An application of the weighted horizontal magnetic gradient to solar compact and eruptive events

We propose to apply the weighted horizontal magnetic gradient (${\mathit{WG}}_M$), introduced in Korsós et al., 2015, for analysing the pre-flare and pre-CME behaviour and evolution of Active Regions (ARs) using the SDO/HMI-Debrecen Data catalogue. To demonstrate the power of investigative capabilities of the ${\mathit{WG}}_M$ method, in terms of flare and CME eruptions, we studied two typical ARs, namely, AR 12158 and AR 12192. The choice of ARs represent canonical cases. AR 12158 produced an X1.6 flare with fast “halo” CME ($v_{\mathit{linear}}$ = 1267 $\text{km}{\text{s}}^{-1}$) while in AR 12192 there occurred a range of powerful X-class eruptions, i.e. X1.1, X1.6, X3.1, X1.0, X2.0 and X2.0-class energetic flares, interestingly, none with an accompanying CME. The value itself and temporal variation of ${\mathit{WG}}_M$ is found to possess potentially important diagnostic information about the intensity of the expected flare class. Furthermore, we have also estimated the flare onset time from the relationship of duration of converging and diverging motions of the area-weighted barycenters of two subgroups of opposite magnetic polarities. This test turns out not only to provide information about the intensity of the expected flare-class and the flare onset time but may also indicate whether a flare will occur with/without fast CME. We have also found that, in the case when the negative polarity barycenter has moved around and the positive one “remained” at the same coordinates preceding eruption, the flare occurred with fast “halo” CME. Otherwise, when both the negative and the positive polarity barycenters have moved around, the AR produced flares without CME. If these properties found for the movement of the barycenters are generic pre-cursors of CME eruption (or lack of it), identifying them may serve as an excellent pre-condition for refining the forecast of the lift-off of CMEs.     

Velocity shear Kelvin-Helmholtz instability with inhomogeneous DC electric field in the magnetosphere of Saturn

In this paper parallel flow velocity shear Kelvin-Helmholtz instability has been studied in two different extended regions of the inner magnetosphere of Saturn. The method of the characteristic solution and kinetic approach has been used in the mathematical calculation of dispersion relation and growth rate of K-H waves. Effect of magnetic field (B), inhomogeneity (P/a), velocity shear scale length ($A_i$), temperature anisotropy ($T_{\perp }/T_{||}$), electric field (E), ratio of electron to ion temperature ($T_e/T_i$), density gradient (${\epsilon }_n{\rho }_i$) and angle of propagation ($\theta$) on the dimensionless growth rate of K-H waves in the inner magnetosphere of Saturn has been observed with respect to $k_{\perp }{\rho }_i$. Calculations of this theoretical analysis have been done taking the data from the Cassini in the inner magnetosphere of Saturn in the two extended regions of Rs ～4.60–4.01 and Rs ～4.82–5.0. In our study velocity shear, temperature anisotropy and magnitude of the electric field are observed to be the major sources of free energy for the K-H instability in both the regions considered. The inhomogeneity of electric field, electron-ion temperature ratio, and density gradient have been observed playing stabilizing effect on K-H instability. This study also indicates the effect of the vicinity of icy moon Enceladus on the growth of K-H instability.     

Time-varying solar radiation pressure on Ajisai in comparison with LAGEOS satellites

This study aims to investigate solar radiation pressure acting on the spherical geodetic satellites, Ajisai, LAGEOS-1, and LAGEOS-2. The solar radiation pressure coefficients ($C_R$) are derived in two independent ways: (a) through precise orbit determination (POD) using satellite laser ranging (SLR) data, and (b) through modeling using the optical properties of the satellite surface material. The average $C_R$ value of Ajisai (1.039), as calculated from the time series of $C_R$ POD estimates every 15?days, is consistently smaller than those of LAGEOS-1 (1.140) and LAGEOS-2 (1.103). This difference can be explained by the fact that the surface of Ajisai is mostly covered by mirrors. The Ajisai $C_R$ values estimated by POD show remarkable semi-annual variation, which disagrees with the results of a previous study (Sengoku et al., 1995) predicting that the $C_R$ of Ajisai varies almost annually. We attribute this semi-annual variation to two physical reasons: the non-spherical additional cross-sectional area due to the “attached fitting ring” and the low reflectivity of the surface material in the polar regions. Furthermore, the solar radiation pressure acting on Ajisai varies annually in a direction perpendicular to the sun-satellite vector. Finally, the two independent $C_R$ values of Ajisai agree more when we assume a total solar irradiance of 1361?W/m², whereas the value 1367?W/m² has been commonly used in POD.     

