Abstract
Abstract The equatorial electrojet (EEJ) is a unique feature of the Earth’s external current systems because it must flow along the dip equator. This provides us with a tool to determine the nature of the variations imposed by competing main field models on the equatorial region. First we show that for certain regions a comparison between scalar geomagnetic measurements that use different models to remove the main field may not be reasonable. Next we found the intrinsic error in the determination of the possible location of the dip equator was ±9.8 km (0.088°) at 108 km altitude for the models shown here. Using scalar measurements from over 14,000 CHAMP satellite passes, the latitude of the maximum of the EEJ field at the satellite altitude was determined by subtracting four different models of the main field. We find that the location can be statistically determined to within ±0.5° of the dip equator (calculated at 108 km altitude) irrespective of longitude, time of the measurement, degree of magnetic activity, and subtracted model. However, variations of the latitude of the maximum EEJ field with longitude are sometimes caused by the actual model and are not always a physical phenomenon. By choosing one model, and assuming it is the best representation of the main field, we have also shown that the accuracy of determination of the position of the EEJ signal is reduced in the morning and evening hours and that a morning and evening shift in the location of the EEJ found using ground measurements is also seen here. There exists a clear annual variation in the position of the EEJ regardless of longitude: it is south of the dip equator in December which is in agreement with the findings of all previous studies.
Highlights
The reason for embarking upon this study was we noticed several colleagues comparing magnetic data obtained from satellite measurements by using different models to remove the main field
It is clear from comparing the model dip equators that when two models are used the maximum intrinsic error imposed upon the data set is
Differences between different main field models show for certain regions a long wavelength signature with amplitude close to 5 nT in the core field component
Summary
The reason for embarking upon this study was we noticed several colleagues comparing magnetic data obtained from satellite measurements by using different models to remove the main field. The dip equator is calculated as the zero point of the Z component of the main field model of angular degrees 1–14 (including secular terms). The difference increases as altitude decreases, being in the range ±0.01◦ at 800 km (approximate altitude of Ørsted), ±0.015◦ at 400 km (CHAMP), ±0.025◦ at 108 km (EEJ), and ±0.027◦ at the surface It is clear from comparing the model dip equators that when two models are used the maximum intrinsic error imposed upon the data set is. The latitude of the dip equator is varies with time
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
