By Rachel Dutton
Medium Term Forecasting
There is a lot to aurora forecasting, however, there are a few essentials that will stand you in good stead for getting a solid start.
Sunspots & Solar Rotation
Image credit – John Axtell
We’ve covered sun spots, but, seeing people posting their beautiful pictures on Facebook such as in the Guildford Astronomical Society Facebook group is a good sign to start paying attention to the forecasts.
Something else to take into account is that the flares from these sunspots need to come towards the Earth. Whilst they don’t need to directly face the Earth exactly head on, the Sun’s rotation means that they aren’t always facing us.
They definitely will not send a flare in our direction if they are on the side of the Sun we can’t see. The equator of the sun rotates faster than the poles which complicates things as well as the Earth moving in its orbit, however, it takes around 27 days for the same part of the Sun to face the Earth again, give or take.
Active Region 3664 later rotated away from us and may still be there when the sun rotates further around again. Many news websites are reporting large flares, but they are pointing away from us.
KP Index
The Kp index (or planetary K index) gives us an idea when to expect aurora strong enough to come to the UK latitude. It quantifies disturbances in the horizontal component of earth’s magnetic field and it is derived from the maximum fluctuations of horizontal components observed on a magnetometer during a three-hour interval.
It has a scale of 0 to 9. A Kp index of 6 is the bare minimum needed for aurora in the UK and that is likely to be up North, but there are possibilities further South. The 10th May 2024 event was measured as 9 in the UK.
This was extremely rare and photos were taken as far south as Namibia at a latitude of 22.5 degrees.
Anything above 6, is a good indicator to keep an eye out.
A free website is the US’ National Oceanic and Atmospheric Administration website’s experimental aurora dashboard. It has the KP index as well as a visual indication of where the aurora will occur. It will focus on the US, but if you keep in mind London is approximately in line with Vancouver, Canada and all the UK is above the Canadian border with the lower 48 states, you can still get a good idea of activity. It is also colour coded green to red so if you see a nice red patch at UK latitudes, that is a good sign, but technically any green over that area can be good too.
Spaceweather.com is also another great website but you do need to pay if you want alerts but it does have free data as well.
The Glendale Aurora app is a great app recommended by most people. Instead of signing up at the app store for your device, go to the website and it will show you how to add it to your home screen and it will create the app for you. You can sign up for free and it offers great information on medium and short term forecasts for your area. You can find this at https://aurora-alerts.uk/.
Short Term Forecasting
There are several things to take into account, but short-term forecasting, we want to see a negative nano Tesla (nT) reading for a chance of seeing the Northern Lights.
Some explanations:
The solar wind forms the interplanetary magnetic field or IMF. This is called Bt and we measure in nT. The direction of the IMF is known as (Bz). If it is positive, then the IMF is facing North, and we are unlikely to experience aurora. When it flips south, the magnetic field lines connect to the magnetosphere and we get Northern lights.
A Northern facing field is denoted by a positive number and South facing is given with a negative number.
In places further North such as Iceland anywhere from 50 nT to negative numbers can indicate aurora, in the UK, we are more likely to see them when the numbers are negative. The more negative, the stronger the lights will appear.
“The Glendale App has this but another great app that is easy to read is Aurorawatch UK, which is run by the University of Lancaster and has a simple red, amber, green status. Red means a good chance of aurora. They have an app which has free alerts. It is worth noting they do not use the negative signage for Southern IMF alignment. It is also more on the optimistic side, but it is considered easier for people to read.”
A Note On Self Reporting Apps
There are a number of apps that rely on user self-reports are less reliable. It relies on people to correctly identify aurora which can include people not recognising the sunset, light pollution reflecting off clouds and light displays going into the air from clubs and even hotels. Take self-reports with a little scepticism unless there are many or they come from a trusted source.
Other Planning Considerations
Weather Forecast
In order to see the Northern Lights, you will need a relatively clear sky, however, you can still see them through clouds if there are sufficient gaps. If you aren’t sure if it’s aurora, there should be stars behind the colours you think are aurora.
So keep an eye out for clouds, rain, sleet, snow or fog.
Light Pollution
The Sun, the Moon once it is past its first quarter (or waxing half-moon) up to its third quarter (waning half-moon) and city lights are all going to brighten the sky especially if there is any cloud.
There is auroral activity during the day, but we can’t see it as it is drowned out by daylight. If you have a bright security light in your garden or a car headlight, that can also wash out the aurora so turn off what lights you can or even cover them such as with a bucket.
Also, scout out potentially safe dark sites near you during the day, but always ensure your safety and never go out in an unsecured area by yourself in the dark. Part of the reason people join GAS is to take part in member observation sessions as we get to know each other and there is safety in groups. You can join us here.
In the Summer, in some latitudes, we don’t get true darkness where the Sun goes 18 degrees below the horizon. In stronger storms, just some darkness is needed but for some weaker displays, we will need to be close to midnight (or 1am as we have moved into Summertime).
Comments are closed