Geometric properties of the coronal neutral surface

The interrelation between the density inhomogeneity and the magnetic field configuration in the solar corona has been studied. The situation of consistency with the regular cellular magnetic field organization, established by the authors based on polarization data, and helmet-shaped coronal structures has been analyzed. Consistency was found when coronal helmets appeared as projections on the plane of the sky of dense layer folds. It turned out that a dense layer on a regularly deformed neutral surface on a scale of 60° generates coronal shapes typical of solar activity minimum epochs. Threby, a weighty argument for the Molodenskii hypothesis that a dense layer is formed on the neutral surface has been obtained and it has been determined that one can find the 3D geometry of the coronal neutral surface based on modeling the visible shape of coronal helmets. The study of this geometry based on the observed coronal structures in the epoch of minimum and low solar activity indicated that the neutral surface longitudinal deformation scale remains stable and the surface latitudinal amplitude at the corona base reaches 50°–70° latitudes and tends to increase with increasing solar activity. This amplitude decreases as a power function with a variable index close to ?1 with increasing distance from the Sun. In addition, a 10° small-scale deformation of the studied surface with a predominant latitudinal flexure direction has been revealed.     

Magnetic fields in a limb flare on July 19, 2012

The magnetic field intensity in the limb solar flare of July 19, 2012, was measured by the Zeeman bisector splitting in the H _α line. An average magnetic field is established to attain 200 G at a measurement error of ±100 G in the top of a radiant flare loop at a height of about 40 Mm. The confinement of a strong magnetic field in the high coronal arcade at a relatively weak external field of the corona (about 1–2 G) is considered using a model of a force-free magnetic flux rope with a fine magnetic structure at a scale of about 300 km.     

Height stratification and polar reversal of the Sun’s magnetic fields in cycles 21–23

Using calculations of the magnetic field in the solar atmosphere in the potential approximation, it is shown that, (1) as distance R from the Sun’s center grows, the area of the positive magnetic field (S _+field) in 10-deg latitude zones tends to 100% (0%) in the neighborhood of the solar minimum. At the distance R = 2.5R _⊙(R _⊙ is the solar radius), these values of the positive field are observed during ≈(12–55) Carrington rotations (CRs) for solar minima between neighboring cycles; (2) polar magnetic field reversals can occur repeatedly. Note that a polar reversal at large heights ends by 6–16 Carrington rotations earlier than on the Sun’s surface. On the Sun’s surface, a field polar reversal begins earlier at lower latitudes than at high ones; (3) for each longitude at different Rs and separately for each solar hemisphere the radial component of the field was averaged on synoptic maps in the 0°–40° latitude range. It is established that the T _R rotation periods of the boundaries between the sectors (areas of longitudes with the same sign of the averaged field) can be shorter than, longer than, and equal to Carrington solar rotation period T _CR. It turned out that boundaries with T _R < T _CR are observed at all heights, while boundaries with T _R > T _CR are observed at relatively small heights.     

Diagnostics of solar wind streams and their sources in the solar corona

The studies are based on the experimental mass sounding of the interplanetary plasma near the Sun at radial distances of R = 4−70 R _S, performed at Pushchino RAO, Russian Academy of Sciences, and on the calculated magnetic fields in the solar corona based on the magnetic field strength and structure measured on the Sun’s surface at J. Wilcox Solar Observatory, United States. The experimental data make it possible to localize the position of the boundary closest to the Sun of the transition transonic region of the solar wind in the near-solar space (R ≈ 10−20 R _S) and to perform an interrelated study of the solar wind structure and its sources, namely, the magnetic field components in the solar corona based on these data. An analysis of the evolution of the flow types in 2000–2007 makes it possible to formulate the physically justified criterion responsible for the time boundaries of different epochs in the solar activity cycle.     

