Current Solar Cycle Research Articles

Total electron content structure in the Middle East

Polarization rotation data recorded from the geostationary satellite SIRIO at Haifa, Israel, have been used to study the structure and variability of the total electron content (TEC) during the maximum phase of the current solar cycle. In addition to the overall diurnal and seasonal variation, the TEC is regularly modulated by the effects of traveling ionospheric disturbances (TID's). The behavior of TID's in terms of their frequency of occurrence, amplitude, period, and time of occurrence is seasonally dependent. Comparison with average behavior of TEC and related parameters observed during the minimum phase indicates the extent of the solar cycle variation.

Solar luminosity variation. III - Calcium K variation from solar minimum to maximum in cycle 21

Measurement of the full disk Ca II H and K profiles has now been completed from minimum to maximum in the current solar cycle 21. The central intensity of the K line increases by 30% on the average, but a peak change of +40% was recorded near the maximum of solar activity in late 1979. The 1 A K index shows a corresponding but smaller increase of 18%. These changes in the Sun viewed as a star appear to be directly attributable to the occurrence of solar plages on the visible solar hemisphere. Similar measurements of a 1' x 3' quiet region at disk center show no significant systematic variability. This suggests that the quiet network has no long-term variability in the rising phase of the solar cycle. Ca II K line widths and asymmetries also show systematic changes associated with the degree of solar activity. In general, spectral features formed above the temperature minimum are all closely correlated in their variablitity, but they are not well related to changes in the strength of narrow photospheric lines and the K/sub 1/ wings. Ca II variability correlates very closely with the plage index, the Zurich sunspot number, and the Ottawa 10more » cm flux measurements. The observing program will continue into the declining phase of cycle 21, so we will have the opportunity to test the constancy of our correlations in a different phase of the cycle when the rate of sunspot formation is decreasing and when Ca II variability may be influenced more by the remnants of active regions formed earlier.« less

What do we expect in magnetic activity in the current solar cycle?

Nearly all geomagnetic perturbations that are of origin external to the earth are directly or indirectly caused by the sun. Therefore one would expect that, in general, geomagnetic activity would be high when the sun becomes active. While this may be true so far as the overall impressions from visual inspection of magnetograms are concerned, the relation between solar activity and geomagnetic activity is by no means simple. This is in part because the geomagnetic field undergoes many different types of variations which have vastly different magnitudes, time scales, and scale sizes. For instance, global effects of a severe magnetic storm may last for several days, or substorms that mainly disturb polar regions typically last from one to a few hours. At another extreme, magnetic pulsations that have periods from a fraction of 1 second to a few tens of minutes may sustain their activity more or less continuously or intermittently for several hours, or even days, or they may have isolated occurrences. Magnetic perturbations that are associated with large‐scale disturbances have magnitudes from several tens to a few thousand nanoteslas (1 nT = 1γ), while magnetic pulsations have amplitudes from the order of picotesla (1 pT = 1 mγ) to tens of nanotesla. Thus one can define several different kinds of geomagnetic activity that represent diversely different disturbance phenomena. However, by the term ‘geomagnetic activity’ we usually mean large‐scale disturbances that are mainly caused by magnetic storms and substorms, and we follow this convention here.

Status of the current solar sunspot cycle

The Solar Maximum Year began August 1,1979. This international cooperative scientific program is to continue through February 28,1981, and involves fundamental research on enhanced activity of the sun, such as extensive active regions, large sunspots, and major solar flares, which usually accompany sunspot maximum.The SMY has created renewed interest in following the present stage of this sunspot cycle—solar cycle 21. The two graphs and the Table can almost speak for themselves. The Table gives the daily record of observed sunspot numbers for the recent 12‐month period. It is of interest to note that the monthly mean numbers have exceeded 150 in January, July, August and September 1979. When active regions have been on the sun, the daily numbers have exceeded 200 for several days in a row in June through September 1979.

