Richard Allan, Tony Slingo ESSC, Reading University Comparison of GERB and Met Office UM broadband fluxes: SINERGEE project results Richard Allan, Tony Slingo ESSC, Reading University
INTRODUCTION - SINERGEE aims Comparison of GERB L2 broadband fluxes with Met Office forecast model (analysis times 00,06,12,18 GMT) July Means, Clear-sky sampling Data issues (geolocation, resolution, bad data, ADMs) Model Issues (Sahara, convection, cloud properties)
Recent Comparison (OLR)
Recent Comparison (Albedo)
Example Comparison (OLR)
Example Comparison (Albedo) Stratocumulus Convection Geolocation
July Mean OLR UM GERB
GERB-UM OLR Difference July Mean Limb effects?? GERB-UM OLR Difference July Mean
Consistently sampled clear-sky “Type-I” OLR July GERB Consistently sampled clear-sky “Type-I” OLR July UM
Clear-sky OLR bias with Ts GERB minus UM OLR (Wm-2) 30 20 10 -10 -20 -30 -40 -50 -60 280 300 320 340 SURFACE TEMPERATURE (K)
Desert Dust? Aerosol?
July Mean Albedo (GERB) 06z Red and Yellow are bright; blue and black are dark Note: Bright 06z albedo
July Mean Albedo (UM) 06z Note dark band above African ITCZ; Sc; Note dark Sahara
Geolocation Mean clear-sky albedo July GERB Geolocation Mean clear-sky albedo July UM
23rd July Geo-location (2): Albedo 11th August Shifting GERB images by 4 pixels to right/East improves geololcation for 20th July-1st August period
Time series (diurnal cycle removed) May June July Aug Reduced spatial coverage amplifies 06z Albedo bias
Light stripe (~25N or 25 S): 06z late May and 11-14th June, 12z 24-29th May Dark Band, 12z: 1-3rd, 5th June; 18z 12th June; 12z 31st July, 1st and 5th Aug OTHER ISSUES Vertical dark stripe: 06z 20th May; 12z 4th June; 00z&18z 10th June; 00z 26th, 27th & 30th June; 18z 30th June/1st July; 00z 2nd/3rd July 22nd June & 10th Aug also dodgy Bad Pixel.
10th August 12z: GERB couldn’t cope with record UK temperature of 38oC!
Conclusions (1) DATA problems Model problems Geolocation (spatial comparison, processing) Resolution Albedo diurnal cycle (problems at 06z) Limb darkening in East? (Lower OLR and Higher albedo) Meteosat data replacement = Bad Model problems Too much stratocumulus 12z Convection (too early, lack of organisation) Dark Sahara / Hot Sahara ITCZ positioning
Conclusions (2) Quality of BARG improved recently (August) ARG - reasonable quality (res/geo probs) ADMs? – bright at 06z, dark at 18z Bad data (manual correction?): Geolocation light stripes, dark bands (E/W) Dark bands (N/S) Future comparison of SEVIRI with UM simulations http://www.nerc-essc.ac.uk/~rpa/GERB/gerb.html