Characteristics of extreme dust events observed over two urban areas in Iran     

Abbas-Ali A Bidokhti  Maryam Gharaylou  Nafiseh Pegahfar  Samaneh Sabetghadam  Maryam Rezazadeh 《Journal of Earth System Science》2016,125(2):431-442

Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area.  相似文献   

Small sized charophyte gyrogonites in the Maastrichtian of Coll de Nargó, Eastern Pyrenees: An adaptation to temporary floodplain ponds     

《Cretaceous Research》2016

Charophytes bearing small sized fructifications dominated in fluviatile floodplain facies (red beds) from the Maastrichtian of Coll de Nargó and neighbouring basins in the southern Pyrenees (Catalonia, Spain). These charophytes mainly belong to the genus Microchara and are often disregarded in biostratigraphic studies, which focus their attention instead on facies from permanent lakes that are richer in species which usually bear fructifications with a larger size range. However, small sized gyrogonites are also significant for biostratigraphic purposes and even include some of the index species for Maastrichtian biozones in Europe. Indeed, the charophyte assemblages from the Maastrichtian of Coll de Nargó belong to the Microchara punctata biozone, recently calibrated to the middle-upper Maastrichtian.Floodplain ponds from the Maastrichtian red beds of Coll de Nargó (Lower Red Unit) were extremely shallow, received considerable terrigenous influx and were frequently exposed, probably resulting in turbid, warm waters with high light availability. These conditions could explain the almost exclusive occurrence of charophytes with small fructifications in the Lower Red Unit. The available data, mainly based on oospores from extant species, indicate that the small size observed in gyrogonites from temporary ponds may represent an adaptation to environmental stress. Fossil species with small gyrogonites of Microchara cristata, M. punctata and Microchara nana would thus develop massively in stressed shallow ponds on fluvial floodplains. To contrast these hypotheses, we compared our results to those of four well-known case studies with similar sedimentological contexts, ranging from the Lower Cretaceous to the upper Eocene–lower Oligocene. Gyrogonite size patterns were similar in all cases, possibly suggesting that characeans display a long history of adaptation to shallow, temporary and turbid floodplain ponds by means of producing a high number of small gyrogonites, probably representing short life cycles and opportunistic strategies.  相似文献   

Biogenic volatile compound emissions from a temperate forest,China: model simulation     

Jianhui?BaiEmail author  Tiffany?Duhl  Nan?Hao 《Journal of Atmospheric Chemistry》2016,73(1):29-59

Emissions of biogenic volatile organic compounds (BVOC) were measured using a relaxed eddy accumulation (REA) technique on an above-canopy tower in a temperate forest (Changbai Mountain, Jilin province, China) during the 2010 and 2011 summer seasons. Solar global radiation and photosynthetically active radiation (PAR) were also measured. Based on PAR energy dynamic balance, an empirical BVOC emission and PAR transfer model was developed that includes the processes of BVOC emissions and PAR transfer above the canopy level, including PAR absorption and consumption, and scattering by gases, liquids, and particles (GLPs). Simulated emissions of isoprene and monoterpenes were in agreement with observations. The averages of the relative estimator biases for the flux were 39.3 % for isoprene, and 27.1 % for monoterpenes in the 2010 and 2011 growing seasons, with NMSE (normalized mean square error) values of 0.133 and 0.101, respectively. The observed and simulated mean diurnal variations of isoprene and monoterpenes in the 2010 and 2011 growing seasons were evaluated for the validation of the empirical model. Under observed atmospheric conditions, the sensitivity analysis showed that emissions of isoprene and monoterpenes were more sensitive to changes in PAR than to water vapor content or to the magnitude of the scattering factor. The emissions of isoprene and monoterpenes in the 2010 and 2011 growing seasons (from June to September) were estimated using this empirical model along with hourly observational data, with mean hourly emissions of 1.71 and 1.55 mg m^?2 h^?1 for isoprene, and 0.48 and 0.47 mg m^?2 h^?1 for monoterpenes in 2010 and 2011, respectively. As formaldehyde (HCHO) is considered as the main oxidation product of isoprene and monoterpenes, it is necessary to investigate the link between HCHO and BVOC emissions. GOME-2 HCHO vertical column densities (VCDs) can be used to estimate BVOC emission fluxes in the Changbai Mountain temperate forest.  相似文献   

