Study of Different Attenuation Correction Methods in Association with Rainfall Estimation for X-Band Polarimetric Radars

Different attenuation correction methods for the X-band dual linear polarimetric radar are analyzed in this paper.The specific differential phase shift K DP is always considered as an effective factor in radar signal attenuation correction.However,the values of K DP for light rains are too small,which results in unstable quality and large errors of rainfall estimation.Therefore,radar horizontal reflectivity Z H and specific differential phase shift are combined together in the Z H –K DP method to correct th...     

不同草地类型对产草量的贡献研究--以巴里坤为例

采用2004年到2008年牧草生长季(2004-2007年4-10月,2008年的仅到8月)的卫星遥感数据,统计出巴里坤县不同草地类型对产草量的贡献.结果表明:低平草甸、高寒草原、温性草原化荒漠、温性草原、温性荒漠草原等5种不同草地类型对巴里坤地区产草量贡献分别为:7.46%、11.05%、19.17%、21.09%、41.23%.这对农牧业生产和农业区域规划有着一定的指导意义.     

不同数字滤波方法在风暴轴研究中的性能比较

比较了Butterworth带通滤波器和不同截断方式下的对称滤波器在风暴轴研究中对天气尺度瞬变波动的滤波性能。理论分析表明：当n≥9时,在天气尺度为2．5～6．0d的定义下,对称滤波器对天气尺度瞬变波动的滤波性能优于Butterworth带通滤波器。针对逐日观测资料,对称滤波器在研究天气尺度瞬变波动问题时取截断参数n=15相对最优。在此截断参数条件下,正弦截断对称滤波器的滤波性能优于梯形截断对称滤波器,且两者均优于Butterworth带通滤波器,这种优势在风暴轴偏强的厄尔尼诺年体现得更为明显。在样本序列较短的情况下,为了得到天气尺度瞬变波动,利用Butterworth带通滤波器并选取带通滤波参数为2．5～8．0d的做法是可取的。     

CO2 Flux Estimation by Different Regression Methods from an Alpine Meadow on the Qinghai-Tibetan Plateau

CO2 efflux was estimated using different regression methods in static chamber observation from an alpine meadow on the Qinghai-Tibetan Plateau. The CO2 efflux showed a seasonal pattern, with the maximun flux occurring in the middle of July. The temperature sensitivity of CO2 efflux (Q10> was 3.9, which was at the high end of the range of global values. CO2 emissions calculated by linear and nonlinear regression were significantly different (p<0.05). Compared with the linear regression, CO2 emissions calculated by exponential regression and quadratic regression were 12.7% and 11.2% larger, respectively. However, there were no significant differences in temperature sensitivity values estimated by the three methods. In the entire growing season, the CO2 efflux estimated by linear regression may be underestimated by up to 25% compared to the real CO2 efflux. Consequently, great caution should be taken when using published flux data obtained by linear regression of static chamber observations to estimate the regional CO2 flux in alpine meadows on the Qinghai-Tibetan Plateau.     

Sensitivity of the DRP-4DVar Performance to Perturbation Samples Obtained by Two Different Methods

The dimension-reduced projection four-dimensional variational data assimilation (DRP-4DVar) approach utilizes the ensemble of historical forecasts to estimate the background error covariance (BEC) and directly obtains the analysis in the ensemble space.As a result,the quality of ensemble members significantly affects the DRP-4DVar performance.The historical-forecast-based initial perturbation samples are flow-dependent and can describe the error-growth pattern of the atmospheric model and the balanced relat...     

Estimation and Long-term Trend Analysis of Surface Solar Radiation in Antarctica: A Case Study of Zhongshan Station

