Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity

Yoshïda, Akio

doi:10.5194/angeo-27-1909-2009

Cited by 9 publications

(8 citation statements)

References 20 publications

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“…Here, it should be noted that mid-latitude indices such as aa are correlated to the product of the square of the solar wind velocity and the southward component of the IMF in GSM coordinates (e.g., Maezawa and Murakami, 1986;Yoshida, 2009) Fig. 8c, which produced an extraordinarily large geomagnetic disturbance (Yoshida, 2008).…”

Section: Discussionmentioning

confidence: 99%

Predicting amplitude of solar cycle 24 based on a new precursor method

Yoshïda

Yamagishi

2010

Ann. Geophys.

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Abstract. It is shown that the monthly smoothed sunspot number (SSN) or its rate of decrease during the final years of a solar cycle is correlated with the amplitude of the succeeding cycle. Based on this relationship, the amplitude of solar cycle 24 is predicted to be 84.5±23.9, assuming that the monthly smoothed SSN reached its minimum in December 2008. It is further shown that the monthly SSN in the three-year period from 2006 through 2008 is well correlated with the monthly average of the intensity of the interplanetary magnetic field (IMF). This correlation indicates that the SSN in the final years of a solar cycle is a good proxy for the IMF, which is understood to reflect the magnetic field in the corona of the sun, and the IMF is expected to be smallest at the solar minimum. We believe that this finding illuminates a physical meaning underlying the well-known precursor method for forecasting the amplitude of the next solar cycle using the aa index at the solar minimum or its average value in the decaying phase of the solar cycle (e.g. Ohl, 1966), since it is known that the geomagnetic disturbance depends strongly on the intensity of the IMF. That is, the old empirical method is considered to be based on the fact that the intensity of the coronal magnetic field decreases in the late phase of a solar cycle in parallel with the SSN. It seems that the precursor method proposed by Schatten et al. (1978) and Svalgaard et al. (2005), which uses the intensity of the polar magnetic field of the sun several years before a solar minimum, is also based on the same physical phenomenon, but seen from a different angle.

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Section: Discussionmentioning

confidence: 99%

Predicting amplitude of solar cycle 24 based on a new precursor method

Yoshïda

Yamagishi

2010

Ann. Geophys.

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“…The largest number of historical documents reporting red auroras was reported on 17 September 1770 (Matsushita, ). The September 1770 event occurred during the equinox season, when the magnetosphere and ionosphere tend to develop intense storms (Bartels, ; McIntosh, ; Russell & McPherron, ; Yoshida, ). The event also occurred during a new moon period, which led people to watch this special nighttime event in detail.…”

Section: Introductionmentioning

confidence: 99%

Inclined Zenith Aurora over Kyoto on 17 September 1770: Graphical Evidence of Extreme Magnetic Storm

Kataoka

Iwahashi

2017

Space Weather

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Red auroras were observed in Japan during an extreme magnetic storm that occurred on 17 September 1770. We show new evidence that the red aurora extended toward the zenith of Kyoto around midnight. The basic appearance of the historical painting of the red aurora is geometrically reproduced based on the inclination of the local magnetic field and a detailed description in a newly discovered diary. The presence of the inclined zenith aurora over Kyoto suggests that the intensity of the September 1770 magnetic storm is comparable to, or slightly larger than that of the September 1859 Carrington storm.

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“…In comparison, no day of June 2004 has an Ap value in excess of 20. It can be observed in Figure 9 that the slope, which can be considered as a measure of the average geomagnetic turbulence, is highest for the month of March 2004 and lowest for the month of June 2004, following the pattern of semiannual variations as observed by Yoshida [2009]. However, the first‐order relationship between the VV indices of IMF and geomagnetic fields is recognized beyond reservation following the analysis of data for 13 months.…”

Section: Resultsmentioning

confidence: 81%

Interplanetary magnetic field–geomagnetic field coupling and vertical variance index

2010

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[1] The solar wind impacting at the geomagnetopause contains transient variations in the embedded interplanetary magnetic field (IMF). These disturbances are mirrored in the horizontal geomagnetic field measured at the Huancayo and Ascension Island stations. This investigation attempts to relate the microtemporal fluctuations in the IMF with the horizontal component of the geomagnetic field by means of a newly developed daily vertical variance index, which permits the quantification of such pulsations. A linear relationship is established between the disturbances observed in the interplanetary and terrestrial fields on a daily basis.

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Physical meaning of the equinoctial effect for semi-annual variation in geomagnetic activity

Cited by 9 publications

References 20 publications

Predicting amplitude of solar cycle 24 based on a new precursor method

Predicting amplitude of solar cycle 24 based on a new precursor method

Inclined Zenith Aurora over Kyoto on 17 September 1770: Graphical Evidence of Extreme Magnetic Storm

Interplanetary magnetic field–geomagnetic field coupling and vertical variance index

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