In the past C.H. Mandrini has collaborated on articles with G. Del Zanna and S. Dasso. One of their most recent publications is Observed signatures of magnetic energy conversion in solar flares and microflares. Which was published in journal Advances in Space Research.

More information about C.H. Mandrini research including statistics on their citations can be found on their Copernicus Academic profile page.

C.H. Mandrini's Articles: (7)

Observed signatures of magnetic energy conversion in solar flares and microflares

AbstractWe follow up on our earlier studies of the characteristics of energy release in solar flares, extending it to weak flare-like transient brightenings which are called “microflares”. We find that all events share similar properties in spite of their large differences in X-ray brightness, including the fact that their trigger seems to be due to the interaction of impacted bipolar regions which leads to the release of their internally stored energy. The overall topology of the energy release region is preserved over a period in which an active region produced numerous events, except at the site of a two ribbon flare, which probably led to a permanent disruption of the magnetic configuration. Our results suggest that transient microflares can be responsible for a large fraction of the coronal heating in active regions, and we propose a picture in which reconnection may act as a catalyst for the release of stored magnetic energy.

Sigmoidal diagnostics with SOHO/CDS

AbstractDuring the third Whole Sun Month Campaign (August 18 – September 14, 1999), the evolution of the active region NOAA 8668 was followed during its meridian passage and at the limb (Sigmoid JOP 106), with simultaneous observations with the Solar and Heliospheric Observatory (SOHO), and with other instruments, both satellite and ground-based. On August 21st, a small flare, associated with a brightening of the sigmoidal structure, occurred. SOHO Coronal Diagnostic Spectrometer (CDS) observations of this small flare are presented. Coronal temperatures and densities of the sigmoid are estimated. High transition region densities (in the range 2.5–7 × 1011 cm−3), obtained using O IV, are present in the brightenings associated with the flare. At coronal level, high temperatures of at least 8 MK were reached, as shown by strong Fe XIX emission. After this small flare, relatively strong blue-shifts (⋍ 30 km/s) are observed in coronal lines, located at the two ends of a small loop system associated with the sigmoid.

Large scale MHD properties of interplanetary magnetic clouds

AbstractMagnetic Clouds (MCs) are the interplanetary manifestation of Coronal Mass Ejections. These huge astrophysical objects travel from the Sun toward the external heliosphere and can reach the Earth environment. Depending on their magnetic field orientation, they can trigger intense geomagnetic storms. The details of the magnetic configuration of clouds and the typical values of their magnetohydrodynamic magnitudes are not yet well known. One of the most important magnetohydrodynamic quantities in MCs is the magnetic helicity. The helicity quantifies several aspects of a given magnetic structure, such as the twist, kink, number of knots between magnetic field lines, linking between magnetic flux tubes, etc. The helicity is approximately conserved in the solar atmosphere and the heliosphere, and it is very useful to link solar phenomena with their interplanetary counterpart. Since a magnetic cloud carries an important amount of helicity when it is ejected from the solar corona, estimations of the helicity content in clouds can help us to understand its evolution and its coronal origin. In situ observations of magnetic clouds at one astronomical unit are in agreement with a local helical magnetic structure. However, since spacecrafts only register data along a unique direction, several aspects of the global configuration of clouds cannot be observed. In this paper, we review the general properties of magnetic clouds and different models for their magnetic structure at one astronomical unit. We describe the corresponding techniques to analyze in situ measurements. We also quantify their magnetic helicity and compare it with the release of helicity in their solar source for some of the analyzed cases.

Multi-scale reconnections in a complex CME

AbstractA series of three flares of GOES class M, M and C, and a CME were observed on 20 January 2004 occurring in close succession in NOAA 10540. Types II, III, and N radio bursts were associated. We use the combined observations from TRACE, EIT, Hα images from Kwasan Observatory, MDI magnetograms, GOES, and radio observations from Culgoora and Wind/ WAVES to understand the complex development of this event. We reach three main conclusions. First, we link the first two impulsive flares to tether-cutting reconnections and the launch of the CME. This complex observation shows that impulsive quadrupolar flares can be eruptive. Second, we relate the last of the flares, an LDE, to the relaxation phase following forced reconnections between the erupting flux rope and neighbouring magnetic field lines, when reconnection reverses and restores some of the pre-eruption magnetic connectivities. Finally, we show that reconnection with the magnetic structure of a previous CME launched about 8 h earlier injects electrons into open field lines having a local dip and apex (located at about six solar radii height). This is observed as an N-burst at decametre radio wavelengths. The dipped shape of these field lines is due to large-scale magnetic reconnection between expanding magnetic loops and open field lines of a neighbouring streamer. This particular situation explains why this is the first N-burst ever observed at long radio wavelengths.

