583 research outputs found
Characterization of cumulus cloud fields using trajectories in the center of gravity versus water mass phase space: 1. Cloud tracking and phase space description
We study the evolution of warm convective cloud fields using large eddy simulations of continental and trade cumulus. Individual clouds are tracked a posteriori from formation to dissipation using a 3âD cloudâtracking algorithm, and results are presented in the phase space of center of gravity altitude versus cloud liquid water mass (CvM space). The CvM space is shown to contain rich information on cloud field characteristics, cloud morphology, and common cloud development pathways, together facilitating a comprehensive understanding of the cloud field. In this part we show how the meteorological (thermodynamic) conditions that determine the cloud properties are projected on the CvM phase space and how changes in the initial conditions affect the clouds\u27 trajectories in this space. This part sets the stage for a detailed microphysical analysis that will be shown in part II
Combining Litter Observations with a Regional Ocean Model to Identify Sources and Sinks of Floating Debris in a Semi-enclosed Basin: The Adriatic Sea
Visual ship transect surveys provide crucial information about the density, and spatial distribution of floating anthropogenic litter in a basin. However, such observations provide a âsnapshotâ of local conditions at a given time and cannot be used to deduce the provenance of the litter or to predict its fate, crucial information for management and mitigation policies. Particle tracking techniques have seen extensive use in these roles, however, most previous studies have used simplistic initial conditions based on bulk average inputs of debris to the system. Here, observations of floating anthropogenic macro debris in the Adriatic Sea are used to define initial conditions (number of particles, location, and time) in a Lagrangian particle tracking model. Particles are advected backward and forward in time for 60 days (120 days total) using surface velocities from an operational regional ocean model. Sources and sinks for debris observed in the central and southern Adriatic in May 2013 and March 2015 included the Italian coastline from Pescara to Brindisi, the Croatian island of Mljet, and the coastline from Dubrovnik through Montenegro to Albania. Debris observed in the northern Adriatic originated from the Istrian peninsula to the Italian city of Termoli, as well as the Croatian island of Cres and the Kornati archipelago. Particles spent a total of roughly 47 days afloat. Coastal currents, notably the eastern and western Adriatic currents, resulted in large alongshore displacements. Our results indicate that anthropogenic macro debris originates largely from coastal sources near population centers and is advected by the cyclonic surface circulation until it strands on the southwest (Italian) coast, exits the Adriatic, or recirculates in the southern gyreVersiĂłn del edito
Radiative signature of absorbing aerosol over the eastern Mediterranean basin
The effects of absorbing aerosols on the atmospheric radiation budget and
dynamics over the eastern Mediterranean region are studied using satellites
and ground-based observations, and radiative transfer model calculations,
under summer conditions. Climatology of aerosol optical depth (AOD), single
scattering albedo (SSA) and size parameters were analyzed using multi-year
(1999â2012) observations from Moderate Resolution Imaging Spectroradiometer (MODIS),
Multi-angle Imaging SpectroRadiometer (MISR)
and AErosol RObotic NETwork (AERONET). Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP)-derived
aerosol vertical distributions and their classifications are used to
calculate the AOD of four dominant aerosol types: dust, polluted dust, polluted
continental, and marine aerosol over the region. The seasonal mean (JuneâAugust
2010) AODs are 0.22 ± 0.02, 0.11 ± 0.04, 0.10 ± 0.04
and 0.06 ± 0.01 for polluted dust, polluted continental, dust and
marine aerosol, respectively. Changes in the atmospheric temperature profile
as a function of absorbing aerosol loading were derived for the same period
using observations from the AIRS satellite. We inferred heating rates in the
aerosol layer of ~1.7 ± 0.8 K dayâ1 between 925
and 850 hPa, which is attributed to aerosol absorption of incoming solar
radiation. Radiative transfer model (RTM) calculations show significant
atmospheric warming for dominant absorbing aerosol over the region. A
maximum atmospheric forcing of +16.7 ± 7.9 Wmâ2 is calculated
in the case of polluted dust, followed by dust (+9.4 ± 4.9 Wm−2)
and polluted continental (+6.4 ± 4.5 Wm−2). RTM-derived heating
rate profiles for dominant absorbing aerosol show warming of 0.1â0.9 K dayâ1 in the aerosol layer (< 3.0 km altitudes), which
primarily depend on AODs of the different aerosol types. Diabatic heating
due to absorbing aerosol stabilizes the lower atmosphere, which could
significantly reduce the atmospheric ventilation. These conditions can
enhance the "pollution pool" over the eastern Mediterranean
Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV
A search for the lightest neutral scalar and neutral pseudoscalar Higgs
bosons in the Minimal Supersymmetric Standard Model is performed using 176.4
pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of
189 GeV. No signal is observed, and the data are consistent with the expected
Standard Model background. Lower limits on the masses of the lightest neutral
scalar and pseudoscalar Higgs bosons are given as a function of tan(beta).
Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h
> 77.1 GeV and m_A > 77.1 GeV
Measurement of the Lifetime of the Tau Lepton
The tau lepton lifetime is measured with the L3 detector at LEP using the
complete data taken at centre-of-mass energies around the Z pole resulting in
tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result
with the muon lifetime supports lepton universality of the weak charged current
at the level of six per mille. Assuming lepton universality, the value of the
strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/-
0.015(exp.) +/- 0.014 (theory)
Formation of the in Two-Photon Collisions at LEP
The two-photon width of the meson has been
measured with the L3 detector at LEP. The is studied in the decay
modes , KK, KK,
KK, , , and
using an integrated luminosity of 140 pb at GeV and
of 52 pb at GeV. The result is
(BR) keV. The dependence of the cross section is studied for
GeV. It is found to be better described by a Vector Meson
Dominance model form factor with a J-pole than with a -pole. In addition,
a signal of events is observed at the mass. Upper limits
for the two-photon widths of the , , and are also
given
Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV
A search for charginos nearly mass-degenerate with the lightest
supersymmetric particle is performed using the 176 pb^-1 of data collected at
189 GeV in 1998 with the L3 detector. Mass differences between the chargino and
the lightest supersymmetric particle below 4 GeV are considered. The presence
of a high transverse momentum photon is required to single out the signal from
the photon-photon interaction background. No evidence for charginos is found
and upper limits on the cross section for chargino pair production are set. For
the first time, in the case of heavy scalar leptons, chargino mass limits are
obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference
Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays
We have measured the probability, n(g->cc~), of a gluon splitting into a
charm-quark pair using 1.7 million hadronic Z decays collected by the L3
detector. Two independent methods have been applied to events with a three-jet
topology. One method relies on tagging charmed hadrons by identifying a lepton
in the lowest energy jet. The other method uses a neural network based on
global event shape parameters. Combining both methods, we measure n(g->cc~)=
[2.45 +/- 0.29 +/- 0.53]%
Search for Extra Dimensions in Boson and Fermion Pair Production in e+e- Interactions at LEP
Extra spatial dimensions are proposed by recent theories that postulate the
scale of gravity to be of the same order as the electroweak scale. A sizeable
interaction between gravitons and Standard Model particles is then predicted.
Effects of these new interactions in boson and fermion pair production are
searched for in the data sample collected at centre-of-mass energies above the
Z pole by the L3 detector at LEP. In addition, the direct production of a
graviton associated with a Z boson is investigated. No statistically
significant hints for the existence of these effects are found and lower limits
in excess of 1 TeV are derived on the scale of this new theory of gravity
Direct Observation of Longitudinally Polarised W Bosons
The three different helicity states of W bosons, produced in the reaction
e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at
sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of
the scattering angle between the W- and the direction of the e- beam. The
analysis demonstrates that W bosons are produced with all three helicities, the
longitudinal and the two transverse states. Combining the results from the two
center-of-mass energies and with leptonic and hadronic W decays, the fraction
of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.)
+/- 0.016(syst.) in agreement with the expectation from the Standard Model
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