Space Physics Seminar - winter-2025

Jan. 17, 2025
3:30 p.m. - 4:30 p.m.
Slichter 3853

Presented By:

• Sergei Kamaletdinov - EPSS, UCLA

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Radial transport of energetic electrons is a key process driving variability in the outer radiation belt. This transport involves a violation of drift motion. One mechanism that enables such a violation, and the associated radial transport, is drift-orbit bifurcation. This naturally arises from solar wind compression of the dayside magnetosphere, creating a local maximum in field strength at the equator and two off-equatorial minima at the north and south segments of the field line. Trapping and subsequent de-trapping from these local minima during azimuthal drift violates the conservation of the second adiabatic invariant. The resulting jumps in the second adiabatic invariant allow for radial transport. While radial transport due to drift-orbit bifurcation has been extensively studied in symmetric East-West and North-South magnetospheric configurations, the effects of IMF By and its variations have largely been overlooked. In this study, we provide a comprehensive analysis of jumps in the second adiabatic invariant caused by global magnetospheric asymmetries associated with IMF By. We demonstrate that East-West asymmetry induces large jumps in the adiabatic invariant. These jumps can be naturally explained through the theory of separatrix crossings in Hamiltonian systems with slow and fast variables, specifically as “geometric jumps.” These jumps have magnitudes comparable to the initial invariant values and are dictated by the magnetic field topology. We show that the long-term evolution driven by such geometric jumps extends beyond the scope of canonical diffusion, resulting in rapid (exponential) phase-mixing. Furthermore, using ELFIN and THEMIS observations in conjunction with ARTEMIS data, we speculate on the potential observational signatures of asymmetric drift-orbit bifurcation caused by abrupt changes in solar wind conditions.

Jan. 17, 2025
3:30 p.m. - 4:30 p.m.
Zoom only

Presented By:

• Sergei Kamaletdinov - EPSS, UCLA

See Event on Google.
Subscribe to Calendar

Radial transport of energetic electrons is a key process driving variability in the outer radiation belt. This transport involves a violation of drift motion. One mechanism that enables such a violation, and the associated radial transport, is drift-orbit bifurcation. This naturally arises from solar wind compression of the dayside magnetosphere, creating a local maximum in field strength at the equator and two off-equatorial minima at the north and south segments of the field line. Trapping and subsequent de-trapping from these local minima during azimuthal drift violates the conservation of the second adiabatic invariant. The resulting jumps in the second adiabatic invariant allow for radial transport. While radial transport due to drift-orbit bifurcation has been extensively studied in symmetric East-West and North-South magnetospheric configurations, the effects of IMF By and its variations have largely been overlooked. In this study, we provide a comprehensive analysis of jumps in the second adiabatic invariant caused by global magnetospheric asymmetries associated with IMF By. We demonstrate that East-West asymmetry induces large jumps in the adiabatic invariant. These jumps can be naturally explained through the theory of separatrix crossings in Hamiltonian systems with slow and fast variables, specifically as “geometric jumps.” These jumps have magnitudes comparable to the initial invariant values and are dictated by the magnetic field topology. We show that the long-term evolution driven by such geometric jumps extends beyond the scope of canonical diffusion, resulting in rapid (exponential) phase-mixing. Furthermore, using ELFIN and THEMIS observations in conjunction with ARTEMIS data, we speculate on the potential observational signatures of asymmetric drift-orbit bifurcation caused by abrupt changes in solar wind conditions.

Jan. 24, 2025
3:30 p.m. - 4:30 p.m.
Slichter Hall # 3853

Presented By:

• Xin An - EPSS, UCLA

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In space plasmas, large-amplitude Alfven waves can drive compressive perturbations, accelerate ion beams, and lead to plasma heating and ion acoustic wave excitation at kinetic scales. This energy channeling from fluid to kinetic scales represents a complementary pathway to the classical turbulent cascade. We present observational and computational evidence validating this hypothesis by simultaneously resolving fluid-scale Alfven waves, kinetic-scale ion acoustic waves, and their imprints on ion velocity distributions in the Earth's magnetopause boundary layer. Our findings reveal that two coexisting compressive modes, driven by the magnetic pressure gradients of Alfven waves, not only accelerate the ion tail population to the Alfven velocity but also heat the ion core population near the ion acoustic velocity and generate Debye-scale ion acoustic waves. Consequently, Alfven-acoustic energy channeling emerges as a viable mechanism for plasma heating near plasma boundaries where large-amplitude Alfven waves are present.