|
|
|
|
Frost Damming
Mon Feb 09, 2004
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook. When air at higher elevations cools, say,
during nighttime heat loss, it usually becomes much heavier than the surrounding air. The cold
air then descends downhill, often following the same local terrain drainage patterns taken by
rain or snow runoff.
This cold-air drainage can occur even with terrain differences of only a few feet, and
although it usually moves at less than ten miles per hour, if the slope is steep, or the air
very cold, the air can reach speeds can of 30 mph. As the air descends to the lowest local
elevation, it can collect in hollows, stream beds, or along the foot of hillsides. When it is
below freezing, the frigid air can damage plants caught in the flow.
But since cold air flows downhill like water, it can also be diverted - and even halted - by
terrain features such as rock outcrops, thick hedges, earth berms, or dense stands of trees,
and that fact has not been lost on certain folks. Farmers, vineyard growers, and gardeners
have taken the hint, and are creating artificial barriers to divert the cold air flow around
their fields and plants. These "frost dams," are most often dense collections of shrubs and
low conifers with tight fencing, although buildings will work too.
While artificial frost dams are generally considered for agricultural or horticultural
protection, the concept can also be used in landscaping around homes and outbuildings to
reduce cold air pooling around them. And in the right location, controlling cold air drainage
could funnel cooler air toward your home and reduce that summer air-conditioning bill.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook is online
at www.weathernotebook.org. We are supported by Subaru of America, and The National Science
Foundation. We are produced by the Mount Washington Observatory.
|
|
