Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this paper, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out an helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by \citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic

Genetic diversity of wild, weedy and cultivated acccessions of Brassica rapa

Restriction Fragment Length Polymorphisms (RFLPs) were used to study the genetic diversity within and between accessions of 'wild' and cultivated B. rapa. Two of the wild accessions were likely to be escapes from cultivation because of their geographical origins (Argentina and California). The nature of the other three wild accessions (from Turkey, Algeria and Sicily) was not known. Principal components analysis placed the Argentinian, Californian and Turkish accessions within a cluster which contained all the cultivated forms of B. rapa. The other two B. rapa accessions were genetically divergent and, on the basis of their RFLP genotypes, would have been considered to be more distant from the cultivated forms of B. rapa than accessions of B. nigra and B. montana. The implications of these results for germplasm conservation, selection of material for breeding programmes and phylogenetic studies on the origin of Brassica crops are discussed