Interplanetary Magnetic Field Sector Polarity Research Articles

Unraveling the Role of IMF Bx in Driving Geomagnetic Activity

AbstractIn this work, we question the existing opinion that the interplanetary magnetic field (IMF) Sun‐Earth (Bx) component is of minor importance for the geomagnetic activity and show that both Bx and By, being two principal components of the Parker's spiral, are equally important factors. We show that the asymmetric behavior of activity indices around solstices can be explained as a combination of symmetric (sign‐independent) effect of IMF By and asymmetric (sign‐dependent) effect of Bx, the latter interpreted as a result of the geodipole tilt influence on the magnetotail stability and nightside reconnection. We also show that, due to the 7.5° inclination of the Earth orbital plane to the solar equatorial plane, the geoeffective IMF Bz component may increase or decrease, depending on the IMF sector polarity and season.

On the association of predominant polarity of North-South component of IMF in the GSE system near 1 AU with solar polar magnetic fields during 1967–2020

The skewness of the monthly distribution of GSE latitudinal angles of Interplanetary Magnetic Field (IMF) observed near the Earth (Sk) is found to show anti-correlation with sunspot activity during the solar cycles 20–24. Sk can be considered as a measure of the predominant polarity of north-south component of IMF (Bz component) in the GSE system near 1 AU. Sk variations follow the magnitude of solar polar magnetic fields in general and polarity of south polar fields in particular during the years 1967–2020. Predominant polarity of Sk is found to be independent of the heliographic latitude of Earth. Sk basically reflects the variations of the solar dipolar magnetic field during a sunspot cycle. It is also found that IMF sector polarity variation is not a good indicator of the magnitude changes in solar polar magnetic fields during a sunspot cycle. This is possibly due to the influence of non-dipolar components of the solar magnetic field and the associated north-south asymmetries in the heliospheric current sheet.

Response of thermosphere density to changes in interplanetary magnetic field sector polarity

[1] A systematic analysis of the thermospheric density response to changes in the interplanetary magnetic field (IMF) sector polarity is carried out. For this purpose we use a high-latitude southern thermospheric total mass density near 400 km altitude, derived from the high-accuracy accelerometer on board the Challenging Minisatellite Payload (CHAMP) spacecraft in 2003, a period of a well-defined IMF sector polarity change. The IMF sector polarity changes appear to strongly influence the high-latitude thermospheric density variations, especially in equinox seasons. After normalization to a constant solar flux level, densities in the Southern Hemisphere near the March equinox show a significant differences, depending on whether the IMF field polarity is toward the Sun (“toward sector,” i.e., +Bx and −By) or away from the Sun (“away sector,” i.e., −Bx and +By). Densities in the toward sector near the March equinox increase before the sector boundary passes the Earth, with strong enhancements in the cusp region and the premidnight sector. Densities in the away sector near the March equinox decrease before the sector boundary passes the Earth, with a significant decrease in the early morning hours. On the other hand, near the September equinox, densities in the Southern Hemisphere do not show significant changes associated with the IMF sector polarity changes. The IMF By and the Bz offsets associated with the IMF sector polarity changes are related to specific behaviors in terms of thermospheric densities. In the toward (away) sector near the March equinox, IMF conditions that increase (decrease) the high-latitude southern thermospheric densities, the negative (positive) By and the negative (positive) Bz offsets, are maintained. On the other hand, in the toward (away) sector near the September equinox, the negative (positive) IMF By condition, which increases (decreases) the high-latitude southern thermospheric densities, and the positive (negative) IMF Bz offset condition, which decreases (increases) the high-latitude southern thermospheric densities, coexist.

Flux enhancement of the outer radiation belt electrons after the arrival of stream interaction regions

The Earth's outer radiation belt electrons increase when the magnetosphere is surrounded by the high‐speed solar wind stream, while the southward interplanetary magnetic field (IMF) is also known as an important factor for the flux enhancement. In order to distinguish the two different kinds of solar wind parameter dependence statistically, we investigate the response of the outer belt to stream interaction regions (SIRs). A total of 179 SIR events are identified for the time period from 1994 to 2005. We classify the SIR events into two groups according to the so‐called “spring‐toward fall‐away” rule: IMF sector polarity after the stream interface is toward in spring or away in fall (group A) and vice versa (group B). According to the Russell‐McPherron effect, groups A and B have a significant negative and positive offset of the IMF Bz after the stream interface, respectively. Comparing groups A and B by superposing about the stream interface, only IMF Bz dependence can be obtained because the other solar wind parameters change in the same manner. As a result, the greatest flux enhancement is found in the highest‐speed streams with a southward offset of the IMF Bz, indicating that only the solar wind speed by itself is not a sufficient condition for the large flux enhancement. It is also found that the large flux enhancement tends to be associated with weak geomagnetic activities with minimum Dst of about −50 nT on average, implying that the existence of intense magnetic storms is not essential for the flux enhancement.

