集合动力因子对登陆台风“莫拉克”(0908)暴雨 落区的诊断与预报研究

“莫拉克”是2009年登陆我国热带气旋中影响范围最广、造成损失最大的台风.“莫拉克”带来的强降水导致台湾南部发生50年来最严重的水灾,福建、浙江等省的部分站点过程雨量超过50年一遇.因此,在台风暴雨(强降水)预报中,能否准确把握其落区就显得尤为重要.本文首先利用中尺度非静力数值模式WRF对台风“莫拉克”进行高分辨率数值模拟(三层嵌套,最高分辨率为2 km).模式较好地再现了台风中心的移动路径、强度;模拟的降水分布区域与实况也较为相符.利用再分析资料及模拟的高分辨率资料对暴雨成因进行诊断分析,表明造成此次强降水过程的水汽主要由西南季风输送,并且垂直运动旺盛,贯穿整个对流层.根据集合动力因子预报方法,运用广义湿位温、对流涡度矢量垂直分量及水汽散度通量对暴雨落区进行了诊断和预报,发现广义湿位温等值线的“漏斗状”区域与暴雨落区对应关系显著;基于NCEP-GFS每日四次的预报场资料,利用对流涡度矢量和水汽散度通量做出的降水落区预报表明,二者对降水落区均有一定的指示意义.强降水主要位于对流层中低层对流涡度矢量垂直积分量的梯度大值区附近,其时间演变与观测降水的演变具有相当高的一致性;水汽通量散度抓住了垂直运动和水汽散度这两个引发暴雨的关键因子,对降水的发生范围和强降水极值中心的判断更为准确.这三个动力因子都可以为“莫拉克”台风暴雨(强降水)落区提供信号,对台风暴雨落区具有一定的诊断和预报意义.     

1215号“布拉万”台风暴雨及降水非对称性分布的成因分析

利用中尺度非静力模式WRF对2012年第15号台风“布拉万”在中国东北地区造成的暴雨过程进行了数值模拟,结合观测资料对模拟结果进行了验证,利用模式输出的高分辨率资料,对“布拉万”台风造成的强降水及其非对称性分布的成因进行了诊断分析。结果表明,模式很好地再现了台风登陆过程中的路径、强度变化和降水分布,受中纬度西风槽带来的干冷空气影响,“布拉万”台风登陆后的降水和环流结构具有明显的不对称性,降水主要集中在台风中心西北侧的能量锋区附近。水汽散度通量和水汽螺旋度能够较好地描述强降水过程的发生、发展及其非对称性分布的时空特征,在强降水区,水汽散度通量表现为正值强信号,而水汽螺旋度表现为负值强信号,在非降水区和弱降水区,两者均表现为弱信号。等熵位涡分析显示,对流不稳定只是此次台风暴雨前期和初始阶段的不稳定条件,而湿位涡(MPV)的湿斜压项(MPV₂)则是暴雨增强和出现非对称性分布的主要机制。在暴雨形成过程中,由于冷空气侵入造成了在台风环流西北侧湿等熵面的陡立倾斜和水平风垂直切变的增强,导致了气旋性涡度的显著增强,气旋性涡度增强造成的强烈上升运动将降水区东南侧输送过来的暖湿空气向上输送,从而导致了暴雨的发生,这其中条件性对称不稳定是降水得以加强的一种重要不稳定机制。     

北雁荡山地形对2020年“黑格比”台风暴雨影响的数值模拟

2020年第4号台风“黑格比”在浙南登陆后过境北雁荡山期间在山区引发了特大暴雨。基于中尺度数值模式WRFV4.0.2对台风进行高分辨率数值模拟，分析北雁荡山地形对此次台风暴雨的作用，并设置了升降地形敏感性试验。结果表明：数值试验较好地模拟了台风移动及特大暴雨的落区和强度，台风大风区明显不对称分布，台风登陆后第一、四象限过境山区，其东侧强偏南气流向山区输送了充足水汽。台风登陆前山区低空存在一条由台风内核拖曳出的狭长螺旋辐合带，水汽通量辐合与风场辐合相一致。台风眼墙过境时沿着降水中心的迎风坡有强烈上升运动，动力条件极好，水汽输送带由近地面向对流层低层延展，山区有零星对流单体触发加强。台风后部环流影响时在高海拔山区风速减弱、绕流激发了中尺度低涡，强降水中心迎风坡上出现持续性、停滞不动的强正涡度中心，是特大暴雨发生的主要原因。地形敏感性试验中无地形时降水减幅40%～50%，地形高度翻倍降水增幅超过60%。     

