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Interannual variability of the Indian summer monsoon rainfall has two dominant periodicities, one on the quasi-biennial (2–3 year) time scale corresponding to tropospheric biennial oscillation (TBO) and the other on low frequency (3–7 year) corresponding to El Niño Southern Oscillation (ENSO). In the present study, the spatial and temporal patterns of various atmospheric and oceanic parameters associated with the Indian summer monsoon on the above two periodicities were investigated using NCEP/NCAR reanalysis data sets for the period 1950–2005. Influences of Indian and Pacific Ocean SSTs on the monsoon season rainfall are different for both of the time scales. Seasonal evolution and movement of SST and Walker circulation are also different. SST and velocity potential anomalies are southeast propagating on the TBO scale, while they are stationary on the ENSO scale. Latent heat flux and relative humidity anomalies over the Indian Ocean and local Hadley circulation between the Indian monsoon region and adjacent oceans have interannual variability only on the TBO time scale. Local processes over the Indian Ocean determine the Indian Ocean SST in biennial periodicity, while the effect of equatorial east Pacific SST is significant in the ENSO periodicity. TBO scale variability is dependent on the local factors of the Indian Ocean and the Indian summer monsoon, while the ENSO scale processes are remotely controlled by the Pacific Ocean. 相似文献
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In order to investigate the spatial patterns of the Tropospheric Biennial Oscillation （TBO） on the global scale, the Climate Prediction Center （CPC） Merged Analysis of Precipitation （CMAP） monthly averaged precipitation and the Climate Diagnostics Center （CDC） monthly outgoing long-wave radiation （OLR） and SST are used in conjunction with TBO bandpass-filtering. The results indicate active biennial variability in the tropical eastern-central Pacific regions. It is evident that observations reflect the biennial component of the ENSO rather than the TBO itself. Since some studies have pointed out that the TBO is a broad-scale phenomenon differing from the ENSO, to investigate the pure TBO the ENSO signal must be excluded. The Scale Interaction Experiment-FRCGC （SINTEX-F） coupled general circulation model （CGCM） developed at Japan Frontier Research Center for Global Change （FRCGC） can capture both the