This work investigates the modulation in dust activity over southwest (SW) Asia attributed to changes in the mean sea level pressure (MSLP) between the Caspian Sea (CS) and Hindu Kush (HK) during the ...summer months (June–July–August–September, JJAS) of the period 2000–2014. The MSLP anomalies obtained via NCEP/NCAR re-analysis are evaluated via a new climatology index, the Caspian Sea–Hindu Kush Index (CasHKI), which is defined as CasHKI=MSLPanom.CS−MSLPanom.HK, over specific domains taken over the CS and HK. The changes in CasHKI intensity are examined against dust activity and rainfall distributions over south Asia. The satellite remote sensing (Meteosat, OMI, MODIS) analyses show that high CasHKI values corresponding to enhanced pressure gradient between the CS and the HK, are associated with intensification of northerly winds, increased dust emissions and transportation over SW Asia and north Arabian Sea. In contrast, variations in CasHKI intensity do not seem to have a significant effect on the Indian summer monsoon. Only a slight decrease of precipitation over the southern Indian peninsula and the neighboring oceanic areas and an increase of precipitation along the Ganges Basin and Himalayan range are found to be related to high CasHKI values. Model (MIROC-SPRINTARS) simulations of dust concentration and dust AOD (Aerosol Optical Depth) over SW Asia are consistent with the satellite observations, highlighting for the first time the modulation of the SW Asian dust activity by CasHKI.
•The CasHKI as a key parameter of SW Asia climate•Changes in CasHKI intensity affect the wind field over SW Asia.•High CasHKI values govern intense north winds and dust emissions over SW Asia.•Increased dust outflow over north Arabian Sea under high CasHKI intensity.•Limited effect of CasHKI variations on the summer monsoon rainfall
This study focuses on analyzing the extreme aerosol loading and the mechanisms, source areas and meteorological conditions that favored the abnormal dust exposure towards Arabian Sea during June ...2008. The analysis reveals that the spatial-averaged aerosol optical depth (AOD) over Arabian Sea in June 2008 is 0.5 (78.2%) higher than the 2000–2013 mean June value and is mostly attributed to the enhanced dust activity and several (18) dust storms originated from the Sistan region (Iran–Afghanistan borders). Landsat images show that the marshy lakes in Sistan basin got dried during the second half of June 2008 and the alluvial silt and saline material got easily eroded by the intense Levar winds, which were stronger (>15–20 m s−1) than the climatological mean for the month of June. These conditions led to enhanced dust exposure from Sistan that strongly affected the northern and central parts of the Arabian Sea, as forward air-mass trajectories show. The NCEP/NCAR reanalysis reveals an abnormal intensification and spatial expansion of the Indian low pressure system towards northern Arabian Sea in June 2008. This suggests strengthening of the convection over the arid southwest Asia and exposure of significant amount of dust, which can reach further south over Arabian Sea favored by the enhanced cyclonic circulation. MODIS imagery highlighted several dust storms originated from Sistan and affecting Arabian Sea during June 2008, while the SPRINTARS model simulations of increased AOD and dust concentration over Sistan and downwind areas are in agreement with ground-based and satellite observations.
•The high AOD over Arabian Sea in June 2008 is mostly attributed to Sistan dust storms.•The role of the Sistan basin in dust aerosol loading over Arabian Sea.•The Hamoun lakes and the Levar wind play a major role in enhancement of dust activity.•The intensity of the cyclonic circulation over Arabian Sea favored the dust exposure.
ABSTRACT
This study examines the influence of the Caspian Sea–Hindu Kush Index (CasHKI) on local and synoptic meteorology as well as on dust emissions over southwest (SW) Asia by means of National ...Center for Environmental Prediction/National Center for Atmospheric Research (NCEP‐NCAR) re‐analysed mean sea‐level pressure (MSLP), geopotential height at 700 hPa and surface meridional wind, along with meteorological data at Zabol, east Iran and Meteosat/Infrared Difference Dust Index (IDDI) retrievals. The analysis focuses on the summer period (June to September) of 2000–2014 and the winter period (November to March) of 1963–2014. The CasHKI values are mostly controlled by the MSLP anomalies over the Caspian Sea (CS) domain, varying from approximately −25 to +35 hPa in winter and from approximately−10 to +14 hPa in summer, but without a clear annual pattern. The CasHKI values are classified into four modes for each month depending on their intensity. In the summer months, the high CasHKI mode is associated with enhanced MSLP over central Asia and deepening of the Indo‐Pakistan thermal low associated with the Indian summer monsoon. At 700‐hPa level, the high CasHKI mode shows an enhancement of the Arabian ridge, expanding it to the north over Iran and the CS, with a concurrent strengthening of the Indian trough, leading to intensification of northerly winds along east Iran. This results in significant increase in dust activity over SW Asia, which is also apparent in the winter months. Furthermore, the intensification of the northerly flow associated with the high CasHKI modes drops the temperature and increases the relative humidity over Zabol, especially during winter. The SPRINTARS‐model simulations also show increased dust emissions and concentrations for the high CasHKI values, confirming that the CasHKI variations modulate the dust activity over SW Asia throughout the year.
