Large Coronal Holes Research Articles

Three-day Forecasting of Solar Wind Speed Using SDO/AIA Extreme-ultraviolet Images by a Deep-learning Model

In this study, we forecast solar wind speed for the next 3 days with a 6 hr cadence using a deep-learning model. For this we use Solar Dynamics Observatory/Atmospheric Imaging Assembly 211 and 193 Å images together with solar wind speeds for the last 5 days as input data. The total period of the data is from 2010 May to 2020 December. We divide them into a training set (January–August), validation set (September), and test set (October–December), to consider the solar cycle effect. The deep-learning model consists of two networks: a convolutional layer–based network for images and a dense layer–based network for solar wind speeds. Our main results are as follows. First, our model successfully predicts the solar wind speed for the next 3 days. The rms error (RMSE) of our model is from 37.4 km s−1 (for the 6 hr prediction) to 68.2 km s−1 (for the 72 hr prediction), and the correlation coefficient is from 0.92 to 0.67. These results are much better than those of previous studies. Second, the model can predict sudden increase of solar wind speeds caused by large equatorial coronal holes. Third, solar wind speeds predicted by our model are more consistent with observations than those by the Wang–Sheely–Arge–ENLIL model, especially in high-speed-stream regions. It is also noted that our model cannot predict solar wind speed enhancement by coronal mass ejections. Our study demonstrates the effectiveness of deep learning for solar wind speed prediction, with potential applications in space weather forecasting.

Analysis of Study Results of the Polar Coronal Hole on the Sun According to Observations in the Microwave Wavelength Range

An overview is presented of the main results of the study of the polar coronal hole over the North pole of the Sun based on observations of the solar eclipse on March 29, 2006, using the RATAN-600 radio telescope in a wide cm-range of wavelengths (1.03, 1.38, 2.7, 6.2, 13.0, 30.7 cm) along with observational and theoretical data about the properties of Solar coronal holes published by various authors. The results obtained are discussed: the distribution of brightness temperatures of polar coronal holes over the North pole of the Sun at distances of 1.005–2.0 in units of the Sun optical disk radius from the center of the solar disk; the increase in microwave radiation of polar coronal holes recorded at short wavelengths; the identity of the temperature properties of the polar coronal holes and low-latitude coronal holes on the Sun during the period of minimum solar activity. Comparison of the obtained brightness temperatures of the polar coronal hole with the brightness temperatures of large low-latitude coronal holes at similar wavelengths observed earlier (1973–1976, 1984–1987 yr) were done. This comparison has indicated an identity of the temperature properties of coronal holes regardless of their location on the Sun and the organization of coronal holes during the period of minimum solar activity.

The sun as a significant agent provoking earthquakes

In this paper we provide significant evidence that the sun is a principal agent provoking seismic activity. In particular the aim of the studies presented is to examine the possible relation of the coronal hole (CH) driven high speed solar wind streams (HSSs) with seismicity We performed several statistical studies of solar space and seismological data between 1980 and 2017 as well as a study for a long time interval from the year 1900 until the year 2017. (A1) Concerning the period 1980–2017 among other results we found that the earthquakes (EQs) with M ≥ 83 between 2010–2017 (including the catastrophic earthquakes of Japan 2011 (M91) Sumatra 2012 (M86) and Chile 2015 (M83)) occurred during times of large coronal holes as seen by the Solar Dynamics Observatory (SDO) satellite and were related with CH-driven HSSs observed by the ACE spacecraft several weeks or a few months before the EQ occurrences. (A2) Further research on the hypothesis of the possible HSS-EQ relationship revealed a surprising novel finding: a power spectrum analysis suggests that during the decay phase of the SCC22 and SC23 and at the maximum of SC23 the values of the global seismic (M ≥ 6) energy output shows a periodic variation of ~27 days, which is the mean rotational period of the Sun. (A3) Moderate (not strong) storms in general precede the great EQs. (B) The study of the data for the time interval 1900–2017 revealed that: (1) all of the giant (M ≥ 85) EQs occurred during the decay minimum and the rising phase of the solar cycle or in the maximum phase but at times of a strong reduction of the monthly averaged sunspot number: Chile M95 1960 EQ – Alaska M92 1964 EQ – Sumatra M91 2004 EQ (decay phase) Japan M91 2011 EQ (rising phase of the "strange" SC24) (2) the global energy release of all EQs with magnitudes M ≥ 55 show the highest values during the decay phase of the solar cycle and in particular three years after the solar maximum and (3) a very significant negative correlation (rS = −042p < 10−4) was found between the SSN and the number of earthquakes with M ≥ 7 during the period 1930–2010 during times of moderate and high amplitude solar cycles. (C) Another result of our study is that the comparison of the yearly numbers of great (M ≥ 7) EQs with the SSN fails to provide correct statistical results whereas this is possible for the global seismic energy or the giant EQs. (D) Finally we infer that the case and statistical studies presented in this paper strongly suggest a close relation between CH-associated HSSs and seismic activity. We present some observational evidence that most probably Alfvèn waves mediate the interaction of CH-driven HSSs with seismicity.

