齐依求金矿中微球粒特征

首次报道齐依求金矿中微球粒的发现，对微球粒形态特征、表面及断面结构、物理特性、矿物组成、化学成分进行分析测试，并就其成因作了初步探讨，认为属宇宙成因。     

中国北方沙尘灾害特点及其下垫面状况的遥感监测

2000年春季,中国北方地区多次受到沙尘灾害的影响,对生产、生活活动造成了多方面的不利影响。采用遥感和GIS技术进行沙尘灾害的过程监测、空间特点分析和下垫面状况分析是一个有效的技术方法,通过对沙尘灾害发生、发展的环境条件的了解,可以减轻沙尘天气的危害、防治等一系列决策措施的制定、实施提供客观、及时的空间信息,有助于制定和实施区域生态环境保护措施,以便减少沙尘天气的次数和减轻灾害性天气的危害程度。     

The effect of magnetic substorms on near-ground atmospheric current

Ionosphere-magnetosphere disturbances at high latitudes, e.g. magnetic substorms, are accompanied by energetic particle precipitation and strong variations of the ionospheric electric fields and currents. These might reasonably be expected to modify the local atmospheric electric circuit. We have analysed air-earth vertical currents (AECs) measured by a long wire antenna at Esrange, northern Sweden during 35 geomagnetic substorms. Using superposed epoch analysis we compare the air-earth current variations during the 3 h before and after the time of the magnetic X-component minimum with those for corresponding local times on 35 days without substorms. After elimination of the average daily variation we can conclude that the effect of substorms on AEC is small but distinguishable. It is speculated that the AEC increases observed during about 2 h prior to the geomagnetic X-component minimum, are due to enhancement of the ionospheric electric field. During the subsequent 2 h of the substorm recovery phase, the difference between substorm and quiet atmospheric currents decreases. The amplitude of this substorm variation of AEC is estimated to be less than 50% of the amplitude of the diurnal variation in AEC during the same time interval. The statistical significance of this result was confirmed using the Van der Waerden X-test. This method was further used to show that the average air-earth current and its fluctuations increase during late expansion and early recovery phases of substorms.     

1998年“4.18”强沙尘暴分析及数值模拟

对1998年4月18－19日发生在新疆、甘肃、宁夏、内蒙古等地的一次强沙尘暴天气过程从天气事实、天气学成因等方面进行了分析和诊断，然后利用非静力MM5模式对这次沙尘暴天气进行了数值模拟。结果表明，西西伯利亚强冷空气迅速东移，在新疆西部上空形成强锋区，对应的地面冷锋东移至前期增暖显著的新疆、内蒙古、甘肃、宁夏等地形成了本次大风、强沙尘暴天气。用非静力MM5模式较好地模拟出了此次强沙尘暴天气过程的地面强风系统、高空锋区的发生发展。     

2000年我国天气气候特点

2000年我国主要天气气候特点为：全国大部地区降水偏少或接近常年，出现全国性干旱，特别是北方地区春夏季遭遇多年来罕见的特大干旱，汛期未发生大范围的暴雨洪涝灾害，秋季黄淮以南地区出现持续连阴雨天气，全国大部分气温接近常年成偏高，持续暖冬态势发生转折，夏季高温酷热，春季北方扬沙和沙尘暴天气异常频繁，登陆我国台风个数偏少，风雹等强对流天气明显偏少。     

珠江三角洲地区由海风锋触发形成的强对流天气过程分析

使用自动气象站、雷达回波、卫星云图、常规天气图、探空和风廓线仪等有关观测资料, 普查了1998年7月上旬珠江三角洲地区8次由海风锋触发形成的强对流天气过程, 并对其中7月3日过程进行了综合分析, 归纳出该类强对流天气过程的一些活动特征和规律。     

Variations in chemical compositions of the eolian dust in Chinese Loess Plateau over the past 2.5 Ma and chemical weathering in the Asian inland

Major and trace elements as well as strontium isotopic composition have been analyzed on the acid-insoluble (AI) phase of the loess-paleosol sequence from Luochuan, Shaanxi Province, China. Results show that the chemical composition of AI phase of loess and paleosols is distinctive to the average composition of upper continental crust (UCC), characterized by depletion of mobile elements Na, Ca and Sr. The distribution pattern of elements in AI phase reveals that initial dust, derived from a vast area of Asian inland, has suffered from Na- and Ca-removed chemical weathering compared to UCC. Some geochemical parameters (such as CIA values, Na/K, Rb/Sr and⁸⁷Sr/⁸⁶Sr ratios) display a regular variation and evolution, reflecting that the chemical weathering in the source region of loess deposits has decreased gradually since 2.5 Ma with the general increase of global ice volume. This coincidence reflects that the aridity of Asian inland since the Quaternary is a possible regional response to the global climate change.     

The aeolian dust accumulation curve

This article presents a simple physical concept of aeolian dust accumulation, based on the behaviour of the subprocesses of dust deposition and dust erosion. The concept is tested in an aeolian dust wind tunnel. The agreement between the accumulation curve predicted by the model and the accumulation curve obtained in the experiments is close to perfect and shows that it is necessary to discriminate between the processes of aeolian dust deposition and aeolian dust accumulation. Two important thresholds determine the accumulation process. For wind speeds below the deflation threshold, the aeolian accumulation of dust increases linearly with the wind speed. For wind velocities between the deflation threshold and the accumulation limit, the sedimentation balance is above unity and there is still accumulation, though it rapidly drops once the deflation threshold has been exceeded. At wind speeds beyond the accumulation limit, the sedimentation balance is below unity and there will no longer be an accumulation of dust. The thresholds have been determined in a wind tunnel test at friction velocity u_* = 0·34 m s^?1 (deflation threshold) and u_* = 0·43 m s^?1 (accumulation limit), but these values are only indicative since they depend heavily on the characteristics of the accumulation surface and of the airborne grains. Copyright © 2001 John Wiley & Sons, Ltd.     

A Synoptic Climatology of Severe Storms in Virginia*

A synoptic climatology is developed for Virginia using 21 years of late spring and summer surface and upper air observations. The climatology is produced by applying a combination of principal components analysis and cluster analysis such that each day is classified into one of a distinct number of synoptic situations. Days on which at least one severe storm occurred in Virginia are merged with the synoptic climatology. A majority of severe storms are associated with one synoptic situation distinguished by moderate instability and a high moisture content.     

Storm catastrophes in the United States

A unique historical data set describing the 142 storms each producing losses in excess of $100 million in the United States during the 1950–89 period were analyzed to describe their temporal characteristics. The storms caused $66.2 billion in losses (in 1991 values), 76% of the nation's insured storm losses in this period. These extreme storm catastrophes (SCs) were most prevalent in the south, southeast, northeast, and central U.S., with few in and west of the Rocky Mountains. Storm incidences were high in the 1950s, low in the 1960s-early 1970s, and increased in the 1980s. Losses due to SCs peaked in the 1950s, again in the late 1960s, with a lesser peak after 1985. The areal extent of storm losses peaked after 1975 and was least in the 1960s. The temporal variations of the three storm measures (incidence, losses, and extent) did not agree except when they all peaked in the 1950s. Regionally-derived time distributions of SCs showed a marked north-south differences in the United States with a U-shaped 40-year distribution in the northern half of the nation, and a relatively flat trend until a peak in the 1980s in the southern regions. The temporal distributions of hurricane-caused catastrophes differed regionally with occurrences in the prime areas, the southern, southeastern, and northeastern U.S., each quite different. Temporal distributions of thunderstorm and winter storm catastrophes were regionally more uniform.