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NASA NTRS2014

Areas of Polar Coronal Holes from 1996 Through 2010

Polar coronal holes (PCHs) trace the magnetic variability of the Sun throughout the solar cycle. Their size and evolution have been studied as proxies for the global magnetic field. We present measurements of the PCH areas from 1996 through 2010, derived from an updated perimeter-tracing method and two synoptic-map methods. The perimeter tracing method detects PCH boundaries along the solar limb, using full-disk images from the SOlar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT). One synoptic-map method uses the line-of-sight magnetic field from the SOHO/Michelson Doppler Imager (MDI) to determine the unipolarity boundaries near the poles. The other method applies thresholding techniques to synoptic maps created from EUV image data from EIT. The results from all three methods suggest that the solar maxima and minima of the two hemispheres are out of phase. The maximum PCH area, averaged over the methods in each hemisphere, is approximately 6 % during both solar minima spanned by the data (between Solar Cycles 22/23 and 23/24). The northern PCH area began a declining trend in 2010, suggesting a downturn toward the maximum of Solar Cycle 24 in that hemisphere, while the southern hole remained large throughout 2010.

Corona↗

NASA NTRS1991

Improved visualization of flow field measurements

A capability is proposed that makes it feasible to apply to measured flow field data the visualization tools developed to display numerical solutions for computational fluid dynamic problems. The measurement monitor surface (MMS) methodology was used for the analysis of flow field measurements within a low-aspect-ratio transonic axial-flow fan rotor acquired with two-dimensional laser anemometry. It is shown that the MMS method may be utilized to generate input for the multidimensional processing and analytical tools developed for numerical flow field simulation data. Thus an experimenter utilizing an interactive graphics program could illustrate scalar quantities such as Mach number by profiles, contour lines, carpet plots, and surfaces employing various color intensities. Also, flow directionality can be shown by the display of vector fields and particle traces.

Miles, Jeffrey Hilton↗

NASA NTRS1991

Source location determination of Uranian kilometric radiation from ray tracing and emission lobe modelling

We use an analytical fit to an emission lobe profile together with three-dimensional ray tracing to model the broad-banded smooth Uranian kilometric radiation (UKR). We assume the radiation is gyroemission from sources along magnetic field lines. Using an iterative technique that modifies the lobe function and source region, the results are compared to observations at a frequency of 481 kHz. The best-fit calculations are compared to previously published models and to recent ultraviolet (UV) observations.

Menietti, J. D.↗

NASA NTRS2007

Hinode Observations of the Onset Stage of a Solar Filament Eruption

We use Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT) filtergraph (FG) Stokes-V magnetogram observations, to study the early onset of a solar eruption that includes an erupting filament that we observe in TRACE EUV images. The filament undergoes a slow rise for at least 20 min prior to its fast eruption and strong soft X-ray flaring; such slow rises have been previously reported, and the new Hinode data elucidate the physical processes occurring during this period. XRT images show that during the slow-rise phase, a soft X-ray (SXR) sigmoid forms from apparent reconnection low in the sheared core field traced by the filament, and there is a low-level intensity peak in both EUV and SXRs during the slow rise. MDI and SOT FG/V magnetograms show that the pre-eruption filament is along a neutral line between opposing-polarity enhanced network cells, and the SOT magnetograms show that these opposing fields are flowing together and canceling for at least six hours prior to eruption. From the MDI data we measure the canceling network fields to be approx. 40 G, and we estimate that approx. 10(exp 19) Mx of flux canceled during the five hours prior to eruption; this is only approx. 5% of the total flux spanned by the eruption and flare, but apparently its tether-cutting cancellation was enough to destabilize the sigmoid field holding the filament and resulted in that field's eruption.

