430 research outputs found

    Studies in upper and lower atmosphere coupling

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    The theoretical and data-analytic work on upper and lower atmosphere coupling performed under a NASA Headquarters contract during the period April 1978 to March 1979 are summarized. As such, this report is primarily devoted to an overview of various studies published and to be published under this contract. Individual study reports are collected as exhibits. Work performed under the subject contract are in the following four areas of upper-lower atmosphere coupling: (1) Magnetosphere-ionosphere electrodynamic coupling in the aurora; (2) Troposphere-thermosphere coupling; (3) Ionosphere-neutral-atmosphere coupling; and (4) Planetary wave dynamics in the middle atmosphere

    Ionospheric Precipitation of Particles in the first 6D Vlasiator run

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    One of the most noticeable effects of solarā€“terrestrial physics is the aurora which regularly appears in the polar regions. This polar light is the result of the excitation of atmospheric species by charged particles originating from the solar wind and magnetosphere that enter the Earthā€™s atmosphere, which are called precipitating particles. We present the first results on auroral proton precipitation into the ionosphere using a global 3-dimensional simulation of near-Earth space plasma with the Vlasiator hybrid-Vlasov model, driven with a southward interplanetary magnetic field and steady solar wind parameters. The hybrid-Vlasov approach describes ions through their velocity distribution function in phase space (3-dimensional ordinary space and 3-dimensional velocity space), while electrons are represented by a massless charge-neutralizing fluid. Vlasiator is a global model describing the whole region of near-Earth space including the Earthā€™s magnetosphere (whole dayside and part of the magnetotail), the magnetosheath, as well as the foreshock region and some solar wind. The precipitating proton differential number fluxes for this run are determined from the proton phase-space density contained within the bounce loss-cone, which is set at a constant angle of 10 degrees everywhere. To determine the precipitation of particles at ionospheric altitudes (in this case a height of 110 km above the Earthā€™s surface), we trace magnetic field lines from the ionosphere to the inner boundary of the Vlasiator domain using the Tsyganenko model. With this, we obtain a magnetic local timeā€“geomagnetic latitude map of differential number flux of precipitating protons in 9 energy bins between 0.5 and 50 keV. From the differential number flux, proton integral energy fluxes and mean energies can be obtained. The integral energy fluxes in the Vlasiator run are then compared to data of the Precipitation Electron/Proton Spectrometer (SSJ) instrument of the Defense Meteorological Satellite Program (DMSP) for several satellite overpasses during events with similar solar wind conditions as in the Vlasiator run. The SSJ instrument bins proton energies between 0.03 and 30 keV. Typical values of the total integral energy flux are between 5 Ā· 10^6 and 5 Ā· 10^7 keV cmāˆ’2 sāˆ’1 srāˆ’1 in the cusp and between 1 Ā· 10^6 and 3 Ā· 10^7 keV cmāˆ’2 sāˆ’1 srāˆ’1 in the evening sector for both Vlasiator and DMSP, although DMSP fluxes can locally be up to an order of magnitude higher. Additionally, global precipitation patterns in Vlasiator are compared to Ovation Prime, which is an empirical model based on data from DMSP which can be used to forecast precipitation of auroral electrons and protons. Although Ovation Prime shows a much wider cusp region compared to Vlasiator, both show similar maximum integral energy fluxes around 1 to 2 Ā· 10^7 keV cmāˆ’2 sāˆ’1 srāˆ’1 in the cusp region, and between 3 Ā· 10^6 and 5 Ā· 10^7 keV cmāˆ’2 sāˆ’1 srāˆ’1 in the nightside oval

    An implementation plan for priorities in solar-system space physics

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    The scientific objectives and implementation plans and priorities of the Space Science Board in areas of solar physics, heliospheric physics, magnetospheric physics, upper atmosphere physics, solar-terrestrial coupling, and comparative planetary studies are discussed and recommended programs are summarized. Accomplishments of Skylab, Solar Maximum Mission, Nimbus-7, and 11 other programs are highlighted. Detailed mission plans in areas of solar and heliospheric physics, plasma physics, and upper atmospheric physics are also described

