On the Importance of Searching for Oscillations of the Jovian Inner Radiation Belt with a Quasi-Period of 40 Minutes

Experiments aboard the Ulysses spacecraft discovered quasi-periodic bursts of relativistic electrons and of radio emissions with ∼ 40−minute period (QP-40) from the south pole of Jupiter in February 1992. Such polar QP-40 burst activities were found to correlate well with arrivals of high-speed solar winds at Jupiter. We advance the physical scenario that the inner radiation belt (IRB) within ∼ 2 − 3 Jupiter’s radius RJ , where relativistic electrons are known to be trapped via synchrotron emissions, can execute global QP-40 magnetoinertial oscillations excited by arrivals of high-speed solar winds. Modulated by such QP-40 IRB oscillations, relativistic electrons trapped in the IRB may escape from the magnetic circumpolar regions during a certain phase of each 40-min period to form circumpolar QP-40 electron bursts. Highly beamed synchrotron emissions from such QP-40 burst electrons with small pitch angles relative to Jovian magnetic fields at ∼ 30− 40RJ give rise to QP-40 radio bursts with typical frequencies ∼ 0.2MHz. We predict that the synchrotron brightness of the IRB should vary on QP-40 timescales upon arrivals of high-speed solar winds with estimated magnitudes ∼ 0.1Jy, detectable by ground-based radio telescopes. The recent discovery of ∼ 45-min pulsations of Jupiter’s polar X-ray hot spot by the High-Resolution Camera (HRC) of the Chandra spacecraft provides a strong supporting circumstantial evidence that the IRB neighborhood did oscillate with QP-40 timescales. Using the real-time solar wind data from the spacecraft Advanced Composition Explorer (ACE), we show here that such QP-40 pulsations of Jupiter’s polar X-ray hot spot did in fact coincide with the arrival of high-speed solar wind at Jupiter. We note also that a properly sampled data of simultaneous far-ultraviolet images of auroral ovals obtained by the Hubble Space Telescope imaging spectrograph (HST-STIS) would have contained QP40 oscillatory signatures. By our theoretical analysis, we offer several predictions that can be tested by further observations.