Effects of space weather on the ionosphere and LEO satellites’ orbital trajectory in equatorial,low and middle latitude

We study the effects of space weather on the ionosphere and low Earth orbit (LEO) satellites’ orbital trajectory in equatorial, low- and mid-latitude (EQL, LLT and MLT) regions during (and around) the notable storms of October/November, 2003. We briefly review space weather effects on the thermosphere and ionosphere to demonstrate that such effects are also latitude-dependent and well established. Following the review we simulate the trend in variation of satellite’s orbital radius (r), mean height (h) and orbit decay rate (ODR) during 15 October–14 November 2003 in EQL, LLT and MLT. Nominal atmospheric drag on LEO satellite is usually enhanced by space weather or solar-induced variations in thermospheric temperature and density profile. To separate nominal orbit decay from solar-induced accelerated orbit decay, we compute $r\text{,}h$ and ODR in three regimes viz. (i) excluding solar indices (or effect), where $r=r_0\text{,}h=h_0$ and $\mathit{ODR}={\mathit{ODR}}_0$ (ii) with mean value of solar indices for the interval, where $r=r_m\text{,}h=h_m$ and $\mathit{ODR}={\mathit{ODR}}_m$ and (iii) with actual daily values of solar indices for the interval ($r\text{,}h$ and ODR). For a typical LEO satellite at h?=?450?km, we show that the total decay in r during the period is about 4.20?km, 3.90?km and 3.20?km in EQL, LLT and MLT respectively; the respective nominal decay ($r_0$) is 0.40?km, 0.34?km and 0.22?km, while solar-induced orbital decay ($r_m$) is about 3.80?km, 3.55?km and 2.95?km. h also varied in like manner. The respective nominal ${\mathit{ODR}}_0$ is about 13.5?m/day, 11.2?m/day and 7.2?m/day, while solar-induced ${\mathit{ODR}}_m$ is about 124.3?m/day, 116.9?m/day and 97.3?m/day. We also show that severe geomagnetic storms can increase ODR by up to 117% (from daily mean value). However, the extent of space weather effects on LEO Satellite’s trajectory significantly depends on the ballistic co-efficient and orbit of the satellite, and phase of solar cycles, intensity and duration of driving (or influencing) solar event.     

Physical characterization of the deep-space debris WT1190F: A testbed for advanced SSA techniques

We report on extensive ${\mathit{BVR}}_c{I}_c$ photometry and low-resolution ($\lambda /\mathrm{\Delta }\lambda ～250$) spectroscopy of the deep-space debris WT1190F, which impacted Earth offshore from Sri Lanka, on 2015 November 13. In spite of its likely artificial origin (as a relic of some past lunar mission), the case offered important points of discussion for its suggestive connection with the envisaged scenario for a (potentially far more dangerous) natural impactor, like an asteroid or a comet.Our observations indicate for WT1190F an absolute magnitude $R_c={32.45}_{\pm 0.31}$, with a flat dependence of reflectance on the phase angle, such as ${\mathit{dR}}_c/d?～{0.007}_{\pm 2}$?mag?deg^?1. The detected short-timescale variability suggests that the body was likely spinning with a period twice the nominal figure of $P_{\mathrm{flash}}={1.4547}_{\pm 0.0005}\mathrm{s}$, as from the observed lightcurve. In the ${\mathit{BVR}}_c{I}_c$ color domain, WT1190F closely resembled the Planck deep-space probe. This match, together with a depressed reflectance around 4000 and 8500 Å may be suggestive of a “grey” (aluminized) surface texture.The spinning pattern remained in place also along the object fiery entry in the atmosphere, a feature that may have partly shielded the body along its fireball phase perhaps leading a large fraction of its mass to survive intact, now lying underwater along a tight ($～1\times 80$?km) strip of sea, at a depth of 1500?m or less.Under the assumption of Lambertian scatter, an inferred size of ${216}_{\pm 30}/\sqrt{\alpha /0.1}$?cm is obtained for WT1190F. By accounting for non-gravitational dynamical perturbations, the Area-to-Mass ratio of the body was in the range $(0.006?\mathit{AMR}?0.011)$?m²?kg^?1.Both these figures resulted compatible with the two prevailing candidates to WT1190F’s identity, namely the Athena II Trans-Lunar Injection Stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module, callsign “Snoopy”. Both candidates have been analyzed in some detail here through accurate 3D CAD design mockup modelling and BRDF reflectance rendering to derive the inherent photometric properties to be compared with the observations.     

