HOPKINS GLOSSARY OF WEATHER TERMS F

free atmosphere

• The earth's atmosphere extending upward from above the planetary boundary layer (or above altitudes ranging between 1-2 kilometers above ground level), where effects of the earth's surface friction upon air motion are negligible.

frequency

• The number of cycles or times that a periodic event occurs during a fixed time interval; the reciprocal of the period of the periodic phenomena. The dimension is reciprocal time, or cycles per time, with the Hertz (Hz) (equal to 1 cycle per second) defined as the standard unit of frequency. Frequency is one of the ways used to identify wave phenomena.