Looking to the light

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One morning I was putting AJ in her carseat when our 5-year-old neighbor came out of the house next door. She waved and asked where we were going, and I told her we were going to a friend’s house for a playdate. She replied, “Now? In the middle of the night?” “It’s not night,” I said, “it’s almost ten in the morning.” She said, “But it’s still dark outside. Whenever I wake up and it’s still dark, my mom always says ‘go back to sleep! It’s not morning yet!’”

Some Alaska moms can get their kids to sleep until noon in the winter using that trick. Unfortunately, my daughter has an impeccable internal clock that wakes her up hours before light breaks the horizon, and she’s progressively waking up earlier and earlier.

Thankfully, so is the sun. Though it still rises at about the same time AJ takes her first nap, the increasing light already makes a big difference. Everything looks better from this side of the solstice.

Winter in interior Alaska lasts for almost three-quarters of the year, and in December we only get a very few short hours of sunlight. It would all be completely unbearable if it weren’t for one thing: seasonal temperature lag, the delay in the Earth’s surface temperature response to solar insolation. The warmest time of the year occurs after the peak of maximum solar insolation (summer solstice), and the coldest time of the year occurs after the time of lowest solar insolation (winter solstice). Temperature can lag insolation by up to three months, caused by the high specific heat of water in the oceans and atmosphere, which absorb incoming heat from the sun and release it slowly.

If there were no seasonal temperature lag, winter would be evenly split between either side of the solstice, and the darkest month of the year would also be the coldest. Our first four months of winter would be an agonizingly slow march towards ever-decreasing temperatures and light. By mid-winter, we would all be in a black hole of depression with nothing to look forward to because the second half of winter would be just as long and terrible as the first.

Thanks to temperature lag, two-thirds of the winter is spent in progressively increasing light, and the second half of winter has longer days than the first half. By the time we reach the coldest days of the year, the days are already longer than they were at the beginning of winter. And even though snow continues to linger long after spring equinox, summer’s constant daylight inches closer and heralds the warmth. Thank goodness for the specific heat of water.