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Jean-Marcel PiriouCentre National de Recherches MétéorologiquesGroupe de Modélisation pour l’Assimilation et la Prévision
Evolution of convective cloud top height:entrainment and humidifying processesEvolutionEvolution of convectiveof convective cloudcloud toptop heightheight::entrainment and humidifying processesentrainment and humidifying processes
EUROCS Workshop, Madrid, 16-19/12/2002
SummarySummary
Questions:
1. (1D EUROCS idealized humidity case, 3D) What impact on diurnal cycle if the ARPEGE convective scheme sensitivity to humidity is removed?
2. (1D EUROCS diurnal cycle of deep convection case, 3D) Cloud topheight evolutions: link with saturation deficit & its diurnal phase
EUROCS idealized humidity case
ARPEGE operational version
MassMass fluxesfluxes forforthethe 44environmental environmental humiditieshumidities
Precipitations vs thePrecipitations vs the44 humiditieshumidities..ContinuousContinuous: CRMs: CRMsDottedDotted: SCM: SCM
ARPEGE NWP ModelARPEGE NWP ModelJ.M.J.M. PiriouPiriou 20022002
IFS NWP ModelIFS NWP ModelBeljaarsBeljaars 20022002
ObservationsObservationsYangYang and Slingoand Slingo MWR 2001MWR 2001
Unified ClimateUnified Climate ModelModelYangYang and Slingoand Slingo MWR 2001MWR 2001
Diurnal cycleof convection / JJA
ObservationsObservationsYangYang and Slingoand Slingo MWR 2001MWR 2001
Diurnal cycleof convection
CONTROL = ARPEGE NWPCONTROL = ARPEGE NWPoperationaloperational model, 10model, 10 two two days preddays pred..décdéc 2002
CONTROLCONTROL++ Reduced entrainment
2002
Reduced entrainment
EUROCS diurnal cycle ofEUROCS diurnal cycle of deepdeep convectionconvection
SCMSCM runrun;; operationaloperational ARPEGEARPEGE physicsphysics
ConvectiveConvective precipprecip.. Cloud topCloud top heightheight
Sensitivity to humidity: top of clouds
TOGARed. 2002
EUROCSId. qv25%
TOGATOGA--COARE / J.L. Redelsperger, D. Parsons, F.COARE / J.L. Redelsperger, D. Parsons, F. GuichardGuichard, JAS 2002, JAS 2002
CRM dataCRM data fromfrom FrançoiseFrançoiseGuichard andGuichard and JeanJean--PierrePierreChaboureauChaboureau, CNRS / , CNRS / MétéoMétéo--FranceFrance
CRM MESOCRM MESO--NHNH
SCM ARPEGE convectionSCM ARPEGE convection switchedswitched offoff
SCM ARPEGE convectionSCM ARPEGE convection switchedswitched onon
EUROCS diurnal cycle ofEUROCS diurnal cycle of deepdeep convectionconvection
Sensitivity to humidity: top of clouds
TOGARed. 2002
EUROCSId. qv25%
EUROCSDiurn. CycleDeep conv.
TOGATOGA--COARE / J.L. Redelsperger, D. Parsons, F.COARE / J.L. Redelsperger, D. Parsons, F. GuichardGuichard, JAS 2002, JAS 2002
Sensitivity to humidity: top of clouds
TOGARed. 2002
EUROCSId. qv25%
EUROCSDiurn. CycleDeep conv.
