From Glossary of Meteorology
(Redirected from Frequencies)


  1. The rate of recurrence of any periodic phenomenon, often associated with waves of all kinds.

    Without qualification frequency often means temporal frequency, the rate of recurrence of a time-varying function, but could mean spatial frequency, the rate of recurrence of a space-varying function. Spatial frequency is the reciprocal of the repeat distance (sometimes the wavelength). The dimensions of (temporal) frequency are inverse time. A common unit for frequency is cycle per second, formerly abbreviated cps, but superseded by hertz, abbreviated as Hz. The symbol ν is often used for frequency but f is common in engineering. Period is inverse frequency. Related to frequency, and applied especially to sinusoidally varying quantities, is angular or circular frequency, often denoted by ω = 2πν, with units radians per unit time (e.g., radians per second).

  2. In statistics, the number of times a specified event occurs in a given series of observations; for example, the number of rainy days observed at a particular station during a certain period of time.

    In many types of studies (hydrometeorological, especially) the reciprocal of frequency, the recurrence interval, is used.

Copyright 2022 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.