Australian Antarctic Division Cosmic Ray Real Time Data at SWS
Historical Australian Antarctic Division Cosmic Ray data from Kingston in Tasmania, and Mawson in Antarctica are available in the SWS World Data Centre.
NOTE: Kingston data no longer available due to equipment failure.
Cosmic rays consist mainly of protons. They can originate from galactic cosmic radiation or from the Sun. Cosmic rays are observed indirectly by a device known as a neutron monitor. When cosmic ray particles enter the Earth's atmosphere they interact with the nuclei of the air molecules to produce secondary radiation. This consists of pions (which decay to muons) and a shower of protons and neutrons. The neutrons predominate in this secondary radiation because the protons, being charged are more easily attenuated in subsequent travel. The cosmic ray detector actual detects these secondary neutrons and as a consequence is referred to as a neutron monitor.
Cosmic Ray Data Applications to Space Weather Forecasting
Forbush Decrease Event
The magnetic fields entrapped in and around coronal mass ejections exert a shielding effect on the galactic cosmic radiation (GCR) which is detected by the neutron monitors. This causes a reduction in the count rate from the monitor. The reduction is typically from about 3 to 20%. The reduction occurs typically over a timescale of several hours to a few days.
Forbush decrease events must be at least 3% for a Forbush decrease alert to be issued.
The reduction in the GCR due to a coronal mass ejection (CME) is dependent upon:
- the size of the CME
- the strength of the magnetic fields in the CME
- the proximity of the CME to the Earth
Because the reduction is dependent on three factors (rather than one), it is difficult to forecast the time from a Forbush Decrease to the arrival of a coronal mass ejection at the Earth. However, previous experience in SWS is that a Forbush Decrease is a reliable indicator of a geomagnetic storm, and that warning times of up to 24 hours or more may be made. The Forbush Decrease can be used in conjunction with other indications (eg coronagraph imagery) to further confirm the event. Detection of a Forbush Decrease is in use at the SWS ASFC for assistance in prediction of geomagnetic storms.
Ground Level Event
In this case, an increase in detector count rate is not due to galactic cosmic radiation, but to the addition of solar cosmic (high energy) radiation (solar cosmic rays) from an previous solar particle event (SPE). The increase in the count rate may be from about 3 to 10,000%. The increase from ambient to peak count rate may take only a few minutes (fast high energy event) to an hour or two (slow and usually lower energy event). The return of the count rate to galactic cosmic ray background may take anywhere from a few hours to a few days.
Neutron Monitor Data from Mawson, Antarctica
Data is transferred at 5 minute intervals, 1 record per minute. For slow ground level event detection (increase in count rate) and forbush decrease (decrease in count rate) hourly averages of the minute data are used. Alert thresholds (above and below) have been set at 4 times the standard deviation obtained over a 48 hour period. In addition Forbush decrease events must be at least 3% for a SWS Forbush Decrease alert to be issued. The threshold shown in the plots are the 5 times standard deviation threshold. The requirement of at least a 3% decrease is necessary for when the cosmic ray data exhibits very little variation, bringing the 4 times standard variation threshold potentially very close in counts to small data count fluctuations, increasing the risk of false alarms being produced.
For fast ground level events the minute data is used with a increase perentage threshold of 10%.
To try and minimize GLE false alarms the GOES solar xray flux must also be greater than M5 at the time of detection of the GLE.
The above thresholds are experimental and may need to be adjusted with experience.
The data displayed below is provided by the Australian Antarctic program in near real time. A neutron monitor located in Antarctica has no geomagnetic (lower) cutoff energy (although there is atmospheric cutoff energy), and thus provides the most sensitive indication of cosmic radiation of any sensor located on the Earth's surface.
Realtime Cosmic Ray detectors (Neutron Monitors) operated by other organizations are also available:
Fast Ground Level Event Detection Plots
Latest Minute Data:
Minute Data over last 24 hours:
Log of Fast Ground Level Events:
(last updated 06 Jun 2018 04:30 UT - empty)
Slow Ground Level Event and Forbush Decrease Detection Plot
Hourly Averaged Data:
Log of Detected Forbush Decrease Events and Slow Ground Level Events:
Forbush Decrease Observed ( 3%) at MAW 20/07/2016 DOY: 202 Hour: 06UT Count: 14356.7 Avg: 14801.8 Lower Alarm Level: 14567.8 Forbush Decrease Observed ( 3%) at MAW 12/10/2016 DOY: 286 Hour: 04UT Count: 14817.0 Avg: 15321.2 Lower Alarm Level: 14893.2 Forbush Decrease Observed ( 3%) at MAW 16/07/2017 DOY: 197 Hour: 13UT Count: 14956.0 Avg: 15535.1 Lower Alarm Level: 15279.0 Forbush Decrease Observed ( 6%) at MAW 16/07/2017 DOY: 197 Hour: 21UT Count: 14460.0 Avg: 15459.9 Lower Alarm Level: 14603.3 Forbush Decrease Observed ( 5%) at MAW 17/08/2017 DOY: 229 Hour: 04UT Count: 13393.7 Avg: 14158.8 Lower Alarm Level: 13395.7 Forbush Decrease Observed ( 3%) at MAW 08/09/2017 DOY: 251 Hour: 02UT Count: 13789.7 Avg: 14236.5 Lower Alarm Level: 13935.4 Forbush Decrease Observed ( 6%) at MAW 08/09/2017 DOY: 251 Hour: 12UT Count: 13276.7 Avg: 14145.3 Lower Alarm Level: 13284.5