Heating Rates for Protons and Electrons in Polar Coronal Holes: Empirical Constraints from the Ultraviolet Coronagraph Spectrometer

Abstract Ultraviolet spectroscopy of the extended solar corona is a powerful tool for measuring the properties of protons, electrons, and heavy ions in the accelerating solar wind. The large coronal holes that expand up from the north and south poles at solar minimum are low-density collisionless regions in which it is possible to detect departures from one-fluid thermal equilibrium. An accurate characterization of these departures is helpful in identifying the kinetic processes ultimately responsible for coronal heating. In this paper, Ultraviolet Coronagraph Spectrometer (UVCS) measurements of the H i Lyα line are analyzed to constrain values for the solar wind speed, electron density, electron temperature, proton temperature (parallel and perpendicular to the magnetic field), and Alfvén-wave amplitude. The analysis procedure involves creating a large, randomized ensemble of empirical models, simulating their Lyα profiles, and building posterior probability distributions for only the models that agree with the UVCS data. The resulting temperatures do not exhibit a great deal of radial variation between heliocentric distances of 1.4 and 4 solar radii. Typical values for the electron, parallel proton, and perpendicular proton temperatures are 1.2, 1.8, and 1.9 MK, respectively. Resulting values for the “nonthermal” Alfvén wave amplitude show evidence for weak dissipation, with a total energy-loss rate that agrees well with an independently derived total heating rate for the protons and electrons. The moderate Alfvén-wave amplitudes appear to resolve some tension in the literature between competing claims of both higher (undamped) and lower (heavily damped) values.

Solar coronal holes and their geo-effectiveness

Solar corona as the outermost part of the Sun is constantly emanating solar wind consisting of charged particles. Coronal holes are rigidly rotating phenomena in the solar corona that are magnetically open to interplanetary space, which allow the solar wind particles to escape from the Sun. The study of coronal holes and their associated high speed solar wind streams is important because they are the sources of space weather disturbances during minimum solar activity. We present some results on the relationship between large solar coronal holes close to the central meridian and solar wind stream with the aim to analyse their geo-effectiveness. The analysis were carried out by considering geomagnetic and solar wind parameters such as total geomagnetic field, Bz component, proton density and plasma speed during Earth-side large solar coronal holes appearance. Using the data during declining phase solar activity we found that a solar coronal hole is geo-effective during and after its transit on the central meridian but not all of them can be the proxy of high speed solar wind.

Critical frequencies of the ionospheric [formula omitted] and [formula omitted] layers during the last four solar cycles: Sunspot group type dependencies

