Handout (1.2 MB)
Motivation. A Nature Run (NR) is used to represent the atmosphere in simulation experiments including Observing System Simulation Experiments (OSSEs). Ideally the NR is generated by a state-of-the-art numerical model and realistically represents all phenomena that affect the new observing system. Since no forecast system is perfect, there should be realistic differences between the NR model and the model used for assimilation and forecasting. For all researchers the value of the new ECMWF NR is that the ECMWF model is very advanced and complete and accurate. For NOAA researchers, an additional value for the reliability of future OSSE results is that there are some differences between the ECMWF and NOAA models, just as there are differences between reality and any model.
Model Configuration. The ECO1280 uses the TCo1279L137 configuration of the ECMWF Integrated Forecast System (IFS) model. This model version has 9-km (average) resolution in gridpoint space, T1279 spectral truncation, and 137 vertical layers. For physical processes (convection, radiation, etc.) the ECO1280 uses an octahedral reduced Gaussian grid (O1280). The vertical model structure is a hybrid sigma-pressure coordinate system. This configuration, denoted IFS cycle 43r1, was operational between Nov 2016 and July 2017. The new NR starts 0000 UTC 30 Sep 2015 with the rapid intensification of Hurricane Joaquin.
Data Archive. All ECO1280 variables are saved every 3 h. During the first month, data is saved every 1 h. ECMWF saves a full restart file at the end of each month. Plans are to rerun at least one additional month at 1-h resolution, during a period with intense mesoscale convective activity over continental U.S. The ECO1280 distribution includes all quantities that are archived operationally at ECMWF. Three additional special variables are also archived: (a) Two experimental fields—the 3d Gaussian grid fields of convective rain and snow flux—to permit simulating all-sky radiances following Geer et al. (2010, doi: 10.1002/qj.681, doi: 10.1002/qj.659); and (b) The geopotential height at model full levels. As a convenience, for the purpose of forecast verification, the ECO1280 distribution includes the standard variables interpolated to 1/2° latitude-longitude grids at the mandatory and other selected pressure levels.
Storage Requirements. Storage required for 1 month of data at 3-h archiving is ~4 TB. We have found that it is best to always interpolate spectral to the model Gaussian grid and then interpolate to the desired latitude-longitude grid. Therefore, after downloading the original archive files additional storage will be needed. For example, converting a 3-h, 1-month archive to a regular grid requires an additional 3.27 TB for the spectral coefficients transformed to Gaussian grids and an additional 7.68 TB for 1/10° resolution latitude-longitude grids interpolated from the Gaussian grids. The storage for the regular latitude-longitude grids will depend on the resolution desired. (Multiple by 0.64 for 1/8° grids and by 2.56 for 1/16° grids.) Instructions for downloading, converting, and interpolating the ECO1280 are given in the ECO1280 FAQ at the ECO1280 website.
Use and Access. The ECO1280 may be used for any research purpose. Interested researchers should acquire the ECO1280 by contacting CIRA/CSU to describe planned usage and to obtain data access instructions. Resulting publications or presentations must acknowledge ECMWF and CIRA/CSU. Consult the ECO1280 website (https://www.cira.colostate.edu/imagery-data/ecmwf-nature-run/) for details.
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