We use the occurrence of unusual or out-of-season dust storms and dissolved ion data as proxies for dust to propose a calendar-year chronology for a portion of the Greenland Ice Sheet Project 2 (GISP2) ice core during the early sixth century A.D. Our new time scale moves a small sulfate peak to early 537 A.D., which is more consistent with recent findings of a 6 mo to 18 mo time lag between volcanic eruptions and atmospheric fallout of their sulfate aerosols. Our new time scale is consistent with a small volcanic input to the A.D. 536–537 climate downturn. We use the time range of Ni-rich fragments and cosmic spherules to provide an independent test of the chronology. The time range of Ni-rich fragments and cosmic spherules matches historical observations of “dancing stars” starting in the summer of A.D. 533 and lasting until A.D. 539 or 540. These dancing stars have been previously attributed to cosmogenic dust loading of Earth's atmosphere. The time scale cannot be shifted to be either younger or older by 1 yr without destroying the match to historical accounts of dancing stars.

Abstract Dust storms, or haboobs, can have a significant effect on military operations in arid regions. Not only does dust cause maintenance problems and slow offensive ground operations, but it can also substantially disrupt air operations. This paper presents a historic vignette of how a dust storm contributed to the failure of Operation Eagle Claw, the mission undertaken to rescue U.S. hostages in Iran in 1980. The flight crews that were involved in that mission encountered a dust storm that was likely generated by thunderstorm activity in the Zagros Mountains of Iran. Weather forecasters were aware that dust storms were a possibility in the region, but they did not forecast haboobs. The pilots were expecting clear weather and had no contingency plans to cope with the adverse weather conditions. The dust storm caused confusion, slowed the helicopters, and greatly increased pilot fatigue. These factors appeared to have contributed to mission failure, and, as a result, the U.S. military later implemented many improvements in mission planning, pilot training, and weather forecasting techniques to manage the risk associated with operations in areas where dust storms are likely.

Abstract Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments, including the coastal zone, cold and hot deserts, and agricultural fields. Common features of these environments are a sparse or nonexistent vegetation cover, a supply of fine sediment (clay, silt, and sand), and strong winds. Aeolian processes are responsible for the emission and/or mobilization of dust and the formation of areas of sand dunes. They largely depend on other geologic agents, such as rivers and waves, to supply sediment for transport. Areas of sand dunes occur in inland and coastal settings, where they often provide a distinctive environment that provides habitats for endemic and rare or threatened species. In both coastal and inland settings, dune migration and sand encroachment may impact neighboring ecosystems and resources, as well as infrastructure. Transport of fine sediment by wind may cause dust storms, events in which visibility is reduced to less than 1 km by blowing dust. Dust storms impact air quality in their immediate vicinity as well as in areas downwind. Deposition of dust may have a significant effect on the composition and nature of soils in arid regions and beyond. Far-traveled dust from distant sources may have a significant effect on soil chemistry and nutrient status (e.g., Farmer, 1993 ).

Measurements show that in many ocean regions the major aerosol constituent is mineral matter derived from the continents. The greatest concentrations of soil aerosol particles are found over marine areas “downwind” from arid regions and deserts. Because of the transport of soil material out of North Africa, the Arabian Peninsula, and India, the geometric mean mineral aerosol concentrations over the tropical North Atlantic, the Indian Ocean, and the Mediterranean were at least an order of magnitude greater than those over the Pacific Ocean and the North and South Atlantic. The concentration of soil aerosols in these regions produces highly turbid sky conditions. The relationship between the concentration distribution of soil aerosols over the oceans and that of haze suggests that climatological records of the frequency of occurrence of haze at sea may be useful for delineating those oceanic regions where soil aerosol transport might be most significant.

Earth-based observations and spacecraft results show that aeolian processes are currently active on Mars. Analyses of various landforms, including dunes, yardangs, and mantling sediments of probable aeolian origin, suggest that aeolian processes have been important in the geological past. Dust storms originate in specific areas of Mars and are most vigorous during the martian summer in the southern hemisphere. In order to understand aeolian processes in the low surface pressure (∼7 mb), carbon dioxide atmosphere of Mars, a special wind-tunnel was fabricated to carry out investigations of the physics of windblown particles under martian conditions. Martian threshold wind speeds have been derived for a range of particle diameters and densities; the threshold curve parallels that for Earth but is offset toward higher wind velocities by about an order of magnitude. The “optimum” size particle (the size most easily moved by minimum wind) is about 100 pm in diameter; minimum freestream winds to generate particle motion are about 40 ms-I. Grains smaller than 100 pm (“dust”) require increasingly higher winds to initiate threshold; yet, estimates of grain sizes in the dust clouds are in the size range of a few microns and smaller. Because the Viking Lander has recorded winds no stronger than those for minimum threshold, it is suggested that some other mechanism than uniform strong winds is required for “dust” threshold. Experiments and theoretical considerations suggest that such mechanisms could be cyclonic (“dust devil”) winds, a saltation cascading effect by larger (more easily moved) particles, and injection of fine grains into the wind stream by outgassing volatiles absorbed on the grains.

