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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.


The baseline correction added to the model. The baseline correction uses a separate quadratic expression for each year. The three coefficients in each quadratic expression are found by minimizing the RMS difference between the model and Kyoto Dst index.
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jgra51951-fig-0001: The baseline correction added to the model. The baseline correction uses a separate quadratic expression for each year. The three coefficients in each quadratic expression are found by minimizing the RMS difference between the model and Kyoto Dst index.

Mentions: To find the baseline correction in the model we have made a quadratic fit to each year separately. The coefficients of each year's quadratic fit are found by minimizing the RMS error between the model and the final Kyoto Dst index. The resulting baseline correction in our model is shown in Figure 1. The baseline correction generally follows the solar cycle. The solar cycle has a minimum based on the sunspot number and the F10.7 index in 1996 and again in 2008 and 2009 and a maximum in 2000 and 2001. Geomagnetic activity has a double peak in 2000 and an even larger peak during the declining phase of the solar cycle in 2003.


The Dst index underestimates the solar cycle variation of geomagnetic activity
The baseline correction added to the model. The baseline correction uses a separate quadratic expression for each year. The three coefficients in each quadratic expression are found by minimizing the RMS difference between the model and Kyoto Dst index.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

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

jgra51951-fig-0001: The baseline correction added to the model. The baseline correction uses a separate quadratic expression for each year. The three coefficients in each quadratic expression are found by minimizing the RMS difference between the model and Kyoto Dst index.
Mentions: To find the baseline correction in the model we have made a quadratic fit to each year separately. The coefficients of each year's quadratic fit are found by minimizing the RMS error between the model and the final Kyoto Dst index. The resulting baseline correction in our model is shown in Figure 1. The baseline correction generally follows the solar cycle. The solar cycle has a minimum based on the sunspot number and the F10.7 index in 1996 and again in 2008 and 2009 and a maximum in 2000 and 2001. Geomagnetic activity has a double peak in 2000 and an even larger peak during the declining phase of the solar cycle in 2003.

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.