Anewparameterizaonoficecloud op-calproper-esbasedonatwo6 … · 2015. 5. 8. ·...
Transcript of Anewparameterizaonoficecloud op-calproper-esbasedonatwo6 … · 2015. 5. 8. ·...
A new parameteriza-on of ice cloud op-cal proper-es based on a two-‐
habit ice par-cle model
Ping Yang,1 Bingqi Yi,1 Souichiro Hioki,1 Patrick Minnis,2 Norman Loeb,2 Seiji Kato2
1. Dept of Atmospheric, Texas A&M University 2. NASA Langley Research Center
MOTIVATION
• Most current ice crystal models used in cloud retrievals and in RTMs are not consistent across all wavelengths and op-cs
-‐ cloud op-cal depths retrieved using VIS channels are ~half of COD for IR channels, use single column model (SHM)
-‐ polariza-on paYerns do not match -‐ needs to match mass to link hydro and radia-ve cycles
• A two-‐habit model (THM) has been provided to the Cloud Working Group for use in future CERES Edi-ons
-‐ currently under evalua-on • If used by CERES, the Fu-‐Liou code will need to accommodate the new model across the SW and LW spectral bands
-‐ parameteriza-on across all wavelengths developed, needs tes-ng
Two-‐habit ice par-cle model (THM)
Liu, Yang, Minnis, Loeb, Kato, Heymsfield, SchmiY , 2014
(a) single hexagonal column with an aspect ra-o of unity;
(b) hexagonal aggregate with 20 solid or hollow columns.
Median Mass Diameter (Dmm) : THM vs. Measurements
Liu, Yang, Minnis, Loeb, Kato, Heymsfield, SchmiY , 2014
Ice Water Content (IWC): THM vs. measurements
Liu, Yang, Minnis, Loeb, Kato, Heymsfield, SchmiY , 2014
Consistency between solar-‐band and IR-‐band retrievals
Liu, Yang, Minnis, Loeb, Kato, Heymsfield, SchmiY , 2014
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012 0.0014 0.0016 0.0018 0.002
Obs
erva
tion
Den
sity
Dis
tribu
tion
Pola
rized
Ref
lect
ivity
Scattering Angle (°)
Smooth ColumnTwo Habit Model
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
100 110 120 130 140 150 160 170 180
Polarized Reflec-vity: THM vs. POLDER
Pola
rized
Ref
lect
ivity
Scattering Angle (°)
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
100 110 120 130 140 150 160 170 180
T < 208 K
208 K < T < 228 K
Observa-on Density Envelopes
Computa-on of Band-‐averaged bulk scaYering proper-es
Effec%ve diameter
Asymmetry factor
Single-‐sca8ering albedo
!
" sca =
" sca, h(D ,#) fh(D )[ ]S(#)n(D )dDd#h=1
M
$Dmin
Dmax%#min
#max%
fh(D )[ ]S(#)n(D )dDd#h=1
M
$Dmin
Dmax%#min
#max%
Sca8ering cross sec%on
Ex%nc%on cross sec%on
!
" ext =
" ext, h(D ,#) fh(D )[ ]S(#)n(D )dDd#h=1
M
$Dmin
Dmax%#min
#max%
fh(D )[ ]S(#)n(D )dDd#h=1
M
$Dmin
Dmax%#min
#max%
!
g =
gh(D ,")# sca, h(D ,") fh(D )[ ]S(")n(D )dDd"h=1
M
$Dmin
Dmax%"min
"max%
# sca, h(D ,") fh(D )[ ]S(")n(D )dDd"h=1
M
$Dmin
Dmax%"min
"max%
!
Deff =32
Vh(D ) fh(D )n(D )dDDmin
Dmax"[ ]h=1
M
#
Ah(D ) fh(D )n(D )dDDmin
Dmax"[ ]h=1
M
#
!
