155 research outputs found
Recommended from our members
Multiâdiagnostic multiâmodel ensemble forecasts of aviation turbulence
Turbulence is one of the major weather hazards to aviation. Studies have shown that clearâair turbulence may well occur more frequently with future climate change. Currently the two World Area Forecast Centres use deterministic models to generate forecasts of turbulence. It has been shown that the use of multiâmodel ensembles can lead to more skilful turbulence forecasts. It has also been shown that the combination of turbulence diagnostics can also produce more skilful forecasts using deterministic models. This study puts the two approaches together to expand the range of diagnostics to include predictors of both convective and mountain wave turbulence, in addition to clearâair turbulence, using two ensemble model systems. Results from a 12 month global trial from September 2016 to August 2017 show the increased skill and economic value of including a wider range of diagnostics in a multiâdiagnostic multiâmodel ensemble
Recommended from our members
Consensus Views on Advance Care Planning for Dementia: A Delphi Study
yesThe uptake of advance care planning (ACP) is particularly low among people with dementia. This may reflect barriers to communication between professionals, patients and families in the face of lack of consensus about the process. This study aimed to methodically investigate consensus views of how ACP should be explained and carried out with people with dementia. A three-round Delphi study explored views of how and when ACP should be addressed, what should be covered, who should be involved and why rates of ACP are low. Seventeen participants took part comprising family members, old age psychiatrists and policy makers. Thirty-two items reached consensus. The panel agreed on 11 different areas for discussion. They concurred that ACP was best addressed after the person has come to terms with the diagnosis when the individual feels ready to do so. There was a consensus view that the process should be couched in terms of âcertain possibilitiesâ. Consensus items emphasised personal choice and autonomy, while also prioritising the need to discuss financial aspects and to include spouses. There was no consensus that professionals should be involved, although the panel viewed them as carrying some responsibility for low uptake. It is suggested that ACP should include general discussion of values as well as coverage of specific points. Professionals need to offer discussion and information on ACP, but also make clear that the patient has the right to choose whether to pursue ACP or not
Recommended from our members
Multi-model ensemble predictions of aviation turbulence
Turbulence remains one of the leading causes of aviation incidents. Climate change is predicted to increase the occurrence of ClearâAir Turbulence (CAT), and therefore forecasting turbulence will become more important in the future. Currently the two World Area Forecast Centres (WAFCs) use deterministic numerical weather prediction models to predict clearâair turbulence operationally, it has been shown that ensemble forecasts improve the forecast skill of traditional meteorological variables. This study applies multiâmodel ensemble forecasting to aviation turbulence for the first time. It is shown in a 12âmonth global trial from May 2016 to April 2017, that combining two different ensembles yields a similar forecast skill to a single model ensemble, and yields an improvement in forecast value at low cost/loss ratios. This finding is consistent with previous work showing that the use of ensembles in turbulence forecasting is beneficial. Using a multiâmodel approach is an effective way to improve the forecast skill and provide pilots and flight planners with more information about the forecast confidence, allowing them to make a more informed decision about what action needs to be taken, such as diverting around the turbulence or requiring passengers and flight attendants to be seatbelted. The multiâmodel ensemble approach is intended to be made operational by both WAFCs in the near future and this study lays the foundations to make this possible
Recommended from our members
Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr â Part 1: A new geomagnetic data composite
We present a new composite of geomagnetic activity which is designed to be as homogeneous in its construction as possible. This is done by only combining data that, by virtue of the locations of the source observatories used, have similar responses to solar wind and IMF (interplanetary magnetic field) variations. This will enable us (in Part 2, Lockwood et al., 2013a) to use the new index to reconstruct the interplanetary magnetic field, B, back to 1846 with a full analysis of errors. Allowance is made for the effects of secular change in the geomagnetic field. The composite uses interdiurnal variation data from Helsinki for 1845â1890 (inclusive) and 1893â1896 and from Eskdalemuir from 1911 to the present. The gaps are filled using data from the Potsdam (1891â1892 and 1897â1907) and the nearby Seddin observatories (1908â1910) and intercalibration achieved using the PotsdamâSeddin sequence. The new index is termed IDV(1d) because it employs many of the principles of the IDV index derived by Svalgaard and Cliver (2010), inspired by the u index of Bartels (1932); however, we revert to using one-day (1d) means, as employed by Bartels, because the use of near-midnight values in IDV introduces contamination by the substorm current wedge auroral electrojet, giving noise and a dependence on solar wind speed that varies with latitude. The composite is compared with independent, early data from European-sector stations, Greenwich, St Petersburg, Parc St Maur, and Ekaterinburg, as well as the composite u index, compiled from 2â6 stations by Bartels, and the IDV index of Svalgaard and Cliver. Agreement is found to be extremely good in all cases, except two. Firstly, the Greenwich data are shown to have gradually degraded in quality until new instrumentation was installed in 1915. Secondly, we infer that the Bartels u index is increasingly unreliable before about 1886 and overestimates the solar cycle amplitude between 1872 and 1883 and this is amplified in the proxy data used before 1872. This is therefore also true of the IDV index which makes direct use of the u index values
