Postsunset midlatitude traveling ionospheric disturbances (TIDs) and equatorial plasma bubbles (EPBs) were simultaneously observed over American sector during the geomagnetic storm on 8 September 2017. The characteristics of TIDs are analyzed by using a combination of the Millstone Hill incoherent scatter radar data and 2‐D detrended total electron content (TEC) from ground‐based Global Navigation Satellite System receivers. The main results associated with EPBs are as follows: (1) stream‐like structures of TEC depletion occurred simultaneously at geomagnetically conjugate points, (2) poleward extension of the TEC irregularities/depletions along the magnetic field lines, (3) severe equatorial and midlatitude electron density (Ne) bite outs observed by Defense Meteorological Satellite Program and Swarm satellites, and (4) enhancements of ionosphere F layer virtual height and vertical drifts observed by equatorial ionosondes near the EPBs initiation region. The stream‐like TEC depletions reached 46° magnetic latitudes that map to an apex altitude of 6,800 km over the magnetic equator using International Geomagnetic Reference Field. The formation of this extended density depletion structure is suggested to be due to the merging between the altitudinal/latitudinal extension of EPBs driven by strong prompt penetration electric field and midlatitude TIDs. Moreover, the poleward portion of the depletion/irregularity drifted westward and reached the equatorward boundary of the ionospheric main trough. This westward drift occurred at the same time as the sudden expansion of the convection pattern and could be attributed to the strong returning westward flow near the subauroral polarization stream region. Other possible mechanisms for the westward tilt are also discussed.

In this work, we develop gradient boosting machines (GBMs) for forecasting the SYM‐H index multiple hours ahead using different combinations of solar wind and interplanetary magnetic field (IMF) parameters, derived parameters, and past SYM‐H values. Using Shapley Additive Explanation values to quantify the contributions from each input to predictions of the SYM‐H index from GBMs, we show that our predictions are consistent with physical understanding while also providing insight into the complex relationship between the solar wind and Earth's ring current. In particular, we found that feature contributions vary depending on the storm phase. We also perform a direct comparison between GBMs and neural networks presented in prior publications for forecasting the SYM‐H index by training, validating, and testing them on the same data. We find that the GBMs yield a statistically significant improvement in root mean squared error over the best published black‐box neural network schemes and the Burton equation.

Polar cap “patches” are ~100 to 1,000 km islands of high‐density plasma at polar latitudes, which can cause scintillation to communication and navigation signals. An automatic algorithm for patch identification has been developed and applied to the observations from the Resolute Bay Incoherent Scatter Radar‐Canada during January to March and September to December, 2016. Four hundred thirty‐seven patches have been identified, and their statistical characteristics have been studied, including their occurrence rate as a function of magnetic local time (MLT) and statistical profiles of plasma parameters at different MLT sectors. About 60% of the patches are observed between 1200 and 2400 MLT, consistent with earlier observations near this latitude (~82° MLat) using different instruments. Superposed epoch analysis has been used to study the vertical profiles of electron density and temperature, ion temperature, vertical velocity, and flux measured within the patches where the density peaks. The patch median density is higher than the sector median with a ratio of ~1.8–2.1 at the altitude of F‐region density peak. Meanwhile, the patch electron temperature is typically lower than the sector median between ~200 and 450 km with the largest difference near noon (~380 K). In contrast, the ion temperature profile of the patches does not show obvious differences except in the noon sector, where the ion temperature is about 150 K higher than the sector median at ~360 km. Additionally, downward ion fluxes with peak exceeding ~1013 m−2 s−1 are found in the patches between ~200 and 400 km at all MLT sectors.

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asymmetries of the mid-latitude ionosphere were observed during the first recovery phase of the September 7-8, 2017 storm • Hemispheric asymmetries were opposite over the European-African and East Asian-Australian sectors simultaneously • Their formation is likely due to the asymmetries of the thermospheric composition change, vertical plasma drift, and Traveling Ionospheric Disturbance activity