Search

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. Plain Language Summary: Space weather plays an important role in the impacts to society by natural sources. Technology is still frequently impacted by Solar activity without proper warnings. It is clear that scientists and institutions are missing some aspects of the physics governing some of these events. In previous works, double H‐spikes have been related to the most dangerous space weather events in history and also proven to go unnoticed by the traditional indicators used by the community. In this work we present new features like their distribution of occurrence, their intensities and their link to higher magnetic latitude activity. We show that this link is one of the reasons for the significant threat posed by H‐spikes but also the key feature to detect them. Their identification will also help in forecasts and release of warnings by responsible centers and institutions. Key Points: Mid‐latitude ground magnetic disturbances observed as double H‐spikes are remote effects of the field‐aligned currents originated during substormsDouble H‐spikes pose a potential risk to damage technology, even located at midlatitudes, by generating geomagnetically induced currentsSuperMAG SMR12 and SMR00 sector indices can monitor H‐spikes for space weather purposes [ABSTRACT FROM AUTHOR]

Two of the most important processes threatening vulnerable plant species are competitive displacement by invasive alien species and water stress due to global warming. Quercus lusitanica, an oak shrub species with remarkable conservation interest, could be threatened by the expansion of the invasive alien tree Paraserianthes lophantha. However, it is unclear how competition would interact with predicted reductions in water availability due to global climate change. We set up a full factorial experiment to examine the direct interspecific competition between P. lophantha and Q. lusitanica seedlings under control and water‐limited conditions.We measured seed biomass, germination, seedling emergence, leaf relative growth rate, biomass, root/shoot ratio, predawn shoot water potential and mortality to assess the individual and combined effects of water stress and interspecific competition on both species.Our results indicate that, at seedling stage, both species experience competitive effects and responses. However, water stress exhibited a stronger overall effect than competition. Although both species responded strongly to water stress, the invasive P. lophantha exhibited significantly less drought stress than the native Q. lusitanica based on predawn shoot water potential measurements.The findings of this study suggest that the competition with invasive P. lophantha in the short term must not be dismissed, but that the long‐term conservation of the native shrub Q. lusitanica could be compromised by increased drought as a result of global change. Our work sheds light on the combined effects of biological invasions and climate change that can negatively affect vulnerable plant species. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: The local indices Local Disturbance index and Local Current index, that were developed in Northern Hemisphere (Spain), have been successfully validated to be used in Southern Hemisphere at similar geomagnetic latitudes. This validation was carried out with the help of geomagnetic data from two South African geomagnetic observatories, Hermanus and Hartebeesthoek, and geomagnetically induced current data from two South African power stations, Grassridge and Matimba, recorded during two major geomagnetic storms, Halloween in October 2003 and Saint Patrick's Day in March 2015. The results show that these indices can now‐cast successfully local space weather events better than the global geomagnetic activity indices like SYM‐H. Key Points: Geomagnetic indices Local Disturbance index (LDi) and Local Current index (LCi) successfully now‐cast local geomagnetic disturbances and geomagnetically induced currents (GICs) respectively in the Southern HemisphereComparison to measured GIC shows that LCi seems to perform slightly better than dH/dt as a proxy for GICWe present a method for rederiving SYM‐H indices using the LDi index [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]