(bottom) The difference once the baseline correction is applied to the model. Note the discontinuity in the difference exactly at the end of the year 2002. (top) The difference (i.e., the error) between the model and the Kyoto Dst index when the baseline correction is not applied to the model for the period shown in Figure 2. Geomagnetic activity has a double peak in 2000 and an even larger peak during the declining phase of the solar cycle in 2003. The solar cycle has a minimum based on the sunspot number and the F 10.7 index in 1996 and again in 20 and a maximum in 20. The baseline correction generally follows the solar cycle. The resulting baseline correction in our model is shown in Figure 1. The coefficients of each year's quadratic fit are found by minimizing the RMS error between the model and the final Kyoto Dst index. To find the baseline correction in the model we have made a quadratic fit to each year separately. Here we report on the effect of changing the baseline correction to the model. We intend to report on these improvements later. These additions produce interesting though minor improvements to the model. We have now extended the model to years 1995–2009 using OMNI solar wind data (instead of using solely Wind and ACE satellite data), added effects based on the F 10.7 index and effects using all three components of the solar wind velocity instead of just the V x component. The model also had a baseline correction with a single discontinuity at the end of 1999 as we were not then aware that there was in fact a discontinuity at the end of each year in the Kyoto Dst index. This model does a good job of duplicating the Kyoto Dst index for the years 1995–2002 using the solar wind magnetic field, velocity, and density as input. We have previously developed a model of the Kyoto Dst index based solely on the solar wind. The main point of this report is that this is the case: the Kyoto Dst index underestimates the solar cycle variation of magnetic activity. Since the baseline for each year is determined using a different set of years, a discontinuity occurs at the end of each year and because quiet days during solar maximum may not be as quiet as quiet days during solar minimum, the average Dst value may underestimate the change in magnetospheric activity between solar maximum and solar minimum. In a second step an additional point is added whose value is the baseline value at the end of the current year as determined in the first step, and then a second quadratic fit is done using this additional point ). Then a quadratic fit is made to those five values. (The five quietest days of each month produce sixty values for that year, which are then averaged to produce a single value for that year. Each year's contribution to the quadratic fit is based on the five quietest days of each month of that year. The Kyoto Dst index baseline is corrected for the secular variation of the Earth's internal magnetic field by making a quadratic fit to each of the four Dst observatories by using the last 5 years of magnetic data from that observatory. As such, it is adjusted for the Sq dayside ionospheric current system and for the secular variation due to changes in the internal magnetic field of the Earth. The Dst index is designed to be a measure of the magnetic perturbation near the equator from currents flowing above the ionosphere. For example, storm types have been defined based on the magnitude of the Dst index: minor storm (−30 nT > Dst > −50 nT), moderate storm (−50 nT > Dst > −100 nT), intense storm ( Dst < −100 nT), and great storm ( Dst < −250 nT). The Kyoto Dst index is widely used as an indicator of geomagnetic activity.
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