Iden%fying CESM cloud and surface biases at Summit, Greenland Nathaniel Miller (CU- ATOC, CIRES) MaEhew Shupe, Andrew GeEleman, Jennifer Kay, Line Bourdages CESM Ice Sheet Surface Biases Cross Working Group Session June 16, 215
ICECAPS Mobile Science Facility Eleva%on 3255m 72 35 N 38 25 W Shupe et. al. BAMS 213 2
Co -1 b) Annual Cycle of Surface Radia%ve Flux All-sky (ETH) Clear-sky (RRTM) J F M A M J J A S O N D Month of Year 4-4 -8 Total Flux [Wm -2 ] Ground- based Radia%on Measurements Swiss Federal Ins%tute, Zürich (ETH)
Co -1 b) Annual Cycle of Surface Radia%ve Flux All-sky (ETH) Clear-sky (RRTM) J F M A M J J A S O N D Month of Year 4-4 -8 Total Flux [Wm -2 ] Cloud radia%ve forcing (CRF) is an es%ma%on of a cloud s impact on the radia%ve flux at the surface. CRF = Flux all- sky, measured Flux clear- sky, modeled Best es%mate atmospheric profiles Rapid Radia%ve Transfer Model (RRTM)
Annual Cycle of Cloud Radia%ve Forcing SW CRF [Wm -2 ] LW CRF [Wm -2 ] CRF [Wm -2 ] -2-4 -6 1 8 6 4 2 8 6 4 2-2 a) b) c) Downwelling Upwelling Net LW SW Total J F M A M J J A S O N D Month of Year 5
Surface albedo important for CRF Cloud Rad. Forcing [Wm -2 ] 6 4 2-2 -4 Summit (211-213) Barrow (1998-28) SHEBA (1997-1998) Arctic Ocean 7-82N (26-211) J F M A M J J A S O N D Month of Year Miller et. al. J. Climate [in press] Dong et. al. 21, JGR Shupe and Intrieri 24, J. of Climate Kay and L Ecuyer 213, JGR Central Greenland is a unique Arc%c loca%on 6
High year round cloud frac%on 86% Cloud phase is important for magnitude of LW CRF LWP [g m -2 ] Cloud Fraction [%] SW CRF [Wm -2 ] LW CRF [Wm -2 ] 1 CRF [Wm -2 ] -2 8-4 -6 1 6 8 4 6 4 2 2 8 1 6 4 8 2 6-2 4 2 a) b) Downwelling Upwelling Net Cloud Fraction All LWP LWP > 5 gm -2 LW SW Total Liquid Present J F M A M J J A S O N D
Summit Summit Figure by Line Bourdages Lidar scaeering ra%o (SR) threshold of 5 = LWP sensi%vity of.1.2 g/m 2 (see poster [J. Kay] for more COSP simulator comparisons)
CAM 5.4 + changes to the aerosol mode widths = runs M1 and M2 New version of cloud microphysics (MG2) Prognos%c precipita%on, New ac%va%on (GeKelman and Morrison 215, J. Climate) New mixed phase ice nulcea%on Mixed phase a func%on of Aerosols
LWP [gm -2 ] 3 25 2 15 1 ICECAPS CESM-M1 CESM-M2 Summit, Monthly averages, LWP 5 J F M A M J J A S O N D Month of Year
SW CRF [Wm -2 ] LW CRF [Wm -2 ] CRF [Wm -2 ] 1-1 -2-3 -4 8 6 4 2 Albedo 8 6 4 2 a) SW CRF 1. Observations ETH CESM-M1 CAM5 CESM-M1 CESM-M2.95 b) LW CRF.9 c) Total CRF.85.8 J F M A M J J A S O N D Month of Year J F M A M J J A S O N D Summer Month CRF Observa%ons CESM CAM5 CESM- M1 Annual CRF 3 Wm - 2 12 Wm - 2 29 Wm - 2 34 Wm - 2 8 Wm - 2 24 Wm - 2
Flux [Wm -2 ] Flux [Wm -2 ] 5 4 3 2 1 Albedo 3 25 2 15 1 5 1. Observations ETH CESM-M1 CESM-M2.95 a) SW down.9 b) LW down.85.8 J FJ M F A M M A J M J J A JS AO NS DO N D Month of Year Month
1. Observations CESM-M1.95 Albedo.9.85.8 J F M A M J J A S O N D Month
Cloud Influence on other surface energy budget terms SEB = SWnet + LWnet + Hsensible + Hlatent + Gstorage Melt þ þ? Turbulent Fluxes (H) Sensible and Latent Heat Fluxes Eddy Covariance method Bulk Aerodynamic method Heat Storage (G) Thermistor String 15
