A pair of northeast-southwest-tilted mid-tropospheric ridges and troughs on the continental scale was observed to be the key circulation feature common among wintertime extensive and persistent low tempera-ture events...A pair of northeast-southwest-tilted mid-tropospheric ridges and troughs on the continental scale was observed to be the key circulation feature common among wintertime extensive and persistent low tempera-ture events (EPLTE) in China.During the persistence of such anomalous circulations,the split flow over the inner Asian continent and the influent flow over the southeast-ern coast of China correspond well to the expanded and amplified Siberian high with tightened sea level pressure gradients and hence,a strong,cold advection over south-eastern China.The western Pacific subtropical high tends to expand northward during the early stages of most EPLTEs.展开更多
By viewing satellite imagery, a striking large-scale dunefield can be clearly perceived, with a size of nearly 63 km long and 11 km wide, and trending NE-SW, on the right flank of the lower Laoha River, Northeast Chin...By viewing satellite imagery, a striking large-scale dunefield can be clearly perceived, with a size of nearly 63 km long and 11 km wide, and trending NE-SW, on the right flank of the lower Laoha River, Northeast China. By means of remote sensing imagery analysis and field observation as well as a comparison with a small-scale dunefield on the right flank of the lower Xiangshui River, analogous to the case of the lower Laoha River, this paper presents a new mechanism for its origin and development. The results show that： （1） the large-scale dunefield bears a tile-style framework overwhelmingly composed of transverse barchanoid ridges perpendicular to the predominant winds, and inlaid diverse blowouts. （2） The small-scale dunefield, referred to as a primary structural unit of the large one, is typical of an incipient dunefield, following the same rules of evolution as the larger. （3） A succession of barchanoid ridge chains can steadily migrate downwind in much the same manner as surface wave propagation in air or water stimulated by an incised valley, and ultimately tend to bear roughly the same wavelength and amplitude under stable climate and hydrologic regimes. （4） The first ridge chain acquires its sand source substantially from the downwind escarpments exposing the loose Quaternary sandy sediments to the air, while the ensuing ridges derive their sands dominantly from in situ deflation of the underlain Quaternary loose sandy sediments in blowouts, partly from the upwind ridges through northern elongated horns. Theoretically, the sands from riparian escarpments can be transported by wind to the downwind distal end of a dunefield after sufficient long du- ration. （5） The lower Laohahe region experienced probably three significant climatic changes in the past, corresponding to the three active dune belts, suggesting that once a large-scale dunefield occurs, it is nearly impossible to be completely stabilized, at least in its central portions. At present, seasonal shrinkage and stagnation of the lower Laoha River, wide-spread farming and afforestation in the valley, and establishing windbreaks downwind of the valley as well as surrounding the dunefield, appear to have significantly modified local flow fields and sand sources, engendering significant degradation of the dunefield.展开更多
Through analysis of satellite images from Google Earth, this article expounds the characteristics of large-scale geomorphic patterns of the complex longitudinal sand ridge zone in the Taklimakan Desert, and reduces th...Through analysis of satellite images from Google Earth, this article expounds the characteristics of large-scale geomorphic patterns of the complex longitudinal sand ridge zone in the Taklimakan Desert, and reduces the large-scale geomorphic patterns to six types: parallel pattern, "日"character-shaped and "乡" character-shaped pattern, comb-shaped pattern, fork-shaped pattern, toe-shaped pattern and miscellaneous pattern. And according to the large-scale geomorphic pattern type (or composition of pattern types) as well as some other factors, the article divides the complex longitudinal sand ridge zone into 55 subzones. Lastly, aiming at the genetic problems of the large-scale geomorphic patterns, the article suggests three connective types of the sand ridges in the complex longitudinal sand ridge zone, i.e., connecting or intersecting after natural elongation, connecting in a narrow place and connecting with the aid of intermediary.展开更多
Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensiv...Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensive coldprecipitation-freezing”events(ECPFEs).In this study,the ECPFEs in southern China(15°−35°N,102°−123°E)are objectively defined by using daily surface observational data for the period 1951−2013.An ECPFE in southern China is defined if the low temperature area,precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days.The identified ECPFEs are shown to be reasonable and reliable,compared with those in previous studies.The circulation anomalies in ECPFEs are characterized by a large-scale tilted ridge and trough pairing over mid-and high-latitude Eurasia,and the intensified subtropical westerlies along the southern foot of the Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific.Comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge,facilitating a favorable environment for the concurrence of extensive low-temperature,precipitation and freezing weather.展开更多
Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-ran...Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.展开更多
The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were ac...The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.展开更多
基金jointly supported by the National Natural Science Foundation of China [grant number 41375064 and41675086]the National Key Technology Research and Development Program of the Ministry of Science and Technology of China [grant number 2015BAC03B03]
基金supported by the National Key Technologies R&D Program of China (Grant No.2009BAC51B02)
文摘A pair of northeast-southwest-tilted mid-tropospheric ridges and troughs on the continental scale was observed to be the key circulation feature common among wintertime extensive and persistent low tempera-ture events (EPLTE) in China.During the persistence of such anomalous circulations,the split flow over the inner Asian continent and the influent flow over the southeast-ern coast of China correspond well to the expanded and amplified Siberian high with tightened sea level pressure gradients and hence,a strong,cold advection over south-eastern China.The western Pacific subtropical high tends to expand northward during the early stages of most EPLTEs.
基金funded by NSFC(Grant No.41271025)the Construct Program of the Key Discipline in Hunan Province,China (2012001)
文摘By viewing satellite imagery, a striking large-scale dunefield can be clearly perceived, with a size of nearly 63 km long and 11 km wide, and trending NE-SW, on the right flank of the lower Laoha River, Northeast China. By means of remote sensing imagery analysis and field observation as well as a comparison with a small-scale dunefield on the right flank of the lower Xiangshui River, analogous to the case of the lower Laoha River, this paper presents a new mechanism for its origin and development. The results show that： （1） the large-scale dunefield bears a tile-style framework overwhelmingly composed of transverse barchanoid ridges perpendicular to the predominant winds, and inlaid diverse blowouts. （2） The small-scale dunefield, referred to as a primary structural unit of the large one, is typical of an incipient dunefield, following the same rules of evolution as the larger. （3） A succession of barchanoid ridge chains can steadily migrate downwind in much the same manner as surface wave propagation in air or water stimulated by an incised valley, and ultimately tend to bear roughly the same wavelength and amplitude under stable climate and hydrologic regimes. （4） The first ridge chain acquires its sand source substantially from the downwind escarpments exposing the loose Quaternary sandy sediments to the air, while the ensuing ridges derive their sands dominantly from in situ deflation of the underlain Quaternary loose sandy sediments in blowouts, partly from the upwind ridges through northern elongated horns. Theoretically, the sands from riparian escarpments can be transported by wind to the downwind distal end of a dunefield after sufficient long du- ration. （5） The lower Laohahe region experienced probably three significant climatic changes in the past, corresponding to the three active dune belts, suggesting that once a large-scale dunefield occurs, it is nearly impossible to be completely stabilized, at least in its central portions. At present, seasonal shrinkage and stagnation of the lower Laoha River, wide-spread farming and afforestation in the valley, and establishing windbreaks downwind of the valley as well as surrounding the dunefield, appear to have significantly modified local flow fields and sand sources, engendering significant degradation of the dunefield.
基金Supported by Major Orientation Foundation of the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX3-SW-342)
文摘Through analysis of satellite images from Google Earth, this article expounds the characteristics of large-scale geomorphic patterns of the complex longitudinal sand ridge zone in the Taklimakan Desert, and reduces the large-scale geomorphic patterns to six types: parallel pattern, "日"character-shaped and "乡" character-shaped pattern, comb-shaped pattern, fork-shaped pattern, toe-shaped pattern and miscellaneous pattern. And according to the large-scale geomorphic pattern type (or composition of pattern types) as well as some other factors, the article divides the complex longitudinal sand ridge zone into 55 subzones. Lastly, aiming at the genetic problems of the large-scale geomorphic patterns, the article suggests three connective types of the sand ridges in the complex longitudinal sand ridge zone, i.e., connecting or intersecting after natural elongation, connecting in a narrow place and connecting with the aid of intermediary.
