7,800 research outputs found
A comparison of GLAS SAT and NMC high resolution NOSAT forecasts from 19 and 11 February 1976
A subjective comparison of the Goddard Laboratory for Atmospheric Sciences (GLAS) and the National Meteorological Center (NMC) high resolution model forecasts is presented. Two cases where NMC's operational model in 1976 had serious difficulties in forecasting for the United States were examined. For each of the cases, the GLAS model forecasts from initial conditions which included satellite sounding data were compared directly to the NMC higher resolution model forecasts, from initial conditions which excluded the satellite data. The comparison showed that the GLAS satellite forecasts significantly improved upon the current NMC operational model's predictions in both cases
Numerical prediction of the Mid-Atlantic states cyclone of 18-19 February 1979
A series of forecast experiments was conducted to assess the accuracy of the GLAS model, and to determine the importance of large scale dynamical processes and diabatic heating to the cyclogenesis. The GLAS model correctly predicted intense coastal cyclogenesis and heavy precipitation. Repeated without surface heat and moisture fluxes, the model failed to predict any cyclone development. An extended range forecast, a forecast from the NMC analysis interpolated to the GLAS grid, and a forecast from the GLAS analysis with the surface moisture flux excluded predicted weak coastal low development. Diabatic heating resulting from oceanic fluxes significantly contributed to the generation of low level cyclonic vorticity and the intensification and slow rate of movement of an upper level ridge over the western Atlantic. As an upper level short wave trough approached this ridge, diabatic heating associated with the release of latent heat intensified, and the gradient of vorticity, vorticity advection and upper level divergence in advance of the trough were greatly increased, providing strong large scale forcing for the surface cyclogenesis
Simultaneous ocean cross-section and rainfall measurements from space with a nadir-pointing radar
A method to determine simultaneously the rainfall rate and the normalized backscattering cross section of the surface was evaluated. The method is based on the mirror reflected power, p sub m which corresponds to the portion of the incident power scattered from the surface to the precipitation, intercepted by the precipitation, and again returned to the surface where it is scattered a final time back to the antenna. Two approximations are obtained for P sub m depending on whether the field of view at the surface is either much greater or much less than the height of the reflection layer. Since the dependence of P sub m on the backscattering cross section of the surface differs in the two cases, two algorithms are given by which the path averaged rain rate and normalized cross section are deduced. The detectability of P sub m, the relative strength of other contributions to the return power arriving simultaneous with P sub m, and the validity of the approximations used in deriving P sub m are discussed
Recent Heavy Ion Results with the ATLAS Detector at the LHC
Results are presented from the ATLAS collaboration from the 2010 LHC heavy
ion run, during which nearly 10 inverse microbarns of luminosity were
delivered. Soft physics results include charged particle multiplicities and
collective flow. The charged particle multiplicity, which tracks initial state
entropy production, increases by a factor of two relative to the top RHIC
energy, with a centrality dependence very similar to that already measured at
RHIC. Measurements of elliptic flow out to large transverse momentum also show
similar results to what was measured at RHIC, but no significant pseudorapidity
dependence. Extensions of these measurements to higher harmonics have also been
made, and can be used to explain structures in the two-particle correlation
functions that had long been attributed to jet-medium interactions. New hard
probe measurements include single muons, jets and high hadrons. Single
muons at high momentum are used to extract the yield of bosons and
are found to be consistent within statistical uncertainties with binary
collision scaling. Conversely, jets are found to be suppressed in central
events by a factor of two relative to peripheral events, with no significant
dependence on the jet energy. Fragmentation functions are also found to be the
same in central and peripheral events. Finally, charged hadrons have been
measured out to 30 GeV, and their centrality dependence relative to peripheral
events is similar to that found for jets.Comment: 9 pages, 9 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
Atmospheric response to variations in sea surface temperature