Recent significant tornadoes in China   总被引：3，自引：0，他引：3  

Ming Xue  Kun Zhao  Mingjung Wang  Zhaohui Li  Yongguang Zheng 《大气科学进展》2016,33(11):1209-1217

正1.Introduction Compared with the United States,whose annual number of tornadoes can exceed 1000,the average number of tornadoes per year in China over the past half a century is estimated to be fewer than 100(Fan and Yu,2015),even though both countries are located in a similar latitudinal zone of the Northern Hemisphere.The annual average recorded number of F1(Fujita scale)or EF1(enhanced Fujita scale)intensity or higher tornadoes in China between 1961 and 2010 is about  相似文献   

Hybrid ETKF-3DVAR方法同化多普勒雷达速度观测资料Ⅰ:模拟资料试验          下载免费PDF全文

沈菲菲  闵锦忠  许冬梅  张冰 《大气科学学报》2016,39(1):81-89

利用WRF(Weather research and forecasting)模式及模式模拟的资料,采用Hybrid ETKF-3DVAR(ensemble transform Kalman filter-three-dimensional variational data assimilation)方法同化模拟雷达观测资料。该混合同化方法将集合转换卡尔曼滤波(ensemble transform Kalman filter)得到的集合样本扰动通过转换矩阵直接作用到背景场上,利用顺序滤波的思想得到分析扰动场;然后通过增加额外控制变量的方式把"流依赖"的集合协方差信息引入到变分目标函数中去,在3DVAR框架基础下与观测数据进行融合,从而给出分析场的最优估计。试验结果表明,Hybrid ETKF-3DVAR同化方法相比传统3DVAR可以提供更为准确的分析场,Hybrid方法雷达资料初始化模拟的台风涡旋结构与位置比3DVAR更加接近"真实场",对台风路径预报也有明显改进。通过对比Hybrid S试验与Hybrid F试验发现,Hybrid的正效果主要来源于混合背景误差协方差中的"流依赖"信息,集合平均场代替确定性背景场带来的效果并不显著。  相似文献   

Is the long-term variation of the estimated GPS differential code biases associated with ionospheric variability?   总被引：1，自引：0，他引：1  

Jiahao Zhong  Jiuhou Lei  Xiankang Dou  Xinan Yue 《GPS Solutions》2016,20(3):313-319

The global positioning system (GPS) differential code biases (DCB) provided by the International GNSS Service (IGS) show solar-cycle-like variation during 2002–2013. This study is to examine whether this variation of the GPS DCBs is associated with ionospheric variability. The GPS observations from low earth orbit (LEO) satellites including CHAMP, GRACE and Jason-1 are used to address this issue. The GPS DCBs estimated from the LEO-based observations at different orbit altitudes show a similar tendency as the IGS DCBs. However, this solar-cycle-like dependency is eliminated when the DCBs of 13 continuously operating GPS satellites are constrained to zero-mean. Our results thus revealed that ionospheric variation is not responsible for the long-term variation of the GPS DCBs. Instead, it is attributed to the GPS satellite replacement with different satellite types and the zero-mean condition imposed on all satellite DCBs.  相似文献   

Three dimensional seismic studies of deep-water hazard-related features on the northern slope of South China Sea     

《Marine and Petroleum Geology》2016

Mass transport deposits and geological features related to fluid flow such as gas chimneys, mud diapirs and volcanos, pockmarks and gas hydrates are pervasive on the canyon dominated northern slope of the Pearl River Mouth basin of the South China Sea. These deposits and structures are linked to serious geohazards and are considered risk factors for seabed installations. Based on high resolution three dimensional seismic surveys, seismic characteristics, distributions and origins of these features are analyzed. A distribution map is presented and geometrical parameters and spatial distribution patterns are summarized. Results show that various groups of the mapped features are closely tied to local or regional tectonism and sedimentary processes. Mass transport complexes are classified as slides near the shelf break, initially deformed slumps on the flanks of canyons and highly deformed slumps on the lower slope downslope of the mouth of canyons. We propose them to be preconditioned by pore pressure changes related to sea level fluctuations, steep topography, and fluid and fault activities. Gas chimneys are mainly located in the vicinity of gas reservoirs, while bottom-simulating reflectors are observed within the gas chimney regions, suggesting gas chimneys serve as conduits for thermogenic gas. Mud diapirs/volcanos and pockmarks are observed in small numbers and the formation of pockmarks is related to underlying gas chimneys and faults. This study aims at reducing risks for deep-water engineering on the northern slope of South China Sea.  相似文献   

