Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop (2006)

Background The 2002 NRC report The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, recommended that the next major ground-based instrumentation initiative be the deployment of arrays of space science research instrumentation. Such arrays would provide continuous real-time observations of Earth-space with the resolution needed to resolve mesoscale phenomena and their dynamic evolution. In addition, ground-based arrays would address the need for observations to support the next generation of space weather data-assimilation models.

Mesoscale and spatially and temporally localized processes and effects play a significant role in the interconnection between the high-altitude magnetosphere and Earth’s ionosphere and lower atmosphere. The various latitude and altitude regimes of Earth-space constitute a highly coupled system. Advances in understanding these regions require widely distributed, continuous observations capable of high spatial and temporal resolution.

Of particular interest because of its influence on “space weather” and effects on Earth is the plasmasphere boundary layer (PBL). The PBL separates the cold plasmas of the inner magnetosphere from the hot particles and solar-driven dynamics of the auroral regions. Dramatic boundary-layer physical processes have been discovered in this region, and these are both highly structured and variable in their spatial and temporal occurrence characteristics. Electric fields unique to the PBL lead to plasmasphere erosion, which distributes the thermal plasmas of the inner region throughout the mid, high, and polar regions of both the ionosphere and magnetosphere. These thermal plasmas constitute a source for the energetic plasmas of the magnetosphere and control many magnetospheric processes. Ionospheric feedback through modification of electric fields alters the development of the magnetospheric ring current which is important for the evolution of geomagnetic storms.

The inner regions of the system, consisting of the low-latitude ionosphere and overlying plasmasphere, exhibit large-scale structure whose causes are not understood. The sources and effects of the causative electric fields are to be investigated. All of these processes and phenomena have significant space weather consequences. Plasma and electric field gradients drive scintillations, and the thermal plasma structures affect the precision of radio navigation.

A partial list of the scientific drivers for the deployment of distributed arrays of small instruments follows:

• Temporal/Spatial Variability of Mesoscale Global Structure in Thermal Plasma, Electric Fields, and Currents

• 3-D Tomography of Plasma Structure

• Distribution of Currents Interconnecting the Magnetosphere and Ionosphere near the PBL

• Continuous Observations That Provide a New Perspective of the Ionosphere-Magnetosphere

• Imaging SAPS Electric Field (2-D) over broad Spatial Regions

• Evolution and Effects of Undershielded Disturbance Electric Fields which Penetrate to Equatorial Latitudes

• Resolution of Longitudinal Asymmetries and Regional Perturbations

• Thermal Plasma Source to Magnetosphere

• Space Weather Effects of Thermal Plasma

• Relationship of Electric Fields, Particle Precipitation, and Thermal Plasma Structuring in Driving Scintillations

• Causes and Evolution of Plasmaspheric Structure

Deployment of DASI will require the development of miniaturized and robust instruments and instrument clusters, real-time communication capabilities, and a system to distribute the resultant data to a wide variety of users. A partial list of the types of instruments that could contribute to space weather distributed arrays includes the following:

• Broad-Band Radio Receivers: GPS TEC, Scintillation, Tomography, VLF

• Passive Radar: Intercepted Signals from non-dedicated transmitters (FM, e.g.)

• Magnetospheric monitors: global, high-time-resolution magnetometers, riometers

• Active Radio: Digisonde, Small Radar

• Optics: All-Sky Imagers, Interferometers (neutral atmosphere dynamics)

• Riometers and Neutron Monitors for Particle Fluxes

• Solar Monitors

• Enhanced Real-Time Communications and Analysis

Plan The Space Studies Board Committee on Solar and Space Physics will organize a 2-day workshop to explore the scientific rationale for such arrays, the infrastructure needed to support and utilize them, and proposals for an implementation plan for their deployment. The committee will summarize workshop discussions in a short report. This report will not make any recommendations.