We analyzed simultaneous EUV data from the Transition Region and Coronal Explorerand Ha data from Big Bear Solar Observatory. In the active region studied, we found several EUV jets that repeatedly occurred where pre-existing magnetic flux was “canceled” by newly emerging flux of opposite polarity. The jets look like Yohkoh soft X-ray jets, but are smaller and shorter lived than X-ray jets. They have a typical size of 4000‐10,000 km, a transverse velocity of 50‐100 km s 21 , and a lifetime of 2‐4 minutes. Each of the jets was ejected from a looplike bright EUV emission patch at the moment that the patch reached its peak emission. We also found dark Ha surges that are correlated with these jets. A careful comparison, however, revealed that the Ha surges are not cospatial with the EUV jets. Instead, the EUV jets are identified with bright jetlike features in the Ha line center. Our results support a picture in which Ha surges and EUV jets represent different kinds of plasma ejection—cool and hot plasma ejections along different field lines—which must be dynamically connected to each other. We emphasize the importance of observed flux cancellation and a small erupting filament in understanding the acceleration mechanisms of EUV jets and Ha surges.

EXTREME-ULTRAVIOLET JETS AND H a SURGES IN SOLAR MICROFLARES

Fil: Mandrini, Cristina Hemilse. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

https://www.lesia.obspm.fr/perso/pascal-demoulin/07/mandrini07-dimmings.pdf

Are CME-Related Dimmings Always a Simple Signature of Interplanetary Magnetic Cloud Footpoints?

We present observations of a blowout jet that experienced two distinct ejection stages. The first stage started from the emergence of a small positive magnetic polarity, which was cancelled by the nearby negative magnetic field and caused the rising of a mini-filament and its confining loops. This further resulted in a small jet due to the magnetic reconnection between the rising confining loops and the overlying open field. The second ejection stage was mainly due to successive removal of the confining field by reconnection: the filament erupted, and the erupting cool filament material directly combined with the hot jet that originated form the reconnection region and therefore formed the cool and hot components of the blowout jet. During the two ejection stages, cool Ha jets are also observed cospatial with their coronal counterparts, but their appearance times are earlier by a few minutes than those of the hot coronal jets. The hot coronal jets are therefor possibly caused by the heating of the cool Ha jets or the rising of the reconnection height from the chromosphere to the corona. The scenario that magnetic reconnection occurred between the confining loops and the overlying open loops is supported by many observational facts, including the bright patches on both sides of the mini-filament, hot plasma blobs along the jet body, and periodic metric radio type III bursts at the very beginnings of the two stages. The evolution and characteristics of these features show the detailed nonlinear process in magnetic reconnection.

https://iopscience.iop.org/article/10.3847/1538-4357/aa9a48/pdf

On a Solar Blowout Jet: Driving Mechanism and the Formation of Cool and Hot Components

Solid evidence of magnetic reconnection is rarely reported within sunspots, the darkest regions with the strongest magnetic fields and lowest temperatures in the solar atmosphere. Using the world's largest solar telescope, the 1.6 m Goode Solar Telescope, we detect prevalent reconnection through frequently occurring fine-scale jets in the Ha line wings at light bridges, the bright lanes that may divide the dark sunspot core into multiple parts. Many jets have an inverted Y-shape, shown by models to be typical of reconnection in a unipolar field environment. Simultaneous spectral imaging data from the Interface Region Imaging Spectrograph show that the reconnection drives bidirectional flows up to 200(.) km(.) s(-1), and that the weakly ionized plasma is heated by at least an order of magnitude up to similar to 80,000 K. Such highly dynamic reconnection jets and efficient heating should be properly accounted for in future modeling efforts of sunspots. Our observations also reveal that the surge-like activity previously reported above light bridges in some chromospheric passbands such as the Ha core has two components: the ever-present short surges likely to be related to the upward leakage of magnetoacoustic waves from the photosphere, and the occasionally occurring long and fast surges that are obviously caused by the intermittent reconnection jets.

https://iopscience.iop.org/article/10.3847/1538-4357/aaa89d/pdf

Frequently Occurring Reconnection Jets from Sunspot Light Bridges

Magnetic clouds (MCs), and more generally, interplanetary coronal mass ejections (ICMEs), are believed to be the interplanetary counterparts of CMEs. The link has usually been shown by taking into account the CME launch position on the Sun, the expected time delay and by comparing the orientation of the coronal and interplanetary magnetic field. Making such a link more quantitative is challenging since it requires a relation between very different kinds of magnetic field measurements: (i) photospheric magnetic maps, which are observed from a distant vantage point (remote sensing) and (ii) in-situ measurements of MCs, which provide precise, directly measured, magnetic field data merely from one-dimensional linear samples. The association between events in these different domains can be made using adequate coronal and MC models. Then, global quantities like magnetic fluxes and helicity can be derived and compared. This review paper describes all the general trends found in the above association criteria. A special focus is given for the cases which do not follow the earlier derived mean laws since interesting physics is usually involved.

