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Analysis of water vapour variability and its links with convection:

Analysis of water vapour variability and its links with convection: some IHOP_2002 preliminary results Guichard, F., Flamant, C., van Baelen, J., Bock, O., Couvreux, F., Parsons, D., Weckwerth, T., Pelon, J., Drobinski, P., Lhomme, K., Doerflinger, E. ~ some information on our activities

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Analysis of water vapour variability and its links with convection:

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  1. Analysis of water vapour variability and its links with convection: some IHOP_2002 preliminary results Guichard, F., Flamant, C., van Baelen, J., Bock, O., Couvreux, F., Parsons, D., Weckwerth, T., Pelon, J., Drobinski, P., Lhomme, K., Doerflinger, E. ~ some information on our activities in the years to come + data

  2. IHOP : International H2O experiment • (see Weckwerth et al. 2003) • PIs: Tammy Weckwerth & D. Parsons • objectives • to get the best possible characterization of the 4D (x,y,z,t) water vapour field; • to evaluate how this can lead to improvement in our current understanding and prediction of convective processes. • motivations • poor forecast skill for rainfall (challenge for future NWP); • behind this, a lack of knowledge and understanding of small-scale processes and mechanisms involved in convective phenomena; • though moisture is a key parameter, it is not properly measured. • the IHOP experiment(when, where, who?) • 13 May – 25 June 2002, in the Southern Great Plains • ~250 researchers (USA, Germany, Canada & France) • ~50 instrumented platforms (fixed and mobiles - 6 airplanes, trucks) • soundings (> 2500), radars, lidars, interferometers, GPS…

  3. Lidar LEANDRE 2 • measures of water vapor mixing ratio rv • (differential absorption, 2 l) • Dx ~ 10 m • on board the P-3 airplane • vertical cross section + • for the first time ever, horizontal cross sections of rv • 142 h of flight, ~ 25 cases • GPS(global positionning system) • measurements ofprecipitable water • continuous flow of data Dt ~ 15 min • tomography(dz ~ 200 m in BL to 1 km above) • 7 stations added to the existing networks • (ongoing projects for future assimilation in NWF models) • seeVan Baelen et al.poster G4- P0637tomorrow

  4. SOME OF THE TOPICS INVESTIGATED WITHIN IHOP • boundary layer processes, diurnal cycle, W-E gradients • organization, rolls, variability • impact on convective initiation • the « dryline », a common mesoscale phenomena there • playing a strong role in convective initiation • moist air from the Gulf of Mexico meeting warm air from the Rockies • Strong moisture gradient in the boundary layer • (width ~10 km, length ~100 km and more) • convection typically develops within a few 10’s of km from the dryline (Bluestein & Parker 1993) • bore-type events(very frequent, surprising observations from IHOP) • life cycle • impact on the maintenance of nighttime convection quantitative precipitation forecast (QPF), see D. Parsons

  5. SOME PRELIMINARY RESULTS boundary layer evolution (diurnal cycle) bore-type events assimilation of boundary layer data in mesoscale model

  6. total hydrometeor mixing ratio, function (time, height) boundary layer evolution: basic considerations r0 (z) CRM simulation Dx =2km diurnal convection over land local solar time r0 (z) - ~1g/kg(z<1.5 km) convection very sensitive to the initial moisture profile (Crook 1996) before the onset of deep convection, the evolution is partly controlled by small scale boundary layer processes; results sensitive to subgrid-scale parameterizations («mechanistic» BL schemes recently developed)

  7. - 10 - 15 - 20 - 25 - 30 - 35 - 40 - 45 ~10 km Boundary layer evolution: WCR (t-x,z) data, courtesy of B. Geerts 7h30 reflectivity (dBz) ~ 8h ~ 9h ~10h 14 June local solar time 10h45 11h30 ~1.5 km bug plumes linked to w

  8. designing an LES case study choice of initial conditions ? evaluation of mean fields?

  9. D rv ~ 1 g/kg D q < 1 K general agreement with Weckwerth (1996)

  10. without large-scale advection with large-scale advection • impact on the BL mean diurnal evolution • of uncertainties in • the initial conditions (mesoscale variability) • surface heat fluxes (Bowen ratio) • larger-scale advection (weak wind conditions) • similar range of sensitivity • (1D tests with MesoNH)

  11. 2 km 6.8 km preliminary LES results with MesoNH (dx = 100m Lx = 5 km) rv distribution z = 1500 m color: rv (kg/kg) / isolines: w (m/s) z = 800 m

  12. spatial & temporal organisation, variability, comparison with LEANDRE 2 data … ongoing work L2 data, 14 June 2002

  13. gravity current stable layer from Locatelli et al. (1998) almost 30 bore-like events observed, not expected impact on convective initiation? bore: type of gravity wave disturbance propagating ahead of a gravity current … that may further evolves into a sequence of solitary waves … a very idealized picture

  14. 3 3 T0 + 40 min 37.2 37.0 36.8 36.6 36.4 36.2 37.4 2 2 1 1 T0 + 2h30 3 2 1 temporal evolution of a bore: mixing ratio rv (x,z) measured by LEANDRE2 height AGL (km) T0 ~22h30 (lst) other observations model performance latitude ~150 km

  15. Couvreux, Weckwerth and Pinto (2003) convective rain along a convergence line assimilation of data from 6 interferometers in a mesoscale model (MM5) Dx ~10 km (q & qv profiles below 3km) can be quite positive (IHOP period investigated) OBS: radar data almost no rain rain MM5 standard model MM5 with assimilation

  16. conclusion, perspectives • a very large dataset has been collected documenting • boundary layer diurnal cycle • boundary layer spatial heterogeneity • convective initiation phases (with/without convection) • bore-type phenomena • On-going activity : • analysis of data, cross-instruments validation • boundary layer evolution (regimes: rolls, plumes…) • LES validation (unique dataset) • modelling: jump to nested simulation, trajectory analysis • bore: true bore? life cycle? role in the maintenance of convection? • agreement with hydraulic theories?

  17. the end

  18. XY section in the middle of CBL (700 m) at 16h local solar time W rv

  19. rolls in the boundary layer dry-line

  20. CI mission 19 June 2002 Blind zone LEANDRE 2 data: horizontal cross section of rv in the boundary layer, 1500 m AGL (sideway pointing) through a « dry-line »

  21. Solitary wavetrain within the bore system as seen in the MAPR vertical velocity data (4 June 2002) S-Pol 0.5-degree elevation angle reflectivity 0645 UTC 4 June 2002. from Weckwerth et al. (2003)

  22. height AGL (km) 3 3 37.2 37.0 36.8 36.6 36.4 36.2 2 2 18 1 1 16 14 height AGL (km) 12 10 8 6 4 ~130 km observations LEANDRE 2 mesoscale model Dx = 10 km (MM5)

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