Yosemite Conference on Ionospheric Plasma in the Magnetosphere: Sources, Mechanisms and Consequences, meeting report

The sixth biennial Yosemite topical conference and the first as a Chapman Conference was held on February 3 to 6, 1986. Due to the recent changes in our perception of the dynamics of the ionospheric/magnetospheric system, it was deemed timely to bring researchers together to discuss and contrast the relative importance of solar versus terrestrial sources of magnetospheric plasma. Although the solar wind was once thought to dominate the supply of plasma in the Earth's magnetosphere, it is now thought that the Earth's ionosphere is a significant contributor. Polar wind and other large volume outflows of plasma have been seen at relatively high altitudes over the polar cap and are now being correlated with outflows found in the magnetotail. The auroral ion fountain and cleft ion fountain are examples of ionospheric sources of plasma in the magnetosphere, observed by the Dynamics Explorer 1 (DE 1) spacecraft. The conference was organized into six sessions: four consisting of prepared oral presentations, one poster session, and one session for open forum discussion. The first three oral sessions dealt separately with the three major topics of the conference, i.e., the sources, mechanisms, and consequences of ionospheric plasma in the magnetosphere. A special session of invited oral presentations was held to discuss extraterrestrial ionospheric/magnetospheric plasma processes. The poster session was extended over two evenings during which presenters discussed their papers on a one-on-one basis. The last session of the conferences was reserved for open discussions of those topics or ideas considered most interesting or controversial

Experimental investigation of possible geomagnetic feedback from energetic (0.1 to 16 keV) terrestrial O(+) ions in the magnetotail current sheet

Data from energetic ion mass spectrometers on the ISEE 1 and AMPTE/CCE spacecraft are combined with geomagnetic and solar indices to investigate, in a statistical fashion, whether energized O(+) ions of terrestrial origin constitute a source of feedback which triggers or amplifies geomagnetic activity as has been suggested in the literature, by contributing a destabilizing mass increase in the magnetotail current sheet. The ISEE 1 data (0.1-16 keV/e) provide in situ observations of the O(+) concentration in the central plasma sheet, inside of 23 R(sub E), during the rising and maximum phases of solar cycle 21, as well as inner magnetosphere data from same period. The CCE data (0.1-17 keV/e) taken during the subsequent solar minimum all within 9 R(sub E). provide a reference for long-term variations in the magnetosphere O(+) content. Statistical correlations between the ion data and the indices, and between different indices. all point in the same direction: there is probably no feedback specific to the O(+) ions, in spite of the fact that they often contribute most of the ion mass density in the tail current sheet

Superthermal ion signatures of auroral acceleration processes

The retarding ion mass spectrometer on the Dynamics Explorer 1 spacecraft has generated a unique data set which documents, among other things, the occurrence of non-Maxwellian superthermal features in the auroral topside ionosphere distribution functions. In this paper, we provide a representative sampling of the observed features and their spatial morphology as observed at altitudes in the range from a few thousand kilometers to a few earth radii. At lower altitudes, these features appear at auroral latitudes separating regions of polar cap and subauroral light ion polar wind. The most common signature is the appearance of an upgoing energetic tail having conical lobes representing significant ion heat and number flux in all species, including O+. Transverse ion heating below the observation point at several thousand kilometers is clearly associated with O+ outflows. In some events observed, transverse acceleration apparently involves nearly the entire thermal plasma, the distribution function becomes highly anisotropic with T⊥ > T∥, and may actually develop a minimum at zero velocity, i.e., become a torus having as its axis the local magnetic field direction. At higher altitudes, the localized dayside source region appears as a field aligned flow which is dispersed tailward across the polar cap according to parallel velocity by antisunward convective flow, so that upflowing low energy O+ ions appear well within the polar cap region. While this flow can appear beamlike in a given location, the energy dispersion observed implies a very broad energy distribution at the source, extending from a few tenths of an eV to in excess of 50 eV. On the nightside, upgoing ion beams are found to be latitudinally bounded by regions of ion conics whose half angles increase with increasing separation from the beam region, indicating low altitude transverse acceleration in immediate proximity to, and below, the parallel acceleration region. These observations reveal a clear distinction between classical polar wind ion outflow and O+ enhanced superthermal flows, and confirm the importance of low altitude transverse acceleration in ionospheric plasma transport, as suggested by previous observations

Optimization of Single-Satellite Operational Schedules Towards Enhanced Communication Capacity

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/97112/1/AIAA2012-4610.pd

A new source of suprathermal O+ions near the dayside polar cap boundary

A new dayside source of O+ ions for the polar magnetosphere is described, and a statistical survey presented of upward flows of O+ ions using 2 years of data from the retarding ion mass spectrometer (RIMS) experiment on board DE 1, at geocentric distances below 3 RE and invariant latitudes above 40°. The flows are classified according to their spin angle distributions. It is believed that the spacecraft potential near perigee is generally less than +2 V, in which case the entire O+ population at energies below about 60 eV is sampled. Examples are given of field-aligned flow and of transversely accelerated “core” O+ ions; in the latter events a large fraction of the total O+ ion population has been transversely accelerated, and in some extreme cases all the observed ions (of all ion species) have been accelerated, and no residual cold population is observed (“toroidal” distributions). However, by far the most common type of O+ upflow seen by DE RIMS lies near the dayside polar cap boundary (particularly in the prenoon sector) and displays an asymmetric spin angle distribution. In such events the ions carry an upward heat flux, and strong upflow of all species is present (H+, He+, O+, O++, and N+ have all been observed with energies up to about 30 eV, but with the majority of ions below about 2 eV); hence, these have been termed upwelling ion events. The upwelling ions are embedded in larger regions of classical light ion polar wind and are persistently found under the following conditions: at geocentric distances greater than 1.4 RE; at all Kp in summer, but only at high Kp in winter. Low-energy conical ions (<30 eV) are only found near the equatorial edge of the events, the latitude of which moves equatorward with increasing Kp and is highly correlated with the location of field-aligned currents. The RIMS data are fully consistent with a “mass spectrometer effect,” whereby light ions and the more energetic O+ ions flow into the lobes and mantle and hence the far-tail plasma sheet, but lower-energy O+ is swept across the polar cap by the convection electric field, potentially acting as a source for the nightside auroral acceleration regions. The occurrence probability of upwelling ion events, as compared to those of low-altitude transversely accelerated core ions and of field-aligned flow, suggests this could be the dominant mechanism for supplying the nightside auroral acceleration region, and subsequently the ring current and near-earth plasma sheet, with ionospheric O+ ions. It is shown that the total rate of O+ outflow in upwelling ion events (greater than 10^25 s^{−1}) is sufficient for the region near the dayside polar cap boundary to be an important ionospheric heavy ion source