Modelling ionospheric vertical drifts over Africa low latitudes using Empirical Orthogonal functions and comparison with climatological model

For the first time, empirical model of daytime vertical $\mathbf{E}\times \mathbf{B}$ drift based on Empirical Orthogonal functions (EOF) decomposition technique is presented. Day-to-day variability of $\mathbf{E}\times \mathbf{B}$ drift inferred from horizontal (H) geomagnetic field data around dip latitude for the period of 2008–2013 is used to both develop and validate the model. Results show that the EOF technique is promising with modelled values and data giving correlation coefficient values of at least 0.90 for geomagnetic conditions of both $K_p?3$ and $K_p>3$ within 2008–2013. Independent model validation shows that in situ $\mathbf{E}\times \mathbf{B}$ values from ion velocity meter (IVM) instrument on-board C/NOFS satellite are closer to model $\mathbf{E}\times \mathbf{B}$ estimates than the climatological Scherliess-Fejer (SF) model incorporated within the International Reference Ionosphere (IRI).     

Upgrading CCIR's foF2 maps using available ionosondes and genetic algorithms

We have developed a new approach towards a new database of the ionospheric parameter $f_{o}F2$. This parameter, being the frequency of the maximum of the ionospheric electronic density profile and its main modeller, is of great interest not only in atmospheric studies but also in the realm of radio propagation. The current databases, generated by CCIR (Committee Consultative for Ionospheric Radiowave propagation) and URSI (International Union of Radio Science), and used by the IRI (International Reference Ionosphere) model, are based on Fourier expansions and have been built in the 60s from the available ionosondes at that time. The main goal of this work is to upgrade the databases by using new available ionosonde data. To this end we used the IRI diurnal/spherical expansions to represent the $f_{o}F2$ variability, and computed its coefficients by means of a genetic algorithm (GA). In order to test the performance of the proposed methodology, we applied it to the South American region with data obtained by RAPEAS (Red Argentina para el Estudio de la Atmósfera Superior, i.e. Argentine Network for the Study of the Upper Atmosphere) during the years 1958–2009. The new GA coefficients provide a global better fit of the IRI model to the observed $f_{o}F2$ than the CCIR coefficients. Since the same formulae and the same number of coefficients were used, the overall integrity of IRI’s typical ionospheric feature representation was preserved. The best improvements with respect to CCIR are obtained at low solar activities, at large (in absolute value) modip latitudes, and at night-time. The new method is flexible in the sense that can be applied either globally or regionally. It is also very easy to recompute the coefficients when new data is available. The computation of a third set of coefficients corresponding to days of medium solar activity in order to avoid the interpolation between low and high activities is suggested. The same procedure as for $f_{o}F2$ can be perfomed to obtain the ionospheric parameter M(3000)F2.     

Simulation-based evaluation of a cold atom interferometry gradiometer concept for gravity field recovery

The prospects of future satellite gravimetry missions to sustain a continuous and improved observation of the gravitational field have stimulated studies of new concepts of space inertial sensors with potentially improved precision and stability. This is in particular the case for cold-atom interferometry (CAI) gradiometry which is the object of this paper. The performance of a specific CAI gradiometer design is studied here in terms of quality of the recovered gravity field through a closed-loop numerical simulation of the measurement and processing workflow. First we show that mapping the time-variable field on a monthly basis would require a noise level below $5\text{mE}/\sqrt{\text{Hz}}$. The mission scenarios are therefore focused on the static field, like GOCE. Second, the stringent requirement on the angular velocity of a one-arm gradiometer, which must not exceed ${10}^{-6}$?rad/s, leads to two possible modes of operation of the CAI gradiometer: the nadir and the quasi-inertial mode. In the nadir mode, which corresponds to the usual Earth-pointing satellite attitude, only the gradient $V_{\mathit{yy}}$, along the cross-track direction, is measured. In the quasi-inertial mode, the satellite attitude is approximately constant in the inertial reference frame and the 3 diagonal gradients $V_{\mathit{xx}}\text{,}{V}_{\mathit{yy}}$ and $V_{\mathit{zz}}$ are measured. Both modes are successively simulated for a 239?km altitude orbit and the error on the recovered gravity models eventually compared to GOCE solutions. We conclude that for the specific CAI gradiometer design assumed in this paper, only the quasi-inertial mode scenario would be able to significantly outperform GOCE results at the cost of technically challenging requirements on the orbit and attitude control.     

