183 research outputs found
Breaking stress of neutron star crust
The breaking stress (the maximum of the stress-strain curve) of neutron star
crust is important for neutron star physics including pulsar glitches, emission
of gravitational waves from static mountains, and flares from star quakes. We
perform many molecular dynamic simulations of the breaking stress at different
coupling parameters (inverse temperatures) and strain rates. We describe our
results with the Zhurkov model of strength. We apply this model to estimate the
breaking stress for timescales ~1 s - 1 year, which are most important for
applications, but much longer than can be directly simulated. At these
timescales the breaking stress depends strongly on the temperature. For
coupling parameter <200, matter breaks at very small stress, if it is applied
for a few years. This viscoelastic creep can limit the lifetime of mountains on
neutron stars. We also suggest an alternative model of timescale-independent
breaking stress, which can be used to estimate an upper limit on the breaking
stress.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letter
Smoke aerosol and its radiative effects during extreme fire event over Central Russia in summer 2010
Different microphysical, optical and radiative properties of aerosol were analyzed during the severe fires in summer 2010 over Central Russia using ground measurements at two AERONET sites in Moscow (Meteorological Observatory of Moscow State University ā MSU MO) and Zvenigorod (Moscow Region) and radiative measurements at the MSU MO. Volume aerosol size distribution in smoke conditions had a bimodal character with the significant prevalence of fine mode particles, for which effective radius was shifted to higher values (<i>r</i><aub>eff-fine</aub> = 0.24 Ī¼m against approximately 0.15 Ī¼m in typical conditions). For smoke aerosol, the imaginary part of refractive index (REFI) in the visible spectral region was lower than that for typical aerosol (REFI<sub>&lambda; =675 nm</sub> = 0.006 against REFI<sub>&lambda; =675 nm</sub> = 0.01), while single scattering albedo (SSA) was significantly higher (SSA<sub>&lambda; =675 nm</sub> = 0.95 against SSA<sub>&lambda; =675 nm</sub> ~ 0.9). Extremely high aerosol optical thickness at 500 nm (AOT500) was observed on 6ā8 August reaching the absolute maximum on 7 August in Moscow (AOT500 = 6.4) and at Zvenigorod (AOT500 = 5.9). A dramatic attenuation of solar irradiance at ground was also recorded. Maximum irradiance loss had reached 64% for global shortwave irradiance, 91% for UV radiation 300ā380 nm, and 97% for erythemally-weighted UV irradiance at relatively high solar elevation 47Ā°. Significant spectral dependence in attenuation of solar irradiance in smoky conditions was mainly explained by higher AOT and smaller SSA in UV (0.8ā0.9) compared with SSA in the visible region of spectrum. The assessments of radiative forcing effect (RFE) at the TOA indicated a significant cooling of the smoky atmosphere. Instant RFE reached ā167 Wm<sup>ā2</sup> at AOT500 = 6.4, climatological RFE calculated with August 2010 monthly mean AOT was about ā65 Wm<sup>ā2</sup>, compared with ā20 Wm<sup>ā2</sup> for typical aerosol according to the 10 yr period of measurements in Moscow
Optical Properties of Aerosols from Long Term Ground-Based Aeronet Measurements
AERONET is an optical ground-based aerosol monitoring network and data archive supported by NASA's Earth Observing System and expanded by federation with many non-NASA institutions including AEROCAN (AERONET CANada) and PHOTON (PHOtometrie pour le Traiteinent Operatonnel de Normalisation Satellitaire). The network hardware consists of identical automatic sun-sky scanning spectral radiometers owned by national agencies and universities purchased for their own monitoring and research objectives. Data are transmitted hourly through the data collection system (DCS) on board the geostationary meteorological satellites GMS, GOES and METEOSAT and received in a common archive for daily processing utilizing a peer reviewed series of algorithms thus imposing a standardization and quality control of the product data base. Data from this collaboration provides globally distributed near real time observations of aerosol spectral optical depths, aerosol size distributions, and precipitable water in diverse aerosol regimes. Access to the AERONET data base has shifted from the interactive program 'demonstrat' (reserved for PI's) to the AERONET homepage allowing faster access and greater development for GIS object oriented retrievals and analysis with companion geocoded data sets from satellites, LIDAR and solar flux measurements for example. We feel that a significant yet under utilized component of the AERONET data base are inversion products made from hourly principal plane and almucanter measurements. The current inversions have been shown to retrieve aerosol volume size distributions. A significant enhancement to the inversion code has been developed and is presented in these proceedings
Characterizing the 2015 Indonesia fire event using modified MODIS aerosol retrievals
The Indonesian fire and smoke event of 2015 was an extreme episode that
affected public health and caused severe economic and environmental damage.
