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THE DEPENDENCE OF THE ANNUAL TOTAL ON THE NUMBER OF RAIN‐SPELLS AND THEIR YIELD IN THE MEDITERRANEAN
Rain‐spells are a key parameter for examining the variation in rainfall amounts, especially in arid and semi‐arid areas. A rain‐spell is defined as a period of consecutive days with rainfall above a certain determined Daily Rainfall Threshold (DRT). Two different seasons or two stations may have the same average TOTAL, but different synoptic conditions are the cause for the differences in their Number of Rain‐Spells (NRS) their Rain‐Spells Yield (RSY) or both. The present study examines whether a season is drier/wetter according to its length, or whether it depends on the NRS in 41 Mediterranean stations. It analyses the relationships between dry/wet seasons and various elements of the rain‐spells. These objectives are analysed both at a basin level of the entire Mediterranean, and at a station level. The main conclusions at the basin level are that precipitation amounts are not related to the length of the seasons, and therefore, a Short or a Long season can be either Dry or Wet. The significant positive correlation between the TOTAL and the annual NRS that was found indicates that a Dry season tends to have Few rain‐spells and a Wet season tends to have Many rain‐spells. At the station level of most stations, a Dry or Wet season is caused mainly by changes in the RSY and less so by changes in the NRS. This tendency is more evident in the southern Mediterranean. Furthermore, Wet seasons are characterized by an increase in the number of Long rain‐spells (longer than three days) and mainly in the RSY of these spells. These conclusions may serve to characterize the rainfall regime under any scenario due to a climatic change. 相似文献
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Frank SOMMER Fiona REISER Anja DUFRESNE Michael H. POELCHAU Tobias HOERTH Alex DEUTSCH Thomas KENKMANN Klaus THOMA 《Meteoritics & planetary science》2013,48(1):33-49
Abstract– Within the frame of the MEMIN research unit (Multidisciplinary Experimental and Numerical Impact Research Network), impact experiments on sandstone targets were carried out to systematically study the influence of projectile mass, velocity, and target water saturation on the cratering and ejection processes. The projectiles were accelerated with two‐stage light‐gas guns (Ernst‐Mach‐Institute) onto fine‐grained targets (Seeberger sandstone) with about 23% porosity. Collection of the ejecta on custom‐designed catchers allowed determination of particle shape, size distribution, ejection angle, and microstructures. Mapping of the ejecta imprints on the catcher surface enabled linking of the different patterns to ejection stages observed on high‐speed videos. The increase in projectile mass from 0.067 to 7.1 g correlates with an increase in the total ejected mass; ejecta angles, however, are similar in range for all experiments. The increase in projectile velocity from 2.5 to 5.1 km s?1 correlates with a total ejecta mass increase as well as in an increase in comminution efficiency, and a widening of the ejecta cone. A higher degree of water saturation of the target yields an increase in total ejecta mass up to 400% with respect to dry targets, higher ejecta velocity, and a steeper cone. These data, in turn, suggest that the reduced impedance contrast between the quartz grains of the target and the pores plays a primary role in the ejecta mass increase, while vaporization of water determines the ejecta behavior concerning ejecta velocity and particle distribution. 相似文献
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