Central Meridian Research Articles

Enhancing adaptive composite map projections: Wagner transformation between the Lambert azimuthal and the transverse cylindrical equal-area projections

ABSTRACTThe adaptive composite map projection technique changes the projection to minimize distortion for the geographic area shown on a map. This article improves the transition between the Lambert azimuthal projection and the transverse equal-area cylindrical projection that are used by adaptive composite projections for portrait-format maps. Originally, a transverse Albers conic projection was suggested for transforming between these two projections, resulting in graticules that are not symmetric relative to the central meridian. We propose the alternative transverse Wagner transformation between the two projections and provide equations and parameters for the transition. The suggested technique results in a graticule that is symmetric relative to the central meridian, and a map transformation that is visually continuous with changing map scale.

Cовершенствование математических моделей проекции Гаусса – Крюгера для вычисления плоских прямоугольных координат по геодезическим координатам

Algorithms with improved convergence for the calculation of rectangular coordinates in the Gauss – Kruger coordinate system according to the parameters of any ellipsoid were designed. The approach of definition the spherical components in the classic series defined variables x, y, represented by the difference between the degrees of longitude l, followed by the replacement of their sums by formulas of spherical trigonometry. For definition of the amounts of spherical components of the relevant decompositions patterns of transverse-cylindrical sphere plane projection in the condition of the initial data equality on the ellipsoid and sphere radius N were used. Analysis of othertransformation methods of classical expansions in series, used in derivation of both logarithmical and non-logarithmical working formulas is carried outfor comparison with developed algorithms. The technique of algorithms development with usage of hyperbolic tangent function, applied by L. Kruger, Yu. Karelin, A. Schödlbauer is considered and their analysis is carried out. Advantages of Krasovskii – Isotov formulas for six-degree strips are pointed out. The usage of the spherical function sin τ in the expansion made it possible not only to obtain a rapidly convergent series, but also to represent the spherical part of the solution of the problem with the help of trigonometric identities in different types. It is proved that derived for the calculation algorithms with the proposed estimates of their accuracy, are optimal in removing points from the central meridian to l ≤ 6°. For the difference of longitudes l > 6°, the expansions of the unknown quantities into Fourier series should be applied. An example of the calculation of coordinates in the system SK-2011 is given. Theoretical studies have been carried out and shortened formulas with a reliability estimate for the determination of coordinates in the area l ≤ 3° have been proposed.

A Database of Flare Ribbon Properties from the Solar Dynamics Observatory. I. Reconnection Flux

Abstract We present a database of 3137 solar flare ribbon events corresponding to every flare of GOES class C1.0 and greater within 45° from the central meridian, from 2010 April until 2016 April, observed by the Solar Dynamics Observatory. For every event in the database, we compare the GOES peak X-ray flux with the corresponding active region and flare ribbon properties. We find that while the peak X-ray flux is not correlated with the active region unsigned magnetic flux, it is strongly correlated with the flare ribbon reconnection flux, flare ribbon area, and the fraction of active region flux that undergoes reconnection. We find the relationship between the peak X-ray flux and the flare ribbon reconnection flux to be . This scaling law is consistent with earlier hydrodynamic simulations of impulsively heated flare loops. Using the flare reconnection flux as a proxy for the total released flare energy E, we find that the occurrence frequency of flare energies follows a power-law dependence: for , consistent with earlier studies of solar and stellar flares. The database is available online and can be used for future quantitative studies of flares.

Statistical analysis of 26 yr of observations of decametric radio emissions from Jupiter