一次江淮暴雨的数值模拟及暴雨落区的诊断分析

利用MM5模式对2003年7月一次江淮暴雨过程进行了数值模拟,结果表明：MM5对本次暴雨落区的模拟较为成功。应用模拟结果对假相当位温、水汽通量散度、z-螺旋度及湿位涡等几个综合性物理量进行了诊断,得出的主要结论为：本次暴雨发生在高能舌的前部、能量锋区南缘和低空急流左前方三者叠加的区域;水汽通量散度比较好地反映本次暴雨的强度和落区;z-螺旋度不仅能反映降水系统,对降水系统的移动也有预报指示意义;本次暴雨过程中湿斜压性和涡度垂直分量与热力不稳定对湿位涡有同等大小的贡献。     

台风“桑美”的数值模拟和地形敏感性试验

用WRF模式对0608号台风“桑美”进行了数值模拟研究,较为成功地模拟出了台风路径和降水,但模拟的台风中心气压远高于实况。为研究“桑美”登陆期间地形的抬升作用对其降水及结构的影响,通过改变特定区域内的地形高度设计了一组敏感性试验。结果表明,台风登陆过程中地形抬升作用对台风降雨量有显著的增幅作用;台风中心位势涡度、气流垂直上升速度、水平水汽通量散度明显增大;地形抬升机制在台风登陆时刻达到最强。     

2008年“凤凰”台风暴雨的水汽和螺旋度分析

本文利用NCEP/NCAR1°×1°再分析格点资料和降水实况数据,对"0808"号台风"凤凰"在登陆福建前后引发浙闽沿海地区的暴雨过程进行水汽和螺旋度分析。结果表明:东海和南海是此次强降水的主要水汽供应源。水汽输送辐合主要出现在低层,950 hPa水汽通量散度幅合场对强降水落区有较好的指示作用。台风登陆福建之前,东边界的水汽输入起主导作用;登陆福建后,南边界的水汽输入逐渐起主导作用。800 hPa螺旋度正值区对未来6 h强降水落区有很好的指示意义。同时,螺旋度强度演变对未来6 h的降水强度有较好的正相关关系。水汽收支演变表明净水汽输入量对于降水强度演变的指示效果不及螺旋度,但是整层净水汽输入明显减小时,可预见其后降水强度减小。     

动力因子对2006“碧利斯”台风暴雨的诊断分析

本文利用2006年登陆台风"碧利斯"暴雨过程高分辨率数值模拟资料, 结合湿热力平流参数、广义对流涡度矢量垂直分量、水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量、热力切变平流参数和 Q *矢量散度等8个动力因子, 对"碧利斯"台风暴雨进行诊断分析。结果指出:(1)8个动力因子在"碧利斯"台风强降水区均表现为强信号, 其中, 水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量等动力因子与降水强度的相关系数均达0.99以上, 与总云水物质的相关系数也均达0.97以上, 而热力切变平流参数与上述二者的相关系数最低, 达0.5左右;(2)8个动力因子中, Q *矢量散度随降水强度先增大后减小, 与"霰融化成雨水造成雨水增长"微物理过程随降水强度的变化相似, 热力切变平流参数随降水强度呈现"增大—减小—再增大"的变化特征, 而其他6个动力因子均呈现单调增长趋势, 与"雨水碰并云水造成雨水增长"微物理过程随降水强度的变化相类似;(3)总体看来, 水汽螺旋度、热力螺旋度、散度垂直通量、热力散度垂直通量4个动力因子与降水强度及雨水收支相关的总的云微物理过程转化率对应更好, 因此, 对降水的指示意义也更好。     