An extended range prediction experiment was performed with the GISS atmospheric model on a global data to test the sensitivity of the model to sea surface temperature (SST) variation over a two-week forecast period. The use of an initial observed SST field in place of the climatological monthly mean sea temperatures for surface flux calculations in the model was found to have a significant effect on the predicted precipitation over the ocean, with enhanced convection computed over areas where moderately large warm SST anomalies are found. However, there was no detectable positive effect of the SST anomaly field on forecast quality. The influence of the SST anomalies on the daily predicted fields of pressure and geopotential is relatively insignificant up to about one week compared with the growth of prediction error, and is no greater over a two-week period than that resulting from random errors in the initial meteorological state. The 14-day average fields of sea level pressure and 500-mb height predicted by the model, appear to be similarly insensitive to anomalies of sea surface temperature
Measurement of elliptic and higher order flow harmonics at TeV Pb+Pb collisions with the ATLAS Detector
The measurements of flow harmonics - using the event plane and two
particle correlations methods in broad , and centrality ranges
using the ATLAS detector at LHC are presented. ATLAS recorded about 9 of lead-lead collision data in the 2010 heavy ion run. The
full azimuthal acceptance of the ATLAS detector in units of
pseudorapidity for charged hadrons and the large amount of data allows for a
detailed study of the flow harmonics. The , centrality and ranges
where the two methods give consistent and where they disagree are
discussed. It is shown that the ridge as well as the so called "mach-cone" seen
in two particle correlations are largely accounted for by the collective flow.
Some scaling relations in the dependence of the are also discussed
Upgrade of the ATLAS Muon Trigger for the SLHC
The outer shell of the ATLAS experiment at the LHC consists of a system of
toroidal air-core magnets in order to allow for the precise measurement of the
transverse momentum p of muons, which in many physics channels are a
signature of interesting physics processes. For the precise determination of
the muon momentum Monitored Drift Tube chambers (MDT) with high position
accuracy are used, while for the fast identification of muon tracks chambers
with high time resolution are used, able to select muons above a predefined
p threshold for use in the first Level of the ATLAS triggering system
(Level-1 trigger). When the luminosity of the LHC will be upgraded to 4-5 times
the present nominal value (SLHC) in about a decade from now, an improvement of
the selectivity of the ATLAS Level-1 triggering system will be mandatory in
order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1
trigger of the ATLAS muon spectrometer this means an increase of the p
threshold for single muons. Due to the limited spatial resolution of the
trigger chambers, however, the selectivity for tracks above ~20 GeV/c is
insufficient for an effective reduction of the Level-1 rate. We describe how
the track coordinates measured in the MDT precision chambers can be used to
decisively improve the selectivity for high momentum tracks. The resulting
increase in latency will also be discussed.Comment: These are the proceedings of a presentation given at the Topical
Workshop of Electronics for Particle Physics 2010 in Aachen, Germany (sept.,
20-24, 2010
LHC Coverage of RPV MSSM with Light Stops
We examine the sensitivity of recent LHC searches to signatures of
supersymmetry with R-parity violation (RPV). Motivated by naturalness of the
Higgs potential, which would favor light third-generation squarks, and the
stringent LHC bounds on spectra in which the gluino or first and second
generation squarks are light, we focus on scenarios dominated by the pair
production of light stops. We consider the various possible direct and cascade
decays of the stop that involve the trilinear RPV operators. We find that in
many cases, the existing searches exclude stops in the natural mass range and
beyond. However, typically there is little or no sensitivity to cases dominated
by UDD operators or LQD operators involving taus. We propose several ideas for
searches which could address the existing gaps in experimental coverage of
these signals.Comment: 41 pages, 12 figures; v2: included new searches (see footnote 10),
minor corrections and improvement
Determination of rain rate from a spaceborne radar using measurements of total attenuation
Studies shows that path-integrated rain rates can be determined by means of a direct measurement of attenuation. For ground based radars this is done by measuring the backscattering cross section of a fixed target in the presence and absence of rain along the radar beam. A ratio of the two measurements yields a factor proportional to the attenuation from which the average rain rate is deduced. The technique is extended to spaceborne radars by choosing the ground as reference target. The technique is also generalized so that both the average and range-profiled rain rates are determined. The accuracies of the resulting estimates are evaluated for a narrow beam radar located on a low earth orbiting satellite
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