Sunday, April 08, 2018

Predicting the Aurora for Photography

I am part of this awesome photography community, and the members constantly share great tips. Here's one I thought a lot would benefit from (Aurora Time-lapse by Jeff here):

By Jeff Wallace (Facebook Page) -  I remember the first time I saw the northern lights. It was sometime in the early 80s, a green glow on the horizon while traveling on a bus in northeast Minnesota. I think everyone was sleeping, but I couldn’t take my eyes away from the window.

Since moving to central Alberta in 2009, I’ve been a regular aurora photographer and happy to share my approach to predicting the aurora for photography.

From time to time, I’m asked if the auroras will be out, or when is the best season to see them. Outside the aurora chasing community, most are unaware that space weather is monitored continuously, and the auroras are more or less predictable now. Their appearance isn’t the random happenstance it once was. 

By Jeff Wallace



Pre-Storm

Find Dark Sky - To avoid the effects of light pollution and find the darkest sky, use Light Pollution Map An excellent resource to help pinpoint the nearest sky that’s good for observing.

Composition

Spend some time exploring your local countryside to find interesting foreground. The aurora will take care of themselves, compelling foreground will make a good shot, a fantastic shot. To be efficient, I use Google Maps and scan for lakes, ponds, sloughs, rivers, abandoned homesteads, pin them, and spend an afternoon scouting to confirm the landscape. Over time, you can amass dozens of good locations.

Space Weather

Subscribe to NOAA’s 3-Day Forecast, enroll here.


Social Media

Join enthusiast group local to your region on Facebook. They’ll have members that are excellent chasers, readers and interpreters of the data from NOAAs DSCOVR satellite. Photos are often posted in near real-time showing current state.

T-3 days – An event happens, then we wait

Northern and Southern lights occur when the sun either ejects several billion tons of plasma, an explosion called a coronal mass ejection (CME) or a coronal hole opens on the sun’s surface and we take a blast of high speed solar winds. These events are assessed, and estimates are made about strength, speed, and direction. Forecasts are issued, and as is customary, all dates and times are given in Universal Coordinated Time (UTC). Be sure to adjust the forecast date/time to your time zone. It usually takes 3 days for the plasma or solar winds to arrive. That said, keep a little in reserve, the Earth is a 93m miles from the Sun and is a tiny target. A lot can happen between the event and arrival. Sometimes, highly anticipated events occasionally result in a complete miss. It's a running joke that when media get wind of a good forecast and hype it, it'll jinx the storm.

T-1 day – Plan for local weather

Local weather: Start monitoring local weather to understand where clear sky is predicted. A good tool for North American observers is Clear Dark Sky. Developed for astronomers, it predicts hourly cloud cover, atmospheric transparency and seeing, but chasers primarily focus on the hourly cloud cover forecast for planning.

T-0 Impact – The Arrival

  • In the short-term, aurora chasers around the globe monitor for the arrival of the interplanetary shockwave. If you’re fortunate, it’ll arrive night side and you’ll enjoy the impact and initial show. If you’re dayside, you’ll need to wait, which feels like an eternity. That said, when it’s a strong geomagnetic storm, the aurora often appears in the evening twilight before true darkness.
  • Monitor near-term cloud movement to gauge where clear sky is likely to appear. For the Canadian prairies I use this website.
  • U.S. observers can use this weather website and I’ve found it helpful too because their satellite data and products extend well north of the Canadian border.
  • When the forecast looks promising and sky is clear, I’ll head out to a good location to photograph the aurora.
  • In the near-term (less than an hour), the plasma and solar winds pass the DSCOVR satellite. From this data, we can understand how the geomagnetic storm is unfolding and is also helpful for predicting the arrival of sub-storms of active auroras.
  •  Space Weather Live (link here) publish current geomagnetic activity and visualize the location and strength of the aurora oval. They also publish key measurements such as solar wind speed, density, the north-south direction of the interplanetary magnetic field (Bz) and its strength (Bt).
  • NOAA also publishes a Space Weather Enthusiasts Dashboard too.

The key indicators I monitor are:
  1. Ovation Aurora Forecast shows the position and probability of seeing the auroras on the globe. It’s updated every 5 minutes for both northern and southern hemispheres.
  2. Bz value. Most important indicator and the needs to be negative, because a southward orientation of the Interplanetary Magnetic Field connects with Earth’s northward magnetosphere. A value of -10 is a good for observing aurora in middle latitudes.
  3. Bt value indicates the strength of the Interplanetary magnetic field and a value of 15 or higher is a good predictor of good aurora, the higher the better.
  4. Solar Wind measured in km/sec, a sudden jump from 300 to 500 km/sec could indicate the arrival of a coronal hole high speed stream or jump to 700 to 1000 km/sec indicating the arrival of coronal mass ejection (CME). These speeds allow observers to calculate arrival from between 30-60 minutes and understand how hard the magnetosphere will be hit, suggesting how active the aurora will appear.
After writing this post, it seems planning northern lights photography is more involved than I assumed, but with time most of these steps become second nature. More often than not, you’re out in the field enjoying the night sky and hopefully watching the auroras go active too.

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