40 research outputs found
Concurrent effect of Alfvén waves and planar magnetic structure on geomagnetic storms
No full textGenerally, interplanetary coronal mass ejection (ICME) triggers intense and strong geomagnetic storms. It has been established that the ICME sheath-moulded planar magnetic structure enhances the amplitude of the storms. Alfvén waves embedded in ICME magnetic clouds or high solar streams including corotating interacting regions (CIRs) in turn extend the recovery phase of the storm. Here, we investigate a geomagnetic storm with a very complex temporal profile with multiple decreasing and recovery phases. We examine the role of planar magnetic structure (PMS) and Alfvén waves in the various phases of the storm. We find that fast decrease and fast recovery phases are evident during transit of PMS regions, whereas a slight decrease or recovery is found during the transit of regions embedded with Alfvénic fluctuations
Forecasting of SYMH and ASYH indices for geomagnetic storms of solar cycle 24 including St. Patrick’s day, 2015 storm using NARX neural network
No full textArtificial Neural Network (ANN) has proven to be very successful in forecasting a variety of irregular magnetospheric/ionospheric processes like geomagnetic storms and substorms. SYMH and ASYH indices represent longitudinal symmetric and the asymmetric component of the ring current. Here, an attempt is made to develop a prediction model for these indices using ANN. The ring current state depends on its past conditions therefore, it is necessary to consider its history for prediction. To account for this effect Nonlinear Autoregressive Network with exogenous inputs (NARX) is implemented. This network considers input history of 30 min and output feedback of 120 min. Solar wind parameters mainly velocity, density, and interplanetary magnetic field are used as inputs. SYMH and ASYH indices during geomagnetic storms of 1998–2013, having minimum SYMH < −85 nT are used as the target for training two independent networks. We present the prediction of SYMH and ASYH indices during nine geomagnetic storms of solar cycle 24 including the recent largest storm occurred on St. Patrick’s day, 2015. The present prediction model reproduces the entire time profile of SYMH and ASYH indices along with small variations of ∼10–30 min to the good extent within noise level, indicating a significant contribution of interplanetary sources and past state of the magnetosphere. Therefore, the developed networks can predict SYMH and ASYH indices about an hour before, provided, real-time upstream solar wind data are available. However, during the main phase of major storms, residuals (observed-modeled) are found to be large, suggesting the influence of internal factors such as magnetospheric processes
Gravity and Pressure‐Gradient Currents Using Ionospheric Electron Density Measurements From COSMIC Satellites
No full textVariable Responses of Equatorial Ionosphere During Undershielding and Overshielding Conditions
No full textCharacteristics of penetration electric fields to the equatorial ionosphere during southward and northward IMF turnings
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Distinctly Different responses of Equatorial F region during Undershielding and Overshielding Conditions
No full textManifestations of Strong IMF‐By on the Equatorial Ionospheric Electrodynamics During 10 May 2024 Geomagnetic Storm
No full textAbstract Understanding the effects of east‐west component of interplanetary magnetic field (IMF‐By) on the equatorial ionospheric electrodynamics is challenging due to the complex response caused by the simultaneous occurrence of multiple mechanisms during disturbed times. The extreme geomagnetic storm on 10 May 2024 caused by multiple‐ICME interactions accompanied with unprecedented IMF‐By magnitudes and its polarity, changed from west to east by 130 nT during northward IMF‐Bz turning. The ground ionosonde observations of h’F from near‐equatorial locations, along with the latitudinal profiles of plasma densities from Swarm satellites reveal the first observational evidence of the impact of strong IMF‐By near the dusk‐terminator (17–19.5 LT), causing strong dawn‐to‐dusk ionospheric electric fields during northward IMF‐Bz. This electric field produces large uplift of the ionospheric plasma near equator and subsequent super‐fountain effect near the dusk. The combined effect of increased IMF‐By amplitudes and viscous terms might have resulted into the enhanced coupling of solar wind with the magnetosphere
Comprehensive Study of Low‐Latitude Pi2 Pulsations Using Observations From Multisatellite Swarm Mission and Global Network of Ground Observatories
No full textTo understand the spatial features of low‐latitude Pi2 (6.6–25 mHz) pulsations, a comprehensive study is carried out for the first time using magnetic field measurements from a global network of low‐latitude ground stations (Mlat: ± 2°− 51°) and the Swarm multisatellites located simultaneously at day and night local times. We have investigated 1‐year data from 2014 and found 15 Pi2 events with coherent oscillations at satellite and ground. The Pi2 oscillations in the compressional, toroidal, and poloidal components at satellite and H, D, and Z components at ground are investigated by estimating its coherence, amplitude, and cross phase with respect to midnight ground H variations. The analogous pairs of magnetic field components (satellite compressional with ground H and satellite toroidal with ground D) above and below the ionosphere are found to have identical phase during night and opposite phase during day, indicating the magnetospheric and ionospheric sources for nighttime and daytime Pi2s, respectively. During nighttime, Pi2 oscillations identified in the poloidal component are found to oscillate in phase (out of phase) in the Southern (Northern) Hemisphere. At ground, the phase and amplitude of H showed significant change near the dawn terminator, whereas H oscillates mostly in phase with respect to midnight ground H at other local times. The oscillations in D component have phase reversal near midnight, dawn, dusk, and noon meridians with opposite hemispheres having opposite phase. These Pi2 characteristics observed globally at ground and at the topside ionosphere suggest that the sources for nighttime and daytime low‐latitude Pi2s are oscillating field‐aligned currents and ionospheric currents, respectively.journal articl
Corrigendum to “Characteristics of equatorial electrojet derived from Swarm satellites” [Adv. Space Res. 59 (2017) 1526–1538]
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