The Cryosphere Radiative Effect in CESM Justin Perket Mark Flanner CESM Polar Climate Working Group Meeting Wednesday June 19, 2013
Cryosphere Radiative Effect (CrRE) A new diagnostic feature is available for CESM: Cryoshere Radiative Effect (CrRE): the instantaneous influence of surface snow and ice on TOA energy budget Analogous to the cloud radiative effect Able to calculate snow & ice related effects on albedo & energy flux at every radiation calculation without altering climate state Realistic portrayal of cryospheric change is critical for accurate climate change modeling Snow and sea-ice cover metrics are important and often used to valuate climate models, but do not capture the cryospheric radiative influence CrRE incorporates influences of vegetation, ice ponding, insolation, cloud cover, and underlying albedo
Computing Cryosphere Radiative Effect Extracts snow-free albedo from CLM and calculates ice-free ocean albedo in CICE New snow-free CLM and ice-free open ocean CICE variables merged in CPL to create cryosphere-free surface albedos, then CAM shortwave driver calculates fluxes for the cryosphere-free situation CLM CICE Land Albedos Snow-Free Albedos Ice Albedos Ice-Free Albedos C P L Surface Albedo Cr-free Albedo CAM Radiation Driver Radiation Driver (II) CrRE
Computing Cryosphere Radiative Effect The original model albedos remain unmodified by code < 20% increase to computation time in B RCP compset Implemented in CESM 1.0.3 & 1.1.1 CLM CICE Land Albedos Snow-Free Albedos Ice Albedos Ice-Free Albedos C P L Surface Albedo Cr-free Albedo CAM Radiation Driver Radiation Driver (II) CrRE
Visible Direct Albedo Unaltered Cr-free
Clearsky FSNT at TOA Unaltered Cr-free
RCP 8.5 Scenario Run CESM 1.1.1, B_RCP8.5_CAM5_CN 1 resolution 21 st simulation to investigation evolution of cryosphere influence Resources from PCWG K K NH Surface Temperature 300 295 290 285 280 J F M A M J J A S O N D Month SH Surface Temperature 294 292 290 288 286 284 J F M A M J J A S O N D Month Year Year 2097 2087 2077 2067 2057 2047 2037 2027 2017 2007 2097 2087 2077 2067 2057 2047 2037 2027 2017 2007
RCP 8.5 Scenario Run, Hemisphere Means NH SH 0.20 0.15 0.10 0.05 0.058 0.056 0.062 0.060 0.058 Land Snow Fraction 0 J F MAM J J A S OND Land Snow Fraction 0.056 J F MAM J J A S OND 0.06 0.04 0.02 0.08 0.06 0.04 0.02 Sea Ice Fraction 0 J F MAM J J A S OND Sea Ice Fraction 0 J F MAM J J A S OND 0-4 -8-12 0-4 -8-12 TOA CrRE J F M A M J J A S O N D TOA CrRE J F M A M J J A S O N D Year 2097 2087 2077 2067 2057 2047 2037 2027 2017 2007 Year 2097 2087 2077 2067 2057 2047 2037 2027 2017 2007
Decadal Change in CrRE from 2007-2016 North Hemisphere South Hemisphere 5 5 2097-2100 2087-2096 4 4 2077-2086 2067-2076 2057-2066 3 2 3 2 2047-2056 2037-2046 2027-2036 2017-2026 2007-2016 1 1 0 0 J F M A M J J A S O N D J F M A M J J A S O N D
Decadal CrRE, 2007-2100 NH SH
Time Evolution of NH Cr Radiative Effect North Hemisphere absorbs additional ~2.0 by 2100 from reduced cryosphere extent Greater decrease in sea-ice radiative influence than land Difference in CrRE 2099-2007 ( ) Total Snow Sea Ice Global 1.8 0.5 1.3 NH 2.0 0.8 1.2 SH 1.6 0.1 1.5 3 NH CrRE Components Land Snow Sea-Ice 2 1 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 % of Total CrRE 0.6 0.55 0.5 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Time Evolution of NH Cr Radiative Effect Effect of normal TOA CrRE not linear with clear-sky TOA CrRE Evolution is influenced by changes in atmospheric conditions, among other factors NH CrRE on TOA SW Flux, and Clearsky TOA SW Flux 6 4 FSNT FSNTC 2 0.63 0.62 0.61 0.6 0.59 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100 Integrated Cloud Fraction 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100
Initial Comparison with Observation Simulation Observation Now have 1979-2008 observational record of CrRE derived from remote sensing measurements (Flanner et al, 2011) Compared with 2 res CESM 1.0.3 CAM4 E_2000 run D J F M A M
Initial Comparison with Observation Simulation Observation Now have 1979-2008 observational record of CrRE derived from remote sensing measurements (Flanner et al, 2011) Compared with 2 res CESM 1.0.3 CAM4 E_2000 run J J A S O N
Comparison with Observation Agreement between model and observation-based TOA CrRE Demonstrates increase in surface downwelling from surface/cloud multiple scattering 4 2 0-2 North Hemisphere Cryosphere Radiative Effect -4-6 -8-10 -12-14 Net at Top of Atmosphere Net at Top of Atmosphere Clear Sky Downwelling at Surface Downwelling at Surface Clear Sky Net at TOA, Observation -16 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Summary Cryosphere Radiative Effect (CrRE) diagnostic in CESM gives exact, instantaneous influence of snow and ice on shortwave radiation including atmosphere effects Initial present-day NH observation assessment favorable, but some regional discrepancies in seasonal cycle Globe absorbs ~0.46 more from snow loss, ~1.3 from ice loss by 2100 in CESM1.1 RCP8.5 Potential incorporation in trunk Future research: Explore influences on CrRE & its evolution, including cloud conditions, ponding, and snow/ice aging