Interplanetary Magnetic Field Sector Structure Research Articles

Effects of the interplanetary magnetic field sector structure in the winter ionosphere

The ionospheric effects of the interplanetary magnetic field (IMF) sector boundary crossings are studied for the winters of 1963–69. They are considerably stronger for “proton” than for “non-proton” sector boundaries. There are two different types of effects. The “geomagnetic” type is a disturbance, observed in geomagnetic activity, the night-time ionosphere and the day-time F2 region near the geomagnetic equator. The effect in the ionosphere is interpreted in terms of the IMF sector boundary crossing related changes in geomagnetic activity. The “tropospheric” type is aquietening, observed in tropospheric vorticity and in the day-time mid-and low-latitude ionosphere (except the geomagnetic equator region). The mechanism of this effect remains unexplained.

Control of diurnal and seasonal variation of particle precipitation by regular changes of the interplanetary magnetic field

Systematic changes of the position of the dipole axis of the Earth's magnetic field with respect to the solar axis induce distinct daily and seasonal variations of the vertical B z -component in the solarmagnetospheric coordinate system ( B ZSM ). Depending on the direction of the interplanetary magnetic field (IMF), negative B ZSM - values are produced in spring by T polarity and in autumn by A polarity, whereas in the diurnal variation lowest B ZSM -values have been calculated to occur near 23 UT for T, and near 11 UT for A polarity, respectively. In different ionospheric and geomagnetic parameters measured at high and midlatitudes increased precipitation of high energetic particles into the lower thermosphere and upper mesosphere has been detected during periods with negative B ZSM -components. The seasonal variation of the parameters investigated, with maximum values near the equinoxes, as well as a part of their diurnal variations, can thus be explained by particle precipitation being markedly controlled by the IMF sector structure.

Does the interplanetary magnetic field and the solar activity contribute to the tropospheric circulation?

A significant tendency is shown for both Etesians and (+, −) sector boundaries of the interplanetary magnetic field (IMF) to occur on the same solar rotation days, during the main period of the Etesians effect (July–August). In addition, the solar activity seems to control the Etesians distribution within the IMF sector structure. In the epoch of maximum there is a significant tendency of Etesians to occur during ‘toward’ IMF days. In contrast, in the epoch of minimum Etesians occur mainly during ‘away’ IMF days. Finally, in the epoch of intermediate the Etesians are uniformly distributed in ‘away’ and ‘toward’ IMF days. Since these conclusions are statistically significant at high confidence levels, it is fair to assume that IMF and solar activity seem to contribute, to some extent, to the Etesians occurrences, as well as to their distribution within the solar rotation and the IMF sector structure; that is, some solar contribution to the tropospheric circulation is implied.

Influence of interplanetary magnetic field sector boundary passages on Jovian decametric radio bursts

Jovian decametric radio emission (DAM) observations from five stations operated by the Goddard Space Flight Centre (GSFC) and from the University of Colorado, Boulder, are used to explore the connection between DAM activity and the interplanetary magnetic field (IMF). Assuming that the IMF sector structure corotates with the Sun, IMF sector boundary crossing times at the orbit of Jupiter have been determined. It is found that in both the frequency ranges covered (16.7 MHz and 22.2 MHz), Jovian DAM activity increases as these sector boundaries pass Jupiter.

Cosmic-ray 13 day oscillation and two-sector interplanetary magnetic field

The cosmic-ray intensity modulation observed at the boundary crossing of the interplanetary magnetic-field sector structure is related with the about 13 day oscillation during the years 1973 and 1974 when the magnetic field presents two sectors.

Effects of the interplanetary magnetic field on the auroral oval and plasmapause

Recent research into the effects of the interplanetary magnetic field (IMF) on the Earth's auroral oval and plasmapause are reviewed. While the IMF sector structure has been known for some time to produce asymmetries in polar-cap convection, recent work has shown these effects to extend into the dayside auroral oval. A restricted region of local times referred to as the convection ‘throat’ is found to move to either side of the noon meridian in response to changes in the IMF By component.

On the possibility of inferring the inter-planetary sector structure from daily variations of geomagnetic ap indices

The linear Bartels ap indices, which by definition should have no average U.T. variations, show in fact two different average U.T. variations if the data is divided into two groups according to the two Interplanetary Magnetic Field (IMF) polarities. These differences are found to be similar for all seasons and activity ranges. Correlating the ap variations of individual days to the average ap variations for days with interplanetary away and toward polarities, a simple but objective precept of calculations is given to infer the IMF sector structure with a success rate of 73% of the days for the years 1963–1973. The same method is employed to infer the IMF sector structure since 1932, and the results are compared to the sector structure inferred from polar cap magnetograms. Some known features of solar sector fields, e.g. the heliographic latitude dependence of the dominant polarity, are also found in the polarity classification based on ap variations, whereas the significant higher geomagnetic activity during intervals of toward polarity before 1963, which was found in the sector structure inferred from polar cap magnetograms, is not observed.

The mean magnetic field of the Sun: Observations at Stanford

A solar telescope has been built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean field magnitude has been about 0.15 G with typical measurement error less than 0.05 G. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (see near the Earth with a 4 day lag). The differences in the observed structures can be understood in terms of a ‘warped current sheet’ model.

The interplanetary magnetic field sector structure and meteorological microseisms

Meteorological microseisms, recorded at the Prague seismic station and, similarly, at other Central Europe stations, reflect certain meteorological situations in the North Atlantic frontal zone. Meteorological elements in this zone are affected by some factors of extra-terrestrial origin, among others by the interplanetary magnetic field (IMF) sector structure. The analysis of the 68 IMF sector boundary passage effects in microseismic activity, expressed in microseismic amplitudes, showed a well-developed minimum of microseismic activity on the day of the boundary passage in winter, but no such effect in spring and autumn. In spring and autumn, however, a tendency was observed to slightly higher microseismic activity in the “away” (+) sector, whereas no such tendency was observed in winter. These results agree with the IMF effect found in the troposphere. Generally, the IMF sector structure is only a modulating rather than a major factor controlling the microseismic activity.

Ionospheric radio wave absorption in the auroral zone and the interplanetary magnetic field sector structure

We have considered the character of radio wave absorption variations in the auroral zone, depending on the relative number of sunspots over a 11-yr cycle and on a interplanetary magnetic field (IMF) sector polarity, by using observations carried out at Murmansk, by the Al method, at noon throughout 1959 to 1967. It was shown that the abnormal absorption occurrence frequencies as well as the background absorption values are generally bigger in the case of the IMF directed away from the Sun. The difference, caused by IMF sector polarity, of both values is subject to regular quasi-two-year variations.

Relationship between solar magnetic sector structure and geomagneticDst

The occurrence of geomagneticDst, AE andKp with respect to the passage of well-defined boundaries of the interplanetary magnetic field sector structure near the earth is studied. It is concluded that the sector structure is not related to the changes inDst and possible reasons for the observed behaviour are discussed.