Significant decreases in the geomagnetic indices in the ascending phase of Solar Cycle 24

Minamoto, Yasuhiro; Taguchi, Yosuke

doi:10.1186/bf03353188

Cited by 8 publications

(10 citation statements)

References 6 publications

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“…The low activity in 2008-2009 is clearly related to the general decrease of geomagnetic activity during the somewhat diffuse transition from the solar cycle 23 to cycle 24 (cf. Minamoto and Taguchi, 2009). A clear increase of activity is evident in 2010, although it still remains at a very low level compared to the previous years 1983-2008.…”

Section: Extended Analysis Of Dh /Dtmentioning

confidence: 91%

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

Viljanen

Tanskanen

2011

Ann. Geophys.

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Abstract.We investigate the characteristics of rapid geomagnetic variations at high latitudes based on the occurrence of large time derivatives of the horizontal magnetic field (dH /dt exceeding 1 nT s −1 ). Analysis of IMAGE magnetometer data from North Europe in 1983-2010, covering more than two solar cycles, confirms and specifies several previous findings. We show that dH /dt activity is high around the midnight and early morning hours, and nearly vanishes at noon and early afternoon. This happens during all seasons, although the midnight maximum is nearly invisible during summer. As indicated by modelled ionospheric equivalent currents, large dH /dt values occur predominantly during westward ionospheric electrojets. Before and around midnight, dH /dt tends to be north-south oriented, whereas in the morning hours, its direction is more west-east directed. dH /dt tends to be more strictly north-south oriented during winter than other seasons. The seasonal occurrence of large dH /dt values is similar to the variation of the maximum amplitude of westward equivalent currents. The yearly fraction of east-west directed large dH /dt vectors at the Kilpisjärvi station (MLAT 65.88) varies from 31 to 47 % without any clear correlation with the general geomagnetic activity nor with the yearly averages of solar wind parameters.

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Section: Extended Analysis Of Dh /Dtmentioning

confidence: 91%

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

Viljanen

Tanskanen

2011

Ann. Geophys.

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“…Also shown for comparison is the R z . It can be seen that the current minimum in geomagnetic ap index is the lowest in the history of ap (see also Minamoto & Taguchi 2009). This indicates that solar wind-magnetosphere energy transfer during the current minimum was very low.…”

Section: Historical Datamentioning

confidence: 99%

“…As it is known that longterm averages of AE have high correlation with the ap index (Echer et al 2004), this would be expected. The Dst index shows very low (in magnitude) values, the lowest in the space era, and comparable to another period of low values during the 1960s (Minamoto & Taguchi 2009). Fig .…”

Section: Historical Datamentioning

confidence: 99%

“…Furthermore, extreme flux enhancements were observed in cosmic rays (Heber et al 2009;. As a consequence, there have been many geophysical effects, both in the magnetosphere and ionosphere/atmosphere (Gibson et al 2009;Minamoto & Taguchi 2009;Kataoka & Miyoshi 2010;Ram, Lin & Su 2010;Russell, Luhmann & Jian 2010;Echer et al 2011;Emery et al 2011;Verkhoglyadova et al 2011).…”

Section: Introductionmentioning

confidence: 99%

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Extremely low geomagnetic activity during the recent deep solar cycle minimum

2011

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Abstract. The recent solar minimum (2008)(2009)) was extreme in several aspects: the sunspot number, Rz , interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era . Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

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“…The daily sum of the eight 3 h Ki values ( K) and monthly means of this sum (< K > monthly ) have been previously used as representative of the irregular geomagnetic activity observed at a certain station (see e.g. Minamoto andTagushi, 2009, or Zhang et al, 2008).…”

Section: Data Descriptionmentioning

confidence: 99%

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

2014

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Abstract. The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) inPortugal has a long history of observation of the geomagnetic field, spanning almost 150 yr since the first geomagnetic measurements in 1866. These long instrumental geomagnetic records provide very important information about variability of geomagnetic elements and indices, their trends and cycles, and can be used to improve our knowledge on the sources that drive variations of the geomagnetic field: liquid core dynamics (internal) and solar forcing (external).However, during the long life of the Coimbra Observatory, some inevitable changes in station location, instrument's park and electromagnetic environment have taken place. These changes affected the quality of the data collected at COI causing breaks and jumps in the series of geomagnetic field components and local K index. Clearly, these inhomogeneities, typically shift-like (step-like) or trend-like, have to be corrected or, at least, minimized in order for the data to be used in scientific studies or to be submitted to international databases.In this study, the series of local K index and declination of the geomagnetic field are analysed: the former because it allows direct application of standard homogenization methods and the latter because it is the longest continuous series produced at COI. For the homogenization, visual and statistical tests (e.g. standard normal homogeneity test) have been applied directly to the local geomagnetic K index series (from 1951 to 2012). The homogenization of the monthly averages of declination (from 1867 to 2012) has been done using visual analysis and statistical tests applied to the time series of the first differences of declination values, as an approximation to the first time derivative. This allowed not only estimating the level of inhomogeneity of the studied series but also detecting the highly probable homogeneity break points. These points have been cross-checked with the metadata, and the COI series have been compared with reference series from the nearest geomagnetic stations and, in the case of declination series, from the recent geomagnetic field model COV-OBS to set up the required correction factors. As a result, the homogenized series measured in COI are considered to be essentially free of artificial shifts starting from the second half of the 20th century, and ready to be used by the scientific community.

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Significant decreases in the geomagnetic indices in the ascending phase of Solar Cycle 24

Cited by 8 publications

References 6 publications

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

Climatology of rapid geomagnetic variations at high latitudes over two solar cycles

Extremely low geomagnetic activity during the recent deep solar cycle minimum

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

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