A type of precipitation. Occurs when liquid rain hits a cold surface and then immediately freezes into ice. For this to occur, a surface temperature inversion is usually required. In such an inversion
, the surface must have a temperature below freezing, while the temperature of the atmosphere where the precipitation forms is above freezing.
Rain that falls in liquid form but freezes upon impact to form a coating of glaze upon the ground and on exposed objects. In aviation weather observations, this hydrometeor is encoded ZR. While the te
mperature of the ground surface and glazed objects is typically near or below freezing (0C or 32F), it is necessary that the water drops be supercooled before striking. Freezing rain can sometimes occur on surfaces exposed to the air (such as tree limbs) with air temperatures slightly above freezing in strong winds. Local evaporational cooling may result in freezing. Freezing rain frequently occurs, therefore, as a transient condition between the occurrence of rain and ice pellets (sleet). When encountered by an aircraft in flight, freezing rain can cause a dangerous accretion of clear icing.
As used by the U.S. Army Corps of Engineers, the period of time between the highest point and the succeeding lowest point on the time curve of cumulative degree-days above and below 32F; the opposite
of thawing season. A less rigorous, but more commonly used, definition is the number of days or months between the first day of fall or winter and the last day of the same winter or the following spring on which the air temperature is below 0C.
Freezing spray occurs when a combination of below freezing temperatures and strong winds, causes a wind-generated spray to freeze and accumulate (or build-up) on any marine infrastructure located in o
r near the vicinity of the water.
An accumulation of freezing water droplets on a vessel caused by some appropriate combination of cold water, wind, cold air temperature, and vessel movement.
he upper region of the ionosphere, above approximately 160 km altitude. F region electron densities are highly variable, depending on the local time, solar activity, season, and geomagnetic activity.
The F region contains the Fl and F2 layers. The F2 layer is more dense and peaks at altitudes between 200 and 600 km. The Fl layer, which forms at lower altitudes in the daytime, has a smaller peak in electron density.
A layer that contains ionized gases at aheight of around 150-800 km above sea level, placing it in the thermosphere.the F region has the highest concentration of free electrons and ionsanywhere in the
atmosphere. It may be thought of as comprising two layers,the F1-and F2-layers. One of several layers in the ionosphere. Also known asthe Appleton layer.