Representation of convection and clouds in the IFS ......20 years and still the same? Peter Bechtold with contributions from Richard Forbes and Maike Ahlgrimm IITM Introspect 2017 workshop: IFS clouds and convection Slide 1
Challenge 1: Convective vs stratiform (grid-scale) precipitation TCo1279 26/4/2016 October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 2 EUROPEAN CENTRE FOR MEDIUM-RANGE WEATHER FORECASTS 2
Challenge 2: represent accurate heating profiles and cloud radiation interaction Dynamics (K/day) Conv (K/day) a ) a ) P P h h ( ( P P 50E 100 150 20W 50E 100 150 20W Cloud (K/day) Radiation (K/day) a ) P h ( P 50E 100 150 20W 50E 100 150 20W Latitude averaged difference in T-tendency MJO in phase 6/7 – MJO in phase 2/3: Convection over West Pacific - convection over Indian Ocean IITM Introspect 2017 workshop: IFS clouds and convection Slide 3
T ask of convection parametrisation total Q1 and Q2 parameterization needs to describe the collective effects of a cloud ensemble: Condensation/Evaporation and Transport ′ ′ ∂ ω s ≡ − ≡ − − Q Q Q L ( c e ) 1 C 1 R ∂ p a b 10 10 ) ) m m trans k k c-e ( ( trans Q1-Qr z 5 z 5 Q2 Q1c is dominated by c-e condensation term -1 2 0 1 -1 0 1 -2 2 (K/h) (K/h) but for Q2 the transport and condensation terms are equally important Caniaux, Redelsperger, Lafore, JAS 1994 IITM Introspect 2017 workshop: IFS clouds and convection Slide 4
The IFS bulk mass flux scheme Link to cloud parameterization Entrainment/Detrainment Type of convection shallow/deep/frontal Cloud base mass flux - Closure Downdraughts Generation and fallout of precipitation Where does convection occur IITM Introspect 2017 workshop: IFS clouds and convection Slide 5
Large-scale budget equations: M=ρw; M u >0; M d <0 Heat (dry static energy): Prec. evaporation Freezing of condensate in in downdraughts updraughts ∂ ∂ s [ ] = + − + + − − − − g M s M s ( M M ) s L ( c e e ) L ( M F ) u u d d u d u d subcld f ∂ ∂ t p cu Prec. evaporation Melting of Mass-flux transport in condensation below cloud base precipitation up- and downdraughts in updraughts Humidity: ∂ ∂ q [ ] ( ) = + − + − − − g M q M q ( M M ) q c e e u u d d u d u d subcld ∂ ∂ t p cu IITM Introspect 2017 workshop: IFS clouds and convection Slide 6
Large-scale budget equations Momentum: ∂ ∂ u [ ] = + − + g M u M u ( M M ) u u u d d u d ∂ ∂ t p cu ∂ ∂ v [ ] = + − + g M v M v ( M M ) v u u d d u d ∂ ∂ t p cu ∂ l = D l ÷ u u ∂ Cloud condensate : t cu IITM Introspect 2017 workshop: IFS clouds and convection Slide 7
Entrainment/Detrainment Entrainment formulation looks sooo simple: ε=1.75x10 -3 (1.3-RH)f(p) RH=relative humidity, so how does it compare to LES ? LES (black) IFS IFS formula with LES data Schlemmer et al. 2017 IITM Introspect 2017 workshop: IFS clouds and convection Slide 8
CAPE closure - the basic idea Convection consumes CAPE large-scale processes generate CAPE 9 IITM Introspect 2017 workshop: IFS clouds and convection Slide 9
Closure - Deep convection − θ − θ T T ∫ ∫ = v u , v ≈ e u , esat CAPE g dz g dz θ T v esat cloud cloud Use instead density scaling, time derivative − Ptop T T = − ∫ then relates to mass v u , v PCAPE dp T flux : v Pbase ∂ − Ptop Ptop ∂ ∂ ∂ T T T PCAPE 1 T 1 p ∫ ∫ ≈ − − v u , + v u , v = v base dp dp ∂ ∂ ∂ ∂ t T t T t T t 1 442 4 4 3 v v v Pbase Pbase 1 4 4 4 4 442 4 4 4 4 4 4 3 base + LS Cu + BL Cu ∂ ∂ ∂ PCAPE PCAPE PCAPE = + + ∂ ∂ ∂ t t t = + LS BL Cu shal deep this is a prognostic CAPE closure : now try to determine the different terms and try to achieve balance ∂ ∂ ∂ ∂ ∂ ∂ = PCAPE / t PCAPE / t , PCAPE / t cu LS IITM Introspect 2017 workshop: IFS clouds and convection Slide 10
Closure - Deep convection Solve now for the cloud base mass flux by equating 1 and 2 − PCAPE PCAPE 1 = ≥ * M M BL ; M 0 ∂ u b , u b , τ u b , g T ∫ * M v dz ∂ T z v cloud pbase ∂ 1 T ∫ = − τ PCAPE v dp BL BL ∂ * T t psurf BL Mass flux from the updraught/downdraught computation = + * M M M u d initial updraught mass flux at base, set proportional to * M 0.1Δp u b , PCAPE contains the boundary-layer tendencies due to surface bl heat fluxes, radiation and advection see Bechtold et al. 2014 JAS and work bei Saolo Freitas IITM Introspect 2017 workshop: IFS clouds and convection Slide 11
