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为了更好地理解西北干旱区大气混合层(ML)厚度的变化特征及其对当地干旱气候形成的影响,我们利用张掖和民勤站夏季及相关月的实测探空资料及T-log P图解法,首先计算了该两地逐日ML厚度,然后分析并讨论了它的时空间变化特征、与干湿天气气候的关系,以及夏半年的深厚ML,对加剧当地干旱气候的影响.结果表明:(1)河西中东部ML厚度的年变化及地区差异明显.冬季最浅薄,夏半年深厚(特别是5、6月),4月及10月分别是ML急剧增厚及变薄的过渡期;同时,更靠近西北干旱区中心的河西西部及北部的ML更深厚.(2)夏季干(湿)天气通过加强(减弱)地气间的感热交换和干对流,而明显影响当地的ML厚度.平均而言,以高温日最深厚,千日次之,小雨日再次之,而中强雨日最浅薄.千年夏季的ML厚度平均比湿年的对应值增厚300 m左右.夏季典型千日的ML厚度比雨日厚3000 m,典型干日的ML厚度昼宿变化不大.(3)反过来夏半年深厚的ML也通过增加雨滴蒸发损耗,减少了干旱区的降水,加剧了当地干旱的程度,因此夏半年深厚的ML也是形成干旱气候背景的成因之一. 相似文献
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Several pressure sensors were deployed in a small lake to determine its storage change. It could be shown that a deep enough deployment and an averaging over a time interval of 1 hour and 5 measuring points allowed for a measurement of 1 or 2 kg/m2 (i.e. 2 mm of water column) of changes in the storage on the scale of the lake size. This accuracy for the lake storage could not be achieved by other methods, especially if conditions were difficult, e.g. snowfall, or in cases when precipitation was small. Finally, the pressure measurement - originally intended to roughly determine the water level - turned out to be a direct measurement of water mass in the lake, which was the proper magnitude for exchanges between atmosphere and lake. Hence the measurement of lake storage could become an interesting approach even for meteorological measurements, such as precipitation and evaporation on a water surface. 相似文献
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Microcatchment is a technique for collecting, storing and conserving local surface runoff in order to grow trees/shrubs. In this system, runoff water is generated on a plot and stored in the soil during runoff events, and trees/shrubs may utilize this water during the next dry season.Microcatchments have relatively small runoff generation areas (from dozens to hundreds sq. m) and are cheap and simple to implement Their collection area is usually a small depression located nearby the runoff generating area in which one or a few trees/shrubs may be planted Due to the short overland flow path runoff generation is efficient and even short low intensity storms may generate runoff. The drawback is however that due to the small size of the generating area small volumes of water are conveyed to the storage plots. Another drawback is susceptibility of the augmented water to evaporation. The main objective of present research presented hereafter was to estimate the effect the depth of the depression has on the efficiency of the water conservation in the soil profile. In the present study the storage plots were circular pits and the effect their depth had on evaporative losses and water distribution were studied.The results clearly show that the depth of the pit significantly affects evaporative water losses. The losses were separately computed for the soil cylinder whose upper surface is the bottom of the pit and for the surrounding shell. No differences between treatments were evident for losses from the inner cylinder. Significant differences in water losses were however observed for the surrounding shell where the shallow pits losing as much as six times more than the deeper pits. 相似文献
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