Comment on "Properties of the recovery phase of extreme storms" by Choraghe et al. (2021)

Choraghe et al. (2021), based on a study of the recovery phase of the SYM-H index of 31 extreme geomagnetic storms, have recently concluded that the hyperbolic decay function is only able to explain the complete recovery phase of about one third of events and that both the exponential or the hyperbolic decay functions fail to explain the late recovery phase of storms. Furthermore, they propose a linear function to model the late recovery phase and claim that the proposed model could throw new light on the relative importance of different physical processes involved during the complete recovery phase of extreme storms. We assert that the Choraghe et al. (2021) conclusions regarding the recovery phase of extreme storms analysis are incorrect and in particular are based on a misunderstanding of the nature of the evolution of the SYM-H index and the energy balance of the ring current

Estimation of the solar wind extreme events

This research provides an analysis of extreme events in the solar wind and in the magnetosphere due to disturbances of the solar wind. Extreme value theory has been applied to a 20-year data set from the Advanced Composition Explorer spacecraft for the period 1998–2017. The solar proton speed, solar proton temperature, solar proton density, and magnetic field have been analyzed to characterize extreme events in the solar wind. The solar wind electric field, vBz has been analyzed to characterize the impact from extreme disturbances in the solar wind to the magnetosphere. These extreme values were estimated for 1-in-40- and 1-in-80-year events, which represent two and four times the range of the original data set. The estimated values were verified in comparison with measured values of extreme events recorded in previous years. Finally, our research also suggests the presence of an upper boundary in the magnitudes under study.Ministerio de Economía y CompetitividadAgencia Estatal de Investigació

Forecasting intense geomagnetic activity using interplanetary magnetic field data

Southward interplanetary magnetic fields are considered traces of geoeffectiveness since they are a main agent of magnetic reconnection of solar wind and magnetosphere. The first part of this work revises the ability to forecast intense geomagnetic activity using different procedures available in the literature. The study shows that current methods do not succeed in making confident predictions. This fact led us to develop a new forecasting procedure, which provides trustworthy results in predicting large variations of Dst index over a sample of 10 years of observations and is based on the value Bz only. The proposed forecasting method appears as a worthy tool for space weather purposes because it is not affected by the lack of solar wind plasma data, which usually occurs during severe geomagnetic activity. Moreover, the results obtained guide us to provide a new interpretation of the physical mechanisms involved in the interaction between the solar wind and the magnetosphere using Faraday's law.Comisión Interministerial de Ciencia y Tecnología (CICYT

Comment on "Interplanetary conditions leading to superintense geomagnetic storms (dst ≤ -250 nt) during solar cycle 23" by E. Echer et al.

Comisión Interministerial de Ciencia y Tecnología-CICY

Deep Neural Networks with Convolutional and LSTM layers for SYM-H and ASY-H forecasting

Geomagnetic indices quantify the disturbance caused by the solar activity on a planetary scale or in particular regions of the Earth. Among them, the SYM-H and ASY-H indices represent the (longitudinally) symmetric and asymmetric geomagnetic disturbance of the horizontal component of the magnetic field at midlatitude with a 1-min resolution. Their resolution, along with their relation to the solar wind parameters, makes the forecasting of the geomagnetic indices a problem that can be addressed through the use of Deep Learning, particularly using Deep Neural Networks (DNNs). In this work, we present two DNNs developed to forecast respectively the SYM-H and ASY-H indices. Both networks have been trained using the Interplanetary Magnetic Field (IMF) and the related index for the solar storms occurred in the last two solar cycles. As a result, the networks are able to accurately forecast the indices 2 h in advance, considering the IMF and indices values for the previous 200 min. The evaluation of both networks reveals a great forecasting precision, including good predictions for large storms that occurred during the solar cycle 23 and comparing with the persistence model for the period 2013-2020.Junta de Comunidades de Castilla-La ManchaMinisterio de Ciencia e InnovaciónMinisterio de Economía y Competitivida

Mid-latitude double H-spikes: their properties and signatures in different geomagnetic indices

