Experiments of DSAEF_LTP Model with Two Improved Parameters for Accumulated Precipitation of Landfalling Tropical Cyclones over Southeast China

The Dynamical-Statistical-Analog Ensemble Forecast model for landfalling tropical cyclones (TCs) precipitation (DSAEF_LTP) utilises an operational numerical weather prediction (NWP) model for the forecast track, while the precipitation forecast is obtained by finding analog cyclones, and making a precipitation forecast from an ensemble of the analogs. This study addresses TCs that occurred from 2004 to 2019 in Southeast China with 47 TCs as training samples and 18 TCs for independent forecast experiments. Experiments use four model versions. The control experiment DSAEF_LTP_1 includes three factors including TC track, landfall season, and TC intensity to determine analogs. Versions DSAEF_LTP_2, DSAEF_LTP_3, and DSAEF_LTP_4 respectively integrate improved similarity region, improved ensemble method, and improvements in both parameters. Results show that the DSAEF_LTP model with new values of similarity region and ensemble method (DSAEF_LTP_4) performs best in the simulation experiment, while the DSAEF_LTP model with new values only of ensemble method (DSAEF_LTP_3) performs best in the forecast experiment. The reason for the difference between simulation (training sample) and forecast (independent sample) may be that the proportion of TC with typical tracks (southeast to northwest movement or landfall over Southeast China) has changed significantly between samples. Forecast performance is compared with that of three global dynamical models (ECMWF, GRAPES, and GFS) and a regional dynamical model (SMS-WARMS). The DSAEF_LTP model performs better than the dynamical models and tends to produce more false alarms in accumulated forecast precipitation above 250 mm and 100 mm. Compared with TCs without heavy precipitation or typical tracks, TCs with these characteristics are better forecasted by the DSAEF_LTP model.     

黑河实验区地表植被指数的区域分布及季节变化

利用具有较高空间分辨率的Ｌａｎｄｓａｔ ＴＭ卫星资料估算了黑河实验区夏季和近冬季地表标准化差值植被指数ＮＤＶＩ,分析了ＮＤＶＩ的区域分布特征和季节变化。结果表明,由于该实验区下垫面的复杂性,ＮＤＶＩ表现出明显的空间和季节变化,ＮＤＶＩ的图像能够很好地反映出地表植被的分布状况。     

Assessing Disagreement and Tolerance of Misclassification of Satellite-derived Land Cover Products Used in WRF Model Applications

As more satellite-derived land cover products used in the study of global change,especially climate modeling,assessing their quality has become vitally important.In this study,we developed a distance metric based on the parameters used in weather research and forecasting(WRF) to characterize the degree of disagreement among land cover products and to identify the tolerance for misclassification within the International Geosphere Biosphere Programme(IGBP) classification scheme.We determined the spatial degree of disagreement and then created maps of misclassification of Moderate Resolution Imaging Spectoradiometer(MODIS) products,and we calculated overall and class-specific accuracy and fuzzy agreement in a WRF model.Our results show a high level of agreement and high tolerance of misclassification in the WRF model between large-scale homogeneous landscapes,while a low level of agreement and tolerance of misclassification appeared in heterogeneous landscapes.The degree of disagreement varied significantly among seven regions of China.The class-specific accuracy and fuzzy agreement in MODIS Collection 4 and 5 products varied significantly.High accuracy and fuzzy agreement occurred in the following classes:water,grassland,cropland,and barren or sparsely vegetated.Misclassification mainly occurred among specific classes with similar plant functional types and low discriminative spectro-temporal signals.Some classes need to be improved further;the quality of MODIS land cover products across China still does not meet the common requirements of climate modeling.Our findings may have important implications for improving land surface parameterization for simulating climate and for better understanding the influence of the land cover change on climate.     

Elucidating Dominant Factors Affecting Land Surface Hydrological Simulations of the Community Land Model over China

In order to compare the impacts of the choice of land surface model(LSM) parameterization schemes, meteorological forcing, and land surface parameters on land surface hydrological simulations, and explore to what extent the quality can be improved, a series of experiments with different LSMs, forcing datasets, and parameter datasets concerning soil texture and land cover were conducted. Six simulations are run for the Chinese mainland on 0.1° × 0.1° grids from 1979 to 2008, and the simulated mon...     

