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1.
Using the multi-source observation data from wind-profiling radar, microwave radiometer, Doppler weather radar, etc. during the blizzard event in 19–20 March 2012 in Urumqi, this paper analyzed the detailed characteristics of the atmospheric dynamics, thermodynamics, intensity and water vapor during the process of this blizzard weather. The findings suggest: (1) in the course of the blizzard weather, the near-surface atmosphere is mainly dominated by northwest airflows, the wind speed and relative humidity increase rapidly, temperature drops and air pressure ascends; (2) the blizzard weather this time is accompanied by cold front system whose entering time is about 16:00 BT 19 March; the shear line that develops from low to high is the position height of the frontal zone, and the variation of the high-level frontal zone directly reflects the altitude and layers where cold and warm air masses interact; (3) the radar equivalent reflectivity factor of the snowstorm process changes within the range 8–25 dBZe and its large-value zone is correlated well with the blizzard duration, the height for the formation of rain (snow) particles and the snow intensity; (4) before the occurrence of the blizzard, atmosphere is in the state of high temperature and high humidity, the maximum vapor density is around 6 g m?3, water vapor mainly stays under the height of 5,000 m; affected by cold front system, cold airs gradually lift warm and moist airs so that the vapor condenses and deposits into water drops and snow particles, forming the snowstorm in the end.  相似文献   
2.
The impact of asymmetric thermal forcing associated with land–sea distribution on interdecadal variation in large-scale circulation and blocking was investigated using observations and the coupled model intercomparison project outputs. A land–sea index (LSI) was defined to measure asymmetric zonal thermal forcing; the index changed from a negative to a positive anomaly in the 1980s. In the positive phase of the LSI, the 500 hPa geopotential height decreased in the polar regions and increased in the mid-latitudes. The tropospheric planetary wave activity also became weaker and exerted less easterly forcing on the westerly wind. These circulation changes were favorable for westerly wind acceleration and reduced blocking. In the Atlantic, the duration of blocking decreased by 38 % during the positive LSI phase compared with that during the negative phase; in Europe, the number of blocking persisting for longer than 10 days during the positive LSI phase was only half of the number during the negative phase. The observed surface air temperature anomaly followed a distinctive “cold ocean/warm land” (COWL) pattern, which provided an environment that reduced, or destroyed, the resonance forcing of topography and was unfavorable for the development and persistence of blocking. In turn, the responses of the westerly and blocking could further enhance continental warming, which would strengthen the “cold ocean/warm land” pattern. This positive feedback amplified regional warming in the context of overall global warming.  相似文献   
3.
An observation localization scheme is introduced into an ensemble-based three-dimensional variational (3DVar) assimilation method based on the singular value decomposition technique (SVD-En3DVar) to improve assimilation skill. A point-by-point analysis technique is adopted in which the weight of each observation decreases with increasing distance between the analysis point and the observation point. A set of numerical experiments, in which simulated Doppler radar data are assimilated into the Weather Research and Forecasting (WRF) model, is designed to test the scheme. The results are compared with those obtained using the original global and local patch schemes in SVD-En3DVar, neither of which includes this type of observation localization. The observation localization scheme not only eliminates spurious analysis increments in areas of missing data, but also avoids the discontinuous analysis fields that arise from the local patch scheme. The new scheme provides better analysis fields and a more reasonable short-range rainfall forecast than the original schemes. Additional forecast experiments that assimilate real data from 10 radars indicate that the short-term precipitation forecast skill can be improved by assimilating radar data and the observation localization scheme provides a better forecast than the other two schemes.  相似文献   
4.