Sterling, Alphonse C.↗

NASA NTRS2007

Hinode Observations of the Onset Stage of a Solar Filament Eruption

Sterling, Alphonse C.↗

NASA NTRS2010

Triggering of Solar Magnetic Eruptions on Various Size Scales Alphonse Sterling

A solar eruption that produces a coronal mass ejection (CME) together with a flare is driven by the eruption of a closed-loop magnetic arcade that has a sheared-field core. Before eruption, the sheared core envelops a polarity inversion line along which cool filament material may reside. The sheared-core arcade erupts when there is a breakdown in the balance between the confining downward-directed magnetic tension of the overall arcade field and the upward-directed force of the pent-up magnetic pressure of the sheared field in the core of the arcade. What triggers the breakdown in this balance in favor of the upward-directed force is still an unsettled question. We consider several eruption examples, using imaging data from the SoHO, TRACE and Hinode satellites, and other sources, along with information about the magnetic field of the erupting regions. In several cases, observations of large-scale eruptions, where the magnetic neutral line spans few x 10,000 km, are consistent with magnetic flux cancellation being the trigger to the eruption's onset, even though the amount of flux canceled is only ~few percent of the total magnetic flux of the erupting region. In several other cases, an initial compact (small size-scale) eruption occurs embedded inside of a larger closed magnetic loop system, so that the smaller eruption destabilizes and causes the eruption of the much larger system. In this way, small-scale eruptive events can result in eruption of much larger-scale systems.

Sterling, A.C.↗

DOE OSTI2021

Constraining the baryon abundance with the kinematic Sunyaev-Zel’dovich effect: Projected-field detection using Planck , WMAP , and unWISE

The kinematic Sunyaev-Zel'dovich (kSZ) effect -- the Doppler boosting of cosmic microwave background (CMB) photons scattering off free electrons with non-zero line-of-sight velocity -- is an excellent probe of the distribution of baryons in the Universe. In this paper, we measure the kSZ effect due to ionized gas traced by infrared-selected galaxies from the \emph{unWISE} catalog. We employ the "projected-field" kSZ estimator, which does not require spectroscopic galaxy redshifts. To suppress non-kSZ foreground signals associated with the galaxies (e.g., dust emission and thermal SZ), this estimator requires cleaned CMB maps, which we obtain from \emph{Planck} and \emph{WMAP} data. Using a new "asymmetric" estimator that combines different foreground-cleaned CMB maps to maximize the signal-to-noise, we measure the kSZ$^2$-galaxy cross-power spectrum for three subsamples of the \emph{unWISE} galaxy catalog, which peak at mean redshifts $z \approx$ 0.6, 1.1, and 1.5, have average halo mass $\sim 1$-$5\times 10^{13}$ $h^{-1} M_{\odot}$, and in total contain over 500 million galaxies. After marginalizing over CMB lensing contributions, we measure the amplitude of the kSZ signal $A_{\rm kSZ^2} = 0.42 \pm 0.31$, $5.02 \pm 1.01$, and $8.23 \pm 3.23$, for the three subsamples, where $A_{\rm kSZ^2} = 1$ corresponds to our fiducial model. The combined kSZ detection S/N $>$ 5. We discuss possible explanations for the excess kSZ signal associated with the $z \approx 1.1$ sample, and show that foreground contamination in the CMB maps is very unlikely to be the cause. Our measurements illustrate clearly that no baryons are missing on large scales at low redshifts.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Absolute throughput calibration of multiple spherical crystals for the Orion High-REsolution X-ray spectrometer (OHREX)

We present absolute throughput analysis of several crystals for the Orion High-REsolution X-ray (OHREX) imaging crystal spectrometer using ray tracing and experimental measurements. The OHREX spectrometer is a high-resolution x-ray spectrometer designed to measure spectral line shapes at the Orion laser facility. The spectrometer is fielded with up to two spherical crystals simultaneously covering two independent spectral ranges. Each crystal has a nominal radius of curvature of R = 67.2 cm and is fielded at a nominal Bragg angle of 51.3°. To cover different bands of interest, several different crystals are available, including Ge (111), KAP, and several cuts of quartz, whose resolving power λ/Δλ exceeds 10 000. The calibrated response of the available crystals has previously been reported from measurements at the EBIT-I electron beam ion trap at Lawrence Livermore National Laboratory. Here, we model the absolute throughput of each crystal using ray tracing and verify the results using experimental data for the quartz $(10\bar{1}1)$ crystal.

