Longitudinal Displacement of the Subtropical High in the Western Pacific in Summer and its Influence

Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights in the previous indices based on geopotential height. The years of extreme westward and eastward extension of SH using the new index are in good agreement with those defined by height index. There exists a distinct difference in large-scale circulation between the eastward and westward extension of SH under the new definition, which includes not only the circulation in the middle latitudes but also the flow in the lower latitudes. It seems that when the SH extends far to the east (west), the summer monsoon in the South China Sea is stronger (weaker) and established earlier (later). In addition, there exists a good relationship between the longitudinal position of SH and the summer rainfall in China. A remarkable negative correlation area appears in the Changjiang River valley, indicating that when the SH extends westward (eastward), the precipitation in that region increases (decreases). A positive correlation region is found in South China, showing the decrease of rainfall when the SH extends westward. On the other hand, the rainfall is heavier when the SH retreats eastward. However, the anomalous longitudinal position of SH is not significantly related to the precipitation in North China. The calculation of correlation coefficients between the index of longitudinal position of SH and surface temperature in China shows that a large area of positive values, higher than 0.6 in the center, covers the whole of North China, even extending eastward to the Korean Peninsula and Japan Islands when using NCEP/NCAR reanalysis data to do the correlation calculation. This means that when the longitudinal position of the SH withdraws eastward in summer, the temperature over North China is higher. On the other hand, when it moves westward, the temperature there is lower. This could explain the phenomenon of the seriously high temperatures over North China during recent summers, because the longitudinal position of SH in recent summers was located far away from the Asian continent. Another region with large negative correlation coefficients is found in South China.     

青藏高原热力异常与华北汛期降水关系的研究

利用1980～1994年NCEP/NCAR再分析资料,以及我国336个测站1956～1994年月降水量资料,通过诊断分析和数值实验,研究了夏季高原上热力异常与华北汛期降水的关系.结果表明:华北汛期干旱年,青藏高压及西太平洋副热带高压偏南、偏东,华北汛期降水偏多年则相反;华北汛期旱年时,高原上升、高原东侧邻近地区下沉的垂直环流明显加强,而降水偏多年时,垂直环流减弱,华北地区为上升气流控制;夏季高原为热源和水汽汇区,它们的异常对华北地区降水有很大影响,当热源和水汽汇增强(减弱)时,华北地区降水偏少(偏多).数值试验表明,高原上潜热加热异常引起青藏高压、西太平洋副热带高压、亚洲季风以及欧亚中高纬地区环流的变化,进而影响到华北地区的降水.     

两种反映东亚夏季风异常的指数的比较研究

本文利用文献^ [4]提出的一种新的反映东亚夏季风异常的海陆温差指数分析了夏季风异常时我国气温、降水异常以及东亚环流状况，通过分析指出，东亚夏季风偏强，则中国东部夏季气温偏高，江淮干旱，华北多雨；夏季风偏弱则夏季气温偏低，江淮多雨，易涝，华北少雨。通过两种夏季风指数的对比，海陆温差指数能更好地反映东亚夏季环流及天气气候异常。文中还指出，海陆温差指数能更好的反映夏季风异常的原因是它的定义方法更科学，更全面的反映东亚海陆热力差异，既包含了东亚纬向海陆热力差异的影响，又考虑了东亚经向海陆热力差异的因素，并用地表气温和海表温度差来表示海陆热力差，好于以往用海平面气压差来反映海陆热力差。     

Effects of rainfall intensity fluctuations on infiltration and runoff: rainfall simulation on dryland soils,Fowlers Gap,Australia