Thank you This research is supported by the Na%onal Science Founda%on under grants PLR133879 and PLR1314156. Thanks to the Swiss Federal Ins%tute for providing the ETH broadband radiometer measurements. Addi%onal broadband radia%on measurements, ozonesonde soundings, CO 2 measurements, and near- surface meteorological tower data are provided by the Na%onal Oceanic and Atmospheric Administra%on s Global Monitoring Division. Thanks to Polar Field Services and the various science technicians for their excellent support of the field experiments at Summit Sta%on. 16
Summer Daily Maximum Temperatures Summer maximum temperatures are cri%cal to represent because they have the greatest impact on melt extent In order to accurately represent surface temperatures à need to capture the frequency of occurrence and phase of clouds above the GIS
Component Flux [Wm -2 ] 1 5-5 a) SW ETH CESM CESM-M1 CESM-M2 Other factors effect upwelling radia%on: Albedo 2-5% too low Temperature inversion strength too weak? -1 b) LW c) Total J F M A M J J A S O N D Month of Year 4-4 Total Flux [Wm -2 ]
For elevated sun angles (low SZA) the op%mal LWP = 1-4 gm - 2 for maximum surface warming 8 2 4 6 8 Mean Total CRF [W/m 2 ] 6 LWP [g/m 2 ] 4 2 55 6 65 7 75 8 85 Solar Zenith Angle
Inputs: Clear- Sky Es%mate via Rapid radia%ve transfer model (RRTM) Merged temperature profiles ECMWF, twice daily radiosondes, MWR derived boundary layer profiles Merged moisture profiles ECMWF, twice daily radiosondes, scaled by MWR derived PWV Snow emissivity =.985 Clear- sky snow albedo à CO 2 mixing ra%o Standard subarc%c winter o N 2 O, CO, CH 4 and O 2 Ozonesonde profile Surface temperature o derived from LW measurements Albedo 1..95.9.85.8.75 y =.74715 +.145x.7 5 6 7 8 9 Solar Zenith Angle [degrees]
Clear- Sky Residuals [Number Bin -1 ] 2 15 1 5 a) LW clear-sky & no rime -4-2 2 4 2 c) SW clear-sky SZA < 9 15 & no rime 1 5-4 -2 2 4 [Number Bin -1 ] 5 4 3 2 b) LW 1-4 -2 2 4 ETH - RRTM [Wm -2 ] 2 d) SW 15 1 5-4 -2 2 4 ETH - RRTM [Wm -2 ] 22
1 LW CRF [Wm -2 ] 8 6 4 2 5 1 15 LWP [gm -2 ] The physical depth of an ice- cloud influences the op%cal depth LW CRF [W/m 2 ] 8 6 4 2 Predominantly Ice Clouds (LWP < 5. gm -2 ) Linear rela%onship between cloud thickness and LW CRF SW CRF [W/m 2 ] -2-4 SZA < 9-6 1 2 3 4 5 6 Cloud Thickness [km]
FIG. 7.ContoursofthecloudLWPvalueatwhichpointtheSW surface cloud cooling effect becomes dominant over the LW warming effect as a function of u and a s.thefollowingparametersareassumed: T c 5218C, z c 5 1km,t al 5.9, and t as 5.75. FIG. 8.Therelation scenes with liquid (do dashed line). The cur parameters in 38 bins.
Greenland Ice Sheet Increasing Greenland melt extent The GIS is over 3.2 km deep at Summit Sta%on Observed increase in GIS melt rate and extent (Mernild et. al. 211, J. Glac.) has global and regional impacts. For surface temperatures close to 273K a small But present-day melt fractio in CESM-LE less than observed change in the surface energy budget can have substan%al implica%ons for the surface mass balance. CESM- LE, J. Kay