Search

Aims. We present the design and pre-launch performance of the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument prepared for inclusion in the ESA/NASA Solar Orbiter mission, currently scheduled for launch in 2020.Methods. The goal of this paper is to provide details of the SoloHI instrument concept, design, and pre-flight performance to give the potential user of the data a better understanding of how the observations are collected and the sources that contribute to the signal.Results. The paper discusses the science objectives, including the SoloHI-specific aspects, before presenting the design concepts, which include the optics, mechanical, thermal, electrical, and ground processing. Finally, a list of planned data products is also presented.Conclusions. The performance measurements of the various instrument parameters meet or exceed the requirements derived from the mission science objectives. SoloHI is poised to take its place as a vital contributor to the science success of the Solar Orbiter mission.

The Special Sensor Ultraviolet Limb Imager (SSULI) instruments are ultraviolet limb scanning sensors flying on the United States Air Force Defense Meteorological Satellite Program (DMSP) Block 5D-3 satellites. The SSULIs cover the 800-1700 A wavelength range at 18 A spectral resolution. This wavelength range contains spectral signatures of all the dominant neutral and ionized species in the thermosphere and F-region ionosphere. The instruments view ahead of the spacecraft and operate as limb imagers covering the 100-750 km altitude range at 10-15 km resolution with a 90-second scan cadence. We describe these instruments and summarize their calibration and on-orbit performance. Day-to-day variability of the nighttime ionosphere at low-latitudes and longer-term variability of the global mean exospheric temperature are highlighted.

We examine the different element abundances exhibited by the closed loop solar corona and the slow speed solar wind. Both are subject to the First Ionization Potential (FIP) Effect, the enhancement in coronal abundance of elements with FIP below 10 eV (e.g. Mg, Si, Fe) with respect to high FIP elements (e.g. O, Ne, Ar), but with subtle differences. Intermediate elements, S, P, and C, with FIP just above 10 eV, behave as high FIP elements in closed loops, but are fractionated more like low FIP elements in the solar wind. On the basis of FIP fractionation by the ponderomotive force in the chromosphere, we discuss fractionation scenarios where this difference might originate. Fractionation low in the chromosphere where hydrogen is neutral enhances the S, P and C abundances. This arises with nonresonant waves, which are ubiquitous in open field regions, and is also stronger with torsional Alfven waves, as opposed to shear (i.e. planar) waves. We discuss the bearing these findings have on models of interchange reconnection as the source of the slow speed solar wind. The outflowing solar wind must ultimately be a mixture of the plasma in the originally open and closed fields, and the proportions and degree of mixing should depend on details of the reconnection process. We also describe novel diagnostics in ultraviolet and extreme ultraviolet spectroscopy now available with these new insights, with the prospect of investigating slow speed solar wind origins and the contribution of interchange reconnection by remote sensing., 21 pages, accepted by ApJ

The techniques for stray light analysis, optimization and testing are described for two space telescopes that observe the solar corona: the Solar Orbiter Heliospheric Imager (SoloHI) that will fly on the ESA Solar Orbiter (SolO), and the Wide Field Imager for Solar Probe (WISPR) that will fly on the NASA Parker Solar Probe (PSP) mission. Imaging the solar corona is challenging, because the corona is six orders of magnitude dimmer than the Sun surface at the limb, and the coronal brightness continues to decrease to ten orders of magnitude below the Sun limb above 5° elongation from Sun center. The SoloHI and WISPR instruments are located behind their respective spacecraft heat shield. Each spacecraft heat shield does not block the instrument field of view above the solar limb, but will prevent direct sunlight entering the instrument aperture. To satisfy the instrument stray light attenuation required to observe the solar corona, an additional set of instrument baffles were designed and tested for successive diffraction of the heat shield diffracted light before entering the telescope entrance pupil. A semi empirical model of diffraction was used to design the baffles, and tests of the flight models were performed in flight like conditions with the aim of verifying the rejection of the design. Test data showed that the baffle systems behaved as expected. A second source of stray light is due to reflections of the sunlight off of the spacecraft structures and towards the instruments. This is especially the case for SoloHI where one of the spacecraft 8m tall solar arrays is located behind the telescope and reflects sunlight back onto the instrument baffles. The SoloHI baffle design had to be adjusted to mitigate that component, which was achieved by modifying their geometry and their optical coating. Laboratory tests of the flight model were performed. The test data were correlated with the predictions of a ray tracing model, which enabled the fine tuning of the model. Finally, end-to-end ray tracing was used to predict the stray light for the flight conditions.