Forecast of the solar wind velocity and the interplanetary magnetic field radial component polarity at the phase of decay of solar cycle 23

The solar wind velocity and polarity of the B _x-component of the interplanetary magnetic field have been analyzed for the first eight months of 2005. The interplanetary magnetic field had a four-sector structure, which persisted during nine Carrington rotations. Three stable clusters of a high-speed solar wind stream and one cluster of a low-speed stream were observed during one solar rotation. These clusters were associated with the interplanetary magnetic field sectors. The predicted solar wind velocity was calculated since July 2005 one month ahead as an average over several preceding Carrington rotations. The polarity of the B _x-component of the interplanetary magnetic field was predicted in a similar way based on the concept of the sector structure of the magnetic field and its relation to maxima of the solar wind velocity. The results indicate a satisfactory agreement of the forecast for two rotations ahead in July–August 2005 and pronounced violation of agreement for the next rotation due to a sudden reconfiguration of the solar corona and strong sporadic processes in September 2005.     

Reconstruction of a Hundred Years Series of Solar Filaments from Daily Observational Data

The preliminary results of solar filaments distinguished in daily H-alpha observations at Kodaikanal (1912–2002) are presented. To mark the boundaries of solar filaments, methods based on automated procedures of marking low-contrast objects on the solar disk, as well as editing of the marked boundaries in a semiautomated manner, were developed. The characteristics of solar filaments were analyzed. Latitudinal diagrams of filaments number in 15–23 activity cycles were constructed. As is shown, one maximum in the filament latitudinal distribution may be clearly distinguished during activity cycles in both hemispheres. This maximum is located slightly higher (θ ~ 25°–30°) than the sunspot distribution maximum (θ ~ 14°–17°). However, there are no other local maxima related to the zonal structure of the large-scale magnetic field (Makarov and Sivaraman, 1989).     

Streamer belt in the solar corona and the Earth’s orbit

It has been indicated that the cross section of the streamer belt in the solar corona and its extension in the heliosphere—heliospheric plasma sheet (HPS)—have the form of two radially oriented closely located (at a distance of d ≈ 2.0–2.5° in the heliocentric coordinate system) rays with increased and generally different densities. The angular dimensions of the rays are ≈d. The neutral line of the magnetic field in the corona and the related sector boundary in the Earth’s orbit are located between the peaks of densities of these two rays. In the events, during which the true sector boundary coincides with the heliospheric current sheet, the transverse structure of the streamer belt in the heliosphere (or the HPS structure) is quasistationary; i.e., this structure slightly changes when the solar wind moves from the Sun to the Earth in, at least, 50% of cases. A hypothesis that a slow solar wind, flowing in the rays with increased density of the streamer belt, is probably generated on the Sun’s surface rather than at the top of the helmet, as was assumed in [Wang et al., 2000], is put forward.     

Dynamics of the ionospheric electric currents and auroral luminosity boundaries during strong magnetic storms

The regularities in the southward drift of the ionospheric current centers and luminosity boundaries during strong magnetic storms of November 2003 and 2004 (with Dst ≈ ?400 and ?470 nT, respectively) are studied based on the global geomagnetic observations and TV measurements of auroras. It has been indicated that the eastward and westward electrojets in the dayside and nightside sectors simultaneously shift equatorward to minimal latitudes of Φ _min ^° ～53°–55°. It has been obtained that the Φ _min ^° latitude decreases with increasing negative values of Dst, IMF B _z component, and westward electric field strength in the solar wind. The dependence of the electrojet equatorward shift velocity (V _av) on the rate of IMF B _z variations (ΔB _z /Δt) has been determined. It is assumed that the electrojet dynamics along the meridian is caused by a change in the structure of the magnetosphere and electric fields in the solar wind and the Earth’s magnetosphere.     

Quantifying and specifying the solar influence on terrestrial surface temperature

This investigation is a follow-up of a paper in which we showed that both major magnetic components of the solar dynamo, viz. the toroidal and the poloidal ones, are correlated with average terrestrial surface temperatures. Here, we quantify, improve and specify that result and search for their causes.We studied seven recent temperature files. They were smoothed in order to eliminate the Schwabe-type (11 years) variations. While the total temperature gradient over the period of investigation (1610–1970) is 0.087 °C/century; a gradient of 0.077 °C/century is correlated with the equatorial (toroidal) magnetic field component. Half of it is explained by the increase of the Total Solar Irradiance over the period of investigation, while the other half is due to feedback by evaporated water vapour. A yet unexplained gradient of ?0.040 °C/century is correlated with the polar (poloidal) magnetic field. The residual temperature increase over that period, not correlated with solar variability, is 0.051 °C/century. It is ascribed to climatologic forcings and internal modes of variation.We used these results to study present terrestrial surface warming. By subtracting the above-mentioned components from the observed temperatures we found a residual excess of 0.31° in 1999, this being the triangularly weighted residual over the period 1990–2008.We show that solar forcing of the ground temperature associated with significant feedback is a regularly occurring feature, by describing some well observed events during the Holocene.     