Probable values of some basic parameters of the current solar cycle no. 21

Abstract In previous papers (Poulakos and Tritakis, 1972; Tritakis, 1974) based on the so‐called areas index la of the solar activity introduced by Xanthakis (1969, 1970) we had defined some empirico‐statistical relations among basic parameters of the solar cycles No. 8–20, such as the time of rise, the period, the maximum values of the areas index la, the relative sunspot numbers, etc. According to those conclusions we had successfully forecasted the values of some basic parameters of the previous 11‐ yr cycle No. 20, (Tritakis, 1974). We hope this method to work for the current solar cycle No. 21 as well.

Some studies on the association of solar optical flares and microwave bursts with sudden ionospheric disturbances

The association of solar optical flares (numbering 8230) reported under the dualclassification and also of different types of microwave bursts (numbering 1670) with the sudden ionospheric disturbances (SID's) during the peak phase of current solar cycle (cycle 20) have been examined. Important results obtained are: 1. (1) Percentage association of flares with SID's of all types increases with the intensity of the flares irrespective of their areas; 2. (2) Out of 51 flares associated simultaneously with all the six different types of SID's, 37 were of bright intensity (b), and only two were of large area (class 3); 3. (3) Microwave burst-SID association increases with the increase of peak flux. Further, percentage association is higher when the bursts are complex or contain ‘fluctuations’; 4. (4) Of the 47 microwave bursts associated simultaneously with all the six SID's, 83 per cent show fluctuations; 5. (5) SFD's are found to have their peaks attained earlier than those of both the associated flares and microwave bursts. Results obtained from the present investigation lead to the conclusion that a bright flare with an associated microwave burst of either complex type or having fluctuations is a true indication of the simultaneous occurrences of all the different types of sudden ionospheric disturbances.

Physical Sciences: Record-breaking Cosmic Ray Storm stemming from Solar Activity in August 1972

AN unusual centre of solar activity was the seat of the most severe disturbances of the current solar cycle early in August 1972. It produced reports from the general public of various visual phenomena in the night sky, surges in electrical systems, radio blackouts and effects upon the navigation of birds in flight. Of the great variety of physical phenomena associated with this remarkable region (sunspot group 331, McMath plage region 11976, centred at Carrington, longitude 009 degrees), we will concentrate on a description of the gross features of the greatest cosmic ray storm ever observed that commenced on August 4, and of which sunspot group 331 was the ultimate source.

Energy and mass content of high-speed solar-wind streams

The mass and energy flux densities of the solar wind measured by the Vela 3, Vela 4, and Explorer 34 satellites between July 1965 and October 1969 have been examined. Three-hour averages were used to study the properties of large-scale high-speed streams, and 27-day averages were employed in an attempt to identify long-term trends during the rising part of the current 11-year solar cycle. If the cross-sectional area of a stream is estimated by assuming that its extent in heliocentric latitude is the same as its extent in longitude, the total energy (at 1 AU) and mass flux can be calculated by integrating the excess mass and energy flux density above the predisturbance level during corotation of the stream past the observing satellite. The average energy and mass fluxes for dominant high-speed streams are found to be 9 × 1025 erg/sec and 8 × 109 g/sec, respectively. The total mass and energy output of all streams emanating from the sun over a typical 27-day interval, assuming that all last for the entire 27 days, is estimated to be less than 10% (∼7%) of the total solar-wind output from the same range of heliocentric latitudes (generally ±15°). Both large-scale streams and interplanetary shocks are found to contribute relatively little to 27-day average values of either mass or energy flux density. Thus, even though the amount of mass or energy or both per disturbance appeared to increase with increasing solar activity, the solar-wind energy and mass flux density averaged over a solar rotation remained remarkably constant.

