Low‐speed solar wind from the vicinity of solar active regions

Kojima, M.; Fujiki, K.; Ohmi, Tetsuo; Tokumaru, M.; Yokobe, A.; Hakamada, K.

doi:10.1029/1999ja900177

Cited by 87 publications

(69 citation statements)

References 23 publications

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“…This prediction could be tested by means of potential field source surface extrapolations or global heliospheric MHD simulations, the calculated field lines of which could be used to check on the occurrence, or lack of, magnetic connections between the low-corona AR outflow regions and the heliospheric steady excess of mass/momentum. This would be a follow-up to previously identified relationships between dense slow solar wind streamers (seen with radio scintillation and with SOHO/LASCO), higher heliospheric Oxygen charge states (measured with ACE and ULYSSES), and dark AR-related EUV emissions at the footpoints of open flux tubes (Kojima et al 1999;Liewer et al 2001Liewer et al , 2004. A relationship between an active region and the solar wind was also found by Janardhan et al (2008).…”

Section: Mass and Momentum Injection Into The Solar Windmentioning

confidence: 99%

A single picture for solar coronal outflows and radio noise storms

Zanna¹,

Aulanier

Klein

et al. 2011

A&A

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We propose a unified interpretation for persistent coronal outflows and metric radio noise storms, two phenomena typically observed in association with quiescent solar active regions. Our interpretation is based on multi-wavelength observations of two such regions as they crossed the meridian in May and July 2007. For both regions, we observe a persistent pattern of blue-shifted coronal emission in high-temperature lines with Hinode/EIS, and a radio noise storm with the Nançay Radioheliograph. The observations are supplemented by potential and linear force-free extrapolations of the photospheric magnetic field over large computational boxes, and by a detailed analysis of the coronal magnetic field topology. We find true separatrices in the coronal field and null points high in the corona, which are preferential locations for magnetic reconnection and electron acceleration. We suggest that the continuous growth of active regions maintains a steady reconnection across the separatrices at the null point. This interchange reconnection occurs between closed, high-density loops in the core of the active region and neighbouring open, low-density flux tubes. Thus, the reconnection creates strong pressure imbalances which are the main drivers of plasma upflows. Furthermore, the acceleration of low-energy electrons in the interchange reconnection region sustains the radio noise storm in the closed loop areas, as well as weak type III emission along the open field lines. For both active regions studied, we find a remarkable agreement between the observed places of persistent coronal outflows and radio noise storms with their locations as predicted by our interpretation.

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Section: Mass and Momentum Injection Into The Solar Windmentioning

confidence: 99%

A single picture for solar coronal outflows and radio noise storms

Zanna¹,

Aulanier

Klein

et al. 2011

A&A

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“…The possible contribution of the surroundings of active regions (ARs) to the slow solar wind was first pointed out by Kojima et al (1999). By comparing velocity distributions at 2.5 R and potential field extrapolations based on Kitt Peak magnetograms, Kojima et al (1999) found that compact low-speed wind regions are associated with large magnetic flux expansions adjacent to ARs.…”

Section: Introductionmentioning

confidence: 99%

“…By comparing velocity distributions at 2.5 R and potential field extrapolations based on Kitt Peak magnetograms, Kojima et al (1999) found that compact low-speed wind regions are associated with large magnetic flux expansions adjacent to ARs. The first identification of continuous intermittent flows with velocities from 5 to 20 km s −1 at the periphery of an AR was made by Winebarger et al (2001) using Transition Region And Coronal Explorer (TRACE) 171 Å data.…”