Long-term,ground-based daily global solar radiation (DGSR) at Zhongshan Station in Antarctica can quantitatively reveal the basic characteristics of Earth’s surface radiation balance and validate satellite data for the Antarctic region.The fixed station was established in 1989,and conventional radiation observations started much later in 2008.In this study,a random forest (RF) model for estimating DGSR is developed using ground meteorological observation data,and a highprecision,long-term DGSR dataset is constructed.Then,the trend of DGSR from 1990 to 2019 at Zhongshan Station,Antarctica is analyzed.The RF model,which performs better than other models,shows a desirable performance of DGSR hindcast estimation with an R~2 of 0.984,root-mean-square error of 1.377 MJ m~(-2),and mean absolute error of 0.828 MJ m~(-2).The trend of DGSR annual anomalies increases during 1990–2004 and then begins to decrease after 2004.Note that the maximum value of annual anomalies occurs during approximately 2004/05 and is mainly related to the days with precipitation (especially those related to good weather during the polar day period) at this station.In addition to clouds and water vapor,bad weather conditions (such as snowfall,which can result in low visibility and then decreased sunshine duration and solar radiation) are the other major factors affecting solar radiation at this station.The high-precision,longterm estimated DGSR dataset enables further study and understanding of the role of Antarctica in global climate change and the interactions between snow,ice,and atmosphere.     

Sensitivity of Potential Evapotranspiration Estimation to the Thornthwaite and Penman–Monteith Methods in the Study of Global Drylands

Drylands are among those regions most sensitive to climate and environmental changes and human-induced perturbations.The most widely accepted definition of the term dryland is a ratio,called the Surface Wetness Index(SWI),of annual precipitation to potential evapotranspiration(PET)being below 0.65.PET is commonly estimated using the Thornthwaite(PET Th)and Penman–Monteith equations(PET PM).The present study compared spatiotemporal characteristics of global drylands based on the SWI with PET Th and PET PM.Results showed vast differences between PET Th and PET PM;however,the SWI derived from the two kinds of PET showed broadly similar characteristics in the interdecadal variability of global and continental drylands,except in North America,with high correlation coefficients ranging from 0.58 to 0.89.It was found that,during 1901–2014,global hyper-arid and semi-arid regions expanded,arid and dry sub-humid regions contracted,and drylands underwent interdecadal fluctuation.This was because precipitation variations made major contributions,whereas PET changes contributed to a much lesser degree.However,distinct differences in the interdecadal variability of semi-arid and dry sub-humid regions were found.This indicated that the influence of PET changes was comparable to that of precipitation variations in the global dry–wet transition zone.Additionally,the contribution of PET changes to the variations in global and continental drylands gradually enhanced with global warming,and the Thornthwaite method was found to be increasingly less applicable under climate change.     

Testing and Improving the Performance of the Common Land Model:A Case Study for the Gobi Landscape

Land surface processes take place on the interface between the earth and atmosphere, exerting significant influences on the weather and climate. Correct modeling of these processes is important to numerical weather forecast and climate prediction. In order to obtain a more thorough understanding of the land surface processes over the Gobi landscape, we evaluated the performance of the Common Land Model(Co LM) at Dunhuang station in Gansu Province of China to determine whether the model formulation, driven by observational data, is capable of simulating surface fluxes over the underlying desert surface. In comparison with the enhanced observation data collected at Dunhuang station over the period 22–28 August 2008, the results showed that the surface albedo simulated by Co LM was larger than that in the observation, and the simulated surface temperature was lower than the observed. After the measured values were used to correct the surface albedo, the solar radiation absorbed by the ground surface was more consistent with the measurements. A new empirical relationship of the surface thermal exchange coefficient rah was used to modify the thermal aerodynamic impedance. The simulated soil surface temperature became significantly closer to the observed value, and the simulated surface sensible heat as well as net radiative fluxes were also improved.     

不同方法在湖南省早稻产量动态预报中的比较

为了提高产量趋势预报的准确性和定量预报的准确率,利用1962—2002年气象、早稻产量和田间观测资料,建立基于气候适宜度、关键气象因子、作物生长模型的湖南省早稻产量动态预报方法,进行回代检验;并利用2003—2012年资料进行预报检验。分析表明:3种方法的预报准确率比较接近,平均在93.8%以上;基于气候适宜度预报方法的趋势预报准确性最高,较基于关键气象因子的预报方法高4%~6%;基于作物生长模型预报方法的误差5%以内样本百分率最高,较基于气候适宜度的预报方法高2%~20%。研究结果为湖南省早稻产量动态预报筛选出了较优的方法,即产量趋势预报选用基于气候适宜度的方法,定量预报选用基于作物生长模型的方法,同时可供我国其他早稻区的产量动态预报方法研究借鉴。     