珠穆朗玛峰北坡山谷太阳辐射和大气的特征与分析

2006年5月27日～6月30日HEST2006大气科学实验对珠峰北坡山谷的辐射(总辐射、净辐射)和温、湿度、风等进行了综合观测.沿珠峰北坡山谷布设了3个观测站,3个测站的辐射、温度、风都表现出明显的日变化规律,它们在08:00或09:00(地方时,下同)达到极大值.3个测站总辐射和净辐射的日变化都七匕较一致.从日变化最大值出现的时间来看,各站的辐射通量早于气温,气温早于风速.3个测站中任意2站之间辐射(总辐射、净辐射)最大值之比与温度和风速最大值之比均比较接近.因辐射状况、地形结构、大气温度等不同,远离珠峰区域的风一天之内多次改变风向,靠近珠峰区域则24h都为南风.珠峰北坡山谷不同区域风向风速变化存在明显时差,南风强于北风,且持续时间长.研究表明,辐射能量对于珠峰北坡大气运动具有重要的驱动作用,是控制和改变其大气运动方式最基本、最重要的因子.净辐射在不同区域风向转变或风速变化过程中起着决定性的作用.     

Changes in Water Use Efficiency Caused by Climate Change,CO2 Fertilization,and Land Use Changes on the Tibetan Plateau

Terrestrial ecosystem water use efficiency(WUE) is an important indicator for coupling plant photosynthesis and transpiration, and is also a key factor linking the carbon and water cycles between the land and atmosphere. However,under the combination of climate change and human intervention, the change in WUE is still unclear, especially on the Tibetan Plateau(TP). Therefore, satellite remote sensing data and process-based terrestrial biosphere models(TBMs) are used in this study to investigate ...     

中国区域秋季旱涝特征预测

利用国家气候中心综合气象干旱指数(CI),以干旱日数为预报对象,以前期500 hPa高度场为预报因子,结合最优子集回归(OSR)方法建立回归预报模型,对1971-2007年期间中国区域秋季干旱形势进行交叉检验预报。针对秋季华西秋雨与华南干旱特征,分别建立以华西洪涝站数与华南干旱站数为预报对象的预报模型,研究OSR方法的预报技巧。研究表明:OSR预报方法对秋季中国区域的干旱日数具有较高的预报技巧,距平相关系数(ACC)在全国大部地区均通过α=0.05的显著性水平检验,中国东部地区整体预报水平高于西部地区,ACC在中国区域平均达到0.45。对于秋季华西洪涝站数与华南干旱站数,OSR方法也体现出较好的预报能力,ACC分别达到0.71和0.55。此外,对华南区域干旱站数的独立预报检验表明,模型能较好地预报出2003-2007年秋季华南地区偏旱的趋势,但对干旱范围的预报有所低估。     

河北大茂山碘化银地面发生器增雪作业影响分析

利用常规气象资料、MICAPS资料和NECP/NCAR再分析资料,结合高斯模拟,分析了2012年11月10日唐县大茂山地基碘化银发生器增雪作业的作业条件。结果发现,此次天气背景为自西南向东北移动的冷涡云系,根据帕斯奎尔(Pasquill)稳定度分类法得出作业时间段大气处于中性层结状态;高斯模式模拟得出,有效的AgI浓度向上扩散范围高达3.0 km;作业点作业时段上空至3.2 km均处于上升气流区,计算出作业点发生器出口温度1.0℃。因冬季人工观测云底高度多为2.5~3.0 km,综合分析认为,该作业点的选址是合适的,此次作业条件较好,可以将催化剂输送到云中,起到催化作用。     

近50年火山喷发和太阳活动对我国气候影响的研究

利用特征向量分析与时序叠加分析和谱分析相结合的方法，分析了近50a来我国地面气温和降水场中火山喷发和太阳活动的气候信号，强烈的火山喷发导致全国大部分地区降温，喷发1a多以后降温最明显，并能持续约半年。除这个主信号以外，青藏高原、东南沿海和东北地区都可能出现较为复杂的温度变化，温度变化与太阳活动之间的联系更多地反映在二者的振荡关系上。在降水场中的火山信号较弱，表现为火山喷发后的秋冬季节南方地区降水偏多。在青藏高原积雪和深层地温的变化中，没有发现火山和太阳活动信号。     

南疆西部一次罕见暴雨过程的成因分析

利用常规观测资料、T639初始场资料、NECP 1°×1°再分析资料、FY-2静止卫星和天气雷达资料,分析了2010年9月16-20日南疆西部一次罕见的暴雨过程.结果表明,暴雨发生在南亚高压双体型(高压中心分别位于伊朗高原和青藏高原东部)及中亚低槽向南的切涡有利大尺度环流背景下,高、中及低空三支急流的有利配置为暴雨的产生提供了动力和水汽条件,中小尺度辐合与对流是暴雨发生的直接始作俑者.这次暴雨过程的水汽来源有3部分:较深厚的中亚低涡西南气流所携带的水汽,中低层哈密南部至南疆盆地偏东气流的水汽集聚与辐合和中高层中亚南部偏南风所携带的暖湿气流接力输送.其中,85％的水汽输送来自偏东和偏南气流.强对流发生在暖区一侧,暴雨落区位于TBB最大梯度区并与云迹风的高层辐散相对应.3个时段的强降水均由混合性降水回波造成.其中,有中小尺度回波发展,但移动路径和强回波中心的位置有所不同.