/pdf/a-review-of-the-quantitative-links-between-cmes-and-magnetic-4w39fuxk6z.pdf

A review of the quantitative links between CMEs and magnetic clouds

Recurrent and homologous jets were observed to the west edge of active region NOAA 11513 at the boundary of a coronal hole. We find two kinds of cancellations between opposite polarity magnetic fluxes, inducing the generation of recurrent jets. First, a satellite spot continuously collides with a pre-existing opposite polarity magnetic field and causes recurrent solar jets. Second, moving magnetic features, which emerge near the sunspot penumbra, pass through the ambient plasma and eventually collide with the opposite polarity magnetic field. Among these recurrent jets, a blowout jet that occurred around 21:10 UT is investigated. The rotation of the pre-existing magnetic field and the shear motion of the satellite spot accumulate magnetic energy, which creates the possibility for the jet to experience blowout right from the standard.

https://iopscience.iop.org/article/10.1088/0004-637X/815/1/71/pdf

Recurrent Solar Jets Induced by a Satellite Spot and Moving Magnetic Features

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Tele- scope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.

http://iopscience.iop.org/article/10.1088/1009-9271/3/6/491/pdf

Three Super Active Regions in the Descending Phase of Solar Cycle 23

Magnetic helicity was found important in understanding solar activities such as flares and coronal mass ejections (CME). Berger and field (1984) derived an expression for helicity flux dHm/dt, that can be applied to an individual solar active region (AR) occupying an area S of the photosphere, (1) 
\begin{linenomath}
dH_{m}/dt=-2\int_{s}[(\mathbf{A_{p}}\cdot \mathbf{V})\mathbf{B}-(\mathbf{A_{p}} \cdot \mathbf{B})\mathbf{V}] dS, \eqno{(1)}
\end{linenomath}
 where Ap is the vector potential of potential field, and V is the plasma velocity at the surface S. The first term describes the effect of magnetic footpoint motions on the surface S. The second term describes the flux of helicity advected through the surface when already twisted and/or writhed flux ropes emerge. Chae (2001) proposed a method of self-consistently determining magnetic helicity injection rate, dH/dt, using a time series of longitudinal magnetograms only: (2) 
\begin{linenomath}
dH/dt=-\int2(\textbf{A}_{p}\cdot \textbf{V}_{LCT})B_{n}dS, \eqno{(2)}
\end{linenomath}
 where n is the normal component of magnetic field. Ap is the vector potential computed from Bn by Fourier transform method. V LCT is the horizontal component of velocity determined by the technique of local correlation tracking (LCT). This technique was applied by some scientists (e.g., Chae et al., 2001; Nindos and Zhang, 2002; Romano et al., 2003). Magnetic helicity injection was found to be strongly correlated with the occurrence of major flares (Moon et al. 2002a, 2002b; Park et al., 2008; Labonte et al., 2007; Maeshiro et al., 2009).

Magnetic helicity injection in NOAA 11261 associated with flares

Abstract With the photospheric vector magnetic fields provided by SDO/HMI team, the helicity accumulation, induced electric field and Poynting flux is calculated for AR 11158 by using the local correlation tracking technique (LCT). It is found that the helicity accumulation reaches 6000×1040 Mx 2, the average densities of the induced electric field about 0.15-0.35 V cm −1, and that of the Poynting flux about 50-240 W m −2, within 50 hours. One main flare of X2.2 occurs in the increasing phase of the helicity accumulation, which also corresponds to the decreasing phase of the induced electric field and the gradual change phase of the Poynting flux. Before the flare, all these quantities increase rapidly for about 20 hours firstly, then increase gradually or even decrease for 8-9 hours.

/pdf/the-helicity-induced-electric-field-and-poynting-flux-of-ar-39b4m9lkpq.pdf

Jihong Liu

Papers

Recurrent Solar Jets Induced by a Satellite Spot and Moving Magnetic Features

Three Super Active Regions in the Descending Phase of Solar Cycle 23

Magnetic helicity injection in NOAA 11261 associated with flares

The helicity, induced electric field and Poynting flux of AR 11158and their relationship with the X-class flare