Executive Summary

To explore the scientific rationale for arrays of small instruments recommended in the 2002 NRC decadal survey for solar and space physics,1 the infrastructure needed to support and utilize such arrays, and proposals for an implementation plan for their deployment, an ad hoc committee established under the Space Studies Board’s Committee on Solar and Space Physics organized the 1.5-day Workshop on Distributed Arrays of Small Instruments held in June 2004 at the National Academies’ Jonnson Center in Woods Hole, Massachusetts. This report summarizes the discussions at the workshop; it does not present findings or recommendations.

Solar-terrestrial science addresses a coupled system extending from the Sun and heliosphere to Earth’s outer magnetosphere and ionosphere to the lower layers of the atmosphere, which are connected via the thermosphere and lower ionosphere. Processes in each region can affect those in the other regions through coupling and feedback mechanisms. As the 2002 decadal survey and other related NRC reports have noted,2 understanding and monitoring the fundamental processes responsible for solar-terrestrial coupling are vital to being able to fully explain the influence of the Sun on the near-Earth environment. These studies emphasize that monitoring the spatial and temporal development of global current systems and flows; the energization and loss of energetic particles; and the transport of mass, energy, and momentum throughout the magnetosphere and coupled layers of Earth’s upper atmosphere is essential to achieving this scientific goal.

At the workshop, speakers asserted that deployment of distributed arrays of small instruments (DASI) would culminate decades of discipline-related local instrument development for the pursuit of aspects of solar-terrestrial science at the subsystem level. With the advent of the Internet and affordable high-speed computing, these local deployments can now become elements of a global instrument system. When different instrument techniques are then combined to observe all aspects of the physical system, the DASI concept will be realized.

Proponents of the DASI concept emphasized that DASI’s strength is that it offers a cost-effective means of performing original and critically important science, with a development strategy that allows resulting new knowledge to enable and flow into future initiatives. DASI will complement and extend the capabilities of the next generation of space-based research and space weather instruments by providing a global context within which to understand in situ and remote sensing observations.

During the course of the workshop, three recurrent themes became evident: (1) the need to address geospace3 as a system, (2) the need for real-time observations, and (3) the insufficiency of current observations.

  1. Geospace as a system—Understanding the Sun’s influence on Earth’s global space environment requires detailed knowledge of the atmosphere-ionosphere-magnetosphere system. This

1  

National Research Council (NRC), 2003, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The National Academies Press, Washington, D.C., p. 73; NRC, 2003, The Sun to the Earth—and Beyond: Panel Reports, The National Academies Press, Washington, D.C., p. 174.

2  

For example, see NRC, 2004, Plasma Physics of the Local Cosmos, The National Academies Press, Washington, D.C.

3  

“Geospace” is the term used to refer to the ensemble of regions including Earth’s magnetosphere, ionosphere, and thermosphere.



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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop Executive Summary To explore the scientific rationale for arrays of small instruments recommended in the 2002 NRC decadal survey for solar and space physics,1 the infrastructure needed to support and utilize such arrays, and proposals for an implementation plan for their deployment, an ad hoc committee established under the Space Studies Board’s Committee on Solar and Space Physics organized the 1.5-day Workshop on Distributed Arrays of Small Instruments held in June 2004 at the National Academies’ Jonnson Center in Woods Hole, Massachusetts. This report summarizes the discussions at the workshop; it does not present findings or recommendations. Solar-terrestrial science addresses a coupled system extending from the Sun and heliosphere to Earth’s outer magnetosphere and ionosphere to the lower layers of the atmosphere, which are connected via the thermosphere and lower ionosphere. Processes in each region can affect those in the other regions through coupling and feedback mechanisms. As the 2002 decadal survey and other related NRC reports have noted,2 understanding and monitoring the fundamental processes responsible for solar-terrestrial coupling are vital to being able to fully explain the influence of the Sun on the near-Earth environment. These studies emphasize that monitoring the spatial and temporal development of global current systems and flows; the energization and loss of energetic particles; and the transport of mass, energy, and momentum throughout the magnetosphere and coupled layers of Earth’s upper atmosphere is essential to achieving this scientific goal. At the workshop, speakers asserted that deployment of distributed arrays of small instruments (DASI) would culminate decades of discipline-related local instrument development for the pursuit of aspects of solar-terrestrial science at the subsystem level. With the advent of the Internet and affordable high-speed computing, these local deployments can now become elements of a global instrument system. When different instrument techniques are then combined to observe all aspects of the physical system, the DASI concept will be realized. Proponents of the DASI concept emphasized that DASI’s strength is that it offers a cost-effective means of performing original and critically important science, with a development strategy that allows resulting new knowledge to enable and flow into future initiatives. DASI will complement and extend the capabilities of the next generation of space-based research and space weather instruments by providing a global context within which to understand in situ and remote sensing observations. During the course of the workshop, three recurrent themes became evident: (1) the need to address geospace3 as a system, (2) the need for real-time observations, and (3) the insufficiency of current observations. Geospace as a system—Understanding the Sun’s influence on Earth’s global space environment requires detailed knowledge of the atmosphere-ionosphere-magnetosphere system. This 1   National Research Council (NRC), 2003, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The National Academies Press, Washington, D.C., p. 73; NRC, 2003, The Sun to the Earth—and Beyond: Panel Reports, The National Academies Press, Washington, D.C., p. 174. 2   For example, see NRC, 2004, Plasma Physics of the Local Cosmos, The National Academies Press, Washington, D.C. 3   “Geospace” is the term used to refer to the ensemble of regions including Earth’s magnetosphere, ionosphere, and thermosphere.

