The Seasonal Prediction of the Exceptional Yangtze River Rainfall in Summer 2020

During June and July of 2020, the Yangtze River basin suffered from extreme mei-yu rainfall and catastrophic flooding. This study explores the seasonal predictability and associated dynamical causes for this extreme Yangtze River rainfall event, based on forecasts from the Met Office GloSea5 operational forecast system. The forecasts successfully predicted above-average rainfall over the Yangtze River basin, which arose from the successful reproduction of the anomalous western North Pacific subtropical high (WNPSH). Our results indicate that both the Indian Ocean warm sea surface temperature (SST) and local WNP SST gradient were responsible for the westward extension of the WNPSH, and the forecasts captured these tropical signals well. We explore extratropical drivers but find a large model spread among the forecast members regarding the meridional displacements of the East Asian mid-latitude westerly jet (EAJ). The forecast members with an evident southward displacement of the EAJ favored more extreme Yangtze River rainfall. However, the forecast Yangtze River rainfall anomaly was weaker compared to that was observed and no member showed such strong rainfall. In observations, the EAJ displayed an evident acceleration in summer 2020, which could lead to a significant wind convergence in the lower troposphere around the Yangtze River basin, and favor more mei-yu rainfall. The model forecast failed to satisfactorily reproduce these processes. This difference implies that the observed enhancement of the EAJ intensity gave a large boost to the Yangtze River rainfall, hindering a better forecast of the intensity of the event and disaster mitigation.     

Assessing the Influence of the ENSO on Tropical Cyclone Prevailing Tracks in the Western North Pacific

Using a statistical model for simulating tropical cyclone (TC) formation and a trajectory model for simulating TC tracks, the influence of the El Nino-Southern Oscillation (ENSO) on the peak-season (July-September) TC prevailing tracks in the western North Pacific basin is assessed based on 14 selected El Nino and 14 selected La Nina years during the period 1950-2007. It is found that the combination of statistical formation model and a trajectory model can simulate well the primary features of TC prevai...     

西风爆发时赤道西太平洋的热量平衡：个例分析

The responses of sea surface temperature (SST) in the western equatorial Pacific warm pool to the west erly wind bursts (WWBs) play an important role in the relationship between WWB and ENSO. By using da ta collected from eight buoys of TOGA (Tropical Ocean-Global Atmosphere)-COARE (Coupled Ocean-Atmosphere Response Experiment), the heat balances of the upper ocean in the western equatorial Pacific around 0°. 156°E during two WWB events were calculated according to Stevenson and Niiler＇s (1983) method. In both events, SST increased before and after the WWBs, while decreased within the WWBs. The SST amplitudes approximated to l℃. Although sometimes the horizontal heat advections may become the biggest term in the heat balance, the variation of SST was dominated by the surface heat flux. On the other aspect, some different features of the two events are also revealed. The two cases have different variation of mixed layer depth. The depth of mixed layer is almost double in the first case (35 m to 70 m), which is caused by Ekman convergence, while only 10m increments due to entrainment in the second one. There are also differences in the currents structure. The different variations of thermal and currents struc ture in the mixing layers accounted for the different variation of the heat balance during the two events, es pecially the advection and residue terms. The seasonal variation of SST in this area is also investigated sim ply. The first WWB event happened just during the seasonal transition. So we considered that it is a normal season transition rather than a so-called anomaly. That also suggested that the seasonal distinction of the WWB is worthy of more attention in the researches of its relationship to ENSO.     

The 30–60-day Intraseasonal Oscillations over the Subtropical Western North Pacific during the Summer of 1998简

The features of 30-60-day convection oscillations over the subtropical western North Pacific （WNP） were investigated, along with the degree of tropical-subtropical linkage between the oscillations over the WNP during summer 1998. It was found that 30-60-day oscillations were extremely strong in that summer over both the subtropical and tro]~ical WNP, providing a unique opportunity to study the behavior of subtropical oscillations and their relationship to tropical oscillations. Further analyses indicated that 30-60-day oscillations propagate westwards over the subtropical WNP and reach eastern China. In addition, 30-60-day oscillations in the subtropics are affected by those over the South China Sea （SCS） and tropical WNP through two mechanisms： （1） direct propagation from the tropics into the subtropics; and （2） a seesaw pattern between the tropics and subtropics, with the latter being predominant.     

城市化对华北地区最高, 最低气温和日较差变化趋势的影响

利用华北地区255个一般站和国家基本、 基准站1961\_2000年的实测资料, 经过质量检验和均一性订正后, 将所有台站根据人口和台站地理位置分为5个类别, 分析了这5个类别台站和国家基本、 基准站地面平均气温、 最高、 最低气温的年和季节变化趋势以及城市化影响。结果表明： 华北全部台站的年平均气温、 最高、 最低气温均呈增加趋势, 且以最低气温上升最为明显, 导致年平均日较差呈现明显下降。就城市化影响而言, 平均气温、 最低气温变化趋势中城市热岛效应加强因素的影响明显, 但城市化对最高气温趋势影响微弱, 个别台站和季节甚至可能造成降温。在国家基本、 基准站观测的年平均气温和年平均最低气温上升趋势中, 城市化造成的增温分别为0.11℃·(10a)-1和0.20℃·(10a)-1, 对全部增温的贡献率分别达39.3%和52.6%。各类台站的四季平均气温和最低气温序列中城市化影响均造成增温。城市化增温以冬季为最大, 夏季最小。城市化还导致乡村站以外的各类台站日较差减小, 近40年华北地区国家基本、 基准站年平均和秋、 冬季平均气温日较差明显下降均由城市化影响造成的。     

