Correlations between microphysical properties of large-scale. semi-transparent cirrus

Transcription

1 Correlations between microphysical properties of large-scale semi-transparent cirrus (from TOVS) and the state of the atmosphere (from ECMWF ERA-40) Gaby Rädel Claudia Stubenrauch, Fadoua Eddounia Laboratoire de Météorologie M Dynamique Ecole Polytechnique, France Gaby Rädel ITSC-13, November

2 Effective ice crystal size (D e ) and IWP retrieval of semi-transparent cirrus based on: spectral difference of cirrus emissivities at 11-8 µm Observations: NOAA , 60 N 60 S, θ v < 25 large-scale cirrus: 1 x1 overcast, p cld <440 hpa T cld < 263K,T meas B (8µm), T meas B (11µm), T cld, T surf ε surf (SARB), closest TIGR H 2 O/T profiles 3R radiative transfer (ε 8µm,ε 11µm ) Method: simulate ε(λ,d e,iwp,θ) hom. cloud, β abs (D e ),<ω 0 (D e )>,<g(d e )> planar polycrystals (mod. ADA) bimodal size distribution radiative transfer (Streamer (J.Key)) vary De, IWP ε(λ,d e,iwp,θ) Gaby Rädel ITSC-13, November

3 D e and IWP retrieval (cont.) produce look-up tables: D e = f(ε 8µm,ε 11µm ), IWP =f (D e,ε 11µm ) ε 11 ε 11 ε 8 ε 11 D e IWP for 0.3 < ε 11µm < < τ VIS < 3.8 sensitivity up to D e 80µm Gaby Rädel ITSC-13, November IWP

4 Sensitivity study on ice crystal size retrieval Rädel et al., J. Geophys. Res., May 2003 NOAA10 global average : <D e > = 55µm <IWP>= 30 g/m 2 possible errors: Overestimation of D e : thin Ci with underlying water cloud partial cover of thick Ci different crystal shapes, e.g. hexagonal columns instead of polycrystals Underestimation of D e : vertical heterogeneity, i.e.: increasing D e with cloud depth broader size distribution Gaby Rädel ITSC-13, November

5 Evaluation of TOVS cloud height with LITE (newest LITE inversion by L. Sauvage) 796 TOVS low clouds 495 TOVS high clouds 560 LITE single- 236 multi-layer 161 LITE single- 334 multi-layer very thin LITE high clouds heterogenous scenes z TOVS 0.5(z top +z base ) LITE (km) single layer: z <1 km: 70% peak at 0 z TOVS 0.5(z top +z base ) LITE (km) z < 2 km : 60 % peak at 0.5 km P cld (TOVS) p cld (mid-cloud) better agreement for low large-scale cirrus clouds LITE: z top -z base : 1.3 km low clouds high clouds 2.7 km Gaby Rädel ITSC-13, November

6 Regional and seasonal variations of D e and IWP TOVS NOAA10 3-year averages eff. emissivity (%) Nε IWP D e win spg sum aut IWP (g/m2) Nε(SHm) > Nε(NHm) > Nε(trop) NH land: Nε(sum) < Nε(win) win spg sum aut eff. Diameter (micron) win spg sum aut NH ocean NH land trop. Ocean trop. Land SH ocean SH land NH z=2km trop. z=2km SH z=2km IWP(trop) > IWP(NHm) > IWP(SHm) land: IWP(midsum) > IWP(midwin) D e (trop) > D e (NHm) > D e (SHm) land: D e (midsum) > D e (midwin) Gaby Rädel ITSC-13, November

7 D e and IWP as function of cloud temperature D e De (micron) Large-scale semi-transparent cirrus 60 N 60 S 7,5 22,5 37,5 all different IWP 55 IWP IWP (g/m2) different D e 32,5 47,5 62,5 82,5 all cold cirrus: Gaby Rädel ITSC-13, November D e depends more on IWP than on T cld IWP increases with T cld

8 Regional dependence for thin and thick Cirrus D e thin cirrus thick cirrus midlatitudes thin cirrus thick cirrus midlatitudes midlatitudes 55 midlatitudes 32,5 47,5 62,5 82,5 all 7,5 22,5 37,5 52,5 all midlatitudes IWP De (micron) De (micron) IWP (g/m2) IWP (g/m2) ,5 22,5 37,5 all tropics tropics >Tcld tropics tropics 32,5 47,5 62,5 82,5 all ,5 47,5 62,5 82,5 all tropics 45 ->Tcld De (micron) De (micron) ,5 22,5 37,5 all 7,5 22,5 37,5 52,5 all >Tcld different behaviour in midlatitudes and tropics thick Ci in tropics: D e and IWP do not depend strongly on T, almost no scatter due to different IWP or D e Gaby Rädel ITSC-13, November IWP (g/m2) IWP (g/m2) ,5 47,5 62,5 82,5 all >Tcld

9 Atmospheric properties accompanying large-scale cirrus ERA-40 ECMWF reanalyses: humidity, U, V and W for 23 pressure levels Every 6 hours, x spatial resolution Co-location with TOVS observations: (1989, 1990) Water vapour (cm) mean RMS tropics: largest water vapour, smallest winds midlat. winter: strongest winds Horizontal wind (m/s) mean RMS Frequency of situations with strong strong updraft no wind downdraft NH midlatitude summer % 38% 3% NH midlatitude winter % 29% 7% tropics % 44% 0.1% SH midlatitude summer % 42% 4% SH midlatitude winter % 34% 4% SH: horizontal winds always strong most large-scale semi-transparent cirrus in situations with no vertical wind Gaby Rädel ITSC-13, November

10 D e and IWP as function of humidity and wind Large-scale semi-transparent cirrus 60 N 60 S, T cld < 233K Stubenrauch et al. 2003, submitted to Atmos.Res. D e and IWP increase with water vapour D e 12 µm smaller in case of strong winds IWP 10 gm -2 larger in case of strong vertical updraft Gaby Rädel ITSC-13, November

11 Regional distributions of D e and IWP as function of humidity and wind dry, strong updraft dry, strong hor. wind D e humid, strong updraft humid, strong hor. wind IWP D e larger in case with no winds than strong winds humid tropics: IWP larger in case of strong w than strong u+v Gaby Rädel ITSC-13, November

12 Cirrus horizontal extent determine horizontal extent of cirrus clouds (ε > 0.3): a. empty boxes are filled with most likely information on cirrus type b. simple clustering algorithm groups adjacent boxes containing deep convection (ε>0.95 ), cirrus (0.95>ε>0.5 ) or thin cirrus (0.5>ε>0.3 ) Examples: 18/07/1989 and 30/12/1989 7h30 PM very thin Ci clear sky mid and low clouds thin Ci Ci deep conv. Gaby Rädel ITSC-13, November

13 Cirrus horizontal extent cirrus clusters: largest in tropics smallest in ML summer D e as fct. of distance to convective centre: D e small if very close to convective centre and in smaller clusters -> dynamics? (1 box = 100 x 100 km) small clusters (<20boxes) large clusters (>500boxes) Gaby Rädel ITSC-13, November

14 Conclusions and Outlook Large-scale semi-transparent cirrus: <D e >=55µm <IWP>=30g/m 2 IWP increases with T cld TOVS Path-B & ECMWF reanalyses D e and IWP increase with atmospheric water vapour, increase depends on vertical updraft, hor. wind, formation processes? Study D e as function of cirrus size and location to convective center for different dynamic situations Find parameterizations IWP =f (q,w,t), D e =f (IWP,q,w,u+v,T) using also cluster information Gaby Rädel ITSC-13, November