Numerical modelling of the interaction of soil moisture with planetary boundary layer features and convection over West Africa Leonhard Gantner, Norbert Kalthoff, and Martin Kohler Photo: J. Schwendike Institut für Meteorologie und Klimaforschung (IMK) Forschungszentrum Karlsruhe in der Helmholtz-Gemeinschaft
Motivation and Overview Convective events very important over West Africa especially the Sahel lifecycle of convective Systems and feedback mechanisms We focus here on soil moisture which is showing strong variation over West Africa African Monsoon Multidisciplinary Analysis (AMMA) project COSMO model Local soil moisture pattern and implication for variables in PBL moist convection (MCS) event: sensitivity to soil moisture
Schematic of flow and African Easterly Jet (AEJ) after Parker et al. 2005 AEJ 90 o C θe θe θ 50 o C θ 60 o C Near surface layer 20 o C
NDVI 21-31 August 2000, Pathfinder AVHRR, pronounced meridional gradient of the surface conditions over Africa Shows zonal symmetry
strong gradients in atmosphere and surface conditions low density of measurements AMMA: Dataset of IOP measurements 2006 and aim to improve situation on long term
COSMO model Version 4.0 Mesoscale pattern Moist Convection 14 km horizontal 2.8 km horizontal 35 levels vertical 50 levels extended model-height 28.5 km Tiedtke convection no parameterization of moist convection Two layer soil model TERRA multilayer (8) soil model TERRA Initial and boundary conditions from (GME) ECMWF analyses
Surface Soil moisture: Advanced Microwave Scanning Radiometer Earth Observing System (AMSR-E) 5. June 2006 Soil moisture: gradient and pattern g/cm 3
Changed soil moisture pattern in initial COSMO model field similar to observations Experiment: Initial soil moisture soil moisture experiment - control Vol %
Synoptic Situation during sensitivity experiment COSMO initial conditions and forecast: specific humidity and streamlines
Changed moisture Control surface temperature in K midlevel cloud cover
Changed moisture Control 2 m temperature; 10 m wind 2 m specific humidity; 10 m wind g/kg
Position of cross-sections
Specific humidity and potential temperature along 12N (south of moisture pattern) along 13.5N (through pattern) 400 cooling
Precipitation after 48 h Control run soil moisture experiment
Moist convection on 11. June 2006: preliminary results 1430UTC 1645UTC RDT: Rapid Developing Thunderstorm Product (SAF) nowcasting, mdetection, tracking and discrimination of convective systems using IR10.8 channel of geostationary satellites grey warmer than -65 C -65 to -81 C orange to red below -81 C black Contours yellow red violet blue System detected System growing System mature System weakening 2015 UTC 12 June 0030 UTC Rapid Developing Thunderstorm (RDT) product
TRMM 24h precipitation COSMO Model 24h precipitation
AMSR-E surface soil moisture Values of soil moisture in standard model initialization to high Soil moisture at Dano: IMK mesurement 16 % AMSR 8-14% COSMO ~20% reduce soil moisture to 65%
Dry BIAS ECMWF data because of sondes 8 7 6 0925 UTC 1645 UTC IMK measurements Dano Specific humidity z in km ASL 5 4 3 2 1 300 320 340 0 5 10 15 20 Θ in K q in g kg -1 Model experiments 65% soil moisture PBL height better, but humidity too low
control
65% soil moisture run Convection starts Burkina Faso Benin
Specific humidity (shaded) potential temperature (contours) 65% soil moisture
Vertical velocity Ascent Descent Observed Profiles from Dano Showing downward mixing of dry air in the rear of the MCS Cloud ice Cloud water
summary: Mesoscale soil moisture patterns local flow Pattern in temperature and humidity Influence on clouds, suppression of convection and precipitation over wet patch Soil moisture has strong influence on amount of precipitation Simulation deep convection shows interesting and some realistic features Outlook: IMK soil moisture and flux measurements at Dano/Bontioli model with standalone TERRA and VEG3D Closer look to case study