Dust storms are considered natural hazards that seriously affect atmospheric conditions, ecosystems and human health. A key requirement for investigating the dust life cycle is the analysis of the ...meteorological (synoptic and dynamic) processes that control dust emission, uplift and transport. The present work focuses on examining the synoptic and dynamic meteorological conditions associated with dust-storms in the Sistan region, southeastern Iran during the summer season (June–September) of the years 2001–2012. The dust-storm days (total number of 356) are related to visibility records below 1 km at Zabol meteorological station, located near to the dust source. RegCM4 model simulations indicate that the intense northern Levar wind, the high surface heating and the valley-like characteristics of the region strongly affect the meteorological dynamics and the formation of a low-level jet that are strongly linked with dust exposures. The intra-annual evolution of the dust storms does not seem to be significantly associated with El-Nino Southern Oscillation, despite the fact that most of the dust-storms are related to positive values of Oceanic Nino Index. National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis suggests that the dust storms are associated with low sea-level pressure conditions over the whole south Asia, while at 700 hPa level a trough of low geopotential heights over India along with a ridge over Arabia and central Iran is the common scenario. A significant finding is that the dust storms over Sistan are found to be associated with a pronounced increase of the anticyclone over the Caspian Sea, enhancing the west-to-east pressure gradient and, therefore, the blowing of Levar. Infrared Difference Dust Index values highlight the intensity of the Sistan dust storms, while the SPRINTARS model simulates the dust loading and concentration reasonably well, since the dust storms are usually associated with peaks in model simulations.
Cylinders and rings fabricated from AerMet® 100 alloy and AISI 1018 steel have been explosively driven to fragmentation in order to determine the fracture strains for these materials under ...plane-strain and uniaxial-stress conditions. The phenomena associated with the dynamic expansion and subsequent break up of the cylinders are monitored with high-speed diagnostics. In addition, complementary experiments are performed in which fragments from the explosively driven cylinders are recovered and analyzed to determine the statistical distribution associated with the fragmentation process as well as to determine failure mechanisms. The data are used to determine relevant coefficients for the Hancock–McKenzie (Johnson–Cook) fracture model. Metallurgical analysis of the fragments provides information on damage and failure mechanisms.
The present study focuses on identifying the main atmospheric circulation characteristics associated with aerosol episodes (AEs) over Kanpur, India during the period 2001–2010. In this respect, mean ...sea level pressure (MSLP) and geopotential height of 700 hPa (Z700) data obtained from the NCEP/NCAR Reanalysis Project were used along with daily Terra-MODIS AOD₅₅₀ data. The analysis identifies 277 AEs AOD₅₀₀ > Formula: see text ₅₀₀ + 1STDEV (standard deviation) over Kanpur corresponding to 13.2 % of the available AERONET dataset, which are seasonally distributed as 12.5, 9.1, 14.7 and 18.6 % for winter (Dec–Feb), pre-monsoon (Mar–May), monsoon (Jun–Sep) and post-monsoon (Oct–Nov), respectively. The post-monsoon and winter AEs are mostly related to anthropogenic emissions, in contrast to pre-monsoon and monsoon episodes when a significant component of dust is found. The multivariate statistical methods Factor and Cluster Analysis are applied on the dataset of the AEs days’ Z700 patterns over south Asia, to group them into discrete clusters. Six clusters are identified and for each of them the composite means for MSLP and Z700 as well as their anomalies from the mean 1981–2010 climatology are studied. Furthermore, the spatial distribution of Terra-MODIS AOD₅₅₀ over Indian sub-continent is examined to identify aerosol hot-spot areas for each cluster, while the SPRINTARS model simulations reveal incapability in reproducing the large anthropogenic AOD, suggesting need of further improvement in model emission inventories. This work is the first performed over India aiming to analyze and group the atmospheric circulation patterns associated with AEs over Indo-Gangetic Plains and to explore the influence of meteorology on the accumulation of aerosols.
Embedded smoothed particle hydrodynamics Tsuji, P.; Puso, M.; Spangler, C.W. ...
Computer methods in applied mechanics and engineering,
07/2020, Letnik:
366, Številka:
C
Journal Article
Recenzirano
Odprti dostop
In this paper, a hybrid method for embedding a meshfree smoothed particle hydrodynamics into mesh-based ALE hydro schemes is presented. The method relies on the embedded mesh framework presented in ...Puso et al. (2015, 2012) and utilizes SPH (Owen, 2010) in the solid foreground; when an appropriate damage or failure model is used with SPH, it becomes a natural way to model material fracture and cracking in high-explosive driven experiments. We provide various examples which validate the coupling between SPH and the embedded mesh method.