Small plots and a dripper rainfall simulator were used to explore the significance of the intensity fluctuations (‘event profile’) within simulated rainfall events on infiltration and runoff from bare, crusted dryland soils. Rainfall was applied at mean rain rates of 10 mm/h. Fourteen simulated rainfall events each involved more than 5000 changes of intensity and included multipeak events with a 25‐mm/h peak of intensity early in the event or late in the event and an event that included a temporary cessation of rain. These are all event profiles commonly seen in natural rain but rarely addressed in rainfall simulation. A rectangular event profile of constant intensity, as commonly used in rainfall simulation experiments, was also adopted for comparative purposes. Results demonstrate that event profile exerts an important effect on infiltration and runoff for these soils and rainfall event profiles. ‘Uniform’ events of unvarying intensity yielded the lowest total runoff, the lowest peak runoff rate and the lowest runoff ratio (0.13). These parameters increased for ‘early peak’ profiles (runoff ratio 0.24) and reached maxima for ‘late peak’ profiles (runoff ratio 0.50). Differences in runoff ratio and peak runoff rate between the ‘uniform’ event profile and those of varying intensity were all statistically significant at p ≤ 0.01. Compared with ‘uniform’ runs, the varying intensity runs yielded larger runoff ratios and peak runoff rates, exceeding those of the ‘uniform’ events by 85%–570%. These results suggest that for small‐plot studies of infiltration and erosion, the continued use of constant rainfall intensity simulations may be sacrificing important information and misrepresenting the mechanisms involved in runoff generation. The implications of these findings for the ecohydrology of the research site, an area of contour‐aligned banded vegetation in which runoff and runon are of critical importance, are highlighted. Copyright © 2011 John Wiley & Sons, Ltd.     

一个海气耦合模式对东亚夏季气候预测潜力的评估

利用一个具有较高分辨率的海气耦合模式SINTEX-F(Scale Interaction Experiment-Frontier Research Center for Global Change coupled GCM)的多年回报结果,评估了该海气耦合模式对东亚区域,尤其是中国地区气候异常的预测潜力.与观测实况的比较结果表明:SINTEX-F模式对夏季降水、500 hPa高度场和地表气温都有一定的预测技巧,但是相比而言降水与高度场的回报技巧要高于地表气温;而且耦合模式对东亚地区气候异常的主要空间分布和年际变化特征也有较好的预测潜力,对500 hPa高度场效果较好;对降水异常的年际变化也有一定的预测潜力,尤其是我国中部地区效果较好,但是模式预测的降水异常的幅值较观测相对偏弱;此外对我国西部的极端气候也有一定的预测潜力.     

坡面溅蚀发生过程及其与坡度关系的模拟研究

通过人工模拟降雨试验,分别观测降雨过程中不同方向上溅蚀强度的变化,根据各影响因子间相互消长及相互制约的关系特点,分析了雨滴溅蚀发生的过程特征及其变化原因,从溅蚀过程的变化特点及溅蚀强度的变化规律比较,定量地探讨了坡度对雨滴击溅侵蚀的影响作用,得出了溅蚀强度与坡度因子之间的关系方程。     

Predicting June Mean Rainfall in the Middle/Lower Yangtze River Basin

We demonstrate that there is significant skill in the GloSea5 operational seasonal forecasting system for predicting June mean rainfall in the middle/lower Yangtze River basin up to four months in advance. Much of the rainfall in this region during June is contributed by the mei-yu rain band. We find that similar skill exists for predicting the East Asian summer monsoon index(EASMI) on monthly time scales, and that the latter could be used as a proxy to predict the regional rainfall. However, th...     

