北半球中高纬度土壤湿度异常的持续性分析及其对大尺度大气环流变率的影响研究

发布时间：2018-04-10 18:19

本文选题：土壤湿度 + 持续性时间尺度　；参考：《南京大学》2015年硕士论文

【摘要】：土壤湿度异常对气候变化有重要的反馈作用。过去有研究利用站点观测资料表明区域土壤湿度异常,特别是深层土壤层,其持续性长达多个月。由于很多地区缺乏可靠的长期土壤湿度观测资料,土壤湿度持续性的大范围特征少有涉及。本文尝试利用44年ERA40再分析资料的土壤湿度资料研究了全球范围土壤湿度异常持续时间的时空演变。结果表明,四个季节中第一土壤层(7cm)在北非北部、近赤道非洲、南美北部等地区土壤湿度异常持续时间达6个月以上,秋冬季节欧亚大陆东部大部分地区和北美北部地区持续时间也达到3-6个月。深层土壤湿度异常的持续时间也有类似特征。对同一格点,土壤湿度异常持续的时间随深度增加。通过观测分析和数值模拟,已有的研究强调了土壤湿度异常在区域气候中的重要性,检查了其对局地温度、降水和区域大气环流的反馈作用,但是较少涉及土壤湿度异常对大尺度大气环流的影响。本文利用ERA40月平均土壤湿度以及500hPa高度场资料,去除趋势影响以及ENSO的信号之后,对连续3个月的资料利用滞后最大协方差方法分析了北半球中高纬度土壤湿度与北大西洋涛动(North Atlantic Oscillation,NAO)的相互作用,发现冬季(JFM)以及夏季(JJA)NAO型的大气环流可以显著影响北半球中高纬度土壤湿度异常。秋季至初冬(春季至初夏)北半球中高纬度土壤湿度异常可以显著影响后期冬季(夏季)NAO型的大气环流,其中前期西伯利亚地区、青藏高原蒙古高原地区和北美北部地区(北美北部地区和青藏高原地区)的土壤湿度异常与后期冬季(夏季)大气环流显著相关,其可能原因是这些地区前期土壤湿度异常持续的时间较长。因此利用北半球中高纬度土壤湿度异常领先大气环流的信号将有助于改善北半球季节气候预报的能力。在此基础上利用CCM3模式PnAn试验(土壤湿度与大气有耦合作用)对ERA40再分析资料的结果进行验证,PnAn试验能够模拟出北半球中高纬度土壤湿度异常与NAO的相互作用。并利用PnAn试验与PnAn_SM试验(土壤湿度只有季节变化,没有年际和长期变化,与大气没有耦合作用)进行对比,结果表明由于加入了土壤湿度的影响,冬季NAO解释方差百分率由40.3%增大到52.7%,夏季由45.2%增大到50.9%,揭示了土壤湿度异常对冬季以及夏季的NAO型大气环流是有影响的。
[Abstract]:Soil moisture anomaly has an important feedback effect on climate change.In the past, it was shown that the regional soil moisture anomaly, especially the deep soil layer, lasted for several months.Due to the lack of reliable long-term soil moisture observation data in many areas, the large-scale characteristics of soil moisture sustainability are rarely involved.This paper attempts to study the temporal and spatial evolution of soil moisture anomaly duration on a global scale using soil moisture data from 44 years of ERA40 reanalysis.The results showed that the first soil layer (7cm) lasted for more than 6 months in northern North Africa, near equatorial Africa and northern South America.In autumn and winter, most of eastern Eurasia and northern North America also lasted 3-6 months.The duration of deep soil moisture anomaly is similar.For the same lattice, the duration of soil moisture anomaly increases with depth.Through observational analysis and numerical simulation, existing studies have emphasized the importance of soil moisture anomalies in regional climate and examined their feedback effects on local temperature, precipitation and regional atmospheric circulation.However, the effect of soil moisture anomaly on large scale atmospheric circulation is less involved.In this paper, the ERA40 monthly average soil moisture and 500hPa height field data are used to remove the trend effect and ENSO signal.The interaction between soil moisture in middle and high latitudes of the Northern Hemisphere and North Atlantic Oscillationnae of the North Atlantic Oscillation (NAO) was analyzed by using the lag maximum covariance method for 3 consecutive months.It is found that the atmospheric circulation of JFM in winter and JJ JJAN NAO in summer can significantly affect the soil moisture anomalies in the northern hemisphere in the middle and high latitudes.From autumn to early winter (spring to early summer), soil moisture anomaly in middle and high latitudes of the Northern Hemisphere can significantly affect the atmospheric circulation in late winter (summer), especially in the early Siberian region.The soil moisture anomalies in Mongolia Plateau and Northern North America (Northern North America and Qinghai-Tibet Plateau) are significantly correlated with the late winter (summer) general circulation.This may be due to the longer duration of soil moisture anomalies in these areas.Therefore, the use of the signal of soil moisture anomaly leading the atmospheric circulation in the middle and high latitudes of the Northern Hemisphere will help to improve the ability of seasonal climate prediction in the Northern Hemisphere.On this basis, the CCM3 model PnAn test (soil moisture and atmosphere coupling) is used to verify the results of ERA40 reanalysis data. The PnAn experiment can simulate the interaction between soil moisture anomaly and NAO in the northern hemisphere.The PnAn test was compared with the PnAn_SM test (soil moisture changed only seasonally, no interannual and long-term changes, and no coupling with the atmosphere). The results showed that the effect of soil moisture was added to the soil moisture.The percentage of variance of NAO interpretation increased from 40.3% in winter to 52.7% in summer and from 45.2% to 50.9 in summer. It was revealed that the abnormal soil moisture had an effect on the NAO type atmospheric circulation in winter and summer.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：S152.71;P434

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