Solar-terrestrial storm of November 18–20, 2003. 1. Near-Earth disturbances in the solar wind

The structure, configuration, dynamics, and solar sources of the near-Earth MHD disturbance of the solar wind on November 20, 2003, is considered. The disturbances of October 24 and November 22 after flares from the same AR 10484 (10501) are compared. The velocity field in the leading part of the sporadic disturbance is for the first time studied in the coordinate system stationary relative to the bow shock. A possible scenario of the physical processes in the course of this solar-terrestrial storm is discussed in comparison with the previously developed scenario for the storm of July 15, 2000. It has been indicated that (1) the near-Earth disturbance was observed at the sector boundary (HCS) and in its vicinities and (2) the disturbance MHD structure included: the complicated bow shock, wide boundary layer with reconnecting fields at a transition from the shock to the magnetic cloud, magnetic cloud with a magnetic cavity including packed substance of an active filament, and return shock layer (supposedly). It has been found out that the shock front configuration and the velocity field are reproduced at an identical position of AR and HCS relative to the Earth on November 20 and 24. It has been indicated that the maximal magnetic induction in the cloud satisfied the condition B _m = (8πn ₁ m _p)^1/2(D ? NV₁), i.e., depended on the dynamic impact on the cloud during all three storms [Ivanov et al., 1974]. When the disturbance was related to solar sources, the attention has been paid to the parallelism of the axes of symmetry of the active filament, transient coronal hole, coronal mass ejection, zero line of the open coronal field (HCS), and the axis of the near-Earth magnetic cloud: the regularity previously established in the scenario of the storm of July 15, 2000 [Ivanov et al., 2005]. It has been indicated that the extremely large B _m value in the cloud of October 20 was caused by a strong suppression of the series of postflare shocks reflected from the heliospheric streamer.     

Magnetic field dynamics based on SOHO/MDI data in the region of flares related to halo coronal mass ejections

Variations in the photospheric magnetic field in the region of solar flares, related to halo coronal mass ejections (HCMEs) with velocities V > 1500, 1000 < V < 1500, and V < 650 km/s, have been studied based on SOHO/MDI data. Using data with a time resolution of 96 min, it has been indicated that on average the ??B _L?? and ??|B _L|?? field characteristics increase nonmonotonically during 1?C1.5 days before a flare and decrease during 0.5?C1 days after a flare for groups of ejections with V > 1000 km/s for all considered HCME groups. Angle brackets designate averaging of the measured B _L magnetic field component and its magnitude |B _L| within an area with specified dimensions and the center coincident with the projection onto the region where the flare center field is measured. It has been established that a solar flare related to an HCME originates when the ??B _L?? and ??|B _L|?? values are larger than the boundary values in the flare region. Based on 1-min data, it has been found for several HCMEs with V > 1500 km/s that the beginning of powerful flares related to ejections is accompanied by rapid impulsive or stepped variations in ??B _L?? and ??|B _L|?? near the center of a flare with a size of approximately 4.5°. It has been established that the HCME velocity positively correlates with the |??B _L??| value at the flare onset.     

Are geostrophic and quasi-geostrophic approximations valid in Venus’ differential super-rotation?

Geostrophic dynamics in the horizontally differential super-rotation of Venus are examined using f_A (the Coriolis parameter defined by the angular velocity of a basic flow in an inertial frame) and Γ (the differential rotation parameter defined by the latitudinal gradient of the angular velocity) under the conditions that vertical shear of the basic field is not considered and the intrinsic phase velocity has a magnitude comparable to that of an eddy horizontal flow. The geostrophic and quasi-geostrophic approximations are valid in the regions of weakly differential and rigid-body super-rotations; however, they are invalid in the regions of strongly differential super-rotation even when the Rossby number R _O is sufficiently smaller than unity for synoptic eddies. In a general circulation model of a Venus-like atmosphere, the horizontal divergence that results from the strong differential cannot be ignored over a wide range within latitudes ±60° and below 60?km elevation because of large Γ/f_A (≥1/2).     

