Fine structure in the sunspot spectrum-2 to 70 years

Application of a new data adaptive approach to power spectrum estimation has yielded evidence for a double solar cycle line in the Zurich sunspot time history. There is significant power from 8 to 15 yr in the spectrum with the primary line at 11.1 yr and three attendant multiplets that may be significant. The first four harmonics of the solar cycle are detected too. Quite marginal evidence for a peak at 65 yr in the spectrum is presented. These results closely correspond to those recently found in the geomagnetic spectrum.     

Geomagnetic tail oscillations in quasihydrodynamics

The effect of pressure anisotropy on geomagnetic tail oscillations is studied using the Chew-Goldberger-Low equations. It is shown that anisotropy of the solar wind plasma pressure may result in generation of waves, assuming no waves in the case of isotropy. Anisotropy of the plasma pressure in the magnetospheric tail may also cause a basic distortion of the oscillation spectra.Generally speaking, the CGL-system is not valid for short wavelengths.Landau damping is neglected.     

Geomagnetic activity and Hale sector boundaries

The variation of the geomagnetic activity index A_p at the IMF sector boundaries (+ to ? and ? to +) has been studied for three solar cycles, separating data into vernal and autumnal equinoxes. It was found that a reported increase in A_p as an effect of a Hale boundary can be better attributed to the occurrence of a negative IMF B_z component in the geocentric solar magnetospheric coordinate system and to the occurrence of high speed solar wind streams.     

Geomagnetic effects of interplanetary sector structure

In this paper the geomagnetic effects of the interplanetary magnetic sector structure are studied on the basis of some new criteria and working hypotheses.Thus, we assume that the recurrence of geomagnetic disturbances should be understood in a dynamical sense, in connection with the evolution of the full sector structure, and not necessarily as a 27-day recurrence. Accordingly, on the representation of the sector structure during 1968, as deduced by Wilcox and Colburn, we have defined four ‘main recurring lines’, which link the sector boundaries recurrent in successive solar rotations. The term ‘group of SC and SI events’, abbreviated as gr(SC + SI), introduced by us in previous works to designate the morphological grouping of the individual SC and SI events in collective events, is also used.It should be pointed out that the bulk of gr(SC + SI) events are either associated with sector boundaries, or recurrent in successive solar rotations. Part of these events reveal the existence of some ‘secondary recurring lines’, within the magnetic sectors.The above working hypotheses and observations have been checked by the superposed epoch analysis, performed for each main recurring line in part and for all the main recurring lines combined.The following parameters are analysed: the number of SC events, the number of collective events gr(SC + SI), the total number of SC and SI events and the geomagnetic activity index Kp.The main result of the superposed epoch analysis consists in the appearance of a sharp maximum for all the parameters considered on the day of sector boundary. This fact proves that the effects of the sector boundaries are important and general, in regard to all aspects of geomagnetic activity. Essentially these effects consist of the occurrence of gr(SC + SI) events and of a specific increase in the Kp index, when the sector boundaries pass by the magnetosphere. This suggests that the sector boundaries are accompanied by corotating shocks and magnetohydrodynamical turbulence.The high frequency in the occurrence of the SC events on the days of sector boundaries is also noticeable.Each main recurring line presents a certain ‘individuality’, expressed particularly by secondary specific maxima in all the parameters, corresponding to the ‘secondary recurring lines’. One suggests that these secondary recurring lines might be due to some corotating distortions within the magnetic sectors and might be related to the ‘subsector’ or ‘filaments’.The distribution of the geomagnetic disturbances near the sector boundaries depends on the direction of the field polarity change.All these results lead to the conclusion that most of the geomagnetic disturbances can be accounted for by the interaction between corotating distortions in the solar wind connected with the sector structure and the magnetosphere, the flare-induced disturbances representing statistically the secondary mechanism.     

Long-Term Variations of Geomagnetic Rigidity Cutoffs

Using trajectory calculations of cosmic rays in the geomagnetic field, the changes of vertical cutoff rigidities in the past are discussed. The computations are done for selected positions at the Earth’s surface using the IGRF model data for 1900–2000. The contour maps of vertical cutoff rigidities using the set of ten Gauss coefficients for the period of years between 0 and 1600 are obtained. The trends in long-term variability of cutoffs at different positions on the Earth’s surface are described.     

