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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

The Coupling of an EUV Coronal Wave and Ion Acceleration in a Fermi-LAT Behind-the-Limb Solar Flare

We present the Fermi-LAT observations of the behind-the-limb (BTL) flare of 2021 July 17 and the joint detection of this flare by STIX on board the Solar Orbiter. The separation between Earth and the Solar Orbiter was $99^{\circ}_{\centerdot}2$ at 05:00 UT, allowing STIX to have a front view of the flare. The location of the flare was S20E140 in Stonyhurst heliographic coordinates, making this the most distant behind-the-limb flare ever detected in >100 MeV gamma-rays. The LAT detection lasted for ~16 minutes, the peak flux was 3.6 ± 0.8 (10 –5 ) ph cm –2 s –1 with a significance >15σ. A coronal wave was observed from both STEREO-A and SDO in extreme ultraviolet (EUV), with an onset on the visible disk in coincidence with the LAT onset. A complex type II radio burst was observed by GLOSS also in coincidence with the onset of the LAT emission, indicating the presence of a shock wave. We discuss the relation between the time derivative of the EUV wave intensity profile at 193 Å as observed by STEREO-A and the LAT flux to show that the appearance of the coronal wave at the visible disk and the acceleration of protons as traced by the observed >100 MeV gamma-ray emission are coupled. We also report how this coupling is present in the data from three other BTL flares detected by Fermi-LAT, suggesting that the protons driving the gamma-ray emission of BTL solar flares and the coronal wave share a common origin.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Anisotropic Turbulent Flows Observed in Above-the-loop-top Regions during Solar Flares

Abstract Solar flare above-the-loop-top (ALT) regions are vital for understanding solar eruptions and fundamental processes in plasma physics. Recent advances in three-dimensional (3D) magnetohydrodynamic (MHD) simulations have revealed unprecedented details on turbulent flows and MHD instabilities in flare ALT regions. Here, for the first time, we examine the observable anisotropic properties of turbulent flows in ALT by applying a flow-tracking algorithm on narrow-band extreme-ultraviolet images that are observed from the face-on viewing perspective. First, the results quantitatively confirm the previous observation that vertical motions dominate and that the anisotropic flows are widely distributed in the entire ALT region with the contribution from both upflows and downflows. Second, the anisotropy shows height-dependent features, with the most substantial anisotropy appearing at a certain middle height in ALT, which agrees well with the MHD modeling results where turbulent flows are caused by Rayleigh–Taylor-type instabilities in the ALT region. Finally, our finding suggests that supra-arcade downflows (SADs), the most prominently visible dynamical structures in ALT regions, are only one aspect of turbulent flows. Among these turbulent flows, we also report the antisunward-moving underdense flows that might develop due to MHD instabilities, as suggested by previous 3D flare models. Our results indicate that the entire flare fan displays group behavior of turbulent flows where the observational bright spikes and relatively dark SADs exhibit similar anisotropic characteristics.

Xie, Xiaoyan (ORCID:0009000705827807)↗
NASA NTRS1966

Thin carbon film serves as UV bandpass filter

Thin carbon film deposited on a 70 percent transparent screen provides a filter for narrow-band detectors in the extreme ultraviolet. The filter also suppresses scattered light and light of unwanted orders in vacuum spectrographs.

Source record↗
NASA NTRS1972

Glancing incidence telescopes for space astronomy

Design optimization is reported for glancing telescopes of increased collecting areas. Considered are nested geometries for X-ray and extreme ultraviolet telescopes, each of which generates only one singular principal surface. In the case of the X-ray telescope, the field curvature of the outer telescope serves as a standard and the focus of each of the inner telescopes is made coplanar by a slight descrease in the collecting area of each of the inner telescopes. In the case of the EUV telescope, a slight change in the maximum slope angle of the inner telescope makes the field curvatures coincide. Five concentric X-ray telescopes form a collecting area of approximately 900 sq cm, and a nested EUV telescope consisting of two concentric telescopes produces a collecting area of about 45 sq cm.

Mangus, J. D.↗
NASA NTRS1972

Structure and variations of the heterosphere

Atmospheric composition is kept almost homogeneous to a height of approximately 90 km (the homosphere) by mixing; above 100 km (the heterosphere), diffusive separation of the atmospheric constituents occurs. The heterosphere is dominated by two energy sources: solar extreme ultraviolet radiation and the solar wind. Many large variations are observed in this region and they can all be related, directly or indirectly, to variations in the intrinsic intensity of these two sources and to variations in the location of the sources relative to the observer. Atmospheric models can be successfully constructed in which the temperature and density variations are empirically related to solar and geomagnetic parameters. Some of the more recent findings concerning the structure and variations in the heterosphere are presented.

Jacchia, L. G.↗
NASA NTRS1972

Some aspects of atmosphere waves in realistic atmospheres

Atmospheric tides travelling from the mesosphere into the upper thermosphere are discussed. As a preliminary, an elementary discussion of internal gravity waves is presented. Tides excited by the absorption of extreme ultraviolet radiation within the thermosphere are described also. Theory suggests a much larger semidiurnal oscillation in the thermosphere than is observed.

Lindzen, R. S.↗
NASA NTRS1972

Photoionization measurement study

An analysis was conducted of a gas window photoionization device for studying cosmic X-rays in the region 20 eV to 1 keV. The detecting element is an argon proportional counter whose window is a two-dimensional supersonic gas jet. Spectroscopic features of the incoming radiation can be determined by the choice of gas forming the jet (as well by the fluid dynamic parameters of the flow). The choice of gas can be made from pure substances and/or compounds with Z between 1 and 10. The counter walls can be prepared for selective analysis of the extreme ultraviolet radiation.

Sandri, G.↗
NASA NTRS1972

Zenith angle dependence of the geocoronal Lyman-alpha glow.

Review of the observations made on the zenith angle dependence and intensity of the geocoronal hydrogen Lyman-alpha glow by means of one of four extreme ultraviolet photometers flown to an altitude of 264 km on a Nike Tomahawk rocket launched from Thumba, India, in March 1970. The results obtained are compared with Meier and Mange's (1970) theoretical predictions. The possible causes for the discrepancies found are discussed.

Paresce, F.↗