Ionospheric spread-F at Huancayo,sunspot activity and geomagnetic activity

A superposed-epoch method is used to investigate the occurrence of spread-F at Huancayo relative to days of high sunspot activity and also relative to days of high geomagnetic activity. A good correlation is found between days of high A_p, index and high spread-F occurrence for a pre-sunrise interval of a few hours. When 3-hourly K_p indices are used they show a peak value approximately 6 hr prior to an above-average occurrence of spread-F. It is suggested that this pre-sunrise spread-F is associated with ionospheric height rises which are produced by travelling disturbances, initiated in polar regions at times of high geomagnetic activity.     

Coronal holes,solar wind streams,and geomagnetic activity during the new sunspot cycle

We have extended our previous study of coronal holes, solar wind streams, and geomagnetic disturbances from the declining phase (1973–1975) of sunspot cycle 20 through sunspot minimum (1976) into the rising phase (1977) of cycle 21. Using daily He I 10830 Å spectroheliograms and photospheric magnetograms, we found the following results:

1. As the magnetic field patterns changed, the solar atmosphere evolved from a structure having a few, large, long-lived, low-latitude coronal holes to one having numerous small, short-lived, high-latitude holes (in addition to the polar holes which persisted throughout this 5-year interval).
2. The high-latitude holes recurred with a synodic rotation period of 28–29 days instead of the 27-day period already known to be characteristic of low-latitude holes.
3. During 1976–1977 many coronal holes were intrinsically ‘weak’ in the sense that their average intensities did not differ greatly from the intensity of their surroundings. Such low-contrast holes were rare during 1973–1975.

An updated Bartels display of the occurrence of holes, wind speed, and geomagnetic activity summarizes the evolution of their characteristics and interrelations as the sunspot cycle has progressed. Long-lived, low-latitude holes have become rare but remain terrestrially effective. The more common high-latitude holes are effective only when the Earth lies at a relatively high heliographic latitude in the same solar hemisphere.     

Using geomagnetic indices to forecast the next sunspot maximum

The Babcock solar dynamo model and known interactions of the interplanetary magnetic field with the earth's magnetosphere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. We augment the work of Kane (1987) by updating his method of analysis, including recent smoothed aa and A_P indices. We predict a smoothed maximum sunspot number of 163±40 to peak in October 1990±9 months for solar cycle 22. This value is close to the Schatten and Sofia (1987) predicted value of 170±25, using more direct solar indicators.Now at Dept. of Astronomy, Univ. of Washington     

Predicting the maximum sunspot number and the associated geomagnetic activity indices a a $aa$ and A p $Ap$ for solar cycle 25

We are considering the spacetime described by the metric proposed by Mannheim and Kazanas. The effective potential and the circular orbits are discussed. The rotational velocity derived from the geodesics equation agrees with the observed flat galactic rotation curves. Finally, solutions to the Gordon equation for massless bosons evolving in this spacetime are obtained in terms of Heun general functions.

     

Recurrent magnetic activity,sunspot number and its rate of decline

Power spectral densities computed from low-latitude horizontal intensity of the Earth's magnetic field over two-year periods of declining phases of solar cycles 16 to 19 show a close relationship with the maximum relative sunspot number of the following solar cycles. The maximum sunspot number shows an exponential rise with the power density near 1/27 cd^?1; maximum R _z,however, increases linearly with power density near 1/14 cd^?1. It is also shown that the rate of decline of sunspot number in a solar cycle is almost exactly related, linearly, to power spectral density for the preceding solar cycle. Power densities near 1/27 and 1/14 cd^?1 in declining phase of solar cycle appear to be satisfactory indices for the maximum relative sunspot number of the following cycle and its rate of decline thereafter.     

On the cause of geomagnetic activity at Hale sector boundary

The solar wind velocity and density have been studied around the interplanetary magnetic field sector boundaries (+ to ? and ? to +) during 1965–1974, separating the data into autumnal and vernal periods. It is noticed that the solar wind velocity shows a sharp increase around the Hale type of sector boundary in both northern and southern heliosphere indicating a more favourable condition for the high speed stream after Hale type of sector boundary crossing than non-Hale boundary.     