黑龙江省中尺度数值预报业务系统

黑龙江省气象台于2001年8月引进了MM5模式，并结合业务和服务的实际需要对其有关参数进行了确定，建立了黑龙江省中尺度数值预报业务系统。已经在黑龙江省气象台实时运行，并应用到短期预报的业务工作中。系统运行稳定，预报结果有一定的参考价值。     

河北省极值气温变化特征

利用河北省60个气象观测站资料,对全省近50年极值气温变化特征进行了分析,结果表明:极端最高气温线性变化趋势不明显,但年代际变化特征突出,而极端最低气温线性升高趋势明显。低于-30℃的极端寒冷日呈线性减少趋势,而高于40℃的极端炎热日线性变化趋势不明显,但年代际变化特征突出,20世纪90年代后期以来呈多发的特点。最低气温出现偏冷段(-10℃)的天数呈线性减少趋势,出现在偏暖段(20～30℃)的天数呈线性增加趋势,在其他界限气温的天数变化趋势不明显。最高气温出现在偏冷段(-30～0℃)的天数呈明显减少趋势,在其他界限气温的天数变化趋势不明显。河北省无霜期、无冰冻期均呈明显延长趋势,平均每10年分别延长4.5天、4.6天。年平均最高气温、最低气温和平均气温都呈显著的线性升高趋势,平均每10年分别升高0.21℃、0.45℃、0.30℃,低温升温速率明显大于高温升温速率。日较差呈逐年减小趋势,平均每10年减小0.25℃。空间上最低气温表现为全省明显升高,而最高气温升温主要集中在中北部和东部沿海地区,南部升温不明显,日较差大部分地区为逐渐减小趋势。     

2003年夏季淮河流域梅雨期西太平洋副高结构和活动特征及动力机制分析

通过资料分析和诊断, 揭示了在2003年6～7月淮河流域暴雨期间, 西太平洋副高相对偏北并且呈现南北变化相对稳定、东西变化明显的特征; 强劲而稳定少动的中纬度西风急流使得西太平洋副高难以北抬, 从而造成了淮河流域降雨带的稳定少动. 同时, 分析表明每一次雨锋的出现伴有高层南亚高压的东伸, 并诱发500 hPa西太平洋副高西伸至我国沿海, 导致淮河流域多雨, 江南干旱高温.分析还发现高、低空副热带高压影响天气系统发展的如下机制: (1) 沿30°N东伸的高层南亚高压脊在东部30°N以北地区引起辐散和上升, 在30°N以南地区引起辐合和下沉; (2) 江南高层的辐合下沉气流在中低空的辐散增强了局地的负涡度, 诱发西太平洋副高西伸; (3) 沿增强了的西太平洋副高西北侧的偏西南气流在30°N以北辐合, 增强了局地的上升运动, 为暴雨的产生创造了大尺度的背景流场; (4) 副高西北侧的暴雨加强了低空的南风和高层的北风, 从而使高层东伸的南亚高压和低层西伸的西太平洋副高在我国东部稳定维持.     

An Optical Disdrometer for Measuring Present Weather Parameters

A new present weather identifier（PWI） based on occlusion and scattering techniques is presented in the study. The present weather parameters are detectable by the meteorological optical range（MOR） approximately up to 50 km and by droplets with diameters ranging from 0.125 mm to 22 mm with velocities up to 16 m s-1. The MOR error is less than 8% for the MOR within 10 km and less than 15% for farther distances. Moreover, the size errors derived from various positions of the light sheet by the particles were checked within ± 0.1 mm ± 5%. The comparison shows that the MOR, in a sudden shower event, is surprisingly consistent with those of the sentry visibility sensors（SVS） with a correlation coefficient up to 98%. For the rain amounts derived from the size and velocity of the droplets, the daily sums by the PWI agree within 10% of those by the Total Rain Weighing Sensor（TRwS205） and the rain gauge. Combined with other sensors such as temperature, humidity, and wind, the PWI can serve as a present weather sensor to distinguish several weather types such as fog, haze, mist, rain, hail, and drizzle.     

东昆仑山东段北坡河流阶地发育及其与构造隆升的关系

河流系统的发育往往能反映相关地质作用的细节.对东昆仑山东段北坡众多河流阶地及其沉积物的研究表明, 该区在早更新世晚期昆仑-黄河运动之后形成的东西向盆岭相间的地貌特征奠定了早期河流为东西向外流水系的基础; 中更新世晚期以来的又一次强烈构造抬升事件———共和运动, 导致昆仑山北坡各主要河流迅速溯源侵蚀发展, 伴随河流袭夺而形成现今的水系格局; 晚更新世晚期存在一段相对较长的构造稳定期, 河谷普遍发生堆积作用, 形成分布广泛且厚度较大的晚更新世冲积层; 接近全新世以来构造运动频繁而隆升的幅度趋于减弱, 形成了5级河流阶地, 并且阶地的发育类型普遍为以高级阶地(T₅) 为基座的上叠阶地, 河流至今未能切穿晚更新世稳定期形成的厚冲积层.