The Tiny Ionospheric Photometer (TIP) is an ultraviolet nadir-viewing photometer that flew aboard the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC also known as FORMOSAT-3), which was launched on April 14, 2006. One TIP flew on each of the six COSMIC/FORMOSAT3 satellites; these compact instruments operated exclusively at nighttime and observed the O I 135.6 nm emission that is a signature of the decay of the F-region ionosphere and, as such, is a diagnostic of the ionospheric state. We describe the TIP instruments and their on-orbit operation. Additionally, some key science highlights of the mission are presented and discussed.

Recent advances in space-based heliospheric observations, laboratory experimentation, and plasma simulation codes are creating an exciting new cross-disciplinary opportunity for understanding fast energy release and transport mechanisms in heliophysics and laboratory plasma dynamics, which had not been previously accessible. This article provides an overview of some new observational, experimental, and computational assets, and discusses current and near-term activities towards exploitation of synergies involving those assets. This overview does not claim to be comprehensive, but instead covers mainly activities closely associated with the authors’ interests and reearch. Heliospheric observations reviewed include the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) on the National Aeronautics and Space Administration (NASA) Solar Terrestrial Relations Observatory (STEREO) mission, the first instrument to provide remote sensing imagery observations with spatial continuity extending from the Sun to the Earth, and the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Japanese Hinode spacecraft that is measuring spectroscopically physical parameters of the solar atmosphere towards obtaining plasma temperatures, densities, and mass motions. The Solar Dynamics Observatory (SDO) and the upcoming Solar Orbiter with the Heliospheric Imager (SoloHI) on-board will also be discussed. Laboratory plasma experiments surveyed include the line-tied magnetic reconnection experiments at University of Wisconsin (relevant to coronal heating magnetic flux tube observations and simulations), and a dynamo facility under construction there; the Space Plasma Simulation Chamber at the Naval Research Laboratory that currently produces plasmas scalable to ionospheric and magnetospheric conditions and in the future also will be suited to study the physics of the solar corona; the Versatile Toroidal Facility at the Massachusetts Institute of Technology that provides direct experimental observation of reconnection dynamics; and the Swarthmore Spheromak Experiment, which provides well-diagnosed data on three-dimensional (3D) null-point magnetic reconnection that is also applicable to solar active regions embedded in pre-existing coronal fields. New computer capabilities highlighted include: HYPERION, a fully compressible 3D magnetohydrodynamics (MHD) code with radiation transport and thermal conduction; ORBIT-RF, a 4D Monte-Carlo code for the study of wave interactions with fast ions embedded in background MHD plasmas; the 3D implicit multi-fluid MHD spectral element code, HiFi; and, the 3D Hall MHD code VooDoo. Research synergies for these new tools are primarily in the areas of magnetic reconnection, plasma charged particle acceleration, plasma wave propagation and turbulence in a diverging magnetic field, plasma atomic processes, and magnetic dynamo behavior., United States. Office of Naval Research, Naval Research Laboratory (U.S.)

We evaluate the potential of imaging for the first time, the near-earth space plasma environment seamlessly from the ionosphere through the magnetosphere by remotely sensing Thomson scattering of solar visible light by geospace electrons. Using state of the art first principles models of the magnetosphere/ionosphere system, we show that the column emission rates are weak, generally less than 10 Rayleighs, but detectable with currently available instrument technology recently deployed for heliospheric imaging. We demonstrate that distinct features such as the bow shock, magnetosheath and magnetopause are detectable in synthetic images simulated using modified solar coronagraphs and white light imagers, providing that the large background signals are properly quantified. The availability of global geospace images of the electron concentration will enable major advances in our understanding of how Earth's near-space environment responds as a coupled system to changing solar forcings. Such images are expected to play a central role in space weather assessment and forecasting, from which significant capabilities will accrue, much as the imaging of the Earth's surface and lower atmosphere has advanced understanding and forecasting of tropospheric weather.

The SoloHI instrument for the ESA/NASA Solar Orbiter mission will track density fluctuations in the inner heliosphere, by observing visible sunlight scattered by electrons in the solar wind. Fluctuations are associated with dynamic events such as coronal mass ejections, but also with the “quiescent” solar wind. SoloHI will provide the crucial link between the low corona observations from the Solar Orbiter instruments and the in-situ measurements on Solar Orbiter and the Solar Probe Plus missions. The instrument is a visible-light telescope, based on the SECCHI/Heliospheric Imager (HI) currently flying on the STEREO mission. In this concept, a series of baffles reduce the scattered light from the solar disk and reflections from the spacecraft to levels below the scene brightness, typically by a factor of 10 12 . The fluctuations are imposed against a much brighter signal produced by light scattered by dust particles (the zodiacal light/F-corona). Multiple images are obtained over a period of several minutes and are summed on-board to increase the signal-to-noise ratio and to reduce the telemetry load. SoloHI is a single telescope with a 40⁰ field of view beginning at 5⁰ from the Sun center. Through a series of Venus gravity assists, the minimum perihelia for Solar Orbiter will be reduced to about 60 Rsun (0.28 AU), and the inclination of the orbital plane will be increased to a maximum of 35⁰ after the 7 year mission. The CMOS/APS detector is a mosaic of four 2048 x 1920 pixel arrays, each 2-side buttable with 11 µm pixels.

