[1] We have used plasma drift and magnetic field measurements during the [2001][2002][2003][2004][2005][2006][2007][2008][2009] December solstices to study, for the first time, the longitudinal dependence of equatorial ionospheric electrodynamic perturbations during sudden stratospheric warmings. Jicamarca radar measurements during these events show large dayside downward drift (westward electric field) perturbations followed by large morning upward and afternoon downward drifts that systematically shift to later local times. Ground-based magnetometer measurements in the American, Indian, and Pacific equatorial regions show strongly enhanced electrojet currents in the morning sector and large reversed currents (i.e., counterelectrojets) in the afternoon sector with onsets near new and full moons during northern winter warming periods. CHAMP satellite and ground-based magnetic field observations indicate that the onset of these equatorial afternoon counterelectrojets is longitude dependent. Our results indicate that these large electrodynamic perturbations during stratospheric warming periods are due to strongly enhanced semidiurnal lunar wave effects. The results of our study can be used for forecasting the occurrence and evolution of these electrodynamic perturbations during arctic winter warmings.Citation: Fejer, B. G., M. E. Olson, J. L. Chau, C. Stolle, H. Lühr, L. P. Goncharenko, K. Yumoto, and T. Nagatsuma (2010), Lunar-dependent equatorial ionospheric electrodynamic effects during sudden stratospheric warmings,

In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field (IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.

[1] Magnetic observations on board the CHAMP satellite are used for the first comprehensive study of magnetic signatures of the postsunset equatorial spread F (ESF) events. This is derived from a continuous database covering the years 2001-2004. On the basis of an extended survey, the global distribution of magnetic signatures is derived. We find a distinct seasonal/longitudinal variation of the occurrence rate of magnetic signatures that is consistent with that obtained from previous satellite observations of plasma depletions. The latitudinal distribution of the ESF magnetic signatures from CHAMP is symmetrical about the dip equator. It can be approximated by two Gaussian curves peaking at ±9.5°magnetic latitude, both exhibiting an 1s-width of 4.5°. We further find a close relation between the occurrence frequency and the solar EUV flux. The global average of the occurrence rate is linearly proportional to solar activity attaining $0.1% times the F10.7 value. The response of the ESF magnetic signatures to geomagnetic activity is also investigated. However, only a weak relation between the signature occurrence rate and the Kp index is found. Using high-resolution magnetic field measurements of the ESF structures, we are able to identify very small spatial scales of spread F of only few tens of meters. The vector magnetic field observations provide experimental evidence of the electromagnetic characteristics of ESF, valuable for testing model predictions. Finally, we discuss the effect of the ESF phenomenon on magnetic field modeling efforts based on satellite data.

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