Geospace Magnetosphere-Ionosphere
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GEospace Magnetosphere-Ionosphere-Neutral Interaction (GEMINI) A science mission framework targeting the core of the globally coupled magnetosphere-ionosphere providing continuous data optimized for global model validation D. Mitchell (JHU/APL), P. Brandt (JHU/APL), E. Donovan (U. Calgary), M-C Fok (GSFC), S. Fuselier (Lockheed), D. Gallagher (MSFC), J. Goldstein (SwRI), J. Kozyra (U. Mich), R. Meier (NRL), S. Mende (UCB), T. Moore (GSFC), P. Newell (JHU/APL), S. Ohtani (JHU/APL), G. Parks (UCB), L. Paxton (JHU/APL), T. Sotirelis (JHU/APL), J. Spann (MSFC), R. Wolf (Rice) Introduction The Solar System is comprised of a collection of coupled systems. In fact it is one large system-of-systems in which the Sun is the primary source of energy. Earth, as our home, is the planet we know most about. We have ventured extensively into Earth’s immediate surroundings, called Geospace, and have learned how Geospace is intrinsically interconnected over diverse scales of space and time. Over time an armada of spacecraft have revealed extraordinary global phenomena such as geomagnetic storms, with plasma energized in the magnetosphere distorting its magnetic and electric fields leading to strong modification of the radiation belts, and ionospheric storms, in which large regions of Earth’s ionosphere are redistributed over the globe. Plasma and fields in both the ionosphere and magnetosphere are coupled with each other and multiple processes (precipitation, Joule heating, particle acceleration, wave generation, mass outflow) are competing simultaneously on global and local scales to produce the global phenomena we observe. Such a system requires simultaneous global and continuous measurements of the critical regions of the magnetosphere and ionosphere. By the very nature of coupled systems, observation of the relationships among components is critical to understand and characterize the collective behavior. Imaging is the most effective (and arguably the only) way to carry out such system-level observations. Understanding of the complex interrelationships is impossible without a global view of Geospace. Imaging provides more information than any practical number of distributed single-point measurements and therefore is indispensable for system-level exploration. In this paper, we outline a science mission framework that targets the core of the globally coupled magnetosphere- ionosphere system from two platforms in a high circular orbit, providing continuous data optimized for global model validation. A range of outstanding mysteries in space physics drives the choice of observational targets. Planetary magnetospheres are efficient particle accelerators, generating a “ring current” that couples the inner magnetosphere with the ionosphere, and produces field distortions and wave activity leading to dramatic radiation belt intensification. In ionospheric storms, plasma is redistributed globally by magnetospheric as well as solar wind driven currents, auroral precipitation and solar irradiation, disrupting communications and navigation systems. GEMINI targets the ring current, plasma sphere, aurora, and the ionospheric-thermospheric plasma redistribution through continuous imaging of both northern and Figure 1: GEMINI targets the core of the coupled magnetosphere-ionosphere system by providing global, southern auroral emissions; mid-latitude far continuous 3D images of the ring current (orange), plasma ultraviolet (FUV) imaging; stereo extreme sphere, aurora, ionospheric-thermospheric dynamics and flows. ultraviolet (EUV) imaging of the plasmasphere; and GEMINI obtains the collective behavior of the complex, coupled, stereo energetic neutral atom (ENA) imaging of the interconnected Geospace system and the measurement resolution ring current and the near-Earth plasma sheet. enabling global model validation and discovery science. These measurements are made together with ground-based radar (both HF SuperDARN and ISR such as AMISR), auroral imaging arrays, and magnetometer chains) as well as other existing space assets such as IRIDIUM/AMPERE, DMSP, GOES, LANL, GPS, whatever is upstream, and any NASA Explorers or other Earth magnetosphere/ionosphere missions that may fly contemporaneously. With ground-based and LEO data providing detailed information on field aligned currents, ionospheric electron densities, temperatures and flows, GEMINI will provide the means to link the global scale magnetospheric state with these detailed ionospheric conditions. Global modeling and assimilation is a core part of the GEMINI concept. We have reached a stage where we no longer can understand the behavior of geospace without the use of physical models to retrieve the mechanisms that compete simultaneously on