Solar burst characteristics in the radio microwave region are used to differentiate between large flares that might produce proton events and those that might not. Proton events produce high-level absorption, disrupt polar communications, and can be dangerous to man and equipment in space. They may precede the auroral and magnetic storms that disturb many radiowave propagation systems. The probability of a proton event can now be predicted, an AFCRL study of the characteristics of flare-associated centimeter radar bursts having established that a signature of proton events is a high flux density in the 3-cm region and a particular burst peak flux spectral configuration. (Author).

Solar burst characteristics in the radio microwave region are used to differentiate between large flares that might produce proton events and those that might not. Proton events produce high-level absorption, disrupt polar communications, and can be dangerous to man and equipment in space. They may precede the auroral and magnetic storms that disturb many radiowave propagation systems. The probability of a proton event can now be predicted, an AFCRL study of the characteristics of flare-associated centimeter radar bursts having established that a signature of proton events is a high flux density in the 3-cm region and a particular burst peak flux spectral configuration. (Author).

A new parameter is introduced for use in forecasting the magnitudes of solar proton and polar cap absorption events. Semi-integrated flux density is the integrated radio flux density under the start-to-maximum burst curve. An approximation to this function was correlated at five operational frequencies against both observed peak proton flux and observed riometer absorption, obtaining correlation coefficients > or = 0.88 at frequencies between 2695- and 8800-MHz. An operational real-time forecast scheme is detailed for the solar forecaster. Results from this study, which uses peak proton fluxes both corrected and uncorrected for solar disk positions, indicate that forecasts have a higher degree of correlation with observations if propagation corrections are not applied as present methods dictate. When used in conjunction with the Castelli 'U' burst spectrum criteria for forecasting the occurrence of proton events, radio data can be used exclusively for both a yes/no and an event magnitude forecast. A comparison with the method presently in use at the Air Weather Service's Aerospace Environmental Support Center, Solar Forecast Branch is made with very favorable results. (Author)

The short-term prediction of solar proton events based on a distinct U-shaped radio burst signature is verified. The prediction techniques uses peak flux density values of discrete frequency solar radio burst observations in the 100 to 10,000 MHz region. The criteria are applied to all major proton events from 1952 to 1969 and afford almost total success in predicting near-earth particle events that eminated from visible hemisphere regions of the sun. A correlation between U-shaped radio burst signatures and solar proton events as detected by the ATS-1 satellite, during 1967 and 1968, is also shown to be highly successful. Finally, a 'modified' U-shaped criterion is set forth for the accurate short-terms prediction of polar cap absorption events that result in at least a 2.0 dB riometer measurement of absorption. This 'modified' spectral configuration is then correlated with the major absorption events of the current solar cycle and it is found that prediction occurred for all principal PCA events that originated from visible solar hemisphere flares. (Author).

Solar energetic particles (SEPs) emitted from the Sun are a major space weather hazard motivating the development of predictive capabilities. This book presents the results and findings of the HESPERIA (High Energy Solar Particle Events forecasting and Analysis) project of the EU HORIZON 2020 programme. It discusses the forecasting operational tools developed within the project, and presents progress to SEP research contributed by HESPERIA both from the observational as well as the SEP modelling perspective. Using multi-frequency observational data and simulations HESPERIA investigated the chain of processes from particle acceleration in the corona, particle transport in the magnetically complex corona and interplanetary space, to the detection near 1 AU. The book also elaborates on the unique software that has been constructed for inverting observations of relativistic SEPs to physical parameters that can be compared with space-borne measurements at lower energies. Introductory and pedagogical material included in the book make it accessible to students at graduate level and will be useful as background material for Space Physics and Space Weather courses with emphasis on Solar Energetic Particle Event Forecasting and Analysis. This book is published with open access under a CC BY license.

The decay phase of solar proton events, as observed at Earth, depends strongly on the proton injection history, the distribution of the proton population in solar longitude, and the state of the interplanetary medium. In an attempt to gain an additional diagnostic of these complex conditions, the evolution of the flux anisotropy is examined, both theoretically and observationally. In relatively simple events, the component of the flux anisotorpy parallel to the interplanetary magnetic field proves to be a useful indicator. In more complicated events additional information from solar wind, magnetic field, and lower energy (