The FIREBIRD Instrument for Relativistic Electrons: Enabling Technologies for a Fast High-Sensitivity, Low-Power Space Weather Radiation Payload

Miniaturized instrument payloads on small satellite and nanosatellite platforms that are deployed in low Earth orbit are demonstrating cost effective weather monitoring platforms with increased temporal and spatial resolution compared to larger weather satellites. The NASA Earth Decadal Survey [1] states that improving the revisit time of microwave radiometers would significantly improve weather forecasting. Radiometers such as the Advanced Technology Microwave Sounder (ATMS) on Suomi National Polar-orbiting Partnership (Suomi-NPP) and the Joint Polar Satellite System-1 (JPSS-1), now NOAA-20, provide an average revisit rate of 7.6 hours; however, a constellation of six CubeSats in three orbital Low Earth Orbit (LEO) planes with microwave radiometers such as the Time-Resolved Observations of Precipitations structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission would provide a refresh rate of better than 60 minutes. In order to effectively use CubeSats in a constellation as a weather monitoring platform, calibration must be used to provide measurements consistent with state of the art measurements, such as ATMS that has a NeDT at 300K of 0.5-3.0K [2]. In this work, we use the Joint Center for Satellite Data Assimilation (JCSDA) Community Radiative Transfer Model (CRTM) to simulate brightness temperatures (https://www.jcsda.noaa.gov/projects_crtm.php), which are used to assess miniaturized microwave radiometer radiometric biases. CRTM is a fast radiative transfer model that uses Fortran functions, structure variables, and coefficient data of the modeled sensor to simulate radiances. The user inputs surface characteristics, scan angles, and atmospheric profiles from sources such as radiosondes, Numerical Weather Prediction (NWP) models, and Global Positioning System Radio Occultation (GPSRO) measurements. The output of CRTM is a simulated brightness temperature that is used to correct radiometric biases in order to meet required instrument NeDT performance. We use radiosonde, GPSRO, and NWP ERA-5 atmospheric profiles in CRTM and compare the results to ATMS brightness temperatures and find an average difference in brightness temperature of 1.95 K, which is comparable to ATMS Integrated Calibration/Validation System (https://www.star.nesdis.noaa.gov/icvs/status_NPP_ATMS.php) reports which show channel bias variations of up to 2 K. We take a similar approach to provide calibration for the Micro-sized Microwave Atmospheric Satellite-2A (MicroMAS-2A), a 3U CubeSat that was launched on January 11th, 2018. MicroMAS-2A carries a 1U 10-channel passive microwave radiometer that provides imagery near 90 and 206 GHz, temperature sounding near 118 GHz, and moisture sounding near 183 GHz. We develop an approach for comparing MicroMas-2A brightness temperatures to radiosonde, GPSRO, and NWP ERA5 atmospheric profiles. Due to the scarcity of GPSRO and radiosonde profiles near the MicroMAS-2A data segments, we determine that NWP models will be the best option for radiance validation. After the next stage of calibration of MicroMAS-2A is completed, we will compare CRTM simulated radiances from ERA profiles to the initial sensor data, with expected results of channel bias variations of \u3c 2 K

An unusual SAR arc observed during ring current development, 4 August 1972

Measurements made from the ISIS-II spacecraft at 1400 km and ground-based measurements from New Zealand provide a detailed description of an unusual SAR arc observed at dusk on 4 August 1972, during the growth phase of the ring current. Proton precipitation was observed over a latitude range of a few degrees, with electron temperature enhancements throughout the region but espeically at its boundaries, and an F-region trough was present at the equatorward boundary. SAR arcs usually occur at equatorward proton boundaries but this one appeared at the poleward boundary, which seems to have given rise to a number of unusual features. Characteristics unique to this event are a high flux of low energy electrons at the SAR arc location, associated with an upward field-aligned current there, and a "slot" in the ambient electron density, which falls to 5% of the background density over a region of 1.5 km half-width. Immediately poleward of the low energy electron flux, intense whistler mode noise (0.1-0.4 MHz) is evident. The 6300 A emission, which has a total intensity of 10.6 kR, appears divided into two components, one at 285 km excited by the low energy electrons, and the other at 400 km, excited thermally by the electron gas. Comparisons are made with S3-A spacecraft observations made in the equatorial region at the same time, with ISIS-II observations of a more normal SAR arc, and with other observations reported in the literature. The kinetic Alfven wave process described by Hasegawa and Mima (1978) seems a candidate for the acceleration of these low energy electrons, but it is not possible to entirely exclude the alternative of an auroral-type acceleration process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23358/1/0000302.pd