We study the development of the terrestrial ring current during the time interval of 13–18 July, 2000, which consisted of
two small to moderate geomagnetic storms followed by a great storm with indices
Dst=−300 nT and
Kp=9. This period of intense geomagnetic activity was caused by three interplanetary coronal mass ejecta (ICME) each driving
interplanetary shocks, the last shock being very strong and reaching Earth at ∼ 14 UT on 15 July. We note that (a) the sheath
region behind the third shock was characterized by
B
z fluctuations of ∼35 nT peak-to-peak amplitude, and (b) the ICME contained a negative to positive
B
z variation extending for about 1 day, with a ∼ 6-hour long negative phase and a minimum
B
z of about −55 nT. Both of these interplanetary sources caused considerable geomagnetic activity (
Kp=8 to 9) despite their disparity as interplanetary triggers. We used our global ring current-atmosphere interaction model
with initial and boundary conditions inferred from measurements from the hot plasma instruments on the
Polar spacecraft and the geosynchronous Los Alamos satellites, and simulated the time evolution of H
+, O
+, and He
+ ring current ion distributions. We found that the O
+ content of the ring current increased after each shock and reached maximum values of ∼ 60% near minimum
Dst of the great storm. We calculated the growth rate of electromagnetic ion cyclotron waves considering for the first time wave
excitation at frequencies below O
+ gyrofrequency. We found that the wave gain of O
+ band waves is greater and is located at larger
L shells than that of the He
+ band waves during this storm interval. Isotropic pitch angle distributions indicating strong plasma wave scattering were
observed by the imaging proton sensor (IPS) on
Polar at the locations of maximum predicted wave gain, in good agreement with model simulations.
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