Nowcasting Solar Energetic Particle Events Using Principal Component Analysis

We perform a principal component analysis (PCA) on a set of six solar variables (i.e. width/size () and velocity () of a coronal mass ejection, logarithm of the solar flare (SF) magnitude (), SF longitude (), duration (), and rise time ()). We classify the solar energetic particle (SEP) event radiation impact (in terms of the National Oceanic and Atmospheric Administration scales) with respect to the characteristics of their parent solar events. We further attempt to infer the possible prediction of SEP events. In our analysis, we use 126 SEP events with complete solar information, from 1997 to 2013. Each SEP event is a vector in six dimensions (corresponding to the six solar variables used in this work). The PCA transforms the input vectors into a set of orthogonal components. By mapping the characteristics of the parent solar events, a new base defined by these components led to the classification of the SEP events. We furthermore applied logistic regression analysis with single, as well as multiple explanatory variables, in order to develop a new index () for the nowcasting (short-term forecasting) of SEP events. We tested several different schemes for and validated our findings with the implementation of categorical scores (probability of detection (POD) and false-alarm rate (FAR)). We present and interpret the obtained scores, and discuss the strengths and weaknesses of the different implementations. We show that holds prognosis potential for SEP events. The maximum POD achieved is 77.78% and the relative FAR is 40.96%

The variation of geomagnetic storm duration with intensity

Variability in the near-Earth solar wind conditions can adversely affect a number of ground- and space-based technologies. Such space-weather impacts on ground infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration, through time-integrated effects. Forecasting storm duration is also necessary for scheduling the resumption of safe operating of affected infrastructure. It is therefore important to understand the degree to which storm intensity and duration are correlated. The long-running, global geomagnetic disturbance index, aa , has recently been recalibrated to account for the geographic distribution of the component stations. We use this aaH index to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Defining storms using a peak-above-threshold approach, we find that more intense storms have longer durations, as expected, though the relationship is nonlinear. The distribution of durations for a given intensity is found to be approximately log-normal. On this basis, we provide a method to probabilistically predict storm duration given peak intensity, and test this against the aaH dataset. By considering the average profile of storms with a superposed-epoch analysis, we show that activity becomes less recurrent on the 27-day timescale with increasing intensity. This change in the dominant physical driver, and hence average profile, of geomagnetic activity with increasing threshold is likely the reason for the nonlinear behaviour of storm duration

Radial evolution of the April 2020 stealth coronal mass ejection between 0.8 and 1 AU - Comparison of Forbush decreases at Solar Orbiter and near the Earth

Aims. We present observations of the first coronal mass ejection (CME) observed at the Solar Orbiter spacecraft on April 19, 2020, and the associated Forbush decrease (FD) measured by its High Energy Telescope (HET). This CME is a multispacecraft event also seen near Earth the next day. Methods. We highlight the capabilities of HET for observing small short-term variations of the galactic cosmic ray count rate using its single detector counters. The analytical ForbMod model is applied to the FD measurements to reproduce the Forbush decrease at both locations. Input parameters for the model are derived from both in situ and remote-sensing observations of the CME. Results. The very slow (~350 km/s) stealth CME caused a FD with an amplitude of 3 % in the low-energy cosmic ray measurements at HET and 2 % in a comparable channel of the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter, as well as a 1 % decrease in neutron monitor measurements. Significant differences are observed in the expansion behavior of the CME at different locations, which may be related to influence of the following high speed solar wind stream. Under certain assumptions, ForbMod is able to reproduce the observed FDs in low-energy cosmic ray measurements from HET as well as CRaTER, but with the same input parameters, the results do not agree with the FD amplitudes at higher energies measured by neutron monitors on Earth. We study these discrepancies and provide possible explanations. Conclusions. This study highlights that the novel measurements of the Solar Orbiter can be coordinated with other spacecraft to improve our understanding of space weather in the inner heliosphere. Multi-spacecraft observations combined with data-based modeling are also essential to understand the propagation and evolution of CMEs as well as their space weather impacts

Review of solar energetic particle models

Solar Energetic Particle (SEP) events are interesting from a scientific perspective as they are the product of a broad set of physical processes from the corona out through the extent of the heliosphere, and provide insight into processes of particle acceleration and transport that are widely applicable in astrophysics. From the operations perspective, SEP events pose a radiation hazard for aviation, electronics in space, and human space exploration, in particular for missions outside of the Earth’s protective magnetosphere including to the Moon and Mars. Thus, it is critical to improve the scientific understanding of SEP events and use this understanding to develop and improve SEP forecasting capabilities to support operations. Many SEP models exist or are in development using a wide variety of approaches and with differing goals. These include computationally intensive physics-based models, fast and light empirical models, machine learning-based models, and mixed-model approaches. The aim of this paper is to summarize all of the SEP models currently developed in the scientific community, including a description of model approach, inputs and outputs, free parameters, and any published validations or comparisons with data.</p

Statistical analysis on the current capability to predict the Ap Geomagnetic Index