Recommended from our members
Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr â Part 2: A new reconstruction of the interplanetary magnetic field
We present a new reconstruction of the interplanetary magnetic field (IMF, B) for 1846â2012 with a full analysis of errors, based on the homogeneously constructed IDV(1d)composite of geomagnetic activity presented in Part 1 (Lockwood et al., 2013a). Analysis of the dependence of the commonly used geomagnetic indices on solar wind parameters is presented which helps explain why annual means of interdiurnal range data, such as the new composite, depend only on the IMF with only a very weak influence of the solar wind flow speed. The best results are obtained using a polynomial (rather than a linear) fit of the form B = Ï Â· (IDV(1d) â ÎČ)α with best-fit coefficients Ï = 3.469, ÎČ = 1.393 nT, and α = 0.420. The results are contrasted with the reconstruction of the IMF since 1835 by Svalgaard and Cliver (2010)
Novel Collective Effects in Integrated Photonics
Superradiance, the enhanced collective emission of energy from a coherent
ensemble of quantum systems, has been typically studied in atomic ensembles. In
this work we study theoretically the enhanced emission of energy from coherent
ensembles of harmonic oscillators. We show that it should be possible to
observe harmonic oscillator superradiance for the first time in waveguide
arrays in integrated photonics. Furthermore, we describe how pairwise
correlations within the ensemble can be measured with this architecture. These
pairwise correlations are an integral part of the phenomenon of superradiance
and have never been observed in experiments to date.Comment: 7 pages, 3 figure
Global QCD Analysis and the CTEQ Parton Distributions
The CTEQ program for the determination of parton distributions through a
global QCD analysis of data for various hard scattering processes is fully
described. A new set of distributions, CTEQ3, incorporating several new types
of data is reported and compared to the two previous sets of CTEQ
distributions. Comparison with current data is discussed in some detail. The
remaining uncertainties in the parton distributions and methods to further
reduce them are assessed. Comparisons with the results of other global analyses
are also presented.Comment: (Change in Latex style only: 2up style removed since many don't have
it.) 35 pages, 23 figures separately submitted as uuencoded compressed
ps-file; Michigan State Report # MSU-HEP/41024 and CTEQ 40
Deep Inelastic Scattering from off-Shell Nucleons
We derive the general structure of the hadronic tensor required to describe
deep-inelastic scattering from an off-shell nucleon within a covariant
formalism. Of the large number of possible off-shell structure functions we
find that only three contribute in the Bjorken limit. In our approach the usual
ambiguities encountered when discussing problems related to off-shellness in
deep-inelastic scattering are not present. The formulation therefore provides a
clear framework within which one can discuss the various approximations and
assumptions which have been used in earlier work. As examples, we investigate
scattering from the deuteron, nuclear matter and dressed nucleons. The results
of the full calculation are compared with those where various aspects of the
off-shell structure are neglected, as well as with those of the convolution
model.Comment: 36 pages RevTeX, 9 figures (available upon request), ADP-93-210/T128,
PSI-PR-93-13, accepted for publication in Physical Review
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Tests of sunspot number sequences: 1. Using ionosonde data
More than 70 years ago it was recognised that ionospheric F2-layer critical frequencies [foF2] had a strong relationship to sunspot number. Using historic datasets from the Slough and Washington ionosondes, we evaluate the best statistical fits of foF2 to sunspot numbers (at each Universal Time [UT] separately) in order to search for drifts and abrupt changes in the fit residuals over Solar Cycles 17-21. This test is carried out for the original composite of the Wolf/ZĂŒrich/International sunspot number [R], the new âbackboneâ group sunspot number [RBB] and the proposed âcorrected sunspot numberâ [RC]. Polynomial fits are made both with and without allowance for the white-light facular area, which has been reported as being associated with cycle-to-cycle changes in the sunspot number - foF2 relationship. Over the interval studied here, R, RBB, and RC largely differ in their allowance for the âWaldmeier discontinuityâ around 1945 (the correction factor for which for R, RBB and RC is, respectively, zero, effectively over 20 %, and explicitly 11.6 %). It is shown that for Solar Cycles 18-21, all three sunspot data sequences perform well, but that the fit residuals are lowest and most uniform for RBB. We here use foF2 for those UTs for which R, RBB, and RC all give correlations exceeding 0.99 for intervals both before and after the Waldmeier discontinuity. The error introduced by the Waldmeier discontinuity causes R to underestimate the fitted values based on the foF2 data for 1932-1945 but RBB overestimates them by almost the same factor, implying that the correction for the Waldmeier discontinuity inherent in RBB is too large by a factor of two. Fit residuals are smallest and most uniform for RC and the ionospheric data support the optimum discontinuity multiplicative correction factor derived from the independent Royal Greenwich Observatory (RGO) sunspot group data for the same interval
- âŠ