Takumi ABE

In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: (A) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? (B) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus.

The acceleration and transport of high-latitude ionospheric ion outflows, both bulk ion flows and suprathermal ion outflows, play a fundamental role in magnetosphere-ionosphere coupling. Bulk ion flows consist mainly of the polar wind and auroral bulk upflows (with flow energies up to a few eV) in the topside polar ionosphere, which are the primary sources of low-energy H+ and O+ ions, respectively, for various ion acceleration processes at higher altitudes. These processes include perpendicular and parallel acceleration in the mid (~1000-5000 km) or high-altitude auroral zone, which produce suprathermal (~10 eV to ~10 keV) ion outflows such as transversely accelerated ions, ion conics, and ion beams; and centrifugal acceleration in regions of curved or changing magnetic field at high altitudes (above ~3-4 RE). A significant fraction of ion outflows remains cold in the magnetosphere, where their transport is strongly influenced by the interplanetary magnetic field (IMF) and the prevailing convection electric field. This results in a preferential feeding of the dusk plasma sheet under duskward IMF, and a stronger transport to the plasma sheet compared to the magnetotail at times of strong convection.

We investigate the forces and atmosphere-ionosphere coupling that create atmospheric dynamo currents using two rockets launched nearly simultaneously on 4 July 2013 from Wallops Island (USA), during daytime Sq conditions with ΔH of −30 nT. One rocket released a vapor trail observed from an airplane which showed peak velocities of >160 m/s near 108 km and turbulence coincident with strong unstable shear. Electric and magnetic fields and plasma density were measured on a second rocket. The current density peaked near 110 km exhibiting a spiral pattern with altitude that mirrored that of the winds, suggesting the dynamo is driven by tidal forcing. Such stratified currents are obscured in integrated ground measurements. Large electric fields produced a current opposite to that driven by the wind, believed created to minimize the current divergence. Using the observations, we solve the dynamo equation versus altitude, providing a new perspective on the complex nature of the atmospheric dynamo.

The Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the International Space Station demonstrated a 4 K mechanical cooler for high-sensitivity submillimeter limb-emission sounding of atmospheric observations. Based on the SMILES heritage, we propose a satellite mission "SMILES-2" to observe temperature and wind fields, and distributions of atmospheric trace gases from the middle atmosphere to the upper atmosphere. We will be able to grasp the 4-D dynamical structure of diurnal variations which are one of the most essential characteristics in the earth's atmosphere. In the upper atmosphere, a transition layer between the atmosphere and the outer space, we will be able to clarify a role of magnetospheric energy inputs from the temperature and wind observations. These outcomes including the atmospheric trace gas data will greatly contribute to improve the reliability of chemistry climate models for future projection and the accuracy of prediction models for space weather.

© 2019 URSI. All rights reserved. The Sq current system occurs in the lower ionosphere in the winter daytime. The Sq current system is appeared the specific plasma phenomenon such as electron heating, strong electron density disturbance. Therefore it is important to measure directly the DC electric field and the plasma waves in the ionosphere.