The Madden-Julian Oscillation is a 30-50 day wave of periodic rainfall enhancement over the Australian tropics signalling a burst in monsoon activity during the tropical wet season.

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A wave which modulates a carrier wave.


A unit of wave length, equal in length to one ten billionth.


Travel of a radio wave to the ionosphere and back to earth. The number of hops a radio signal has experienced is usually designated by the expression one-hop, two-hop, multihop, etc


A plane polarized electromagnetic wave in which the electric field vector is in a horizontal plane.


A radio wave which reaches a given reception point by a path from the transmitting point other than the direct line path between the two. An example is the SKYWAVE received after reflection from one of the layers of the ionosphere.


Any non-frontal line or band of convective activity in the atmosphere. This is the general term and includes the developing, mature, and dissipating stages. However, when the mature stage consists of a line of active thunderstorms, it is properly called SQUALL LINE; therefore, in practice, instability line often refers only to the less active phases. Instability lines are usually hundreds of miles long (not necessarily continuous), 10 to 50 miles wide, and are most often formed in the warm sectors of wave cyclones. Unlike true fronts, they are transitory in character, ordinarily developing to maximum intensity in less than 12 hours and then dissipating in about the same time. Maximum intensity is usually attained in late afternoon.


A sea condition where waves are moving perpendicular to the direction a ship is moving


1. Unwanted and confusing signals or patterns produced by nearby electrical equipment or machinery, or by atmospheric phenomena. 2. The variation of wave amplitude with distance or time, caused by superposition of two or more waves. Sometimes called WAVE INTERFERENCE.


An apparatus used to produce and measure interfer- ence from two or more coherent wave trains from the same source. Used to measure wavelengths, to measure angular width of sources, to determine the angular position of sources (as in satellite track- ing), and for other purposes.


The type of buoy with a large bell and hanging hammers that sound by wave action.

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