Results 41 to 50 of about 1,264 (196)

Observations of the upper solar chromosphere with SUMER

, 2003
The structure and dynamics of the solar chromosphere are still matters of debate. The chromospheric network reflecting the supergranulation of the outer convection zone of the Sun is a prominent feature of the lower solar atmosphere that extends into the
Kalkofen, W., K. Wilhelm, Wilhelm, K., W. Kalkofen   +3 more
core   +1 more source

Multiwavelength High-resolution Observations of Chromospheric Swirls in the Quiet Sun [PDF]

The Astrophysical Journal, 2019
Abstract We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca ii ...
Juie Shetye, Erwin Verwichte, Marco Stangalini, Philip G. Judge, J. G. Doyle, Tony Arber, Eamon Scullion, Sven Wedemeyer   +7 more
openaire   +3 more sources

Periodic Density Structures Observed in Ulysses Data: First Results

Journal of Geophysical Research: Space Physics, Volume 131, Issue 3, March 2026.
Abstract Periodic density structures (PDSs) are advecting quasi‐periodic (periodicities between several minutes and several hours) density enhancements observed in the solar wind and corona. There is strong evidence that PDSs are formed at the Sun.
Brent M. Randol, Nicholeen Viall, Larry Kepko, Simone Di Matteo   +3 more
wiley   +1 more source

The multi-thermal chromosphere: Inversions of ALMA and IRIS data

, 2020
Context. Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular typically feature broader and brighter chromospheric lines, which suggests that they ...
De Pontieu, Bart Walter, Wedemeyer, S., G. Chintzoglou, J. Leenaarts, J. de la Cruz Rodríguez, da Silva Santos, João Manuel, de la Cruz Rodriguez, Jaime, M. Szydlarski, De Pontieu, B., Chintzoglou, G., Leenaarts, Jorrit, de la Cruz Rodriguez, Jaime,, Szydlarski, M., da Silva Santos, Joäo Manuel,, S. Wedemeyer, Leenaarts, Jorrit,, Wedemeyer, Sven, J. M. da Silva Santos, Chintzoglou, Georgios, B. De Pontieu, Szydlarski, Mikolaj Marcin   +20 more
core   +1 more source

On the Freeze‐In Distance of Solar Wind Fluid Entropy Variability in the Corona

Journal of Geophysical Research: Space Physics, Volume 131, Issue 3, March 2026.
Abstract The strong correlation between solar wind entropy and the frozen‐in ion charge state ratio O7+/O6+ ${\mathrm{O}}^{7+}/{\mathrm{O}}^{6+}$ indicates that entropy variability on timescales of hours or longer is preserved from its solar source. This prompts the question: where in the solar atmosphere does this entropy variability come from, and at
Aidan J. Nakhleh, Nicholeen M. Viall, Susan T. Lepri, Jim M. Raines   +3 more
wiley   +1 more source

Solar Activity Impacts on Ionospheric Scintillation and Precise Point Positioning Based on Multi‐Year GNSS and Scintillation Observations

Space Weather, Volume 24, Issue 3, March 2026.
Abstract Solar activity induces ionospheric irregularities that degrade Global Navigation Satellite System (GNSS) performance through amplitude and phase scintillation. Although numerous studies have investigated event‐driven or regional responses, the nonlinear coupling between solar radiation, ionospheric scintillation, and precise point positioning (
Jincheng Li, Qi Liu, Xiaomin Luo, Manuel Hernández‐Pajares, Enric Monte‐Moreno, Guangxia Wang, Heng Yang, Chuanding Zhang, Li Yang, Yaoyao Liu   +9 more
wiley   +1 more source

A New Method for Probabilistic Spatiotemporal Forecasts of Solar Soft X‐Ray “S‐Class” (>X10) Superflares

Journal of Geophysical Research: Space Physics, Volume 131, Issue 2, February 2026.
Abstract Solar superflares of S‐class (>X10 in soft X‐rays) pose extreme space weather hazards, yet their prediction remains a fundamental challenge owing to their rapid and transient natures and the limitations of conventional event‐based forecasts. We introduce for the first time, a probabilistic spatiotemporal framework designed to identify extended
V. M. Velasco Herrera, G. Velasco Herrera, W. Soon, A. Özgüç, N. Babynets, A. Tlatov, M. Švanda, S. Qiu, S. Baliunas, B. Kotan, G. González González, L. A. Bautista Flores, M. Pazos   +12 more
wiley   +1 more source

Space Weather Impact of Three Solar Flares Observed by the POEMAS Telescope at 45 and 90 GHz

Journal of Geophysical Research: Space Physics, Volume 130, Issue 11, November 2025.
Abstract Solar flares are often associated with coronal mass ejections (CMEs) that, when directed toward Earth, can disrupt the magnetosphere and impact space weather. In this study, we investigate three long‐duration solar flares observed in 2012 by the POlarization Emission of Millimeter Activity at the Sun (POEMAS) telescopes at 45 and 90 GHz.
Adriana Valio, Karla F. Lopez, José Luis Gamonal Valenzuela, Ruben M. Romero Ramírez, Dougas F. da Silva   +4 more
wiley   +1 more source

Solar Flare Activity, 1937–2024: Introducing the New Hemispheric Solar Flare Index (hSFI) in the Context of 2024's Major Solar Storm Events

Space Weather, Volume 23, Issue 11, November 2025.
Abstract A new daily composite of the solar flare index (SFI) and the hemispherically‐resolved versions (hSFI) are presented for 1937 to 2024. The data set confirms that the northern hemisphere (NH) dominated solar flare activity during Solar Cycles 17 to 21, but that the southern hemisphere has dominated from Solar Cycle 22 to present.
V. M. Velasco Herrera, W. Soon, S. Knoška, A. Özgüç, G. Velasco Herrera, H. Yeşilyaprak, N. Babynets, M. Švanda, J. Muraközy, S. Qiu, D. Riveros‐Rosas, R. Connolly, M. Connolly, A. Tlatov, L. Cappellotto   +14 more
wiley   +1 more source

Dynamics of the Quiet Solar Chromosphere [PDF]

, 1999
The solar chromosphere has never been static although it was often modeled so.Even the quiet-sun internetwork chromosphere has become thoroughly dynamic with the acoustic shock interpretation of the Ca II K 2V grains.
Rutten, R.J., Shine, R.A., Berger, T.E., Lites, Bruce W.   +3 more
core