•Foreground SPH particles with immersed type coupling to the background ALE mesh.•Proposed a simple scheme to form an airtight surface around the SPH particles.•Extending the semi-explicit coupling using a stabilized Lagrange multiplier approach to handle the SPH equations.•Verification of the method with previous embedded mesh calculations of a plate blast problem.•Validation of the method on hypervelocity impact and high explosive experiments with fragmentation.
The gravitational
separation of major atmospheric components, in addition to the age of air,
would provide additional useful information about stratospheric circulation.
However, observations of the ...age of air and gravitational separation are
still geographically sparse, especially in the tropics. In order to address
this issue, air samples were collected over Biak, Indonesia in February 2015
using four large plastic balloons, each loaded with two compact cryogenic
samplers. With a vertical resolution of better than 2 km, air samples from
seven different altitudes were analyzed for CO2 and SF6 mole
fractions, δ15N of N2, δ18O of O2, and δ(Ar∕N2) to examine the vertically dependent age and
gravitational separation of air in the tropical tropopause layer (TTL) and
the equatorial stratosphere. By comparing their measured mole fractions with
aircraft observations in the upper tropical troposphere, we have found that
CO2 and SF6 ages increase gradually with increasing altitude from
the TTL to 22 km, and then rapidly from there up to 29 km. The CO2 and
SF6 ages agree well with each other in the TTL and in the lower
stratosphere, but show a significant difference above 24 km. The average
values of δ15N of N2, δ18O of O2, and δ(Ar∕N2) all show a small but distinct upward decrease due to the
gravitational separation effect. Simulations with a two-dimensional
atmospheric transport model indicate that the gravitational separation effect
decreases as tropical upwelling is enhanced. From the model calculations with
enhanced eddy mixing, it is also found that the upward increase in air age is
magnified by horizontal mixing. These model simulations also show that the
gravitational separation effect remains relatively constant in the lower
stratosphere. The results of this study strongly suggest that the
gravitational separation, combined with the age of air, can be used to
diagnose air transport processes in the stratosphere.
Summary Interstitial pneumonia (IP) is a chronic progressive interstitial lung disease associated with poor prognosis and high mortality. However, the pathogenesis of IP remains to be elucidated. The ...aim of this study was to clarify the role of pulmonary gammadeltaT cells in IP. In wild-type (WT) mice exposed to bleomycin, pulmonary gammadeltaT cells were expanded and produced large amounts of interferon (IFN)-gamma and interleukin (IL)-17A. Histological and biochemical analyses showed that bleomycin-induced IP was more severe in T cell receptor (TCR-delta-deficient (TCRdelta-/-) mice than WT mice. In TCRdelta-/- mice, pulmonary IL-17A+CD4+ Τ cells expanded at days 7 and 14 after bleomycin exposure. In TCRdelta-/- mice infused with gammadeltaT cells from WT mice, the number of pulmonary IL-17A+ CD4+ T cells was lower than in TCRdelta-/- mice. The examination of IL-17A-/- TCRdelta-/- mice indicated that gammadeltaT cells suppressed pulmonary fibrosis through the suppression of IL-17A+CD4+ T cells. The differentiation of T helper (Th)17 cells was determined in vitro, and CD4+ cells isolated from TCRdelta-/- mice showed normal differentiation of Th17 cells compared with WT mice. Th17 cell differentiation was suppressed in the presence of IFN-gamma producing gammadeltaT cells in vitro. Pulmonary fibrosis was attenuated by IFN-gamma-producing gammadeltaT cells through the suppression of pulmonary IL-17A+CD4+ T cells. These results suggested that pulmonary gammadeltaT cells seem to play a regulatory role in the development of bleomycin-induced IP mouse model via the suppression of IL-17A production.
Aerosol optical depth (AOD), Ångström Exponent (AE), and single scattering albedo (SSA) simulated by a new aerosol-coupled version of Nonhydrostatic ICosahedral Atmospheric Model (NICAM) have been ...compared with corresponding AERONET retrievals over a total of 196 sites during the 2006–2008 period. The temporal and spatial distributions of the modeled AODs and AEs match those of the AERONET retrievals reasonably well. For the 3-year mean AODs and AEs for all sites show the correlations between model and AERONET of 0.753 and 0.735, respectively, and 82.1% of the modeled AODs agree within a factor of two with the retrieved AODs. The primary model deficiency is an underestimation of fine mode aerosol AOD and a corresponding underestimation of AE over pollution region. Compared to the retrievals, the model underestimates the global 3-year mean AOD and AE by 0.022 (10.5%) and 0.329 (31.2%), respectively. The probability distribution function (PDF) of the modeled AODs is comparable to that of the retrieved ones, however, the model overestimates the occurrence frequencies of small AEs and SSAs.
•We simulate aerosol key optical properties using a new aerosol transport model.•The correlations between model and AERONET are strong for both AOD and AE.•82.1% of the simulated AODs agree within a factor of two with the measurements.•Model underestimates both the global 3-year mean AOD and AE.
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