This paper summarizes a unique observation of
storm-time VLF chorus emissions obtained during investi-
gation of VLF data collected over a period of about one
year at our low latitude ground-based Indian station Jammu
(geomag. lat., 22 deg 26 min North, L = 1.17) in order to
connect the peculiarities of this ground-observed VLF cho-
rus with the plasma processes in the magnetosphere during
geomagnetic disturbances. The upper boundary frequency
method (UBF-method) based on the measurement of the
upper boundary frequency of the ground-observed chorus
is used for the determination of the location of the source
of storm-time chorus emissions observed at our ground sta-
tion Jammu. Dynamics of chorus spectra of the emissions
observed at Jammu on 18 February 1998 in daytime dur-
ing magnetic storm period are investigated in detail in or-
der to solve the physics of the ground-observed chorus
emissions at low latitudes. To explain various temporal and
spectral features of storm-time VLF chorus emissions ob-
served at Jammu, a generation mechanism based on the
backward wave oscillator (BWO) regime of the magneto-
spheric cyclotron maser has been presented. Using BWO
model, the calculation of some magnetospheric parameters
such as plasma density, large-scale electric field etc. are car-
ried out. The conformity between the calculated and typi-
cal measured parameters is shown and discussed. Finally the
conclusion of this study is reported.

EB00000004130K

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• Observation of a unique storm-time VLF chorus emissions at low latitude Indian ground station Jammu (L = 1.17)