Jupiter is a complex and at the same time very powerful radio source in the decameter wavelength range. The emission is anisotropic, intrinsically variable at millisecond to hour timescales, and also modulated by various external processes at much longer periods, ranging from ~10 h to months or years (including Jovian day and year, solar activity and solar wind variations, and for ground-based observations, terrestrial day and year). As a consequence, long-term observations and their statistical study have proved to be necessary for disentangling and understanding the observed phenomena. We have built a database from the available 26 yr of systematic, daily observations conducted at the Nançay Decameter Array and recorded in digital format. This database contains all observed Jovian decametric emissions, classified with respect to the time-frequency morphology, their dominant circular polarization, and maximum frequency. We present the results of the first statistical analysis of this database. We confirm the earlier classification of Jovian decameter emissions in Io-A, -A′, -B, -C, -D and non-Io-A, -B, -C types, but we also introduce new emission types (Io-A′′ and Io-B′) and precise and characterize the non-Io-D type. We determine the contours of all emission types in the CML− ΦIo plane (Central Meridian Longitude in Jupiter’s System III coordinates versus Io Phase), provide representative examples of their typical time-frequency patterns, and the distribution of emission’s maximum frequency as a function of ΛIo (Io’s Longitude). Finally, we present a statistical analysis of the distributions of the occurrence rate, duration, intensity and polarization for each emission type. non-Io-DAM appears to be related to small-scale, possibly bursty auroral structures.

Small Coronal Holes Near Active Regions as Sources of Slow Solar Wind

Abstract We discuss the nature of the small areas of rapidly diverging, open magnetic flux that form in the strong unipolar fields at the peripheries of active regions (ARs), according to coronal extrapolations of photospheric field measurements. Because such regions usually have dark counterparts in extreme-ultraviolet (EUV) images, we refer to them as coronal holes, even when they appear as narrow lanes or contain sunspots. Revisiting previously identified “AR sources” of slow solar wind from 1998 and 1999, we find that they are all associated with EUV coronal holes; the absence of well-defined He i 1083.0 nm counterparts to some of these holes is attributed to the large flux of photoionizing radiation from neighboring AR loops. Examining a number of AR-associated EUV holes during the 2014 activity maximum, we confirm that they are characterized by wind speeds of ∼300–450 km s−1, O7+/O6+ ratios of ∼0.05–0.4, and footpoint field strengths typically of order 30 G. The close spacing between ARs at sunspot maximum limits the widths of unipolar regions and their embedded holes, while the continual emergence of new flux leads to rapid changes in the hole boundaries. Because of the highly nonradial nature of AR fields, the smaller EUV holes are often masked by the overlying canopy of loops, and may be more visible toward one solar limb than at central meridian. As sunspot activity declines, the AR remnants merge to form much larger, weaker, and longer-lived unipolar regions, which harbor the “classical” coronal holes that produce recurrent high-speed streams.

Ứng dụng tin học vào bài toán chuyển đổi hệ quy chiếu bản đồ số địa hình

Digital map can be established in coordinate systems with different central meridians in diversity of graphic data formats. Therefore, it is necessary to transform the maps into the same identified coordinate system for more effective management and application, especially in the era of international integration. To effectively perform this task, this study generated a software by linking various mudules programed by Visual Basic 6.0 and C++. The program was tested on standard data. Recently, it has been beeing applied in real projects.

Latitude dependence of the solar granulation during the minimum of activity in 2009

Context.Knowledge of the latitude variation of the solar granulation properties (contrast and scale) is useful to better understand interactions between magnetic field, convection, differential rotation, and meridional circulation in the solar atmosphere.Aims.We investigated the latitude dependence of the contrast and scale of the solar granulation, with the help of HINODE/SOT blue continuum images taken in the frame of the HOP 79 program, along the central meridian and along the equator on a monthly basis in 2009 during the last solar minimum of activity.Methods.We selected the sharpest images in latitude and longitude intervals. The selected images in all the N-S and E-W scans taken in 2009 were combined to get statistically reliable results.Results.The contrast of the solar granulation decreases towards the poles and the scale increases, but not regularly since a perturbation occurs at around 60° where both quantities return close to their values at the disk center.Conclusions.Such a latitude variation in a period of minimum of activity (2009), is probably not due to magnetic field, neither the quiet magnetic field at the surface, nor the strong magnetic flux tubes associated with active regions, which could be embedded more or less deeply in the convection zone before they reach the surface. The decrease in contrast and increase in scale towards the pole seem to be related to the differential rotation and the perturbation around 60° to the meridional circulation.