"(#) =$ sca(#)$ ext(#)
9
Bulk sca8ering proper%es parameterized as func%ons of effec%ve diameter:
IWC = !ice Vh (D) fh (D)n(D)dDDmin
Dmax!"#$%&'
h=1
M
(
Ice water content
Gamma distribu%on
n(D) = N0D(1!3!eff )/!eff exp(! D
Deff!eff
)
Band-‐averaged ice cloud bulk op-cal proper-es: two-‐habit model versus CAM5
Two-‐habit
CAM5
λ
Ice cloud radia-ve forcing at TOA and surface as func-on of THM effec-ve diameter and op-cal thickness, SZA = 60°
Minimal Dependence on De
Comparison of CERES observa-ons and simula-ons using Fu-‐Liou RTM
• CERES data: – SSF level-‐3 1°x1° daily observa-ons containing cloud informa-on (cloud phase, op-cal thickness, cloud frac-on, effec-ve diameter, etc.)
– SW and LW flux at the TOA under clear-‐sky and cloudy-‐sky. • Simula-ons: – MERRA reanalysis daily atmospheric profiles are used; – Fu-‐Liou RTM is used for two cases:
• Default: Fu-‐Liou RTM with SCM ice op-cs parameteriza-on • Two-‐habit model: Fu-‐Liou RTM with new THM ice op-cs parameteriza-on
• Data -me range: January, April, July, and October 2010
Defini-on: CRF at TOA = TOA cloudy-‐sky flux – TOA clear-‐sky flux
Methodology
• Use grid points with only ice clouds from CERES SSF
• Select corresponding atmospheric profiles from MERRA
• Determine cloud level from CERES cloud effec-ve pressure
• Select necessary cloud parameters for RTM simula-ons: cloud frac-on, cloud op-cal thickness, De, etc.;
• Carry out Fu-‐Liou RTM simula-on for clear-‐sky, cloudy-‐sky with SCM, and cloudy-‐sky with THM
• Calculate cloudy-‐sky TOA radia-ve flux and ice cloud radia-ve forcing. Compare simula-ons with CERES observa-ons.
CRFs: THM minus SCM
• THM has larger solar CRF than SCM. • THM LW CRF similar to SCM, but slightly smaller • Net forcing is several Wm-‐2 larger for THM
Unit: W/m2
Top of the atmosphere Surface
TOA FLUX THM vs CERES preliminary results
Unit: W/m2
• Discrepancies in SW is likely due to uncertainty in surface albedo • Observa-on and simula-on are similar in the case of IR flux.
Clear-‐sky Cloudy-‐sky
TOA CRF Simula-on vs CERES
Preliminary results
Two-‐habit model vs CERES Default vs CERES
• Only nega-ve SWC RF is simulated, CERES shows both posi-ve and nega-ve CRF
• Net CRF is seldom posi-ve in the simula-on, but again both posi-ve & nega-ve in CERES;
• CERES solar/IR CRF may have uncertain-es by themselves;
Unit: W/m2
Red number panel shows the average difference: Simula-on -‐ CERES
-‐8.6
-‐3.8
-‐12.4
-‐7.5
-‐3.6
-‐11.1
Cloud radia-ve forcing: observa-on vs simula-on CERES EBAF CAM5 with two-‐habit model
Unit: W/m2
deep convec-on microphysics parameteriza-on problem
Conclusions • Two-‐habit ice cloud op-cs parameteriza-on scheme is
developed and implemented in the Fu-‐liou RTM. • Preliminary results show good agreement between CERES
satellite observa-on of radia-ve flux at the top of the atmosphere (TOA) under clear-‐sky and ice cloudy-‐sky.
• Longwave ice cloud radia-ve forcing is well simulated by Fu-‐liou RTM with two-‐habit ice op-cs. However, shortwave radia-ve forcing simula-ons have some problems
• GCM simula-on with two-‐habit ice op-cs also shows some improvements in the global longwave cloud forcing while shortwave forcing improvement is difficult to discern because of large biases due to convec-ve clouds in the tropics.
Future work • Improve the ice cloud radia-on simula-on by consistently represen-ng ice microphysical and op-cal proper-es in the model.
• Data from several field campaigns are used and we found a new IWC-‐Deff rela-onship that depends on the cloud temperature. This new IWC-‐Deff rela-onship may further improve the specifica-on of ice cloud effec-ve par-cle size.
• Ground-‐based measurements at ARM sites will be used to test the two-‐habit model.