Effect of cirrus microphysical parameterizations on radiative fluxes

Transcription

1 Effect of cirrus microphysical parameterizations on radiative fluxes using TOVS-ScaRaB observations Claudia Stubenrauch Fadoua Eddounia, Gaby Rädel Laboratoire de Météorologie Dynamique, Ecole Polytechnique, France John Edwards MetOffice,, Exeter, UK C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 1

2 Colocation of TOVS Path-B and ScaRaB data NOAA11 & NOAA12 METEOR-3 satellites Improved Cirrus SW Angular Direction Models - using ScaRaB cloud properties - based on neural network (LMD) / Monte Carlo (IfMK) Cirrus radiative flux analysis TOVS atmospheric profiles cirrus properties D e radiative transfer model ScaRaB observations simulated fluxes C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 2

3 Colocated TOVS ScaRaB data set: 3/94-8/94 TOVS large-scale semi-transparent cirrus, 1 long x 1 lat grids, daytime, t =15 min 50 <θ 0 <70 Φ<40 or Φ>140 ocean/land: 1800 / 1060 cases hour ScaRaB observation time month T cld K α SW C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 3

4 TOVS atm. T / humidity profiles p cld, T cld, ε cld IR, T surf ScaRaB θ 0 global D e reg./seas. D e D e =f(t), D e =f(iwc) D e =f(iwp,hum,w,uv) eliminate multi-layer clouds ScaRaB L LW, L SW ADMs radiative transfer model: p cld = p(mid-cloud) p = 100hPa( 2 km) 50 hpa ( 1 km) flux parameterization: SSPs of Mitchell, Fu, Baran choose IWP with ε(iwp,d e ) ε cld IR - create Streamer look-up tables ε cld IR (IWP,D e ), depending on θ v, z, SSPs F LW, F SW at TOA C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 4

5 SW Angular Direction Models (LMD, IfMK) C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 5

6 α SW cloud reflected solar flux from ScaRaB ( θ 0) = R ( θ 0, θ v π L φ, τ, phase, het ) E, Angular correction R depends on: cloud phase, opt. thickness, heterogeneity, underlying surface SW 0 cos θ 0 ScaRaB: narrow-band VIS, IR and broad-band SW, LW radiances cloud properties training: L SW meas ISCCP cloud retrieval neural networks simulated L SW geometry L sim SW d φ d θ C. Stubenrauch Final CIRAMOSA meeting 20-21/11/ L SW sim -LSW meas water ice θ -> α SW

7 simulated radiances - > cloud reflected solar flux integration over all geometries in network I { α sim ( θ ) 2 π θmax θ 63 0 φ θ cosθ sinθ π 0 0 L sim < = d d SW adjustement using L SW meas II { α θ < 63 = α sim θ < 63 L L meas SW sim SW ( θ, θ0, φ) ( θ, θ0, φ) extension to total albedo III { = 90 2( τ) 4( τ) 63 = 63 1( τ) + + cos( ( ) ) 2 α α θ a a αtot αθ αθ a θ 63 a3 τ θ0 cos ( a5( τ) θ0) α α θ θ from Monte Carlo simulations (Andreas Macke) C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 7

8 energy not observed between 63 <θ V <90 : Monte Carlo simulation of (Andreas Macke) τ =1.1 τ =2.6 τ=4.6 θ 90 (θ 63 0,τ) α α θ ~ 23% 40% of energy not observed by ScaRaB This fraction increases with θ 0 and decreasing τ! (~ 8% - 25% not observed by ERBE, depending on θ 0 and τ) [θ v <72 ] θ 0 ( ) C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 8

9 Viewing angle dependence of SW albedo using ERBE ADMs using neural network/mc model & cloud properties water ice water ice α(θ v )-<α> α(θ α(θ v )-<α> v )-<α> θ v ( ) θ v ( ) bias linked to viewing geometry considerably reduced! C. Stubenrauch Final CIRAMOSA meeting 20-21/11/2003 9

10 Select isolated Cirrus C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

11 Detection of multi-layer clouds (1) transform L VIS into α cld VIS and then into τ cld VIS : ScaRaB α VIS θ ( π 0 ) L VIS cos = R ( θ 0, θ v, φ, τ ) E 0 θ => α VIS (0 ) = > τ VIS 0 cld Angular corrections Monte Carlo simulation ice aggregates A. Macke R α (0 ) α( θ0) θ V ( ) Monte Carlo simulation ice aggregates A. Macke θ 0 ( ) Rossow et al C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

12 Detection of multi-layer clouds (2) thin cirrus & underlying water cloud : 1-exp(-τ cld VIS /2) > ε cld IR thick Ci thin Ci C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

13 First steps of ANALYSIS C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

14 (Historical) Motivation test SW-LW coherence for given D e, shape, SSP parametrization first computations using Mitchell s radiative model (1996) C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

15 SW albedo comparison of isolated cirrus mod=mitchell SSPs D e =55µm, p cld =100hPa α SW obs using ScaRaB ADMs closer to model! α SW mod does not increase as much with IWP as observations C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

16 SW albedo as fnct of IWP D e =55µm slightly better agreement between observed and model α SW in tropics Cloud thickness and Fu SSPs-Mitchell SSPs only small effect for D e =55µm C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

17 LW absorption OLR = (1-A(T scene )) σ B T scene 4 with T scene4 =Nε T cld4 +(1-Nε) T surf 4 LW absorption A(T scene ) decreases with ε cld IR For same ε cld IR, atmospheric A is larger in tropics than in midlatitudes Effect most important for medium cloud emissivity C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

18 LW absorption as fnct of IWP LW absorption A(T scene ) decreases also with IWP Differences between parametrizations should result in differences of cloud absorption D e =55µm A of models larger than computed A from observed variables for small IWP -> check T surf and atmospheric profiles! Ci LW absorption larger using Fu s SSP than Mitchell s SSP (5%) Mitchell s SSP better agreement with observations, esp. for large IWP C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

19 SW albedo comparison as function of IWP for different D e s p=100hpa small IWP: smaller D e s seem more plausible to fit α SW obs large IWP: larger D e s seem more plausible to fit α SW obs C. Stubenrauch Final CIRAMOSA meeting 20-21/11/

20 Conclusions and Outlook α SW obs using ScaRaB ADMs (instead of ERBE ADMs) closer to model! α SW mod (const. D e, const. p) does not increase as much with IWP as α SW obs smaller D e more plausible at small IWP and larger D e at large IWP more difference between Fu SSP and Mitchell SSP in LW than SW (for D e =55µm) LW comparison more dependent on quality of atmospheric and surface input implement Baran SSP into Streamer for ε cld IR (IWP,D e ) look-up tables study LW absorption sensitivity to T surf and atmospheric profiles test D e parametrizations C. Stubenrauch Final CIRAMOSA meeting 20-21/11/