Geomagnetic Effects of Corotating Interaction Regions

We present an analysis of the geoeffectiveness of corotating interaction regions (CIRs), employing the data recorded from 25 January to 5 May 2005 and throughout 2008. These two intervals in the declining phase of Solar Cycle 23 are characterised by a particularly low number of interplanetary coronal mass ejections (ICMEs). We study in detail how four geomagnetic-activity parameters (the Dst, Ap, and AE indices, as well as the Dst time derivative, \(\mathrm{dDst}/\mathrm{d}t\)) are related to three CIR-related solar wind parameters (flow speed, \(V\), magnetic field, \(B\), and the convective electric field based on the southward Geocentric solar magnetospheric (GSM) magnetic field component, \(\mathit{VB}_{s}\)) on a three-hour time resolution. In addition, we quantify statistical relationships between the mentioned geomagnetic indices. It is found that Dst is correlated best to \(V\), with a correlation coefficient of \(\mathrm{cc}\approx0.6\), whereas there is no correlation between \(\mathrm{dDst}/\mathrm{d}t\) and \(V\). The Ap and AE indices attain peaks about half a day before the maximum of \(V\), with correlation coefficients ranging from \(\mathrm{cc}\approx0.6\) to \(\mathrm{cc}\approx0.7\), depending on the sample used. The best correlations of Ap and AE are found with \(\mathit{VB}_{s}\) with a delay of 3 h, being characterised by \(\mathrm{cc}\gtrsim 0.6\). The Dst derivative \(\mathrm{dDst}/\mathrm{d}t\) is also correlated with \(\mathit{VB}_{s}\), but the correlation is significantly weaker \(\mathrm{cc}\approx 0.4\)?–?0.5, with a delay of 0?–?3 h, depending on the employed sample. Such low values of correlation coefficients indicate that there are other significant effects that influence the relationship between the considered parameters. The correlation of all studied geomagnetic parameters with \(B\) are characterised by considerably lower correlation coefficients, ranging from \(\mathrm{cc}=0.3\) in the case of \(\mathrm{dDst}/\mathrm{d}t\) up to \(\mathrm{cc}=0.56\) in the case of Ap. It is also shown that peak values of geomagnetic indices depend on the duration of the CIR-related structures. The Dst is closely correlated with Ap and AE (\(\mathrm{cc}=0.7\)), Dst being delayed for about 3 h. On the other hand, \(\mathrm{dDst}/\mathrm{d}t\) peaks simultaneously with Ap and AE, with correlation coefficients of 0.48 and 0.56, respectively. The highest correlation (\(\mathrm{cc}=0.81\)) is found for the relationship between Ap and AE.     

Geomagnetic disturbances associated with disappearing solar filaments

To gain an insight into the origin of enhanced geomagnetic activity that is recently reported to follow the disparition brusque (DB) of quiescent solar filaments, a study is made of the interplanetary plasma and magnetic field data at 1 AU, in relation to DBs over the period January 1967 through March 1978. The investigation revealed that the minor (Ap 30) and major (Ap 50) geomagnetic disturbances that manifested within 8 days of DBs, almost invariably occurred (in 28 out of the 30 events studied) in association with the passage at Earth of high-speed streams in the solar wind. A majority of the streams (19 out of the 28 streams) exhibited a 27-day recurrence pattern and, thus, the associated enhancement in geomagnetic activity (and apparently followed DBs). The date of transit of the high-speed stream at Earth seems to control the delay time of the geomagnetic disturbance, rather than the size of the filament. A systematic spatial relationship between DB's and the potential solar sources of the high-speed streams (coronal holes and flares) does not appear to be present. The results point out the relevance and a prominent role of recurrent and transient high-speed structures in the solar wind in the enhancement of geomagnetic activity that accompagnies DBs.     

Geomagnetic storm fields near a synchronous satellite

An apparent early recovery of the main phase of geomagnetic storms at the distance of the synchronous satellite is examined in terms of changing electric current distributions in the magnetosphere during magnetic storms. It is suggested that a rapid recession of the edge of the plasma sheet (after the advance toward the Earth during an early epoch of the main phase) is partly responsible for the early recovery. Relevant plasma sheet variations during geomagnetic storms are found to be in agreement with the inferred variations.     

