Scale-aware and definition-aware evaluation of CESM1 near-surface precipitation frequency using CloudSat observations Jen Kay, University of Colorado (CU) Tristan L Ecuyer (UW-Madison), Angie Pendergrass (NCAR) Helene Chepfer/Rodrigo Guzman (LMD-Paris), and Vineel Yettella (CU)
Evaluation of CESM1 Rain Frequency GPCP 1DD TRMM CESM1 Latitude Figure adapted from Pendergrass and Deser (2017) Problem: This evaluation is NOT definition-aware. TRMM and GPCP do not detect light rain (< 1 mm/day) (Berg et al. 2010; Behrangi et al. 2014)
How often does it rain? Let s look at CloudSat Observations Data from Tristan L Ecuyer (U. Wisconsin) 2C-PRECIP-COLUMN (Haynes et al. 2009)
Upscaling CloudSat observations to evaluate the dreary state of models! Global Rain Frequency (%) 100 50 0 Stephens et al. 2010 CONCLUSION: models overestimate rain frequency, but underestimate rain intensity. This evaluation scale-aware but NOT definition-aware.
Goal: Use CloudSat to make definition-aware and scale-aware precipitation frequency comparisons But how? And what is new? vs. Model Gridbox Profiles 1) Downscale using sub-column generator (COSP1.4) Model Sub- Column Profiles 2) Apply satellite forward model (COSP1.4) Model Sub- Column CloudSat dbz Model Near- Surface Precipitation Frequency 3) Apply 2C-PRECIP- COLUMN algorithm (Haynes et al.. 2009) vs. Observed Near-Surface Precipitation Frequency 4) Apply 2C-PRECIP- COLUMN algorithm (Haynes et al.. 2009)
Global Rain and Light Rain Kay et al. (in prep)
Global Snow Kay et al. (in prep)
What about future near-surface precipitation changes projected by CESM1? Let s compare 2010s with 2080s! CESM1 Large Ensemble, (Kay et al. 2015)
CESM1-Projected 21 st Century Change: What would CloudSat Observe? Three CESM1-projected Changes: 1) Snow becoming Rain (esp. in mid-latitude storm tracks) 2) Less Off-Equatorial Rain, More Equatorial Rain (esp. in Pacific) 3) Increase in Sub-tropical Light Rain Frequency Kay et al. (in prep)
Tropical Rain and Light Rain Maps Kay et al. (in prep)
Conclusions Kay et al. 1) Scale-aware and definition-aware comparisons of near-surface precipitation frequency show CESM1 rains and snows too frequently when compared to CloudSat observations. 2) 21st Century precipitation frequency change shows conversion of snow to rain, narrowing of the tropical overturning circulation, increased light rain in sub-tropics, more snow in high Arctic and over Greenland. If CESM1 realistic all would be detectable by a future CloudSat launched in 2080 J. 3) Happy to Share COSP Code!! Feedback Welcome!
Arctic Snow and Rain Maps CESM1-projected 21 st century changes: 1) More Snow in High Arctic and Over Greenland 2) More Rain Except over Greenland and Central Russia
Recent/ Upcoming papers using CALIPSO: Guzman, R., Chepfer, H., Noel, V., Vaillant de Guélis, T., Kay, J.E., Raberanto, P., Cesana, G., Vaughan, M.A. and Winker, D.M., 2017. Direct atmosphere opacity observations from CALIPSO provide new constraints on cloud-radiation interactions. JGR-Atmospheres, 122(2), 1066-1085. Vaillant de Guélis, T., Chepfer, H., Noel, V., Guzman, R., Dubuisson, P., Winker, D. M., and Kato, S. (in review): Link between the Outgoing Longwave Radiation and the altitude where the space-borne lidar beam is fully attenuated, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-115 Vaillant de Guélis, T., Chepfer, H., Noel, V., Guzman, R., Winker, D.M., and Plougonven, R.: Using space lidar observations to decompose Longwave Cloud Radiative Effect variations over the last decade, GRL, in review Morrison, A., J. E. Kay, H. Chepfer, and R. Guzman, Isolating the liquid cloud response to recent Arctic sea ice loss using spaceborne lidar observations, JGR-Atmospheres, revised Frey, W, A. Morrison, and J. E. Kay, Relationships between Southern Ocean sea ice and clouds and implications for shortwave cloud feedbacks, in prep
EXTRA/FOR REFERENCE/STILL THINKING
Evaluation of CESM1 Rain Figure 15 Pendergrass and Deser 2017
Tropical precipitation response to greenhouse warming (RCP8.5 2090 = 4xCO 2 ) Precipitation climatology 21 st Century precipitation change Change due to thermodynamics Change due to dynamics Panel shows the thermodynamic response resulting from wet get wetter dry get drier Panel shows the dynamic response resulting from reduced overturning circulation Figure 1 Bony et al. 2013
Upscaling CloudSat observations to evaluate the dreary state of models! ECMWF T511 (0.62) CAM 2 degree (0.80) Up-scaled CloudSat Obs. (0.33) Up-scaled CloudSat Obs. (0.61) Stephens et al. 2010 Is up-scaling the best strategy when evaluating rain frequency?