An instrument used to indicate wind direction.

A wind blowing in a direction opposite to the heading of a moving object, thus opposing the object's intended progress; the opposite of a tailwind.

Wind with a speed between 4 and 6 knots (4 and 7 mph), Beaufort scale number 2.

The pressure unit of the meter-ton-second system of physical units. equal to 10 millibars or 101 dynes per cm2.

A general term for instruments which sample atmospheric suspensoids by impaction. Same as impactometer.

The difference between the air temperature and the dew-point. Also called dew-point deficit, dew-point depression.

The record obtained from a bolometer.

The temperature at which the liquid and solid forms of a substance may exist in equilibrium at a given pressure (usually one standard atmosphere). The true freezing point of water is known as the ice point.

A type of modulation in which the frequency of a continuous radio carrier wave is varied in accordance with the properties of a second (modulating) wave.

A weakly colored lunar halo identical in form and optical origin to the solar parhelion.

The value of the quantity measured, as indicated or otherwise provided by a measuring instrument.

A cover which fits over a large inflated balloon to facilitate handling in high or gusty winds.

The total area drained by a river and its tributaries. Same as watershed.

A common unit used in measurement of atmospheric pressure. Defined as that pressure exerted by a one-inch column of mercury at standard gravity and a temperature of 0'C.

Readily taking up and retaining moisture.

Very generally, any moving- stream of air. It has no particular technical connotation.

The measurement and computation of wind speeds and directions at various levels above the surface of the earth. Methods include pilot balloon observations, rabals, rawin or rawinsonde observations, radar tracking, or acoustic sounding.

Upwarddirected solar radiation, reflected by the earth's surface and the atmosphere.

See mote.

The general term for anemometers operating on the principle that the heat transfer to air from an object at an elevated temperature is a function of the air speed. Examples are the hot-wire anemometer and the katathermometer.