不同强风天气系统风特性的个例分析

利用广东省东莞市的80 m气象塔在台风莫拉菲、强对流和强冷空气期间的观测数据,分析不同强风天气系统近地面边界层的平均风和脉动风特性参数。研究发现:(1)1号强对流的风速变化最为剧烈,风速的10 min升幅可分别达台风和强冷空气大风的1.8和3. 7倍。强对流的10 min平均风向变幅也最剧烈,可达到120°·(10 min)~(-1)。(2)台风强风廓线的幂指数值为0. 177,要大于建筑结构荷载规范(GB 5009—2012)给出的B类下垫面0.15的参考值,而强对流的幂指数值接近规范给出的A类下垫面的参考值0. 12,强冷空气的幂指数值则仅为0. 10。(3)1号强对流强风平均湍流强度分别是台风和强冷空气大风平均湍流强度的1.4～2.1和1.7～2.0倍。(4)台风和强对流的风攻角在-3°～3°范围内,强冷空气大风的风攻角在0°附近变动。(5)强风影响期间湍流空间积分尺度均有增大的现象,台风强风经过时,水平(纵向和横向)湍流空间积分尺度明显增大了一个量级。(6)台风强风的湍流功率谱不满足在惯性子区湍流能谱密度的-5/3次方与频率成正比的规律和各向同性假设。台风强风的湍流能谱值要显著高于强对流和强冷空气,其中,在桥梁敏感频域台风的平均湍流能谱值约为强对流和强冷空气的3倍。     

A Case Study of the Near-Neutral Coastal Internal Boundary-Layer Growth: Aircraft Measurements Compared with Different Model Estimates

A simplified version of a model of the internalboundary layer evolution is compared with aircraftmeasurements across the southern part of the east coast ofSweden (Blekinge). The two flight occasions used hererepresent relatively high wind velocities and negligiblesurface heat flux. Both the vertical potential temperaturegradient and the surface temperaturedifference between land and sea are small. Modelpredictions of the internal boundary-layer (IBL)height agree well with data, for both short and largerdistances from the coastline. The contributions to theIBL growth from the mechanical turbulence and theZilitinkevich correction are discussed, as are thesensitivities of the growth to a number of physicalparameters. In near neutralconditions, the vertical potential temperaturegradient is found to be an important parameter for thegrowth of the IBL.A comparison with several simple model estimates forthe height of the IBL is presented. The majority ofthe models overestimate the IBL height. Some of themodels give reasonable results close to the coast, butgenerally the simple models perform less well atlarger distances.     

高温热浪支付意愿人群分异及其影响因素——以福州市为例

本文以高温热浪突出的福州市为典型研究区域,采取简单随机抽样的方式进行面对面访谈,获取了962份有效问卷,并对部分样本进行深度访谈,问卷内容涵盖社会经济、高温热浪的支付意愿及其影响因素等。利用条件价值评估法(CVM)与Spike修正模型,探究本地居民与外来流动人口在支付意愿上存在的人群分异及其影响因素。结果显示：1)本地居民和外来流动人口的高温热浪支付意愿总体较高,且前者高于后者;2)本地居民E(WTP)非负为68.78元/月,而流动人口E(WTP)非负为46.78元/月,存在明显差异（WTP指支付意愿);3)导致高温热浪支付意愿相对较低的因素包括居民类型、性别、受教育水平、职业、在福州时间和经济实力。本地居民与外来流动人口高温热浪支付意愿和支付金额的差异及其影响因素将为福州及同类地区制定相关政策提供借鉴。     

