Iden%fying CESM cloud and surface biases at Summit, Greenland

Transcription

1 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

2 ICECAPS Mobile Science Facility Eleva%on 3255m N W Shupe et. al. BAMS 213 2

3 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 Total Flux [Wm -2 ] Ground- based Radia%on Measurements Swiss Federal Ins%tute, Zürich (ETH)

4 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 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)

5 Annual Cycle of Cloud Radia%ve Forcing SW CRF [Wm -2 ] LW CRF [Wm -2 ] CRF [Wm -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

6 Surface albedo important for CRF Cloud Rad. Forcing [Wm -2 ] Summit ( ) Barrow ( ) SHEBA ( ) 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

7 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 ] 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

8 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)

9

10 CAM 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

11 LWP [gm -2 ] 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

12 SW CRF [Wm -2 ] LW CRF [Wm -2 ] CRF [Wm -2 ] Albedo 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 Wm Wm Wm Wm Wm - 2

13 Flux [Wm -2 ] Flux [Wm -2 ] Albedo 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

14 1. Observations CESM-M1.95 Albedo J F M A M J J A S O N D Month

15 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

16 Thank you This research is supported by the Na%onal Science Founda%on under grants PLR and PLR 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

17 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

18

19 Component Flux [Wm -2 ] 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 ]

20 For elevated sun angles (low SZA) the op%mal LWP = 1-4 gm - 2 for maximum surface warming Mean Total CRF [W/m 2 ] 6 LWP [g/m 2 ] Solar Zenith Angle

21 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 y = x Solar Zenith Angle [degrees]

22 Clear- Sky Residuals [Number Bin -1 ] a) LW clear-sky & no rime c) SW clear-sky SZA < 9 15 & no rime [Number Bin -1 ] b) LW ETH - RRTM [Wm -2 ] 2 d) SW ETH - RRTM [Wm -2 ] 22

23 1 LW CRF [Wm -2 ] LWP [gm -2 ] The physical depth of an ice- cloud influences the op%cal depth LW CRF [W/m 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 < Cloud Thickness [km]

24 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 FIG. 8.Therelation scenes with liquid (do dashed line). The cur parameters in 38 bins.

25 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