several scales. Meanwhile, the existing global models are continually starved for global data against the models can be validated. Imaging plays a natural and necessary role in providing global validating observations of system level interactions and processes that are not possible otherwise. Dynamics Explorer made a good beginning to the investigation of this coupling. DE imaging and ionospheric and magnetospheric in situ observations gave us a simultaneous view of small-scale physical processes and geospace at the system-level, albeit projected onto the 2D ionosphere. The DE images provided context, and more importantly, they provided our first means of assessing how the smaller scales probed by the in situ observations coupled to the larger system. ISTP took this to another level, using multiple coordinated in situ probes in combination with auroral imaging. The IMAGE Explorer mission expanded the kinds of imaging available to characterize the global scale of the Geospace system, adding magnetospheric energetic ENA and plasmaspheric EUV imaging to the FUV imaging that had been used on the earlier missions. And the many in situ measurements provided by FAST, DMSP, Polar, Geotail, and other missions provided the means of assessing how the smaller-scale processes drove (or were driven by) the larger scale system. Features as fundamental as plasmaspheric drainage plumes (which were still argued about until the IMAGE EUV images proved their existence), the local time distribution of the partial ring current (which was shown by ENA imaging to vary between early morning and dusk from one storm to another), and the substorm acceleration of oxygen in the context of storms (revealed by ENA imaging) became instantly clear using the IMAGE global images. Combined with in-situ measurements it provided the global context required to interpret the in-situ measurements correctly. For example, was a spacecraft inside or outside of the partial ring current? Where was the plasmapause relative to the spacecraft measuring a particular plasma wave signature? Mission Objective and Science Questions GEMINI seeks to determine how the Figure 2. The magnetosphere-ionosphere-thermosphere system is complex. magnetosphere-ionosphere-thermosphere Global scale measurements are critical to placing in situ (HEO, MEO, and LEO) system is coupled and responds to solar and and ground-based measurements in an appropriate framework. Global models are strongly constrained by global scale imaging. The combination (global magnetospheric forcing and to provide a imaging, in situ, ground based, and models) will enable understanding the long-duration mission framework into coupling among these interconnected plasmas. which additional science missions can naturally fit. GEMINI’s science questions are chosen to address critical pieces in the global redistribution, acceleration and response in the magnetosphere and IT system as illustrated in Figure 2. We discuss these overarching science questions in terms of the global system and identify “ports” where external science investigations fit in naturally, enabled by GEMINI’s long lifetime. 1. How does MI-coupling control plasma redistribution in the magnetosphere and ionosphere/thermosphere? (GEMINI) Both magnetospheric and solar forcing gives rise to IT plasma redistribution. Plasma accumulation in the afternoon/dusk sector at low latitudes appear to be funneled to higher latitudes that eventually reach the cusp, where most of the ionospheric outflow is seen in statistical studies. Is this snaking pattern a how plasma is supplied to the breathing hole of the Earth’s ionosphere to space? The funnel coincides with the Sub-Auroral Polarization Stream (SAPS) channel, which appears almost perfectly reflected in the plasmaspheric drainage plume in the magnetosphere. The SAPS phenomena is believed to be an effect of the closure of the ring current through the low- conductance gap in the ionospheric trough region, which leads to Figure 3: Strong ionospheric flows (SAPS) is enhanced ionospheric flows in a narrow region. Fundamental plasma only one example of a coupled phenomena physics mysteries are nicely illustrated in this interface region. As that requires simultaneous imaging of both magnetospheric currents close through the different and dynamically the magnetospheric “driver” and the changing conductances of the ionosphere, the global electric field of ionospheric response. The SAPS flow is an the ionosphere is altered and feeds back to the large-scale electric field effect of magnetospheric currents closing of the magnetosphere producing macroscopic effects in the location through the low-conductance ionospheric and dynamics of both the ring current and the plasma sphere. Defying trough region [Brandt et al., 2008]. expectations that the ring current would