CAOSP abstracts, Volume: 27, No.: 2, year: 1997

Abstract: The autocorrelation analysis of solar soft X-ray parameters was performed with a time lag ranging from 1 to 32 days (acf_j, with j=1, ..., 32) for the 1969-76 period. Consecutive sequences containing daily data for a 2-year interval were considered. From the comparison of the autocorrelation functions for both flare (TOT) and nonflare (XBG) soft X-ray variables we selected the different recurrent tendency over the years. During the maximum (1969-71) and minimum (1975-76) phases of the 20th solar cycle the recurrency of all the SXR parameters is included between 18 and 23 days, but during the decreasing activity phase (1972-74) recurrencies approach the expected 27-day synodic rate of rotation. The nonflare X-ray corona has a particularly stable 27-day recurrency (from 1971-72 to 1974-75), but the flare TOT variable displays the 27-day recurrency only in the 1972-73 sequence (Figure 5). The most stable 25-day TOT recurrency was observed in 1973-75. Our results of the atypical "solar periodicity" of TOT values (i.e., acf_lm < 27 days) are in agreement with past findings based on other solar activity indices and cycles. However, we have also noted, on a short time scale (1 day), that there exists a strong coherence (acf_1 ~ 0.8) of the XBG variables for all the investigated intervals. While this coherence is high (acf_1 ~ 0.7) in the TOT variable only for 1973-75, when long-lived coronal holes covered a large fraction of the solar surface, in the other periods the parameter acf_1(TOT) =< 0.55. The above findings were never explicitly emphasized in solar soft X-ray studies.

Full text version of this article in PostScript (600dpi) format compressed by gzip; or in PDF.

Back to:
CAOSP Vol. 27 No. 2 index
CAOSP archive main index
CAOSP main page
Astronomical Institute home page

Valid HTML 4.01! Valid CSS!

Last update: February 12, 2003