Abstract.We assess the contribution of various types of solar wind structures (coronal mass ejections (CMEs), high-speed streams, and slow solar wind) to averages of the aa geomagnetic activity index (•-5) during the solar cycle. We

Abstract. We determine the solar wind structures (coronal mass ejection (CME) -related, corotating high-speed streams, and slow solar wind) driving geomagnetic storms of various strength over nearly three solar cycles (

No abstract

We have analyzed periodicities in the occurrence rate of proton flares for solar cycles 19 through 21 (1955-86) and have identified two epochs that exhibit a 154-day periodicity. These epochs are a 14-year interval from 1958 January through 1971 December and a 5.5-year intervl-from 1978 February to 1983 August. The best-determined period is 154.4±0.6) day.) We have found that the phase of this periodicity changed between the abovementioned two epochs by about one half of a period0(¢0.5±0.16). It appears that the occurrence rate of proton flares is more sensitive to the 154-day periodicity than the occurrence rate of flares selected by other criteria* ,

Observations of the Sun's corona during the space era have led to a picture of relatively constant, but cyclically varying solar output and structure. Longer-term, more indirect measurements, such as from 10 Be, coupled by other albeit less reliable contemporaneous reports, however, suggest periods of significant departure from this standard. The Maunder Minimum was one such epoch where:(1) sunspots effectively disappeared for long intervals during a 70 yr period; (2) eclipse observations suggested the distinct lack of a visible K-corona but possible appearance of the F-corona; (3) reports of aurora were notably reduced; and (4) cosmic ray intensities at Earth were inferred to be substantially higher. Using a global thermodynamic MHD model, we have constructed a range of possible coronal configurations for the Maunder Minimum period and compared their predictions with these limited observational constraints. We conclude that the most likely state of the corona during-at least-the later portion of the Maunder Minimum was not merely that of the 2008/2009 solar minimum, as has been suggested recently, but rather a state devoid of any large-scale structure, driven by a photospheric field composed of only ephemeral regions, and likely substantially reduced in strength. Moreover, we suggest that the Sun evolved from a 2008/2009-like configuration at the start of the Maunder Minimum toward an ephemeral-only configuration by the end of it, supporting a prediction that we may be on the cusp of a new grand solar minimum.