ENSO and the biennial signals. Air-sea interactions in the tropical eastern-central Pacific are decoupled to eliminate the effects of ENSO in a experiment by SINTEX-F and the results show that biennial variability still exists even without ENSO. It seems to mean that the TBO and ENSO are independent from each other. Furthermore, the model results indicate that the two key regions are southwest Sumatra and the tropical western Pacific for the TBO cycle. 相似文献
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The results of this study prove that there is significant troposphere biennial oscillation （TBO） in the South Asian climate, especially with the Indian summer monsoon rainfall. In order to explore the mechanism of TBO in the South Asian region, we defined a unified South Asian monsoon index to depict South Asian summer monsoon （SASM） and South Asian winter monsoon （SAWM） and the transition features between SASM and SAWM. Through further analysis, the connection between the abnormity of SASM and SAWM was discovered. Normally, a strong SAWM is beneficial for a weak SASM later, while a weak SAWM favors a strong SASM. Meanwhile, a strong SASM is favorable for a weak SAWM and a weak SAWM always happens after a weak SASM. Such results suggest the evolution of the South Asian monsoon, which may be an important mechanism to excite TBO in South Asia. 相似文献
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TBO的原因－异常东亚冬季风与ENSO循环的相互作用 总被引：21，自引：3，他引：21
基于对 ＮＣＥＰ／ ＮＣＡＲ再分析资料以及其他资料（ＯＬＲ，降水和气温等）的分析研究，结果表明东亚和西北太平洋地区的对流层环流和气候变化都有明显的准两年振荡（ＴＢＯ）特征。同时，异常东亚冬季风可以影响次年夏季的大气环流和气候变化，特别是在东亚地区；而异常东亚冬季风和ＥＮＳＯ循环间又有明显相互作用：持续的强（弱）东亚冬季风通过海─气相互作用可以激发 Ｅｌ Ｎｉ ｏ（Ｌａ Ｎｉ ａ）， Ｅｌ Ｎｉ ｏ（Ｌａ Ｎｉ ａ）反过来又可通过遥相关或遥响应而导致东亚冬季风偏弱（强）。强或弱的冬季风和ＥＮＳＯ循环是相互衔接在一起的，因此可以认为异常东亚冬季风与ＥＮＳＯ循环的相互作用是ＴＢＯ对流层准两年振荡）的基本原因。 相似文献
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中国东部夏季降水准两年周期振荡的长期演变? 总被引：6，自引：0，他引：6
采用中国气象局整编的中国160站月降水量资料 (1951年1月～2005年12月), 研究了中国东部地区夏季降水准两年周期振荡 (TBO) 的长期演变特征。最大熵谱分析和相对最大熵谱分析表明, 中国东部地区夏季降水TBO信号显著, 高值区基本呈带状分布, 方差最大值中心分布在江淮流域及南部沿海地区。根据中国东部夏季降水TBO分量的旋转经验正交函数展开 (REOF), 将东部地区划分为东北地区、 河套地区、 淮河流域、 长江流域、 华南西部、 华南中部及华南东部7个降水区。对各降水区的研究结果表明: (1) 东部夏季降水振幅变化TBO信号明显; (2) 各降水区夏季降水TBO有着不同的长期演变特征, 表现出不同的年代际变化。淮河流域、 长江流域和华南中部降水TBO特征较明显; 华南西部和东北地区降水TBO特征较弱; 河套地区在1990年代以前表现有较显著的TBO特征, 但1990年代后, TBO特征趋于不明显; 华南东部地区在1970年代中期以前TBO特征明显, 以后TBO特征减弱; (3) 淮河流域是中国东部地区由南向北的过渡带, 是夏季降水TBO的敏感地区。 相似文献
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全球海表温度场中主要的年代际突变及其模态 总被引：11，自引：2，他引：11
