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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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113 records · Page 7
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NASA NTRSDate not supplied

3-D Mapping of the Magnetic Field in the Active Region by the CLASP2.1 Rocket Experiment

Comprehensive magnetic field measurements of the solar atmosphere are crucial for understanding energy transport from the photosphere to the corona and its dissipation. However, observations of the magnetic field in the chromosphere and the upper atmospheric layers above the chromosphere, where the gas pressure dominance changes from (β>1) to magnetic pressure dominance (β<1), are overwhelmingly lacking. Therefore, we have focused on the polarization of ultraviolet radiation emitted from the upper chromosphere and transition layer and have conducted the Japan-U.S.-EU observation rocket experiment CLASP in order to demonstrate its usefulness. In CLASP2.1 conducted on October 8, 2021, scan observations were made at 16 locations in the active region, and Stokes (intensity $I$, linearly polarized $Q$, $U$, circularly polarized $V$) spectra in the 280~nm wavelength range were obtained. Looking at the observed region with AIA 171~{¥AA} on board the SDO satellite, we see that it consists of a region where a structure corresponding to the foot of a high-temperature loop called moss (moss) is seen, and a region where a low-temperature loop spreading from a sunspot is seen. We focused on the ionized magnesium $h$ & $k$ lines (emitted from the middle and uppermost of the chromosphere) and the manganese lines (emitted from the low part of the chromosphere), which show particularly prominent circular polarization, and derived the line-of-sight magnetic fields in the low, middle and uppermost parts of the chromosphere by applying weak field approximation to them. Furthermore, by combining the results with observations by the Solar Optical Telescope onboard the solar observing satellite HINODE, we obtained three-dimensional information on the magnetic field in the active region from the photosphere to the uppermost part of the chromosphere. In general, the magnetic field in the active region becomes weaker and smoother as one goes up in the sky, as reported by the CLASP2 observation (Ishikawa et al. 2021). However, in some regions, polarity reversal was observed only in the uppermost part of the chromosphere, and comparison with high spatial resolution transition layer and coronal images recorded by SDO/AIA revealed the connection between the magnetic field structure in the chromosphere and coronal loops.

R. Ishikawa↗
NASA NTRSDate not supplied

Determining The Nanoflare Heating Frequency of an X-Ray Bright Point Observed by MaGIXS

Nanoflares are thought to be one of the prime candidates that can heat the solar corona to its multi-million kelvin temperature. Individual nanoflares are difficult to detect with the present generation instruments, however their presence can be inferred by comparing simulated nanoflare-heated plasma emissions with the observed emission. Using HYDRAD coronal loop simulations, we model the emission from an X-ray bright point (XBP) observed by the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS), along with nearest-available observations from the Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO) and X-Ray Telescope (XRT) onboard Hinode observatory. The length and magnetic field strength of the coronal loops are derived from the linear-force-free extrapolation of the observed photospheric magnetogram by Helioseismic and Magnetic Imager (HMI) onboard SDO. Each loop is assumed to be heated by random nanoflares, whose magnitude and frequency are determined by the loop length and magnetic field strength. The simulation results are then compared and matched against the measured intensity from AIA, XRT, and MaGIXS. Our model results indicate the observed emissions from the XBP under study could be well matched by a distribution of nanoflares with average delay times 1500 s to 3000 s, which suggest that the heating is dominated by high-frequency events. Further, we demonstrate the high sensitivity of MaGIXS and XRT to diagnose the heating frequency using this method, while AIA passbands are found to be the least sensitive.

coronal heating↗
NASA NTRSDate not supplied

Heating of Coronal X-Ray Bright Points

The X-ray bright points (XBPs) are consistently present on the solar disk throughout time and space. Studying their contribution to overall coronal emissions and heating is intriguing. XBPs are prominently visible during the solar minimum, especially in the absence of bright active regions (ARs). In this discussion, we'll talk about the contribution of XBPs to coronal X-ray emissions during the cycle minimum. This analysis is based on spectroscopic observations by Solar X-ray Monitor (XSM) onboard Chandrayaan 2, alongside concurrent observations from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) and the X-Ray Telescope (XRT) on the Hinode observatory. Similar to ARs, XBPs consist of coronal loops visible in EUV/X-ray images. We investigated the possibility of nanoflares sustaining the heating of these XBP loops by comparing observed emissions with field-aligned hydrodynamic simulations. Our results suggest that nanoflares could indeed maintain the heating of the XBPs. Furthermore, we conducted a detailed study of a single XBP observed during the successful flight of the Marshall Grazing Incidence Spectrometer (MaGIXS). The unique observations made by MaGIXS, combined with 1D hydrodynamic simulations, enabled us to determine the nanoflare heating frequency for this particular XBP.

coronal heating↗
NASA NTRSDate not supplied

Examining the Early Onset of Selected Large Solar Eruptions During the 2024 May Superstorm Episode

Recent studies indicate that solar flares are preceded by a period of above-ambient coronal heating, along with an increase in coronal X-ray emissions (Hudson et al. 2021). Despite being extremely common, the cause of these enhanced preflare emissions has not yet been understood. Here, our team examines in detail several of the large eruptions during the May 2024 superstorm period that resulted in significant geomagnetic disturbances. We use data from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI), from the Hinode satellite, and from other sources. For several of the GOES X-class events on 8-10 May, we find that the preflare heating signature is more complex than in the case of flares occurring in less dynamic solar regions, but nonetheless distinct hot (>~ 10 MK) preflare coronal signatures are present. Understanding of the cause of such preflare activity prior to the onset of geoeffective solar eruptions is essential to developing an eventual robust prediction algorithm for warning of impending solar eruptions that threaten Space Weather consequences.

Alphonse C. Sterling↗