142 research outputs found
Three-dimensional reconstruction of CME-driven shock-streamer interaction from radio and EUV observations: a different take on the diagnostics of coronal magnetic fields
On 2014 October 30, a band-splitted type II radio burst associated with a
coronal mass ejection (CME) observed by the Atmospheric Imaging Assembly (AIA)
on board the Solar Dynamic Observatory (SDO) occurred over the southeast limb
of the Sun. The fast expansion in all directions of the plasma front acted as a
piston and drove a spherical fast shock ahead of it, whose outward progression
was traced by simultaneous images obtained with the Nan\c{c}ay Radioheliograph
(NRH). The geometry of the CME/shock event was recovered through 3D modeling,
given the absence of concomitant stereoscopic observations, and assuming that
the band-splitted type II burst was emitted at the intersection of the shock
surface with two adjacent low-Alfven speed coronal streamers. From the derived
spatiotemporal evolution of the standoff distance between shock and CME leading
edge, we were finally able to infer the magnetic field strength in the
inner corona. A simple radial profile of the form nicely fits our results, together with previous estimates, in the range
solar radii.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Differential rotation of the solar corona: A new data-adaptive multiwavelength approach
For the purpose of investigating the differential rotation of the solar
corona, we analyzed ultraviolet (UV) spectral line observations acquired on
both the east and west limbs at 1.7 by SOHO/UVCS during the solar
minimum preceding solar cycle 23. To obtain a reliable and statistically robust
picture of the rotational profile, we used a set of simultaneous 400-day long
spectral line intensities of five different spectral lines: O VI 1032 A, O VI
1037 A, Si XII 499 A, Si XII 521 A, and H I 1216 A, which are routinely
observed by UVCS. The data were analyzed by means of two different techniques:
the generalized Lomb-Scargle periodogram (GLS) and a multivariate data-adaptive
technique called multichannel singular spectrum analysis (MSSA). Among many
other positive outcomes, this latter method is unique in its ability to
recognize common oscillatory modes between the five time series observed at
both limbs. The latitudinal rotation profile obtained in this work emphasizes
that the low-latitude region of the UV corona (about from the
solar equator) exhibits differential rotation, while the higher-latitude
structures do rotate quasi-rigidly. The differential rotation rate of the solar
corona as evinced at low-latitudes is consistent with the rotational profile of
the near-surface convective zone of the Sun, suggesting that the rotation of
the corona at 1.7 is linked to intermediate-scale magnetic bipole
structures anchored near 0.99 . The quasi-rigid rotation rate found
at mid and high latitudes is instead attributed to the influence of large-scale
coronal structures linked to the rigidly rotating coronal holes. We further
suggest that the methodology presented in this paper could represent a
milestone for future investigations on differential rotation rates when dealing
with simultaneous multiwavelength data.Comment: A&A, in press (12 pages, 8 figures
Long-term heliomagnetic field variation based on cosmogenic 44Ti in meteorites
Reconstructions of the heliospheric magnetic field (HMF) in the past centuries are mainly based on the analysis of sunspot activity, geomagnetic data or on measurement of cosmogenic radioisotopes stored in terrestrial reservoirs (tree rings and ice cores). There are, however, significant discrepancies among the results obtained by various techniques using different proxies of solar magnetic activity. In this work, new results obtained from a unique approach based on the measurement of the cosmogenic 44Ti activity detected in meteorites are presented and compared with the most recent reconstructions of the near-Earth HMF strength. The very low level of 44Ti activity in several meteorites fallen in the last 250 years was determined by using gamma-ray spectrometers (HPGe+NaI) located in the underground laboratory of Monte dei Cappuccini (INAF-OATo) in Torino, Italy. This approach, specifically designed to overcome the main problems affecting other methods, yields a powerful independent tool to reconstruct the long-term evolution of the HMF through the last two and a half centuries
Measurement of UV light emission of the nighttime Earth by Mini-EUSO for space-based UHECR observations
The JEM-EUSO (Joint Experiment Missions for Extreme Universe Space
Observatory) program aims at the realization of the ultra-high energy cosmic
ray (UHECR) observation using wide field of view fluorescence detectors in
orbit. Ultra-violet (UV) light emission from the atmosphere such as airglow and
anthropogenic light on the Earth's surface are the main background for the
space-based UHECR observations. The Mini-EUSO mission has been operated on the
International Space Station (ISS) since 2019 which is the first space-based
experiment for the program. The Mini-EUSO instrument consists of a 25 cm
refractive optics and the photo-detector module with the 2304-pixel array of
the multi-anode photomultiplier tubes. On the nadir-looking window of the ISS,
the instrument is capable of continuously monitoring a ~300 km x 300 km area.
In the present work, we report the preliminary result of the measurement of the
UV light in the nighttime Earth using the Mini-EUSO data downlinked to the
ground. We mapped UV light distribution both locally and globally below the ISS
obit. Simulations were also made to characterize the instrument response to
diffuse background light. We discuss the impact of such light on space-based
UHECR observations and the Mini-EUSO science objectives.Comment: 11 pages, 5 figures, presented in 37th International Cosmic Ray
Conference (Berlin
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