CME Prediction
☞ German
The trajectory of coronal mass ejections (CMEs) can be calculated after their origin, launch speed, direction, latitude, etc. have been determined by analysing the image data from the SOHO/LASCO, STEREO/SECCHI and SDO/AIA satellites/instruments. The analyses by NASA and MOSWOC (Met Office UK) are published and also used by other services to run their models. NOAA/SWPC does not publish its analyses, only the results of the latest model run.
NOAA/SWPC
WSA-Enlil model run by the US Space Weather Prediction Center – at the bottom of the image is the mode: Ambient if no CME was calculated; CME if one or more CMEs were calculated.
In the centre of the circle is the sun, the green dot to the right is the earth. The ecliptic plane is shown, i.e. the plane in which the planets move around the sun. We are looking at the plane from above (north). The semicircle shows a cross-section with a north-south axis – so we are looking at the situation from the side. The right-hand side of the image shows the one-dimensional progression of the density and velocity parameters. At the bottom of the image is the time at which the model run was started (2024-10-19 0000 UT in this case). At the bottom right is the time when the run was completed, i.e. when the corresponding image was rendered. NOAA often only renders one CME, even if there are several on the way, and only those that have the potential to hit the earth and trigger significant effects.
☞ www.swpc.noaa.gov/products/wsa-enlil-solar-wind-prediction
NASA Moon 2 Mars
The WSA-Enlil model runs of the Community Coordinated Modeling Center (CCMC), which are fed with data and executed by the NASA Moon to Mars Space Weather Analysis Office (M2M), are somewhat more complicated to find and more for advanced users. Both departments are located at the Goddard Space Flight Centre in Maryland, north-east of Washington, D.C.
All analysed CMEs and, for the more relevant ones, the associated WSA-Enlil model runs can be found in the Space Weather Database Of Notifications, Knowledge, Information (DONKI). NASA’s focus is not necessarily primarily on Earth-directed CMEs, so there are runs for individual planets, probes and different distances from the Sun. Furthermore, there are sometimes separate runs for the Shockfront and the Leading Edge, where the Shockfront is only used to support further calculations of SEPs (Solar Energetic Particles) and should not be used for CME prediction. It also happens that CME trajectories are recalculated after better data is available. The older runs are then labelled as ‘false’. The data in DONKI is only displayed after clicking on the ‘Search’ button.
☞ kauai.ccmc.gsfc.nasa.gov/DONKI
Earth-directed CMEs are usually placed on the CME Scoreboard together with calculations by other agencies and individuals. The main purpose of the scoreboard is to record the different forecasts in a systematic and standardised way in order to be able to evaluate them scientifically. What is interesting here is the sometimes extremely wide range of forecasts, which can occasionally be significantly longer than 48 hours – especially if images from coronographs are missing at the start time. This shows that
Prediction is very difficult, especially if it’s about the future!
☞ kauai.ccmc.gsfc.nasa.gov/CMEscoreboard
The latest Enlil run is linked on some World Wide Web homepages, but this is usually of little use, as unlike NOAA/SWPC there is not one official run but many different ones with different parameters for different CMEs. You can conveniently click through the individual runs in the ISWA web app, but you have to assemble it yourself first or download a JSON file that already contains the configuration:
☞ ccmc.gsfc.nasa.gov/tools/ISWA/
☞ iswa.gsfc.nasa.gov/IswaSystemWebApp/ (Loading in the browser usually takes a while)
On the left you can see the run for the CME from 9 October 2024, on the right an ensemble run for a CME from 1 October 2024 (did not reach us).
The JSON file is zipped and must be unzipped before use (‘Load Layout’).
ASWO
The Austrian Space Weather Office in Graz is at the forefront of space weather forecasting and operates the information-packed website helioforecast.space, where the output of the ELEvo model is also made available every hour. It calculates and displays all the trajectories of all analysed CMEs from NASA’s DONKI database. The model is unrealistic in that it does not include any background solar wind and does not calculate any CME interactions; instead, fast CMEs simply pass by slower ones, which would probably not happen in real space, as CMEs of different speeds lined up next to each other are pancaked – slowed down, compressed and their magnetic fields amplified – according to the latest research.
But that doesn’t matter, because ELEvo provides a good overview of current events in interplanetary space and often has better hit rates than the Enlil model runs described here, in which the background solar wind is often set too high or too low.
The circle represents the ecliptic plane, we are looking from above at the north pole of the sun at the centre of the disc. At the right edge – the green circle is the Earth, the other spots are spacecrafts and planets. The blue arcs with the shadows are simplified representations of CME shock fronts. At the top right of the image is magnetometer data for the interplanetary magnetic field at the L1 Lagrange point, below for the STEREO-A satellite. At the bottom is the speed of the solar wind at L1 and at STEREO.
☞ To see the animation, click on the image on the helioforecast.space/cme page (it is not obvious at first glance that it is a video).
UK Met Office Space Weather Operations Centre (MOSWOC)
The Met Office is the national weather service for the United Kingdom and has its own department for space weather. Text forecasts, watches and warnings for geomagnetic storms of Kp 7 (G3 STRONG STROM) and above as well as image-based aurora oval forecast can be found on their website www.metoffice.gov.uk/weather/specialist-forecasts/space-weather.
The Met Office Space Weather Operations Centre (MOSWOC) is one of a handful of 24/7 space weather prediction centres around the globe.
If you want to see detailed information and the results of the Enlil runs, you need either a Met Office professional account (you can apply for this by e-mail) or an account with the esa Space Weather Portal. The latter is free of charge and can be set up quickly.
Another possibility is to create a professional account on their website.
The link there: swe.ssa.esa.int/metoffice-enlil-e-federated. Ensemble runs are not always performed and are therefore sometimes missing from the page. It is important to read the commentary of the forecaster on duty, as this often describes the quality or usefulness of the results – this is also recommended for every other model run presented here.
HUXt Forecast (University of Reading)
The University of Reading in England has developed its own model for calculating CME propagation. It is straightforward, nice to look at and can simulate several interacting CMEs at the same time. It takes the background solar wind into account.
Its unique feature is the fast calculation of ensembles with several hundred ‘members’. This makes it easy to visualise probability ranges, i.e. ranges for arrival time and speed. The analyses of the starting parameters for CMEs come from the Met Office – the model can therefore only ever be as good as the Met Office analyses are.
The results often change several times after the first run for a particular CME, sometimes because the CME parameters are subsequently changed, sometimes because the values for the background solar wind or the currently measured solar wind change. So be careful and have another look before the expected impact!
Under the URL
☞ research.reading.ac.uk/met-spate/huxt-forecast/
you can find the 2D animation – with the small peculiarity that the Earth continues to rotate during the animation. There is also an overview of the ensemble forecast showing the probability distribution and a cross-section of the 1 AU radius around the sun with the Earth in the centre, and the CMEs with hit potential highlighted in colour:
Fun Fact: Reading is also home to the ECMWF – the European Centre for Medium-Range Weather Forecasts.
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To be continued…
▷ WSA ► Wang-Sheeley-Arge model, semi-empirical model that simulates the outflow of the solar wind near the surface of the sun
▷ Enlil ► God of the wind – the main god of the Sumerian and Akkadian pantheon – and a sophisticated three-dimensional magneto-hydro-dynamic numerical model that simulates the flow development all the way to earth.