用滑动t检验法对NOAA提供的改进扩展重建的全球海表温度场（1867～2005年）的年平均时间序列进行了年代际突变的定量检验。给出了几个年代际突变时期的时空分布，这些时期有:1894～1901年、1905～1909年、1920～1930年、1939～1945年、1954～1958年、1973～1979年和1994～1998年，并确定了全球海表温度年代际突变的时间，不仅发现了大家熟知的1924、1942和1976年左右的突变，还发现了1894、1907、1956年和最近的1997年的突变。分析表明，赤道太平洋和南太平洋是海温变化的敏感区的可能性较大，其次是北太平洋和南印度洋。用合成差分析得到了全球海表温度场的年代际模态的空间分布，1895～1906年和1908～1923年、1925～1941年和1943～1955年以及1977～1996年和1998～2005年这三对模态分别在大部分海域大体上存在较为明显的反位相结构，太平洋上各个时期均表现为PDO模态，只是强度和范围有所不同，大西洋的南北结构具有不对称性，增暖占主导地位。用滑动t检验法对PDO的年代际突变的信号进行了定量的检验，发现其年代际突变的时间依次为:1908、1924、1942、1956、1976和1997年，除了1894年的突变外，其余突变年份与上述全球海表温度场的年代际突变时间基本上是一致的，这说明PDO是全球海表温度场年代际突变的重要成员之一。假如存在1997年左右的突变，1998至今时段就是全球海表温度场一个新的年代际背景，就其年代际模态而言，目前的强度比1943～1955时段的年代际背景还要强；就PDO目前的强度来说， 与1909～1923和1957～1975这两个时段的强度大体相当。 相似文献
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对近百年观测资料的分析表明赤道印度洋海温(SST)确实存在着偶极子型振荡的变化特征,它在9～11月最强,而在1～4月最弱;年际变化(4～5年周期)和年代际变化(主要为20～25年周期)也十分清楚.这个偶极子主要有正位相型(海温西高东低)和负位相型(海温东高西低);一般正位相型的振幅强于负位相型.尽管在极个别年赤道印度洋海温偶极子似乎与太平洋ENSO无关,但总体而论,赤道印度洋海温偶极子与赤道太平洋海温偶极子(类似ENSO)有很好负相关.它们的联系主要是赤道大气纬向(Walker)环流.资料分析表明,赤道印度洋海温偶极子与亚洲南部流场、青藏高压和西太平洋副高都有明显关系,表明它对亚洲季风活动有重要影响. 相似文献
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本文是对我们近五年在亚洲夏季风年代际与年际变率及其未来预测方面研究的一个综述.主要包括下列三个问题:(1)根据123年中国夏季降水资料和印度学者的分析,检测出亚洲夏季风具有明显的年代际尺度减弱,这种年代际变化使中国东部(包括东亚)和南亚夏季降水的格局在过去60年中发生了明显变化.在东亚,从1970年代后期开始,主要异常雨带有不断南移的趋势,结果造成了南涝北旱的降水分布,这主要受到60～80年年代际振荡的影响.青藏高原前冬和春季积雪的年代际减少与热带中东太平洋海表温度的年代际增加是东亚降水型改变的主要原因,这是通过减弱亚洲地区夏季海陆温差与夏季风强度而实现的.未来亚洲夏季风的预测表明,东亚夏季风和南亚夏季风对气候变暖有十分不同的响应.东亚夏季风在本世纪将增强,雨带北推,尤其在2040年代之后;而南亚夏季风环流将继续减弱.这种不同的变化是由于两者对高低层海陆热力差异的不同响应造成.(2)年际尺度的变率在亚洲夏季风区主要表现为2年与4～7年的振荡.本文着重分析了2年振荡(TBO)形成的过程、机理及其对东亚降水的影响.对TBO-海洋机理进行了具体的改进,说明了东亚夏季风降水深受TBO影响的原因,尤其是阐明了长江型(YRV) TBO和淮河型(HRV) TBO的特征及其形成的循环过程.(3)在总结亚洲夏季风时期遥相关型的基础上,本文提出了季节内和年际尺度的低空遥相关型:即西北太平洋季风的遥相关型与印度“南支”和“北支”遥相关型.它们基本上反映了沿低空夏季风强风速带Rossby波群速度传播的结果.据此可以根据西北太平洋和印度夏季风的变化分别预测中国梅雨和华北雨季来临和降水异常.最后研究还表明,在本世纪亚洲夏季风可能更显著地受到人类活动造成的全球变暖的影响,未来的亚洲夏季风活动是人类排放的CO2引起的全球变暖与自然变化(海洋和陆面过程(积雪))共同作用的结果. 相似文献
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利用欧洲中期数值预报中心的ERA40再分析逐日的200 hPa风场资料,选取1958—1977年和1980—1999年各20年,对比分析了在全球变暖背景下前后两个时段热带大气季节内振荡(ISO)的特征及其变化。研究表明:近20 a来,原来在赤道中太平洋上活跃的ISO减弱,而在中印度洋、孟加拉湾地区ISO变得活跃;全球变暖背景下,ISO的强度变化幅度加大,表明ISO更加活跃,且季节变化明显,冬、春季强,夏、秋季弱;对流层上层的纬向风能量更集中于1—3波,ISO的频率有加大的趋势。还利用中国科学院大气物理研究所LASG发展的耦合气候系统模式FGOALS-1.0g中的控制试验及其二氧化碳浓度加倍试验结果,分别对应实测资料的前后20年进行对比分析。发现模式对ISO的空间结构模拟较好,但低估了ISO的强度;时空谱分析表明模式结果中包含有更多的纬向风的高频成分,由于能量的分散,导致对ISO活动强度的低估。但通过对模式的控制试验和温室气体增加试验结果的对比分析,发现耦合模式还是较好地反映出在全球变暖背景下ISO在中印度洋、孟加拉湾地区变得活跃、频率加大等变化特征。 相似文献
11.