The MODIS Dark Target (DT) aerosol algorithm, developed for global
applications, significantly underestimated regional aerosol optical depth
(AOD) during this episode. The larger-than-global-averaged uncertainties in
the DT product over this event were due to both an overly zealous set of masks
that mistook heavy smoke plumes for clouds and/or inland water, and also an
aerosol model developed for generic global aerosol conditions. Using Aerosol
Robotic Network (AERONET) Version 3 sky inversions of local AERONET stations,
we created a specific aerosol model for the extreme event. Thus, using this
new less-absorbing aerosol model, cloud masking based on results of the MODIS
cloud optical properties algorithm, and relaxed thresholds on both inland
water tests and upper limits of the AOD retrieval, we created a research
algorithm and applied it to 80 appropriate MODIS granules during the event.
Collocating and comparing with AERONET AOD shows that the research algorithm
doubles the number of MODIS retrievals greater than 1.0, while also
significantly improving agreement with AERONET. The final results show that
the operational DT algorithm had missed approximately 0.22 of the regional
mean AOD, but as much as AOD = 3.0 for individual 0.5ā grid
boxes. This amount of missing AOD can skew the perception of the severity of
the event, affect estimates of regional aerosol forcing, and alter aerosol
modeling and forecasting that assimilate MODIS aerosol data products. These
results will influence the future development of the global DT aerosol
algorithm.</p
Reduction of Aerosol Absorption in Beijing Since 2007 from MODIS and AERONET
An analysis of the time series of MODIS-based and AERONET aerosol records over Beijing reveals two distinct periods, before and after 2007. The MODIS data from both the Terra and Aqua satellites were processed with the new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. A comparison of MAIAC and AERONET AOT shows that whereas MAIAC consistently underestimated peak AOT values by 10-20% in the prior period, the bias mostly disappears after mid-2007. Independent analysis of the AERONET dataset reveals little or no change in the effective radii of the fine and coarse fractions and of the Angstrom exponent. At the same time, it shows an increasing trend in the single scattering albedo, by approx.0.02 in 9 years. As MAIAC was using the same aerosol model for the entire 2000-2010 period, the decrease in AOT bias after 2007 can be explained only by a corresponding decrease of aerosol absorption caused by a reduction in local black carbon emissions. The observed changes correlate in time with the Chinese government's broad measures to improve air quality in Beijing during preparations for the Summer Olympics of 2008
Ordered arrays of multiferroic epitaxial nanostructures
Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe2O4 (NFO) and FE PbZr0.52Ti0.48O3 or PbZr0.2Ti0.8O3, with large range order and lateral dimensions from 200 nm to 1 micron
Advancements in the Aerosol Robotic NetworkĀ (AERONET) VersionĀ 3 database ā automated near-real-time quality control algorithm with improved cloud screening for Sun photometer aerosol optical depthĀ (AOD) measurements
The Aerosol Robotic NetworkĀ (AERONET) has provided highly
accurate, ground-truth measurements of the aerosol optical depthĀ (AOD) using
Cimel Electronique Sunāsky radiometers for more than 25Ā years. In VersionĀ 2Ā (V2)
of the AERONET database, the near-real-time AOD was semiautomatically
quality controlled utilizing mainly cloud-screening methodology, while
additional AOD data contaminated by clouds or affected by instrument
anomalies were removed manually before attaining quality-assured status
(LevelĀ 2.0). The large growth in the number of AERONET sites over the past
25Ā years resulted in significant burden to the manual quality control of millions
of measurements in a consistent manner. The AERONET VersionĀ 3Ā (V3) algorithm
provides fully automatic cloud screening and instrument anomaly quality
controls. All of these new algorithm updates apply to near-real-time data as
well as post-field-deployment processed data, and AERONET reprocessed the
database inĀ 2018. A full algorithm redevelopment provided the opportunity to
improve data inputs and corrections such as unique filter-specific