Kelvin–Helmholtz instability in a twisting solar polar coronal hole jet observed by SDO/AIA

We investigate the conditions under which the fluting ($m=2$), $m=3$, and $m=12$ magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin–Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. We employed the dispersion relations of MHD modes derived from the linearized MHD equations. We assumed real wavenumbers and complex angular wave frequencies, namely complex wave phse velocities. The dispersion relations were solved numerically at fixed input parameters (taken from observational data) and varying degrees of torsion of the internal magnetic field. It is shown that the stability of the modes depends upon five parameters: the density contrast between the flux tube and its environment, the ratio of the external and internal axial magnetic fields, the twist of the magnetic field lines inside the tube, the ratio of transverse and axial jet’s velocities, and the value of the Alfvén Mach number (the ratio of the tube axial velocity to Alfvén speed inside the flux tube). Using a twisting jet of 2010 August 21 by SDO/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of $9.8$ Mm, at a density contrast of $0.474$ and fixed Alfvén Mach number of $?0.76$, for the three MHD modes there exist instability windows whose width crucially depends upon the internal magnetic field twist. It is found that for the considered modes an azimuthal magnetic field of $1.3$–$1.4$ G (computed at the tube boundary) makes the width of the instability windows equal to zero, that is, it suppress the KH instability onset. On the other hand, the times for developing KH instability of the $m=12$ MHD mode at instability wavelengths between 15 and 12 Mm turn out to be in the range of $1.9$–$4.7$ min that is in agreement with the growth rates estimated from the temporal evolution of the observed unstable jet’s blobs in their initial stage.     

An attempt to inverse the ionospheric sporadic-E layer critical frequency based on the COSMIC radio occultation data

Ionospheric sporadic E layer refers to localized thin irregularity with enhanced plasma density appearing in the height range of ionospheric E layer (～90–130?km). The much higher electron density in the sporadic E layer than the background ionosphere would cause sudden TEC enhancement in the occultation TEC profile. A wavelet decomposition and reconstruction method is applied to extract the TEC fluctuation in this paper, and then $S_{\text{max}}$ index is defined to represent the intensity of the sudden TEC enhancement. $S_{\text{max}}$ index is compared with sporadic E critical frequency ($\mathit{foEs}$) observed by the ionosonde. The results show a well linear correlation between them with mean correlation coefficient about 0.7. Thus, an empirical linear model is established to inverse the $\mathit{foEs}$. The monthly/hourly mean values and global distribution of sporadic E intensity and occurrence ratio are calculated using this method based on the COSMIC occultation data from 2007 to 2011. The statistical analysis results indicate that it is feasible to inverse the $\mathit{foEs}$ based on the occultation TEC profile data and the inversion results can be applied to the long-term global variations of sporadic E investigations.     

Detailed analysis of dynamic evolution of three Active Regions at the photospheric level before flare and CME occurrence

We present a combined analysis of the applications of the weighted horizontal magnetic gradient (denoted as ${\mathit{WG}}_M$ in Korsós et al. (2015)) method and the magnetic helicity tool (Berger and Field, 1984) employed for three active regions (ARs), namely NOAA AR 11261, AR 11283 and AR 11429. We analysed the time series of photospheric data from the Solar Dynamics Observatory taken between August 2011 and March 2012. During this period the three ARs produced a series of flares (eight M- and six X-class) and coronal mass ejections (CMEs). AR 11261 had four M-class flares and one of them was accompanied by a fast CME. AR 11283 had similar activities with two M- and two X-class flares, but only with a slow CME. Finally, AR 11429 was the most powerful of the three ARs as it hosted five compact and large solar flare and CME eruptions. For applying the ${\mathit{WG}}_M$ method we employed the Debrecen sunspot data catalogue, and, for estimating the magnetic helicity at photospheric level we used the Space-weather HMI Active Region Patches (SHARP’s) vector magnetograms from SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager). We followed the evolution of the components of the ${\mathit{WG}}_M$ and the magnetic helicity before the flare and CME occurrences. We found a unique and mutually shared behaviour, called the U-shaped pattern, of the weighted distance component of ${\mathit{WG}}_M$ and of the shearing component of the helicity flux before the flare and CME eruptions. This common pattern is associated with the decreasing-receding phases yet reported only known to be a necessary feature prior to solar flare eruption(s) but found now at the same time in the evolution of the shearing helicity flux. This result leads to the conclusions that (i) the shearing motion of photospheric magnetic field may be a key driver for solar eruption in addition to the flux emerging process, and that (ii) the found decreasing-approaching pattern in the evolution of shearing helicity flux may be another precursor indicator for improving the forecasting of solar eruptions.     

