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To investigate the response of ionosphere to strong geomagnetic storms at different latitudes, this paper focuses on the response characteristics of global ionospheric ROTI at different latitudes during the September 2017 strong geomagnetic storms based on global ROTI maps and GPS dual-frequency observation data, and explores the PPP accuracy of GPS stations at each latitude during two different types of strong geomagnetic storms. The results show that (i) the daily mean ROTI values during the September 2017 strong geomagnetic storms show a spatial distribution of higher in the global region in the high-latitude region of North America, the northern European region and the whole Antarctic region, and lower in other regions. (ii) The highest ROTI time mean value in the high-latitude belt, with a peak value of 0.30 TECU/min, exceeds twice the peak value of the global time mean value; within the mid-latitude belt, the ROTI time mean value in the northern hemisphere is larger, with values exceeding three times those of the Southern Hemisphere. (iii) During the strong geomagnetic storm in September 2017, the PPP results of high-latitude GPS stations were affected to a greater extent, and the mean value of positioning error in the vertical direction exceeded 2.0 m. (iv) During the strong geomagnetic storm in November 2021, the changing trend of the mean value of PPP positioning error at different latitudes was consistent with that of 2017, but the mean value of positioning error and RMS at high latitudes in 2021 was higher than those in 2017. [ABSTRACT FROM AUTHOR]

This manuscript presents the analysis of data from multiple ground‐ and space‐based sensors in the North American region before, during, and after the 12 October 2021 geomagnetic storm. Total electron content (TEC) and electron density data show the formation and equatorward propagation of a mid‐latitude trough at ∼50°N followed by the appearance of a wider depletion region (∼15° in latitude) at lower latitudes. During the recovery phase on the 13th, the equatorward edge of this depletion region settled at around 30° latitude and exhibited a steep density gradient. By the 14th, this sharp boundary had disappeared. Near this edge on the 13th, small‐scale irregularities formed. The impact of these was observed within Global Positioning System data as elevated rate of TEC index (ROTI) and presented as strong 35 MHz scintillations of cosmic radio sources as well as spread‐F within ionograms from multiple digisonde systems. GPS and 35‐MHz data demonstrated that the irregularity region was narrowly confined (≲5° wide) near the edge of the depletion region. The 35‐MHz scintillation data also showed that the irregularities were moving relatively slowly at ∼7 m s−1, likely toward the southeast. Density and velocity measurements demonstrated that the conditions near the depletion boundary were highly favorable to the gradient drift instability (GDI) with the one‐dimensional growth rate estimated to be ∼0.01 s−1. Since these conditions persisted for many hours, this growth rate was more than sufficient for the GDI to be considered the primary driver of irregularity formation in this case. Plain Language Summary: Earth's ionosphere, the ionized portion of the upper atmosphere, is a dynamic environment, often beset with irregularities and disturbances that interfere with radio frequency signals that travel through it. In this regard, mid‐latitudes are usually quite tame relative to the equatorial and polar regions. However, when significant geomagnetic disturbances, or "storms," occur, this normally placid region can become anything but. This paper presents the results of a study that examines the impact of a storm over North America, using several space‐ and ground‐based sensors. Of particular interest is the formation of a density depletion region during the recovery period following the onset of the storm. Multiple sensors show evidence of this depletion and still others show a preponderance of small‐scale irregularities (as small as a few kilometers) near its southern boundary. A holistic analysis indicates that these irregularities are consistent with a turbulent cascade moving relatively slowly, likely toward the south or southeast. Conditions near the depletion edge were observed to be conducive with the so‐called gradient drift instability. This is known to be a primary driver of irregularity formation within other settings, and appears to be the culprit in this case as well. Key Points: A multitude of ground‐ and space‐based sensors were used to study a storm‐induced mid‐latitude ionospheric depletion over North AmericaIrregularities at the equatorward edge of the depletion at ∼30°N were detected with radio frequency systems from a few MHz to 1.5 GHzSpace‐based in situ and remote sensing data point to the gradient drift instability as the most likely driver of irregularity formation [ABSTRACT FROM AUTHOR]

