We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusually high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). In one event, the spectral–temporal forms of the emissions looked like a series of giant bullets, with very abrupt cessation. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations. Hide

Present work reports seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere region. All-sky images of the hydroxyl airglow emission layer over São João do Cariri (7.4° S, 36.5° W) were observed from September 2000 to December 2010, during a total of 1496 nights and obtained 2343 SSGW and 537 MSGW events. The horizontal propagation directions of SSGWs and MSGWs showed clear seasonal variations based on the influence of the wind filtering process. Hide

The solar wind reshapes Earth's magnetic field to create our magnetosphere and powers many dynamic processes in our plasma-filled environment, some of which produce the aurora. Networks of ground-based all-sky cameras are valuable tools that offer a large field-of-view with which to study the aurora. Using sequences of auroral images, this study defines criteria for differentiating an important type of aurora whose subcategories are often conflated. Hide

The Kelvin–Helmholtz waves are believed to be an effective way to transport solar wind mass and energy into Earth's magnetosphere. In this study, we show that the ion-scale flux rope generated at the trailing edge of Kelvin–Helmholtz waves by multiple X-line reconnection could be directly related to this transfer process. The lower hybrid drift waves detected at the edges of the flux rope can also contribute to this process and then affect the revolution of the flux rope. Hide

This paper performs a statistical study of the spatial distribution and source region size along a filed line of both rising tone and falling tone whistler waves based on the Van Allen Probes data. The results suggest that both types of chorus waves are generated near the equatorial plane, roughly consistent with previous theoretical estimates. The work should be useful to further understand the generation mechanism of chorus waves. Hide

We have established that, over the East African region, the trough of the equatorial ionisation anomaly (EIA) during high solar activity and quiet geomagnetic conditions lies slightly south of the magnetic equator. During the equinox and December solstice seasons, and a local time interval of 13:00–15:00, the probability of observing the EIA on days with daytime equatorial electrojet (EEJ) strength ≥ 40 nT was mostly > 80 %. Hide

Using Voyager 1 observations of Jupiter's Io plasma torus, we have determined the location of maximum brightness depending on longitude and the location of Jupiter’s moon Io. We obtain a third viewing direction of the torus (after Voyager 2 and ground observations) and thus two locations, left and right of Jupiter, which are important for the correct modeling of this structure. We also find that a narrow ribbon-like structure only appears when the brightness of the torus exceeds a certain value. Hide

Atmospheric tides are produced by solar heating of the lower atmosphere. The tides propagate to the upper atmosphere and ionosphere playing an important role in the vertical coupling. Ground radar measurements of the seasonal variability of tides are compared with global numerical simulations. The agreement with radar data and limitations of the numerical model are discussed. The work represents a first step in modelling the impact of tidal dynamics on the upper atmosphere and ionosphere. Hide

Using an empirical approach put forward by Makela et al. (2001), firstly, we propose a novel technique to calibrate OI 777.4 and 630.0 nm emission intensities using COSMIC/FORMOSAT-3 electron density profiles. Next, electron density maximum (Nm) and its height (hmF2) of the F layer are derived from the information of two calibrated intensities. Sample Nm and hmF2 maps are also generated to show the usefulness of this technique in studying ionospheric processes. Hide

We present a comprehensive statistical analysis of mirror mode waves and the properties of their plasma surroundings in sheath regions driven by interplanetary coronal mass ejection (ICME) to deepen our understanding of these geo-effective plasma environments. The results imply that mirror modes are common structures in ICME sheaths and occur almost exclusively as dip-like structures and in mirror stable stable plasma. Hide

To predict the satellite's motion or its re-entry, the density surrounding the satellite needs to be known as precisely as possible. Usually empirical models are used to estimate the neutral density of the thermosphere, which is the region of the neutrally charged atmosphere. Here, based on calibrated accelerations measured by instruments on board satellites, we compute daily global maps to correct modeled densities. During times of high solar activity, corrections of up to 28 % are necessary. Hide

Fast jets of solar wind particles drive through a slower environment in the magnetosheath, located sunward of the region dominated by the Earth’s magnetic field. THEMIS multi-spacecraft observations show that jets push ambient particles out of their way. These particles flow around the faster jets into the jets’ wake. Thereby, jets stir the magnetosheath, changing the properties of this key region whose particles and magnetic fields can directly interact with the Earth’s magnetic field. Hide