Characteristics and Numerical Simulation of the Tropical Intraseasonal Oscillations under Global Warming 
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下载免费PDF全文 Using the ECMWF reanalysis daily 200-hPa wind data during the two 20-yr periods from 1958 to 1977 and from 1980 to 1999,the characteristics and changes of Intraseasonal Oscillations (ISO) in the two periods associated with global warming are analyzed and compared in this study.It is found that during the last 20 years,the ISO has weakened in the central equatorial Pacific Ocean,but becomes more active in the central Indian Ocean and the Bay of Bengal;under the background of the global warming,increase in the amplitude of ISO intensity suggests that the ISO has become more active than before,with an obvious seasonal cycle,i.e.,strong during winter and spring,but weak during summer and autumn;the energy of the upper tropospheric zonal winds has more concentrated in wave numbers 1-3,and the frequency of ISO tended to increase. Comparison between the results of control experiment and CO_2 increase (1% per year) experiment of FGOALS-1.0g (developed at LASG) with the first and second 20-yr observations,is also performed. respectively.The comparative results show that the spatial structure of the ISO was well reproduced,but the strength of ISO was underestimated.On the basis of space-time spectral analysis,it is found that the simulated ISO contains too much high frequency waves,leading to the underestimation of ISO intensity due to the dispersion of ISO energy.However,FGOALS-1.0g captured the salient features of ISO under the global warming background by two contrast experiments,such as the vitality and frequency-increasing of ISO in the central Indian Ocean and the Bay of Bengal. 相似文献
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依据东英吉利大学气候研究中心（CRU）1930-2009年0.5°×0.5°分辨率的月降水量及NCEP/NCAR 1948-2009年2.5°×2.5°分辨率再分析逐月位势高度资料,分析了中亚干旱区年降水和季节降水的准两年周期振荡（TBO）特征和突变的时空变化及其可能影响机制。结果发现,中亚干旱区降水具有显著的TBO特征,其I区(哈萨克斯坦西区)、II区(哈萨克斯坦东区)、IV区（吉尔吉斯斯坦区）的年降水TBO相对具有连续性,而III区（中亚平原区）和V区（伊朗高原区）大致以20世纪60-70年代为分界点,存在相反变化。对季节降水而言,除II区年降水的TBO信号主要由夏季的变化决定,其他分区年降水TBO主要由冬季决定。降水突变分析发现,中亚干旱区降水的突变与TBO信号变化有很好的一致性,突变点上降水周期都有向TBO的跃变。另外,对整个亚洲中部干旱区而言,中亚干旱区西部降水突变发生在20世纪50年代初,东部于60年代末发生突变,新疆自80年代末出现气候转型,时间间隔为20年左右。季风区和受西风环流控制的亚洲内陆干旱区降水尽管都表现出TBO基本特征,但其控制因子可能有很大差异,对流层中上层的西风强度TBO可能是导致亚洲中部干旱区降水TBO的重要因子。 相似文献
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G. A. Meehl R. Lukas G. N. Kiladis K. M. Weickmann A. J. Matthews M. Wheeler 《Climate Dynamics》2001,17(10):753-775
Interactions involving various time and space scales, both within the tropics and between the tropics and midlatitudes, are
ubiquitous in the climate system. We propose a conceptual framework for understanding such interactions whereby longer time
scales and larger space scales set the base state for processes on shorter time scales and smaller space scales, which in
turn have an influence back on the longer time scales and larger space scales in a continuum of process-related interactions.
Though not intended to be comprehensive, we do cite examples from the literature to provide evidence for the validity of this
framework. Decadal time scale base states of the coupled climate system set the context for the manifestation of interannual
time scales (El Nino/Southern Oscillation, ENSO and tropospheric biennial oscillation, TBO) which are influenced by and interact
with the annual cycle and seasonal time scales. Those base states in turn influence the large-scale coupled processes involved
with intraseasonal and submonthly time scales, tied to interactions within the tropics and extratropics, and tropical–midlatitude
teleconnections. All of these set the base state for processes on the synoptic and mesoscale and regional/local space scales.
Events at those relatively short time scales and small space scales may then affect the longer time scale and larger space
scale processes in turn, reaching back out to submonthly, intraseasonal, seasonal, annual, TBO, ENSO and decadal. Global coupled
models can capture some elements of the decadal, ENSO, TBO, annual and seasonal time scales with the associated global space
scales. However, coupled models are less successful at simulating phenomena at subseasonal and shorter time scales with hemispheric
and smaller space scales. In the context of the proposed conceptual framework, the synergistic interactions of the time and
space scales suggest that a high priority must be placed on improved simulations of all of the time and space scales in the
climate system. This is particularly important for the subseasonal time scales and hemispheric and smaller space scales, which
are not well simulated at present, to improve the prospects of successfully forecasting phenomena beyond the synoptic scales.
Received: 3 April 2000/ Accepted: 6 November 2000 相似文献
14.
