Thursday, February 10, 2011

Coldest day of winter

       Today, my routine drive across Delaware County, Ohio registered below zero readouts on my vehicle thermometer from -2 to -8 degrees F. The below zero temperatures today, our season lows, do not telegraph the inexorable seasonal change underway. Ohio maple sugar season will begin next week, without fail. Sap will rise in sun-warmed trees as daytime temperatures reach the mid-forties.

       The seasonal symphony of careening, colliding polar air masses is nearly past. Mountains of piled air, high pressure zones holding arctic stations, and depressions of low pressure air holding stations in temperate latitudes, are weakening, finally. This Northern Hemisphere airscape, with our earth's coriolis force, swinging trains of air masses westerly, have locked North America in an icy holding pattern for months. The holding pattern is disintegrating under warm sun arcing higher and higher across our southern sky each day. Southern air masses will soon break north, the loud bite of winter's chill released.

       Cold will return for brief internals, but repeated warmth will wake our sleepy plant and animal communities in time for early returning migrating birds this month. Waterfowl will return with open water. American Woodcock will follow thawing soils northward. Hardy earlybird migrants will arrive to exploit the rise of flying insects and the availability of soil and water invertebrates.

Olentangy River, Delaware County, Ohio
       A sluggish Olentangy River, nearly frozen for weeks now, exhales icy mist. Nearly all of its seasonal low flow rises from groundwater seeping into the river channel from permeable limestones, alluvium, and glacial deposits along the length of the Olentangy River Valley. The tension between the geothermal warmth of groundwater and atmospheric cold sustains slushy ice formations and ice shelves along the river, and the icy mists of very cold mornings.

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