Proper assessment of geomagnetic disturbances is a key aspect of space weather as technology is often impacted by space weather activity without previous warnings or proper forecasts. Double H-spikes are a form of longitudinal asymmetry observed at midlatitudes. They are geomagnetic disturbances occurring simultaneously on the dayside and nightside as a negative/positive H-spike, which go unnoticed through common geomagnetic indices. This work presents the results of a systematic search for double H-spikes occurred over a 23-year period and analyzes characteristics of the double H-spikes such as the occurrence dependence on the solar cycle, season, intensity and phase of the geomagnetic storm. Our outcomes indicate that double H-spikes are a global phenomenon closely related with the substorm phenomenon and the ground magnetic disturbances observed at mid-latitude are remote effects of field-aligned currents (FACs). FACs would be the part of the substorm current wedge developed from the expansion onset of intense substorms whose effects have wide longitudinal extend as they are observed on the dayside and the nightside. Also mid-latitude global SYM and ASY indices are affected by FACs during those periods. Time derivatives of the SuperMAG SMR12 and SMR00 sector indices allow us to conclude that double H-spikes, as short-time high-intensity magnetic disturbances, pose a potential risk to damage ground-technological systems at midlatitudes.Agencia Estatal de InvestigaciónUniversidad de Alcal

Hyperbolic Decay of the Dst Index during the Recovery Phase of Intense Geomagnetic Storms

What one commonly considers for reproducing the recovery phase of magnetosphere,as seen by the Dst index, is exponential function. However, the magnetosphererecovers faster in the first hours than in the late recovery phase. The early steepnessfollowed by the late smoothness in the magnetospheric response is a feature that leadsto the proposal of a hyperbolic decay function to reproduce the recovery phase instead ofthe exponential function. A superposed epoch analysis of recovery phases of intensestorms from 1963 to 2003 was performed, categorizing the storms by their intensity intofive subsets. The hyperbolic decay function reproduces experimental data better than whatthe exponential function does for any subset of storms, which indicates a nonlinearcoupling between dDst/dt and Dst. Moreover, this kind of mathematical function, wherethe degree of reduction of the Dst index depends on time, allows for explaining differentlifetimes of the physical mechanisms involved in the recovery phase and provides newinsights for the modeling of the Dst index.Ministerio de Ciencia e InnovaciónJunta de Comunidades de Castilla La Manch

Validating the LDi and LCi Indices in the Southern Hemisphere

The validation of the Local Disturbance index (LDi) and its first time derivative Local Current index (LCi) is performed in the Southern Hemisphere. Two South African magnetic observatories, Hermanus and Hartebeesthoek contributed data for this study, and two South African power stations, Grassridge and Matimba, provided geomagnetically induced current (GIC) data. This validation focused on two major geomagnetic storms, Halloween and Saint Patrick's Day events that occurred in October 2003 and March 2015, respectively. The comparative evaluation of the LDi and LCi indices was executed with the help of the local horizontal component (H) and also comparing them to the global index SYM-H. A direct comparison to measured GIC shows that LCi performs slightly better than dH/dt as a proxy for GIC. The comparison of the LDi 1-hr magnetic disturbances values to ones calculated applying a Linear phase Robust Non-Smoothing method to the H component yields a Pearson correlation coefficient R greater than 0.960 for different groups of magnetic storms based on intensity. The estimated SYM-H index from LDi data showed a possible difference of about 300 nT from the published SYM-H index values around 20:00 UT on 29 October 2003, during the Halloween storm. This study has shown that the LDi and LCi indices, developed in the Northern Hemisphere, can be calculated at similar latitudes in the Southern Hemisphere for studying local space weather conditions and now-casting successfully local geomagnetic events.Agencia Estatal de Investigació

Flux emergence event underneath a filament

Flux emergence phenomena are relevant at different temporal and spatial scales.We have studied a flux emergence region underneath a filament. This filament elevated itselfsmoothly, and the associated CME reached the Earth. In this study we investigate the size andthe amount of flux in the emergence event. The flux emergence site appeared just beneath afilament. The emergence acquired a size of 24 Mm in half a day. The unsigned magnetic fluxdensity from LOS-magnetograms was around 1 kG at its maximum. The transverse field as wellas the filament eruption were also analysed.Ministerio de Economía y Competitivida

Searching for Carrington-like events and their signatures and triggers

The Carrington storm in 1859 is considered to be the major geomagnetic disturbance related to solar activity. In a recent paper, Cid et al. (2015) discovered a geomagnetic disturbance case with a profile extraordinarily similar to the disturbance of the Carrington event at Colaba, but at a mid-latitude observatory, leading to a reinterpretation of the 1859 event. Based on those results, this paper performs a deep search for other ?Carrington-like? events and analyses interplanetary observations leading to the ground disturbances which emerged from the systematic analysis. The results of this study based on two Carrington-like events (1) reinforce the awareness about the possibility of missing hazardous space weather events as the large H-spike recorded at Colaba by using global geomagnetic indices, (2) argue against the role of the ring current as the major current involved in Carrington-like events, leaving field-aligned currents (FACs) as the main current involved and (3) propose abrupt southward reversals of IMF along with high solar wind pressure as the interplanetary trigger of a Carrington-like event.Ministerio de Economía y Competitivida