WP4200 Simulations with the DWD Lokal-Modell at different horizontal resolutions Case studies during CNN2 and BCC Felix Ament, Susanne Crewell (University of Bonn)
Model domains and selected cases of WP4200 a) CNN1: b) CNN2, BBC: • 02 Aug. 2000 • 13 April 2001 • 25 Aug. 2000 • 02 Aug. 2001 • 04 Sep. 2000 • 23 Sep. 2001 • size of model domain: 400x400km • horizontal grid spacing: 7.0, (5.5), 2.8, (2.2), 1.1 km • no additional information at small scales
Available model data Special analysis • mean quantities 5min • mean profiles 10min • cell detection 10min area ave. Station output analysis time series ∆ t=40s..10s time +0h +12h +36h Standard output spin-up 3d-fields every hour
Budgets and fluxes I Reference values: relative deviations 7km run without runs with 7 , 2.8 and Example: 13. April 2001 convection scheme 1.1 km grid spacings average over model domain and 24h 200 150 Water vapour Results: 100 Results: 6.5kg/m 2 50 0 • water vapour, 200 • water vapour, 150 Ice 200 100 cloud cover and 3.4g/m 2 cloud cover and 50 150 surface fluxes 0 surface fluxes Cloud 100 300 250 remain unchanged 50 Liquid water cover 59% remain unchanged 200 0 7.6g/m 2 150 • LWP and rain rate • LWP and rain rate 100 50 increase due to increase due to Radiation 0 refinement Heatflux Evapo. 80W/m 2 refinement Rain 36W/m 2 99W/m 2 0.9mm/d 200 200 200 200 150 150 150 150 100 100 100 100 50 50 50 50 0 0 0 0
Budgets and fluxes II 7 , 2.8 , 1.1 km 13. April 2001 Water vapour 23 Sep.2001 Water vapour Water vapour 02 Aug.2001 6.5kg/m 2 27.9kg/m 2 19,5kg/m 2 Ice Ice Ice 3.4g/m 2 7.5g/m 2 1.7g/m 2 Cloud Cloud Cloud Liquid water Liquid water Liquid water cover 59% cover 83% cover 86% 7.6 g/m 2 21.2g/m 2 57g/m 2 Radiation Rain Radiation Radiation Rain Rain Heatflux Heatflux Heatflux Evapo. 138W/m 2 Evapo. Evapo. 80W/m 2 40W/m 2 0.9mm/d 0.5mm/d 3.4mm/d 36W/m 2 20W/m 2 18W/m 2 99W/m 2 99W/m 2 60W/m 2 2 Aug.2000 Water vapour 25 Aug.2000 4 Sep.2000 Water vapour Water vapour 28kg/m 2 17kg/m 2 17kg/m 2 Cloud Cloud Cloud Liquid water Liquid water Liquid water cover 74% cover 73% cover 76% 47g/m 2 43g/m 2 90g/m 2 Radiation Rain Radiation Radiation Rain Rain Heatflux Heatflux Heatflux 108W/m 2 Evapo. Evapo. Evapo. 78W/m 2 15W/m 2 4.7mm/d 0.3mm/d 4.4mm/d 0.6W/m 2 32W/m 2 10W/m 2 91W/m 2 54W/m 2 53W/m 2
Convection scheme on/off - influence on averaged quantities No effect: Small deviations: • water vapour • sensible heat flux • cloud cover • latent heat flux • radiative fluxes 7 , 2.8 , 1.1 km Differences: no convection convection LWP [g/m 2 ] IWP [g/m 2 ] RR [mm/d] 70 9 10 9 8 60 8 7 50 7 6 6 40 5 5 4 30 4 3 3 20 2 2 10 1 1 0 0 0 13 Apr 01 02 Aug 01 23 Sep 01 13 Apr 01 02 Aug 01 23 Sep 01 13 Apr 01 02 Aug 01 23 Sep 01
IWV - measurement and simulation Example: 02 August 2001, Station Cabauw Extreme wet air is advected during the afternoon from the south to Cabauw.
Direct LWP-rain effect grid refinement more LWP variations nonlinear LWP-RR relation Result of LM cloud scheme more RAIN ! using idealized cloud profiles
200 175 150 Direct LWP-rain effect 125 100 Example 14 April 01 75 50 25 0 averaged rainfall Domain average Cabauw Probably poor statistic!
Comparison of LWP time series microwave radiometer - model output CNN1 ⇒ no better match, but statistic is improved!
No rule without exception :-) Example: 23 Sep 01 Domain average 200 175 150 125 but 100 75 50 25 0 averaged rainfall ==> additional mechanism: • vertical cloud structure, humidity below cloud • ???
Results of WP4200 - so far ... • boundary effects can be larger than refinement effect ==> use the same boundary conditions at all resolutions! • Average cloud water content and rain rates are the only mean quantities affected by refinement • LM simulations without convection scheme produce quite realistic LWP values • The size of resolved convective cells depends on the grid spacing at scales larger than 1km.
Interesting issues Increase of LWP and rain • understanding of mechanisms • (validation with measurements) Convection scheme • Partitioning of resolved and parameterized convection at different grid spacings • vertical transport Cloud cover • Is there really no refinement effect? Cell shrinking • Which parameters control the cell size? Horizontal diffusion?
Recommend
More recommend
