MAGNETIC FLUX TUBES AT 3 AU?

We present an analysis of plasma and magnetic field data acquired by the Ulysses spacecraft on May 1994. Our study is motivated by the result of Poletto et al. (1996) who found some evidence for a peak in the power spectrum of magnetic pressure at a frequency 2 × 10–⁵ Hz, during that period. A re-evaluation of the plasma pressure power spectrum, on the basis of better data than used in the previous work, gives only marginal evidence for a peak at that frequency. If both spectra had excess power in the same spectral range, one might hypothesize that the Pressure Balanced Structures (PBS) detected in the data trace periodically distributed coronal structures which maintain their identity up to large distances. A careful data analysis, however, shows that this interpretation is hardly tenable. Hence, we consider the alternative hypotheses that the observed PBS are either a bundle of magnetic flux tubes, with no characteristic periodicity, in pressure equilibrium with the ambient, or the manifestation, at large distances, of waves generated close to the Sun. To prove the latter case, we made a test simulation of the evolution with heliocentric distance of an ensemble of Alfvén and slow mode waves, generated close to the Sun, and show that structures similar to those we analyzed may form in the interplanetary medium. Our simulations also seem to show that together with PBS, magnetic holes, frequently observed in the Ulysses data, could also originate from the nonlinear evolution of large amplitude slow waves in quasi-perpendicular propagation. We conclude that the observed PBS most likely arise via an in situ generation mechanism, rather than being remnants of solar structures.     

DO SOLAR FLARES EXHIBIT AN INTERVAL–SIZE RELATIONSHIP?

Some models for flare statistics predict or assume that there is a relationship between the times between flares and the energy of flares. This question is examined observationally using the WATCH solar X-ray burst catalogue. A rank correlation test applied to the data finds strong evidence for a correlation between the time since the last event, t _b, and the size (peak count rate) of an event, and for a correlation between the time to the next event, t _a, and the size of an event. A more sophisticated statistical test, taking into account a probable bias in event selection, does not support the hypothesis that event size depends on t _b or t _a.     

COMMENTS ON THE PAPER: RECALCULATION OF H-Lα SKY SURVEYS: NO NEED FOR ANISOTROPIC SOLAR WIND MASS OUTFLOWS?

In a recently published paper, Scherer and Fahr (1995) claimed that the departures of sky L emission measured by Prognoz 5 and 6 from an optically thin model can be attributed entirely to deficiencies of the optically thin approximation, and are not due to variations of solar wind ionization rate with latitude, as advocated since many years by our research group. They base their claim on the result of their new sophisticated model of L radiation transport.It is shown here that their new model, in the simple case of isotropic solar wind, predicts a distribution of intensity in a simple geometry which is completely contradicted by the observations: they find a minimum of intensity near the upwind direction, where a maximum has been observed consistently by all L instruments. Therefore, their conclusion based on an erroneous model must be rejected.     

BIG LOOP PROMINENCE SYSTEM AT THE WEST LIMB OF SOLAR DISK ON THE DAYS 15 TO 17, AUG.IN 1989

Using the 18 cm Hα-Photoheliograph at Yunnan Observatory,we obtained theAR5629(S17,L75)data.The AR existed at the southern hemisphere of solar disk duringthe days from Aug.4 to 16.Except Aug.16th when the AR partly moved away from thedisk,sunspot group type was HRX,the AR kept its complex type in McIntoshclassfication on the other 12 days and there were 8 days,spot group areas over 1,000     

CAN WE OBSERVE THE TEMPERATURE INHOMOGENEITIES AND MAGNETIC FLUX TUBES AS THE FINE STRUCTURE ON THE EXTREME LIMB OF THE SUN?

Fine structure of brightness inhomogeneities with I r.m.s. = 2.9% was discovered on the extreme limb of the Sun on the best quality white-light photographs obtained at the Soviet Stratospheric Solar Observatory. The concept is that temperature inhomogeneities are responsible for the limb structure. The real value T r.m.s. = 109K is required to explain our observations. Another possible explanation is that small-scale magnetic flux tubes with the realistic filling factor f* = 1% are the source of the limb brightness fluctuations.