TOGATOGA--COARE / J.L. Redelsperger, D. Parsons, F.COARE / J.L. Redelsperger, D. Parsons, F. GuichardGuichard, JAS 2002, JAS 2002
EUROCS diurnal cycle ofEUROCS diurnal cycle of deepdeep convectionconvection
ConvectiveConvective precipprecip.. Cloud topCloud top heightheight
SCMSCM runrun;; modifiedmodified ARPEGEARPEGE physicsphysics: ad hoc TOC : ad hoc TOC
as aas a functionfunction of saturationof saturation deficitdeficit
Conclusions / perspectives Conclusions / perspectives (1/2)(1/2)
• ARPEGE convection scheme sensitivity to humidity seems OKonly for « wet » atmospheres, i.e. sat. defs (2.5 > 4.5km) < 2.5 g/kg, but likely underestimated for dry atmospheres
• Reducing entrainment rates to suppress the sensitivity in the idealized case � small impact on diurnal cycle. The 3h phase lagof precipitation of ARPEGE vs other models remains yet unexplained
Conclusions / perspectives Conclusions / perspectives (2/2)(2/2)
The sensitivity of cloud top height to environmental humidity seems to befor saturation deficits (2.5 > 4.5km) between 2 and 3 g/kg:
1. TOGA-COARE (Redelsperger, Parsons and Guichard, JAS 2002)2. CRM MESO-NH in EUROCS diurnal cycle of deep convection case3. 5sat image versus ARPEGE global analysis of saturation deficits
> Humidifying a dry atmosphere: a good candidate to explain large phase lags of precipitation vs surface forcings, from diurnal to 10days time scales?
Perspectives: (i) retune the entrainment in drier contexts than previously done, to get the right cloud tops / (ii) increase humidification ratebelow cloud top / (iii) see impact on diurnal cycle!
Entrainment: undilute plume relaxation
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Towards environment
Towards undilute: easy way to take into account that a ratherconstant fraction of ascents remain undiluted, without havingto use negative entrainments in the expression just on the left
TimeTime--heightheight crosscross--sections ofsections of the the difference between current difference between current humidityhumidity (g/kg)(g/kg) andand initial oneinitial one
SCMSCM operationaloperational ARPEGE ARPEGE
CRM MESOCRM MESO--NH (NH (referencereference))predictionprediction; data; data fromfrom FrançoiseFrançoiseGuichard andGuichard and JeanJean--PierrePierreChaboureauChaboureau, CNRS / Météo, CNRS / Météo--FranceFrance
TimeTime--heightheight crosscross--sections ofsections of the the difference between current difference between current humidityhumidity (g/kg)(g/kg) andand initial oneinitial one
CRM MESOCRM MESO--NH (NH (referencereference))predictionprediction; data; data fromfrom FrançoiseFrançoiseGuichard andGuichard and JeanJean--PierrePierreChaboureauChaboureau, CNRS / Météo, CNRS / Météo--FranceFrance
SCMSCM modifiedmodified ARPEGE: ad hoc TOC ARPEGE: ad hoc TOC as aas a functionfunction of saturationof saturation deficitdeficit
Trends, or under progress
Present operational schemes
1st order closure scheme afterLouis (1979), Louis and al. (1981), using a flux-gradient K-theory with Ri dependency, variable roughness lengths over sea (Charnock)
mass-flux scheme, CISK-typeclosure and triggering, watervapour budget using a Kuo-type closure, downdrafts,momentum flux
Diagnostic in ql/i, allsupersaturation removed,liquid/ice condensation � T,melting/ freezing/ evaporation/Kessler (1979), Clough and Franks (1991)
Geleyn and Hollingsworth(1979), Ritter and Geleyn(1992)
PrognosticTKE scheme,mixing « Betts »conservative variablesthetal and qt instead oftheta and qv
Turbulence
Entrainment & dry intrusions, modified triggerfunctions (use of TKE, CIN) / Revised shallowand deep conv.
Subgrid-scale cloud scheme(convection)
Prognostic ql/i and/or qr/sGrid-scale cloud scheme
More accurate infra-red exchanges betweensurface and layers
Radiation
ARPEGE NWP modelARPEGE NWP modelJJA 2002JJA 2002
ObservationsObservationsYangYang and Slingoand Slingo MWR 2001MWR 2001
Diurnal cycleof convection
ARPEGE NWP modelARPEGE NWP model1010 daysdays CAPECAPE decdec 20022002
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