Gerard J. Fasel, Jennifer Lau,
Ever since Dungey proposed the model of the magnetic merging between the interplanetary magnetic field and the Earth’s terrestrial magnetic field, there has been a quest to find observations that support his theory. Satellite observations in the 1970’s found the first evidence of magnetic reconnection. Shortly afterwards ground observations identified possible ionospheric footprints of newly reconnected magnetic flux tubes. Auroral features were observed to drift poleward after initially brightening at the dayside auroral oval. There have been many discussions regarding the possibility of poleward-moving auroral forms (PMAFs) being associated with magnetic merging at the dayside magnetopause. This talk will first introduce past studies regarding PMAFs. Next, a series of questions will be posed: (i) Are PMAFs associated with combinations of IMF configurations needed for magnetic merging on the dayside? (ii) Are PMAFs associated with the solar wind speeds? (iii) Is there any PMAF feature that is correlated with the IMF By-component? Data will be presented and discussed for each of the above questions.
Whistler waves have been observed frequently in the upstream foot region of planetary bow shocks and interplanetary shocks. These waves are believed to be created in the shock ramp and propagate towards upstream as standing wave packets in the shock frame. We present case studies on the interplanetary shock and bow shock observations from the electromagnetic fields and plasma instruments on board of Magnetosphere Multiscale (MMS) spacecraft. The Mach number of the interplanetary shock is marginally super critical but smaller than the critical Mach number for whistler wave propagation, thus these whistler waves could propagate from their origin at the ramp to the upstream. On the other hand, even though the Mach number of Earth’s bow shock is usually higher, upstream whistlers are also seen when the shock Mach number is less than the whistler critical Mach number. By studying the whistler waves upstream of the interplanetary shock and of the Earth bow shock, we can understand the wave properties for shocks of different Mach numbers, as well as the wave’s roles in affecting the upstream plasma parameters and shock dissipation.
The Aerospace Corporation, Space Science Department
Understanding the physics behind ionospheric disturbances, which are initiated mainly by two major coupling processes, namely: thermosphere-ionosphere coupling (forcing from below) and magnetosphere-ionosphere coupling (forcing from above), become the top-priority of the U. S. National Space Weather Program. Over the past decades' significant progress has been done to understand the origin and mechanisms of ionospheric disturbances. However, characterization of the global ionospheric disturbance as a function of local time, longitude, geomagnetic conditions, and season is still a challenge for the modeling community. Recent advances in networks of distributed ground instruments provide new evidence of longitudinal variations in the mid- and low-latitude ionospheric disturbances/irregularities on a large variety of spatial and temporal scales. Ionospheric irregularity is stronger and has a more prominent impact at low-latitudes where geomagnetic field is nearly horizontal. However, during an intense magnetic storm, ionospheric disturbances may not be restricted to the low-latitude region but can occur at mid-latitudes due to the sharp density gradient at the edge of storm enhanced densities (SEDs) plumes. In this colloquium presentation, the combined diagnostic observations of everything, but the kitchen sink, will be portrayed to demonstrate that forcing from lower thermosphere, like the localized tropospheric gravity waves (GWs) seeding, may be responsible for the formation of the strong longitudinal dependence of ionospheric disturbance/irregularity distribution. Furthermore, potential future research contributions using data from the upcoming ICON, GOLD, and GDC missions will be presented. Finally, results from the successful international scientific team leadership and from participation at the international outreach programs that are designed to expand space science education and instruments (UCLA also involved through AMBER project) into the developing nations will also be discussed.
Swedish Institute of Space Physics
I will present my recent studies on the Venusian plasma environment. First, I have studied the ion dynamics in the Venusian ionosphere near the North Pole, where we find a surprising dusk-to-dawn flow near the polar terminator region. This contrasts the previous measurements by Pioneer Venus in the equatorial region where they found a day-to-night flow. Second, I will show our recent findings on the H+/O+ escape rates and its dependence on upstream parameters. We have shown that the ratio of H+/O+ escape rate decreases from solar minimum to maximum. This is an important characteristic of the Venusian atmospheric escape as it is highly connected to the escape of water and the atmospheric evolution. Last, I will present some preliminary results from a recent study on the O+ escape rates and its dependence on various upstream parameters.