A NEW METHOD TO QUANTIFY AND REDUCE THE NET PROJECTION ERROR IN WHOLE-SOLAR-ACTIVE-REGION PARAMETERS MEASURED FROM VECTOR MAGNETOGRAMS

ABSTRACT Projection errors limit the use of vector magnetograms of active regions (ARs) far from the disk center. In this Letter, for ARs observed up to 60° from the disk center, we demonstrate a method for measuring and reducing the projection error in the magnitude of any whole-AR parameter that is derived from a vector magnetogram that has been deprojected to the disk center. The method assumes that the center-to-limb curve of the average of the parameter’s absolute values, measured from the disk passage of a large number of ARs and normalized to each AR’s absolute value of the parameter at central meridian, gives the average fractional projection error at each radial distance from the disk center. To demonstrate the method, we use a large set of large-flux ARs and apply the method to a whole-AR parameter that is among the simplest to measure: whole-AR magnetic flux. We measure 30,845 SDO/Helioseismic and Magnetic Imager vector magnetograms covering the disk passage of 272 large-flux ARs, each having whole-AR flux >1022 Mx. We obtain the center-to-limb radial-distance run of the average projection error in measured whole-AR flux from a Chebyshev fit to the radial-distance plot of the 30,845 normalized measured values. The average projection error in the measured whole-AR flux of an AR at a given radial distance is removed by multiplying the measured flux by the correction factor given by the fit. The correction is important for both the study of the evolution of ARs and for improving the accuracy of forecasts of an AR’s major flare/coronal mass ejection productivity.

Evolution of the Bochner Laplacian for magnetograms of solar active regions

A search for powerful flare predictors remains a problem of current interest in solar—terrestrial physics. The magnetograms (LOS SDO/HMI instrument) for active regions (ARs) 1158, 1166, 1283, and 1520, which produced an X-ray flare located near the central meridian, are analyzed. АR 1654, which was rather complex but generated only M flares near western limb, remaining quiet during the passage over the disk, has been analyzed in a similar manner for comparison. The combinatorial Bochner Laplacian was used as a complexity descriptor. We calculate it for each magnetogram, which was converted into the magnetic energy density of the longitudinal field component, and analyze its maximal spatial variation. It has been shown that the maximal spatial Laplacian values trace the neutral line during AR evolution, demonstrating sharp peaks before and after the flare in this case. Although this signature has no established statistical reliability, it can be interesting as an effective parameter when flares are predicted.

Latitudinal variability in Jupiter’s tropospheric disequilibrium species: GeH4, AsH3 and PH3

Jupiter’s tropospheric composition is studied using high-resolution, spatially-resolved 5-µm observations from the CRIRES instrument at the Very Large Telescope. The high resolving power (R = 96,000) allows us to spectrally resolve the line shapes of individual molecular species in Jupiter’s troposphere and, by aligning the slit north-south along Jupiter’s central meridian, we are able to search for any latitudinal variability. Despite the high spectral resolution, we find that there are significant degeneracies between the cloud structure and aerosol scattering properties that complicate the retrievals of tropospheric gaseous abundances and limit conclusions on any belt-zone variability. However, we do find evidence for variability between the equatorial regions of the planet and the polar regions. Arsine (AsH3) and phosphine (PH3) both show an enhancement at high latitudes, while the abundance of germane (GeH4) remains approximately constant. These observations contrast with the theoretical predictions from Wang et al. (2016) and we discuss the possible explanations for this difference.

SDO/HMI survey of emerging active regions for helioseismology

Observations from the Solar Dynamics Observatory (SDO) have the potential for allowing the helioseismic study of the formation of hundreds of active regions, which would enable us to perform statistical analyses. Our goal is to collate a uniform data set of emerging active regions observed by the SDO/HMI instrument suitable for helioseismic analysis up to seven days before emergence. We restricted the sample to active regions that were visible in the continuum and emerged into quiet Sun largely avoiding pre-existing magnetic regions. As a reference data set we paired a control region (CR), with the same latitude and distance from central meridian, with each emerging active region (EAR). We call this data set, which is currently comprised of 105 emerging active regions observed between May 2010 and November 2012, the SDO Helioseismic Emerging Active Region (SDO/HEAR) survey. To demonstrate the utility of a data set of a large number of emerging active regions, we measure the relative east-west velocity of the leading and trailing polarities from the line-of-sight magnetogram maps during the first day after emergence. The latitudinally averaged line-of-sight magnetic field of all the EARs shows that, on average, the leading (trailing) polarity moves in a prograde (retrograde) direction with a speed of 121 +/- 22 m/s (-70 +/- 13 m/s) relative to the Carrington rotation rate in the first day. However, relative to the differential rotation of the surface plasma, the east-west velocity is symmetric, with a mean of 95 +/- 13 m/s. The SDO/HEAR data set will not only be useful for helioseismic studies, but will also be useful to study other features such as the surface magnetic field evolution of a large sample of EARs.