Evolution of the outer radiation belt during the November 1993 storms driven by corotating interaction regions

Evolution of energetic electron fluxes, related solar wind conditions, and relevant plasma waves in the inner magnetosphere are examined during the two corotating interaction region (CIR)‐driven magnetic storms in November 1993. In this paper we focus on the fact that the flux of the outer radiation belt electrons increased significantly during the 3 November storm, while it did not increase above the prestorm level during the 18 November storm. The recovery phase of the 3 November storm is associated with the prolonged substorm activity; continuous injections of hot and subrelativistic electrons, and enhanced chorus wave activity which can accelerate subrelativistic electrons to MeV energies by means of wave‐particle interactions. In contrast, the recovery phase of the 18 November storm is associated with reduced substorm activity, weak injections of hot and subrelativistic electrons, and low chorus wave activity. These differences in the recovery phase can be related to the southward offset of interplanetary magnetic field (IMF) in the high‐speed coronal hole stream, which is influenced by the IMF sector polarity via the Russell‐McPherron effect (dipole tilt effect associated with the IMF polarity).

USE OF COSMIC RAY MEASUREMENTS TO IDENTIFY THE SECTOR POLARITIES OF THE INTERPLANETARY MAGNETIC FIELD

The knowledge of the interplanetary magnetic field sector polarity at the Earth's location is relevant to study many phenomena related to the Space Climatology. We filled the gaps in the daily polarities of the interplanetary magnetic field derived from spacecraft observations by using two sets of ground-based measurements: i) the cosmic ray muon component intensities supplied by the multidirectional Nagoya telescope; ii) the geomagnetic field from the Antarctic Vostok Observatory. We discuss the time variability of the sector polarities inferred from the wavelet technique in the period 1971–1992.

Interplanetary magnetic field polarities inferred from the north–south cosmic ray anisotropy

The interplanetary magnetic field sector polarity at the Earth's location can be inferred from ground measurements of the cosmic ray north‐south anisotropy. We present here the results of a systematic comparison between inferred and directly measured polarities in the period from January 1971 through December 1997. The overall success rate of the prediction method is 72%, in rather good agreement with previous findings. On the other hand, our analysis shows for the first time the limits of the method and calls for warning in its use. In fact, it turns out that the inferred polarities are affected by a bias, which becomes more relevant around the sunspot minimum. Even though the bias cannot be removed, it is possible to select conditions, occurring for 30% of the time, under which the inferred polarities are very reliable (the success rate being 95%).

The magnetic field of the equatorial magnetotail from 10 to 40 RE

A statistical study of IMP 6, 7, and 8 magnetotail magnetic field measurements near the equatorial plane reveals new information about various aspects of magnetospheric structure. More magnetic flux crosses the equatorial plane on the dawn and dusk flanks of the tail than near midnight, but no evidence is found for a dependence on the interplanetary magnetic field sector polarity. Field magnitudes within 3 RE of the equatorial plane near dawn are more than twice as large as those near dusk for −20 < Xsm < −10 RE. The frequency of occurrence of southward fields is greatest near midnight, and such fields are seen almost twice as often for −20 < Xsm < −10 RE as for Xsm beyond −20 Re. This latter result supports the idea that the midnight region of the tail between 10 and 20 RE is a special location where neutral lines are particularly apt to form. Such a neutral line will approach nearest the earth in the midnight and premidnight region, where substorms are thought to have their onset.

Influence of IMF-sector polarity on the North-South asymmetry of geomagnetic activity and its relationship with solar wind parameters

Relationships between the North-South asymmetry of the geomagnetic activity associated with the sector polarity of the interplanetary magnetic field (IMF) and various solar wind parameters are examined using the subauroral zone magnetic activity indices an and as. It is found that: (1) the effect of the sector polarity of IMF on the North-South asymmetry is due to the By-component of IMF, not to the Bx-component; (2) the asymmetry appears only when IMF is directed southward, being augmented by the increment of the magnitudes of the southward component and the solar wind velocity.

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.