海表面风场可以用于获取许多大气和海洋现象的信号,高质量、高时空分辨率的海表面风场数据产品将有利于海洋-大气动力过程的研究.本文使用全球热带系泊浮标阵列计划（Global Tropical Moored Array Programs）的锚定浮标风场数据和西沙通量塔气象观测资料验证了Cyclone Global Navigation Satellite System （CYGNSS）的35°N~35°S海面遥感风场观测数据.结果表明,CYGNSS海表面风场与实测资料存在着2.17 m/s左右的平均均方根误差（RMSD）,它可能源于观测数据和卫星遥感资料的观测误差,以及两者在空间和时间上未严格匹配而引起的代表性误差.另外,CYGNSS海表面风速的时间演变与实测资料非常一致,展现了CYGNSS在研究海洋-大气能量和动量交换过程方面的潜在应用价值.本文使用Madden-Julian Oscillation （MJO）和赤道东部印度洋上升流事件作为两个个例,说明了CYGNSS海表面风场资料的潜在应用价值. 相似文献
15.
Summary The Tropospheric Biennial Oscillation (TBO), a major interannual variation phenomenon in the Indo-Pacific region, is the result
of strong ocean-atmosphere coupling over the Asian-Australian monsoon area. Along with other meteorological and oceanographic
parameters, the tropical circulation also exhibits interannual oscillations. Even though the TBO is the result of strong air–sea
interaction, the circulation cells during TBO years are, as yet, not well understood. In the present study, an attempt has
been made to understand the interannual variability of the mean meridional circulation and local monsoon circulation over
south Asia in connection with the TBO. The stream function computed from the zonal mean meridional wind component of NCEP/NCAR
reanalysis data for the years 1950–2003 is used to represent the mean meridional circulation. Mean meridional mass transport
in the topics reverses from a weak monsoon to a strong monsoon in the presence of ENSO, but in normal TBO years mean transport
remains weak across the Northern Hemisphere. The meridional temperature gradient, which drives the mean meridional circulation,
also shows no reversal during the normal TBO cycle. The local Hadley circulation over the monsoon area follows the TBO cycle
with anomalous ascent (descent) in strong (weak) monsoon years. During normal TBO years, the Equatorial region and Indian
monsoon areas exhibit opposite local Hadley circulation anomalies.
Authors’ addresses: Prasanth A. Pillai, Research Scholar, Department of Atmospheric Sciences, Cochin University of Science
and Technology, Lakeside Campus, Cochin 682016, India; K. Mohan Kumar, Professor & Dean, Department of Atmospheric Sciences,
Faculty of Marine Sciences, Cochin University of Science and Technology, Lakeside Campus, Cochin 682016, India. 相似文献
16.
亚洲—太平洋夏季风系统的基本模态特征分析 总被引：5，自引：1，他引：4
亚洲—太平洋季风区各季风子系统间的相互作用对季风区甚至全球的气候变化都有着显著的影响.整个亚洲—太平洋夏季风系统都处于高层辐散、低层辐合的庞大辐散环流中,从高层辐散中心流出的三支气流分别对推动印度夏季风、东亚副热带夏季风和南海夏季风起着重要的作用,很好地表现了亚洲—太平洋夏季风系统的整体性特征.季风区多种气象要素的基本模态在年代际和年际尺度上都表现出较为一致的变化特征:年代际尺度上亚洲—太平洋夏季风系统整体呈现减弱趋势;年际尺度上存在准2年和准4年的两个周期,其中准2年振荡特征表现为若印度西南季风偏强,则印度季风雨带偏强偏北,导致印度大陆中北部地区降水偏多;同时,由于西太平洋副热带高压的北移和偏强的印度西南季风显著向东延伸,10°N~30°N范围内的西北太平洋地区则表现为异常的气旋性环流,而30°N~50°N之间为反气旋性环流异常,对应东亚夏季风偏强,季风雨带能够北推至我国华北地区.也就是说,当亚洲夏季风中某一季风子系统表现为异常偏强时,另一季风子系统在这一年中也将表现为异常偏强,反之亦然.准2年的振荡周期可能是亚洲—太平洋夏季风系统的一种固有振荡,它从年际尺度上反映了亚洲—太平洋夏季风受热带太平洋—印度洋海温的强迫表现出明显的整体一致特征. 相似文献
17.
