Statistical analysis of solar H-alpha flares

A statistical analysis of a large data set of H-alpha flares comprising almost 100000 single events that occurred during the period January 1975 to December 1999 is presented. We analyzed the flares evolution steps, i.e. duration, rise times, decay times and event asymmetries. Moreover, these parameters characterizing the temporal behavior of flares, as well as the spatial distribution on the solar disk, i.e. N-S and E-W asymmetries, are analyzed in terms of their dependency on the solar cycle. The main results are: 1) The duration, rise and decay times increase with increasing importance class. The increase is more pronounced for the decay times than for the rise times. The same relation is valid with regard to the brightness classes but in a weaker manner. 2) The event asymmetry indices, which characterize the proportion of the decay to the rise time of an event, are predominantly positive (90%). For about 50% of the events the decay time is even more than 4 times as long as the rise time. 3) The event asymmetries increase with the importance class. 4) The flare duration and decay times vary in phase with the solar cycle; the rise times do not. 5) The event asymmetries do not reveal a distinct correlation with the solar cycle. However, they drop during times of solar minima, which can be explained by the shorter decay times found during minimum activity. 6) There exists a significant N-S asymmetry over longer periods, and the dominance of one hemisphere over the other can persist for more than one cycle. 7) For certain cycles there may be evidence that the N-S asymmetry evolves with the solar cycle, but in general this is not the case. 8) There exists a slight but significant E-W asymmetry with a prolonged eastern excess.

[1]  A. Paliatsos,et al.  Possible east side predominance of the optical emissions of the solar corona , 1997 .

[2]  V. Verma.  On the increase of solar activity in the southern hemisphere during solar cycle 21 , 1988 .

[3]  J. Roy.  The north-south distribution of major solar flare events, sunspot magnetic classes and sunspot areas (1955–1974) , 1977 .

[4]  M. Minnaert.  On the Inclination of the Normal Axes of Sunspots , 1946 .

[5]  H. Newton,et al.  Bright Solar Eruptions and Radio Fadings During the Years 1935–36 , 1937 .

[6]  A. Maunder.  An apparent influence of the Earth on the numbers and areas of sun-spots in the Cycle 1889-1901 , 1907 .

[7]  M. Shea,et al.  Some comments on the east-west solar flare distribution during the 1976–1985 period , 1990 .

[8]  John Wilson.  Machine-aided indexing for NASA STI , 1987 .

[9]  T. Bai.  Distribution of flares on the sun - Superactive regions and active zones of 1980-1985 , 1987 .

[10]  R. Mcmath,et al.  Photometry of Solar Flares. , 1956 .

[11]  M. A. Ellison.  Characteristic Properties of Chromospheric Flares , 1949 .

[12]  A. Joshi.  Asymmetries during the maximum phase of solar cycle 22 , 1995 .

[13]  L. Altaş,et al.  The duration of spotless flares , 1992 .

[14]  A. Özgüç,et al.  Flare Index During the Rising Phase of Solar Cycle 23 , 2001 .

[15]  H. Garcia.  Evidence for solar-cycle evolution of north-south flare asymmetry during cycles 20 and 21 , 1989 .

[16]  C. Warwick.  Some Characteristics of Solar Flares. , 1954 .

[17]  B. Schmieder,et al.  Statistical analysis of the X-ray flares (M ≥ 1) during the maximum period of solar cycle 22 , 1998 .

[18]  T. Ataç,et al.  North-South asymmetry in the solar flare index , 1996 .

[19]  Z. Svestka.  A comparison of solar activity during the decline of several solar cycles , 1995 .

[20]  E. W. Cliver.  Solar flare nomenclature , 1995 .

[21]  V. Verma,et al.  On the periodicities of sunspots and solar strong hard X-ray bursts , 1987 .

[22]  T. Bai.  Distribution of Flares on the Sun during 1955--1985: ``Hot Spots'' (Active Zones) Lasting for 30 Years , 1988 .

[23]  J. Reid.  Cape Lyot Hα-heliograph results , 1968 .