1. Results for the COPS Region
: General Observation Period (GOP) 2007
Results for the COPS Region
Christoph Selbach1, Thorsten Reinhardt1, Susanne Crewell1, Mario Mech1 and GOP Team
1 IGMK: Universität zu Köln, Institut für Geophysik und Meteorologie, Kerpener Str. 13, Köln
GOP Outline
The main goal of the General Observation Period (GOP) within the German Research Foundation’s Priority Program on Quantitative Precipitation Forecasting (SPP-PQP) is to gather a comprehensive data set suitable for testing hypotheses and new modeling techniques developed within the SPP-PQP. The GOP encompasses the Convectively and Orographically induced Precipitation Study COPS performed in south-west Germany in summer 2007 both in time and space to provide information of all kinds of precipitation types and to relate the COPS results to a broader perspective (longer time series and larger spatial domain). The duration of one year will open up the possibility to statistically approach model problems and better pin down specific model weaknesses. The GOP collected as many data about the atmospheric state as possible within an area covering Germany and it neighboring states. Furthermore the GOP optimized the exploitation of existing instrumentation by gathering routine measurements normally not available to the scientific community. Focus has been put on continuous/coordinated observations using existing instrumentations which are suitable for statistical evaluation and on measurements, which are available in near real-time to enable a timely use within the PQP. The GOP group performed a rigorous quality control, cross-checking, and error estimation of the data and tailored the observations to model output (e.g., COSMO-DE, COSMO-EU forecasts. By launching a web site an easy access to data, quicklooks and first order analysis has been enabled. To make the data available to the scientific community the data were archived at the World Data Center for Climate in Hamburg. By developing techniques to bring together observations and model forecasts an optimal evaluation environment has been created.
Data Sets
Models
Here focus on GPS and Ceilometer data: COPS region compared to flat topographic region
COSMO-EU and COSMO-DE:
Model domain of COSMO-DE
North West Germany + Netherlands
Operational NWP forecast models of DWD
COSMO-EU driven by GME
COSMO-DE driven by COSMO-EU
Grid size: x = 7 km in COSMO-EU and 2,8 km in COSMO-DE
Explicit deep convection in COSMO-DE
Parameterized convection in COSMO-EU
Forecast time: up to 78 h in COSMO-EU and 21 h in COSMO-DE
Started every 3 h
Matching:
GPS- network (GOP-5)
Model data of the grid points nearby stations have been extracted and stored in the GOP data
The cloud base data has been diagnosed by the following approach:
The model cloud base height is diagnosed as the height of the first model layer (from bottom) where cloud fraction exceeds 1%. In ceilometer-observed cloud base heights we use the minimum cloud base heights of 40-min periods for the comparison between model and observation. These are assumed to best match with the 1 % threshold used to derive cloud base heights in the models. Only cases with cloud heights < 3000 m both in model and observation are taken into account.
GPS network for integrated water vapor (IWV) measurements
operated by Geoforschungszentrum Potsdam (> 100 stations in Germany)
COPS Region
Forecasts started every 3 h: Lagged forecast ensemble:
Ceilometer-network (GOP-4)
7 forecasts for given target time!
Day 1 9 UTC
Day 1 6 UTC
Day 1 3 UTC
DWD ceilometer network
( > 100 stations in Germany)
Ceilometer stations
GPS stations
Day 1 00UTC
Day 1 21 UTC
Day 2 00UTC
+ 21 h forecast
Evaluation
Time series (COSMO models minus observation):
Diurnal cycles (COSMO models minus observation):
COPS Region
North West Germany + Netherlands
COPS Region
North West Germany + Netherl.
IWV
IWV
COSMO-DE
COSMO-EU
COSMO-DE
COSMO-EU
IWV
IWV
cloud base (height in m asl) + cloud fraction
cloud base (height in m asl) + cloud fraction
cloud base (height in m asl)
cloud base (height in m asl)
Forecasts: -3 h, -12 h, -21 h / black line = obs.
Forecasts: -3 h, -12 h, -21 h / black line = obs.
IOPs: Intensive Operation Periods = grey shaded
Almost always lower mean RMSE values in both models for the COPS region.
Time series reveal some days in which different forecasts or the two models differ (interesting for case studies) Some days with conspicuous problems of the models: Almost no clouds and high values of IWV Bias and RMSE at July: models simulate too much moisture in COPS area. (IOP-8b: thunderstorms occured under high pressure conditions).
For both regions: 12 UTC model runs start drier and with higher cloud base Possible reason for that: assimilated radiosondes with dry bias at daytime.
COSMO-DE resolves the mean diurnal cycle of cloud base heights very well in COPS region.
Compared to GPS observations model runs are moister in COPS region and drier in North West Germany.
Big problems of COSMO-EU cloud base forecasts in COPS region (cloud base heights significantly too low in model forecasts).
Very low cloud base heights in the morning in North West Germany (probably fog). This phenomenon did not appear in COPS region.
General GOP results: The results include e.g. that (i) both models in winter and COSMO-EU also in summer underestimate cloud base height slightly, while COSMO-DE in summer overestimates cloud base height by m, that (ii) on average cloud base height is higher in COSMO-DE than in COSMO-EU, and that (iii) sites near the North Sea show in all seasons a much higher bias than other sites. A further comparison with IWV reveals a negative correlation of IWV bias and cloud base height bias in winter while in summer no correlation is found (shown in figures on the right).
Winter
Summer
Bias of cloud base [m]
Bias of cloud base [m]
Bias of IWV [kg/m2]
Bias of IWV [kg/m2]
Related publications:
Crewell, S., M. Mech, T. Reinhardt, C. Selbach, H.-D. Betz, E. Brocard, G. Dick, E. O’Connor, J. Fischer, T. Hanisch, T. Hauf, A. Hünerbein, L. Delobbe, A. Mathes, G. Peters, H. Wernli, M. Wiegner and V. Wulfmeyer, 2008: General Observation Period 2007: Concept and first results. Met.Z. accepted
Bias of IWV vs. bias of cloud base height
Outlook: The GOP is an ongoing project (2008 and 2009) and it will be interesting to follow if there are changes in further statistics in the next two years.
7th. COPS Workshop, 27. – 29. October, Strasbourg.