Ionospheric response to X-class solar flares in the ascending half of the subdued solar cycle 24

The signature of 11 X-class solar flares that occurred during the ascending half of the present subdued solar cycle 24 from 2009 to 2013 on the ionosphere over the low- and mid-latitude station, Dibrugarh (27.5∘N, 95∘E; magnetic latitude 17.6∘N), are examined. Total electron content (TEC) data derived from Global Positioning System satellite transmissions are used to study the effect of the flares on the ionosphere. A nonlinear significant correlation (R 2 = 0.86) has been observed between EUV enhancement (ΔEUV) and corresponding enhancement in TEC (ΔTEC). This nonlinearity is triggered by a rapid increase in ΔTEC beyond the threshold value ∼1.5 (×1010 ph cm−2 s−1) in ΔEUV. It is also found that this nonlinear relationship between TEC and EUV flux is driven by a similar nonlinear relationship between flare induced enhancement in X-ray and EUV fluxes. The local time of occurrence of the flares determines the magnitude of enhancement in TEC for flares originating from nearly similar longitudes on the solar disc, and hence proximity to the central meridian alone may not play the dominating role. Further, the X-ray peak flux, when corrected for the earth zenith angle effect, did not improve the correlation between ΔX-ray and ΔTEC.

Detailed Analysis of Solar Data Related to Historical Extreme Geomagnetic Storms: 1868 – 2010

An analysis of historical Sun–Earth connection events in the context of the most extreme space weather events of the last $\sim150$ years is presented. To identify the key factors leading to these extreme events, a sample of the most important geomagnetic storms was selected based mainly on the well-known aa index and on geomagnetic parameters described in the accompanying paper (Vennerstrom et al., Solar Phys. in this issue, 2016, hereafter Paper I). This part of the analysis focuses on associating and characterizing the active regions (sunspot groups) that are most likely linked to these major geomagnetic storms. For this purpose, we used detailed sunspot catalogs as well as solar images and drawings from 1868 to 2010. We have systematically collected the most pertinent sunspot parameters back to 1868, gathering and digitizing solar drawings from different sources such as the Greenwich archives, and extracting the missing sunspot parameters. We present a detailed statistical analysis of the active region parameters (sunspots, flares) relative to the geomagnetic parameters developed in Paper I. In accordance with previous studies, but focusing on a much larger statistical sample, we find that the level of the geomagnetic storm is highly correlated to the size of the active regions at the time of the flare and correlated with the size of the flare itself. We also show that the origin at the Sun is most often a complex active region that is also most of the time close to the central meridian when the event is identified at the Sun. Because we are dealing with extremely severe storms, and not the usual severe storm sample, there is also a strong correlation between the size of the linked active region, the estimated transit speed, and the level of the geomagnetic event. In addition, we confirm that the geomagnetic events studied here and the associated events at the Sun present a low probability of occurring at low sunspot number value and are associated mainly with the maximum and descending part of the solar cycle.

Motions and oscillations in a filament preceding its eruption

The Doppler motions in a filament and the underlying photosphere over the several days before its eruption are analyzed. A large filament in the northern hemisphere near the central meridian observed from August 31-September 2, 2014 erupted on September 2, 2014. The filament lost the bulk of its mass as a result of its eruption, and the process of its reconstruction had begun a day later. Observations of this filament in a spectral range encompassing the Hβ λ 486.1 nm (chromospheric) and Fe I λ 485.9 nm (photospheric) lines were carried out on the Horizontal Solar Telescope of the Sayan Solar Observatory on August 31-September 2, 2014. Analysis of the Doppler motions in and beneath the filament yielded the following results. Strong rotational motions were present in the filament over a prolonged period (the entire three days of observations). The coincidence of the steady-state motions of the photosphere and filament was disrupted at the moment of destabilization of the filament by the emergence of new magnetic flux. Short-period (about five-minute) photospheric oscillationswith a train-like character arose in filament from time to time several hours before the eruption. Large segments underwent nearly vertical oscillations in the initial phase of the ascent of the filament.