Some studies on the solar microwave bursts in relation to the slowly varying component

The occurrences of 5772 microwave bursts recorded by the Sagamore Hill and Manilla Solar Radio Observatories over the period January 1968 to July 1970, covering the maximum phase of the current solar cycle at frequencies 2695, 4995 and 8800 MHz and their energy excesses have been examined in relation to the S-component of solar radio emission. The average slowly varying component has been determined by the superposed epoch method commonly known as the Chree analysis. Similar treatment of the bursts, data, mentioned above has been made to examine any probable 27-day variation and the results obtained have been compared with that of the S-component. Further, spectra of the microwave bursts under the so-called spectral type - ‘inverted U’, particularly those having a peak at 4995 MHz, have also been examined and compared with the average spectrum of the S-component. Some of the important results obtained from the present analysis are: (1) the nature of variation of both the average number of occurrences and energy excesses of the microwave bursts follow in general the average 27-day variation of the S-component, (2) the number of occurrences and energy excesses of the microwave bursts are comparatively greater in the ascending phase of the 27-day cycle than those in the descending phase, (3) bursts at progressively higher frequencies originate at lower levels in the solar atmosphere than those of the associated S-component, and (4) the average spectrum of the microwave bursts of ‘inverted U’ spectral type having a peak at 4995 MHz is quite identical in nature to that of the S-component.

The semi-annual variation in air density at a height of 1100 km from 1964 to 1967

The orbit of Echo 2 is used to derive values of exospheric density at heights near 1100 km during 1967. The results are combined with those from two earlier studies to show the behaviour of the semi-annual variation at solar minimum and throughout the entire rising phase of the current solar cycle. The July minima are consistently deeper than the January minima, while there is no systematic difference between the April and October maxima. It appears that the ratio of the mean maximum density to the mean minimum in the semi-annual variation decreased from about 2.5 in 1964 to about 1.8 (or possibly even lower) in 1966, as the 10.7 cm radiation flux increased from 70 to 120 × 10 −22 W m −2 Hz −1, and the ratio then increased slightly to about 2.0 in 1967.

Prediction of Sunspot Numbers for Cycle 20

IN a recent communication, P. Herrinck1 has given a table of predicted sunspot numbers for the current solar cycle (No. 19), based upon the striking coincidence of values between the two periods 1749–85 and 1918–54. A good fit was obtained by multiplying figures observed 169 years before by a factor of proportion. This means, essentially, that cycles 16, 17, and 18 have been made to correspond with the cycles 169 years earlier, namely, cycles 1, 2, and 3, respectively.

SPECTRA OF THREE BRIGHT PROMINENCES

The Sacramento Peak Observatory has made routine spectral observations at the sun's limb on every possible day for the past eight years. The purpose of this patrol is to record principally the red and green coronal lines. In the course of this series of observations, spectra of thousands of solar prominences have been recorded. Newkirk has reported on the spectroscopic composition of prominences in the first five years of operation of the patrol.1 The brightest prominence he found showed some continuous emission, and about a dozen atomic emission lines. In the past few months, just at maximum of the current solar cycle, this same routine program has produced spectra of several prominences incomparably brighter and richer in spectral features. This report concerns observations of three of these objects. Previous descriptions of prominence spectra observed in eclipse (Unsold2), and outside eclipse (Richardson3), agree essentially with those reported below. However, no other prominence spectrum discussed has equaled two of these objects in plenitude, nor the third in degree of excitation. It is important to understand the nature of coronal spectrographs in order to appreciate the limitations of such spectra in this connection. A coronagraph is a monochromatic instrument, since the occulting disk completely eliminates scattered disk light from the secondary optical system only for a unique wavelength range, in practice about 100 A wide. Moreover, since the first objective of a coronagraph is a simple lens, the diameter of the sun's first image is wavelength dependent. Without a hyperchromatic secondary optical system, the diameter of the final image will be so also. As a result, the spectrograph slit images differ-

Variations of Ultra-Violet and Daylight Rays

A DAILY record of daylight and near ultra-violet rays has boon kept for the last eleven years, covering a sunspot cycle, at a site on the slopes of the Pennine hills about ten miles north-east of Manchester. The results of daily and seasonal observations are of considerable interest, but passing over these, attention may be given to what has taken place in the current solar cycle. At the time of sunspot minimum the daylight and ultra-violet rays had a maximum intensity ; and as the number of sunspots increased, the light rays of both classes gradually diminished, and at the sunspot maximum, which occurred in 1937, they came sharply to a minimum intensity. Since then, as the sunspots have grown fewer in number, the rays have again risen to greater intensity and are increasing in intensity as the period of sun-spot minimum approaches.