Solar flares are one mechanism to release stored magnetic energy in the Sun’s atmosphere. This thesis aims to determine whether sunspot rotation can inject the energy required for solar flares into the corona. This thesis investigates the relationship between sunspot rotation and solar flares, and the impact that sunspot rotation has on the strength and frequency of flare events. A robust analysis tool is developed which uses continuum images of the Sun to determine the rotation of sunspots. This tool is used throughout the thesis, first on the active region 11158, in an in-depth case study of the rotation and flaring properties of the region as it traverses the solar disc. The case study develops analysis techniques, such as introducing sunspot selection criteria, which are used in the following statistical studies. The first statistical study involves the analysis of the rotation and flaring properties of a sample of all sunspots that meet the selection criteria within all X-class flaring regions since the launch of the Solar Dynamics Observatory. As this first statistical study is biased towards higher flare-energy active regions, a second unbiased statistical study is carried out on all sunspots that meet the sunspot selection criteria between 1 May 2013 and 31 August 2013. The results of these statistical studies are combined and analysed, concluding that sunspot rotation injects enough energy (and in the majority of cases, an excess of energy) to account for the energy output by solar flare radiation. On average, the radiated bolometric flare energy outputs 65.6% of the injected energy due to the absolute sunspot rotation for the X-class flare sample, and 59.2% for the four-month sample.

Solar Energetic Particles (SEPs) are known to be accelerated by high-energy events in the Sun's corona: coronal mass ejections (CMEs) with high speed, solar flares with high peak emission in soft X-rays, or a combination of the two. SEPs, however, are not detected following all fast CMEs or intense flares. Those large solar events, which might reasonably have been expected to produce SEPs at Earth but which failed to do so, may be termed “false alarms”. In this work, two simple SEP forecasting algorithms are defined: one (algorithm A.1) is based upon the observation of a magnetically well-connected CME with a speed of 1,500 km/s or greater (a ``fast CME''), and the other (algorithm A.2) is based upon the observation of a magnetically well-connected X class flare. The algorithms were applied to historical data sets to ascertain which produced an enhancement of >40 MeV protons, and which were false alarms. The algorithms have been evaluated using standard verification scores. Both algorithms correctly forecast approximately the same percentage of SEP events (47% and 49% respectively); the false alarm ratio for algorithm A.1, however, was much lower than for A.2 (29% and 51% respectively). Both algorithms failed to forecast almost the same number of SEP events (53% for A.1, and 51% for A.2). The parameters of the false alarms were compared to those of the SEP-producing events. False alarm fast CMEs tended to be associated with flares of class less than M3; X class flares which were either not associated with any CME, or were associated with a CME slower than 500 km/s, were false alarms. A third forecasting algorithm, based upon these results, was defined. This algorithm, which takes into account parameters of both CMEs and flares, performed better than either A.1 or A.2, correctly forecasting a significantly greater percentage of SEP events than both (68%), having a false alarm ratio similar to A.1 (30%), but missing a significantly lower percentage (32%) of SEP events. A small number of case studies were carried out. It was found that for accurate forecasting of SEP events it may not be sufficient simply to consider the accelerating events, but that the location of the heliospheric current sheet relative to the site of the solar event and of the Earth's footpoint may be an important consideration. SEP forecasts produced by the SPARX simulation were evaluated with a view to providing a benchmark against which future versions of the model may be tested.

This thesis investigates the topology of the magnetic field in the solar corona, due to a variety of source configurations and types. To fully understand the complex behaviour of the Sun's magnetic field, it is important to have a complete description of the features present in its structure. The magnetic topologies due to network source configurations are investigated using both the point source description and the continuous source description. A series of case studies involving an emerging bipole in a hexagonal arrangement to simulate a supergranular cell are studied. This has a particular focus on the behaviour of coronal nulls located in the topology, and a particular case may form the underpinning of a model for polar plumes. A new topological feature, called a null-like point, is defined by relaxing the definition of a magnetic null point. Separatix-like surfaces, originating from null-like points, allow quasi-separatrix layers to be found in magnetic topologies due to continuously distributed sources. The squashing factor, Q, is mapped across the source configuration, highlighting the locations of the quasi-separatrix layers. Finally, an algorithm is developed which automatically detects and classifies magnetic events local to X-ray bright points (XBPs). Significant peaks are identified in the gradients of flux curves (positive, negative and absolute flux) local to XBP footpoints, allowing instances of flux emergence and cancellation to be identified and linked to the onset and demise of the XBPs studied. The algorithm correctly classifies 90% of all emergence and cancellation events related to the studied XBPs.

In this thesis, an analysis of solar energetic particle (SEP) data from multiple instruments onboard the ACE, SOHO and STEREO spacecraft is presented. The temporal variation and the dependence of heavy ion abundances on solar longitude were studied and quantitatively characterised during SEP events between 2006 and 2016. Ionic abundances vary over the duration of SEP events, e.g. Fe/O often shows a decrease over time. This behaviour was identified as a common characteristic within the data. The time variation of 36 different ionic pairs was studied for a number of SEP events. The fit constant describing time evolution was found to show ordering by the value of S, given e.g. for Fe/O by SFe/O = (M/Q)Fe/(M/Q)O, where M is the mass number and Q the charge number. The ionic ratios with S > 1 decreased over time and those with S < 1 showed increases, while ratios with a large S decayed at a higher rate. Anomalous behaviour of ratios involving protons was identified in several events. The longitudinal dependence of Fe/O simultaneously observed by multiple spacecraft at 1 AU was studied in 12 SEP events. The event-averaged Fe/O values observed by spacecraft at different longitudes varied within a single event, but this variation was less significant than the event-to-event variation. Although the longitudinal dependence was a complicated one, in some events the Fe/O values were higher at a remote observer. The temporal evolution of heavy ion ratios, which was studied quantitatively for a number of ionic pairs, is consistent with an MQ-dependent interplanetary transport mechanism. The observed longitudinal dependence of event-averaged Fe/O, where higher Fe/O values are observed at a spacecraft that is not well magnetically connected to the source region, cannot be fully explained by the two-class paradigm for classification of SEP events.