New method for separating K- and F-corona brightness based on LASCO/SOHO data

A relatively simple (in technology) method for separating K- and F-corona brightness based on LASCO data, which makes it possible to obtain the latitude distribution of this brightness in the field of view of the LASCO C2 and C3 coronographs at any instant for which white light corona images are available, has been proposed. It has been estimated that the error in determining K-corona brightness varies from 20 to 50% at distances of R ≤ 6R _⊙ (R _⊙ is the solar radius). At distances of R > (5–6)R _⊙, the accuracy of the K-corona brightness determination decreases and is of an estimative character. Nevertheless, it is often possible to trace the brightest coronal rays and the K-corona regions of decreased brightness (including such regions in coronal holes) to distances of R ≈ 15R _⊙ and 25–30R _⊙ for some events. This makes it possible to estimate and compare electron densities in different coronal structures to large distances. Examples of method testing are presented. For the first time, we have managed to obtain continuous (in latitude) distributions of K- and F-corona brightness, using this method.     

Experimental investigation of reaction coronas on olivine in Apollo 14 high-grade breccias

Reaction coronas of pyroxene ± ilmenite occur around clasts of olivine in Apollo 14 high-grade metamorphic breccias. In experiments of several months duration, there was no evidence of corona formation at 1000°C, but at 1050°, withfO₂ at or above Ilm-Ru-Fe and below Fe-Fe₁?x O, incipient coronas formed around Fo_50–70 in synthetic 14311 matrix. In addition, withfO₂ controlled by Ilm-Ru-Fe at 1050°C, the olivines reduced to Fo₆₈, En₆₉ + Fe. Reduction of olivine under these conditions is inconsistent with the calculated stability relations and is attributed to uncertainties in the activity coefficient for olivine or pyroxene. The experiments also suggest that vesicularity in the Apollo 14 high-grade breccias may correlate with the amount of glassy material in their unmetamorphosed precursors. The metamorphic event is attributed to burial in a hot ejecta blanket, such as that of the Imbrium event.     

Probing the magnetic topology of coronal mass ejections by means of Ulysses/HI-SCALE energetic particle observations

In this work, solar flare energetic particle fluxes (E_e 42 keV) observed by the HI-SCALE instrument onboard Ulysses, a spacecraft that is probing the heliosphere in 3-D, are utilized as diagnostics of the large-scale structure and topology of the interplanetary magnetic field (IMF) embedded within two well-identified interplanetary coronal mass ejection (ICME) structures. On the basis of the energetic solar flare particle observations firm conclusions are drawn on whether the detected ICMEs have been detached from the solar corona or are still magnetically anchored to it when they arrive at 2.5 AU. From the development of the angular distributions of the particle intensities, we have inferred that portions of the ICMEs studied consisted of both open and closed magnetic field lines. Both ICMEs present a filamentary structure comprising magnetic filaments with distinct electron anisotropy characteristics. Subsequently, we studied the evolution of the anisotropies of the energetic electrons along the magnetic field loop-like structure of one ICME and computed the characteristic decay time of the anisotropy which is a measure of the amount of scattering that the trapped electron population underwent after injection at the Sun.     

Observations of neutral hydrogen in the corona

Measurements of the linear polarization degree (p) of the emission in the inner corona (<1.5 R _⊙) in the green and red continuum ranges are discussed. “Excess p” (Δp = pgreen — pred), which reaches its maximum at 1.2–1.3 R _⊙ (<5%) in the polar regions and 20% within large-scale streamers, is present everywhere in the corona. It has been mentioned that excess p can be explained by the presence of neutral hydrogen in the corona.     