Delayed outburst of H 1743–322 in 2003 and relation with its other outbursts

The Galactic transient black hole candidate H 1743–322 exhibited a long duration outburst in 2003 after more than two and a half decades of inactivity. The 2003 event was extensively studied in multi-wavelength bands by many groups. The striking feature is that the total energy released is extremely high as compared to that in tens of outbursts which followed. In this paper, we look at this event and study both the spectral and temporal properties of the source using two component advective flow (TCAF) paradigm. We extract accretion flow parameters for each observation from spectral properties of the decay phase and determine the mass of the black hole. We computed the energy released during all the known outbursts since 2003 and showed that on an average, the energy release in an outburst is proportional to the duration of the quiescent state just prior to it, with the exception of the 2004 outburst. A constant rate of supply of matter from the companion cannot explain the energy release in 2004 outburst. However, if the energy release of 2003 is incomplete and the leftover is released in 2004, then the companion’s rate of matter supply can be constant since 1977 till date. We believe that erratic behaviour of viscosity at the accumulation radius $X_p$ of matter as well as location the $X_p$ itself, rather than the random variation of mass transfer rate from the companion, could be responsible for non-uniformity in outburst pattern. We discuss several factors on which the waiting time and duration of the next outburst could depend.     

Real-time spacecraft intercept strategy on J2-perturbed orbits

A real-time intercept strategy for spacecraft under the non-uniform gravitational perturbation of Earth is addressed in this paper. To intercept a target spacecraft on general conic sections, an interceptor considered in this work makes use of a thruster propelling the constant thrust which is comparable to unrealistic impulse-type thrust. The $J_2$ perturbation introduces critical dynamic variations of spacecraft orbiting the Earth, which results in a considerable amount of position error of the interceptor at the final intercept point. In order to release the burden of $J_2$ disturbance and make the miss distance between the target and interceptor small, a real-time intercept technique with an optimal intercept algorithm is suggested. The strategy proposed is to obtain an optimized output iteratively for a given time interval with previously obtained optimal values. These parameters are evaluated by the optimal intercept algorithm suggested. Once the optimal velocity change is obtained to satisfy intercept requirements, although the orbital system is perturbed, it is easy to regenerate a new solution by setting the previous solution as new initial guesses. This strategy is employed iteratively until the interceptor meets the target. Several numerical simulations are performed to highlight the proposed real-time strategy for spacecraft intercept missions.     

Constraining the mass of the black hole GX 339-4 using spectro-temporal analysis of multiple outbursts

We carried out spectro-temporal analysis of the archived data from multiple outbursts spanning over the last two decades from the black hole X-ray binary GX 339-4. In this paper, the mass of the compact object in the X-ray binary system GX 339-4 is constrained based on three indirect methods. The first method uses broadband spectral modelling with a two component flow structure of the accretion around the black hole. The broadband data are obtained from RXTE (Rossi X-ray Timing Explorer) in the range 3.0 to 150.0?keV and from Swift and NuSTAR (Nuclear Spectroscopic Telescope Array) simultaneously in the range 0.5 to 79.0?keV. In the second method, we model the time evolution of Quasi-periodic Oscillation (QPO) frequencies, considering it to be the result of an oscillating shock that radially propagates towards or away from the compact object. The third method is based on scaling a mass dependent parameter from an empirical model of the photon index ($\mathrm{\Gamma }$) – QPO ($\nu$) correlation. We compare the results at 90 percent confidence from the three methods and summarize the mass estimate of the central object to be in the range $8.28–11.89M_{\odot }$.