On the importance of searching for oscillations of the Jovian inner radiation belt with a quasi-period of 40 minutes
Abstract
Experiments aboard the Ulysses spacecraft discovered quasi-periodic bursts of relativistic electrons and of radio emissions with ~40-min period (QP-40) from the south polar direction of Jupiter in 1992 February. 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 a distance of ~2-3 RJ (where RJ is the radius of Jupiter), where relativistic electrons are known to be trapped using the diagnostics of synchrotron emissions, can execute global QP-40 magnetoinertial oscillations excited by arrivals of high-speed solar winds at the Jovian magnetosphere. 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 relativistic electron bursts. Highly beamed synchrotron emissions from such QP-40 burst electrons with small pitch angles relative to Jovian magnetic fields at ~30-40 RJ give rise to QP-40 radio bursts with typical frequencies <~0.2 MHz. We predict that the synchrotron brightness of the IRB should vary on QP-40 time-scales upon arrivals of high-speed solar winds with estimated magnitudes >~0.1 Jy, detectable by existing ground-based radio telescopes. The recent discovery of ~45-min pulsations of Jupiter's north polar X-ray hot spot by the High-Resolution Camera (HRC) of the Chandra spacecraft provides strong supporting circumstantial evidence that the IRB neighborhood did oscillate with QP-40 time-scales. 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 north polar X-ray hot spot did in fact coincide with the arrival of high-speed solar wind at Jupiter. We note also that properly sampled data of simultaneous far-ultraviolet images of auroral ovals obtained by the Hubble Space Telescope imaging spectrograph (HST-STIS) would have contained QP-40 oscillatory signatures. Based on our theoretical analysis, we offer several predictions that can be tested by further spacecraft and ground-based telescope observations.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- September 2003
- DOI:
- 10.1046/j.1365-8711.2003.06987.x
- arXiv:
- arXiv:astro-ph/0307276
- Bibcode:
- 2003MNRAS.344L...1L
- Keywords:
-
- MHD;
- polarization;
- radiation mechanisms: non-thermal;
- waves;
- solar wind;
- planets and satellites: individual: Jupiter;
- Astrophysics
- E-Print:
- 5 pages, 0 figures, uses mn.sty