Global electron content during solar cycle 23

Global electron content (GEC) as a new ionospheric parameter was first proposed by Afraimovich et al. [2006]. GEC is equal to the total number of electrons in the near-Earth space. GEC better than local parameters reflects the global response to a change in solar activity. It has been indicated that, during solar cycle 23, the GEC dynamics followed similar variations in the solar UV irradiance and F _10.7 index, including the 11-year cycle and 27-day variations. The dynamics of the regional electron content (REC) has been considered for three belts: the equatorial belt and two midlatitude belts in the Northern and Southern hemispheres (±30° and 30°–65° geomagnetic latitudes, respectively). In contrast to GEC, the annual REC component is clearly defined for the northern and southern midlatitude belts; the REC amplitude is comparable with the amplitude of the seasonal variations in the Northern Hemisphere and exceeds this amplitude in the Southern Hemisphere by a factor of ～1.7. The dayside to nightside REC ratio, R(t), at the equator is a factor of 1.5 as low as such a GEC ratio, which indicates that the degree of nighttime ionization is higher, especially during the solar activity maximum. The pronounced annual cycle with the maximal R(t) value near 8.0 for the winter Southern Hemisphere and summer Northern Hemisphere is typical of midlatitudes.     

Source Characteristics of the 22 January 2003 M w?=?7.5 Tecom��n, Mexico, Earthquake: New Insights

Aftershock locations, source parameters and slip distribution in the coupling zone between the overriding North American and subducted Rivera and Cocos plates were calculated for the 22 January 2003 Tecomán earthquake. Aftershock locations lie north of the El Gordo Graben with a northwest-southeast trend along the coast and superimposed on the rupture areas of the 1932 (M _w?=?8.2) and 1995 (M _w?=?8.0) earthquakes. The Tecomán earthquake ruptured the northwest sector of the Colima gap, however, half of the gap remains unbroken. The aftershock area has a rectangular shape of 42?±?2 by 56?±?2?km with a shallow dip of roughly 12° of the Wadati-Benioff zone. Fault geometry calculated with the Náb??lek (1984) inversion procedure is: (strike, dip, rake)?=?(277°, 27°, 78°). From the teleseimic body wave spectra and assuming a circular fault model, we estimated source duration of 20?±?2?s, a stress drop of 5.4?±?2.5?MPa and a seismic moment of 2.7?±?.7?×?10²⁰?Nm. The spatial slip distribution on the fault plane was estimated using new additional near field strong motion data (54?km from the epicenter). We confirm their main conclusions, however we found four zones of seismic moment release clearly separated. One of them, not well defined before, is located toward the coast down dip. This observation is the result of adding new data in the inversion. We calculated a maximum slip of 3.2?m, a source duration of 30?s and a seismic moment of 1.88?×?10²⁰?Nm.     

On the formation mechanism of the sporadic solar wind

In this paper, we examine the nature of the main source of the sporadic solar wind on the Sun: coronal mass ejections (CMEs). Analysis of data from Mark 3 and Mark 4, the Digital Prominence Monitor (MLSO), and STEREO (EUVI) spacecraft has revealed the existence of two types of CMEs: gradual and impulse. They differ in the place, velocity, and angular size at the instant of their emergence. The source of gradual CMEs is located in the corona, at a distance of 1.1 R ₀ < R ≤ 1.7 R ₀ from the center of the Sun. They start moving from a state of rest, having an angular size ≈15–65° (in the heliographic coordinate system). Impulse CMEs are probably formed under the Sun’s photosphere. This may be due to the supersonic emergence of magnetic tubes (ropes) from the convective zone. The possibility of this phenomenon has been demonstrated earlier in theory. The radial velocity of such tubes at the photospheric level may be 100 km/s or higher; the minimum angular size is ∼1°.     

Beginning of the new solar cycle (cycle 24) in the large-scale open solar magnetic field

It is proposed to determined minimums of the 11-year solar cycles based on a minimal flux of the large-scale open solar magnetic field. The minimal fluxes before the finished cycle 23 (Carrington rotation CR 1904) and the started cycle 24 (CR 2054, April 2007) were equal to 1.8 × 10²² and 1.2 × 10²² μs, respectively. The long-term tendency toward an approach to a deep minimum of solar activity is confirmed. On the assumption that magnetic flux variations from minimums to maximums are proportional to each other, the anticipated value of the maximal Wolf number during cycle 24 is estimated as W _max = 80.