Iron K-emission line from Cygnus X-2

The iron K-emission line of Cyg X-2 was detected from the TENMA observation. The centre energy, the equivalent width and the intrinsic line width are 6.7 keV, 30 eV, and less than 0.6 keV, respectively. These properties indicate that the observed line is mostly due to helium-like iron and the electron scattering depth of the line emitting region is smaller than three.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Solar Cycle Signal in Geomagnetic Activity and Climate

Historical geomagnetic and climate records were analyzed to study long-term trends and relationships with solar activity. Wavelet technique and recurrence plot analysis are applied to the data to find their coherence and similarities at different times and time-scales. It is shown that the solar cycle signal is more pronounced in climatic data during the last 60 years.     

Impacts on Cosmic-Ray Intensity Observed During Geomagnetic Disturbances

Geomagnetic disturbances are the results of interplanetary causes such as high-speed streamers (HSSs), interplanetary coronal mass ejections (ICMEs), corotating interaction regions (CIRs), and magnetic clouds. During different forms of geomagnetic disturbances, we observed changes in the count rate at neutron monitors that are kept at various locations. We studied the count rates measured by neutron monitors at four stations at various latitudes during different categories of geomagnetic events and compared them. We analysed five events: a geomagnetically quiet event, a non-storm high-intensity long-duration continuous AE activity (HILDCAA) event, a storm-preceded HILDCAA event, a geomagnetic substorm event, and a geomagnetic moderate storm event. We based our analysis on geomagnetic indices, solar wind parameters, and interplanetary magnetic field (IMF) parameters. We found that the strength of the modulation was least during the quiet event and highest during the storm-preceded HILDCAA. By analysing the cause of these geomagnetic disturbances, we related each decrease in the neutron monitor data with the corresponding solar cause. For the ICME-driven storm, we observed a decrease in neutron monitor data ranging from 6% to 12% in all stations. On the other hand, we observed a decrease ranging from 2% to 5% for the HSS-driven storm. For the non-storm HILDCAA, we observed a decrease in neutron monitor data of about 1% to 1.5%. For the quiet event, the neutron monitor data fluctuated such that there was no overall decrease in all stations.     

An Approach to the Relationship Between Magnetic Clouds and the Recovery Phase of Geomagnetic Storms

Using an elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to their relationship with geomagnetic storms. Assuming an axially symmetric ring current and once we have obtained the disturbances produced in its current density due to the passage of a MC through it (whose axis has a latitude θ, a longitude φ, and its cross-section has an orientation ζ), then we determine the decrease in the value of the geomagnetic field at the Earth's equator, i.e., the D _st index. The D _st model presented allows us to estimate the physical parameters which characterize the symmetric ring current during the recovery phase of the storm time. The theoretical and experimental D _st indexes are compared for four intense geomagnetic storms (D _st<−100 nT), all of them associated with MCs. As seen in the figures presented, the fits are good for every storm. In view of these results we conclude that the effects of a MC over the symmetric ring current can explain the main profile of the recovery phase of a geomagnetic storm.     

Absorption line redshifts of QSOs in relation to their emission line redshifts

Analysis of the recent data indicate that absorption line redshifts of QSOs are significantly correlated to their emission line redshifts. It is concluded that the absorption lines originate in materials intrinsic to the QSOs.     

Fitting a line to a sine

In the numerical integrations of the outer planets, when the inner planets are not considered, the initial conditions are determined by least square adjustment with a complete ephemeris. In the present work, we compute the resulting uncertainty on the initial conditions by the analysis of the very simple problem which consists in fitting by least squares a straight line to a sine curve. Explicit formulae for the computation of the error due to the fitting process are given. In particular, fitting over an integer number of periods is very close to the worst case. The determination of the initial conditions in the LONGSTOP project (Milani,et al., 1987) is analysed as an example. It is shown that the uncertainty on the main frequencies of the secular system due to the determination of the initial conditions is of the order of 0.01 arcsec/year.     