PM10 samples were collected over three years at Monzenmachi, the Japan Sea coast, the Noto Peninsula, Ishikawa, Japan from January 17, 2001 to December 18, 2003, using a high volume air sampler with quartz filters. The concentrations of the water-soluble inorganic ions in PM10 were determined with using ion chromatography. By analyzing the characteristics of these, the evidences were found that the Asian outflow had an obviously influence on the air quality at our study site. The results were as follows: the secondary pollutants SO42−, NO3 and NH4+ were the primary water-soluble inorganic ions at our study site. The monthly mean concentrations of SO42−, NH4+, NO3 and Ca2+ have prominent peak in spring due to the strong influence of the Asian continent outflow—these according to backward air trajectory analysis, the maximum of which were 6.09 for nss-SO42− in May, 2.87 for NO3 and 0.68 μg m−3 for nss-Ca2+ in April, respectively. Comparable to similar data reported from various points around East Asia, it had the characteristics of a polluted coastal area at our study site. The concentration of nss-Ca2+ in PM10 drastically increased when the Asian dust invaded, the mean value during the Asian dust days(AD) was 0.86 μg m−3, about 4 times higher than those of normal days (NAD). Meanwhile, the mean concentrations of nss-SO42−, NO3 and NH4+ in AD periods were higher than those in NAD periods which were 5.87, 1.76 and 1.82 μg m−3, respectively, it is due to the interaction between dust and secondary particles during the long-range transport of dust storms. Finally, according to the source apportionment with positive matrix factorization (PMF) method in this study, the major source profiles of PM10 at our study site were categorized as (1) marine salt, (2) secondary sulfate, (3) secondary nitrate and (4) crustal source.  相似文献   
5.
This study validates a method for discriminating between daytime clouds and dust aerosol layers over the Sahara Desert that uses a combination of active CALIOP(Cloud-Aerosol Lidar with Orthogonal Polarization) and passive IIR(Infrared Imaging Radiometer) measurements;hereafter,the CLIM method.The CLIM method reduces misclassification of dense dust aerosol layers in the Sahara region relative to other techniques.When evaluated against a suite of simultaneous measurements from CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations),CloudSat,and the MODIS(Moderate-resolution Imaging Spectroradiometer),the misclassification rate for dust using the CLIM technique is 1.16%during boreal spring 2007.This rate is lower than the misclassification rates for dust using the cloud aerosol discriminations performed for version 2(V2-CAD;16.39%) or version 3(V3-CAD;2.01%) of the CALIPSO data processing algorithm.The total identification errors for data from in spring 2007 are 13.46%for V2-CAD,3.39%for V3-CAD,and 1.99%for CLIM.These results indicate that CLIM and V3-CAD are both significantly better than V2-CAD for discriminating between clouds and dust aerosol layers.Misclassifications by CLIM in this region are mainly limited to mixed cloud-dust aerosol layers.V3-CAD sometimes misidentifies low-level aerosol layers adjacent to the surface as thin clouds,and sometimes fails to detect thin clouds entirely.The CLIM method is both simple and fast,and may be useful as a reference for testing or validating other discrimination techniques and methods.  相似文献   
6.
平流层对对流层的作用是准确评估、预测对流层气候变化的一个重要方面。其中平流层成分尤其是臭氧的变化,可以改变平流层乃至对流层的辐射平衡,从而影响平流层、对流层的热动力过程。本文从辐射、动力2个角度介绍了平流层臭氧影响对流层气候变化的若干研究进展。平流层臭氧可以通过长短波辐射的方式对对流层大气造成辐射强迫,利用大气化学气候模式可以定量计算平流层臭氧变化引起的辐射强迫,但是辐射强迫的估算受模式中辐射传输模块本身缺陷的影响存在不确定性。动力方面,平流层臭氧变化产生的辐射效应可以改变温度的垂直和经向梯度,造成波折射指数的变化,进而影响平流层甚至对流层内波的折射与反射,通过上对流层下平流层区域内的波—流相互作用,对对流层气候产生影响。另外,南极臭氧损耗可通过大气环状模影响冬春季中高纬度对流层的天气气候,但是其影响的强度大小以及物理机制仍需进一步的确认。值得注意的是,北极平流层臭氧的变化与北半球中高纬度气候变化之间的关系相比南半球要更加复杂,需要更为深入的研究。  相似文献   
7.
The temperature anomaly and dust concentrations recorded from central Antarctic ice core records display a strong negative correlation. The dust concentration recorded from an ice core in central Antarctica is 50-70 times higher during glacial periods than interglacial periods. This study investigated the impact of dust aerosol on glacial-interglacial climate, using a zonal energy balance model and dust concentration data from an Antarctica ice core. Two important effects of dust, the direct radiative effect and dust-albedo feedback, were considered. On the one hand, the direct radiative effect of dust significantly cooled the climate during the glacial period, with cooling during the last glacial maximum being as much as 2.05℃ in Antarctica. On the other hand, dust deposition onto the ice decreased the surface albedo over Antarctica, leading to increased absorption of solar radiation, inducing a positive feedback that warmed the region by as much as about 0.9℃ during the glacial period. However, cooling by the direct dust effect was found to be the controlling effect for the glacial climate and may be the major influence on the strong negative correlation between temperature and dust concentration during glacial periods.  相似文献   
8.
