and Global Positioning System (GPS) receivers, ionosondes, coherent scatter radars, and other small, relatively inexpensive devices. Broadly interpreted, the instruments could also include small satellites, sounding rockets, and balloons. The arrays could be assembled on an ad hoc basis for campaigns of short or intermediate duration. Instruments could be rotated in and out of service, possibly in a rotation in the EarthScope model. Instruments could possibly be checked in and out of central reserves in the way that seismometers are currently within the Earth sciences. Arrays of instruments could furthermore be anchored by large, class-I facilities (incoherent scatter radars, wind-temperature lidars, and so on, as needed).
Among such measurements, there has been much progress in lidar measurements. A giant leap forward in understanding of meteorological influences and neutral-plasma interactions on the atmosphere-ionosphere-magnetosphere (AIM) system can be achieved if neutral wind, temperature, and mass density measurements can be obtained simultaneously at subscale-height altitude resolution from the lower atmosphere to the mid-thermosphere (~200 km altitude). Beyond providing the first continuous measurements of Earth’s thermal and wind structure from the lower atmosphere to the mid-thermosphere, this measurement capability would enable new discoveries in understanding wave-mean flow interactions, gravity wave propagation into the thermosphere, mesosphere turbulence, secondary wave generation in the thermosphere, eddy diffusivity, wave fluxes of momentum, heat, and constituents, and heating and cooling processes. In addition, these areas of study would significantly advance models, as many of these physical processes are presently parameterized in numerical simulations. For example, eddy diffusivity in the mesosphere is a parameter that is poorly characterized and parameterized in models but is absolutely crucial to understanding and modeling the chemistry and thermal balance of the mesosphere and thermosphere.
Combining such a neutral gas measurement capability with existing altitude-resolved plasma measurements provided by the incoherent scatter radar technique, along with other complementary instrumentation, would further broaden the potential for scientific discovery in areas of ion-neutral thermal and momentum exchange, Hall and Pedersen conductivity behavior, neutral wind effects on current flow and dissipation, neutral wind dynamo processes, and ion-neutral chemical interactions.
HOSTED PAYLOADS ON COMMERCIAL AND GOVERNMENT PLATFORMS
There are opportunities to leverage distributed systems for commercial and government use by adding sensors and finding secondary uses of data from these systems, in the context of breakthrough science investigations of solar and space physics.
As a prime example for secondary data use, the International GNSS Service (IGS) has been very successful in creating a leveraged global network of GPS/GNSS (Global Navigation Satellite Systems) receivers that provides excellent science data to the geophysics community without unduly taxing the resources of any single country or agency. The AIM community has been leveraging this global network to great success. The AIM community would benefit from adopting a proactive approach to the evolving and growing global GNSS network. The community should develop a leadership role in coordinating GNSS networks for AIM science, following the IGS model of leveraging an international effort across multiple institutions. Activities could include developing standards for data access; facilitating institutional hosting of GNSS receivers for AIM science; and providing scientific leadership in the use of global GNSS networks for AIM science.
An example of a successfully hosted payload is the Two Wide-Angle Imaging Neutral-Atom Spectrometer (TWINS) instrument, which provides stereoscopic imaging of the magnetosphere from twin platforms hosted on DOD spacecraft. TWINS is in a Molniya orbit with 63.4 degree inclination and 7.2 Earth radius (RE) apogee, which is ideal for its imaging objectives. Also, the Los Alamos National Laboratory geosynchronous Earth orbit satellites have been providing important particle measurements for decades.