MODES has provided a global perspective of the limits of the prediction skill of the numerical weather prediction (NWP) models. The modal analysis of scale-dependent predictability analysis showed that the larger the spatial scale, the greater the amplitude of uncertainties in the initial conditions for the global prediction systems. A large part of these uncertainties is found in the tropical region in relation to the lack of wind observations and challenges of the tropical data assimilation and NWP modelling. It has been suggested that the upscale error cascade may not be the key process for the loss of useful predictability in the 10-day range. MODES has quantified the levels of inertio-gravity (IG) wave energy across many scales. Although the IG waves constitute a small portion of the global atmospheric wave energy, it is crucial to validate their spectrum in NWP and climate models as it reflects the fundamental dynamical processes developing in response to nonhomogeneous forcings.
COBISS.SI-ID: 348585
The Fractions Skill Score (FSS) is a spatial verification measure that is used for assessing the performance of precipitation forecasts from Numerical Weather Prediction models. Previous studies have shown that the FSS is able to give a direct measure of the error in the placement of the rain. This paper takes the approach further and derives analytical expressions and uses Monte-Carlo simulations for randomly positioned observed and forecast rainfall to reveal further characteristics of the FSS in both infinite and bounded domains. It reveals that the definition of an FSS value that determines the minimum scale at which a forecast should be deemed “useful” (useful forecast criteria) is a meaningful concept and shows how this value increases with increasing fractional rainfall coverage. A study of real forecast data is also presented using 8-years of European Centre for Medium-Range Weather Forecasts (ECMWF) model forecasts, out to a lead time of 9 days, over domains of differing sizes covering parts of Europe and North Africa. The FSS is examined using different strategies for dealing with the domain boundary and is compared with the analytical study. The findings give practical guidance on how to use the FSS. For most situations a FSS value of )0.5 serves as a good indicator of a useful forecast. The choice of domain size for rainfall forecast verification should consider the typical spatial errors of the forecast. For a domain that is large compared to the typical spatial error, the boundaries have little adverse affect, but this is not the case if the spatial errors start to become comparable to the size of the domain. The evaluation of ECMWF forecasts reveals the extent of the spatial errors that emerge for medium range forecasts and show the value of verifying those forecasts using the FSS over an appropriately-sized region.
COBISS.SI-ID: 335273
Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way using the fossil remnants of disrupted star formation sites that are now dispersed around the Galaxy. It is targeting a randomly selected magnitude-limited (V ≤ 14) sample of stars, with the goal of observing one million objects. To date, 300,000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines, and we need to know about them. We present a semi-automated classification scheme that identifies different types of peculiar spectral morphologies in an effort to discover and flag potentially problematic spectra and thus help to preserve the integrity of the survey results. To this end, we employ the recently developed dimensionality reduction technique t-SNE (t-distributed stochastic neighbor embedding), which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighborhoods of spectra. We find that the majority (178,483) of the 209,533 Galah spectra considered in this study represents normal single stars, whereas 31,050 peculiar and problematic spectra with very diverse spectral features pertaining to 28,579 stars are distributed into 10 classification categories: hot stars, cool metal-poor giants, molecular absorption bands, binary stars, Hα/Hβ emission, Hα/Hβ emission superimposed on absorption, Hα/Hβ P-Cygni, Hα/Hβ inverted P-Cygni, lithium absorption, and problematic. Classified spectra with supplementary information are presented in the catalog, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution.
COBISS.SI-ID: 761217
Gamma-ray burst GRB 140430A was detected by the Swift satellite and observed promptly with the imaging polarimeter RINGO3 mounted on the Liverpool Telescope, with observations beginning 124 seconds after the GRB trigger, while the prompt gamma-ray emission was still ongoing. In this paper, we present densely sampled (10-second temporal resolution) early optical light curves in 3 optical bands and limits to the degree of optical polarization. We compare optical, X-ray and gamma-ray properties and present an analysis of the optical emission during a period of high- energy flaring. The complex optical light curve cannot be explained merely with a combination of forward and reverse shock emission from a standard external shock, implying additional contribution of emission from internal shock dissipation. We estimate an upper limit for optical polarization during the prompt phase to be as low as P ( 12% (1sigma). This low value is in contrast to previous detections of highly polarized prompt gamma-ray flares at P ) 30% from INTEGRAL and IKAROS satellites, and could be reconciled if individual components in GRB 140430A are highly polarized but have significantly different or variable position angles which would produce an apparent net low polarization degree when combined.
COBISS.SI-ID: 567937
In this paper we study the soft X-ray (SXR) signatures of one particular prominence on the Sun. The X-ray observations used here were made by the Hinode/X-Ray Telescope instrument using two different filters. Both of them have a pronounced peak of the response function around 10 Å. One of them has a secondary smaller peak around 170 Å, which leads to a contamination of SXR images. The observed darkening in both of these filters has a very large vertical extension. The position and shape of the darkening correspond nicely with the prominence structure seen in SDO/AIA images. First, we have investigated the possibility that the darkening is caused by X-ray absorption. However, detailed calculations of the optical thickness in this spectral range show clearly that this effect is completely negligible. Therefore, the alternative is the presence of an extended region with a large emissivity deficit, which can be caused by the presence of cool prominence plasmas within an otherwise hot corona. To reproduce the observed darkening, one needs a very large extension along the line of sight of the region amounting to around 10^5 km. We interpret this region as the prominence spine, which is also consistent with SDO/AIA observations in EUV.
COBISS.SI-ID: 548225