Our current knowledge of the geomagnetic poleward and equatorward boundary dynamics is limited, particularly, how deep those two latitudinal boundaries can extend into lower geomagnetic latitudes during magnetic storms. We want to understand the motion of the boundary because it is important in terms of the location and magnitude of the effects of geomagnetic disturbances associated with storms on the ground. In this study we derive spherical elementary ionospheric currents from ground magnetometer arrays covering North America and Greenland during six magnetic storms in 2015 and 2018. With two dimensional maps of the auroral region current, we select the equatorward boundary of the region 2 currents by‐eye and fit the boundary with an ellipse to derive the location of the equatorward boundary at magnetic midnight. We have obtained over 500 boundaries and find that the midnight boundary location varies between 45° and 66° magnetic latitude. We examine the influence of the interplanetary magnetic field (IMF), solar wind plasma, and geomagnetic indices on the location of the magnetic midnight equatorial boundary and find that the equatorial boundary location is best correlated with the IMF Bz, VBz, and the Sym‐H index. We demonstrate that as the Bz component becomes more negative, the magnitude of VBz increases, and the magnitude of the Sym‐H index increases, the magnetic midnight equatorial boundary shifts equatorward during periods of moderate to high geomagnetic activity. Plain Language Summary: Our current knowledge of the geomagnetic poleward and equatorward boundary dynamics is limited, particularly, how deep the equatorward boundary of the auroral current system can extend into lower magnetic latitudes during magnetic storms. In this study we use two dimension ionospheric current maps derived from ground magnetometer arrays covering North America and Greenland during magnetic storms in 2015 and 2018 to understand the variability of the equatorward boundary of the auroral currents at magnetic midnight. We examine the influence of the interplanetary magnetic field (IMF), solar wind plasma, and geomagnetic indices on the location of the magnetic midnight equatorial boundary and find that the magnetic midnight equatorial boundary location is best correlated with the Bz component of the interplanetary magnetic field, the solar wind electric field (VBz), and the Sym‐H geomagnetic index. We demonstrate that as the Bz becomes more negative, the magnitude of VBz increases, and as the magnitude of the Sym‐H increases the magnetic midnight equatorial boundary moves equatorward. Key Points: We show the temporal and spatial development of the region 2 current system equatorward boundary during magnetic stormsWe show that the equatorward boundary at magnetic midnight varies in magnetic latitude between 45° and 71° MLatWe demonstrate a correlation between the equatorward boundary location and IMF Bz southward, VBz, Sym‐H, and the ε parameter [ABSTRACT FROM AUTHOR]

Assessing space weather modeling capability is a key element in improving existing models and developing new ones. In order to track improvement of the models and investigate impacts of forcing, from the lower atmosphere below and from the magnetosphere above, on the performance of ionosphere‐thermosphere models, we expand our previous assessment for 2013 March storm event (Shim et al., 2018, https://doi.org/10.1029/2018SW002034). In this study, we evaluate new simulations from upgraded models (the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model version 4.1 and the Global Ionosphere Thermosphere Model (GITM) version 21.11) and from the NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) version 2.2 including eight simulations in the previous study. A simulation from the NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model version 2 (TIE‐GCM 2.0) is also included for comparison with WACCM‐X. TEC and foF2 changes from quiet‐time background are considered to evaluate the model performance on the storm impacts. For evaluation, we employ four skill scores: Correlation coefficient (CC), root‐mean square error (RMSE), ratio of the modeled to observed maximum percentage changes (Yield), and timing error (TE). It is found that the models tend to underestimate the storm‐time enhancements of foF2 (F2‐layer critical frequency) and TEC (Total Electron Content) and to predict foF2 and/or TEC better in North America but worse in the Southern Hemisphere. The ensemble simulation for TEC is comparable to results from a data assimilation model (Utah State University‐Global Assimilation of Ionospheric Measurements (USU‐GAIM)) with differences in skill score less than 3% and 6% for CC and RMSE, respectively. Plain Language Summary: The Earth's ionosphere‐thermosphere (IT) system, which is present between the lower atmosphere and the magnetosphere, is highly variable due to external forcings from below and above as well as internal forcings mainly associated with ion‐neutral coupling processes. The variabilities of the IT system can adversely affect our daily lives, therefore, there is a need for both accurate and reliable weather forecasts to mitigate harmful effects of space weather events. In order to track the improvement of predictive capabilities of space weather models for the IT system, and to investigate the impacts of the forcings on the performance of IT models, we evaluate new simulations from upgraded models (Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics model version 4.1 and Global Ionosphere Thermosphere Model version 21.11) and from NCAR Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM‐X) version 2.2 together with 8 simulations in the previous study. A simulation of NCAR Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model version 2 is also included for the comparison with WACCM‐X. Quantitative evaluation is performed by using four skill scores including Correlation coefficient, root‐mean square error, ratio of the modeled to observed maximum percentage changes (Yield), and timing error. The findings of this study will provide a baseline for future validation studies of new and improved models. Key Points: F2‐layer critical frequency/Total Electron Content (foF2/TEC) and their changes during a storm predicted by ionosphere‐thermosphere coupled models are evaluated against Global Ionosphere Radio Observatory foF2 and GPS TEC measurementsModel simulations tend to underestimate the storm‐time enhancements of foF2 and TEC and to predict them better in the northern hemisphereEnsemble of all simulations for TEC is comparable to the data assimilation model (USU‐GAIM) [ABSTRACT FROM AUTHOR]