VLF hiss,visual aurora and the geomagnetic activity

Observations and analyses of hiss events, recorded at College (dp. lat. 64.62°N) and Bar 1 (dp. lat. 70.20°N) during periods of varying auroral and geomagnetic activity, reveal three different types of events. These are (1) auroral substorm events with associated hiss bursts during disturbed period, (2) quiet-time hiss events accompanying stationary quiet auroral arcs and (3) hissless events at times of auroral and magnetic activity. Quiet-time observations seem to suggest that the substorm activity is not a necessary requirement for generating wideband hiss. On the other hand, examples of auroral and magnetic activity with complete absence of VLF hiss indicate that the ground reception of VLF/ELF natural emissions is largely controlled by propagation conditions in the ionosphere. There is either little or no correlation found between hiss observations at the two stations separated by about 600 km.     

A pictorial comparison of interplanetary magnetic field polarity,solar wind speed,and geomagnetic disturbance index during the sunspot cycle

Observations of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index (C9) during the years 1962–1975 are compared in a 27-day pictorial format that emphasizes their associated variations during the sunspot cycle. This display accentuates graphically several recently reported features of solar wind streams including the fact that the streams were faster, wider, and longer-lived during 1962–1964 and 1973–1975 in the declining phase of the sunspot cycle than during intervening years (Bame et al., 1976; Gosling et al., 1976). The display reveals strikingly that these high-speed streams were associated with the major, recurrent patterns of geomagnetic activity that are characteristic of the declining phase of the sunspot cycle. Finally, the display shows that during 1962–1975 the association between long-lived solar wind streams and recurrent geomagnetic disturbances was modulated by the annual variation (Burch, 1973) of the response of the geomagnetic field to solar wind conditions. The phase of this annual variation depends on the polarity of the interplanetary magnetic field in the sense that negative sectors of the interplanetary field have their greatest geomagnetic effect in northern hemisphere spring, and positive sectors have their greatest effect in the fall. During 1965–1972 when the solar wind streams were relatively slow (500 km s^-1), the annual variation strongly influenced the visibility of the corresponding geomagnetic disturbance patterns.Visiting Scientist, Kitt Peak National Observatory, Tucson, Arizona.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Hale sector boundary and geomagnetic activity

The variation of the geomagnetic activity index, Ap, at the IMF sector boundaries (+ to ? and ? to +) has been studied for three solar cycles, separating the data into vernal and autumnal equinoxes. It has been found that at the Hale boundary, geomagnetic activity index, Ap, shows a sharp increase compared to that around the non-Hale boundary.     

The 17-month periodicity of sunspot activity

A statistical study of sunspot activity during 1969 to 1986 was carried out by using the number of sunspot groups and their areas. We found a 17-month periodicity, which is consistent with the 500-day periodicity of flare occurrence (Ichimoto et al., 1985).Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 281.     

Disappearing solar filaments and geomagnetic activity

As a sequel to our recent identification of the high-speed stream as the candidate structure in the solar wind at 1 AU, that is primarily responsible for the geomagnetic disturbances occasionally noticed after disparition brusques (DBs) of solar filaments (Sastri et al., 1985), we report here that the streams, inferred to be recurrent in our earlier study, were consistently preceded by a stream interface, as expected of corotating streams. This observation substantiates the role of corotating streams of coronal hole origin in the apparent link between DBs and geomagnetic activity, and strengthens the view that DBs are not a unique source of geomagnetic activity.     

Magnetic flux emergence and geomagnetic activity,a close correlation

We analyse data of magnetic flux emergence for solar cycles 21 and 22, Helios 1 interplanetary shocks for cycle 21, and sudden storm commencements (SSCs) for cycles 11–22. A dominant variation of 3-year periodicity was found for all three phenomena during cycles 21 and 22. This indicates a correlation and a possible influence of the rate of solar magnetic flux emergence to produce the interplanetary phenomena studied in this work; in particular, the suggested role of coronal mass ejections as a means by which magnetic flux and stresses are taken out of the corona seems to be plausible. When taking cycles 11–22 in SSCs, the main periodicity changes to around 4 years; this may be an indication of flux emergence rate variations over the cycles.     