The long term solar activity dependencies of ionospheric F1 and F2 regions’ critical frequencies (f0F1 and f0F2) are analyzed for the last four solar cycles (1976–2015). We show that the ionospheric F1 and F2 regions have different solar activity dependencies in terms of the sunspot group (SG) numbers: F1 region critical frequency (f0F1) peaks at the same time with the small SG numbers, while the f0F2 reaches its maximum at the same time with the large SG numbers, especially during the solar cycle 23. The observed differences in the sensitivity of ionospheric critical frequencies to sunspot group (SG) numbers provide a new insight into the solar activity effects on the ionosphere and space weather. While the F1 layer is influenced by the slow solar wind, which is largely associated with small SGs, the ionospheric F2 layer is more sensitive to Coronal Mass Ejections (CMEs) and fast solar winds, which are mainly produced by large SGs and coronal holes. The SG numbers maximize during of peak of the solar cycle and the number of coronal holes peaks during the sunspot declining phase. During solar minimum there are relatively less large SGs, hence reduced CME and flare activity. These results provide a new perspective for assessing how the different regions of the ionosphere respond to space weather effects.

Manifestation of the Identity of Brightness Temperatures of the Polar Coronal Hole and Low-Latitude Coronal Holes in the Centimeter Wave Range

This paper is devoted to an analysis of brightness temperatures of the polar and low-latitude coronal holes on the Sun in the cm-wave range during periods of minimum solar activity. Data from observations of the polar coronal hole received by the RATAN-600 radio telescope during the solar eclipse of March 29, 2006, and low-latitude observations of coronal holes and quiet Sun received earlier with the RATAN-600 and BPR radio telescopes in the period of minimum solar activity have been used in the paper. The obtained good agreement between the brightness temperatures of cm-wave emission of the polar coronal hole above the North Pole of the Sun and of the low-latitude coronal holes against the background of the quiet Sun reveals the identity of the temperature properties of large coronal holes, irrespective of the mode of their arrangement and location on the Sun during the periods of minimum solar activity.

Origins of the Ambient Solar Wind: Implications for Space Weather

The Sun's outer atmosphere is heated to temperatures of millions of degrees, and solar plasma flows out into interplanetary space at supersonic speeds. This paper reviews our current understanding of these interrelated problems: coronal heating and the acceleration of the ambient solar wind. We also discuss where the community stands in its ability to forecast how variations in the solar wind (i.e., fast and slow wind streams) impact the Earth. Although the last few decades have seen significant progress in observations and modeling, we still do not have a complete understanding of the relevant physical processes, nor do we have a quantitatively precise census of which coronal structures contribute to specific types of solar wind. Fast streams are known to be connected to the central regions of large coronal holes. Slow streams, however, appear to come from a wide range of sources, including streamers, pseudostreamers, coronal loops, active regions, and coronal hole boundaries. Complicating our understanding even more is the fact that processes such as turbulence, stream-stream interactions, and Coulomb collisions can make it difficult to unambiguously map a parcel measured at 1 AU back down to its coronal source. We also review recent progress -- in theoretical modeling, observational data analysis, and forecasting techniques that sit at the interface between data and theory -- that gives us hope that the above problems are indeed solvable.

The 26 December 2001 Solar Eruptive Event Responsible for GLE63: III. CME, Shock Waves, and Energetic Particles

The SOL2001-12-26 moderate solar eruptive event (GOES importance M7.1, microwaves up to 4000 sfu at 9.4 GHz, CME speed 1446 km/s) produced strong fluxes of solar energetic particles and ground-level enhancement of cosmic-ray intensity (GLE63). To find a possible reason for the atypically high proton outcome of this event, we study multi-wavelength images and dynamic radio spectra and quantitatively reconcile the findings with each other. An additional eruption probably occurred in the same active region about half an hour before the main eruption. The latter produced two blast-wave-like shocks during the impulsive phase. The two shock waves eventually merged around the radial direction into a single shock traced up to $25R_\odot$ as a halo ahead of the expanding CME body, in agreement with an interplanetary Type II event recorded by the Radio and Plasma Wave Investigation (WAVES) experiment on the Wind spacecraft. The shape and kinematics of the halo indicate an intermediate regime of the shock between the blast wave and bow shock at these distances. The results show that i) the shock wave appeared during the flare rise and could accelerate particles earlier than usually assumed; ii) the particle event could be amplified by the preceding eruption, which stretched closed structures above the developing CME, facilitated its lift-off and escape of flare-accelerated particles, enabled a higher CME speed and stronger shock ahead; iii) escape of flare-accelerated particles could be additionally facilitated by reconnection of the flux rope, where they were trapped, with a large coronal hole; iv) the first eruption supplied a rich seed population accelerated by a trailing shock wave.

