A halo consisting of a faint white circle passing through the Sun and running parallel to the horizon for as much as 360

A thermograph in which ventilation is provided by a suction fan.

An inert gas. An element found in the atmosphere to the extent of only 0.000114 percent by volume. Its molecular weight is 83.7.

The stage on a fixed river gauge at which it is necessary to begin issuing warnings or river forecasts if adequate precautionary measures are to be taken before flood stage is reached.

Pyrheliometer based on the comparison of the heating of two identical metal strips, one exposed to radiation, the other to a joule effect.

The visibility along an identified runway, determined from a specified point on the runway with the observer facing in the same direction as a pilot using the runway. Compare to runway visible range.

A system of physical units based upon the use of the meter, the metric ton (106 grams), and the second as elementary quantities of length, mass, and time, respectively.

The atmospheric pressure computed using station elevation as the reference datum level. Station pressure is usually the base value from which sea level pressure and altimeter setting are determined.

A mercury barometer in which the tube is U-shaped and the upper and lower mercury surfaces have the same diameter.

A photometer which measures the intensity of radiation as a function of the frequency (or wavelength) of the radiation.

By international agreement, a period during which greatly increased observation of world-wide geophysical phenomena is undertaken through the co-operative effort of participating nations. July 1957-December 1958 was the first such year. However, precedent ...

Wind with a speed between 17 and 21 knots (19 and 24 mph); Beaufort scale number 5.

NEXt Generation RADar. A NWS network of about 140 Doppler radars operating nationwide.

The height at which the maximum wind speed occurs, determined in a winds-aloft observation.

The process by which small particles suspended in a medium of a different refractive index diffuse a portion of the incident radiation in all directions. In scattering no energy transformation results, only a change in the spatial distribution of the radi ...

Any sudden and heavy rain, almost always of the shower type.

The programs and instructions which direct a computer.

In a system of moist air, the dimensionless ratio of the mass of water vapor to the mass of dry air. For many purposes, the mixing ratio may be approximated by the specific humidity.

An absolute pyhrliometer, developed by C.G. Abbott, in which the radiation-sensing element is a blackened water-calorimeter.

Name sometimes used in place of pyranometer as a generic term.