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1. Solar Cycle and Solar Wind Dependence of the Occurrence of Large dB / dt Events at High Latitudes

   https://doi.org/10.1029/2022JA030953  

   Milan, S. E.; Imber, S. M.; Fleetham, A. L.; Gjerloev, J. (April 2023, Journal of Geophysical Research: Space Physics)

   Key Points Large dB / dt “spikes” in ground magnetometer data occur in three local time hotspots in the pre‐midnight, dawn, and pre‐noon sectors These are consistent with spikes produced by substorm onsets, omega bands, and the Kelvin‐Helmholtz instability, respectively Spike occurrence is controlled by solar activity, maximizing in the declining phase of the solar cycle, esp. solar cycle 23 

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2. Cold Solar Flares. I. Microwave Domain

   https://doi.org/10.3847/1538-4357/acea20  

   Lysenko, Alexandra_L; White, Stephen_M; Zhdanov, Dmitry_A; Meshalkina, Nataliia_S; Altyntsev, Aleksander_T; Motorina, Galina_G; Fleishman, Gregory_D (August 2023, The Astrophysical Journal)

   Abstract We identify a set of ∼100 “cold” solar flares and perform a statistical analysis of them in the microwave range. Cold flares are characterized by a weak thermal response relative to nonthermal emission. This work is a follow-up of a previous statistical study of cold flares, which focused on hard X-ray emission to quantify the flare nonthermal component. Here, we focus on the microwave emission. The thermal response is evaluated by the soft X-ray emission measured by the GOES X-ray sensors. We obtain spectral parameters of the flare gyrosynchrotron emission and reveal patterns of their temporal evolution. The main results of the previous statistical study are confirmed: as compared to a “mean” flare, the cold flares have shorter durations, higher spectral peak frequencies, and harder spectral indices above the spectral peak. Nonetheless, there are some cold flares with moderate and low peak frequencies. In the majority of cold flares, we find evidence of the Razin effect in the microwave spectra, indicative of rather dense flaring loops. We discuss the results in the context of the electron acceleration efficiency. 

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3. Predicting the Solar Wind at the Parker Solar Probe Using an Empirically Driven MHD Model

   https://doi.org/10.3847/1538-4365/ab58c9  

   Kim, T. K.; Pogorelov, N. V.; Arge, C. N.; Henney, C. J.; Jones-Mecholsky, S. I.; Smith, W. P.; Bale, S. D.; Bonnell, J. W.; Dudok de Wit, T.; Goetz, K.; et al (February 2020, The Astrophysical Journal Supplement Series)
4. Turbulence Transport Modeling and First Orbit Parker Solar Probe ( PSP ) Observations

   https://doi.org/10.3847/1538-4365/ab5852  

   Adhikari, L.; Zank, G. P.; Zhao, L.-L.; Kasper, J. C.; Korreck, K. E.; Stevens, M.; Case, A. W.; Whittlesey, P.; Larson, D.; Livi, R.; et al (February 2020, The Astrophysical Journal Supplement Series)
5. Observational study of intermittent solar jets: p -mode modulation

   https://doi.org/10.1051/0004-6361/202348053  

   Cai, Qiuzhuo; Ruan, Guiping; Zheng, Chenxi; Schmieder, Brigitte; Guo, Jinhan; Chen, Yao; Su, Jiangtao; Liu, Yang; Liu, Jihong; Cao, Wenda (February 2024, Astronomy & Astrophysics)

   Aims.Recurring jets are observed in the solar atmosphere. They can erupt intermittently over a long period of time. By the observation of intermittent jets, we wish to understand what causes the characteristics of the periodic eruptions. Methods.We report intermittent jets observed by the Goode Solar Telescope (GST) with the TiO Broadband Filter Imager (BFI), the Visible Imaging Spectrometer (VIS) in H_α, and the Near-InfraRed Imaging Spectropolarimeter (NIRIS). The analysis was aided and complemented by 1400 Å and 2796 Å data from the Interface Region Imaging Spectrograph (IRIS). These observational instruments allowed us to analyze the temporal characteristics of the jet events. By constructing the H_αdopplergrams, we found that the plasma first moves upward, but during the second phase of the jet, the plasma flows back. Working with time slice diagrams, we investigated the characteristics of the jet dynamics. Results.The jet continued for up to 4 h. The time-distance diagram shows that the peak of the jet has clear periodic-eruption characteristics (5 min) during 18:00 UT–18:50 UT. We also found a periodic brightening phenomenon (5 min) during the jet bursts in the observed bands in the transition region (1400 Å and 2796 Å), which may be a response to intermittent jets in the upper solar atmosphere. The time lag is 3 min. Evolutionary images in the TiO band revealed a horizontal movement of the granulation at the location of the jet. By comparison to the quiet region of the Sun, we found that the footpoint of the jet is enhanced at the center of the H_αspectral line profile, without significant changes in the line wings. This suggests prolonged heating at the footpoint of the jet. In the mixed-polarity magnetic field region of the jet, we observed the emergence of magnetic flux, its cancellation, and shear, indicating possible intermittent magnetic reconnection. This is confirmed by the nonlinear force-free field model, which was reconstructed using the magneto-friction method. Conclusions.The multiwavelength analysis indicates that the events we studied were triggered by magnetic reconnection that was caused by mixed-polarity magnetic fields. We suggest that the horizontal motion of the granulation in the photosphere drives the magnetic reconnection, which is modulated byp-mode oscillations. 

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