Method for the determination of the height of a solar filament

A comparison of the actual filament height above the solar photosphere with the limiting height calculated by magnetic data provides information about the filament stability margin and its readiness for eruption. A method is proposed for the determination of the height of solar filaments by a comparison of the position of the upper edge of the filament (spine) with the position of the polarity-inversion line of the potential magnetic field calculated for different heights. The line closest to the filament spine corresponds to its height. Observations of the Solar Terrestrial Relations Observatory (STEREO) spacecraft were used to verify the proposed method when they were at an angular distance of ~90° from the Earth and provided a side view of the filaments near the central meridian in observations from the Earth and near-Earth orbits. The proposed method can be useful in the estimation of the possible geoeffectiveness of filaments on the solar disk.

基于极点到坐标原点的距离函数的常规地图投影分类体系

地球椭球面上的经线交于极点而纬线则相互平行。地图上的经纬网是地球椭球面上的经纬网的拓扑映射。投影网中极点到坐标原点的距离函数关联着7类常规地图投影的分类。距离等于零时对应着方位投影；距离为有限值时对应着圆锥投影和多圆锥投影;距离为无穷大时对应着圆柱投影。方位和伪方位投影的纬线为同心圆；圆锥和伪圆锥投影的纬线为同心圆弧；多圆锥投影的纬线为同轴圆弧；圆柱和伪圆柱投影的纬线为赤道的平行线。所有正常投影的经线均为直线，而伪型投影只有作为投影网对称轴的中央经线是直线，其余经线为中央经线的轴对称曲线。多圆锥投影的经线与伪型投影相同。极点到坐标原点的距离函数，与常规地图投影的分类具有等价关系，从而可以推出常规地图投影的一般定义。 The longitudes of earth ellipsoid intersect at the poles and the latitudes are parallel to each other. The grid of longitudes and latitudes on the map is the topological map of the grid of longitudes and latitudes on earth ellipsoid. The distance function of the poles to the coordinate origin in the pro-jection grid is related to the classification of seven types of routine map projection. When the dis-tance is equal to zero, it is azimuthal projection; when the distance is finite, it is conic projection or polyconic projection; when the distance is infinite, it is cylindrical projection. The latitude of azi-muthal projection and pseudo-azimuthal projection are homocentric circles. The latitude of conic projection and pseudo-conic projection are homocentric circular arc. The latitude of polyconic projection is coaxial arc. The latitude of cylindrical projection and pseudo-cylindrical projection are parallel lines of the equator. All the longitudes of normal projection are straight, while for the pseudo-projection, only the central meridian of symmetry axis of a projection grid is a straight line and the remaining longitudes is the axisymmetric curve of the central longitudes. Meridian of polyconic projection is identical with the pseudo type projection. The distance function of the pole to the coordinate origin is equivalent to the classification of the routine map projection, so that the general definition of routine map projection can be deduced.

Predicting coronal mass ejections transit times to Earth with neural network

Predicting transit times of Coronal Mass Ejections (CMEs) from their initial parameters is a very important subject, not only from the scientific perspective, but also because CMEs represent a hazard for human technology. We used a neural network to analyse transit times for 153 events with only two input parameters: initial velocity of the CME, $v$, and Central Meridian Distance, CMD, of its associated flare. We found that transit time dependence on $v$ is showing a typical drag-like pattern in the solar wind. The results show that the speed at which acceleration by drag changes to deceleration is $v\approx$500 km s$^{-1}$. Transit times are also found to be shorter for CMEs associated with flares on the western hemisphere than those originating on the eastern side of the Sun. We attribute this difference to the eastward deflection of CMEs on their path to 1 AU. The average error of the NN prediction in comparison to observations is $\approx$12 hours which is comparable to other studies on the same subject.