不同人为源排放清单对大气污染物浓度数值模拟的影响:以浙江省为例

应用大气化学模式WRF-Chem(Weather Research and Forecast-Chemistry),分别选用亚洲排放源清单INTEX-B(Intercontinental Chemical Transport Experiment-Phase B)、REASv2.1(Regional Emission inventory in Asia version 2.1)以及全球排放源清单HTAP_v2(Hemispheric Transport of Air Pollution version 2),对浙江省2013年12月进行模拟,分别记为IN、RE和HT试验,研究人为源排放清单对大气污染物浓度数值模拟的影响。结果表明,3组试验合理的反映出PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物,即细颗粒物)、PM10(空气动力学当量直径小于等于10μm的颗粒物,即可吸入颗粒物)和NO_2近地面浓度的时空分布特征,相关系数为0.5~0.8,85%以上的模拟值落在观测值的0.5~2倍范围内,但对SO_2近地面浓度模拟较差。IN、RE、HT试验对PM2.5和PM10的模拟偏差均成递减趋势,约为30%、16%和6%,HT试验的模拟值更加接近观测。INTEX-B清单中PM2.5的一次排放与二次气溶胶前提物SO_2均高于REAS与HTAP清单,因此会导致更多的硫酸盐生成,从而进一步增加PM2.5浓度。HTAP_v2清单中较低的NH3排放会抑制硝酸盐的生成,从而有助于降低PM2.5浓度。3个清单的基准年与模拟年的差异对SO_2浓度模拟的准确性影响更大,INTEX-B清单中SO_2排放量明显高于REASv2.1与HTAP_v2清单,尤其在浙北和沿海工业发达地区,导致IN试验模拟的SO_2在这些地区存在明显高估。3组试验模拟的NO_2浓度偏差最小且更为接近(-8%~4%),主要原因是3个清单在浙江省的NOx排放十分一致。从3组试验结果之间的差异程度来看,浙江省范围内PM2.5、PM10、SO_2和NO_2逐日浓度模拟值之间的平均差异程度分别约为14%、15%、51%和16%,最大差异程度分别为69%、78%、137%和132%。月均浓度与逐日浓度的平均差异程度基本一致,但最大差异程度明显更低。总体来看3组试验模拟的PM2.5、PM10与NO_2的差异程度明显低于SO_2。     

不同选样方法对Pilgrim&Cordery设计暴雨雨型的对比研究

采用宜昌市主城区国家基本站长序列的逐分钟降雨过程资料,利用PilgrimCordery法(简称"PC法")比较通过自然降雨过程和最大历时过程两种降雨场次样本选样方法推求的设计暴雨雨型,并分析结果差异。结果表明:基于自然降雨过程和最大历时过程选样,利用PC法推求的宜昌市主城区短历时设计暴雨雨型基本都为单峰型,且雨峰均出现在整场降雨过程的前1/3时段。两种选样方法推求的短历时设计暴雨雨型的雨量分配比例存在较大差异,自然降雨过程选样推求的雨型雨峰峰值占总雨量的比例相较于最大历时过程的数值偏大,更为突出。实际工程设计中,设计师应当根据最大历时过程的选样规则进行推求,结合一定重现期下各个历时的降雨量值,进而得到各历时时程分配的具体雨强;计算得到宜昌市主城区重现期2a历时60、120、180 min的雨峰时段雨强分别为1.16、0.86、0.72 mm/min。     

喀什地区一场大雪天气过程分析

从天气学角度，对造成2001年1月14－17日喀什地区大雪天气过程进行了分析，着重从低值系统、冷高、高中低三支气流的配置，探讨降雪天气的机制。     

针对模式风场的格点预报订正方案对比

为了将格点观测融合产品用于模式预报产品的滚动订正中,获得精准的预报效果,使用国家气象信息中心HRCLDAS（High Resolution China Meteorological Administration Land Data Assimilation System）业务系统产生的高频次格点风场融合产品作为实况资料,采用两种风场模型和8种格点误差订正方案,对模式风预报产品进行订正预报试验,试验选择欧洲中期天气预报中心10 m风预报产品的2017年1月1日—2月28日以及2017年6月1日—7月31日两个时间段,进行了预报模拟试验,对8种格点误差订正方案的订正结果进行检验,同时将订正场插值到站点,使用国家级2400个地面气象站风场资料进行站点检验,结果表明:无论从格点还是站点检验的平均绝对偏差、准确率、绝对偏差分布频率结果看,采用基于模式和实况因子的全格点滑动建模订正方案具有最佳的订正效果。     

A Comparison of De-noising Methods for Differential Phase Shift and Associated Rainfall Estimation

