la matière FAR Saclay Sciences du vivant DIF Valduc Nanotechnologies / NTE Le Ripault Gramat Grenoble Marcoule CESTA Déchets et cycle du combustible Cadarache Fission et fusion research CEA & Cadarache CEA: Atomic Energy Agency 10 research centres, different domains: 1km

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