47 OTHER INSTRUMENTATION↗

NASA NTRS2021

Absolute throughput calibration of multiple spherical crystals for the Orion High-REsolution X-ray spectrometer (OHREX)

M. J. MacDonald↗

NASA NTRS1980

Ray tracing of Jovian kilometric radiation

Results of computer ray tracing of Jovian kilometric radiation from 56.2 kHz to 1 MHz in a model Jovian magnetosphere with an Io torus are presented. Ray tracing calculations indicate that the Io torus presents a propagation barrier to the radiation and that the Jovian kilometric radiation must be generated in the L-O mode from a source near Jupiter on field lines passing through the Io torus. One effect of the Io torus is to refract the rays away from the magnetic equator forming a shadow zone at radial distances beyond the torus. In general, at radial distances greater than 10 Jovian radii, as the wave frequency increases (greater than 200 kHz) so does the magnetic latitude of the shadow zone. These and other features of the ray tracing calculations are in good qualitative agreement with the observations from the plasma wave receiver and planetary radio astronomy experiment on board both Voyagers 1 and 2.

Green, J. L.↗

NASA NTRS1990

Source of O mode radio emissions from the dayside of Uranus

During the inbound trajectory toward Uranus, the Planetary Radio Astronomy instrument on Voyager 2 observed narrow-band smooth (n-smooth) emission at frequencies centered near 60 kHz and O-mode emission (the dayside source) in a frequency range narrowly confined around 160 kHz. Assuming empirical models of the plasma density for the dayside magnetosphere of Uranus, and using cold plasma theory together with observational constraints, ray-tracing calculations are performed to determine the source location of the O-mode emission. The dayside source appears to originate along magnetic field lines with a footprint near the north magnetic pole. Sources of nightside high-frequency broadband smooth (b-smooth) emission observed by Voyager after encounter are believed to exist near the conjugate footprint of these same field lines. This would indicate that the particle population supplying the free energy source has energies at least as high as a few keV.

Menietti, J. D.↗

NASA NTRS2013

NIR Imaging Spectroscopy of the Inner Few Arcseconds of NGC 4151 with OSIRIS at Keck

We present H- and K-band data from the inner arcsecond of the Seyfert 1.5 galaxy NGC 4151 obtained with the adaptive optics assisted near-infrared imaging field spectrograph OSIRIS at the Keck Observatory. The angular resolution is about a few parsecs on-site and thus competes easily with optical images taken previously with the Hubble Space Telescope. We present the morphology and dynamics of most species detected but focus on the morphology and dynamics of the narrow line region (as traced by emission of [FeII]λ1.644 μm), the interplay between plasma ejected from the nucleus (as traced by 21 cm continuum radio data) and hot H2 gas and characterize the detected nuclear HeIλ2.058 μm absorption feature as a narrow absorption line (NAL) phenomenon. Emission from the narrow line region (NLR) as traced by [FeII] reveals a biconical morphology and we compare the measured dynamics in the [FeII] emission line with models proposing acceleration of gas in the NLR and simple ejection of gas into the NLR. In the inner 2.5 arcseconds the acceleration model reveals a better fit to our data than the ejection model.We also see evidence that the jet very locally enhances emission in [FeII] at certain positions in our field-of-view such that we were able to distinct the kinematics of these clouds from clouds generally accelerated in the NLR. Further, the radio jet is aligned with the bicone surface rather than the bicone axis such that we assume that the jet is not the dominant mechanism responsible for driving the kinematics of clouds in the NLR. The hot H2 gas is thermal with a temperature of about 1700 K. We observe a remarkable correlation between individual H2 clouds at systemic velocity with the 21 cm continuum radio jet. We propose that the radio jet is at least partially embedded in the galactic disk of NGC 4151 such that deviations from a linear radio structure are invoked by interactions of jet plasma with H2 clouds that are moving into the path of the jet because of rotation of the galactic disk of NGC 4151. Additionally, we observe a correlation of the jet as traced by the radio data, with gas as traced in Brγ and H2, at velocities between systemic and +/- 200 km/s at several locations along the path of the jet. The HeIλ2.058 μm line in NGC 4151 appears in emission with a blueshifted absorption component from an outflow. The emission (absorption) component has a velocity offset of 10 km/s (-280 km/s) with a Gaussian (Lorentzian) full-width (half-width) at half maximum of 160 km/s (440 km/s). The absorption component remains spatially unresolved and its kinematic measures differ from that of UV resonance absorption lines. From the amount of absorption we derive a lower limit of the HeI 2S column density of 1 × 10(exp 14) cm−2 with a covering factor along the line-of-sight of C(sub los) approximately equal to 0.1.