Low-dimensional chaos and fractal properties of long-term sunspot activity

Two primary solar-activity indicators sunspot numbers(SNs)and sunspot areas(SAs)in the time interval from November 1874 to December 2012 are used to determine the chaotic and fractal properties of solar activity.The results show that(1)the long-term solar activity is governed by a low-dimensional chaotic strange attractor,and its fractal motion shows a long-term persistence on large scales;(2)both the fractal dimension and maximal Lyapunov exponent of SAs are larger than those of SNs,implying that the dynamical system of SAs is more chaotic and complex than SNs;(3)the predictions of solar activity should only be done for short-to mid-term behaviors due to its intrinsic complexity;moreover,the predictability time of SAs is obviously smaller than that of SNs and previous results.     

Total sunspot area as a solar activity index

Observational time series of the total sunspot area A in the visible solar hemisphere are analyzed. A technique that allows the instability of the scale of these series to be found and corrected has been developed. An internally homogeneous series of the index A on the Greenwich scale can be obtained from 1875 to the present. A method for the approximate calculation of the yearly mean A from the Wolf sunspot numbers known since 1700 is suggested to extend this series into the past. The resulting series of the index A characterizes the solar activity variations over a period of ～300 years. These data are used to study processes in the Solar System related to the variability of the central star.     

Ten cycles of solar and geomagnetic activity

Series of 110 years of sunspot numbers and indices of geomagnetic activity are used with 17 years of solar wind data in order to study through solar cycles both stream and shock event solar activity. According to their patterns on Bartels diagrams of geomagnetic indices, stable wind streams and transient solar activities are separated from each other. Two classes of stable streams are identified: equatorial streams occurring sporadically, for several months, during the main phase of sunspot cycles and both polar streams established, for several years, at each cycle, before sunspot minimum. Polar streams are the first activity of solar cycles. For study of the relationship between transient geomagnetic phenomena and sunspot activity, we raise the importance of the contribution, at high spot number, of severe storms and, at low spot number, of short lived and unstable streams. Solar wind data are used to check and complete the above results. As a conclusion, we suggest a unified scheme of solar activity evolution with a starting point every eleventh year, a total duration of 17 years and an overlapping of 6 years between the first and the last phase of both successive series of phenomena: first, from polar field reversal to sunspot minimum, a phase of polar wind activity of the beginning cycle is superimposed on the weak contribution of shock events of the ending cycle; secondly, an equatorial phase mostly of shock events is superimposed on a variable contribution of short lived and sporadic stable equatorial stream activities; and thirdly a phase of low latitude shock events is superimposed on the polar stream interval of the following cycle.     

Ionospheric disturbances: Evidence for the contraction of the plasmasphere during severe geomagnetic storms

Continuous measurements of the ionospheric total electron content (TEC) provide a parameter well suited for the study of F-region disturbance effects. In this investigation, five cases of large and rapid drops in TEC observed near the sunset period are interpreted as being due to the contraction of the plasmasphere to L values less than 3. A model calculation is performed for the specific case of 1 November 1968 using simultaneous Alouette I data to define the position and magnitude of the ionospheric trough. The results indicate that the motion of a deep trough across the ray path from a geostationary satellite to an observing station can cause drastic changes in the measured amounts of Faraday rotation and therefore in the derived values of TEC. All of the TEC data sources available for the five events are then examined in an attempt to describe more completely the latitude dependence of the effects. It is suggested that during severe geomagnetic storms, the large and rapid decays in TEC during the 18–21 LT period to values significantly below normal can be used as a criterion to determine the approximate latitudinal extent of the contracted plasmasphere.     

Pulsation,rotation and sunspot cycle

A suggestion is made that the periods for solar pulsation, solar rotation, and sunspot cycle may be closely related one to another.     

Relationship between sunspot numbers during years of sunspot maximum and sunspot minimum

A correlation analysis shows that the sunspot numbers at the peaks of the last eight solar cycles are well-correlated with the sunspot numbers in heliolatitudes 20°–40° (specially in the southern hemisphere) occurring in the solar minimum years immediately preceding the solar maximum years.On leave from Physical Research Laboratory, Ahmedabad, India.