By Dan Weaver
Ph.D. Candidate, University of Toronto
You have likely noticed the days are getting longer.1 It’s a welcome relief from the short dark days of winter. Toronto, for example, will enjoy over 12 hours of sunlight on April 20. Two months earlier there was only 9.5 hours of sunlight. The seasonal change in sunlight hours is small near the equator, and larger as latitude increases. In the high Arctic, where a Canadian research team is conducting fieldwork at the Polar Environment Atmospheric Research Laboratory (PEARL), the sunlight shift is extreme.
The pre-campaign team arrived at PEARL on Saturday, February 20 – the last day of Polar Night. There hadn’t been any sunlight yet in 2016. That quickly changed. A week later, on February 27, the intensive phase research team had their first day at PEARL, having arrived the previous evening. Watching the sunrise and sunset was very convenient that day: sunrise was at 10:15 AM; the sun set at 3:45 PM. That’s five and a half hours of sunlight. On the intensive phase team’s last day at PEARL (March 18) there was over 12 hours of sunlight: the sun rose before 7 AM and set after 7 PM. A couple of team members will stay an additional two weeks. On their last day, April 1, the sun will rise at ~4:30 AM and set ~9:15 PM. There will be nearly 17 hours of sunlight!
A variety of PEARL instruments, such as the Cimel sun photometer and the Bruker 125 high resolution (FTIR) spectrometer, use sunlight to measure the atmosphere. As the sunlight hours increase, scientists are able to take more and more data. (Other instruments don’t depend on sunlight, but they have other limitations).
One of PEARL’s technicians wrote an interesting blog last year about his experience working in complete darkness during Polar Night, and watching as the landscape slowly revealed itself throughout February.
Why does this happen?
Every year, the Earth’s axis tilts the Polar Regions into complete darkness for part of the winter (“Polar Night”), and into 24-hour sunlight for part of the summer (“Midnight Sun”). This has profound impacts on the people who live and work there, the animals and plants, and the atmospheric chemistry. (Read about the impact sunlight has on ozone chemistry in a blog post here.)
In Eureka, Nunavut – where PEARL is located – Polar Night lasts for 4 months. It is perpetually dark from mid-October until mid-February. (See a neat photo of Eureka taken during the start of Polar Night last year here.) On the other extreme, on the sun will rise on April 12 and stay in the sky until August 29. It will circle in the sky for four months.
I hope this puts the experience of our research team and the changing daylight hours you experience in a new light!
Sources & Notes
Data for Toronto, Yellowknife and Eureka sunrise and sunset times were downloaded from the U.S. Naval Observatory.
Note 1: Sunlit-hours, not the actual length of the day. Though in a small way, that is also happening. The length of the day is continuously getting longer due to the influence of the moon.