Ecological economic problems and development patterns of the arid inland river basin in Northwest China.

The Arno River seasonal discharge as an index of climate variability: trends and connections to the larger scale variability. The research of the historical record of ice falls brings together many cases that are apparently similar (1–3). Practically all clear-sky ice falls were not appropriately researched because they were routinely assigned, without verification, to aircraft icing processes, to wastewater from aircraft lavatories (blue ice), or to the leakage of aircraft water tanks. However, it is important to take into account, first, that documented historical references about these events go back to the first half of the 19th century, so many cases existed before the invention of airplanes (1–3), and second, that a detailed search of scientific databases (Web of Science, GeoRef) regarding well-known aircraft icing processes revealed a lack of precedents that corroborate that ice formation on any part of aircraft can reach dimensions of approximately 1 m and weights of up to several hundred kilograms. A simplistic analysis of these events as a whole can thus lead to misunderstanding because different types of ice falls correspond to different formation scenarios in the earth's atmosphere, either natural in the strict sense of the term, or with a direct or indirect relation with human activities. Consequently, it is necessary to define differentiation criteria (e.g., texture, and structural and compositional characteristics of the ice) to distinguish among them (4). The term megacryometeor was recently coined (5) for the following reasons: to try to avoid terminological confusion; to emphasize the existence of such atmospheric phenomenon; and to describe large atmospheric ice conglomerations that, despite sharing many textural, hydrochem-ical, and isotopic features detected in large hailstones, are formed under unusual atmospheric conditions that clearly differ from those of the cumulonimbus cloud scenario (i.e., clear-sky conditions). The fall of large ice blocks (weighing approximately 1 kg to hundreds of kilograms) from the clear sky is one of the most interesting (and controversial) issues in the atmospheric sciences (6). Meaden (6) used the term ice meteors to name them and proposed that their origin had to be different from that of large hailstones. Later, Corliss (1) used the term hydro-meteors. Corliss also differentiated them from classic hailstones and suggested that they have an atmospheric origin, but different possible formation scenarios. Probably the largest and most impressive events of megacryometeors have occurred in China, Brazil, and Spain. In 1995, an ice block approximately 1 m in size …