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Observations of Saharan dust layer electrification
Electrification of atmospheric dust influences the coagulation, wet removal and fall speeds of dust particles. Alignment of dust particles can also occur in fair weather atmospheric electrical conditions if the particles are charged. However, very few electrical measurements made in elevated dust layers exist. Balloon-borne charge and particle instrumentation have been used to investigate the electrical properties of elevated Saharan dust layers. Soundings from the Cape Verde Islands, which experience frequent Saharan dust outbreaks, intercepted several dust layers. Two balloon soundings during summer 2009 detected dust particles in layers up to 4 km altitude. Simultaneous electrical measurements showed charge inside the dust layers, with a maximum measured charge density of 25 pC m ā 3, sufficient to influence wet removal processes
Hydrology and Biogeochemistry of a Bog-Fen-Tributary Complex in the Hudson Bay Lowlands, Ontario, Canada
The Hudson Bay Lowlands (HBL) contains 26 Gt C sequestered in a 2 meter thick layer of peat which blankets a quarter of Ontario, Canada. The hydrological and chemical influence of the HBL peatlands to surface waters is recognized, but information on peatland runoff processes and the evolution of groundwater through this vast, carbon-rich landscape remain scant. This study focused on elucidating the groundwater flow patterns of a bog-fen-tributary complex in the central region of the HBL, and estimating exports of groundwater, dissolved organic carbon (DOC), total (THg), and methyl (MeHg) mercury during the 2011 ice-free season. Hydrometric data, combined with ions and stable water isotopes, reveal lateral flows in the uppermost meter of peat dominate the bulk transfer of groundwater in the bog (73-137 mm) and fen (55-131 mm). The direction and magnitude of the measured vertical gradients in the bog (-0.2 to 0.1) and fen (-0.1 to 0.2) are dictated by water table position and micro-to-mesoscale topography. The seasonal exports of DOC from the bog and fen are small, and comprise 5.4% (2.0Ā±0.3 g C m-2 yr-1) and 1.4% (0.5Ā±0.1 g C m-2 yr-1) of the Net Ecosystem Carbon Balance, respectively. Exports of THg and MeHg from the bog (132.9Ā±45.4 and 3.4Ā±2.8 ng m-2 yr-1) and fen (50.0Ā±8.4 and 1.9Ā±1.2 ng m-2 yr-1) are lower than reported in other boreal wetlands. The swamp and thicket riparian zone between the ribbed fen and tributary appears to influence the quality of water and augment solute concentrations of the water in small surface flows that flow directly into the nearby second-order stream
Coherent and Purcell-Enhanced Emission from Erbium Dopants in a Cryogenic High-Q Resonator
The stability and outstanding coherence of dopants and other atom-like
defects in tailored host crystals make them a leading platform for the
implementation of distributed quantum information processing and sensing in
quantum networks. Albeit the required efficient light-matter coupling can be
achieved via the integration into nanoscale resonators, in this approach the
proximity of interfaces is detrimental to the coherence of even the
least-sensitive emitters. Here, we establish an alternative: By integrating a
19 micrometer thin erbium-doped crystal into a cryogenic Fabry-Perot resonator
with a quality factor of nine million, we can demonstrate 59(6)-fold
enhancement of the emission rate, corresponding to a two-level Purcell factor
of 530(50), while preserving lifetime-limited optical coherence up to 0.54(1)
ms. With its emission at the minimal-loss wavelength of optical fibers and its
outcoupling efficiency of 46(8) %, our system enables coherent and efficient
nodes for long-distance quantum networks
Spectral multiplexing of telecom emitters with stable transition frequency
In a quantum network, coherent emitters can be entangled over large distances
using photonic channels. In solid-state devices, the required efficient
light-emitter interface can be implemented by confining the light in
nanophotonic structures. However, fluctuating charges and magnetic moments at
the nearby interface then lead to spectral instability of the emitters. Here we
avoid this limitation when enhancing the photon emission up to 70(12)-fold
using a Fabry-Perot resonator with an embedded 19 micrometer thin crystalline
membrane, in which we observe around 100 individual erbium emitters. In
long-term measurements, they exhibit an exceptional spectral stability of < 0.2
MHz that is limited by the coupling to surrounding nuclear spins. We further
implement spectrally multiplexed coherent control and find an optical coherence
time of 0.11(1) ms, approaching the lifetime limit of 0.3 ms for the
strongest-coupled emitters. Our results constitute an important step towards
frequency-multiplexed quantum-network nodes operating directly at a
telecommunication wavelength
The Universal Cloud and Aerosol Sounding System (UCASS): a low-cost miniature optical particle counter for use in dropsonde or balloon-borne sounding systems
Ā© Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. An earlier version of this work was published in Atmospheric Measurement Techniques Discussions: https://dx.doi.org/10.5194/amt-2019-70.A low-cost miniaturized particle counter has been developed by The University of Hertfordshire (UH) for the measurement of aerosol and droplet concentrations and size distributions. The Universal Cloud and Aerosol Sounding System (UCASS) is an optical particle counter (OPC), which uses wide-angle elastic light scattering for the high-precision sizing of fluid-borne particulates. The UCASS has up to 16 configurable size bins, capable of sizing particles in the range 0.4ā40āĀµm in diameter. Unlike traditional particle counters, the UCASS is an open-geometry system that relies on an external air flow. Therefore, the instrument is suited for use as part of a dropsonde, balloon-borne sounding system, as part of an unmanned aerial vehicle (UAV), or on any measurement platform with a known air flow. Data can be logged autonomously using an on-board SD card, or the device can be interfaced with commercially available meteorological sondes to transmit data in real time. The device has been deployed on various research platforms to take measurements of both droplets and dry aerosol particles. Comparative results with co-located instrumentation in both laboratory and field settings show good agreement for the sizing and counting ability of the UCASS.Peer reviewe
Effects of surface roughness with two scales on light scattering by hexagonal ice crystals large compared to the wavelength : DDA results
Peer reviewe
Polarization of tightly focused laser beams
The polarization properties of monochromatic light beams are studied. In
contrast to the idealization of an electromagnetic plane wave, finite beams
which are everywhere linearly polarized in the same direction do not exist.
