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Noctilucent clouds are lit by sunlight in an area of the night sky called the Twilight Arc.
My twilight-arc tracker is constantly monitoring the position of the sun at your location and calculating the position and height of the twilight arc.
The centre of the twilight arc is at the sun's azimuth. The sun's elevation is its angle above (or below, if -ve) the horizon.
The 'Max Heights' are the maximum angles above the horizon that Noctilucent Clouds and Cirrus can be lit directly by sunlight.
NLCs are only visible when the sun is between 6° and 16° below the horizon and the times when you are able to see them are shown.
The headline figure (with nT beside it) equates to the strength of the aurora in the sky right now. You want it negative. The more negative it is, the stronger the aurora is. Falling is good, rising is bad.
When it says 'growth', the substorm is charging up like a battery. When it says 'expansion' that energy is being released as aurora. When it says 'recovery', the aurora will slowly begin to fade.
The trendline shows the changes in strength over the last hour. The line dropping sharply downwards is good. Rising is bad. The green shaded area indicates the ambient level.
I am indebted to the kindness and generosity of the Tromsø Geophysical Observatory and Swedish Institute of Space Physics for letting me access their live data feeds and use them to alert you when the aurora can be photographed in the UK, Iceland & Europe.
The table shows an analysis of the interplanetary magnetic field in the 30 minute window that is currently arriving at Earth, together with the 30 minute windows either side of it.
The 'percentage' figure indicates how negative the Bz was, the ideal is 100% negative.
This the the mean velocity, density, pressure and power of the solar wind that is currently arriving at the Earth. The higher the pressure and power of the solar wind the better.
The trendline shows the changes in the solar wind speed over the last 24 hours, with the density shown behind. When both of these are rising it normally indicates arrival of a co-rotating interaction region. When speed rises and density falls this indicates a coronal hole stream. The green shaded area indicates the ambient level.
Coronal holes cause most of our auroras and they are regular, repeating on a 27 day cycle. Plasma from an Earth-facing coronal hole typically takes 3 to 4 days to reach us and spark auroras.
Flipping between the 'now' and '-27 days' tabs allows you to see how coronal holes have changed since their last rotation 27 days ago.
The '-4 days' tab allows you to see how the coronal hole looked when it was in the geoeffective position 4 days ago.
Solar imagery courtesy of NASA/SDO and the AIA, EVE, and HMI science teams.
Long-duration solar flares often produce a CME which, if directed earthward, can cause geomagnetic substorms between two and four days after the eruption.
Flares are classed B, C, M or X with B being weakest and X being strongest. The number indicates how strong the flare was within its class.
These are the dates when solar wind streams that gave us good auroras will rotate around again. There is no guarantee that the coronal holes that caused the substorms on the previous rotation won't have closed but they also may have got larger. You can only use these as a guide but this is the most accurate long-range forecast for the UK, Ireland, Iceland and Scandinavia that you will find anywhere in the world.
This forecast is based on my own data collected in the UK and is specific to Western Europe & Iceland. You may see more than one entry per day if there were multiple, strong substorms in the same day on the previous rotation.
* You need to register to view the full 28-day forecast.
Entering your details here will allow you to make instant, live, aurora reports to let others know what the current situation is where you are. You will also be able to see reports from other users and access all features of the app.
Enter the exact same details on all devices where you use the app to synchronise your history and reports across them all.
If you work as an aurora tour guide, researcher, scientist or are an admin on an aurora facebook site you can enter those details and they may be shown to other users.
This app collects sighting reports you make for purposes of scientific research, to improve the accuracy of aurora forecasting and for alerting users when the aurora is active.
Your personal data is not shared with any other organisations or third parties.
You will not be spammed. You may be contacted about interesting reports you have made, problems you are having with the app or security/authentication issues.
Your phone is android and is capable of receiving alerts but you need to install the Chrome app and make it your default web browser.
To install this web app on your device:
Go to aurora-alerts.uk.
Press SHARE button in Safari (square with an arrow).
Add to Home Screen.
Add (top right).
Open Chrome or Firefox.
Go to aurora-alerts.uk.
Click the red 'install the app' button.
Open the Chrome App.
Go to aurora-alerts.uk.
Click three vertical dots icon (top right).
Add To Home Screen.
Click 'Enable Alerts'.
App installed and tile added.
The basic alerts are push notifications that the app sends automatically when it detects that an aurora is developing. An 'onset' alert is sent first as a warning that an aurora is starting, followed by yellow, amber, red, major, severe and extreme alerts as activity develops. Your device will receive these even when the app is not running.
The 'Expansion Alarm' is designed for desktop users. If you leave the app running permanently on your PC, the app will start bleeping as soon as it detects a substorm heading into expansion phase to give you time to head out and catch it at its peak.
'Activity Alerts' are notifications that can be set to 'ping' your device only when the app is running. These occur much more frequently than the basic alerts. They alert you to all thresholds being crossed, auroras being reported by users and photos being uploaded. These are great for users of desktop PCs who want to keep constantly updated on the current aurora situation.
The plot shows the substorm strength over the last 24 hours, which allows you to see the periods when the aurora was most active.
The more negative the figure, the stronger the aurora was.
The plot shows the clock angle (θ) over the last 24 hours, which allows you to see the periods when the IMF was best aligned.
The plot shows the IMF Bt & Bz over the last 24 hours, which allows you to see the periods when the IMF was strongest.
This app was created by Andy Stables of the Glendale Skye Auroras Facebook Page to make it easy for people to photograph the Aurora Borealis. It is the result of research carried out on a daily basis since September 2012 in the Isle of Skye.
The total accuracy of the app is only possible due to the generosity of the Tromsø Geophysical Observatory in allowing me to access the live data feeds from their entire magnetometer array in Norway.
The wonderful icons for the tiles, badges and logo were the work of Andrew Liley from Portree.
The Iceland Version of the App was only made possible thanks to many hours of detailed observation and recording by Caroline Weir from Reykjavik, who runs the Aurora Iceland Facebook Group.
Read the full behind-the-scenes story of this app here.