Impact of closure on diurnal cycle JJA 2011-2012 against Radar Obs radar NEW=with PCAPEBbl term Bechtold et al., 2014, J. Atmos. Sci. ECMWF Newsletter No 136 Summer 2013 IITM Introspect 2017 workshop: IFS clouds and convection Slide 12
Resolution scaling +absolute mass flux limit ′ Φ′ ω = ω Φ − ω Φ Developed in collaboration with ) ( )( ) ( = σ − σ ω − ω Φ − Φ c e c e 1 Deutsche f(Δx ) Wetterdienst and ICON model 10 5 km km Kwon and Hong, 2016 MWR independently developed very similar relations October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 13
Resolution scaling and a bit of light in the grey zone Obs 9 Aug 2015 Cy42r1 Tco1999 no deep Convection parameterisation at 5km resolution Cy42r1 TCo1999 5 km Cy42r1 TCo1999 5 km scaled Mfl 14 October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 14
Convection issue 1: inland penetration of (winter snow) showers Obs 42r1 TCo1279 advection Oper October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 15 EUROPEAN CENTRE FOR MEDIUM-RANGE WEATHER FORECASTS 15
Realism of heating profiles: DYNAMO MJO campaign Importance of melting level and mixed-phase microphysics: : green shows smaller discontinuity at the melting level with J-E Kim and C. Zhang IITM Introspect 2017 workshop: IFS clouds and convection Slide 16
Issue: Global models are not reflective enough over the Southern Ocean, but too reflective over tropical oceans Li et al. 2013 (blue = not reflective enough) Annual mean 10-20 Wm -2 difference from CERES-EBAF MODIS IFS Also true for IFS even if total cloud cover against ISCCP and MODIS looks pretty good October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 17 EUROPEAN CENTRE FOR MEDIUM-RANGE WEATHER FORECASTS 17
Issue: not reflective enough storm tracks Effect of detraining more liquid phase condensate to cloud scheme corrects SW radiation error in SH storm tracks (during cold air outbreaks) by around 5 W/m2 or 20% future tests: producing only liquid for shallow, but requires more technical developments and might produce biases IITM Introspect 2017 workshop: IFS clouds and convection Slide 18
Issue too reflective subtropics: sensitivity to shallow detrainment C42r1- MODIS low cloud cover: annual mean 43r1-42r1 change in low cloud cover 19 October 29, 2014 IITM Introspect 2017 workshop: IFS clouds and convection Slide 19
Moist process parametrizations: The integrated view Examples: Increased consistency between existing Radiation Dynamics parametrizations Prognostic cloud PDF Subgrid Subgrid schemes convection cloud (e.g. Tompkins et al 2002) Microphysics Eddy-diffusivity + multiple mass flux plumes (e.g. Surface EDMF Dual-M) Subgrid BL interactions turbulent Higher order closure (e.g. mixing CLUBB) How the different parametrizations interact can be as important as the parametrizations themselves IITM Introspect 2017 workshop: IFS clouds and convection Slide 20
Microphysics Parametrization: The “category” view Single moment schemes Water vapour q v Condensation Deposition Evaporation Sublimation Cloud Cloud Freezing – Melting - Bergeron water Rutledge and ice Hobbs (1983) q l q i Autoconversion Autoconversion Collection Collection Collection Freezing - Melting Rain Snow q r q s Sedimentatio n IITM Introspect 2017 workshop: IFS clouds and convection Slide 21
Microphysics Parametrization: The “category” view Double moment schemes Water vapour q v Condensation Deposition e.g. Evaporation Sublimation Ferrier (1994) Cloud Cloud Freezing – Melting - Bergeron water ice Seifert and q l + N l q i + N i Beheng (2001) Morrison et al. Autoconversion Autoconversion Collection (2005) Collection Collection Freezing - Melting Rain Snow q r + N r q s + N s Sedimentatio n IITM Introspect 2017 workshop: IFS clouds and convection Slide 22
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