Magnetic field sector structure and origins of solar wind streams in 2012

The origins of the solar wind and the interplanetary magnetic field sector structure in the beginning of the magnetic polarity reversal of 24th solar cycle were investigated using the Wilcox Solar Observatory magnetic field measurements and their products as well as the solar wind data from ACE and the SDO/AIA EUV images. The dominance of the quadrupole harmonics in the solar magnetic field in this period resulted in a four-sector structure of the interplanetary magnetic field. The dominating source of recurrent high-speed solar wind stream was a large trans-equatorial coronal hole of negative polarity evolving in the course of the polarity reversal process. The contribution of ICMEs to the high-speed solar wind did not exceed 17% of the total flux. The solar wind density flux averaged over the year amounted to 1 × 108 cm−2 s−1 which is considerably lower than the typical long-term value (2–4 × 108 cm−2 s−1 ). The slow-speed component of solar wind density flux constituted in average more than 68% of the total flux, the high-speed component was about 10%, reaching the maximum of 32% in some Carrington rotations.

High-latitude coronal holes and polar faculae in the 21st–23rd solar activity cycles

The latitude-time evolution of large high-latitude coronal holes (CHs) and polar faculae (PF) during the period 1975–2010 has been studied. Their spatial distribution relative to each other has been considered. CHs and PF are shown to pass two significantly different phases in their evolution during an 11-year cycle. At phase I, i.e., during the period of an increase and maximum in the 11-year cycle, large CHs and PF exhibit a sequential motion from heliolatitudes of 40°–50° to the polar region and form a series of discrete chains with a periodicity of 1.25 ± 0.3 years in the 21st cycle. The magnetic field in CH chains corresponds to the trailing polarity of spot groups of this cycle. The anomaly of the 23rd cycle at high latitudes manifested itself in a break of the aforesaid periodicity in the N-hemisphere by the formation of a discontinuity between the second and third chains with a duration of three years. This shifted the beginning of the next 24th cycle by three years.

Long-term temporal variations in the areas of sunspot groups

Recently, ħ0125protectJavaraiah2012a) analyzed the combined Greenwich and Solar Optical Observing Network (SOON) sunspot group data during the period 1874–2011 and studied variations in the annual numbers (counts) of the small (maximum area AM<100 millionth of solar hemisphere, msh), large (100⩽AM<300msh), and big (AM⩾300msh) sunspot groups. Here that analysis is extended and studied variations in the mean maximum sizes (the mean values of maximum areas) of the aforementioned three classes of sunspot groups and also their combination. It is found that there is no significant correlation between the mean maximum size of any class of sunspot groups and the International Sunspot Number (RZ), probably due to in a given time interval small sunspot groups/sunspots outnumber the large ones. A pattern of an approximate 9-year period cycle is seen in the variations of the mean maximum sizes of the large and the big sunspot groups during a solar cycle. On long-time scales it is found that there exists a strong 130 or more years cycle in the variation of the mean size of the small sunspot groups, whereas there is a hint on the existence of ≈44-year cycles in the variations of the mean maximum sizes of the large and the big sunspot groups. During the decline phase of cycle 23, there was a scarcity in the sunspot groups whose AM⩽37msh, which may be related to the slow growth of sunspot groups during this period. During the minimum between cycles 23 and 24 may be due to the presence of a number of small sunspot groups whose AM>37 was larger than that of whose AM⩽37, the relatively large size coronal holes were present at low-latitudes and the total solar irradiance was very low.