K-band data↗

NASA NTRS2007

Hinode Observations of the Onset Stage of a Solar Filament Eruption

We used Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT) filtergraph (FG) Stokes-V magnetogram observations, to study the early onset of a solar eruption that includes an erupting filament that we observe in TRACE EUV images. The filament undergoes a slow rise for at least 20min prior to its fast eruption and strong soft X-ray (SXR) flaring; such slow rises have been previously reported, and the new Hinode data elucidate the physical processes occurring during this period. XRT images show that during the slow-rise phase, an SXR sigmoid forms from apparent reconnection low in the sheared core field traced by the filament, and there is a low-level intensity peak in both EUV and SXRs during the slow rise. MDI and SOT FG Stokes-V magnetograms show that the pre-emption filament is along a neutral line between opposing-polarity enhanced network cells, and the SOT magnetograms show that these opposing fields are flowing together and canceling for at least six hours prior to eruption. From the MDI data we measured the canceling network fields to be approx. 40 G, and we estimated that approx. 10(exp 19)Mx of flux canceled during the five hours prior to eruption; this is only approx.5% of the total flux spanned by the eruption and flare, but apparently its tether-cutting cancellation was enough to destabilize the sigmoid field holding the filament and resulted in that field's eruption.

Sterling, Alphonse C.↗

NASA NTRS1999

"Driverless" Shocks in the Interplanetary Medium

Many interplanetary shocks have been detected without an obvious driver behind them. These shocks have been thought to be either blast waves from solar flares or shocks due to sudden increase in solar wind speed caused by interactions between large scale open and closed field lines of the Sun. We investigated this problem using a set of interplanetary shock detected {\it in situ} by the Wind space craft and tracing their solar origins using low frequency radio data obtained by the Wind/WAVES experiment. For each of these "driverless shocks" we could find a unique coronal mass ejections (CME) event observed by the SOHO (Solar and Heliospheric Observatory) coronagraphs. We also found that these CMEs were ejected at large angles from the Sun-Earth line. It appears that the "driverless shocks" are actually driver shocks, but the drivers were not intercepted by the spacecraft. We conclude that the interplanetary shocks are much more extended than the driving CMEs.

Gopalswamy, N.↗

DOE OSTI2020

Detecting Magnetic Fields in Exoplanets with Spectropolarimetry of the Helium Line at 1083 nm

The magnetic fields of the solar system’s planets provide valuable insights into their interiors and can have dramatic consequences for the evolution of their atmospheres and interaction with the solar wind. However, we have little direct knowledge of magnetic fields in exoplanets. Here we present a method for detecting magnetic fields in the atmospheres of close-in exoplanets based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. This methodology has been successfully applied for exploring magnetic fields in solar coronal filaments. Strong absorption signatures (transit depths on the order of a few percent) in the 1083 nm line have recently been observed for several close-in exoplanets. We show that in the conditions in these escaping atmospheres, metastable helium atoms should be optically pumped by the starlight and, for field strengths more than a few × 10 -4 G, should align with the magnetic field. This results in linearly polarized absorption at 1083 nm that traces the field direction (the Hanle effect), which we explore by both analytic computation and the HAZEL numerical code. The linear polarization $\sqrt{{Q}^{2}+{U}^{2}}/I$ ranges from ~10 -3 in optimistic cases down to a few × 10 -5 for particularly unfavorable cases, with very weak dependence on field strength. The line-of-sight component of the field results in a slight circular polarization (the Zeeman effect), also reaching $V/I\sim \mathrm{few}\times {10}^{-5}({B}_{\parallel }/10\,{\rm{G}})$. We discuss the detectability of these signals with current (SPIRou) and future (Extremely Large Telescope) high-resolution infrared spectropolarimeters, and we briefly comment on possible sources of astrophysical contamination.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1993

N-bursty emission from Uranus: A cyclotron maser source?