“碧利斯”暴雨增幅高分辨率数值模拟及诊断分析

利用中尺度非静力数值模式ARPS (Advanced Regional Prediction System),对2006年第4号强热带风暴“碧利斯”的登陆过程,尤其是登陆后的暴雨增幅过程开展了高分辨率数值模拟,并利用观测资料对模拟结果进行了验证,进一步基于该高分辨率模拟资料对该暴雨增幅过程开展了诊断分析.结果表明,ARPS模式较好地模拟再现了“碧利斯”的登陆过程以及登陆后在广东、江西、湖南三省交界处引发的暴雨增幅过程;散度垂直通量和湿位涡的大值区与暴雨增幅地区均有良好的对应关系,对强降水落区有较好指示意义,其中散度垂直通量的对应关系更好.湿位涡不仅很好地反映了与暴雨增幅相关的湿位涡分布,同时也很好地反映了“碧利斯”环流本身所对应的湿位涡分布特征.     

一次华北暴雨过程的数值模拟及水汽螺旋度和水汽涡度收支应用分析

运用WRF模式对2009年8月发生在华北地区的一次暴雨过程进行了数值模拟,按照性质的不同对模拟降水进行了研究,还进行了湿度场试验,最后利用模式输出结果对水汽螺旋度和水汽涡度收支进行了诊断分析。结果表明,数值模式比较合理地再现了本次暴雨天气过程。显式降水在模拟的总降水量中占了很大的比重,但是在暴雨爆发初期,积云降水起了重要作用。对流层中层的水汽饱和程度对模拟降水性质及降水量大小有重要影响,显式降水一般发生在空气饱和程度较高的区域,而位势不稳定则是诱发积云降水的主要原因。对流层中低层水汽螺旋度的强度变化在一定程度上代表了降水系统的强弱变化,其高值区与强降水落区在出现的时间和空间上都存在较好的一致性。水汽涡度收支对于水汽涡度及水汽螺旋度的变化具有很好的指示意义,可以作为预报降水的一个动力指标。     

四川暴雨过程动力因子指示意义与预报意义研究

本文利用2010年8月18~19日四川盆地西部地区一次引发了泥石流等次生灾害的暴雨天气过程的数值模拟资料及0.5°×0.5°分辨率、每6 h一次的GFS(Global Forecast Model)预报资料,结合集合动力因子预报系统中的广义对流涡度矢量垂直分量、质量散度、垂直螺旋度、质量垂直螺旋度、水汽垂直螺旋度、热力垂直螺旋度、湿热力平流参数、密度散度垂直通量、散度垂直通量、热力散度垂直通量、水汽散度通量、广义 Q 矢量散度等12个动力因子成员对此次暴雨过程进行诊断分析和预报研究,结果显示:(1)集合动力因子预报系统中的动力因子对此次降水落区诊断效果良好;(2)各动力因子区域均值随时间的变化曲线都能表现出降水区域均值随时间变化曲线双峰形态,其中,广义 Q 矢量散度、水汽垂直螺旋度、热力垂直螺旋度、质量垂直螺旋度、垂直螺旋度与降水的相关系数较大(达0.9以上),对此次降水的诊断效果较好;(3)动力因子对此次强降水过程的发展演变具有一定的预报能力。     

Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO₃ ^-(H₂O) _n and NO₃ ^-(H₂O) _n with HNO₃. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N₂-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH^-, O₂ ^-, O₃ ^-, CO₄ ^-, CO₃ ^-, CO₃ ^-H₂O, NO₃ ^-, and NO₃ ^-H₂O were measured relative to the known rate k=3.0×10^-9 cm³ s^-1 for the reaction of O^- with HNO₃. The main product ion of the reaction of CO₃ ^-H₂O with HNO₃ was found to be (CO₃HNO₃)^- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO₃ ^- with HNO₃ three product ions were observed, namely NO₃ ^-, (NO₃OH)^-, and (CO₃HNO₃)^-. The reaction rate coefficients for CO₃ ^-H₂O (1.7×10^-9 cm³ s^-1) and NO₃ ^-H₂O (1.6×10^-9 cm³ s^-1) were found to be close to the collision rate. The measured k values for bare CO₃ ^- (1.3×10^-9 cm³ s^-1) and NO₃ ^- (0.7×10^-9 cm³ s^-1) are somewhat smaller. The collisional dissociations of CO₃ ^-(H₂O) _n , NO₃ ^-(H₂O) _n (n=1, 2), (CO₃HNO₃)^- and (NO₃HNO₃)^-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO₃ detection was also affected by the conversion of CO₃ ^-(H₂O) _n to NO₃ ^-(H₂O) _n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.     

