Introduction
Storm Karl affected northern Europe regionally with high-impact weather at the end of September 2016. The storm was created through extra-tropical conversion of a previous Tropical Storm event. When crossing the North Atlantic it merged with other lower pressure systems and invigorated, resulting in high wind speeds in Scotland and intense precipitation (with local flooding) in Norway.
This storm event was studied extensively during the NAWDEX flight campaign in connection with atmospheric moisture transport. The following table points to some of the published material related to the situation in the North Atlantic during this time period.
Literature
The table below points to material related to this storm event. This is obviously not an exclusive list, and if we become aware of more published material we will add this to the table. The published article in BAMS gives a good overview of the weather situation in the North Atlantic region during that time.
| Publications | Andreas Schäfler et al., The North Atlantic Waveguide and Downstream Impact Experiment, BAMS, 1607-1637, 2018. https://doi.org/10.1175/BAMS-D-17-0003.1 |
| Web sites | NAWDEX flight campaign web portals of various project partners: DLR, KIT, ETHZ |
| Other material | Presentation by Ben Harvey (University of Reading) at the 5th OpenIFS User Meeting 2019 (PDF) US National Hurricane Center Tropical Cyclone Report - Tropical Storm Karl (PDF) |
Important dates
The dates shown below were obtained from the US NHC Tropical Cyclone Report and from ECMWF ERA5 reanalysis data. They represent important milestones in the development and lifetime of Storm Karl. The first four dates describe events during the tropical storm phase, the following events occurred after the extra-tropical conversion in the North Atlantic and later.
| 12 Sep 2016 | Karl forms from tropical wave on the western coast of Africa) | tropical storm |
| 15 Sep 2016 | Karl strengthens into a tropical storm | |
| 21 Sep 2016 | Karl weakens to a depression | |
| 25 Sep 2016 | Karl strengthens again and reaches peak intensity (0600 UTC) | |
| 25 Sep 2016 | Karl undergoes extra tropical conversion (12 UTC) |
|
| 26 Sep 2016 | Karl merges with another ET low pressure system | |
| NN | Karl causes maximum wind speed (10m) in the United Kingdom (Scotland) | |
| NN | Karl causes maximum 6-hourly precipitation in Norway (Bergen) |
OpenIFS initial experiment data
We provide experiment data packs that allow to simulate the time period of Storm Karl in the North Atlantic with the global OpenIFS forecasting model. The initial experiment data and boundary conditions were created from ECMWF reanalysis data at horizontal model grids N80 and N128, with either 60 or 91 levels, respectively.
The experiment data packs include a model namelist file (fort.4) which contain suggested 6-hourly outputs for instantaneous and derived model fields and diagnostics.
All OpenIFS experiments begin on 25th September 2016 00:00 UTC, shortly before the extra tropical conversion of Storm Karl.
Model | Exp ID | Model Grid | Spectral Truncation | Vertical Levels | Data Source | Initial Date | Forecast Length |
|---|---|---|---|---|---|---|---|
| 43r3 | hc5q | N80 | TL159 | 60 | ERA5 | 2016-09-25 00:00 UTC | 6 days (144 hours) |
| 43r3 | hc4y | N128 | TL255 | 91 | ERA5 | 2016-09-25 00:00 UTC | 6 days (144 hours) |
| 48r1 | ab7z | N80 | TL159 | 60 | ERA5 | 2016-09-25 00:00 UTC | 6 days (144 hours) |
| 48r1 | ab2a | N128 | TL255 | 91 | ERA5 | 2016-09-25 00:00 UTC | 6 days (144 hours) |
Suggested experiments
In this section we describe a series of suggested experiments that can be carried out with OpenIFS to study the model's ability to simulate this particular event.
Requirements
Requirements to carry out these exercises include:
- A working installation of the OpenIFS forecasting model.
- Some of the suggested exercises below involve changes to the model source code. This may not be possible if the model has been installed in a shared space location. In this case we recommend to build the model in the local disk space area. Instructions how to do this can be found in the OpenIFS User Guides.
- Sufficient computing resources and disk space to carry out forecast experiments with OpenIFS. To run a forecast with the N80 model grid the user requires approximately XX GB of RAM and YY GB of disk space. For the N128 grid this increases to AA GB RAM and BB GB of disk space.
- Software to read model output encoded in GRIB format and to visualise the results. We suggest to use the Metview software package that is produced at ECMWF. For the post-processing of the model output the metview-python bindings will also be required.
Control forecast experiment
As a first exercise a forecast experiment for the time period of the storm should be carried out. This experiment can subsequently serve as a reference or control forecast against which any later perturbation experiments can be compared.
- Select one of the two experiments that match your model cycle (N80 or N128). Extract the tgz archive with the experiment data in your local disk space. This will be your experiment directory.
- Run a 6-day forecast with OpenIFS, using the namelist settings as they are provided. This will provide 6-hourly output for a number of model fields and diagnostics. See Setting up and running a forecast experiment for further details.
- If Metview is to be used, convert the output into a Metview database and visualise the results. Otherwise use your own post-processing method and data visualisation software of your choice.
Variants
- Repeat with a different model grid (i.e. run the other experiment) and compare how the model represents the storm.
lhboxmodify case explained
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