We used the global navigation satellite system-total electron content (TEC) and Super Dual Auroral Radar Network (SuperDARN) radar to elucidate the characteristics of the plasma bubble extending to midlatitudes over North America during a geomagnetic storm on 27 and 28 May 2017. To identify plasma bubbles, we analyzed the rate of the TEC index (ROTI), which is a good indicator of the occurrence of plasma bubbles. The enhanced ROTI region expanded up to 50°N (geomagnetic latitude), and the upper limit of this region coincided with the equatorward wall of the midlatitude trough. Two-dimensional ROTI maps show that the enhanced midlatitude ROTI region moved westward at a bulk speed of approximately 310 m/s. The Fort Hays East SuperDARN radar also detected the radar echo, showing the existence of plasma density irregularities at ~10-m scales within the midlatitude plasma bubble. The radar echo had a westward velocity of ~300 m/s, which is almost consistent with the westward motion of the enhanced midlatitude ROTI region. We deduced that the westward propagation of the plasma bubble could be caused by a poleward sub-auroral polarization stream electric field. The observed radar echo overlapping with the enhanced ROTI region had a narrower spectral width (<50 m/s) than that of the auroral activity. This feature resembled that of the type 1 echo, although the Doppler velocity was smaller than the ion acoustic speed at the F-region height. This is the first case in which plasma density irregularities within plasma bubbles were captured by the SuperDARN radar. [ABSTRACT FROM AUTHOR]

Today, the scientists and researchers from almost every corner of the world are well aware of the adverse effects of geomagnetic storms on our highly expensive electrical and electromagnetic systems such as power grid transmission, satellite communication, RF communication systems, etc. The severe damaging effects of these storms on human health and on other inhabitants of the biosphere are also not unknown. A survey of literature on space science reveals that location or space dependency of these geomagnetic storms has already been established. Now the question may arise—Are geomagnetic storms time-dependent? To answer this question, a laborious exercise has been performed. K-index data obtained from the US Department of Commerce, NOAA, Space Weather Prediction Center, for the year, started from 1994 to 2014 (21 years) over three different locations namely Fredericksburg, College, and Estimated Planetary, are analyzed statistically for the eight different time periods namely 00:00–03:00, 03:00–06:00, 06:00–09:00, 09:00–12:00, 12:00–15:00, 15:00–18:00, 18:00–21:00, 21:00–24:00 hours respectively. Results thus obtained have concluded that apart from space or location dependency the geomagnetic storms are time-dependent also. [ABSTRACT FROM AUTHOR]

Explains the relevance of geomagnetic storm forecasting to electric power system operations. Overview of power system reliability and related space weather climatology; Widespread power system failure that occurred across North America during the geomagnetic storm of March 13, 1989; Coupling of the electric fields to a power network.

This study aims to investigate the features of the ionospheric mid-latitude trough over North America by using the MIT total electron content data obtained during three geomagnetic storms that occurred in August 2018, September 2017, and March 2015. The mid-latitude trough position sharply moves equatorward from the quiet-time subauroral latitude to mid-latitude with the decrease in SYM-H during geomagnetic storms. We find that the ionospheric behavior of TEC around the mid-latitude trough position displays three kinds of ionospheric storm effect: negative ionospheric storm effect, unchanged ionospheric behavior, and positive ionospheric storm effect. These ionospheric storm effects around the mid-latitude trough position are not always produced by the mid-latitude trough. The ionospheric storm effects produced by the mid-latitude trough are limited in the narrow mid-latitude trough regions, and are transmitted to other regions with the movement of the mid-latitude trough. [ABSTRACT FROM AUTHOR]

Magnetic field changes in the coupled magnetosphere-ionosphere-ground system can induce electric fields that drive geomagnetically-induced currents (GIC) in terrestrial electric power grids and other conductive infrastructure. Since ground dB/dt can be used as a GIC proxy, arrays of ground magnetometers can therefore be used to study their temporal and spatial evolution and to examine both the spatio-temporal scales of the disturbances and their connection to drivers in geospace. Here we study the spatial scales of large dB/dt events using data from two complementary magnetometer arrays: The temporarily deployed very dense Baltic Electromagnetic Array Research (BEAR) Project in Scandinavia and the continent scale permanently deployed Canadian Array for Realtime Investigations of Magnetic Activity (CARISMA) array in North America. We analyse a number of nightside substorms, revealing a large amplitude but small ~ 100 km scale geomagnetic disturbances (GMD) which may pose a GIC risk. We further identify and analyse large dB/dt events on the flanks, a local time region which has so far been neglected as a region of GIC risk, and propose that the drivers of these flank GMD are connected to magnetopause and/or large scale auroral disturbances such as omega-bands especially in the dawn sector. Analysis of the spatio-temporal characteristics specifically allows a determination of the optimal distance between magnetometers, in latitude and longitude, for future instrument deployments targeting the monitoring of GMD associated with large GIC impacts in the electric power grid. [ABSTRACT FROM AUTHOR]