Very intense geomagnetic storms and their relation to interplanetary and solar active phenomena

AbstractWe revisit previous studies in which the characteristics of the solar and interplanetary sources of intense geomagnetic storms have been discussed. In this particular analysis, using the Dst time series, we consider the very intense geomagnetic storms that occurred during Solar Cycle 23 by setting a value of Dstmin⩽-200nT as threshold. After carefully examining the set of available solar and in situ observations from instruments aboard the Solar and Heliospheric Observatory (SOHO) and the Advanced Composition Explorer (ACE), complemented with data from the ground, we have identified and characterized the solar and interplanetary sources of each storm. That is to say, we determine the time, angular width, plane-of-the-sky, lateral expansion, and radial velocities of the source coronal mass ejection (CME), the type and heliographic location of the CME solar source region (including the characteristics of the sunspot groups), and the time duration of the associated flare. After this, we investigate the overall characteristics of the interplanetary (IP) main-phase storm driver, including the time arrival of the shock/disturbance at 1 AU, the type of associated IP structure/ejecta, the origin of a prolonged and enhanced southward component (Bs) of the IP field, and other characteristics related to the energy injected into the magnetosphere during the storm (i.e. the solar wind maximum convected electric field, Ey). The analyzed set consists of 20 events, some of these are complex and present two or more Dst minima that are, in general, due to consecutive solar events. The 20 storms are distributed along Solar Cycle 23 (which is a double-peak cycle) in such a way that 15% occurs during the rising phase of the cycle, 45% during both cycle maxima, and, surprisingly, 40% during the cycle descending phase. This latter set includes half of the superstorms and the only cycle extreme event. 85% of the storms are associated to full halo CMEs and 10% to partial halo events. One of the storms occurred at the time contact with SOHO was lost. The CME solar sources of all analyzed storms, but one, are active regions (ARs). The source of the remaining CME is a bipolar low-field region where a long and curved filament erupts. The ARs where the CMEs originate show, in general, high magnetic complexity; δ spots are present in 74% of the ARs, 10% are formed by several bipolar sunspot groups, and only 16% present a single bipolar sunspot group. All CMEs are associated to long duration events (LDEs), exceeding 3 h in all cases, with around 75% lasting more than 5 h. The associated flares are, in general, intense events, classified as M or X in soft X-rays; only 3 of them fall in the C class, with the one happening in the bipolar low field region hardly reaching the C level. We calculate the lateral expansion velocity for most of the CMEs. The values found exceed in all cases but one the fast solar wind speed (≈750 km s−1). The average lateral expansion velocity is 2400 km s−1. The spatial distribution of the solar CME sources on the solar disk shows an evident asymmetry; while there are no sources located more eastward than 12° in longitude, there are 7 events more westward than 12°. Nevertheless, the bulk of the solar sources are located near Sun center, i.e. at less than 20° in longitude or latitude. Considering the IP structures responsible for a long and enhanced Bs, we find that 35% correspond to magnetic clouds (MCs) or ICME fields, 30% to sheath fields, and 30% to combined sheath and MC or ICME fields. For only one storm the origin of Bs is related to the back compression of an ICME by a high speed stream coming from a coronal hole in the neighborhood of the corresponding CME source region. We have also found that for this particular set of storms the linear relation between Ey and the storm intensity holds (with a correlation coefficient of 0.73). These results complement and extend those of other works in the literature.

Tracing magnetic helicity from the solar corona to the interplanetary space

AbstractOn October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity.

Submillimeter-wave and Hα observations of the event on 28 November, 2001

AbstractWe present a detailed study of a 1B/M6.9 impulsive flare combining high time resolution (1 ms) and instantaneous emission source localization observations at submillimeter frequencies (212 GHz), obtained with the solar submillimeter telescope (SST), and Hα data from the Hα solar telescope for argentina (HASTA). The flare, starting at 16:34 UT, occurred in active region (AR) 9715 (NOAA number) on November 28, 2001, and was followed by an Hα surge. We complement our data with magnetograms from the Michelson Doppler Imager (SOHO/MDI). SST observed a short impulsive burst at 212 GHz, presenting a weak bulk emission (of about 90 sfu) composed of a few shorter duration (<5s) structures. The integrated Hα and the 212 GHz light curves present a remarkable agreement during the impulsive phase of the event. The delay between both curves stays below 12 s (the time resolution of the Hα telescope). The flare as well as the surge are linked to new flux emergence very close to the main AR bipole. Taking into account the AR magnetic field evolution, we infer that magnetic field reconnection, occurring at low coronal levels, could have been at the origin of the flare; while in the case of surge this would happen at the chromospheric level.

Join Copernicus Academic and get access to over 12 million papers authored by 7+ million academics.
Join for free!

Contact us