We propose that the temperature of the Na exosphere of Mercury near the subsolar point is not at high as proposed in previous works. Using a numerical model and the appropriate energy distributions for each release mechanism, we can explain observations made by MESSENGER in April 2012. Our results show that close to the surface, the dominant release mechanism for Na is evaporation due to the solar irradiation, and at high altitudes the best candidate is the release by micro-meteoroid impacts.

The sun’s radiation exhibits a cycle with a period of ~11 years. We need to understand how the atmospheric temperature and ozone react to this solar variation, as it can affect climate. The response depends on energy transfer, chemical reactions, and atmospheric motions. There is no consensus as to some details. For example, the responses depend on the local times of the variations. This study provides results of effects of local time on the responses, from 20 to 100 km, based on measurements.

In this paper, for the first time, absolute gravity wave momentum flux (GWMF) on temporal scales from terannual variation up to solar cycle length is investigated. The systematic spectral analysis of SABER absolute GWMF is presented and physically interpreted. The various roles of filtering and oblique propagating are discussed, which is likely an important factor for MLT dynamics, and hence can be used as a stringent test bed of the reproduction of such features in global models.

Simulations of locally breaking gravity wave hot spots in the stratosphere show a suppression of wave propagation at midlatitudes, which is partly compensated for by additional wave propagation through the polar region. This leads to a displacement of the polar vortex towards lower latitudes. The effect is highly dependent on the position of the artificial gravity wave forcing. It is strongest (weakest) for hot spots at lower to middle latitudes (higher latitudes).

We observe the planetary and gravity wave activity in the vertical profile of ozone at the mid-European ozonosonde stations The performance of the used detection method is satisfactory. There are differences in the following characteristics of the structure caused by the planetary and gravity wave: the annual variation, the size, and the vertical distribution. The results are influenced by the ozonosonde vertical resolution only for small and medium structures.

This paper concerns the question of whether the maximum Earth ring current strength exists and at which moment the ring current can start to break up, thus making a new mechanism of the ring current decrease during the magnetic storm. We study this effect using the Stormer theory of particle motion. After transition of critical strength, Stormer's inner trapping region opens up and the ring current charged particles get the opportunity to leave it, thus decreasing the current strength.

In this work we present an analysis of the dynamics of suprathermal ions of different masses (H⁺, He⁺, O⁺) during prolonged dipolarizations in the near-Earth magnetotail according to Cluster/RAPID observations in 2001–2005. All dipolarizations from our database were associated with fast flow braking and consisted of multiple dipolarization fronts (DFs). We found statistically that fluxes of suprathermal ions started to increase ~ 1  min before the dipolarization onset and continued.

We study how the Earth's space environment responds to two different amplitude interplanetary coronal mass ejection (ICME) events that occurred in 2012 and 2014 by using the GUMICS-4 global MHD model. We examine local and large-scale dynamics of the Earth's space environment and compare simulation results to in situ data. It is shown that during moderate driving simulation agrees well with the measurements; however, GMHD results should be interpreted cautiously during strong driving.

The paper presents the variability in thermal tides in the middle atmosphere from temperature observations as well as from horizontal wind data using a new diagnostic approach which takes into account a possible intermittency of tides. The data are analyzed from a local as well as from a global perspective to distinguish between different tidal modes. Surprisingly, there are dominating tidal modes, which are seen in the local data, and a phase relation between temperature and winds is evaluated.

We describe a technique used to locate and classify critical points in 2-D flow fields at the solar photosphere obtained from the evolution of the line-of-sight magnetic field in a region close to the magnetic polarity inversion line of a fully emerged active region. We apply this technique to locate a particular kind of critical point associated to vortex flows, which are considered important, since they can twist and interweave the foot points of flux tubes and generate magnetic reconnection.