The Tiny Ionospheric Photometer (TIP) sensors aboard the Constellation Observing System for Meterology, Ionosphere and Climate (COSMIC, also called FORMOSAT-3) spacecraft comprise a suite of six nadir-viewing ultraviolet photometers for characterizing the Earth's nightside ionosphere. The TIP instruments complement the ionospheric capabilities of the GPS occultation experiment (GOX) by characterizing horizontal ionospheric density gradients. These photometers target OI 135.6 nm emission produced by ionospheric O + +e recombination and measure ionospheric structure with a spatial resolution of 10-30 km. The TIP instrument design had to solve several design challenges in order to achieve its intended science and mission requirements within operational constraints imposed by the spacecraft and budget constraints. The photometers have a simple design which excludes OI 130.4 nm emission and achieves a sensitivity of approximately 500 counts/s/Rayleigh at 135.6nm. The satellites initially orbited in the same plane at 500 km, then over the course of 13 months they were individually raised to their final 800 km orbits in six planes separated by 24° in right ascension. These maneuvers provided opportunities for cross-calibration among the sensors, for multipass observations as the satellites orbit together early in the mission, and for observations at different spatial resolutions as the spacecraft operate at different altitudes. In this paper we evaluate on-orbit sensor performance of the TIP sensors, and discuss improvements for follow-on missions.

[1] The timescales and phases of auroral substorm activity are quantified in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) observations. With this approach we are able to determine substorm phase self consistently from the UVI optical measurements without needing any ancillary metrics for auroral activity. This technique also allows us to combine a quantitative measurement of substorm timescales with the qualitative description of auroral morphology during each event. We show how the characteristics of substorms vary with IMF BZ orientation and season for several hundred substorm events. Substorm intensity, as measured by the rate of energy deposition by electron precipitation, exhibits greater variation with IMF BZ orientation than with season. The timescale of substorm expansion shows comparable variation with both IMF BZ orientation and season. On the other hand, substorm recovery times vary more strongly with season than with IMF BZ direction. The recovery time for substorm activity is well ordered by whether or not the nightside auroral region is sunlit: substorms occurring in the winter and equinox periods have similar recovery timescales which are both roughly a factor of two longer than that for summer when the auroral oval is sunlit. However, IMF BZ orientation is shown to have a strong modulating effect on both substorm expansion and recovery timescales during the summer. The winter-summer asymmetries in the aurora described by previous studies are more completely explained by the seasonal variations of substorm recovery timescales characterized in this work. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.

[1] We present new FUV observations of Doppler-shifted Lyman-α emissions from proton aurora obtained from the High Resolution Ionospheric and Thermospheric Spectrograph (HITS) aboard the Advanced Research and Global Observation Satellite (ARGOS). The HITS instrument observes the Doppler-shifted H Lyman-α emissions from proton precipitation with 1.5 A resolution. The high spectral resolution of these measurements allows the auroral Lyman-α emissions to be separated from the intense geocoronal background. The measured proton aurora Doppler spectra are modeled using a Monte Carlo simulation of proton flux transport. The forward modeling performed with this code allows us to infer the characteristic energies of the incident protons from the measured Lyman-α Doppler spectra. The inferred characteristics of dayside versus nightside proton precipitation are compared and used to identify the magnetospheric regions from which the particles likely originated.

The Volumetric Imaging System for the Ionosphere (VISION) is designed to use limb and nadir images to reconstruct the three-dimensional distribution of electrons over a 1000 km wide by 500 km high slab beneath the satellite with 10 km x 10 km x 10 km voxels. The primary goal of the VISION is to map and monitor global and mesoscale (> 10 km) electron density structures, such as the Appleton anomalies and field-aligned irregularity structures. The VISION consists of three UV limb imagers, two UV nadir imagers, a dual frequency Global Positioning System (GPS) receiver, and a coherently emitting three frequency radio beacon. The limb imagers will observe the O II 83.4 nm line (daytime electron density), O I 135.6 nm line (nighttime electron density and daytime O density), and the N2 Lyman-Birge-Hopfield (LBH) bands near 143.0 nm (daytime N2 density). The nadir imagers will observe the O I 135.6 nm line (nighttime electron density and daytime O density) and the N2 LBH bands near 143.0 nm (daytime N2 density). The GPS receiver will monitor the total electron content between the satellite containing the VISION and the GPS constellation. The three frequency radio beacon will be used with ground-based receiver chains to perform computerized radio tomography below the satellite containing the VISION. The measurements made using the two radio frequency instruments will be used to validate the VISION UV measurements.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.