More Like this

1. Solar Cycle and Solar Wind Dependence of the Occurrence of Large dB / dt Events at High Latitudes

   https://doi.org/10.1029/2022JA030953  

   Milan, S. E.; Imber, S. M.; Fleetham, A. L.; Gjerloev, J. (April 2023, Journal of Geophysical Research: Space Physics)

   Key Points Large dB / dt “spikes” in ground magnetometer data occur in three local time hotspots in the pre‐midnight, dawn, and pre‐noon sectors These are consistent with spikes produced by substorm onsets, omega bands, and the Kelvin‐Helmholtz instability, respectively Spike occurrence is controlled by solar activity, maximizing in the declining phase of the solar cycle, esp. solar cycle 23 

   more » « less
2. Characterization of Transient‐Large‐Amplitude Geomagnetic Perturbation Events

   https://doi.org/10.1029/2021GL094076  

   McCuen, Brett A.; Moldwin, Mark B.; Engebretson, Mark (July 2021, Geophysical Research Letters)

   Abstract We present a characterization of transient‐large‐amplitude (TLA) geomagnetic disturbances that are relevant to geomagnetically induced currents (GIC). TLA events are defined as one or more short‐timescale (<60 s) dB/dt signature with magnitude ≥6 nT/s. The TLA events occurred at six stations of the Magnetometer Array for Cusp and Cleft Studies throughout 2015. A semi‐automated dB/dt search algorithm was developed to identify 38 TLA events in the ground magnetometer data. While TLA dB/dts do not drive GICs directly, we show that second‐timescale dB/dts often occur in relation to or within larger impulsive geomagnetic disturbances. Sudden commencements are not the main driver, rather the events are more likely to occur 30 min after a substorm onset or within a nighttime magnetic perturbation event. The characteristics of TLA events suggest localized ionospheric source currents that may play a key role in generating some extreme geomagnetic impulses that can lead to GICs. 

   more » « less
3. Probabilistic Forecasting of Ground Magnetic Perturbation Spikes at Mid‐Latitude Stations

   https://doi.org/10.1029/2023SW003446  

   Coughlan, Michael; Keesee, Amy; Pinto, Victor; Mukundan, Raman; Marchezi, José_Paulo; Johnson, Jeremiah; Connor, Hyunju; Hampton, Don (May 2023, Space Weather)

   Abstract The prediction of large fluctuations in the ground magnetic field (dB/dt) is essential for preventing damage from Geomagnetically Induced Currents. Directly forecasting these fluctuations has proven difficult, but accurately determining the risk of extreme events can allow for the worst of the damage to be prevented. Here we trained Convolutional Neural Network models for eight mid‐latitude magnetometers to predict the probability thatdB/dtwill exceed the 99th percentile threshold 30–60 min in the future. Two model frameworks were compared, a model trained using solar wind data from the Advanced Composition Explorer (ACE) satellite, and another model trained on both ACE and SuperMAG ground magnetometer data. The models were compared to examine if the addition of current ground magnetometer data significantly improved the forecasts ofdB/dtin the future prediction window. A bootstrapping method was employed using a random split of the training and validation data to provide a measure of uncertainty in model predictions. The models were evaluated on the ground truth data during eight geomagnetic storms and a suite of evaluation metrics are presented. The models were also compared to a persistence model to ensure that the model using both datasets did not over‐rely ondB/dtvalues in making its predictions. Overall, we find that the models using both the solar wind and ground magnetometer data had better metric scores than the solar wind only and persistence models, and was able to capture more spatially localized variations in thedB/dtthreshold crossings. 

   more » « less
4. Dayside Magnetic Depression Following Interplanetary Shock Arrivals During the February 1958 and July 1959 Superstorms

   https://doi.org/10.1029/2024SW004017  

   Ohtani, Shinichi; Odagi, Yoko; Matsuoka, Ayako; Iyemori, Toshihiko (September 2024, Space Weather)

   Abstract The present study investigates mid‐ and low‐latitude ground magnetic disturbances observed following the arrival of three interplanetary (IP) shocks during the super‐geomagnetic storms of February 1958 and July 1959. One may expect that after IP shocks, the H (northward) magnetic component increases globally but especially on the dayside. However, in each event, the H component was depressed sharply for 1–2 hr in the dawn‐to‐noon sector, whereas it increased in other local time (LT) sectors. Observed magnetic deflections suggest that there existed field‐aligned currents (FACs) flowing into and out of the auroral zone around the western and eastern edges of the LT sector of the dayside H depression. These features strongly suggests that the observed H depression was a remote effect of a R1‐sense FAC system. It was previously reported that similar ground magnetic disturbances were observed after the SSC of the 2003 Halloween storm, which reveals striking similarities to the well‐known H depression observed at Colaba during the 1859 Carrington storm. It is therefore suggested that the external driving behind IP shocks, especially those associated with major storms, is most optimum for the sharp reduction of the dayside H component through the formation and intensification of the dayside FAC system. Associated magnetic disturbances are considered to be larger in magnitude with increasing magnetic latitude, and oriented azimuthally as well as meridionally. Such magnetic disturbances in dayside midlatitudes may not be discussed very often as a target of space weather, but their potential impacts on ground infrastructures probably require closer attention. 

   more » « less
5. Intensification of the Electron Zebra Stripes in the Earth's Inner Magnetosphere During Geomagnetic Storms

   https://doi.org/10.1029/2023GL107822  

   Pandya, Megha; Ebihara, Yusuke; Tanaka, Takashi; Manweiler, Jerry W; Vines, Sarah K (February 2024, Geophysical Research Letters)

   Abstract We examined rapid variations in the electron zebra stripe patterns, specifically atL = 1.5, over a three‐month duration, using twin Van Allen Probes within Earth's inner magnetosphere. During geomagnetically quiet intervals, these stripes exhibit a peak‐to‐valley ratio (Δj) ∼1.25 in detrended electron fluxes. However, during geomagnetic storms, they became highly prominent, with Δj > 2.5. The correlation between Δjand net field‐aligned currents (FACs) is observed to be high (0.70). Global magnetohydrodynamic (MHD) simulation results indicate that the westward electric field at midnight at low latitudes in the deep inner magnetosphere correlates well with net FACs. An increase in net FACs could amplify the dawn‐to‐dusk electric field in the deep inner magnetosphere, thereby causing the inward transport of electrons. Given that FACs are linked to the interaction between solar wind and the magnetosphere, our findings emphasize the importance of solar wind‐magnetosphere coupling in the deeper regions of the inner magnetosphere. 

   more » « less