Neither do beams which are everywhere circularly polarized in a fixed plane. It
is also shown that transversely finite beams cannot be purely transverse in
both their electric and magnetic vectors, and that their electromagnetic energy
travels at less than c. The electric and magnetic fields in an electromagnetic
beam have different polarization properties in general, but there exists a
class of steady beams in which the electric and magnetic polarizations are the
same (and in which energy density and energy flux are independent of time).
Examples are given of exactly and approximately linearly polarized beams, and
of approximately circularly polarized beams.Comment: 9 pages, 6 figure
Linear polarization signatures of atmospheric dust with the SolPol direct-sun polarimeter
Dust particles in lofted atmospheric layers may present a
preferential orientation, which could be detected from the resulting
dichroic extinction of the transmitted sunlight. The first indications were
provided relatively recently on atmospheric dust layers using passive
polarimetry, when astronomical starlight observations of known polarization
were found to exhibit an excess in linear polarization, during desert dust
events that reached the observational site. We revisit the previous
observational methodology by targeting dichroic extinction of transmitted
sunlight through extensive atmospheric dust layers utilizing a direct-sun
polarimeter, which is capable to continuously monitor the polarization of
elevated aerosol layers. In this study, we present the unique observations
from the Solar Polarimeter (SolPol) for different periods within 2 years,
when the instrument was installed in the remote monitoring station of PANGEA
ā the PANhellenic GEophysical observatory of Antikythera ā in Greece. SolPol
records polarization, providing all four Stokes parameters, at a default
wavelength band centred at 550ānm with a detection limit of 10ā7.
We, overall, report on detected increasing trends of linear polarization,
reaching up to 700 parts per million, when the instrument is targeting away
from its zenith and direct sunlight propagates through dust concentrations
over the observatory. This distinct behaviour is absent on measurements we
acquire on days with lack of dust particle concentrations and in general of low aerosol content. Moreover, we investigate the dependence of the degree of linear polarization on the layers' optical depth under various dust loads
and solar zenith angles and attempt to interpret these observations as an
indication of dust particles being preferentially aligned in the Earth's
atmosphere.</p
Phase and transport velocities in particle and electromagnetic beams
In a coherent monoenergetic beam of non-interacting particles, the phase
velocity and the particle transport velocity are functions of position, with
the strongest variation being in the focal region. These velocities are
everywhere parallel to each other, and their product is constant in space. For
a coherent monochromatic electromagnetic beam, the energy transport velocity is
never greater than the speed of light, and can even be zero. The phase
velocities (one each for the non-zero components of the electric and magnetic
fields, in general) can be different from each other and from the energy
transport velocity, both in direction and in magnitude. The phase velocities at
a given point are independent of time, for both particle and electromagnetic
beams. The energy velocity is independent of time for the particle beam, but in
general oscillates (with angular frequency 2w) in magnitude and direction about
its mean value at a given point in the electromagnetic beam. However, there
exist electromagnetic steady beams, within which the energy flux, energy
density and energy velocity are all independent of time.Comment: 9 pages, 12 figure
Cloud Ice Properties: In Situ Measurement Challenges
Baumgardner D., S.J. Abel, D. Axisa, R. Cotton, J. Crosier, P. Field, C. Gurganus, A. Heymsfield, A. Korolev, M. KrƤmer, P. Lawson, G. McFarquhar, Z. Ulanowski, and J. Um, 'Cloud ice properties: in situ measurement challenges', Meteorological Monographs, Vol. 58, pp. 9.1ā9.23, April 2017. The version of record is available online at doi: 10.1175/AMSMONOGRAPHS-D-16-0011.1.1 Ā© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).Understanding the formation and evolution of ice in clouds requires detailed information on the size, shape, mass and optical properties of individual cloud hydrometeors and their bulk properties over a broad range of atmospheric conditions. Since the 1960s, instrumentation and research aircraft have evolved providing increasingly more accurate and larger quantities of data about cloud particle properties. In this chapter we review the current status of electrical powered, in situ measurement systems with respect to their strengths and weaknesses and document their limitations and uncertainties. There remain many outstanding challenges. These are summarized and accompanied by recommendations for moving forward. through new developments that fill the remaining information gaps. Closing these gaps will remove the obstacles that continue to hinder our understanding of cloud processes in general and the evolution of ice in particular.Peer reviewe
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