Nonparametric analysis of high wind speed data

In this paper, nonparametric curve estimation methods are applied to analyze time series of wind speeds, focusing on the extreme events exceeding a chosen threshold. Classical parametric statistical approaches in this context consist in fitting a generalized Pareto distribution (GPD) to the tail of the empirical cumulative distribution, using maximum likelihood or the method of the moments to estimate the parameters of this distribution. Additionally, confidence intervals are usually computed to assess the uncertainty of the estimates. Nonparametric methods to estimate directly some quantities of interest, such as the probability of exceedance, the quantiles or return levels, or the return periods, are proposed. Moreover, bootstrap techniques are used to develop pointwise and simultaneous confidence intervals for these functions. The proposed models are applied to wind speed data in the Gulf Coast of US, comparing the results with those using the GPD approach, by means of a split-sample test. Results show that nonparametric methods are competitive with respect to the standard GPD approximations. The study is completed generating synthetic data sets and comparing the behavior of the parametric and the nonparametric estimates in this framework.     

Solar-Cycle Variation of Subsurface Zonal Flow

We study the solar-cycle variation of the zonal flow in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm covering the period from mid-2001 to mid-2013 or from the maximum of Cycle 23 through the rising phase of Cycle 24. We have analyzed Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams with a ring-diagram analysis. The zonal flow varies with the solar cycle showing bands of faster-than-average flows equatorward of the mean latitude of activity and slower-than-average flows on the poleward side. The fast band of the zonal flow and the magnetic activity appear first in the northern hemisphere during the beginning of Cycle 24. The bands of fast zonal flow appear at mid-latitudes about three years in the southern and four years in the northern hemisphere before magnetic activity of Cycle 24 is present. This implies that the flow pattern is a direct precursor of magnetic activity. The solar-cycle variation of the zonal flow also has a poleward branch, which is visible as bands of faster-than-average zonal flow near 50° latitude. This band appears first in the southern hemisphere during the rising phase of the Cycle 24 and migrates slowly poleward. These results are in good agreement with corresponding results from global helioseismology.     

A Full-Sun Magnetic Index from Helioseismology Inferences

Solar magnetic indices are used to model the solar irradiance and ultimately to forecast it. However, the observation of such indices is generally limited to the Earth-facing hemisphere of the Sun. Seismic maps of the far side of the Sun have proven their capability to locate and track medium–large active regions at the non-visible hemisphere. We present here the possibility of using the average signal from these seismic far-side maps, combined with similarly calculated near-side maps, as a proxy to the full-Sun magnetic activity.     

A cosmological study of the star formation history in the solar neighbourhood

We use a cosmological galactic evolutionary approach to model the Milky Way. A detailed treatment of the mass aggregation and dynamical history of the growing dark halo is included, together with a self-consistent physical treatment for the star formation processes within the growing galactic disc. This allows us to calculate the temporal evolution of star and gas surface densities at all galactic radii, in particular, the star formation history (SFH) at the solar radius. A large range of cosmological mass aggregation histories (MAHs) is capable of producing a galaxy with the present-day properties of the Milky Way. The resulting SFHs for the solar neighbourhood bracket the available observational data for this feature, the most probable MAH yielding the optimal comparison with these observations. We also find that the rotation curve for our Galaxy implies the presence of a constant density core in its dark-matter halo.