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop extremely complex natural system involves many different interacting elements, and Earth is the only planetary system that scientists can expect to study in detail. Today, the science of space plasma physics has matured to the level of being able to both describe and model many of these interactions. A major goal in solar-terrestrial science now is to unify scientific understanding so as to achieve a more comprehensive computational framework that will enable prediction of the properties of this system—leading to conditions known as space weather that affect Earth and its technological systems. To do this accurately, however, requires an understanding of Earth’s global behavior as it exists, rather than as it occurs in an idealized representation. Realizing such goals requires the assimilation and integration of data from disparate sources. The need for real-time observations—The magnetosphere-ionosphere-thermosphere (M-I-T) system is a highly dynamic, nonlinear system that can vary significantly from hour to hour at any location. The coupling is particularly strong during geomagnetic storms and substorms, but there are appreciable time delays associated with the transfer of mass, momentum, and energy between the different domains. Also, it is now becoming clear that a significant fraction of the flow of mass, momentum, and energy in the M-I-T system occurs on relatively small spatial scales and over a wide range of temporal scales. Consequently, elucidation of the fundamental coupling processes requires continuous, coordinated, real-time measurements from a distributed array of diverse instruments, as well as physics-based data assimilation models. Insufficiency of current observations—Observational space physics is data-starved, leading to large gaps in the ability to both characterize and understand important phenomena. This is particularly true for space weather events, which often are fast-developing and dynamic and which extend well beyond the normal spatial coverage of current (ground-based or space) sensor arrays. Issues addressed in presentations and discussion sessions at the workshop can be summarized in a number of fundamental science questions reflecting what participants saw as opportunities for the DASI concept to contribute to progress in understanding the Sun’s influence on the near-Earth environment. They included the following: What is the configuration of the magnetosphere-ionosphere-thermosphere system that is most vulnerable to space weather? What are the processes and effects associated with plasma redistribution during disturbed conditions? What is the role of the ionosphere-thermosphere system in the processes associated with particle energization? What are the effects of preconditioning in the ionosphere and magnetosphere on the evolution of disturbances? What processes affect ion-neutral coupling in the presence of particle precipitation? What are the causes of thermosphere-ionosphere variability during geomagnetically quiescent periods? What are the structure and dynamics of the Sun’s interior? What are the causes of solar activity? How does the structure of the heliosphere modify the solar wind? Can low-frequency interplanetary scintillations be used to make global determinations of solar wind velocity? Among the major ground-based remote sensing instruments described by workshop participants were the following: Very-low-frequency and high-frequency receivers and radio telescopes; High- and medium-power active radars and low-power passive radars;

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Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop Ionosondes; Magnetometers; Passive and active optical instruments (interferometers, spectrometers, lidars); and Solar imagers, spectrographs, polimeters, magnetographs, and radio telescopes. Speakers also noted the importance of computer models that are capable of assimilating the observations made with such instruments. Attention at the workshop sessions was also devoted to issues regarding the infrastructure needs for future distributed arrays of ground-based instruments. Information technology was especially emphasized. Speakers cited the Virtual Observatory model that is being used in the solar and astronomy communities as an excellent starting point and template for DASI. Other information technology capabilities of note included the use of Internet and computer grid technology and high-data-rate, near-real-time communications systems. Finally, the workshop illuminated logistics considerations for the DASI concept, including key instrument spacing and size requirements for some classes of instruments as well as opportunities for and constraints on instrument placement in key locations for realizing DASI science objectives. Throughout the workshop participants discussed a number of areas in which the space research community can begin an organized effort to develop a coordinated space-research instrumentation system. Although no consensus on priorities was sought or attempted, participants identified the following near-term actions as means to further evaluate the potential of the DASI concept and to prepare for its future development and implementation: Hold community workshops to address in greater detail the instrumentation, science, and deployment issues associated with DASI. Identify areas in which existing and planned instrument arrays and clusters can share technology, data distribution architectures, and logistics experience. Consolidate currently planned systems to form a regional implementation of next-generation coordinated instrument arrays. Establish closer connections with other research communities that are developing similar distributed instrumentation systems. Coordinate efforts in the U.S. community with similar international efforts. Move toward developing rugged, miniaturized instruments that use a common data format. Support efforts to establish standards for data communication technologies and protocols. Work with agency sponsors to begin a phased implementation of the DASI program. Achieving the science objectives for DASI will require a global deployment of instruments and a large commitment of resources. Although the workshop did not go into detail on the areas of collaboration or opportunities to be pursued, participants felt strongly that international collaboration should be a fundamental part of the DASI plan.