11 research outputs found
Long-term photometric monitoring of RR Lyr stars in M3
The period-change behaviour of 134 RR Lyrae stars in the globular cluster
Messier 3 (M3) is investigated on the ~120-year time base of the photometric
observations. The mean period-change rates (\beta \approx 0.01 d Myr^-1) of the
subsamples of variables exhibiting the most regular behaviour are in good
agreement with theoretical expectations based on Horizontal-Branch stellar
evolution models. However, a large fraction of variables show period changes
that contradict the evolutionary expectations. Among the 134 stars studied, the
period-change behaviour of only 54 variables is regular (constant or linearly
changing), slight irregularities are superimposed on the regular variations in
23 cases and the remaining 57 stars display irregular period variations. The
light curve of ~50 per cent of the RRab stars is not stable, i.e., these
variables exhibit Blazhko modulation. The large fraction of variables with
peculiar behaviour (showing light-curve modulation and/or irregular O-C
variation) indicate that, probably, variables with regular period changes
incompatible with their evolutionary stages also could display some kind of
instability of the pulsation light curve and/or period, but the available
observations have not disclosed it yet. The temporal appearence of the Blazhko
effect in some stars, and the 70-90 years long regular changes preceded or
followed by irregular, rapid changes of the pulsation period in some cases
support this hypothesis.
[...] Abstract truncated due to the limitations of astroph. See full abstract
in the paper.Comment: 22 pages, 14 figures, accepted for publication in MNRA
Surface wind regionalization in complex terrain
Daily wind variability in the Comunidad Foral de Navarra in northern Spain was studied using wind observations at 35 locations to derive subregions with homogeneous temporal variability. Two different methodologies based on principal component analysis were used to regionalize: 1) cluster analysis and 2) the rotation of the selected principal components. Both methodologies produce similar results and lead to regions that are in general agreement with the topographic features of the terrain. The meridional wind variability is similar in all subregions, whereas zonal wind variability is responsible for differences between them. The spectral analysis of wind variability within each subregion reveals a dominant annual cycle and the varying presence of higher-frequency contributions in the subregions. The valley subregions tend to present more variability at high frequencies than do higher-altitude sites. Last, the influence of large-scale dynamics on regional wind variability is explored by studying connections between wind in each subregion and sea level pressure fields. The results of this work contribute to the characterization of wind variability in a complex terrain region and constitute a framework for the validation of mesoscale model wind simulations over the region
Surface wind regionalization over complex terrain: Evaluation and analysis of a high-resolution WRF simulation
This study analyzes the daily-mean surface wind variability over an area characterized by complex topography through comparing observations and a 2-km-spatial-resolution simulation performed with the Weather Research and Forecasting (WRF) model for the period 1992-2005. The evaluation focuses on the performance of the simulation to reproduce the wind variability within subregions identified from observations over the 1999-2002 period in a previous study. By comparing with wind observations, the model results show the ability of the WRF dynamical downscaling over a region of complex terrain. The higher spatio-temporal resolution of the WRF simulation is used to evaluate the extent to which the length of the observational period and the limited spatial coverage of observations condition one's understanding of the wind variability over the area. The subregions identified with the simulation during the 1992-2005 period are similar to those identified with observations (1999-2002). In addition, the reduced number of stations reasonably represents the spatial wind variability over the area. However, the analysis of the full spatial dimension simulated by the model suggests that observational coverage could be improved in some subregions. The approach adopted here can have a direct application to the design of observational networks