The global distribution and variations of the monthly mesopause temperature are presented during 2002–2019 covering the latitudes of 83°S to 83°N based on Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observations. To investigate the long‐term trend and solar response of the mesopause temperature, a three‐component harmonic fit is first applied to remove the seasonal variation from the monthly temperature data series. Then a multiple linear regression model is performed to residual temperatures versus constant, linear trend, solar activity, and geomagnetic activity terms. In this study, the mesopause temperature shows a cooling trend through all latitudes ranging from ~0 to −0.14 K/year with a mean of −0.075 ± 0.043 K/year. The cooling trends in the Southern Hemisphere are stronger than those in the Northern Hemisphere. For high latitudes (60–80°), significant negative trends can be observed during nonsummertime, while no significant trends are found for summertime. The mesopause temperature shows apparent positive responses to solar activity through all latitudes ranging from 3.03 to 4.80 K per 100 solar flux units (sfu) with a mean of 3.99 ± 0.49 K per 100 sfu, which is more significant and stable in the Northern Hemisphere. There is a pronounced drop for mesopause height at polar latitudes, which reflects the shrinking effect at lower altitudes mainly caused by greenhouse gas cooling. We show that the length of the time interval analyzed strongly influences the results. Our results, obtained from 18‐year SABER observations, are expected to be a robust measure of the mesopause temperature variability.

Ionospheric sporadic E layer is thin irregularity with much higher plasma density in the ionospheric E region (~90‐120 km). Morphology of sporadic E intensity is investigated by using the COSMIC radio occultation data during 2007‐2012. Maximum gradient value of total electron content fluctuation is defined as S_max index, and it shows good linear relationship with the sporadic E intensity parameter (ordinary critical frequency, foEs) in the low‐latitude and midlatitude regions. By using this S_max index as the sporadic E layer intensity, distribution of sporadic E intensity is obtained. Some known features are confirmed such as the hemisphere summer enhancement, diurnal and semidiurnal behavior, and intensity depression anomaly regions. New findings are also obtained, especially the different behavior pattern in the low‐latitude region. (1) Both positive and negative correlations exist between sporadic E intensity and solar activity, and this correlation also shows complex magnetic latitude dependency. (2) Weaker seasonal variation is found in the low‐latitude region. Besides, hemisphere asymmetries of sporadic E intensity/location are also found during the equinox. (3) Longitudinal wave number‐4 feature of sporadic E intensity is prominent in the lower latitude region, which may be related to the diurnal eastward wave number‐3 tide. In a word, it is feasible to investigate the sporadic E layer intensity distribution based on radio occultation data, which also allows for a global morphology analysis.

Key Points: The Artificial Neural Network Model (ANNM) has good capability of characterizing the variability of the satellite drag‐derived densities The density data during either 1967–2005 or 1967–2013 intervals are used to give a similar long‐term trend from the ANNM The thermospheric density trend relative to the ANNM from 250 to 575 km is about −1.5% to −2.0% per decade without obvious solar flux dependence

During the geomagnetic storm on September 8–9, 2017, shoulder‐like structures were persistently captured in the lower‐mid latitudes at multiple local times, by Swarm and DMSP satellite observations. A more telling terminology of such shoulder‐like structure called strip‐like bulge is proposed in this study, due to its global presence that spanning over 150° in longitude but only over 1°–5° in latitude. The strip‐like bulges can be categorized into sharp and blunt types depending on the sharpness of the density peaks. The blunt type was short‐lived and appeared earlier than the sharp type in the afternoon‐sunset sector. The sharp type was long‐lived and appeared at all the observed local times. Both two types of strip‐like bulges were dominated by the ion composition of the H⁺/He⁺, rather than O⁺. This is the first evidence that the plasmaspheric particles are involved in forming the ionospheric structure at such low latitude. Moreover, the equatorward movement of the bulges shared the same trends with the earthward movement of the plasmapause. These two types of strip‐like bulges showed different longitudinal dependencies controlled by the magnetic declination. We suggest that the combined effects from the plasmaspheric downwelling and disturbance neutral wind were responsible for the appearance of the strip‐like bulges.

Thermospheric mass densities from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite for Sun-synchronous orbits between 83.5∘ S and 83.5∘ N, normalized to 270 km during 2009–2013, have been used to develop an empirical mass density model at dawn/dusk local solar time (LST) sectors based on the empirical orthogonal function (EOF) method. The main results of this study are that (1) the dawn densities peak in the polar regions, but the dusk densities maximize in the equatorial regions; (2) the relative seasonal variations to the annual mean have similar patterns across all latitudes regardless of solar activity conditions; (3) the seasonal density variations show obvious hemispheric asymmetry, with large amplitudes in the Southern Hemisphere; (4) both amplitude and phase of the seasonal variations have strong latitudinal and solar activity dependences, with high amplitude for the annual variation at higher latitudes and semiannual variation at lower latitudes; (5) the annual asymmetry and effect of the Sun–Earth distance vary with latitude and solar activity. Keywords. Atmospheric composition and structure (pressure, density, and temperature)