associated with migratory lows and generally disperse
inland as the systems lose their moisture.
WINDS.Wind speeds are generally light in the
continental arctic interior throughout the year. The
strongest winds in the interior normally occur during
the summer and fall. During the winter, the interior
continental regions are areas of strong anticyclonic
activity that produce only light surface winds.
Strong winds occur more frequently along the
arctic coast than in the continental interiors. The
frequency with which these high winds occur in coastal
areas is greater in the fall and winter than in the
summer. These winds frequently cause blowing snow.
Very strong wind speeds have been observed at
infrequent over the ice pack, but the wind blows almost
continuously because there are no natural barriers (such
as hills and mountains) to retard the wind flow. As a
result, the combination of wind speed and low
temperatures that are extreme and severely limit
outdoor human activity.
PRECIPITATION.Precipitation amounts are
small, varying from 5 to 15 inches annually in the
continental interior and 3 to 7 inches along the arctic
coastal area and over the ice pack. The climate over the
Arctic Ocean and adjoining coastal areas is as dry as
some of the desert regions of the mid-latitudes. Most of
the annual precipitation falls as snow on the Arctic
Ocean and adjacent coastal areas and ice caps. On the
other hand, most of the annual precipitation falls as rain
over the interior.
RESTRICTION TO VISIBILITY.Two factors
make the visibility in the Polar Regions a very complex
matter. Arctic air, being cold and dry, is exceptionally
transparent, and extreme ranges of visibility are
possible. On the other hand, there is a lack of contrast
between objects, particularly when a layer of new snow
covers all distinguishable objects. Limitations to
visibility in the Arctic are primarily blowing snow, fog,
and local smoke. Local smoke is serious only in the
simultaneously with shallow radiation fogs of winter.
Blowing snow. Blowing snow constitutes a
more serious hazard to flying operations in the Arctic
than in mid-latitudes because the snow is dry and fine
and is easily picked up by moderate winds. Winds in
excess of 8 knots may raise the snow several feet off the
ground, and the blowing snow may obscure surface
objects such as runway markers.
Fog. Of all the elements that restrict flying in
the Arctic regions, fog is perhaps most important. The
two types of fog most common to the Polar Regions are
advection fog and radiation fog.
Fog is found most frequently along the coastal
areas and usually lies in a belt parallel to the shore. In
the winter, the sea is warmer than the land, and
relatively warm, moist air is advected over the cool land
causing fog. This fog may be quite persistent. In the
summer, warm, moist air is advected over sea ice,
which is now melting, creating the same situation,
which is found over land in winter.
Ice fog. A fog condition peculiar to Arctic
climates is ice fog. Ice fog is composed of minute ice
crystals rather than water droplets of ordinary fog and is
most likely to occur when the temperature is about
45°C (50°F) or colder but can occur when
temperatures are as warm as -30°C (20°F).
Sea smoke or steam fog. The cold temperatures
in the Arctic can have effects, which seem peculiar to
people unfamiliar with the area. During the winter
months, the inability of the air to hold moisture results
in an unusual phenomenon called sea smoke. Open
simultaneously with low air temperature cause this.
Actually, this phenomenon is similar to that of steam
forming over hot water.
In the case of sea smoke, the temperatures of both
the air and the water are quite low, but the air
temperature is still by far the lower of the two, causing
steam to rise from the open water to form a fog layer.
This fog occurs over open water, particularly over leads
(navigable passages) in the ice pack and is composed
entirely of water droplets.
Arctic haze. This is a condition of reduced
horizontal and slant visibility (but good vertical
visibility) encountered by aircraft in flight over arctic
regions. Color effects suggest this phenomenon to be
caused by very small ice particles. Near the ground, it is
called arctic mist or frost smoke; when the sun shines
on the ice particles, they are called diamond dust.
ARCTIC WEATHER PECULIARITIES.The
strong temperature inversions present over the Arctic
during much of the winter causes several interesting
phenomena. Sound tends to carry great distances under
these inversions. On some days, when the inversion is
very strong, human voices can be heard over extremely
long distances as compared to the normal range of the
voice. Light rays are bent as they pass through the
inversion at low angles. This may cause the appearance