Cloud Feedbacks in the Superparameterized Climate Model SP- CCSM4

Transcription

1 Cloud Feedbacks in the Superparameterized Climate Model SP- CCSM4 Christopher S. Bretherton Peter N. Blossey University of Washington Cris9ana Stan George Mason University

2 Summary SP- CCSM4 has moderate posi9ve shortwave and longwave cloud feedbacks and an ECS of 2.8 K It shows weak rapid adjustments in all cloud types As the climate warms: 1. Low cloud decreases over land as surface dries. 2. Midlevel cloud decreases and polar cloud increases (like CMIP5 models).

3 Coupled Experiments 4x: abrupt4co2 control (15 years) Ini9alized from Jan. 26 of 2C CCSM4 run Years 1-15 used for means Specified SST 4xP: amip4co2 amip (35 years) P4: amip4k amip (35 years) 4xLC: 4xP +.87P4 (same CO2 and T as 4x) amip = monthly- mean SST Years 2-35 used for means

4 SP- CCSM4 4x response to abrupt 4xCO 2 T [K] a) R [W m 2 ] Control abrupt4xco d) ICEFRAC Time [yrs] CLDTOT Time [yrs]

5 4x Gregory Plot: Radia9on components R [W m 2 ] (LW+SW) full sky LW clear sky SW clear sky LW CRE SW CRE T [K] 4xP 4xLC

6 4x Gregory plot: clouds and precipita9on a) CLDHGH xP T [K] 4xLC CLDMED xP Tropical Mid latitude High latitude T [K] 4xLC CLDLOW d) e) f) 4xP T [K] 4xLC Negligible rapid adjustment of cloud proper9es Large increase in high- la9tude low and high cloud as ΔT increases Decrease in mid- level cloud except at high la9tudes (Tropical: 3N- 3S, Mid- lat: 3-6 N/S, High- lat: 6-9 N/S)

7 Low cloud decreases with ΔT over land x: global mean =. 4x: global mean =.97 % Longitude [deg E].1.2 Highly correlated with rela9ve humidity decrease Due to decreased surface moisture availability CLDMED CLDLOW Surface RH, %

8 9 5 3 a) 4x: global mean = ï ï3 ï5 ï9 ï.1 CLDMED Midlevel cloud reduc9ons ï.2 4x: global mean = ï. CLDLOW ï.1.2 4x: global mean = ï.97 % ï2 ï1 4x: global mean = ï.35 W m K 9 ï.2 2 ï.2 1 ï.4 5 6t5 [Pa s ] 9 ï3 5 ï5 3 ï9.4 ï1 a) 9 5 ï3 3 ï5 ï9 4x: global mean = ï. Pa sï1 rface RH, % tude [deg Latitude N] Latitude ] [deg N] [deg N] 9 nearly everywhere (above)!.2 occur 5 are 3 modulated by ver9cal velocity changes (below).1

9 Cloud feedbacks ISCCP simulator method (Zelinka et al. 212) Posi9ve al9tude- driven global LW feedback Posi9ve global SW feedback due to less low cloud over land Local feedbacks affected by circula9on changes Global net cloud feedback comparable to many CMIP5 models a) 4x: global mean =.49 W m 2 K 1 4x: global mean =.3 W m 2 K 1 4x: global mean =.19 W m 2 K Longitude [deg E] SW Cld Fdbk [W m 2 K 1 ] LW Cld Fdbk [W m 2 K 1 ] Net Cld Fdbk [W m 2 K 1 ]

10 Zelinkagrams for 4x climate change 4x: Cloud Fraction from ISCCP Simulator Global cloud, avg =.7 Land cloud, avg =.22 Ocean cloud, avg =.1 Pressure Net Cld Fdbk =.49 W m 2 K 1 LW Cld Fdbk =.3 W m 2 K 1 SW Cld Fdbk =.19 W m 2 K Net Cld Fdbk =.99 W m 2 K 1 LW Cld Fdbk =.2 W m 2 K 1 SW Cld Fdbk =.79 W m 2 K Net Cld Fdbk =.28 W m 2 K 1 LW Cld Fdbk =.34 W m 2 K 1 SW Cld Fdbk =.5 W m 2 K Optical Depth Optical Depth Optical Depth Highest cloud tops rise Most other cloud categories reduce Op9cally- thick low clouds increase over ocean but not land

11 4x vs. specified- SST response: Low cloud 6CLDLOW ï ï.1 4x: global mean = ï. a) ï3 ï5 ï9 ï3 ï5 ï xP: global mean = ï.1 ï3 ï5 ï xLC: global mean = ï.1 d) P4: global mean = Longitude [deg E] 3 ï3 ï5 ï Longitude [deg E] x regional palerns of low cloud changes fairly well matched by 4xLC linear combina9on of specified- SST experiments. Rapid adjustment (4xP): less low cloud over many land areas.

12 4x vs. specified- SST response: Precipita9on 6PREC [mm d ï1] ï ï2.5 a) 4x: global mean =.15 mm d ï ï3 ï5 ï9 ï3 ï5 ï xP: global mean = ï.15 mm d ï1 ï3 ï5 ï xLC: global mean =.18 mm d ï1 d) P4: global mean =.39 mm d ï Longitude [deg E] 3 ï3 ï5 ï Longitude [deg E] Rapid adjustment smaller than most CMIP5 models 3 36

13 References Bretherton, Blossey, and Stan (214), Cloud feedbacks on greenhouse warming in the superparameterized climate model SP- CCSM4, JAMES, submiled. Stan and Xu (214), Climate simula9ons and projec9ons with the super- parameterized CCSM4. Env. Model. So.., accepted. Acknowledgements This work was supported by the NSF CMMAP STC, with compu9ng resources from NERSC (DOE) and XSEDE (NSF). CMMAP Reach for the sky.