基金This research was funded by the National Natural Science Foundation of China(Grant Nos.41975072 and 41675086)the National Science and Technology Support Program of China(Grant No.2015BAC03B03).
文摘Concurrence of low temperature,precipitation and freezing weather in an extensive area would cause devastating impacts on local economy and society.We call such a combination of concurrent disastrous weather“extensive coldprecipitation-freezing”events(ECPFEs).In this study,the ECPFEs in southern China(15°−35°N,102°−123°E)are objectively defined by using daily surface observational data for the period 1951−2013.An ECPFE in southern China is defined if the low temperature area,precipitation area and freezing area concurrently exceed their respective thresholds for at least three consecutive days.The identified ECPFEs are shown to be reasonable and reliable,compared with those in previous studies.The circulation anomalies in ECPFEs are characterized by a large-scale tilted ridge and trough pairing over mid-and high-latitude Eurasia,and the intensified subtropical westerlies along the southern foot of the Tibetan Plateau and the anomalous anticyclonic circulation over the subtropical western Pacific.Comparative analysis reveals that the stable cold air from the north and the warm and moist air from the south converge,facilitating a favorable environment for the concurrence of extensive low-temperature,precipitation and freezing weather.
基金jointly supported by the National Key Research and Development Project (Grant No. 2018YFC1505601)the National Natural Science Foundation of China (Grant No. 41975072)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA23090102).
文摘Two supercold waves straddling 2020 and 2021 successively hit China and caused record-breaking extremely low temperatures.In this study,the distinct features of these two supercold waves are analyzed on the medium-range time scale.The blocking pattern from the Kara Sea to Lake Baikal characterized the first cold wave,while the large-scale tilted ridge and trough over the Asian continent featured the second cold wave.Prior to the cold waves,both the northwest and hyperpolar paths of cold air contributed to a zonally extensive cold air accumulation in the key region of Siberia.This might be the primary reason why strong and extensive supercold waves occur even under the Arctic amplification background.The two cold waves straddling 2020 and 2021 exhibited distinct features:(1)the blocking circulation occurred to the north or the east of the Ural Mountains and was not confined only to the Ural Mountains as it was for the earlier cold waves;(2)the collocation of the Asian blocking pattern and the polar vortex deflection towards East Asia preferred the hyperpolar path of cold air accumulation and the subsequent southward outburst;and(3)both high-and low-frequency processes worked in concert,leading to the very intense cold waves.The cold air advance along the northwest path,which coincides with the southeastward intrusion of the Siberian High(SH)front edge,is associated with the high-frequency process,while the cold air movement along the hyperpolar path,which is close to the eastern edge of the SH,is controlled by the low-frequency process.
基金supported by the National Key Technologies R&D Program of China (Grant No. 2009BAC51B02)
文摘The distinct precursory signals of countrywide extensive and persistent extreme cold events (CECs) were investigated and contrasted with those of countrywide cold wave events (CCWs). It is shown that most CECs were accompanied by a CCW in the initial stages. From the comparison between the CECs and the CCWs that were independent of any CEC, it is found that a south- west-northeast-oriented tilted ridge at 500 hPa was present around the Europe-Barents Sea regions approximately 10 days prior to the start of the CEC. Consistent with this feature, a high sea level pressure and strong cold air accumulation occurred over a broad extent of northern Eurasia one week prior to the start of the CEC. The tilted ridge and the strong cold air accumulation were the precursory signals that were absent for the CCW, and they provide important clues for the early prediction of whether a CCW event might evolve into a CEC.
