February: Snow and Sun in the Biosphere
February is called ‘Bright sun Time’ (Apiknajit) or ‘Snow blinder month’ in Mi’kmaq. To shine a light on the ‘bright sun characteristics’ of February in the Bras d’or Lake Biosphere, I consulted the solar angle calculator made available by the National Research Council of Canada and the climate normals (averages) for 1981 to 2010 collected by the Meteorological Service of Canada.
In January and February you need eye protection when enjoying winter sports in the Biosphere. Snow blindness, caused by ultraviolet light from the sun, is a painful eye condition which can be described as a sun-burned eye. In northern regions, this condition was traditionally avoided by using protection in the form of snow goggles, constructed of wood or bone with a thin slit.
Between 1981 and 2010, snow has been recorded in all months between October and May in the Biosphere. However, in October and May the accumulation is minimal. So, for our purposes, I will designate November to April as the ‘snowy months’. Besides, it feels better to say that it snows on 50% of the months of the year rather than 67%!
Bright sunshine observations are made with a glass sphere (Campbellstokes sunshine recorder) which focuses the sun’s rays on a card to generate measureable burn marks. These measurements are not available for Baddeck, so we will look at bright sun averages measured in Sydney over the 1981 to 2010 period. April is the standout at 141 hours, twice the number of hours of bright sunlight in December. February is 80% of April’s average.
Anyone who drives regularly over Kelly’s mountain in the winter will tell you that there are distinct microclimates throughout the Biosphere. In the period of 1981 to 2010, average recorded snowfall for the year was 283 cm in Sydney and about 10% higher in Baddeck at 312 cm. As expected, the best time for skiing was probably in January because the largest amounts of snow fell (81.7 cm in Baddeck). That may not be the case this year. Although the month of February is not usually the time of maximum snowfall, the amount recorded between 1981 and 2010 is impressive (66.6 cm in Baddeck) when compared to the amount recorded in some other parts of the province such as the Halifax Citadel (35 cm).
How does the snow cover affect the amount of sun that is reflected from the ground and into the eyes? During summer, landscape elements such as green grass absorb light. However, during the snowy months, snowflakes scatter and reflect the sun’s rays increasing the amount of light that is available to enter the eye. The ratio of light reflected to the amount of light that falls on a surface is called ‘albedo’. This is not to be confused with ‘libido’ which is an entirely different thing! Interestingly, snow exhibits a large amount of variability in albedo as a function of the age of the snow surface and amount of cloud cover. To see what makes February rate as ‘snow blinder month’, let’s take a look at how these things change over the snowy months.
Fresh new snow greater than 1 cm in depth has an albedo of about 0.85, meaning that it reflects about 85% of the sun’s rays that hit it and absorbs the rest. The characteristics of that snowpack change as it ages. The delicate crystalline structure of the snowflakes breaks down, spaces between the grains are infilled with wind-blown particles and surface melting causes a change from powder to a more granular consistency. Because of these factors, the albedo of a melting snowpack can change rapidly, up to 9% per day. A fresh fall of greater than 1 cm will reverse this trend. So, what about the duration of snowfall? Again, January tops the list in the Biosphere, with snow falling on about 50% of the days of the month. This is about double the number of snowy January days than the Halifax Citadel. In the Biosphere, snow falls on 40% of February days, an impressive statistic!
The relationship between cloud cover and snowpack albedo is very surprising and not what you might predict. When skies are clear, the sun’s rays reach the snow surface directly. When the rays reach the snow surface, the surface roughness casts shadows and separate surface snow grains reflect a direct beam only on one side. There is less of a shadow cast when skies are overcast and diffuse light from the sun reaches surface snow crystals on all sides from all directions. Thus, the albedo of a snowpack is higher under overcast skies. During the snowy months it is very cloudy between 60 and 70% of the time according to the climate normal of Sydney (no measurements are available for Baddeck). There is less cloud in January and February than November and December. The thinner clouds enhance Ultraviolet levels because of scattering. Remember that when you embark on a ski trip in lightly overcast conditions. Take your snow goggles!
So, where does that leave us in our exploration of February as ‘Bright sun time’ in the Bras d’or Lake Biosphere? Conditions are right in February for ‘Bright Sun Time’ but that descriptor may also apply to January or March in some years. This analysis dealt with climate normals, or averages over long time periods. Every year is different. Remember January, 2015? The Biosphere looked a lot whiter than it did in January, 2017. The diversity of weather patterns from year to year and the globally changing climate may mean that ‘bright sun time’ will occur in December or March for the climate normal analysis of 2017 to 2046. Maybe we won’t have a ‘bright sun time’ or as much snow in 2046 and the Biosphere residents who normally leave for Florida during the snowy months will just stay put!
Dr. Annamarie Hatcher is an adjunct professor in Unama’ki College, Cape Breton University, and a board member of the Bras d’or Lake Biosphere Reserve Association. For more information about the Bras d’or Lake Biosphere Reserve Association, please visit http:// blbra.ca/.
Friends of the author, Sam and Graham, are seen skiing Ben Eoin while wearing eye protection. Photo by Annamarie Hatcher.