Physics & Astronomy, UCLA
Mercury is the smallest planet in our solar system, but nevertheless is internally magnetized and has a robust magnetosphere. Due to it's relatively small size and proximity to the Sun, Mercury's magnetosphere is highly dynamic and kinetic plasma processes dominate plasma transport, acceleration and loss throughout the Hermian magnetosphere. A unique aspect of Mercury is that since it has no ionosphere or atmosphere, precipitating plasma particles directly impact the regolith. The bombardment of the surface by magnetospheric particles has a number of consequences that include the generation of x-rays, the ejection of planetary heavy ions and space weathering. In this presentation, state of the art global kinetic simulations together with MESSENGER spacecraft data are used to examine Mercury's magnetosphere and the space plasma-surface interactions that take place.
The magnetic and plasma structures on the dayside magnetopause are examined with unprecedented detail with the exceptionally high temporal resolution measurements of both magnetic field and plasma properties as well as the capability to disentangle the spatial and temporal variations. This capability is enabled by the closely-formed four-spacecraft-tetrahedron of the MMS mission. With this detailed examination using definitive criteria, we have been able to distinguish and identify different current structures in the vicinity of magnetopause, namely: the magnetopause current layer, flux transfer events (FTEs), and the magnetosheath field enhancement (MFE). Furthermore, with observations from MMS, the detailed properties of FTEs are studied for their better understanding. With these detailed analyses, we then show that there are two types, one with mixed plasma originated from two regimes (type A) and the other without the mix of signatures (type B); and that these two types of FRs are the same phenomena. Both FTEs are generated by dayside magnetic reconnection and are responsible for the magnetic flux transfer.
The NASA Discovery mission InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) placed the first lander on Mars devoted to geophysics on November 26, 2018. A fluxgate magnetometer (IFG), which measures the magnetic signals in the same passband of the seismometer, is carried by InSight to help remove any signals that are observed by the highly sensitive seismometer that may be associated with magnetic activity in the environment and on the spacecraft. We will present an overview of the preliminary results measured by the InSight IFG, including much more strongly magnetized of Martian crust than model predicted, magnetic field variations caused by ionospheric current magnetic pulsations on the surface and so on.
Una Schneck & Kyle Kung,
In February 11, 1982 a strange magnetic signature was measured in the orbit of Venus by PVO. This event (dubbed an Interplanetary Magnetic Field Enhancement or IFE) was measured as a thorn-like enhancement in the magnetic field. Further investigation found a surprising correlation between the rate of IFEs measured around Venus and the triennial perihelion arrival of the asteroid 2201 Oljato. In this talk, we will discuss how charged co-orbiting dust clouds around asteroids like Oljato could produce massive perturbations in the IMF by obstructing the flow of the highly conductive solar wind. We will also discuss how IFEs may be related to Magnetospheric Field Enhancements (MFES) (aka 'high-speed jets') measured in the Earth’s magnetosheath. Finally, we will discuss the results of a newly-developed procedure for the rapid and accurate identification of IFEs and MFEs using a neural network.
Understanding atmospheric loss on Mars is one of the keys to revealing the history of our red neighbor. The interaction between the upper atmosphere of Mars and the solar wind results in gas escape from the atmosphere of Mars. It is thought that this interaction has caused a once robust Martian atmosphere to evolve into the thin, arid one we see today. This escape process is dependent upon the characteristics and composition of the ionosphere of Mars. Data collected from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has shed light on the current evolution of the Martian atmosphere by observing the evolving characteristics of the Martian upper atmosphere and ionosphere. This talk analyzes the factors that impact the composition of these atmospheric regions. First, the influence of solar forcing is discussed. The influences of solar variation are normalized in order to help analyze the impact of other atmospheric processes, including dust storms and atmospheric waves. Ionospheric impacts from the recent Planet Encircling Dust Event in 2018 as well as other regional dust storms in previous Martian years are shown and discussed in this talk.
Solar wind dynamic pressure controls the size of the Earth’s magnetosphere. When the dynamic pressure increases, the magnetotail contracts. This contraction moves the closer magnetic reconnection point in the current sheet closer to Earth than during normal dynamic pressure conditions. The locations of the x-line in the current sheet are expected to be associated with stronger magnetotail and ionospheric plasma responses. We compile events when MMS observed reconnection in the current sheet and Wind observed elevated solar wind dynamic pressure on the dayside (propagated to 20 RE upstream). By comparing the locations of tail reconnection events at high solar wind dynamic pressure to those of reconnection events at low solar wind dynamic pressure, we can further understand why substorms can vary in their effects on magnetospheric plasma.