Did tillage erosion play a role in millennial scale landscape development?

Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250 km² Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale. Copyright © 2012 John Wiley & Sons, Ltd.     

南海ODP1148站中中新世(12～18.3 Ma) 天文调谐的年代标尺

ODP1148站深海沉积岩心的磁化率记录显示出较强的周期性变化规律．研究发现,中新世和渐新世的深海地层物性参数具有很强的斜率周期．Shackletoneta1．利用这一规律,以北半球高纬太阳辐射曲线作为天文调谐的目标,以ODP154航次的深海沉积岩心的磁化率记录作为调谐对象,将磁化率的极大值与北半球天文辐射的极小值相对应,建立了14～34Ma的天文调谐的年代标尺．采用相同的方法,利用南海北部ODP1148站深海沉积岩心的磁化率记录和北半球高纬太阳辐射曲线建立了南海中中新世天文调谐的年代标尺．调谐后的磁化率记录显示了很强的斜率周期和较强的岁差周期,并与太阳辐射在这2个记录上高度相关,此外偏心率周期在磁化率记录中也较显著．调谐后1148站的浮游有孔虫事件年龄与ODP154航次采用相同的天文调谐方法获取的事件年龄异常接近,而与传统方法获取的生物地层事件年龄有较大差距,这在一定程度上证明了利用天文调谐的方法建立中新世深海地层年代标尺的可行性．     

1998年夏季HUBEX/GAME期间热量和水汽收支

使用1998年夏季高分辨率的GAME再分析资料，通过计算热量和水汽收支，分析了江淮梅雨的热力和动力特征。梅雨期间，江淮整个地区为强热源及水汽汇控制，并伴有强上升运动。热量和水汽收支计算表明，非绝热加热主要是降水产生的凝结潜热释放，地面感热和蒸发耗热均较小。江淮梅雨降水是对流云和层状云共同产生的混合性降水。子波分析显示，热源、水汽汇和垂直运动有相似的时间变化和多尺度特征。江淮梅雨期间，周期约为6天的天气尺度扰动以及周期约为2天和12小时的中尺度扰动同时发展，使江淮地区产生暴雨，亚引起了热源、水汽汇和上升运动的最大值，对此中尺度扰动起了主要作用。     

夏季对流和环流10-25天季内变化-5西太平洋暖池热力状况的关系

主要讨论了西太平洋暖池热力状况年际变化相联系的10－25天季内振荡的特征。在西太平洋暖池处于“暖”夏季和“冷”夏季两种状态时，10－25天季内振荡呈现出明显差异，在所讨论的亚洲－太平洋大部分区域，“暖”夏季时对流活动的10－25天季内变化和“冷”夏季时对流活动的10－25天季内变化表现出显的反相关关系，表明对流活动的年际变化与季内变化的相互作用。当西太平洋暖池上空对流活动的10－25天季内振荡处于最强和最弱阶段时，低层大气表现为Gill型环流响应，即气旋式（反气旋式）环流出现在最强（最弱）对流活动的西北，这种对流和环流关系在西太平洋暖池出于“暖”夏季和“冷”夏季两种状态时均成立。而当西太平洋暖池上空对流活动的10－25天季内振荡处于除此以外其他阶段时，就看不到Gill型环流响应。     

海气耦合系统中的季节内振荡模态

从海气相互作用的观点出发研究了热带大气季节内振荡产生的一种可能原因,发现在不考虑大气内部大尺度凝结反馈过程的条件下,线性简单海气耦合系统在真实的参数取值范围内存在一类和实际观测类似的季节内振荡模态,这种模态可以不稳定缓慢东传或西传或表现为驻波,海洋边界波反射效应对这种振荡模态的形成无根本性影响。这一结果为解释洋面上观测到的热带大气低频振荡的局地特征提供了理论背景。     

初秋孟加拉湾－日本海遥相关的特征及其与大气环流和中国降水的关系

用ＥＣＭＷＦ１９８０－１９８３年资料探讨了亚洲季风区水汽汇季节内变化的标准差分布、空间型及传播，并讨论了水汽汇与热源（本文第Ｉ部分）季节内变化特点的异同。结果表明：一方面，季节内时间尺度上水汽汇的变化特征与热源比较一致（尤其是在夏季），变化显著区主要位于季风活跃区及其附近地区，与季风雨带的位置极为接近，且夏季陆地上清楚，冬季海洋上明显；ＥＯＦ分析的主要空间型反映了印缅地区、中国东部及沿海、西太平洋     

Potential vorticity aspects of the MJO

Considering linearized motion about a resting basic state, we derive analytical solutions of the equatorial β-plane primitive equations under the assumption that the flow is steady in a reference frame moving eastward with a diabatic forcing resembling a Madden–Julian Oscillation (MJO) convective envelope. The solutions are analyzed in terms of potential vorticity (PV) dynamics. Because the diabatic source term for PV contains a factor βy, the diabatic heat source is ineffective at generating a PV anomaly at the equator but maximizes the PV response near the poleward edges of the heat source. In this way a moving heat source can produce two ribbons of lower tropospheric PV anomaly, a positive one off the equator in the northern hemisphere and a negative one off the equator in the southern hemisphere, with oppositely signed PV anomalies in the upper troposphere. Associated with these PV anomalies are geopotential anomalies that are shifted several hundred kilometers poleward. In the lower troposphere these zonally elongated geopotential anomalies resemble ITCZ trough zones, which demonstrates the close connection between the MJO wake dynamics and the formation of double ITCZs.To demonstrate that the MJO wake response can be described by simple PV dynamics, we propose an invertibility principle relating the PV to the streamfunction, which in turn is locally related to the geopotential. This equatorial invertibility principle accurately recovers the balanced wind and mass fields found in the MJO wake in the primitive equation model. However, while the invertibility principle highlights the ability of simple PV dynamics to accurately describe the flow in the wake of an MJO convective envelope, it also clearly illustrates the inability of such dynamics to describe the Kelvin-like flow pattern ahead of the convection.     

北半球平流层低层大气季节内振荡特征

利用奇异谱分析方法（SSA）分析了1975年1月1日至12月31日北半球30hPa高度场变化特征，结果发现:平流层低层大气除了年变化及季节变化趋势外，还存在明显的季节内振荡，最显著的周期为20～60天；在持续性异常多发地区，30hPa高度场变化中20～40天周期振荡占优势，而在其它一些地区则盛行40～60天周期振荡；对流层持续性异常主要同对流层高度场的20～40天振荡有关，并可能通过这种周期振荡同平流层低层相同周期的振荡的相互作用影响平流层低层大气季节内变化。     

SST日变化对西太平洋暖池海表热通量季节内变化的影响(英文)

基于利用日最大太阳辐射、日平均海面风和日降水量近似计算海表温度（SST）日变化的振幅的方法,发展了一个计算SST日循环的参数化方案。利用周平均SST强迫美国国家大气研究中心（NCAR）的CCM3大气模式进行了有、无考虑SST日变化的比较试验。热带海洋与全球大气计划之耦合海气响应实验（TOGA COARE）的强化观测期间 IMET浮标的逐时海表观测资料不仅验证了该参数化方案的合理性,也表明了利用参数化方案对强迫场SST迭加日变化使CCM3较真实地模拟出西太平洋暖池海表热通量的季节内变化的位相结构。