Weather-wise, aurora watching conditions are best in March
In Interior Alaska, March is the driest month with respect to precipitation and cloudiness on climate average. According to the World Meteorological Organization, a climate mean is the average over the weather conditions over 30 years. Of course, in individual years, the weather deviates from the 30-years average. In other words, you may end up visiting in a March that is much more cloudy than on average. Under these circumstances, your chances to see the aurora are lower than on average. Note that aurora activity also varies with time depending on the activity of the Sun.
In clear nights, temperature seems to be in free fall
Daily minimum and maximum temperatures vary also from their long-term mean. Thus, packing for the climate mean temperature is by no means sufficient for protection from frostbite and/or hypothermia. Add wind to the mix, you feel even colder than it actually is due to wind chill.
Hourly mean temperature in Fairbanks on March 29, 2016 Hourly mean temperature in Fairbanks on March 6, 2016
Daily mean temperature in Fairbanks in March averaged over 1988 to 2016
Hourly mean temperature in Fairbanks on March 13, 2007
Color coding of the thermal stress categories used in the figures
Energy exchange between your body and the ambient air causes thermal discomfort
Energy from Sun radiates thru space to the Earth. Incoming solar radiation differs by latitude, cloudiness, season, time of the day, pollution. Radiation transfers heat by electromagnetic waves.
According to Planck’s law, every body including the air radiates at its own temperature. Cold bodies radiate with lower energy than hot bodies. This means the energy flows from the higher to the lower energy, or in other words from the warm to the cold body. Thus, clothes or exposed skin loose energy by radiation when they are warmer than the ambient air.
There will be no loss by radiation when your clothes’ and the air have the same temperature (see plot above). However, even when you are dressed appropriately, your body looses heat when the environment is colder than the body temperature. The bigger the difference between the surface temperature of your outerwear and the environment is, the higher the loss of radiation energy will be.
You also loose body heat due to conduction, which refers to the transfer of heat by molecules. For example, heat from your feet is transferred to the sole of your boots to the frigid cold soil. Consequently, your feet loose energy that your body has to compensate for by means of chemical energy (food).
Furthermore, there is a huge temperature gradient between your skin and the ambient air. The skin increases the temperature in the vicinity of the skin. This slightly warmer, buoyant near-skin air rises transporting heat away from your skin. This process is called convection. Add wind to the mix, and the energy loss due to convection will accelerate.
High humidity can not only make you feel uncomfortable at high, but also at low temperatures. Air feels colder than it is under cool conditions with high relative humidity. Being in the shadow or in the sun makes a difference in thermal comfort. Walking causes movement and mixing in the air layers between your clothes or your skin and the first layer. Thus, the heat exchange is higher than when just standing.
In a nutshell:
How we feel our environment when dressed appropriately depends on energy exchange. Thermal stress depends on solar radiation, thermal radiation, air temperature, wind, relative humidity, clothes, and your body metabolism, i.e. activity.
Researchers used manekins warmed to skin temperature and various artifical “sweating methods on them” and equipet the various clothes layers with temperature sensors and/or measured the heat they had to replace to hold the manekins’ temperature. Researchers also asked appropriately dressed people about their thermal comfort. Using these data empirical relationships have been derived that determine a to determine the universal thermal comfort index (UTCI) that is expressed as a temperature. I used this empirical model to calculate the UTCI that measures how we feel the temperature under the respective environmental conditions. Depending on the environmental conditions the environment can feel warmer or colder than it actually is (see temperature and UTCI plots in this post).
Insulation is important for thermal comfort
Clothing hinders energy loss. Fabrics with low conduction coefficient are great for creation of a good body insulation. Thin air layers are best as air is a bad thermal conductor. Consequently, layering is key to create appropriate insulation to stay outside for several hours when watching the aurora. Wherever the fabric is in direct contact with your body and/or the environment, conduction takes place. A down coat that has a water resistant outer coating is a great insulator.
Fabrics also have moisture properties
Sweating serves to regulate body temperature by evaporation that causes cooling. In cold climate, evaporative cooling is unwanted. Thus, you will have to choose a wicking fabric closest to your body to avoid that the fabric gets wet.
Wicking and layering is key
Modal, rayon, viscose, tencel, lyocell, and bamboo take up sweat. Once they are wet, insulation is zero! Thus, these materials are not a great choice for thermal comfort at temperatures in the the negative double digits. On the contrary, merino wool can take up a lot of moisture without feeling wet.
How to stay comfortable when visiting the Interior in March
Wool socks are a must! Wear two pairs for extra insulation and always buy your winter boots a size larger than your summer shoes. Recall squeezing your feet in means you have contact between the feet, the socks, and boots and hence conduction of heat to the environment.
Go for silk or polypropylene long underwear. Pile on layers of polar fleece or wool for insulation. The outermost layer should protect against wind and moisture from outside, i.e. melting snow or under warmer conditions rain.
Adjustable openings avoid cold bridges where cold air can enter and mix with the air between your layers. A high percentage of body heat is lost via the head followed by the extremities. Thus, a hat, scarf, and gloves are must-haves. In March, the Sun is still low in the sky. Sunglasses are needed during the days because of the refection of the sun beams on snow and icy roads. The snow acts like a mirror which means that sunscreen with a high SPF is needed when you do sightseeing during the day. Since temperatures may go above the freezing point during the day, waterproof shoes with thick insulating soles are needed. Avoid rubber boots as the thermal conductivity of rubber is high.
In a nutshell:
Clothing materials need low conductivity, must reduce convection and radiation loss. Thin air layers are perfect for insulation, and layering is key.
Together these facts mean that how we feel our environment when dressed appropriately depends on energy exchange (wind, radiation, humidity, etc.), and our activity. Air can feel warmer/colder than its actual temperature. Clothing materials need low conductivity, must reduce convection and radiation loss. Thin air layers are perfect for insulation meaning layering with the right fabrics is key to prolong the time you can stay outside. Layering is key, style is optional.
You may also be interested in reading what to pack for aurora watching and what you need to increase safety when traveling in Alaska. You can find a video of my talk about the physics of clothes – what Alaska’s climate means for body heat exchange at the link.
What do you want to see when visiting Alaska? Let me know by email. I am curious.
Happy Monday! A few of my blogger friends and I wanted to kick start your week by joining together to bring you a giveaway – a $125 Kate Spade gift card! Are you the one lucky reader? Simply enter the Kate Spade giveaway via the widget at the link.
Prize: $125 Kate Spade gift card
Giveaway open: Monday, December 12 at 12AM PST through Friday, December 23 at 11:59PM PST.
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Giveaway is closed. The winner is Emilyne O.. Liz at Shopping My Closet contacted her on Saturday to inform her of the great news, and she was quite ecstatic in her response!
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Photos: G. Kramm
Graphics: N. Mölders
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