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A study of the green corona rotation rate, during the period 1970–1974, confirms that the differential rotation degree varies systematically through a solar cycle and that the corona rotates in an almost rigid manner before sunspot minimum. During the first two years, 1970–1971, the differential rotation degree, characteristic of high solar activity periods is detected. While during the years of declining activity, 1972–1974, a drastic decrease of the differential rotation degree occurs and the green corona rotates almost rigidly, as the coronal holes observed in the same period. These conclusions are valid only for the rotation of coronal features with lifetime of at least one solar rotation. 相似文献
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During the year 1969 two long-lived centres were active on the Sun at Carrington longitudes 50° < L < 100° and 250° < L < 300°. About 80% of the flares of importance 1B, produced during this period, originated in these zones.The solar modulation of galactic cosmic ray intensity during 1969 was dominated by effects resulting from the activity in the two zones. In fact all the decreases can be related to the passage at the central meridian of the active centres. Persistence of the effects connected to solar regions is found also during rotations in which they do not produce flares in front of the Earth.Seventeen among the twenty-six intensity decreases, observed during this period, can also be correlated to individual flares belonging to the region at central meridian (longitudes ± 40° with respect to the CM).The data suggest that two phenomena are operative to produce decreases of the cosmic ray flux: the passage of the interplanetary corotating stream associated with the active region near the central meridian and the blast wave produced by the flares in front of the Earth. 相似文献
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A study on the differences of rotation properties, based on the lifetime of coronal features, has been performed for the period 1972–1974. The short-lived component of the green corona associated with solar activity is differentially rotating, while long-lived coronal features persisting more than one synodic rotation period, show little or no differential rotation. These two components coexist at a same latitude within a wide latitude range at least in one of the solar hemispheres. 相似文献
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Solar Wind Velocity and Anisotropic Coronal Kinetic Temperature Measured with the O Vi Doublet Ratio
Doppler dimming of the Ovi resonance lines (1032 Å, 1037 Å) in an expanding corona is calculated including the pumping effect on the Ovi 1037.61 Å of both Cii lines at 1036.34 Å and 1037.02 Å, and the effect of the width of the absorption profiles of the coronal oxygen ions along the incident radiation. The pumping effect of the Cii line at 1036.34 Å allows us to extend to approximately 450 km s–1 the measurement of solar wind velocities with the Ovi line ratio technique. Since the emissivity ratio of the Ovi doublet depends on the width of the oxygen coronal absorbing profiles, this ratio can provide an accurate measurement of the solar wind velocity in the case that the width of the absorbing profile along the direction of the incident radiation is independently determined. However, if on the one hand the ratio of the emissivities of the Ovi doublet has limitations in probing the wind velocity, on the other hand it can be used as a diagnostics for inferring the velocity distribution of the coronal Ovi ions along the radial, and detecting possible velocity anisotropies. This diagnostics, applied to recent observational results, allows us to infer that the velocity distribution of the oxygen ions is much broader in the direction perpendicular to the magnetic field direction, and that the acceleration of the fast solar wind in the first 2 solar radii is high. 相似文献
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We have correlated intensity decreases in the galactic component of cosmic rays observed at the Earth with solar phenomena. We have found that there exist intensity decreases detected underground, which are probably associated with long-lived interplanetary streams and which are not directly associated with single flares. We expect to detect the streams with underground monitors before the arrival of the streams at the Earth. The early detection will be in the northern or in the southern hemisphere, depending on the sign of the interplanetary field. 相似文献
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We present a study of the outflow velocity of the fast wind in the northern polar coronal hole observed on 21 May 1996, during the minimum of solar activity, in the frame of a joint observing program of the SOHO (Solar Heliospheric Observatory) mission. The outflow velocity is inferred from an analysis of the Doppler dimming of the intensities of the Ovi 1032, 1037 and Hi L 1216 lines observed between 1.5 R
and 3.5 R
with the Ultraviolet Coronagraph Spectrometer (UVCS), operating onboard SOHO. The analysis shows that for a coronal plasma characterized by low density, as derived for a polar hole at solar minimum by Guhathakurta et al. (1999), and low temperature, as directly measured at the base of this coronal hole by David et al. (1998), the oxygen outflow speed derived spectroscopically is consistent with that implied by the proton flux conservation. The hydrogen outflow is also consistent with flux conservation if the deviation from isotropy of the velocity distribution of the hydrogen atoms is negligible. Hence, for this cool and tenuous corona, the oxygen ions and neutral hydrogen atoms flow outward roughly at the same speed, which increases from 40 km s–1 at 1.5 R
to 360 km s–1 at 3.1 R
, with an average acceleration of the order of 4.5×103 cm s–2. The highly anisotropic velocity distributions of the Ovi ions found in the analysis confirm that the process which is heating the oxygen ions acts preferentially across the magnetic field. 相似文献
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