Subjects: Geosciences >> Atmospheric Sciences submitted time 2023-12-16 Cooperative journals: 《干旱区研究》
Abstract： Based on daily temperature observation data and reanalysis data of the geopotential height, sea levelpressure, and wind field from 1961 to 2020, the characteristics of spatial and temporal change of cold waves,strong cold waves, and exceptionally strong cold waves lasting 24 h, 48 h, and 72 h were studied in Ningxia overthe past 60 years. The causes of atmospheric circulation anomalies of cold waves were also revealed. The resultsshow the following: (1) In the past 60 years, cold waves of different intensities and different durations in Ningxiaconsistently showed the distribution characteristics of“shifting eastwards and northwards.”(2) The cumulativefrequencies of cold waves, strong cold waves, and exceptionally strong cold waves in the region accounted for71.7%, 22.6%, and 5.7% of the total annual cold wave frequencies, respectively, among which cold wavesdominated by process lasting 24 h and 48 h. The proportions of various durations for strong cold waves andexceptionally strong cold waves were equivalent. They mainly occured in October to April, during which theaccumulated cold waves, strong cold waves, and exceptionally strong cold waves in the region accounted for99%, 98%, and 95% of those throughout the year, and there was a decreasing trend from January to April andincreasing trend from October to December. (3) In the past 60 years, the cold waves, strong cold waves, andexceptionally strong cold waves have been decreasing at a rate of 4.5, 2.8, and 0.18 per station every 10 years,respectively. Among them, the frequencies of waves of 24 h and 48 h as short durations were decreasing, but thatof waves of 72 h as a long duration was decreasing. All types of cold waves decreased from the 1960s to the1990s, reaching a minimum in the 1990s and increasing since the 2000s, with a sudden change around 1990. (4)Under the influence of global warming, the atmospheric circulation showed completely the opposite distributioncharacteristics between before and after the sudden change of cold waves in Ningxia. The key systemsinfluencing cold waves in Ningxia are consistent. When the blocking high pressure in the Ural Mountains wasstronger, the East Asian trough was deeper, the west Pacific subtropical high was weaker, the western side ofLake Baikal was dominated by cyclonic circulation, and cold high pressure at the ground was active, this wasconducive to the southward movement of cold air in middle and high latitudes, and more cold waves in Ningxia.
Subjects: Geosciences >> Atmospheric Sciences submitted time 2023-05-30 Cooperative journals: 《干旱区研究》
Abstract： This study was conducted to reveal the impact and mechanism of the North Atlantic sea surface temperature anomaly (SSTA) associated with Ningxia precipitation and to improve the accuracy of precipitation prediction ability in Ningxia. Based on the monthly precipitation data of 20 meteorological stations in Ningxia, NCEP/NCAR atmospheric data, Hadley center sea surface temperature data, and utilizing empirical orthogonal decomposition, composite, and correlation methods, we studied the relationships and their decadal changes between the North Atlantic SSTA and Ningxia precipitation anomaly from late spring to early summer (April- June). It was found that the relationship had continuously increased since 1961 but nonsignificantly until the 1980s. Since then, the North Atlantic Ocean“triple type”(NAT) SSTA in early winter and spring has caused precipitation anomalies in Ningxia from April to June but it differs each month. Corresponding to the positive (negative) phase NAT, Ningxia precipitation is more (less) in April, less(more) in May, and less northerly and more southerly (more northerly and less southerly) in June. Furthermore, the mechanism is revealed of NAT affecting Ningxia precipitation anomaly by inducing an atmosphere anomaly wave train in the area from Europe to the Asia-Pacific. The positivephase NAT can induce a wave train with atmosphere circulation anomaly pattern of geopotential height“west lower and east higher”at 500 hPa around Ningxia in April, which is the typical atmosphere anomaly pattern of more precipitation in Ningxia in April. Additionally, at the low layer of 850 hPa, the southerly wind anomalies transform warmer and humid air into Ningxia, contributing to more precipitation. In May and June, with the transition from spring to summer, the abnormal wave train polar shifts. In May, Ningxia is affected by the positive abnormal height field at 500 hPa in Baikal Lake area to East Asia, and the abnormal wind field in the low level of 850 hPa divergence, with less precipitation. In June, the positive height anomaly center at 500 hPa in East Asia continues to develop northward from south to north to Baikal Lake area, and splits from the positive anomaly height in the east of China into two anomaly centers. At 500 hPa, Ningxia north and south areas are affected by the atmospheric circulation pattern of geopotential height anomaly being“north higher and south lower”and“west lower and east higher”, respectively. Meanwhile, at low level 850 hPa weak northerly and southerly anomaly wind prevails in the north and south area of Ningxia respectively, being with divergence and convergence. All of these atmosphere anomalies are conducive to less precipitation in the north and more in the south of Ningxia. For negative NAT phase, all the atmospheric circulation and precipipation anomalies are vice versa.
Subjects: Geosciences >> Atmospheric Sciences submitted time 2023-05-30 Cooperative journals: 《干旱区研究》
Abstract： The dominant sea surface temperature anomaly (SSTa) modes of decadal and interannual variations in summer precipitation over the eastern part of Northwest China (ENC) were here analyzed by power spectrum and composite analyses. The summer precipitation averaged at 155 stations over the ENC, the monthly SSTa, and circulation reanalysis data from 1961 to 2020 were used. The SSTa predictors before and after the timescale decomposition were obtained to establish precipitation prediction models by using linear regression. The results showed that the summer precipitation over the ENC has not only an decadal period of about 30 years but also a 3-year interannual cycle. The Pacific Decadal Oscillation (IPO) has played a leading role in decadal variations in summer precipitation. The positive phase of IPO in the precedent spring is conducive to more precipitation; meanwhile, it is in the background of less precipitation . The tropical Indian Ocean, the tropical western Pacific, and the North Atlantic provide interannual SSTa signals. The negative (positive) phase of tropical Indian Ocean SSTa, the positive (negative) phase of the Atlantic tripole SSTa, and the cold (warm) SSTa in the tropical western
Pacific Ocean in the precedent spring, corresponding to the high (low) pressure anomalies over Lake Balkhash in mid- to high latitudes, with northward (southward) and weak (strong) characteristics in the subtropical High over the Western Pacific, favor less (more) summer precipitation over the ENC. Moreover, taking the decadal and interannual variations of SSTa into account can potentially contribute to improving forecasting of summer precipitation over the ENC, with the annual average Ps and Pc scores during the independent test samples based on the scale decomposition model being 6% and 7% higher than those in the original model, respectively.