On the use of synthetic tropical cyclones and hypothetical events for storm surge assessment under climate change     

Ruiz-Salcines  Pablo  Appendini  Christian M.  Salles  Paulo  Rey  Wilmer  Vigh  Jonathan L. 《Natural Hazards》2021,105(1):431-459

Natural Hazards - This study presents a new approach to assess storm surge risk from tropical cyclones under climate change by direct calculation of the local flood levels using a limited number of...  相似文献   

Synoptic analysis of sea level pressure patterns and Vertically Integrated Moisture Flux Convergence VIMFC during the occurrence of durable and pervasive rainfall in Iran     

《Dynamics of Atmospheres and Oceans》2019

To carry out this research, interpolated data of daily rainfall from Iran’s Asfazari data base during 1/1/1979–31/12/2013 is used. The day along with pervasive rainfall considered a day that at least 50% of Iran’s territory has received more than 1 mm for at least two consecutive days. Based on mentioned thresholds, 224 days selected for statistical analysis. The sea level pressure data, zonal and meridional wind components and specific humidity with spatial resolution of 0.25*0.25 Gaussian degree in spatial domain of 10 °N to 60 °N and 15 °E to 75 °E obtained from the European Center for Medium range Weather Forecasting (ECMWF) ERA-Interim for selected days. Then on the data matrix of sea level pressure, the cluster analysis by Ward linkage method done and 4 sea level pressure patterns with different configuration of synoptic systems were identified. The findings showed that in the sea level, the interaction between southern thermal low pressure systems (Arabia low pressure) with Europe and Siberia cold immigrant high pressure both by individual and integration and anticyclone circulation of Arab sea from the low level of 1000–500 hPa of troposphere have the most role on occurrence of durable and pervasive rainfall of Iran. The most Vertically Integrated Moisture Flux Convergence in the first layer of troposphere (1000–850 hPa) observed in low height regions, in the second layer of troposphere (775–700 hPa) on Zagros Mountains and in third layer of troposphere (600–500 hPa) is seen in mountains leeward of Iran. Also the results showed that the maximum rainfall cores has the most coordination with Vertically Integrated Moisture Flux Convergence (VIMFC) in the second layer of troposphere (775–700 hPa) on the Zagros heights in the southwest of Iran.  相似文献   

Response of ocean dynamics to multiple equilibria of the Kuroshio path South of Japan     

《Dynamics of Atmospheres and Oceans》2019

Variability of the Kuroshio path to the south of Japan plays a central role in the local climate change and exerts tremendous influences on the local atmosphere and ocean. In this study, the response of ocean dynamics, in terms of the eddy kinetic energy (EKE), potential vorticity (PV), relative vorticity, and eddy-mean flow interaction, to the Kuroshio path change is discussed. Kuroshio path south of Japan includes the near-shore non-large meander (nNLM), the off-shore non-large meander (oNLM), and the typical large meander (tLM). Analyses reveal that the distribution of EKE, PV, relative vorticity, and energy exchange between the eddy field and the mean flow respectively varies with the Kuroshio path: (1) The tLM has the maximum EKE along the path; (2) The positive and negative PV are located at the onshore and offshore side of Kuroshio axis, respevetively; (3) The distributions of anomalous relative voritcity of nNLM, oNLM, and tLM are consistent with sea surface height anomalies (SSHAs); (4) The tLM has the largest energy exchange between the eddy field and the mean flow in terms of the rate of barotropic energy conversion. On the other hand, the stability analysis of ocean currents suggests that the three Kuroshio paths south of Japan have their own intrinsic properties of the instability.  相似文献