Section: Introductionmentioning

confidence: 99%

Active region upflows

Vanninathan

Madjarska

Galsgaard

et al. 2015

A&A

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Context. We study upflows at the edges of active regions, called AR outflows, using multi-instrument observations. Aims. This study intends to provide the first direct observational evidence of whether chromospheric jets play an important role in furnishing mass that could sustain coronal upflows. The evolution of the photospheric magnetic field, associated with the footpoints of the upflow region and the plasma properties of active region upflows is investigated with the aim of providing information for benchmarking data-driven modelling of this solar feature. Methods. We spatially and temporally combine multi-instrument observations obtained with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode, the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory and the Interferometric BI-dimensional Spectro-polarimeter installed at the National Solar Observatory, Sac Peak, to study the plasma parameters of the upflows and the impact of the chromosphere on active region upflows. Results. Our analysis shows that the studied active region upflow presents similarly to those studied previously, i.e. it displays blueshifted emission of 5-20 km s −1 in Fe xii and Fe xiii and its average electron density is 1.8 × 10 9 cm −3 at 1 MK. The time variation of the density is obtained showing no significant change (in a 3σ error). The plasma density along a single loop is calculated revealing a drop of 50% over a distance of ∼20 000 km along the loop. We find a second velocity component in the blue wing of the Fe xii and Fe xiii lines at 105 km s −1 reported only once before. For the first time we study the time evolution of this component at high cadence and find that it is persistent during the whole observing period of 3.5 h with variations of only ±15 km s −1 . We also, for the first time, study the evolution of the photospheric magnetic field at high cadence and find that magnetic flux diffusion is responsible for the formation of the upflow region. High cadence Hα observations are used to study the chromosphere at the footpoints of the upflow region. We find no significant jet-like (spicule/rapid blue excursion) activity to account for several hours/days of plasma upflow. The jet-like activity in this region is not continuous and blueward asymmetries are a bare minimum. Using an image enhancement technique for imaging and spectral data, we show that the coronal structures seen in the AIA 193 Å channel are comparable to the EIS Fe xii images, while images in the AIA 171 Å channel reveal additional loops that are a result of contribution from cooler emission to this channel. Conclusions. Our results suggest that at chromospheric heights there are no signatures that support the possible contribution of spicules to active region upflows. We suggest that magnetic flux diffusion is responsible for the formation of the coronal upflows. The existence of two velocity components possibly indicates the presence of two different flows, which are produce...

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“…By using interplanetary scintillation analysis, Kojima et al (1999) found slow wind flows during the minimum of solar activity. These were associated with open magnetic field lines that apparently originated in one of the polarities of an AR.…”

Section: Introductionmentioning

confidence: 99%

Evolution of active region outflows throughout an active region lifetime

Zangrilli

Poletto

2016

A&A

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Context. We have shown previously that SOHO/UVCS data allow us to detect active region (AR) outflows at coronal altitudes higher than those reached by other instrumentation. These outflows are thought to be a component of the slow solar wind. Aims. Our purpose is to study the evolution of the outflows in the intermediate corona from AR 8100, from the time the AR first forms until it dissolves, after several transits at the solar limb. Methods. Data acquired by SOHO/UVCS at the time of the AR limb transits, at medium latitudes and at altitudes ranging from 1.5 to 2.3 R , were used to infer the physical properties of the outflows through the AR evolution. To this end, we applied the Doppler dimming technique to UVCS spectra. These spectra include the H i Lyα line and the O vi doublet lines at 1031.9 and 1037.6 Å. Results. Plasma speeds and electron densities of the outflows were inferred over several rotations of the Sun. AR outflows are present in the newly born AR and persist throughout the entire AR life. Moreover, we found two types of outflows at different latitudes, both possibly originating in the same negative polarity area of the AR. We also analyzed the behavior of the Si xii 520 Å line along the UVCS slit in an attempt to reveal changes in the Si abundance when different regions are traversed. Although we found some evidence for a Si enrichment in the AR outflows, alternative interpretations are also plausible.Conclusions. Our results demonstrate that outflows from ARs are detectable in the intermediate corona throughout the whole AR lifetime. This confirms that outflows contribute to the slow wind.

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Low‐speed solar wind from the vicinity of solar active regions

Cited by 87 publications

References 23 publications

A single picture for solar coronal outflows and radio noise storms

A single picture for solar coronal outflows and radio noise storms

Active region upflows

Evolution of active region outflows throughout an active region lifetime

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