Winter wheat mapping using a random forest classifier combined with multi-temporal and multi-sensor data

Wheat is a major staple food crop in China. Accurate and cost-effective wheat mapping is exceedingly critical for food production management, food security warnings, and food trade policy-making in China. To reduce confusion between wheat and non-wheat crops for accurate growth stage wheat mapping, we present a novel approach that combines a random forest (RF) classifier with multi-sensor and multi-temporal image data. This study aims to (1) determine whether an RF combined with multi-sensor and multi-temporal imagery can achieve accurate winter wheat mapping, (2) to find out whether the proposed approach can provide improved performance over the traditional classifiers, and (3) examine the feasibility of deriving reliable estimates of winter wheat-growing areas from medium-resolution remotely sensed data. Winter wheat mapping experiments were conducted in Boxing County. The experimental results suggest that the proposed method can achieve good performance, with an overall accuracy of 92.9% and a kappa coefficient (κ) of 0.858. The winter wheat acreage was estimated at 33,895.71?ha with a relative error of only 9.3%. The effectiveness and feasibility of the proposed approach has been evaluated through comparison with other image classification methods. We conclude that the proposed approach can provide accurate delineation of winter wheat areas.     

长江中下游地区冬夏干湿韵律特征分析

通过分析中国160站1952—2013年的月平均降水观测资料,揭示了长江中下游地区冬季和夏季降水间存在显著的韵律现象,即当该地区冬季降水异常偏少(偏多)时,次年夏季降水也趋于异常偏少(偏多),这里称之为干(湿)韵律现象。对干、湿韵律年大气环流背景的分析结果显示,干韵律年和湿韵律年对应的环流形势基本相反:在干(湿)韵律年冬季,东亚地区500 hPa位势高度距平呈现西高东低(东高西低)的分布型,中国南方东部主要受偏北(南)风异常控制,这不利(有利)于低纬度暖湿气流向长江中下游地区输送,导致该地区冬季降水异常偏少(多);在次年夏季,西北太平洋副热带高压异常偏弱(强),不利(有利)于西南暖湿气流向中国东部地区输送,使得长江中下游地区夏季降水也异常偏少(多)。研究进一步指出,长江中下游地区的冬夏干、湿韵律现象与东亚冬夏季风活动的强度密切相关。干、湿韵律现象多在东亚冬夏季风强度变化一致的情况下出现:冬、夏季风一致偏强时多导致干韵律现象,而一致偏弱时易导致湿韵律现象。     

中国冬季气温月际变化特征及其对大气环流异常的响应

基于1951—2014年中国160站月气温和NCEP/NCAR再分析资料,利用季节的经验正交函数分解（S-EOF）等方法,研究了中国冬季气温月际变化的时、空演变特征及其对大气环流异常的响应。结果表明,中国冬季气温在月尺度上常常出现前、后冬相反甚至冷暖交替的现象。中国冬季气温月际变化存在3个主模态:全冬一致型、前后反相型和冷暖交替型。当西伯利亚高压冬季一致偏强（偏弱）时,冬季一致冷（暖）;当海陆热力差异由强变弱、西伯利亚高压强度由强变弱,东亚西风急流比较稳定,强度偏强,位置由南向北移动时,冬季前冷后暖;当大气环流发生突变,尤其是海平面气压场和500 hPa位势高度场上大气活动中心的频繁调整,西伯利亚高压强度在月时间尺度上强弱交替时,冬季气温呈冷—暖—冷交替变化。      

Possible connection between anomalous activity of Scandinavian Atmospheric Teleconnection Pattern and winter snowfall in the Yangtze-Huaihe River Basin of China

利用中国地面气候资料日值数据集(V3.0)逐日气象资料研究了我国江淮冬季降雪的时空变化及其与斯堪的纳维亚遥相关型(SCAND)的可能联系。结果表明:江淮冬季降雪表现出空间一致的年际变化,SCAND与江淮地区冬季降雪异常关系密切。江淮冬季降雪偏多通常对于SCAND正位相,500hPa阻塞高压、东亚大槽加强,有利于冷空气活动增强,江淮地区垂直运动增强,水汽输送增强;降雪偏少则对应SCAND负位相。研究结果有助于深入理解江淮冬季降雪异常的相关机理。     