In this work, forecasting results of the daily Ap geomagnetic index by different Space Weather Prediction Centers (SWPCs) covering the time period from October 2014 up to July 2020, are considered. A three-day forecast of this index obtained from the space weather prediction centers, is analyzed. Standard forecast verification measures, descriptive statistics with correlation coefficients, and error analysis between forecasts and observations have been performed to evaluate the quality or the skill of the predictions. In particular, an error analysis using fit performance metrics, such as the mean average error (MAE) and the root mean squared error (RMSE) among others, as well as the threshold performance metrics, such as the Hansen-Kuipers, Gilbert and Heidke skill scores, the probability of detection (POD), the probability of false detection (POFD) and the area under the curve in receiving the operating characteristic (ROC) plot among others, are calculated. For the Ap geomagnetic index predictions during Day-0, the Pearson&apos;s correlation coefficient is ranging between the values of 0.57 and 0.79, while during the Day-2 it is decreased to the range from 0.37 to 0.44. In conclusion, the majority of the used SWPCs perform quite accurately on the conditions of Space Weather in active as well as in quiet periods showing a reliable effort for predicting geomagnetic storms. © 2021 Elsevier B.V

Large Forbush Decreases and their Solar Sources: Features and Characteristics

One of the factors responsible for the wide variety of Forbush decreases is the different solar sources related to them. In this investigation the different features and characteristics of Forbush decreases, with emphasis on large Forbush decreases and their association with solar sources, are examined. Initially, a wider selection of events from the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation of the Russian Academy of Sciences Forbush decreases database served as a starting point for this study, which was then narrowed down to a group of large Forbush decreases. According to the helio-longitude of the solar source, the events under study were separated into three subcategories: western (21 ∘≤ helio-longitude ≤ 60 ∘), eastern (− 60 ∘≤ helio-longitude ≤ − 21 ∘), and central (− 20 ∘≤ helio-longitude ≤ 20 ∘). The selected events cover the period 1967 – 2017. The “Global Survey Method” was used for analyzing the aforementioned Forbush decreases, along with data on solar flares, solar-wind speed, geomagnetic indices (Kp and Dst), and interplanetary magnetic field. The superimposed epoch method was applied to display the temporal profiles for the selected events. This detailed analysis reveals interesting results concerning the features of cosmic-ray decreases in relation to the helio-longitude of the solar sources. Specifically, Forbush decreases related to central or eastern solar sources are more often observed, have a greater magnitude, and present a slower development than Forbush decreases related to western sources, which are rarer, have a smaller magnitude, and have a shorter lifespan. Nevertheless, regardless of the helio-longitude of the solar source, large Forbush decreases are accompanied by increased geomagnetic activity and increased anisotropy, including anisotropy before the events, which can serve as a typical precursor of Forbush decreases. © 2020, Springer Nature B.V

Precursory Signs of Large Forbush Decreases

The study of space-weather effects and more specifically Forbush decreases of the cosmic-ray intensity depends on space and ground measurements. Very often Forbush decreases and geomagnetic storms are accompanied by pre-increases and/or pre-decreases manifested in cosmic-ray behavior, known as precursory signs. These cosmic-ray intensity variations do not coincide with the shock arrival but begin well before (up to 24 hours) the onset of the main event. In this study a group of large Forbush decreases with amplitude ≥ 4% was examined for precursors. According to the helio-longitude of the solar source, the events were separated into three categories: western (21 ∘≤ helio-longitude ≤ 60∘), eastern (− 60 ∘≤ helio-longitude ≤ − 21 ∘), and central (− 20 ∘≤ helio-longitude ≤ 20 ∘). The selected events cover 1967 – 2017. The analysis of the Forbush decreases and the plotting of the asymptotic longitudinal cosmic-ray distribution diagrams were based on the “Global Survey Method” and the “Ring of Stations” method, respectively. Data on solar flares, solar-wind speed, interplanetary magnetic field, and geomagnetic indices (Kp and Dst) were also used. The results show the clear signs of precursors in a significant number of events. © 2021, The Author(s), under exclusive licence to Springer Nature B.V

Precursors of Forbush decreases connected to western solar sources and geomagnetic storms

It is suggested in many studies that the pre-increases or pre-decreases of the cosmic ray intensity (known as precursors) which usually precede a Forbush decrease could serve as a useful tool for studying space weather effects. The events under consideration in this particular investigation were chosen based on two criteria. Firstly, the heliolongitude of the solar flare associated with each cosmic ray intensity decrease was in the 50 degrees-70 degrees W sector and secondly, the values of geomagnetic activity index (Kp(max)) were &gt;= 5. As a result only Forbush decreases connected to western solar flares and accompanied by a geomagnetic storm were selected. In total 25 events were gathered for the time period from 1967 to 2006. For the detailed analysis of the aforementioned cosmic ray intensity decreases data on solar flares, solar wind speed, geomagnetic indices (Kp and Dst) and interplanetary magnetic field were used. The asymptotic longitudinal cosmic ray distribution diagrams for all events were plotted using the “Ring of Stations” method. The results revealed clear signs of precursors in 60% of selected events