Results 1 - 10 of 2454
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[en] Despite the small interannual variation in the stratosphere in the northern summer, there is a distinct signal of the 11-year solar cycle in the geopotential heights and temperatures. Unlike the stratosphere in winter, when it is necessary to group the data according to the phase of the quasi-biennial oscillation (QBO) to obtain a statistically significant response to the solar cycle, the summer stratosphere has the same pattern for the full time series as for east and west years in the QBO. In all three series the pattern is statistically significant in summer
[en] Dates of solar maxima and minima extending back to c. 1610 were estimated by Wolf and Wolfer at Zuerich (Waldmeier, 1961) in the nineteenth century, and those back to c. 1710 have been generally accepted. Slight modifications have already been suggested by the author (Schove, 1967) for the seventeenth century, although, in that century, even the existence of the eleven-year cycle has been questioned (Eddy, 1976). In the course of any sunspot cycle one finds a pattern of the aurorae in place and time characteristic of sunspot cycles of the particular amplitude-class. These patterns since c. 1710 can be linked to the precise dates of the Zuerich turning-points by a set of empirical rules. A sunspot rule is based on the Gnevyshev gap, the gap in large sunspots near the 'smoothed' maximum. These rules are here applied to the period c. 1510-1710 to give improved determination of earlier turning-points, and approximately confirm the dates given for the seventeenth century by Wolfer and for most of the later sixteenth century by Link (1978). Some turning-points for the fifteenth century and revised sunspot numbers for the period 1700-48 are also given. (Auth.)
[en] It is shown that the maximum of the present 80-year sunspot period, as the period of the importance of sunspot groups, occurred in 11-year cycle No. 18 (1944 to 1953) according to the Zurich numbering. (author)
[en] This article presents a survey of studies incorporating methods of evaluation of Greenwich observations. It also describes some extreme sunspot groups (i.e., groups with a very large area, a very long life, and/or in very high heliographic latitudes); data on the total areas of the largest sunspots are given, and a survey of the parameters concerning individual 11-year cycles, resulting from Greenwich Photoheliographic Results, is presented. (orig.)
[en] Sunspot data from the Catania Astrophysical Observatory, covering cycles 18, 19, and 20 (1943-1977) have been analyzed, taking into account, besides the usual parameters, the number n of zones, namely latitude belts 50 wide, showing sunspot activity and the area covered by spots for each of these zones. A comparison between these conclusions and those drawn from other authors on the same subject is made. (Auth.)
[en] Based on the dependence of the maximum relative RM-number of the odd 11-year cycle on the RM of the previous even cycle, it is forecast that RM should exceed 200 in the next 11-year sunspot cycle, No. 23. (author). 1 fig., 8 refs
[en] The properties of kinematic αω-dynamos are briefly reviewed. The mean field concept, including turbulent diffusivity, is defended against recent criticism. It is pointed out that although the Maunder minimum cannot be explained by kinematic dynamo theory alone, this does not invalidate dynamo theory in general. A special discussion is devoted to attempts to evaluate the coefficients of the mean field induction equation in the case of very large conductivity. The field then behaves intermittent, in the form of locally concentrated flux tubes, and the α-effect and the turbulent diffusivity may be determined by assymptotic techniques or with the help of an exact solution of the non-dissipative induction equation in Lagrangian co-ordinated. Magnetic cycles of main sequence stars other than the Sun are briefly discussed. Besides rotation, the depth of the convection zone is probably the most influencial parameter for period and amplitude of the stellar cycle. Observational programmes to advance the theory of the solar cycle must include the solar magnetic and velocity fields, over the entire Sun and on all scales. In particular the angular velocity as a function of depth should be studied further with the help of the p-eigenmodes. The knowledge of luminosity, radius and (or) temperature variations with the solar cycle would also stimulate the theoretical approach. (orig.)
[en] We present an analysis of facular/network and sunspot areas (and their ratio) covering most of cycle 22 and all of cycle 23. The data are corrected areas (in microhemispheres) from full-disk solar images using two photometric telescopes at the San Fernando Observatory, CFDT1 and CFDT2. Images from CFDT2 have approximately twice the spatial resolution of CFDT1. Sunspot areas are obtained from red images where spots are determined as those pixels darker than -8.5%. Facular/network areas are from Ca II K-line images where facular/network pixels are brighter than 4.8%. Regressions of facular area versus spot area for CFDT1 give a slope term of 25. For CFDT2, the slope term is 33. The average ratio of facular to spot area for cycle 22 is 45 and for cycle 23 the ratio is 42. These values are substantially higher than those from earlier studies. The increase is due to a combination of higher spatial resolution and the removal of a correction factor in μ. For the 0.3 nm K-line images, the spot to facular/network ratio is 138 for six years of cycle 23. A relation is given for the dependence of facular/network area on contrast. The relationship of facular/network area to sunspot area is linear for data from both telescopes.
[en] In this paper, the problem of the unusually long 4th sunspot cycle is discussed: was the length of this cycle exceptionally large or really composed of two short cycles? Analyzing the latitude-time diagram in 1784-1798, reconstructed from the drawings by Staudacher, Hamilton, and Gimingham, we suggest that the 4th cycle length can be a result of an impulse of activity in the northern hemisphere during the descending phase. The local minimum in 1793 can be just a gap between impulses of the solar activity, similar to the declining phase in the southern hemisphere of the long cycle 20. The long declining phase of cycle 4 is that the minimum in 1793 may also be due to lack of data. We have shown that sparse observations of the sunspots, in the second half of cycle 4, do not prove the existence of the 'lost' tiny cycle from 1793 to 1800.