The potential for using the ensemble square root filter data assimilation technique to estimate soil moisture profiles, surface heat fluxes, and the state of the planetary boundary layer (PBL) is explored. An observing system simulation experiment is designed to mimic the assimilation of near-surface soil moisture observations (θo ) and in-situ measurements of 2-m temperature (To ), 2-m specific humidity (Qo ), and 10-m horizontal winds [Vo =(Uo , Vo )]. The background forecasts are generated by a one-dimensional coupled land surface-boundary layer model (CLS-BLM) with soil, surface-layer and PBL parameterization schemes similar to those used in the Weather Research and Forecasting (WRF) model. Soil moisture, surface heat fluxes, and the state of the PBL evolve on different characteristic timescales, so the minimum assimilation time intervals required for skillful estimates of each target component are different. Correct estimates of the soil moisture profile are obtained effectively when a 6-h update time interval is used, while skillful estimates of surface fluxes and the PBL state require more frequent updates. The CLS-BLM requires a shorter assimilation time interval to correctly estimate the soil moisture profile than previously indicated by experiments using an off-line land surface model (LSM). Results from assimilating different subsets of observations show that θo makes a larger contribution to soil moisture estimates, while To , θo , and Vo are more important for estimates of surface heat fluxes and the PBL state. It is therefore necessary to combine these variables to accurately estimate the states of both the land surface and the PBL. Experimentation with different prescribed observational errors shows that the assimilation system is more sensitive to increases in observational errors than to reductions in observational errors.  相似文献   
9.
利用兰州大学半干旱气候与环境观测站(SACOL)2006—2011年晴空无云时激光雷达(CE-370—2)资料,结合2006年12月至2007年5月多波段太阳光度计(CE-318)资料,对比验证了激光雷达资料的反演结果,并分析了兰州地区气溶胶光学厚度的分布特征。结果表明:激光雷达反演得到的光学厚度与光度计观测得到的光学厚度,两者具有较好的相关性,相关系数为0.86。兰州地区气溶胶光学厚度3—5月和11-12月较大,主要原因是3—5月是当地沙尘频发期,11—12月是居民集中采暖期,沙尘排放和燃煤排放显著增加了大气气溶胶光学厚度。气溶胶光学厚度6~10月偏小,湿沉降清除是主要的影响因素。光学厚度季节分布为春季0.42,冬季0.36,秋季0.30,夏季0.21。光学厚度频数分布于0.0~0.3的最多,占总数的一半,且存在季节差异。兰州上空夏季干净,春季浑浊,冬季次浑浊。  相似文献   
10.
利用NCEP/NCAR 2.5°×2.5°再分析资料和PV-θ阻高指数,分析了2008年初我国南方发生的低温雨雪冰冻灾害。结果表明,欧亚大陆3个关键区的阻塞高压(简称阻高)在此次灾害发生的环流背景中起着非常重要的作用,并存在异常特征。与1950—2008年历史同期相比,2008年初乌拉尔山和贝加尔湖阻高发生的日数显著偏多,而鄂霍茨克海地区无阻高发生;乌拉尔山阻高的强度偏强,而贝加尔湖阻高的强度则偏弱;乌拉尔山地区最大PV-θ阻高指数发生的位置比大多数年份偏东,而贝加尔湖地区最大PV-θ阻高指数发生的位置比大多数年份偏西,这种位置的异常特征说明此次我国南方低温雨雪冰冻灾害期间欧亚大陆关键区阻高在位置上很集中。3个关键区的阻高在发生日数、强度以及位置上异常特征的共同配置,使得分裂出的小槽活动偏多,造成冷空气活动频繁并不断南下补给,加之此时的异常环流特征,共同造成这次低温雨雪冰冻灾害。  相似文献   
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