The Whole Heliosphere Interval in the Context of a Long and Structured Solar Minimum: An Overview from Sun to Earth

Throughout months of extremely low solar activity during the recent extended solar-cycle minimum, structural evolution continued to be observed from the Sun through the solar wind and to the Earth. In 2008, the presence of long-lived and large low-latitude coronal holes meant that geospace was periodically impacted by high-speed streams, even though solar irradiance, activity, and interplanetary magnetic fields had reached levels as low as, or lower than, observed in past minima. This time period, which includes the first Whole Heliosphere Interval (WHI 1: Carrington Rotation (CR) 2068), illustrates the effects of fast solar-wind streams on the Earth in an otherwise quiet heliosphere. By the end of 2008, sunspots and solar irradiance had reached their lowest levels for this minimum (e.g., WHI 2: CR 2078), and continued solar magnetic-flux evolution had led to a flattening of the heliospheric current sheet and the decay of the low-latitude coronal holes and associated Earth-intersecting high-speed solar-wind streams. As the new solar cycle slowly began, solar-wind and geospace observables stayed low or continued to decline, reaching very low levels by June – July 2009. At this point (e.g., WHI 3: CR 2085) the Sun–Earth system, taken as a whole, was at its quietest. In this article we present an overview of observations that span the period 2008 – 2009, with highlighted discussion of CRs 2068, 2078, and 2085. We show side-by-side observables from the Sun’s interior through its surface and atmosphere, through the solar wind and heliosphere and to the Earth’s space environment and upper atmosphere, and reference detailed studies of these various regimes within this topical issue and elsewhere.

Polar magnetic fields and coronal holes during the recent solar minima

AbstractThe slow decline of solar Cycle 23 combined with the slow rise of Cycle 24 resulted in a very long period of low magnetic activity during the years 2007–2009 with sunspot number reaching the lowest level since 1913. This long solar minimum was characterized by weak polar magnetic fields, smaller polar coronal holes, and a relatively complex coronal morphology with multiple streamers extending to mid latitudes. At the same time, low latitude coronal holes remained present on the Sun until the end of 2008 modulating the solar wind at the Earth in co-rotating, fast solar wind streams. This magnetic configuration was remarkably different from the one observed during the previous two solar minima when coronal streamers were confined near the equator and the fast solar wind was mainly originating from the large coronal holes around the Sun's poles. This paper presents the evolution of the polar magnetic fields and coronal holes during the past minimum, compare it with the previous minima, and discuss the implications for the solar wind near the Earth. It also considers the minimum of Cycle 23 in an historical perspective and, in particular, compares it to the long minima at the turn of the 19th century.

Rolling motion in erupting prominences observed by STEREO

We analyze the large-scale dynamical forms of three erupting prominences (filaments) observed by at least one of the two STEREO spacecraft and which reveal evidence of sideways rolling motion beginning at the crest of the erupting filament. We find that all three events were also highly non-radial and occurred adjacent to large coronal holes. For each event, the rolling motion and the average non-radial outward motion of the erupting filament and associated CME were away from a neighboring coronal hole. The location of each coronal hole was adjacent to the outer boundary of the arcade of loops overlying the filaments. The erupting filaments were all more non-radial than the CMEs but in the same general direction. From these associations, we make the hypothesis that the degree of the roll effect depends on the level of force imbalances inside the filament arcade related to the coronal hole and the relative amount of magnetic flux on each side of the filament, while the non-radial motion of the CME is related to global magnetic configuration force imbalances. Our analyses of the prominence eruption best observed from both STEREO-A and STEREO-B shows that its spine retained the thin ribbon-like topology that it had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption.

Solar geoeffective phenomena: Impact on the near-Earth space and the opportunity to forecast

the state of near-Earth space (NES) are extremely large flare events and coronal holes. We attribute to the class of flare phenomena solar flares with a complete spectrum of dynamic manifestations of the mass motion and radiation in all ranges of the electromagnetic spectrum as well as solar filament eruptions with all accompanying phenomena. The possibility to predict geoeective solar phenomena and their eects on NES is based on the analysis of correlations: emergence of new magnetic fluxes in the solar atmosphere, their physical characteristics, and the character of their interaction with the already present magnetic field; time distribution of large flares within active regions; temporal and spatial distribution of solar filament eruptions; formation, distribution, and evolution of solar coronal holes (CH). The agents causing NES disturbances are transient structures: coronal mass ejections, which result from active processes in flares and filament eruptions; high-speed flows of solar plasma following a shock wave from large solar flares and solar filament eruptions or outflowing from regions with an open magnetic configuration. Prediction for the beginning of NES disturbances and of their duration is possible for a period from 1 to 5 days and for coronal holes for a period of one solar revolution (27.3 days). This makes possible planning various technological, biological, and medical experiments together with protective measures for the team and instruments of space laboratories. INDEX TERMS: 7536 Solar Physics, Astrophysics, and Astronomy: Solar activity cycle; 7899 Space Plasma Physics: General or miscellaneous; 7974 Space Weather: Solar eects; 7984 Space Weather: Space radiation environment; KEYWORDS: Solar geoeective phenomena, near-Earth space, forecasting, cyclicity of solar activity.