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions: Temperature dependences of the rate coefficients

Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:

The solubility of SO2 and the dissociation of H2SO3 in NaCl solutions

The pK ₁ ^* and pK ₂ ^* of H₂SO₃ have been determined in NaCl solutions as a function of ionic strength (0.1 to 6 m) and temperature (5 and 25 °C). The extrapolated values in water were found to be in good agreement with literature data. The experimental results have been used to determine the Pitzer interaction parameters for SO₂, HSO ₃ ^- and SO ₃ ^- in NaCl solutions. The resultant parameters for NaHSO₃ and Na₂SO₃ were found to be in reasonable agreement with the values for NaHSO₄ and Na₂SO₄. It, thus, seems reasonable to assume that the interactions of Mg²⁺ and Ca²⁺ with HSO ₃ ^- and SO ₃ ^- can be estimated from the values with HSO ₄ ^- and SO ₄ ^- until experimental values are available. Measurements of pK ₁ ^* and pK ₂ ^* in artificial seawater were found to be in good agreement with the calculated values using the derived Pitzer parameters. It is, thus, possible to make reasonable estimates of the activity coefficients of HSO ₃ ^- and SO ₃ ^- ions and pK ₁ ^* and pK ₂ ^* for the ionization of H₂SO₃ in marine aerosols.     

Rate constants for reactions of OH radicals with some Br-containing haloalkanes

Rate constants have been measured for the gas-phase reactions of hydroxyl radical with two halons and three of their proposed substitutes and also with CHClBr-CF₃ using the discharge-flow-EPR technique over the temperature range 298–460 K. The following Arrhenius expressions have been derived (units are 10^–13 cm³ molecule^–1 s^–1): (9.3 _–0.9 ^+1.0 ) exp{–(1326±33)/T} for CHF₂Br; (7.2 _–0.6 ^+0.7 ) exp{–(1111±32)/T} for CHFBrCF₃; (8.5 _–0.8 ^+0.9 ) exp{–(1113±35)/T} for CH₂BrCF₃; (12.8 _–1.2 ^+1.5 ) exp{–(995±38)/T} for CHClBrCF₃. The rate constants at 298 K have been estimated to be <2×10^–17 cm³ molecule^–1 s^–1 for CF₃Br and CF₂Br—CF₂Br. The atmospheric lifetimes due to hydroxyl attack have been estimated to be 5.5, 3.3, 2.8, and 1.2 years for CHF₂Br, CHFBr—CF₃, CH₂Br—CF₃ and CHClBr—CF₃, respectively.     

Chemical characteristics of wet precipitation at an urban site of Guangzhou, South China

The pH variation and chemical characteristics of rainwater were investigated from January 2006 to December 2006 at an urban site of Guangzhou, South China. The rainwater was typically acidic with a volume-weighted mean pH value of 4.49, which ranged from 3.52 to 6.28. The volume-weighted mean equivalent concentration of components followed the order: SO₄²⁻ > Ca²⁺ > Cl⁻ > NH₄⁺ > Na⁺ > NO₃⁻ > K⁺ > Mg²⁺ > F⁻, indicating that SO₄²⁻, Cl⁻ and NO₃⁻ were the main anions, while Ca²⁺ and NH₄⁺, were the main cations. Ca²⁺ and NH₄⁺ were major neutralization constituents of the precipitation. Furthermore, correlation analysis and principal component analysis method were performed to identify possible common sources of major ions. Sources of the major ions were assessed based on enrichment factor method.     

