基于Logistic回归和多指标叠加的短时强降水预报模型

大气低涡是造成我国南方地区暴雨洪涝的重要天气系统,大气低涡背景下的暴雨突发性、局地性强,其发生时间、强度和落区一直是气象预报业务的难点。为提高浙江省暴雨预报准确率,本文利用1979—2020年浙江省逐日格点降水观测数据和美国国家环境预测中心气候预测系统再分析数据集,首先分析了浙江省内近42 a由大气低涡造成的区域性暴雨事件(以下简称低涡型暴雨)的气候特征;然后将850 hPa垂直速度、水汽通量散度、速度散度、低空急流、切变线以及700 hPa垂直速度作为预报因子,基于“配料法”并结合逻辑回归方法构建了低涡型暴雨落区预报模型;最后基于该模型利用2021年欧洲中期天气预报中心预报产品进行暴雨落区预报,并使用同期实况降水进行了系统性检验和天气过程检验。结果表明,该模型总体性能较好,提前24 h和12 h时效的暴雨预报能力均有提升,可将12%的准确率和20%左右的命中率分别提升至14%和40%附近,漏报率从75%以上降至60%附近,但存在着一定程度的空报。

     

Generation and propagation of the ULF planetary-scale electromagnetic wavy structures in the ionosphere

In the present article, the results of theoretical investigation of the dynamics of generation and propagation of planetary (with wavelength 10³ km and more) ultra-low frequency (ULF) electromagnetic wave structures in the dissipative ionosphere are given. The physical mechanism of generation of the planetary electromagnetic waves is proposed. It is established, that the global factor, acting permanently in the ionosphere—inhomogeneity (latitude variation) of the geomagnetic field and angular velocity of the earth's rotation—generates the fast and slow planetary ULF electromagnetic waves. The waves propagate along the parallels to the east as well as to the west. In E-region the fast waves have phase velocities (2-20) km s⁻¹and frequencies (10⁻¹-10⁻⁴) s⁻¹; the slow waves propagate with local winds velocities and have frequencies (10⁻⁴-10⁻⁶) s⁻¹. In F-region the fast ULF electromagnetic waves propagate with phase velocities tens-hundreds km s⁻¹ and their frequencies are in the range of (10-10⁻³) s⁻¹. The slow mode is produced by the dynamoelectric field, it represents a generalization of the ordinary Rossby-type waves in the rotating ionosphere and is caused by the Hall effect in the E-layer. The fast disturbances are the new modes, which are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field and are connected with the large-scale internal vortical electric field generation in the ionosphere. The large-scale waves are weakly damped. The features and the parameters of the theoretically investigated electromagnetic wave structures agree with those of large-scale ULF midlatitude long-period oscillations (MLO) and magnetoionospheric wave perturbations (MIWP), observed experimentally in the ionosphere. It is established, that because of relevance of Coriolis and electromagnetic forces, generation of slow planetary electromagnetic waves at the fixed latitude in the ionosphere can give rise to the reverse of local wind structures and to the direction change of general ionospheric circulation. It is considered one more class of the waves, called as the slow magnetohydrodinamic (MHD) waves, on which inhomogeneity of the Coriolis and Ampere forces do not influence. These waves appear as an admixture of the slow Alfven- and whistler-type perturbations. The waves generate the geomagnetic field from several tens to several hundreds nT and more. Nonlinear interaction of the considered waves with the local ionospheric zonal shear winds is studied. It is established, that planetary ULF electromagnetic waves, at their interaction with the local shear winds, can self-localize in the form of nonlinear solitary vortices, moving along the latitude circles westward as well as eastward with velocity, different from phase velocity of corresponding linear waves. The vortices are weakly damped and long lived. They cause the geomagnetic pulsations stronger than the linear waves by one order. The vortex structures transfer the trapped particles of medium and also energy and heat. That is why such nonlinear vortex structures can be the structural elements of strong macroturbulence of the ionosphere.     