The Solar Eclipse of 2006 and the Origin of Raylike Features in the White‐Light Corona

Solar eclipse observations have long suggested that the white-light corona is permeated by long fine rays. By comparing photographs of the 2006 March 29 total eclipse with current-free extrapolations of photospheric field measurements and with images from the Solar and Heliospheric Observatory (SOHO), we deduce that the bulk of these linear features fall into three categories: (1) polar and low-latitude plumes that overlie small magnetic bipoles inside coronal holes, (2) helmet streamer rays that overlie large loop arcades and separate coronal holes of opposite polarity, and (3) pseudostreamer rays that overlie twin loop arcades and separate coronal holes of the same polarity. The helmet streamer rays extend outward to form the plasma sheet component of the slow solar wind, while the plumes and pseudostreamers contribute to the fast solar wind. In all three cases, the rays are formed by magnetic reconnection between closed coronal loops and adjacent open field lines. Although seemingly ubiquitous when seen projected against the sky plane, the rays are in fact rooted inside or along the boundaries of coronal holes.

Introduction to special section on corotating solar wind streams and recurrent geomagnetic activity

[1] This special section of the Journal of Geophysical Research (Space Physics) is devoted to research papers on corotating solar wind streams, corotating interaction regions (CIRs), and many facets of the associated recurrent geomagnetic storms and/or activity. The topics cover the physics related to these events at the Sun all the way to their effects in the Earth’s ionosphere. This portion of space weather is complementary to the interplanetary and geomagnetic activity produced by solar flares and/or coronal mass ejections (CMEs), which occur most predominantly during the maximum sunspot phase of the solar cycle. Collisionless shocks ahead of fast interplanetary CMEs (ICMEs) accelerate energetic protons and higher Z ions to flux levels that can be hazardous to satellites and to humans in space. ICMEs and their upstream plasma sheaths cause intense and dramatic magnetic storms and auroras noted at Earth. On the other hand, high-speed streams associated with large coronal holes occur predominantly in the declining and minimum phases of the solar cycle. The interaction of the high-speed streams with upstream (further from the Sun) slow-speed streams leads to the formation of the magnetic compression regions called CIRs. Collisionless shocks typically form at CIR boundaries at distances greater than 1.5 to 2.0 AU from the Sun, so energetic particle radiation formed at these (corotating) shocks is not a hazard at Earth. CIR interactions with the Earth’s magnetosphere are gentler and produces only weak to moderate intensity magnetic storms. [2] The history of recurrent magnetic storms and their solar origin is a long one and goes back for more than a century. Maunder [1904] noted a strong 27 day recurrence in geomagnetic activity and speculated that this could be caused by particle streams emanating from the Sun. Chree [1912, 1913] was the first to quantitatively establish a 27 day quasi-periodicity in geomagnetic activity using a superposed epoch method of analyses (this is the origin of what we now call ‘‘Chree analyses’’). Bartels [1934], not being able to observe any obvious solar features that could be responsible for the recurrent storms, suggested that these ‘‘time patterns’’ were caused by unseen ‘‘M-regions’’ on the Sun (M stood for ‘‘magnetically active’’). Later, beginning in the space age, knowledge of the cause of these storms and their effects accelerated rapidly. Direct, in situ, measurements of the time variability of the solar wind were first made by Mariner 2, which revealed a 27-day modulation of the solar wind speed [Snyder et al., 1963; Neugebauer and Snyder, 1966]. Krieger et al. [1973] demonstrated that the source of these high-speed streams were ‘‘coronal holes’’ [Altschuler and Perry, 1972; Munro and Withbroe, 1972]. Coronal holes are detectable in soft X rays and not in visible light, thus solving what Bartels’ mysterious M-regions were. These coronal hole streams, or some facet of them, were clearly the cause of the recurrent geomagnetic activity at Earth [Sheeley et al., 1976]. For the reader interested in more details concerning the early history of this subject, we recommend the comprehensive Chapman and Bartels [1940] books and the references therein. An abridged and more recent historical account is given by Crooker and Cliver [1994]. [3] As previously mentioned, the high-speed solar wind streams do not simply propagate unimpeded to the Earth, but interact with upstream slower speed streams to form CIRs [Smith and Wolfe, 1976]. The antisunward portions of CIRs are compressed and accelerated slow stream plasma and the sunward portions are compressed and decelerated high-speed stream plasma [Pizzo, 1985]. It is the CIRs that cause recurrent magnetic storm main phases [Tsurutani et al., 1995]. These recurrent magnetic storms are unique in that their ‘‘recovery’’ phases are exceptionally long, lasting from many days to weeks. These storm phases occur within the high speed streams characterized by large amplitude Alfven waves. It has been shown that the southward component of the Alfven waves leads to magnetic reconnection with magnetopause magnetic fields. The latter results in bursts of plasma injections into the magnetosphere sustaining the storm ‘‘recoveries’’ [Soraas et al., 2004]. The resultant geomagnetic activity is called high-intensity, longduration continuous AE activity or HILDCAAs [Tsurutani and Gonzalez, 1987, 1997]. It has been argued that at times, more solar wind energy is introduced into the magnetoJOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, A07S00, doi:10.1029/2006JA011745, 2006 Click Here for Full Article