Subjects: Geosciences >> Atmospheric Sciences submitted time 2023-05-17 Cooperative journals: 《干旱区地理》
Abstract： Based on the routine observation data of ground visibility, temperature, relative humidity, wind and other meteorological stations in Longde, Jingyuan and Liupan Mountain Meteorological Station obtained from the observation of mountain fog in Liupan Mountain, northwest China in 2020, and the vertical observation data of microwave radiometer temperature and relative humidity, the circulation situation and the vertical evolution characteristics of temperature and humidity in Liupan Mountain were preliminarily analyzed when the fog occurred in a large range and only at the top of the mountain. The results show that both the large-scale fog process and the mountaintop fog process in Liupan Mountain areas are caused by the warm and humid air flow in front of the trough and the cooling and humidification. The relative humidity on the ground during the two types of fog is more than 95%, mainly southerly winds. The visibility of Longde and Jingyuan Meteorological Stations is more than 200 m, and the visibility of Liupan Mountain Meteorological Station is less than 200 m for more than half of the time; The fog at Liupan Mountain is generated and dissipated rapidly, and the strong fog lasts for a long time. The thickness of inversion layer thickens earlier than the time of strong fog, when the fog is mature, the thickness of the inversion layer reaches 1130 m, with the development of fog, the thickness of inversion layer at Longde Meteorological Station has also increased, but it is far less than that at Liupan Mountain Meteorological Station, and the intensity of inversion at Liupan Mountain Meteorological Station is weaker than that at Longde Meteorological Station. With the development of fog, the relative humidity has an obvious upward extension phenomenon, with more than 90% of the relative humidity extending to 1040 m, at the same time, the microwave radiometer of Longde Meteorological Station can observe a saturated area of about 600 m when there is strong fog at Liupan Mountain Meteorological Station, which is of great significance to analyze the vertical evolution of typical mountain fog in Liupan Mountain.
Subjects: Geosciences >> Atmospheric Sciences submitted time 2021-09-14 Cooperative journals: 《干旱区研究》
Abstract：选取近57 宁夏20个气象站夏季逐日最高气温、NCEP/NCR再分析及北极海冰资料，利用气候统计诊断方法，分析了宁夏夏季极端高温的气候异常特征及其与北极海冰的联系。结果表明：宁夏夏季极端高温总强度、事件频次及最长持续日数自1961年以来总体呈增加趋势，尤其1990s后期至2000s中期是年代际增加最快的时段；极端高温总强度偏强年，宁夏处于500 hP位势高度场正中心的南边，北边冷空气不易入侵，有利于宁夏夏季极端高温偏强；前期春季格陵兰海、巴伦支海、喀拉海地区海冰密集度偏高时，激发500 hP位势高度距平场上出现正负相间的波列自北向南、自西向东往欧亚地区稳定传播，造成乌拉尔山高压脊减弱，使得欧亚中高纬地区以纬向环流为主，导致宁夏夏季极端高温强度偏强。本研究结果旨在为宁夏夏季极端高温预测提供理论依据。
Subjects: Geosciences >> Geography submitted time 2021-06-13 Cooperative journals: 《干旱区研究》
Abstract：利用1981—2018年西藏地区38个气象站点的逐日气象观测资料，采用联合国粮农组织Food and Agricul⁃ture Organization of the United Nations（FAO）推荐的Penman-Monteith公式估算了各站点的潜在蒸散量（ET0），分别从趋势性、突变性以及周期性分析了ET0的时空变化格局及其影响因素。结果表明：在时间尺度上，西藏地区ET0均表现出先“下降”后“升高”的趋势，其中“下降”阶段ET0整体呈显著的降低趋势（除冬季外），“升高”阶段呈显著的增加趋势（除春、夏季）。在空间尺度上，春、夏季表现出减少和秋冬季、年际表现出增加的趋势。发生突变的站点主要分布在中南部和东北部区域，时间集中在20世纪80年代；年均ET0变化的第一主周期为33 a（2013年）。此外，平均风速和相对湿度是影响年及季节ET0的主要因素，同时平均风速、相对湿度和最高温度对ET0的影响趋势具有很强的一致性。
Subjects: Geosciences >> Geography submitted time 2019-11-15 Cooperative journals: 《干旱区地理》
Abstract：针对隆德站地基微波辐射计温度资料，根据数据本身规律及各类疑误数据表现形式，结合历史探空资料，利用垂直变化强度极值检查、标准差检查、极值检查、奇异值检查和僵值检查5种检查方法进行质量控制实验，与同期探空资料比对，分析其应用效果。结果表明：各质量检查结果对数据质量均有一定的区分能力，且对控制参数是敏感的；数据质量以晴空最优、云天次之、降水稍差，各高度层数据质量基本相当。质量控制结果相关性分析表明各高度层上晴空相关性最好，云天次之，降水稍差，相关性都处在较高的水平上；降水情况下质量控制效果最显著。
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