热带大气季节内振荡对西北太平洋台风的调制作用 总被引：5，自引：1，他引：4
利用澳大利亚气象局的RMM-MJO (Real-time Multivariate MJO) 指数, 分析研究了热带大气季节内振荡 (简称MJO) 对西北太平洋台风的调制作用及其机理, 结果表明MJO活动对西北太平洋台风的生成有比较明显调制作用。在MJO活跃期, 对流中心位于赤道东印度洋 (即MJO第2、3位相) 和对流中心越过海洋性大陆来到西太平洋地区 (即MJO 第5、6位相) 时台风生成的个数比例为2∶1。本文对西太平洋地区的大气环流场进行了多种气象要素的合成分析, 在MJO的不同位相, 西太平洋地区的动力因子分布形势有很明显不同。在第2、3位相, 各种因子均呈现出抑制西太平洋地区对流及台风发展的态势; 而在第5、6位相则明显有促进对流发生发展, 为台风生成和发展创造了有利条件的大尺度环流动力场。这说明MJO 在不断东移的过程中, 将改变大气环流形势, 最终影响了台风的生成和发展。接着, 我们从积云对流这个联系台风和MJO的重要因子出发, 研究了不同MJO位相时凝结加热的水平和垂直分布, 以及与台风环流、 水汽通量的配置情况。结果表明在MJO不同位相, 热源分布明显不同, 而这种水平和垂直方向的不同分布特征必然反映潜热释放和有效位能向有效动能转换的差异, 再与水汽的辐合辐散相配合, 就从台风获得的能量角度揭示了大气MJO调节台风的生成和发展, 造成不同位相时台风生成有根本差别的原因。 相似文献
18.
High-resolution satellite-derived data and NCEP-NCAR reanalysis data are used to investigate intraseasonal oscillations （ISO） over the tropical Indian Ocean.A composite evolution of the ISO life cycle is constructed,including the initiation,development,and propagation of rainfall anomalies over the tropical Indian Ocean.The characteristics of ISO over the tropical Indian Ocean are profoundly different before and after the onset of the Indian summer monsoon.Positive precipitation anomalies before monsoon onset appear one phase earlier than those after monsoon onset.Before monsoon onset,precipitation anomalies associated with ISO first initiate in the western tropical Indian Ocean and then propagate eastward along the equator.After monsoon onset,convective anomalies propagate northward over the Indian summer monsoon region after an initial eastward propagation over the equatorial Indian Ocean.Surface wind convergence and air-sea interaction play critical roles in initiating each new cycle of ISO convection. 相似文献
19.
New Metrics of the Tropospheric Biennial Oscillation in the East Asian Summer Monsoon and Its Interdecadal Shift 下载免费PDF全文
下载免费PDF全文 DAI Zhi-Xiu 《大气和海洋科学快报》2013,(6):440-444
This study designed a simple index for measuring irregular tropospheric biennial oscillation（TBO） activities, which was used to determine that the TBO in the East Asian Summer Monsoon（EASM）, the most important summer precipitation system for China, has strengthened rather than weakened since the late 1970s. The lead/lag correlations between the EASM and tropical Indian-Pacific sea surface temperature（SST） suggest a relationship between interbasin SST and EASM coupling processes and that this alternative correlation pattern is likely related to TBO. Significant correlation occurred only in recent decades, which implies a reinforcement of TBO in the EASM. From records of representative points in the Indian-Pacific, the interdecadal intrinsic SST modes of the areas can be obtained with ensemble empirical mode decomposition owing to its good temporal locality. Statistical results show Indian-Pacific SST interdecadal trends that include out-of-phase and in-phase warming before and after the late 1970s, respectively, which may be responsible for the TBO interdecadal augmentation present since the late 1970s. 相似文献
20.
The interlinked Eastern Indian Ocean (EIO) and Western Pacific Ocean (WPO), known as the Indo-Pacific warm pool, are highly active regions for intraseasonal oscillations (ISOs). Interestingly, distinct behaviors exist in ISO seasonality in these two basins. In the WPO, ISO intensity peaks in winter, decays rapidly starting from spring and reaches a minimum in summer. While in the EIO, ISO intensity exhibits a bimodal distribution, with a stronger peak in spring and a weaker one in autumn, followed by two troughs in summer and winter, respectively. Here, the regional ISO seasonality is understood in view of the regional differences in the background fields. For the bimodal ISO seasonality in the EIO, the increase from winter to spring is primarily due to elevated moisture content, the decrease from spring to summer is due to the decline in moisture and the meridional variation in vertical wind shear, and the increase from summer to autumn is mainly attributed to the meridional variation in vertical wind shear. In the WPO, the significant winter-summer contrast is mainly caused by change in moisture content. 相似文献