Simple Magnetic Flux Balance as an Indicator of Ne viii Doppler Velocity Partitioning in an Equatorial Coronal Hole

We present a novel investigation into the relationship between simple estimates of magnetic flux balance and the Ne VIII Doppler velocity partitioning of a large equatorial coronal hole observed by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer (SUMER) on the Solar and Heliospheric Observatory (SOHO) in November 1999. We demonstrate that a considerable fraction of the large scale Doppler velocity pattern in the coronal hole can be qualitatively described by simple measures of the local magnetic field conditions, i.e., the relative unbalance of magnetic polarities and the radial distance required to balance local flux concentrations with those of opposite polarity.

Large-scale activity in solar eruptive events of October–November 2003 observed from SOHO/EIT data

Large-scale solar disturbances associated with powerful flares and coronal mass ejections (CMEs) during two passages of a grand system of three active regions in October–November 2003 are analyzed using data obtained with the SOHO/EIT EUV telescope. Dimmings (transient coronal holes) and, to a lesser extent, coronal waves (traveling emitting fronts) are studied using fixed-difference derotated images, in which a correction for the solar rotation is applied and a single heliogram preceding the event is subtracted from all subsequent heliograms. This method allows us to study difference heliograms in both the 195 A line (with an interval of 12 min) and the various-temperature channels of 171, 195, 284, and 304 A (with an interval of six hours). Our analysis shows, in particular, that the disturbances associated with CMEs demonstrated a global character and occupied almost the entire southern half of the disk in virtually all eruptive events during the two solar rotations. At the same time, the northern half of the disk, which had a large coronal hole, was only slightly disturbed. The dominant dimmings were observed on the disk as narrow, long features stretched mainly between three main, well-separated regions of the system and as long structures located along lines of solar latitude in the south polar sector. For repetitive events with intervals between them being not so long, the dominant dimmings demonstrated a clear homology in their forms and locations. During the very powerful event of October 28, one homologous global set of dimmings changed to another set. Many dimmings were observed to be identical or very similar in the three coronal channels and the transition-region line. It follows from the analysis that rapidly recovering global structures in the corona and transition region were involved in the eruption of running CMEs and the corresponding reconstruction of the large-scale magnetic fields.