    Modeling the generation and propagation of dispersive waves in the giant magnetospheres through mass loading and transport using hybrid simulation

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    Thesis (Ph.D.) University of Alaska Fairbanks, 2018The magnetodiscs of Jupiter and Saturn are characterized by turbulence in the magnetic field. Broadband spectra of precipitating electrons at Jupiter suggest that a process is underway whereby large scale perturbations undergo a turbulent cascade in the magnetodisc. The cascade couples large perturbations to dispersive scales (kinetic and inertial AlfveĢn waves). Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally-driven flux tube interchange instability, similar to the Rayleigh-Taylor (RT) instability. Mass loading from satellites such as Io and Enceladus also cause dispersive wave formation in the magnetosphere, which is a source for broadband aurora. This dissertation presents a set of hybrid (kinetic ion/fluid electron) plasma simulations of the RT instability and the Io flux tube using conditions appropriate for the magnetospheres of Jupiter and Saturn. Both the Io torus and the planetary magnetodisc act as resonant cavities for counter propagating waves, which creates turbulence. The transmission ratio of wave power from the Io torus is 53%, an improvement from previous models (20% transmission), which is important to the generation of the Io auroral footprint. The onset of the RT instability begins at the ion kinetic scale and cascades to larger wavelengths. Strong guide field reconnection is a mechanism for radial transport of plasma in the magnetodisc. Counter propagating waves within the RT instability is the origin of turbulence within the magnetodisc

    A 3-D Model of the Auroral Ionosphere

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    A new 3-D model of the high latitude ionosphere is developed to study the coupling of the ionosphere with the magnetosphere and neutral atmosphere. The model consists of equations describing conservations of mass, momentum and energy for the six ionospheric constituents (O+, NO+, N+2 , O+2 , N+ and e-) and an electrostatic potential equation. This 3-D model is used to examine interrelated processes of ion heating, plasma structuring due to perpendicular transport, ion upflow, molecular ion generation, and neutral wave forcing. It is first validated by comparisons with a 2-D model, which uses similar mathematical and numerical approaches, and is additionally compared against incoherent scatter radar data. Results from a simulation of ionospheric response to a large amplitude acoustic wave also suggests an important role for these waves in generating local dynamo currents and density variations. Results of this model also shed some light on the interplay of perpendicular and parallel transports of plasma in producing structures in density and drift velocity profiles

    Global Geospace Science/Polar Plasma Laboratory: POLAR

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    The Global Geospace Science (GGS) Project is discussed as part of the International Solar-Terrestrial Physics (ISTP) Science Initiative. The objectives of Polar Plasma Laboratory (POLAR), one of the two spacecraft to be used by the Project to fill critical gaps in the scientific understanding of solar and plasma physics, are outlined. POLAR Laboratory is described, along with POLAR instrumentation, support subsystems, and orbits. Launch vehicle and injection into orbit are also addressed

    Mode Conversion Processes in Magnetized Plasmas

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    Mode conversion processes in plasmas allow wave energy to transferred between two or more different wave modes, and are often invoked in theories of space and astrophysical phenomena. For instance, electrostatic Langmuir waves which are trapped in the solar wind plasma can be converted to electromagnetic radiation and produce radio bursts, which can propagate through the plasma and thus be observed remotely. In environments where mode conversion has been invoked there is often a significant ambient magnetic field. This modifies the dispersion relations of the wave modes and can result in additional wave modes. However, magnetization effects have been neglected in the analyses of certain mode conversion processes. This thesis presents a number of investigations into mode conversion processes as they occur in magnetized plasmas, focusing on the magnetization of the Langmuir mode

