Presentation on theme: "Joint ECMWF-University meeting on interpreting data from spaceborne radar and lidar: AGENDA 09:30 Introduction University of Reading activities 09:35 Robin."— Presentation transcript:
Joint ECMWF-University meeting on interpreting data from spaceborne radar and lidar: AGENDA 09:30 Introduction University of Reading activities 09:35 Robin Hogan - Overview of CloudSat/CALIPSO/EarthCARE work at University 09:50 Julien Delanoe - Ice cloud retrievals from CloudSat, CALIPSO & MODIS 10:05 Lee Smith - Retrieval of liquid water content from CloudSat and CALIPSO 10:20-10:35 Coffee ECMWF Activities 10:35 Marta Janiskova- Overview of CloudSat/CALIPSO activities at ECMWF 10:50 Olaf Stiller - Estimating representativity errors 11:05 Richard Forbes - ECMWF model cloud verification 11:20 Maike Ahlgrimm - Lidar derived cloud fraction for model comparison 11:35-12:30 Discussion Retrievals, forward models and error characteristics Verification of models Possibilities for collaboration 12:30 Lunch in the canteen
Recent CloudSat/CALIPSO/EarthCARE- related work at University of Reading Forward models and model evaluation –Lidar forward modelling to evaluate the ECMWF model from IceSAT –Multiple scattering model for spaceborne radar and lidar (Hogan) Retrievals and model evaluation –LITE lidar estimates of supercooled water occurrence –Radar retrievals of liquid clouds (Lee Smith, Anthony Illingworth) –Variational radar-lidar-radiometer retrieval of ice clouds (Delanoe) ESA CASPER project (Clouds and Aerosol Synergy Products from EarthCARE Retrievals) –Defined the required cloud, aerosol and precipitation products –Developed variational ice cloud retrieval for EarthCARE that uses the cloud radar, the High Spectral Resolution Lidar (HSRL; the same technology as ADM) and the infrared channels of the multispectral imager
Ongoing/future work Forward models and model evaluation –Use the CloudSat simulator to evaluate the 90-km resolution HiGEM version of the Met Office climate model (Margaret Woodage) –Use the CloudSat simulator to evaluate 1-km large-domain simulations of tropical clouds in CASCADE (Thorwald Stein) Retrievals and model evaluation –Ongoing comparisons with MO and ECMWF models (Smith & Delanoe) –Use of retrievals to evaluate the CASCADE model (Thorwald Stein) CloudSat, CALIPSO and EarthCARE algorithm development –Develop a unified retrieval algorithm for clouds, precipitation and aerosols simultaneously using radar, lidar, infrared radiances and possibly microwave radiances (Nicola Pounder, Hogan, Delanoe) Science questions –What is the radiative impact of errors in model clouds? Use retrievals, CERES observations and radiative transfer calcs. (Nicky Chalmers) –What is the distribution of supercooled water in the atmosphere and why is it so difficult to model? (Andrew Barrett)
ECMWF clouds vs IceSAT using a lidar forward model Cloud observations from IceSAT 0.5-micron lidar (first data Feb 2004) Global coverage but lidar attenuated by thick clouds: direct model comparison difficult Optically thick liquid cloud obscures view of any clouds beneath Solution: forward-model the measurements (including attenuation) using the ECMWF variables Lidar apparent backscatter coefficient (m -1 sr -1 ) Latitude Wilkinson, Hogan, Illingworth and Benedetti (Monthly Weather Review 2008)
Simulate lidar backscatter: –Create subcolumns with max-rand overlap –Forward-model lidar backscatter from ECMWF water content & particle size –Remove signals below lidar sensitivity ECMWF raw cloud fraction ECMWF cloud fraction after processing IceSAT cloud fraction
Global cloud fraction comparison ECMWF raw cloud fraction ECMWF processed cloud fraction IceSAT cloud fraction Results for October 2003 –Tropical convection peaks too high –Too much polar cloud –Elsewhere agreement is good Results can be ambiguous –An apparent low cloud underestimate could be a real error, or could be due to high cloud above being too thick
Examples of multiple scattering LITE lidar (r)Stratocumulus Intense thunderstorm Surface echo Apparent echo from below the surface
Fast multiple scattering forward model CloudSat-like example New method uses the time- dependent two-stream approximation Agrees with Monte Carlo but ~10 7 times faster (~3 ms) Added to CloudSat simulator Hogan and Battaglia (J. Atmos. Sci. 2008) CALIPSO-like example
Combining radar and lidar… Cloudsat radar CALIPSO lidar Preliminary target classification Insects Aerosol Rain Supercooled liquid cloud Warm liquid cloud Ice and supercooled liquid Ice Clear No ice/rain but possibly liquid Ground Radar and lidar Radar only Lidar only Global-mean cloud fraction Radar misses a significant amount of ice
Unified retrieval framework New ray of data: define state vector Use classification to specify variables describing each species at each gate Ice: extinction coefficient and N 0 * Liquid: liquid water content and number concentration Rain: rain rate and mean drop diameter Aerosol: extinction coefficient and particle size Radar model Including surface return and multiple scattering Lidar model Including HSRL channels and multiple scattering Radiance model Solar and IR channels Compare to observations Check for convergence Gauss-Newton iteration Derive a new state vector Forward model Not converged Converged Proceed to next ray of data (Black) Ingredients already developed (Delanoe and Hogan JGR 2008) (Red) Ingredients remaining to be developed
Supercooled water layers have large radiative impact Poorly modelled Hogan et al. (GRL 2004) Mixed-phase clouds LITE lidar showed more supercooled water in SH than NH Two independent methods from MODIS show the same thing What does CALIPSO show? What is the explanation? How can we model mixed- phase clouds?
Discussion points Is the intention to assimilate cloud radar and lidar directly? –If so, are fast radar and lidar forward models of interest? If retrievals are to be assimilated, what variables are needed? Do you need error covariances, averaging kernels and information content? Straightforward to calculate, but: –Complicated to store (state vector is a different size for each profile) –Increases the data volume by an order of magnitude What are best diagnostics for assessing model performance? –Means, PDFs, skill scores… ECMWF model variables are required by retrievals –What is the error of model temperature, pressure and humidity?
CloudSat simulator (Bodas et al) Simulated radar reflectivity from sub-grid model Simulated radar reflectivity averaged to model grid –How would this look with high-res model? Observed CloudSat radar reflectivity
Example of mid-Pacific convection CloudSat radar CALIPSO lidar MODIS 11 micron channel Time since start of orbit (s) Height (km) Cirrus detected only by lidar Mid-level liquid clouds Deep convection penetrated only by radar Retrieved extinction (m -1 )
Supercooled water in models A year of data from the Met Office and ECMWF –Easy to calculate occurrence of supercooled water with > 0.7 Prognostic ice and liquid+vapour variables Prognostic cloud water: ice/liquid diagnosed from temperature