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Fully resolved observations of auroral medium frequency burst radio emissions
Author(s) -
Bunch N. L.,
LaBelle J.
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2009gl038513
Subject(s) - waveform , substorm , ionosphere , physics , superposition principle , plasma , geophysics , atmospheric sciences , computational physics , environmental science , astrophysics , meteorology , magnetosphere , quantum mechanics , voltage
Auroral MF burst is a naturally occurring spontaneous emission characterizing substorm onsets. Between March 21 and April 19, 2008, a full‐waveform receiver at Toolik Lake, Alaska, detected 23 examples of MF burst. The high‐resolution continuous waveform data show that MF burst consists of a superposition of structured emissions, defined as those with sharp boundaries on frequency‐time diagrams, and unstructured emissions which are more diffuse. Structured emissions account for 30–40% of the wave power, although this should be considered a lower bound since unstructured emission could represent weak or overlapping structured emissions. Structured emissions have a repeatable frequency‐time pattern in which their leading edge decreases from a well‐defined upper bound, at first slowly and then more rapidly over about 100 ms. This timescale is too long to be explained by wave propagation delay alone. Assuming emission at the local electron plasma frequency in the bottomside ionosphere, the source must move downward at 400–1000 km/s in order to explain the observed time delay.