RCA and CLIWANET results Ulrika Willn Rossby Center
RCA and CLIWANET results Ulrika Willén, Rossby Center SMHI, Norrköping Sweden • The RCA model • Cloud vertical distribution • Subgrid Overlap (& radiation) • Overlap (&radiation)
RCA – SMHI HIRLAM • 106*114, 44 km, L 24 - climate run • New land surface scheme - not in HIRLAM • Clouds and condensation: Rasch-Kristjánsen and Kain-Fritsch • Turbulence: TKE • Radiation: dry variables – CBR scheme Savijärvi and Sass plus modifications by Räisienen etc.
Cloud fraction and radiation in RCA Cloud fraction (Slingo 1987): High (> 400 h. Pa) - RH thresholds mid (750 h. Pa< p <400 h. Pa) – RH thresholds Low (surface p < 750 h. Pa) – RH thresholds, ω and Γ SW: H 2 O and O 3 explicitly (O 2 and CO 2 implicitly). Cloud absorption and transmission (cloud water, cloud fraction, Reff). Aerosols constant correction factors LW: clear-sky gaseous emission, H 2 O explicitly, (CO 2, O 3, CH 4, N 2 O, CFC’s empirical). Cloud emission (cloud water, Tcloud base, cloud fraction, Reff)
Cloudiness in RCA and ERA compared to satellite data Winter SCANDIA AVHRR Autumn Spring (%) RCA 22 km RCA 44 km ERA 40 100 km Jones and Karlsson Summer 1993 -2000
Cloudiness and surface radiation in RCA and ERA RCA 44 ERA SCANDIA LW SW OBS ERA Jones and Karlsson RCA 44
Change of cloud overlap in RCAO • RCAO coupled run had too much ice. Changing from maximum to maximum-random overlap reduced ice cover and improved SST’s Maximum LW Error (RCA-OBS) Maximum–Random Sea ice area Döscher et al 2001
BBC campaign of CLIWANET August and September 2001 Susanne Crewell, Henk Klein Baltink and Olivier Sievers Models ECMWF RACMO RCA 2 LM • 50 km, 60 levels 18 km, 24 levels 7 km, 35 levels Observations at Cabauw 35 GHz KNMI cloud radar 95 GHz GKSS cloud radar CT 75 K lidar ceilometer SW and LW surface fluxes
Cloud vertical structure Cabauw August 2001 Cabauw September 2001
New cloud fraction scheme for RCA 3… Slingo C=f(RH, ω, Γ) Xu Randall C=f(RH, TCW) Cabauw July 2004 Cabauw January 2004 Ewan O’Connor
Cloud thickness and layer frequency distributions M Haeffelin 2% 8% 24% 48% 18%
Cloud volume and cloud area fraction Cabauw September 2001 maximum random 2 -range gates K=2 K=6 Brooks et. al. fliq (T>273 K), fice(T<273 K) Random: Random 2: K=16 minimum
Using cloud area fraction and scaled optical depth in the radiation Cv Δz Ca Area fraction Cloud thickness Optical depth Del Genio et. al. Brooks et. al. fliq (T>273 K), fice(T<273 K) Random: Random 2:
Using cloud area fraction and scaled optical depth in the ECMWF radiation scheme LW down (W/m 2) 12 Aug 13 Aug Cloud fraction (%) ECMWF Time (days) ECMWF (W/m**2) Height (km) KNMI RADAR SW down (W/m 2) 12 Aug 13 Aug Observed (W/m**2) 12 & 13 August 2001, Cabauw
2 -layer cloud overlap Cabauw September 2001
Accumulated cloud fraction - overlap Cabauw September 2001 Maximum. Random M-R gradient Random Minimum
Cloud overlap matrix Cabauw September 2001 Two-layer overlap Accumulated overlap
Cloud overlap matrix Cabauw September 2001
Mean value of overlap matrix CLIWANET and CLOUDNET
Cloud overlap and radiation 12 August 2001, Cabauw RADAR LW down (W/m 2) Observed Maximum M-R Random RCA Height (km) Cloud fraction (%) Time (hrs) SW down (W/m 2) Time (hrs)
Julklappslista – Xmas list… • Vertical profiles of humidity, temperature and total cloud water • Ozone, effective radius and optical depth of aerosols
Cabauw August 2001
CLIWANET BBC campaign Susanne Crewell, Henk Klein Baltink and Olivier Sievers September 2001
Cabauw August 2001
Cabauw September 2001
- Slides: 24