In this article we would like to shed some light on our plotter graphs. In this particular case we are going to focus on the graphs we are using to monitor auroral activity. That is Greystones to Grindavik (TFK/NRK, Iceland) and NAA Cutler (Maine, USA). TFK and NRK stations were chosen as particularly well responding to auroral ionospheric disturbances on the radio path to Ireland. NAA station has been additionally selected as fairly responsive to severe auroral disturbances, allowing to estimate intensity and lowest latitude of an Aurora.
To start with, just browse through our Plotter Archive section where we have collected Grindavik plots for every single night starting from March 2023 Although seeing all sorts of various graphs' shapes could make anyone flustrated at first, there are graphs which stands out clearly. Fortunately, these are indeed records of strong aurorae which were well visible on lower Irish latitudes with numerous photographic evidences in social media. There were just few strong auroral nights in Ireland since March 2023 where lights went as far south as Waterford. You can see most of them below.
As you see from the above plots, the graphs' shapes are quite distinctive. Graphs are very uneven, deflecting rapidly up or down in short period of time. Sometimes, deflection rate can be as high as 25db (decibel), that is 316 times in power! More typical deflections are around 10db though. That is exactly how geomagnetic storms are affecting the Earth's ionosphere, resulting some certain Very Low Frequency radio signals to fade in and out rapidly, helping us to research VLF propagation during such events.
In contrast, quiet nights' graphs appears to be much more settled. See few examples below. Although, there could still be some deflections, but normally those are fairly slow or rare, which indicates normal, not enhanced ionosphere state and absolutelly no mid-latitude аurorae.
Sometimes, we can see graphs' trembling or having some very minor deflections as on the image below. That indicates an unsettled ionosphere, probably after some geomagnetic event, a weak Aurora can be expected, likely only visible on high latitudes.
Our plotter is updating data automatically and re-uploading the plots to the website each every 30 seconds. To have the most up-to-date data displayed just click your browser Refresh button. Watching the updated data, combined with other monitoring tools and indexes we have on the website, should make aurorae hunting a bit easier or, if you've been away, you can always check did you miss anything significant.
Finally, to help better understand the plots in detail, we would like to describe a typical quiet night's auroral plot. The important detail to remember is that due to peculiarities of VLF radio propagation, the plotter is only responsive to auroral ionospheric disturbances some time after local sunsets at each end of the path, that is here in Ireland we have to wait until after a sunset in Grindavik to start gather meaningful data. Same applies to local sunrises, the auroral data is only reliable before a local sunrise in Ireland.
We have selected a recording timespan accordingly, to run unified, between 1900 - 0700 UTC The timespan fully covers spring-summer-autumn seasons. Although the span is not wide enough to cover full winter season the coverage is still sufficient for most users. Please note, all times on our site are in UTC.
On the below plot we can see all three NAA, TFK and NRK graphs, recorded during the night of 2023-09-10/11 (note, we are labelling plotters' date as a date next after midnight) You can see local sunset/sunrise periods. If you look through the Plotter Archive data, you will see, how those periods are shifting daily, marking a time of the year seasons' shift. In between sunset and sunrise we have all the valuable auroral data we can use for our research. On the below plot there was a quiet night with only minimal enhancement around 0200-0300, likely not noticed in Ireland at all.
At the end of this article it is worth to mention some situations where ionosphere is fairly disturbed on the path, however geomagnetic and forecast tools doesn't show anything worthy. That could be a result of a still settling ionosphere after a previous geomagnetic storm or an Aurora reaching only higher latitudes, say as far North as Iceland. A good example is on the below plot. Although forecasts and indexes were low, good photographic reports were still coming from Iceland for that night.