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The Dst index underestimates the solar cycle variation of geomagnetic activity

View Article: PubMed Central - PubMed

ABSTRACT

It is known that the correction of the Kyoto Dst index for the secular variation of the Earth's internal field produces a discontinuity in the Kyoto Dst index at the end of each year. We show that this secular correction also introduces a significant baseline error to the Kyoto Dst index that leads to an underestimate of the solar cycle variation of geomagnetic activity and of the strength of the ring current as measured by the Kyoto Dst index. Thus, the average value of the Kyoto Dst index would be approximately 13 nT more negative for the active year 2003 compared to quiet years 2006 and 2009 if the Kyoto Dst index properly measured the effects of the ring current and other currents that influence the Dst observatories. Discontinuities in the Kyoto Dst index at the end of each year have an average value of about 5 nT, but the discontinuity at the end of year 2002 was approximately 12 nT, and the discontinuity at the end of year 1982 may have been as large as 20 nT.

No MeSH data available.


(top) A comparison of the 27 day running average of the Kyoto Dst index with the model with no baseline correction applied. The model with no correction shows a larger solar cycle variation. (bottom) The good agreement between the 27 day running averages when the baseline correction is applied to the model. It is important to note that our point is that the model without the baseline correction is a far more accurate representation of the effects of magnetospheric currents that affect the magnetic field at Dst observatories than the Kyoto Dst index.
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jgra51951-fig-0004: (top) A comparison of the 27 day running average of the Kyoto Dst index with the model with no baseline correction applied. The model with no correction shows a larger solar cycle variation. (bottom) The good agreement between the 27 day running averages when the baseline correction is applied to the model. It is important to note that our point is that the model without the baseline correction is a far more accurate representation of the effects of magnetospheric currents that affect the magnetic field at Dst observatories than the Kyoto Dst index.

Mentions: Figure 4 (top) shows the 27 day running average of the Kyoto Dst index and of the model if no baseline correction is applied. Note that there is less solar cycle variation in the averaged Kyoto Dst index than in the modeled Dst index. There is substantially more solar cycle variation in the modeled Dst index when no baseline correction is applied. Since the Kyoto Dst index is corrected using quiet days and since quiet days during solar maximum are likely to be less quiet than during solar minimum, the baseline correction we apply to our model to make it agree with the Kyoto Dst index removes much of the solar cycle variation in the averaged data. The modeled Dst with no baseline correction, however, does not remove the solar cycle variation in the process of removing the secular variation.


The Dst index underestimates the solar cycle variation of geomagnetic activity
(top) A comparison of the 27 day running average of the Kyoto Dst index with the model with no baseline correction applied. The model with no correction shows a larger solar cycle variation. (bottom) The good agreement between the 27 day running averages when the baseline correction is applied to the model. It is important to note that our point is that the model without the baseline correction is a far more accurate representation of the effects of magnetospheric currents that affect the magnetic field at Dst observatories than the Kyoto Dst index.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036309&req=5

jgra51951-fig-0004: (top) A comparison of the 27 day running average of the Kyoto Dst index with the model with no baseline correction applied. The model with no correction shows a larger solar cycle variation. (bottom) The good agreement between the 27 day running averages when the baseline correction is applied to the model. It is important to note that our point is that the model without the baseline correction is a far more accurate representation of the effects of magnetospheric currents that affect the magnetic field at Dst observatories than the Kyoto Dst index.
Mentions: Figure 4 (top) shows the 27 day running average of the Kyoto Dst index and of the model if no baseline correction is applied. Note that there is less solar cycle variation in the averaged Kyoto Dst index than in the modeled Dst index. There is substantially more solar cycle variation in the modeled Dst index when no baseline correction is applied. Since the Kyoto Dst index is corrected using quiet days and since quiet days during solar maximum are likely to be less quiet than during solar minimum, the baseline correction we apply to our model to make it agree with the Kyoto Dst index removes much of the solar cycle variation in the averaged data. The modeled Dst with no baseline correction, however, does not remove the solar cycle variation in the process of removing the secular variation.

View Article: PubMed Central - PubMed

ABSTRACT

It is known that the correction of the Kyoto Dst index for the secular variation of the Earth's internal field produces a discontinuity in the Kyoto Dst index at the end of each year. We show that this secular correction also introduces a significant baseline error to the Kyoto Dst index that leads to an underestimate of the solar cycle variation of geomagnetic activity and of the strength of the ring current as measured by the Kyoto Dst index. Thus, the average value of the Kyoto Dst index would be approximately 13 nT more negative for the active year 2003 compared to quiet years 2006 and 2009 if the Kyoto Dst index properly measured the effects of the ring current and other currents that influence the Dst observatories. Discontinuities in the Kyoto Dst index at the end of each year have an average value of about 5 nT, but the discontinuity at the end of year 2002 was approximately 12 nT, and the discontinuity at the end of year 1982 may have been as large as 20 nT.

No MeSH data available.