Measured differential phase shift ΦDP is known to be a noisy unstable polarimetric radar variable, such that the quality of ΦDP data has direct impact on specific differential phase shift KDP estimation, and subsequently, the KDP-based rainfall estimation. Over the past decades, many ΦDP de-noising methods have been developed; however, the de-noising effects in these methods and their impact on KDP-based rainfall estimation lack comprehensive comparative analysis. In this study, simulated noisy ΦDP data were generated and de-noised by using several methods such as finite-impulse response(FIR), Kalman, wavelet,traditional mean, and median filters. The biases were compared between KDP from simulated and observedΦDP radial profiles after de-noising by these methods. The results suggest that the complicated FIR, Kalman,and wavelet methods have a better de-noising effect than the traditional methods. After ΦDP was de-noised,the accuracy of the KDP-based rainfall estimation increased significantly based on the analysis of three actual rainfall events. The improvement in estimation was more obvious when KDP was estimated with ΦDP de-noised by Kalman, FIR, and wavelet methods when the average rainfall was heavier than 5 mm h-1.However, the improved estimation was not significant when the precipitation intensity further increased to a rainfall rate beyond 10 mm h-1. The performance of wavelet analysis was found to be the most stable of these filters.     

沙尘暴热力结构的个例研究

利用民勤站L波段探空雷达2004年5月23—24日的一次强沙尘暴过程加密探测资料,从气象要素的垂直廓线和能量天气学两个方面,分析了沙尘暴发生发展过程中大气层结及其演变特征。结果表明：沙尘暴过境前,500hPa以下的高空风速较小,低层800hPa以下基本为偏东气流,中高层为偏西气流,沙尘暴过境时近地层风速明显加大,700hPa以下为西北气流,高层为西南气流;相对湿度在沙尘暴过境前,高层明显高于低层,而过境后,整层大气的湿度明显增加,且800hPa附近出现逆湿现象,沙尘暴过境前后整层大气相对湿度在垂直方向上的变化趋势基本一致。沙尘暴发生前,近地层气温较高,200hPa附近存在超低温现象,250hPa附近存在比较厚的下沉逆温层,随着沙尘暴过境,低层的气温显著下降,近地层约800hPa处出现逆温层,而250hPa处的逆温层逐渐减弱;地面气象要素的变化为：沙尘暴过境之前,地面气压比较低,温度较高,风速也比较小,而沙尘暴一到,顿时气压升高,风速猛增,温度下降;沙尘暴过境前,500hPa以下处于对流不稳定,过境期间饱和能差逐渐减小,不稳定能量由高层向低层传递,单站的垂直运动发展加剧;沙尘天气结束后．整层大气的结构基本稳定．不稳定能量衰竭,饱和能差进一步减小,整层大气湿度有了较大的增加。     

新疆北部一次罕见暴雪过程分析

以大气环流分析入手，从大气稳定度，水汽条件，高空急流、高低空风场切变等不同视有，试图揭示1999年12月29日至2000年1月3日世纪之交的新疆北部一次罕见暴雪天气的机制，并通过卫星云图图像，再现本次过程的表象特征。     

多种均一性检验方法比较研究

气候资料的均一性检验对气候观测及变化研究有着重要作用。本文从四川省160个台站近50年气温资料中,选取具有连续观测记录的站点105个,综合SNHT(标准正态均一性检验)、Buishand检验、Pettitt检验、MASH(均一性序列多元分析)、TPR(二位相回归检验)和von Neumann比率法,对该省年平均气温进行均一性检验。结果表明有42个台站存在序列间断点,占40%;而不均一台站中,因迁站导致的有29个,更换仪器引起的有19个。对气温序列分年代统计发现不均一台站数目有增加的趋势,其中20世纪60—70和80—90年代不均一性均由台站迁移所致。评估不同检验方法的敏感度和适用性,发现SNHT法与Buishand法、Pettitt法检验结果相符率为48.6%,TPR法与其他方法相符率偏低,但该法不涉及邻近站是否均一,在分析中可做补充判断。参考四川省地形特征分析,SNHT法在盆地及山地台站的断点显露率最高,分别为67.6%和57.1%,漏检和误判较少;高原地区SNHT法和Buishand法显露率较高,其中Buishand法漏检和误判率最低。鉴于减小对元数据依赖度的均一化检验思路,应采用多种检验方法综合,有助于气候资料在区域气候变化研究中的有效利用。