热带西太平洋沉积物的环境磁学特征对东亚冬季风的响应

西太平洋暖池(Western Pacific Warm Pool,WPWP)指位于热带太平洋中、西部(包括南海南部和苏禄海)年平均水温超过 28 ℃的广大海域。由于巨厚的表层暖水覆盖,西太平洋暖池成为全球热量和水汽交互的重要源区,对驱动温盐环流、调节全球气候变化具有重要作用。东亚冬季风(EAWM)是全球气候系统中最活跃的组成部分之一,它可能会通过寒潮侵入热带地区,引起深层对流,以此加强暖池区的对流活动和降水异常,从而影响赤道地区的潜热释放。但地质历史时期西太平洋暖池与东亚冬季风的相互作用关系尚不明确。由于东亚冬季风携带的风尘中往往包含有大颗粒的高矫顽力磁性矿物,我们可以通过沉积物中磁性矿物的组合、含量、颗粒大小和形态变化,分析不同时间尺度上气候环境变化和风尘物质的输入情况,进而反演东亚冬季风的强度变化。本文对取自热带西太平洋B10钻孔的岩心样品进行了环境磁学测试,以揭示地质历史时期西太平洋暖池沉积物环境磁学特征对东亚冬季风的响应。实验结果表明,沉积物中的主要载磁矿物为低矫顽力的磁铁矿,属于亚铁磁性矿物,并含有少量高矫顽力磁性矿物。沉积物中的磁性颗粒以准单畴(PSD)颗粒为主。高矫顽力的磁性矿物含量和细颗粒磁铁矿相对含量在冰期和间冰期呈现出显著相对变化,对东亚冬季风的变化有敏感响应:冰期沉积物中高矫顽力矿物含量增多,磁性颗粒粒径变大;间冰期沉积物中高矫顽力矿物含量降低,磁性颗粒粒径变细。在干燥、寒冷的冰期,由风尘携带而来的高矫顽力磁性矿物相对含量增加,沉积物中的磁性颗粒粒径变大,反映冰期东亚冬季风强度增大;在气候温暖湿润的间冰期,风尘的输入量较小,由风尘携带的高矫顽力磁性矿物含量相对较低,沉积物中的磁性颗粒粒径变小,反映间冰期东亚冬季风的强度减弱。     

小极距井下地电阻率观测数据质量浅析

为加强2022年北京冬奥会举办地区的震情保障工作,2019—2020年,依托原有地电台网,建设平谷、通州、阳原、大同、代县、临汾、宝昌、和林格尔等8个小极距井下地电阻率观测站（点）,目前均运行良好,与同台地表大极距地电观测相比,观测数据精度提高。选取2021年9—11月井下地电阻率观测站数据记录,就相对均方差、日精度、月精度、月离散度、变化幅度等指标,分析小极距井下地电阻率观测数据质量。结果表明,8个井下地电阻率观测站（点）运行稳定,观测数据精度较高,具备一定映震效能,可为冬奥会举办区域及周边地区的震情跟踪有效服务。     

冬季华南准静止锋的结构和类型特征研究

利用12年(2000～2011年)逐日的FNL(Final Operational Global Analysis)分析资料和逐日的中国站点降水资料, 定义了一个冬季华南准静止锋强度指数, 并根据该指数挑选出强准静止锋事件, 研究了强事件的结构特征、环流分型及其与降水的关系。结果表明:冬季强准静止锋事件多发于1、2月, 其发生频次在近12年里呈现明显上升趋势。强准静止锋锋区表现为等假相当位温线、等温线的密集带, 但是锋区湿度变化不明显, 并有明显逆温, 锋区由南北风辐合构成, 上升气流主要位于锋区上部, 纬向有两个次级环流与锋区相对应, 伴随正相对涡度和水汽通量辐合。根据850 hPa风场在锋区的辐合情况, 强准静止锋可分为北风辐合型、南北风辐合型、南风辐合型三种类型。在这三种类型中, 北风辐合型对应的北方冷空气最强, 华南降水最少;南风辐合型对应的南支槽最活跃, 华南降水最多;南北风辐合型介于两者之间。冬季华南准静止锋与冬季华南降水有一定相关, 在强准静止锋的背景下, 降水偏多时, 锋区低层的水汽通量辐合和上升运动偏强, 华南处于偏强南支槽前。     

林带冬季相立木疏透度及其设计方法的研究

研究林带冬季相结构设计方法是针对我国北方干旱沙区气候和风沙活动特点,为沙区新垦绿洲防护林体系建设服务的。用随机概率法推导曹新孙立木疏透度与疏透度之间的近似数值关系,得知立木疏透度最佳值为3.3;根据生物器官间生长量的相关性提出林带冬季相结构设计方法,测算了新疆杨、沙枣等六个常用防护林树种的设计参数。     

The influence of surface layer salinity on wintertime convection in Wilkinson Basin,Gulf of Maine

Observations suggest that the interannual variability of wintertime convection in Wilkinson Basin (WB) during 1977–2005 is related to the variation in the surface layer salinity in the western Gulf of Maine (wGOM). When the winter convection is stronger (weaker), the resulting deep-layer temperatures in the wGOM are colder (warmer), and the likelihood of deep winter mixing is greater when the wGOM salinities are high. This hypothesis was tested using a one-dimensional mixed layer model to simulate the water column structure over the cooling period. Comparisons were made between the convection potential for the range of observed late-fall salinity values. Model results indicated that the mixed layer depth could deepen by as much as 50% when the surface layer salinities in the wGOM were high. Sensitivity tests revealed that the surface layer salinity variability, and its influence on the water column density structure, was a significant factor, along with local climate variability, in determining the observed time series trend in springtime bottom layer temperatures.     

Winter counter-wind currents off the southeastern China coast: A review

This review covers the discovery and studies of the year-round northeastward currents off the southeastern China coast, paying special attention to its upwind characteristic in winter, mainly focusing on work by Chinese oceanographers. This current system is a prominent and unique phenomenon in the shelf circulation of the world ocean. The general features of the current system are summarized. The evidence for the existence and the variation of the three parts of the currents—the South China Sea Warm Current, the Taiwan Strait Warm Current and the Taiwan Warm Current—are separately elucidated. The formation mechanisms of the current as a whole are explained using dynamic analysis and numerical simulation results. Some suggestions for further studies are also made.