temperature characterizations for all visible and near-infrared wavelengths,
updated gaseous and water vapor absorption coefficients, and ancillary data
sets. The LevelĀ 2.0 AOD quality-assured data set is now available within a
month after post-field calibration, reducing the lag time from up to several
months. Near-real-time estimated uncertainty is determined using data
qualified as V3Ā LevelĀ 2.0 AOD and considering the difference between the AOD
computed with the pre-field calibration and AOD computed with pre-field and
post-field calibration. This assessment provides a near-real-time
uncertainty estimate for which average differences of AOD suggest a +0.02Ā bias
and one sigma uncertainty ofĀ 0.02, spectrally, but the bias and uncertainty
can be significantly larger for specific instrument deployments. Long-term
monthly averages analyzed for the entire V3Ā and V2Ā databases produced
average differencesĀ (V3āV2) ofĀ +0.002 with a Ā±0.02 SD (standard
deviation), yet monthly averages calculated using time-matched observations
in both databases were analyzed to compute an average difference ofĀ ā0.002
with a Ā±0.004 SD. The high statistical agreement in
multiyear monthly averaged AOD validates the advanced automatic data
quality control algorithms and suggests that migrating research to the
V3Ā database will corroborate most V2Ā research conclusions and likely lead to
more accurate results in some cases.</p
Maritime Aerosol Network as a Component of AERONET - First Results and Comparison with Global Aerosol Models and Satellite Retrievals
The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. Over 80 cruises were completed through early 2010 with deployments continuing. Measurement areas included various parts of the Atlantic Ocean, the Northern and Southern Pacific Ocean, the South Indian Ocean, the Southern Ocean, the Arctic Ocean and inland seas. MAN deploys Microtops handheld sunphotometers and utilizes a calibration procedure and data processing traceable to AERONET. Data collection included areas that previously had no aerosol optical depth (AOD) coverage at all, particularly vast areas of the Southern Ocean. The MAN data archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we present results of AOD measurements over the oceans, and make a comparison with satellite AOD retrievals and model simulations
Optical Properties of Boreal Region Biomass Burning Aerosols in Central Alaska and Seasonal Variation of Aerosol Optical Depth at an Arctic Coastal Site
Long-term monitoring of aerosol optical properties at a boreal forest AERONET site in interior Alaska was performed from 1994 through 2008 (excluding winter). Large interannual variability was observed, with some years showing near background aerosol optical depth (AOD) levels (<0.1 at 500 nm) while 2004 and 2005 had August monthly means similar in magnitude to peak months at major tropical biomass burning regions. Single scattering albedo (omega (sub 0); 440 nm) at the boreal forest site ranged from approximately 0.91 to 0.99 with an average of approximately 0.96 for observations in 2004 and 2005. This suggests a significant amount of smoldering combustion of woody fuels and peat/soil layers that would result in relatively low black carbon mass fractions for smoke particles. The fine mode particle volume median radius during the heavy burning years was quite large, averaging approximately 0.17 micron at AOD(440 nm) = 0.1 and increasing to approximately 0.25 micron at AOD(440 nm) = 3.0. This large particle size for biomass burning aerosols results in a greater relative scattering component of extinction and, therefore, also contributes to higher omega (sub 0). Additionally, monitoring at an Arctic Ocean coastal site (Barrow, Alaska) suggested transport of smoke to the Arctic in summer resulting in individual events with much higher AOD than that occurring during typical spring Arctic haze. However, the springtime mean AOD(500 nm) is higher during late March through late May (approximately 0.150) than during summer months (approximately 0.085) at Barrow partly due to very few days with low background AOD levels in spring compared with many days with clean background conditions in summer
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