The strong winds of the first winter storm to reach the drouth-stricken High Plains in February 1977 caused the largest dust storm yet observed by geostationary orbit environmental satellites (GOES). Two dust plumes, one in eastern Colorado-western Kansas, another near the Texas-New Mexico border, were first observed on GOES-1 images taken at 1700 GMT February 23, and the east-south-eastward progression of the dust pall was observed on later images. By 2030 GMT February 24, dust totally obscured about 400,000 km 2 of ground surface in the south-central United States, as seen on satellite pictures. By 1600 GMT February 26, a discrete dust pall was still visible over the mid-Atlantic Ocean. The enormity of this single dust storm and the historical recurrence of such events suggest that atmospheric transport of dust eastward from the Great Plains to the Atlantic Ocean is of sedimentologic significance. One point source of the dust, the Clovis-Portales area, New Mexico, has a long history of episodic aridity and associated eolian activity that extends from Tertiary time to the Dust Bowl events of the 1930s and similar occurrences during the 1950s. The authors have investigated wind erosion and deposition due to the February 1977 storm by aerial and ground reconnaissance of this area, which is in the windiest part of the southern High Plains. During the 1977 storm, plowed fields were locally eroded to depths of greater than 1 m, and myriads of small yardangs were formed. Fine sand winnowed from certain vulnerable soils was deposited in lobate sheets from several centimetres to more than a metre deep that extended several kilometres downwind from the plowed fields and blowouts. Several key factors contributed to the severe effects of the storm. A persistent Pacific high-pressure ridge, which had diverted earlier storms northward, contributed to a prolonged drouth in the Great Plains. Breakdown of this high permitted passage of the first winter storm into the region, accompanied by very strong winds. Soils of the Portales Valley, composed mainly of eolian sand, silt, and clay, were unusually dry and vulnerable to the wind, which accelerated suddenly on the morning of February 23. The erosive power of the wind in that area may have been further enhanced as it blew upward over the cap-rock escarpment of the Llano Estacado. Other factors that probably contributed to the severity of wind damage from this storm included certain land-use practices that had resulted from a coincidence of economic conditions and governmental policies.

Six dust plumes, arising from a Santa Ana wind and covering an area of 1,700 km 2 of the western Mojave Desert, were photographed by the National Aeronautics and Space Administration LANDSAT/ERTS-1 satellite on January 1, 1973. The cause of erosion was identified as man’s destabilization of the natural surface through road building, agriculture, urbanization, stream-channel modification, and off-road vehicle recreation. The extensive, and growing, destabilization of the California desert surface provides for ever-increasing dust yields in storms of the future.

An extraordinary wind storm on December 20, 1977, caused moderate to severe damage to structures, crops, orchards, vehicles, wildlife, and soils in an area of about 2,000 km 2 in the Southern San Joaquin Valley, California. Wind that may locally have reached velocities of 300 km/hr mobilized more than 25 million metric tons of soil from grazing lands alone within a 24-hour period, yielding a depositional plume that extended at least to the northern end of the Sacramento Valley; comparable amounts of soil may have been displaced in adjacent agricultural lands. The wind-stripped land in the Tehachapi and San Emigdio mountains caused accelerated runoff during ensuing rainstorms that exacerbated the problem of flooding in the southern valley and initiated numerous gullies that will continue to extend the loss of soil. The principal factors contributing to the severity of the storm’s impact were drouth, overgrazing, and the general lack of windbreaks in the agricultural land. Vegetation in the grazing lands bordering the valley showed the combined stresses of drouth and grazing before the storm and provided little forage and only slight protection to the soil. Broad areas of agricultural land had recently been plowed in preparation for planting, and additional areas had been stripped of natural vegetation and leveled in preparation for agricultural uses making them vulnerable to wind erosion. Other quantitatively less important contributing factors included stripping of vegetation for urban expansion in the Bakersfield area, extensive denudation of land in the oil fields north of Bakersfield and elsewhere, and local denudation of land by récréation vehicles.

Large areas in the Soviet Union are subjected to dust storms that harm soils and crops; 52% of the storms occur in the spring, and most are accompanied by easterly winds. The relationship between dust storm devlopment and wind speed is not simple. However, a degree of predictive success occurs when the moisture deficit (the difference between the saturation vapor pressure and the actual vapor pressure) is considered with wind velocity in regression analysis of observed dust storms. Various groupings of dust storm data show that for a given wind velocity, a dust storm is likely when the moisture deficit reaches a certain critical value. Similarly, for a given moisture deficit a dust storm is likely when a certain velocity is attained. These results did not involve a large sample size, but coefficients of correlation were statistically highly significant.