千年时间尺度南亚高压和西太平洋副热带高压关系的时空变化特征

利用全新世的气候模拟结果(KCM)以及1948~2013年NCEP/NCAR 逐月再分析资料, 分析了大型大气环流系统南亚高压和西太平洋副热带高压(以下简称"西太副高")在千年时间尺度上的特征和它们之间的空间位置变化关系以及与东亚夏季风的关系, 并比较了它们与现代气候背景年际时间尺度变化特征的异同。结果表明, 在千年尺度上, 南亚高压的东进(西移)对应西太副高的西伸(东撤)。这与年际尺度上南亚高压与西太副高存在的"相向而行"及"相背而去"的时空特征是一致的。耦合气候模式模拟的全新世9.5ka B.P. 以来东亚夏季风总体呈现振荡减弱趋势。早全新世(9.5~7.5ka B.P.)时期, 东亚夏季风强度较强, 此时南亚高压位置偏东而西太副高位置偏西; 在中全新世(7~4ka B.P.)期间, 东亚夏季风呈现百年尺度大幅振荡, 而此时南亚高压(西太副高)的位置大致位于112°~115°E(145°~155°E)之间; 晚全新世(4~0ka B.P.)期间, 东亚夏季风持续减弱, 对应南亚高压位置向东移动、西太副高位置向西移动。全新世时期(9.5~0ka B.P.), 北半球春季(4月、5月份)赤道地区接收的太阳辐射呈现先减弱,至5~4ka B.P. 期间达到最低值, 之后逐渐增强的变化趋势, 这与南亚高压的位置变化趋势一致, 而与西太副高位置变化趋势相反, 即赤道春季太阳辐射强(弱)时, 南亚高压位置偏东(偏西)、西太副高位置偏西(偏东)。同时, 模拟的全新世热带印度洋-西太平洋夏季温度变化也呈现出与春季赤道太阳辐射一致的变化趋势, 且与南亚高压有显著的正相关关系, 海温的加热作用可以通过激发Matsuno-Gill型大气响应使得南亚高压增强。西太副高主要由哈德莱环流在副热带地区的下沉作用造成, 而热带印度洋-西太平洋夏季的增温可引起哈德莱环流增强, 从而使西太副高的强度增强、面积扩大导致其西脊点位置偏西。因此, 赤道春季太阳辐射可以通过影响热带印度洋-西太平洋夏季温度对南亚高压东脊点和西太副高西脊点的位置产生影响。     

近年华中地区不同级别强降水事件变化趋势

利用1981—2017年近37 a华中区域241个气象观测站年最大小时降水资料,分析了该区域年极端小时降水的时空分布特征。结果表明：阈值分别为30~ < 40 mm·h^-1、40~ < 50 mm·h^-1和≥50 mm·h^-1的年极端小时降水频次,河南和湖北中东部均较高,湖南则随其阈值增大而降低;年极端小时降水频次日变化特征较为明显,午后至傍晚发生最多,前半夜至凌晨次之,后半夜至早晨、上午至午后明显减少;年极端小时降水平均强度大值区多集中在河南和湖北的中东部地区,湖北最强年极端小时降水大值区主要位于沿江汉平原边缘地带;年极端小时降水频次日峰值主要出现在午后至傍晚和后半夜至早晨,其区域性差异较为明显;不同阈值的年极端小时降水频次均表现出明显的年际和年代际变化特征,1980年代呈波动减小趋势,1990年代呈波动增加趋势,21世纪初期呈现低频波动变化,之后波动加大;不同阈值的极端小时降水频次日变化均表现为明显的单峰型特征,峰值出现在17时前后。

     

涝渍对夏花生光合特性及产量影响

夏花生常因汛期雨水偏多形成涝渍灾害而减产,探索不同耕作方式下涝渍持续日数对花生光合特性及产量的影响,可为花生涝渍动态监测评估和农业防灾减灾提供参考。选择2019年、2020年每年6—9月,在花生主产区河南驻马店土壤质地为粘土的大田平作、垄作方式下,以豫花22为试验材料,将花生产量形成过程分前期、中期、后期3个时段,分别设计3 d,5 d,7 d,9 d灌水处理。结果表明：相同过程灌水量条件下,垄作比平作涝渍持续日数减少1~5 d,其中淹涝日数偏少3~5 d;3 d灌水处理的涝渍持续日数4~5 d,叶绿素含量和净光合速率等光合参数呈正效应造成茎叶干物质积累增加;各时段涝渍影响均随持续日数的增加而加重,除百仁重涝渍影响表现为中期最大、前期次之、后期最小,其他均为前期最大、中期次之、后期最小;各处理水平涝渍持续日数4~16 d,光合参数影响幅度为1.3%~64.2%,生物量和产量影响幅度为0.6%~44.9%;垄作花生与平作花生相比,因涝渍持续日数减少而使灾害影响减小,前期各处理花生产量减少灾损达3.4%~11.6%。