Limb Event Brightenings and Fast Ejection Using IRIS Mission Observations

The Interface Region Imaging Spectrograph (IRIS) of the NASA small explorer mission provides significantly more complete and higher resolution spectral coverage of the dynamical conditions inside the chromosphere and transition region (TR) than has heretofore been available. Near the solar limb high temporal, spatial (0.3") and spectral resolution observations from the ultraviolet IRIS spectra reveal high-energy limb event brightenings (LEBs) at low chromospheric heights, around 1 Mm above the limb. They can be characterized as explosive events producing jets. We selected two events showing spectra of a confined eruption just off or near the quiet Sun limb, the jet part showing obvious moving material with short duration large Doppler shifts in three directions identified as macrospicules on slit-jaw (SJ) images in Si IV and He II 304 A. The events are analyzed from a sequence of very close rasters taken near the central meridian and the South pole limb. The processed SJ images and the simultaneously observed fast spectral sequences having large Doppler shifts, with a pair of red shifted elements together with a faster blue shifted element from almost the same position, are analyzed. Shifts correspond to velocities of up to 100 km/s in projection on the plane of the sky. The occurrence of erupting spicules and macrospicules from these regions is noticed from images taken before and after the spectra. The cool low first ionization potential (FIP) element simultaneous line emissions of the MgII h and k resonance lines do not clearly show a similar signature due to optical thickness effects but the Si IV broad-band SJ images do. The bidirectional plasma jets ejected from a small reconnection site are interpreted as the result of coronal loop-loop interactions leading to reconnection in nearby sites.

Coronal Mass Ejections from the Same Active Region Cluster: Two Different Perspectives

The cluster formed by active regions (ARs) NOAA 11121 and 11123, approximately located on the solar central meridian on 11 November 2010, is of great scientific interest. This complex was the site of violent flux emergence and the source of a series of Earth-directed events on the same day. The onset of the events was nearly simultaneously observed by the Atmospheric Imaging Assembly (AIA) telescope aboard the Solar Dynamics Observatory (SDO) and the Extreme-Ultraviolet Imagers (EUVI) on the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite of telescopes onboard the Solar-Terrestrial Relations Observatory (STEREO) twin spacecraft. The progression of these events in the low corona was tracked by the Large Angle Spectroscopic Coronagraphs (LASCO) onboard the Solar and Heliospheric Observatory (SOHO) and the SECCHI/COR coronagraphs on STEREO. SDO and SOHO imagers provided data from the Earth's perspective, whilst the STEREO twin instruments procured images from the orthogonal directions. This spatial configuration of spacecraft allowed optimum simultaneous observations of the AR cluster and the coronal mass ejections that originated in it. Quadrature coronal observations provided by STEREO revealed a notably large amount of ejective events compared to those detected from Earth's perspective. Furthermore, joint observations by SDO/AIA and STEREO/SECCHI EUVI of the source region indicate that all events classified by GOES as X-ray flares had an ejective coronal counterpart in quadrature observations. These results have direct impact on current space weather forecasting because of the probable missing alarms when there is a lack of solar observations in a view direction perpendicular to the Sun-Earth line.

THE PECULIAR BEHAVIOR OF HALO CORONAL MASS EJECTIONS IN SOLAR CYCLE 24

We report on a remarkable finding that the halo coronal mass ejections (CMEs) in cycle 24 are more abundant than in cycle 23, although the sunspot number in cycle 24 has dropped by about 40%. We also find that the distribution of halo-CME source locations is different in cycle 24: the longitude distribution of halos is much flatter with the number of halos originating at central meridian distance >/=60 degrees twice as large as that in cycle 23. On the other hand, the average speed and the associated soft X-ray flare size are the same in the two cycles, suggesting that the ambient medium into which the CMEs are ejected is significantly different. We suggest that both the higher abundance and larger central meridian longitudes of halo CMEs can be explained as a consequence of the diminished total pressure in the heliosphere in cycle 24 (Gopalswamy et al. 2014). The reduced total pressure allows CMEs expand more than usual making them appear as halos.