Accession Number : AD0673325

Title :   THE LOW FREQUENCY CUTOFF OF ELF EMISSIONS,

Corporate Author : IOWA UNIV IOWA CITY DEPT OF PHYSICS AND ASTRONOMY

Personal Author(s) : Gurnett,Donald A. ; Burns,Thomas B.

Report Date : MAY 1968

Pagination or Media Count : 37

Abstract : ELF and VLF radio noises observed by satellites in the ionosphere often have a very sharp lower cutoff frequency near the proton gyrofrequency. The paper summarizes the experimentally observed characteristics of this low frequency cutoff and proposes an explanation for the cutoff based on the reflection of downward propagating, extraordinary mode, waves near the two-ion cutoff frequency between the proton and helium gyrofrequencies. This explanation, if correct, provides the first direct evidence that chorus and ELF hiss emissions are generated at high altitudes (above 3000 km) and not near the base of the ionosphere. Ground-based observations of 700 Hz noise bands near the auroral zone, previously attributable to proton cyclotron radiation at low altitudes in the ionosphere, can now be explained by this reflection mechanism. Other possibly related effects (such as multiple ELF noise bands and the reflection of whistlers at the two-ion cutoff frequency) are discussed. (Author)

Descriptors :   (*RADIO INTERFERENCE, IONOSPHERIC PROPAGATION), REFLECTION, HELIUM, PROTONS, FREQUENCY, DETECTION, SCIENTIFIC SATELLITES, EXTREMELY LOW FREQUENCY, VERY LOW FREQUENCY, AURORAE, MAGNETOSPHERE, WHISTLERS, DAWN CHORUS

Subject Categories : Meteorology
      Radio Communications

Distribution Statement : APPROVED FOR PUBLIC RELEASE