极移的地震激发研究

本文采用Harvard目录中1977－1994年间的地震有关参数，及Dahlen计算的地震引起地球惯量矩的变化有关公式，得到由地震引起的极移要比观测值小2个量级．单个地震引起的极漂移呈现随机特性，但它的累积效应却表现出长期的变化，地震引起激发极的运动方向趋向于130—150°E，它与观测极漂移的方向相反．本文这一分析结果将随着观测技术的不断改进及观测精度的提高而得到证实．当考虑地球液核效应时，地震也可能对地球液核自由章动产生影响．我们的分析表明，大地震的这一影响与VLBI检测出的结果相比较，它在观测精度以下．     

MHD oscillations in the solar spike radiation

In this paper the observed 1.4–1.6 s quasi-periodic oscillations in the spike radiation of the microwave outburst of 1981 May 16 are analysed in teras of MHD waves. We point out that the fast magnetoacoustic waves (“sausage” mode) propagating inside and outside a loop can modulate the magnetic field and the pitch angle distribution of the electron beams in the source region. The growth rate of electron-cyclotron-maser instability is then affected to give rise to the quasi-periodic oscillations. Quantitative estimates of relevant physical parameters are given.     

湖北省荆江大堤沿堤地基土的分类特征

利用脉动测振方法对荆江大堤堤面沿线土层进行了实测研究,并对实测记录进行了傅氏谱分析。结果表明,沿堤土层绝大部分属于二类土地基,但有若干堤段土层属于由松散的粉、细砂所构成的三类土地基,且饱和程度非常高,有产生管涌和地震动液化的可能,应予特别注意。     

大气和极移的高频变化比较

采用从1988－1999年的现代技术测定的高精度极移序列EOP（IERS97C04）推导出激发函数χ^m）和美国国家环境预测中心和美国国家大气研究中心（CNEP／NCAR）提供的大气角动量激发函数χp和χib^p，使用几种数据分析方法，分析了大气对极移高频振荡（12－42cpy)激发贡献，复数小波变换和功率谱分析表明，χ^m和χ^p序列在高频段内呈现比较强的谱峰，它们具有相似的谱特征，比较而言，χib^p在这个频率段内比χ^p要弱些，χ^m和χ^p之间的相关系数分别为0．75（逆向）和0．6（顺向），两个序列之间的平方相关谱的估计值分别在0．5－0．9之间（负频）和0．4－0．6（正频），相位谱表明χ^p(AAM)超前x^m一天左右，这些大气是极移高频变化的主要激发源，特别是在逆向运动上具有更大的贡献，由于它们之间位相差和振幅变化的不稳定性，说明可能存在AAM以外的其他激发源，这个问题有待进一步深入研究。χ     

On verification of the new criterion of adiabaticity by numerical simulation of acoustic propagation through the polar front

To assess the adiabaticity of acoustic propagation in the ocean is very important for acoustic field calculation (forward problem) and tomographic retrieving (inverse problem). A new criterion of adiabaticity is proposed recently (Shang et al., 2001). In this paper, numerical simulation has been conducted for acoustic propagation through the Polar Front to verify the new criterion. Numerical results on the f (frequency)-m (mode number) plan demonstrate that the new criterion works very well for this extremely non-gradual ocean structure.     

低涡切变影响下河湟谷地两类强降水环境条件及成因对比

利用2018—2020近三年青海河湟谷地低涡切变影响下强降水天气个例地面观测、NCEP 1°×1°再分析、FY-2G云图相当黑体亮温温度、模式及雷达拼图等资料,对比分析相同环流背景影响下不同类型强降水环境条件和成因差异,以及初步评估模式预报能力。结果表明:伴有雷暴、冰雹、雷暴大风等混合性强降水天气称为强降水Ⅰ型,以纯短时强降水为主的强降水天气称为强降水Ⅱ型。低涡切变是两种类型强降水的影响系统,强降水Ⅰ型400～300 hPa高空冷平流入侵促使低涡切变系统加强东移,地面冷锋发展在河湟谷地形成锢囚锋。强降水Ⅱ型受副热带高压西进阻挡,低涡切变系统和地面冷锋减弱消失;强降水Ⅰ型主要具有较强的高空干冷急流、高的下沉对流有效位能,较高的700 hPa和400 hPa温差以及强的垂直风切变均为强对流发生提供动力条件,产生的强天气以风雹类为主,而强降水Ⅱ型具有较高的0℃层和-20℃层高度、较高的抬升凝结高度,产生的强天气以短时强降水为主;强降水Ⅰ型云图特征主要表现为午后发展起来组织化程度高的冷涡云系,相当黑体亮温(TBB)初始中心数值在-45～- 35℃,发展阶段TBB下降至-75～-40℃,强降水Ⅱ...