The Open Polar Cap of Rotating Magnetospheres

<p>The classic Dungey cycle plays an essential role in understanding the dynamics of the terrestrial magnetosphere. However, its direct applicability to planetary magnetospheres such as Jupiter is limited, especially when the planetary rotation is much faster than the Earth. We use a series of numerical experiments to show the transition of the terrestrial magnetosphere from a classic Dungey cycle, convection-dominated system to rotation-dominated configurations. The numerical experiments use the Earth's magnetosphere-ionosphere system as a testbed, with modified rotation speed to increase the influence of planetary rotation over solar wind driving, characterized by the ratio between the solar wind merging potential and the polar cap rotation potential. Results show that when the rotation potential of the polar magnetosphere becomes comparable to the merging potential of the solar wind, the classic Dungey cycle is modified by azimuthal transport of magnetic flux, resulting in a more closed polar magnetosphere with a crescent-shaped open flux region in the ionosphere. These numerical experiments provide a theoretical framework for understanding the fundamentals of magnetospheric physics, which is potentially applicable to the Saturn, Jupiter, and exo-planetary systems.</p>

Magnetic Fields, Atmospheres, and the Connection to Habitability (MACH) – Using Team Science to determine how magnetic fields influence habitability

<p>In order to determine the extent to which a global magnetic field is required for a planet to be habitable at its surface, expertise is required from diverse communities, some of which have diverged from each other over the past several decades. For example, modelers and observers of the terrestrial magnetosphere have limited overlap and interaction with modelers and observers of unmagnetized planets or the giant planets in our solar system. There is relatively limited interaction between any of the above communities and those who study exoplanets, though efforts are increasing to bridge the solar system and exoplanet communities.</p><p> </p><p>We describe a NASA Heliophysics DRIVE Science Center selected to answer the central question of this session: “Do Habitable Worlds Require Magnetic Fields”. This Center, named MACH (Magnetic Fields, Atmospheres, and the Connection to Habitability) includes scientists who study atmospheric escape from Earth, unmagnetized planets, and exoplanets. Over the next several years MACH will construct a framework that enables the evaluation of atmospheric loss from an arbitrary rocky planet, given information about the planet and its host star. The MACH Center hosted a community-wide workshop in June 2021 centered around this topic, and is seeking to grow their interactions with interested scientists from relevant disciplines.</p>

Indices of geomagnetic activity derived from space-born magnetic data from the Swarm mission

<p>Ground based indices, such as the Dst and AE, have been used for decades to describe the interplay of the terrestrial magnetosphere with the solar wind and provide quantifiable indications of the state of geomagnetic activity in general. These indices have been traditionally derived from ground based observations from magnetometer stations all around the Earth. In the last 7 years though, the highly successful satellite mission Swarm has provided the scientific community with an abundance of high quality magnetic measurements at Low Earth Orbit, which can be used to produce the space-based counterparts of these indices, such the Swarm-Dst and Swarm-AE Indices. In this work, we present the first results from this endeavour, with comparisons against traditionally used parameters, and postulate on the possible usefulness of these Swarm based products for space weather monitoring and forecasting.</p>

Magnetospheric Multiscale (MMS) Observations of ULF Waves and Correlated Low-Energy IonMonoenergetic Acceleration

<div>Low‐energy ions of ionospheric origin with energies below 10s of electron volt dominate most</div><div>of the volume and mass of the terrestrial magnetosphere. However, sunlit spacecraft often become</div><div>positively charged to several 10s of volts, which prevents low‐energy ions from reaching the particle</div><div>detectors on the spacecraft. Magnetospheric Multiscale spacecraft (MMS) observations show that</div><div>ultralow‐frequency (ULF) waves drive low‐energy ions to drift in the E × B direction with a drift velocity</div><div>equal to VE×B, and low‐energy ions were accelerated to suffificient total energy to be measured by the</div><div>MMS/Fast Plasma Investigation Dual Ion Spectrometers. The maximum low‐energy ion energy flflux peak</div><div>seen in MMS1's dual ion spectrometer measurements agreed well with the theoretical calculation of H+ ion</div><div>E × B drift energy. The density of ions in the energy range below minimum energy threshold was</div><div>between 1 and 3 cm−3 in the magnetosphere subsolar region in this event.</div>