    Solar Terrestrial Physics: Present and Future

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    The following topics relating to solar-terrestrial interactions are considered: (1) reconnection of magnetic fields; (2) particle acceleration; (3) solar magnetic flux; (4) magnetohydrodynamic waves and turbulence in the Sun and interplanetary medium; (5) coupling of the solar wind to the magnetosphere; (6) coronal transients; (7) the connection between the magnetosphere and ionosphere; (8) substorms in the magnetosphere; (9) solar flares and the solar terrestrial environment; (10) shock waves in the solar terrestrial environment; (11) plasma transport and convection at high latitudes; and (12) high latitude ionospheric structure

    Space-time sampling strategies for electronically steerable incoherent scatter radar

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    Incoherent scatter radar (ISR) systems allow researchers to peer into the ionosphere via remote sensing of intrinsic plasma parameters. ISR sensors have been used since the 1950s and until the past decade were mainly equipped with a single mechanically steerable antenna. As such, the ability to develop a two or three dimensional picture of the plasma parameters in the ionosphere has been constrained by the relatively slow mechanical steering of the antennas. A newer class of systems using electronically steerable array (ESA) antennas have broken the chains of this constraint, allowing researchers to create 3-D reconstructions of plasma parameters. There have been many studies associated with reconstructing 3-D fields of plasma parameters, but there has not been a systematic analysis into the sampling issues that arise. Also, there has not been a systematic study as to how to reconstruct these plasma parameters in an optimum sense as opposed to just using different forms of interpolation. The research presented here forms a framework that scientists and engineers can use to plan experiments with ESA ISR capabilities and to better analyze the resulting data. This framework attacks the problem of space-time sampling by ESA ISR systems from the point of view of signal processing, simulation and inverse theoretic image reconstruction. We first describe a physics based model of incoherent scatter from the ionospheric plasma, along with processing methods needed to create the plasma parameter measurements. Our approach leads to development of the space-time ambiguity function, forming a theoretical foundation of the forward model for ISR. This forward model is novel in that it takes into account the shape of the antenna beam and scanning method along with integration time to develop the proper statistics for a desired measurement precision. Once the forward model is developed, we present the simulation method behind the Simulator for ISR (SimISR). SimISR uses input plasma parameters over space and time and creates complex voltage samples in a form similar to that produced by a real ISR system. SimISR allows researchers to evaluate different experiment configurations in order to efficiently and accurately sample specific phenomena. We present example simulations using input conditions derived from a multi-fluid ionosphere model and reconstructions using standard interpolation techniques. Lastly, methods are presented to invert the space-time ambiguity function using techniques from image reconstruction literature. These methods are tested using SimISR to quantify accurate plasma parameter reconstruction over a simulated ionospheric region

    The Study of Ionospheric Response to Precipitation Using Sounding Rocket Observations

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    Understanding the role that the ionosphere plays in phenomena such as the development of auroral arcs and ion outflow is basic to the investigation of these processes and critical to the advancement of the broader study of magnetosphere-ionosphere coupling. Sounding rockets present an optimal platform for such studies, allowing low-cost access to altitudes that are difficult to reach by other means. Additionally, these measurements are key to validating current models and furthering understanding of the near-Earth space environment. This thesis highlights two particular rocket-borne instruments that measure electron populations in the ionosphere: the Electron Retarding Potential Analyzer (ERPA) and the Electron PLASma (EPLAS) instrument. It also presents analysis of the first in situ measurements of the ionospheric feedback instability (IFI) occurring within the AlfvƩn resonator in the vicinity of an auroral arc, a phenomenon that may play a role in the upward acceleration of ions and contribute to upflow. Another study highlights correlations between electron temperature and density and ion upflows. Simulation results, validated by rocket observations, show that increased ionospheric density inhibits the strength of the ambipolar field considered necessary for Type-2 ion outflow. Despite this however, the simulations show that increased densities result in increased net upflow fluxes. New radar data shows that sunlight effects might play an important role in controlling upflows, as photoionization can change ionospheric densities by as much as an order of magnitude seasonally
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