Ray tracing studies of RX-mode emission from the north polar regions of Uranus indicate that the n-bursty radio emission may have a source along field lines with footprints near the northern magnetic pole (perhaps in the cusp), but not necessarily associated with regions of strong UV emission. This is in contrast with similar studies for the Uranus nightside smooth radio emission, which are believed to be due to the cyclotron maser instability. Source regions can be found for both hollow and filled emission cones and for frequencies well above the local gyrofreuquency implying that mechanisms other than the cyclotron maser mechanism may be operating.

Curran, D. B.↗

NASA NTRS2016

Flux Cancellation Leading to CME Filament Eruptions

Solar filaments are strands of relatively cool, dense plasma magnetically suspended in the lower density hotter solar corona. They trace magnetic polarity inversion lines (PILs) in the photosphere below, and are supported against gravity at heights of up to approx.100 Mm above the chromosphere by the magnetic field in and around them. This field erupts when it is rendered unstable, often by magnetic flux cancellation or emergence at or near the PIL. We have studied the evolution of photospheric magnetic flux leading to ten observed filament eruptions. Specifically, we look for gradual magnetic changes in the neighborhood of the PIL prior to and during eruption. We use Extreme Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA), and magnetograms from the Helioseismic and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO), to study filament eruptions and their photospheric magnetic fields. We examine whether flux cancellation or/and emergence leads to filament eruptions. We find that continuous flux cancellation was present at the PIL for many hours prior to each eruption. We present two CME-producing eruptions in detail and find the following: (a) the pre-eruption filament-holding core field is highly sheared and appears in the shape of a sigmoid above the PIL; (b) at the start of the eruption the opposite arms of the sigmoid reconnect in the middle above the site of (tether-cutting) flux cancellation at the PIL; (c) the filaments first show a slow-rise, followed by a fast-rise as they erupt. We conclude that these two filament eruptions result from flux cancellation in the middle of the sheared field, and thereafter evolve in agreement with the standard model for a CME/flare filament eruption from a closed bipolar magnetic field [flux cancellation (van Ballegooijen and Martens 1989 and Moore and Roumelrotis 1992) and runaway tether-cutting (Moore et. al 2001)].

filament↗

NASA NTRS2012

Evidence for Two Separate but Interlaced Components of the Chromospheric Magnetic Field

Chromospheric fibrils are generally thought to trace out horizontal magnetic fields that fan out from flux concentrations in the photosphere. A high-resolution (0.2") image taken in the core of the Ca IJ854.2 nm line shows the dark fibrils within an active region remnant as fine, loop-like features that are aligned parallel to each other and have lengths on the order of a supergranular diameter (approx.30 Mm). Comparison with a line-of-sight magnetogram confirms that the fibrils are centered above intranetwork areas, with one end rooted just inside the neighboring plage or strong unipolar network but the other endpoint less clearly defined. Focusing on a particular arcade-like structure lying entirely on one side of a filament channel (large-scale polarity inversion), we find that the total amount of positive-polarity flux underlying this "fibril arcade' is 50 times greater than the total amount of negative-polarity flux. Thus, if the fibrils represent closed loops, they must consist of very weak fields (in terms of flux density), which are interpenetrated by a more vertical field that contains most of the flux. This surprising result suggests that the fibrils in unipolar regions connect the network to the nearby intranetwork flux, while the bulk of the network flux is diverted upward into the corona and connects to remote regions of the opposite polarity. We conclude that the chromospheric field near the edge of the network has an interlaced structure resembling that in sunspot penumbrae, with the fibrils representing the low-lying horizontal flux that remains trapped within the highly nonpotential chromospheric layer.

Muglach, K.↗