Abstract. On the basis of S4max data retrieved from COSMIC GPS radio occultation measurements, the long-term climatology of the intensity of Es layers is investigated for the period from December 2006 to January 2014. Global maps of Es intensity show the high-spatial-resolution geographical distribution and strong seasonal dependence of Es layers. The maximum intensity of Es occurs over the mid-latitudes, and its value in summer is 2–3 times larger than that in winter. A relatively strong Es layer is observed at the North Pole and South Pole, with a distinct boundary dividing the mid-latitudes and high latitudes along the 60–80∘ geomagnetic latitude band. The simulation results show that the convergence of vertical ion velocity could partially explain the seasonal dependence of Es intensity. Furthermore, some disagreements between the distributions of the calculated divergence of vertical ion velocity and the observed Es intensity indicate that other processes, such as the vertical motions of gravity waves, magnetic-field effects, meteoric mass influx into Earth's atmosphere, and the chemical processes of metallic ions, should also be considered as they may also play an important role in the spatial and seasonal variations in Es layers.

Magnetic Reconnection Magnetic reconnection (MR) has been observed in the magnetospheres of planets with an intrinsic magnetic field, such as Earth, Mercury, Jupiter, and Saturn. MR is a universal plasma process that occurs in regions of strong magnetic shear and converts magnetic energy into kinetic energy. On Earth, MR is responsible for magnetic storms and auroral events. Using data from the European Space Agency Venus Express spacecraft, Zhang et al. (p. 567 , published online 5 April; see the Perspective by Slavin ) present surprising evidence for MR in the magnetosphere of Venus, which is a nonmagnetized body.

[1] In this paper, observations from CHAMP and GRACE during 2002-2010 are used to study the seasonal variations of thermospheric density by characterizing the dominant modes of thermospheric density variability as empirical orthogonal functions (EOFs). Our results showed that the first three EOFs captured most of the density variability, which can be as large as 98% of total density variability. Subsequently, the obtained mean field, first three EOFs and the corresponding amplitudes of three EOFs are applied to construct a thermospheric density model at 400 km to study seasonal variations of thermospheric density under geomagnetically quiet conditions. Thermospheric density shows strong latitudinal dependence in seasonal variation, although it usually has maxima near the equinoxes and minimum in the local winter at middle and high latitudes. Semiannual variations imbedded in the annual variations are seen at all latitudes; annual variations however become dominant in the southern hemisphere. Specifically, the observations show that the annual amplitude can reach as large as 40-50% of the annual mean at high latitudes in the southern hemisphere and it decreases gradually from the southern to northern hemisphere. The semiannual component to the annual mean is about 15-20% without significant latitudinal dependence. Additionally, the relative amplitudes of annual and semiannual variations in the MSISE00 density agree fairly well with the observations, albeit the MSISE00 gives an opposite solar activity dependence for the annual and semiannual variations compared with the positive F107 dependence seen in the observations. Citation: Lei, J., T. Matsuo, X. Dou, E. Sutton, and X. Luan (2012), Annual and semiannual variations of thermospheric density: EOF analysis of CHAMP and GRACE data,

In this study, multiple data sets from Beidou geostationary orbit satellites total electron contents (TECs), ionosonde, meteor radar, magnetometer, and model simulations have been used to investigate the ionospheric responses in the Asian‐Australian sector during the September 2017 geomagnetic storm. It was found that long‐duration daytime TEC enhancements that lasted from 7 to 12 September 2017 were observed by the Beidou geostationary orbit satellite constellation. This is a unique event as the prominent TEC enhancements persisted during the storm recovery phase when geomagnetic activity became quiet. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model predicted that the TEC enhancements on 7–9 September were associated with the geomagnetic activity, but it showed significant electron density depletions on 10 and 11 September in contrast to the observed TEC enhancements. Our results suggested that the observed long‐duration TEC enhancements from 7 to 12 September are mainly associated with the interplay of ionospheric dynamics and electrodynamics. Nevertheless, the root causes for the observed TEC enhancements seen in the storm recovery phase are unknown and require further observations and model studies.