1 / 11

Impact of Surface Properties on Convective Initiation in the Sahel

Impact of Surface Properties on Convective Initiation in the Sahel. Amanda Gounou (1) , Christopher Taylor (2) , Francoise Guichard (1) , Phil Harris (2) , Richard Ellis (2) , Fleur Couvreux (1) and Martin De Kauwe (3) CNRM (CNRS, Météo France), Toulouse, France

iram
Download Presentation

Impact of Surface Properties on Convective Initiation in the Sahel

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Impact of Surface Properties on Convective Initiation in the Sahel Amanda Gounou(1), Christopher Taylor(2) , Francoise Guichard(1), Phil Harris(2) , Richard Ellis(2), Fleur Couvreux(1) and Martin De Kauwe(3) CNRM (CNRS, Météo France), Toulouse, France CEH, Wallingford, United Kingdom Macquarie University, Sydney, Australia

  2. Introduction and Motivations • 80% rainfallgenerated by MCSs AMSR-E soilmoisture • MCS createstrong surface moistureheterogeneities in the Sahel • Boundary layer properties (& instability) • largely influenced by soil moisture • (Taylor et al.,2007, Couvreux et al., 2009) • Cases studies (obs, modelling) suggest that convection is more favoured over dry surface and moisture gradients could be important for initiations • (Taylor and Ellis, 2006, Taylor, 2009, Gantner and Kalthoff, 2009) Fig. Taylor • Whatis the climatologicalsignificance of thesemechanisms?

  3. Methodology of the study => StatisticalApproachbased on large datasets of satellite observations • Combine datasets of: • satellite observations of MCS initiations • satellite estimates of surface properties • Atdifferentspacescales: • mesoscale (1°x1°) • atfinerscale (few tens of kms)

  4. Satellite Datasets Location of daytime MCS initiations Backtrackingmethod: IRT MSG contours at -40°C (CEH) Domain: Sahel (10N-20N and 10E-10W) 5 years of data: Jun-Sept 2006-2010 Underlying Surface PropertyEstimates SoilMoistureEstimates ~1cm MicrowaveAMSR-E (AQUA) ……………… Resolution: ~40km ………………………… Data available in all atmospheric conditions…. Land Surface Temperature Anomalies (LSTA) (Proxi for soilmoisture anomalies) Infrared MSG Resolution: ~3km Data available in clearsky conditions Precise location of more than 3000 observed initiations of MCS Underlying surfaces characterised by twodifferentproducts

  5. Systems preferentiallydevelop over particular surface properties? AMSR-E soilmoisture More variability Dry 1°x1° Initiation? Land Surface Temperature Anomalies yes no More variability Initiation distribution Reference Distribution Warm (dry) MCS initiations more likely over drier surface presenting more variabilityat 1°x1° scale

  6. Atfinerscale, influence of LSTA gradients? Computation of LSTA gradient alongwind direction: -centeredat initiation (I) - in the environment I 2° Synoptic wind + - 4° 44 gradients sampled in the environment on a regulargridcentered on initiation Sampling of the gradients at initiation location compared to itsenvironment negative gradients

  7. Atfinerscale, influence of LSTA gradients? 38% of initiations occur over gradients < 1st decile (25%) =>13% additional initiations over large negative gradients => 1 in 8 of all MCS Synoptic wind + - MCS initiations preferentially over warm to cool transitions along the wind direction (1 in 8 of all MCS) negative gradients

  8. Atfinerscale, influence of LSTA gradients? Composite of LSTA centered on initiations Variability of LSTA sorted as a function of LFC Low LFC Cross-wind distance (km) High LFC= Lessfavourable for MCS initiation Along-wind distance (km) High LFC: initiations increasewithsoilmoisturevariability. => Heterogeneities help the triggering of convection thatwould not happenotherwise Initiations preferentially over the warm part of a cold-warm-cold transition Circulation opposite to synopticwind direction induced by moisture gradient allows to overcome inhibition

  9. Conclusions At 1°x1° scale: development of convection over dry surfaces presenting more variability (sameresultswith 2 differentproducts) At few tens of km scale: Development of MCS over negative gradients mesoscale circulation in opposite direction withsynopticwindthathelpstriggering of deep convection AdaptedfromGarcia-Carreras et al., 2010 1 MCS over 8 triggered over large negative gradients => Important triggeringmechanism

  10. Perspectives • Need to parameterisethismechanism in numericalmodels? • Is thismechanismobserved in other parts of the world?

  11. Thankyou for your attention Taylor, Gounou, Guichard, Harris, Ellis, Couvreux and De Kauwe: Frequency of Sahelian storm initiation doubled over mesoscale soil moisture patterns, Nature Geosciences, in revision See also: Poster XY30: Simulation of daytime convective initiation in the Sahel: an evaluation of numericalweatherforecastmodelswith satellite dataFrançoise Guichard, Christopher M. Taylor, Amanda Gounou, Fleur Couvreux, Richard J. Ellis, and Philip P. Harris

More Related