Solar rotational period of cosmic rays and solar activity during the maximum phase of solar cycle 24

To study the solar rotational oscillation on daily averaged time series of solar activity proxies: sunspot number (SSN), modified coronal index (MCI), solar flare index (FI), and cosmic ray intensity (CRI) are subjected to Lomb/Scargle periodogram, and continuous wavelet transform. For this purpose, we have used data of all the considered parameters from 2012 to 2015, which covers the maximum phase including the polarity reversal period of the solar cycle 24. Both spectral analysis techniques are carried out to study the behavior of 27-days on the time scale of the synodic period and to follow their evolution throughout the epoch. Further, we have used R package RobPer (least square regression) techniques and obtained a significant true period ~27 days is present in this study. It is noted that the ~27-day period of solar activity parameters and cosmic rays is much prominent during the examined period.

Investigating the Compatibility of IRI and ASAPS Models in Predicting the foF2 Ionospheric Parameter over the Mid Latitude Region

In this research, an investigation for the compatibility of the IRI-2016 and ASAPS international models was conducted to evaluate their accuracy in predicting the ionospheric critical frequency parameter (foF2) for the years 2009 and 2014 that represent the minimum and maximum years of solar cycle 24. The calculations of the monthly average foF2 values were performed for three different selected stations distributed over the mid-latitude region. These stations are Athens - Greece (23.7o E, 37.9 o N), El Arenosillo - Spain (-6.78 o E, 37.09 o N), and Je Ju - South Korea (124.53 o E, 33.6 o N). The calculated values using the two tested models were compared with the observed foF2 datasets for each of the three selected locations. The results showed that the two tested models gave good and close results for all selected stations compared to the observed data for the studied period of time. At the minimum solar cycle 24, the ASAPS model showed in general better values than the IRI-2016 model at Athens, El Arenosillo and Je Ju stations for all tested methods. At maximum solar cycle 24, the IRI-2016 model showed higher and closer values to the observed data at Athens and El Arenosillo stations, while the ASAPS model showed better values at Je Ju station.

Earth-affecting solar transients: a review of progresses in solar cycle 24

This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. It is a part of the effort of the International Study of Earth-affecting Solar Transients (ISEST) project, sponsored by the SCOSTEP/VarSITI program (2014–2018). The Sun-Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field, and radiation energy output of the Sun in varying timescales from minutes to millennium. This article addresses short timescale events, from minutes to days that directly cause transient disturbances in the Earth’s space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi-viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction, and morphology of CMEs in both 3D and over a large volume in the heliosphere. Many CMEs, fast ones, in particular, can be clearly characterized as a two-front (shock front plus ejecta front) and three-part (bright ejecta front, dark cavity, and bright core) structure. Drag-based kinematic models of CMEs are developed to interpret CME propagation in the heliosphere and are applied to predict their arrival times at 1 AU in an efficient manner. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved. An outlook of how to address critical issues related to Earth-affecting solar transients concludes this article.