Predicting Solar Cycle 24 Using a Geomagnetic Precursor Pair

We describe using Ap and F_10.7 as a geomagnetic-precursor pair to predict the amplitude of Solar Cycle 24. The precursor is created by using F_10.7 to remove the direct solar-activity component of Ap. Four peaks are seen in the precursor function during the decline of Solar Cycle 23. A recurrence index that is generated by a local correlation of Ap is then used to determine which peak is the correct precursor. The earliest peak is the most prominent but coincides with high levels of non-recurrent solar activity associated with the intense solar activity of October and November 2003. The second and third peaks coincide with some recurrent activity on the Sun and show that a weak cycle precursor closely following a period of strong solar activity may be difficult to resolve. A fourth peak, which appears in early 2008 and has recurrent activity similar to precursors of earlier solar cycles, appears to be the “true” precursor peak for Solar Cycle 24 and predicts the smallest amplitude for Solar Cycle 24. To determine the timing of peak activity it is noted that the average time between the precursor peak and the following maximum is ≈?6.4 years. Hence, Solar Cycle 24 would peak during 2014. Several effects contribute to the smaller prediction when compared with other geomagnetic-precursor predictions. During Solar Cycle 23 the correlation between sunspot number and F_10.7 shows that F_10.7 is higher than the equivalent sunspot number over most of the cycle, implying that the sunspot number underestimates the solar-activity component described by F_10.7. During 2003 the correlation between aa and Ap shows that aa is 10 % higher than the value predicted from Ap, leading to an overestimate of the aa precursor for that year. However, the most important difference is the lack of recurrent activity in the first three peaks and the presence of significant recurrent activity in the fourth. While the prediction is for an amplitude of Solar Cycle 24 of 65±20 in smoothed sunspot number, a below-average amplitude for Solar Cycle 24, with maximum at 2014.5±0.5, we conclude that Solar Cycle 24 will be no stronger than average and could be much weaker than average.     

The line integral approach to radarclinometry

Radarclinometry, the invention of which has been previously reported, is a technique for deriving a topographic map from a single radar image by using the dependence upon terrain-surface orientation of the integrated signal of an individual image pixel. The radiometric calibration required for precise operation and testing does not yet exist, but the imminence of important applications justifies parallel, rather than serial, development of radarclinometry and radiometrically calibrated radar. The present investigation reports three developmental advances: (1) The solid angle of integration of back-scattered specific intensity constituting a pixel signal is more accurately accounted for in its dependence on surface orientation than in previous work. (2) The local curvature hypothesis, which removes the requirement of a ground-truth profile as a boundary condition and enables the formulation of the theory in terms of a line integral, has been expanded to include the three possibilities of Local Cylindricity, Local Biaxial Ellipsoidal Hyperbolicity, and Least-Squares Local Sphericity. (3) The theory is integrated in the cross-ground-range direction, which is ill-conditioned compared to the ground-range direction, whereas the original formulation was based on enforced isotropy in the two-dimensional power spectrum of the topography. It was found necessary to prohibit the hypothesis of Local Biaxial Ellipsoidal Hyperbolicity in the cross-range stepping, for reasons not completely clear. Variation in the proportioning between curvature assumptions had produced topographic maps that are in good mutual agreement but not realistic in appearance. They are severely banded parallel to the ground-range direction, most especially at small radar zenith angles. Numerical experimentation with the falsification of topography through incorrect decalibration as performed on a Gaussian hill suggests that the banding and its exaggeration at high radar incidence angles could easily be due to our lack of radiometric calibration.     

Slow and Fast Rotating Coronal Holes from Geomagnetic Indices

The evolution of the 27-day recurrence in the series of two solar indices (Wolf number WN and 10.7 cm radio flux F) and two geomagnetic indices (Dst and ζ, variance of the geomagnetic field recorded at a magnetic observatory) have been studied over the 1957 – 2007 time span. Spectral energies contained in two period domains (25 – 27.3 and 27.3 – 31 days), designated as E ₁ and E ₂, have been computed. Whereas the evolution of E ₁ is the same for the four indices, that of E ₂ is essentially different for WN and F on the one hand, Dst and ζ on the other hand. Some general conclusions on the dynamics of the solar outer layers are inferred from these results. First the solar activity, as measured by WN, and when averaged over a few years, evolves in the same way whatever the latitude. Second, two families of coronal holes (CHs) are identified; the rapidly and the slowly rotating CHs evolve quite differently.