We analysed an event of short-term ozone variability due to the passage of the polar vortex over Río Gallegos (southern Argentina) with the aim of highlighting the capability of a millimetre-wave radiometer to observe ozone in the stratosphere and the low mesosphere with a high temporal resolution. It is particularly important in this subpolar region due to the high variation that this gas can suffer as a consequence of the passage of the polar vortex and the ozone hole during spring.

Using the Beijing MST radar echo-power observations collected during the period November 2011–May 2017, the structure and variability of the tropopause over Xianghe, China (39.75° N, 116.96° E), was presented. Our comparison results showed a good agreement between the radar and thermal tropopauses during all seasons. In contrast, the consistency between the radar and dynamical tropopauses is poor during summer. Diurnal oscillation in tropopause height is commonly observed during all seasons.

To check the difference between data observed at different altitudes of the DEMETER satellite, a statistical method is adopted to evaluate whether data difference is caused by normal data fluctuation or by altitude adjustment. Based on the method, in situ electron density data at higher altitudes are found to be greater than those at lower altitudes. We speculate that this phenomenon is caused by stratification above F2 peak region. The proposed method is useful when comparing fluctuated data.

This study concerns postmidnight ionospheric irregularities observed during low solar activity conditions. We analyze data from digisondes and optical imaging systems located in an equatorial region over Brazil. The results show that they occur under unfavorable and unexpected conditions. This work can be useful for space weather forecasting during low solar activity.

Before the solar wind encounters the Earth's magnetic field, it is first slowed down and deflected by the Earth's bow shock. We find that downstream of the bow shock regions where the shock normal and the solar wind magnetic field are almost parallel and the shock is more rippled, plasma jets with high earthward velocities are observed significantly more often than elsewhere downstream of the shock. Our results help us forecast the occurrence of these jets and their effects on Earth.

This paper describes an approach to model VTEC solely from NRT GNSS observations by generating a multi-scale representation (MSR) based on B-splines. The unknown model parameters are estimated by means of a Kalman filter. A number of products are created which differ both in their spectral and temporal resolution. The validation studies show that the product with the highest resolution, based on NRT input data, is of higher accuracy than others used within the selected investigation time span.

The Earth’s radiation belt (ERB) is formed by energetic particles caught in the geomagnetic trap. Within the last two solar cycles (from 2001 to 2018), observations of the ERB by a fleet of low-altitude POES satellites have allowed for the discovery of an abnormal equatorward displacement of the outer part of ERB in the Siberian sector. This displacement can partially explain the increase in the occurrence rate of midlatitude aurora borealis observed in the Eastern Hemisphere.

The equatorial spread F (ESF) is a nighttime phenomenon that can have a deleterious effect on the radio communication system. We investigated the parameters influencing the seasonal morphology of the range type spread F (RSF) using ionosonde data from different longitude sectors. The observed RSF occurrence features showed distinct patterns across these sectors, including seasonal asymmetry. This asymmetry was attributed to the probable effect of the zonal wind reversal and gravity waves.

The solar flare effects on ionosphere at midlatitudes and low latitudes were investigated with the systematic analysis of ionospheric parameters derived from ionograms (total radio fade-out, f_min, df_min: deviation from the reference days). The duration of the total fade-out varied with the solar zenith angle. Furthermore, a solar-zenith-angle-dependent enhancement of the f_min and df_min parameters was detected but the observed values also depended on the flare intensity.

Blanco-Cano et al. (2018) intended to find a type of transient event in the solar wind before the terrestrial bow shock using a special type of simulation. However, the simulation results cannot reproduce the main features of the event. Based on the remarks described below, I am sure that the features in the simulations are not those types of events. The Vlasiator code simulated proto-SHFAs.

Chromospheric flows are of significant importance in understanding the mechanisms of transfer of plasma and energy from the lower atmosphere of the Sun to the corona through the transition region. We study the quiescent loop system in terms of Doppler velocities at the foot points of individual loop strands to understand the plausible heating mechanisms driving plasma flows in such loop systems.