Analysis of Carbon Dioxide Variations in the Atmosphere of Srednja Bijambarska Cave,Bosnia and Herzegovina

The results of one year’s monitoring in Srednja Bijambarska Cave (Bosnia and Herzegovina) are presented and discussed. Temporal variations of the carbon dioxide (CO₂) concentration are controlled by the switching between two ventilation regimes driven by outside temperature changes. A regression model with a simple perfectly mixed volume applied to a cave sector (“Music hall”) resulted in an estimate of ventilation rates between 0.02 h⁻¹ and 0.54 h⁻¹. Carbon dioxide input per plan surface unit is estimated by the model at around 50 × 10⁻⁶ mh⁻¹ during the winter season and up to more than 1000 × 10⁻⁶ mh⁻¹ during the first temperature falls at the end of summer (0.62 μmoles m⁻² s⁻¹ and 12.40 μmoles m⁻² s⁻¹ for normal conditions respectively). These values have been found to be related to the cave ventilation rate and dependent on the availability of CO₂ in the surrounding environment. For airflow close to zero the values of CO₂ input per plan surface have a range in the order of magnitude of a few units × 10⁻⁶ mh⁻¹. Based on two experiments, the anthropogenic contribution from cave visitors has been calculated, at between 0.35 l_CO2 min⁻¹ person⁻¹ and 0.45 l_CO2min⁻¹person⁻¹.     

Quantitatives zur Elektrizitätserzeugung durch den Wasserfalleffekt auf Eis

Zusammenfassung Um die Wirksamkeit des Aufschlags von Wolkentröpfchen auf Eis (Faraday-Sohncke-Effekt) für die Elektrizitätserzeugung in Gewittern beurteilen zu können, werden quantitative Ladungsmessungen im Laboratorium beim Aufprall fallender Wassertropfen auf Hindernisse aus Eis unter möglichst variierten Bedingungen vorgenommen. Ein Tropfen von 20 mg und 20° C aus 75 cm Höhe befreit die Ladung von 3,6·10^–13 Coul. Während eine Änderung der Tropfentemperatur den Effekt wenig beeinflußt wird er stark reduziert, wenn man die Temperatur der Eisplatte kräftig erniedrigt, da der Tropfen schließlich sofort festfriert. Veränderung der Fallhöhe und der Tropfenmasse führt zu dem Ergebnis, daß in gewissem Bereich die getrennte LadungQ in Annäherung allein der kinetischen EnergieW des Tropfens proportional ist:Q=2,75·10^–16 Coul/erg·W für einen Tropfen von 20° C auf Eis von 0° C. Die Anwendbarkeit dieser Gleichung auf Wolkentröpfchen wird diskutiert. Messungen bei verringertem Reinheitsgrad des Wassers bestätigen die Erfahrung, daß gleichzeitig die befreite Ladung abnimmt.

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Summary To study the effect of the impact of cloud droplets upon ice (Faraday-Sohncke-effect) for the production of electricity in thunderstorms laboratory experiments were carried out under various conditions to measure quantitatively electric charges originating from the collision of falling water drops with ice. A droplet of 20 mg and 20° C falling from a height of 75 cm releases the charge of 3,6·10^–13 Coul. While the effect is not considerably influenced by a change of the temperature of the droplet it is strongly reduced if the temperature of the ice plate is lowered to such a degree that the droplet immediately freezes. Variation of falling-height and mass of droplets leads to the result that, in a certain range, the separated chargeQ is approximately proportional solely to the kinetic energyW of the droplet:Q=2,75·10^–16 Coul/erg·W for a droplet of 20° C on ice of 0° C. Applicability of this equation to cloud droplets is discussed. Measurements carried out with water of reduced purity confirm the experience that in such cases the released charge is smaller.

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Résumé En vue d'étudier quantitativement la production d'électricité orageuse par la chute de gouttelettes d'eau sur des grêlons (effet Faraday-Sohncke), les auteurs ont réalisé des expériences et mesuré la charge libérée lors de la chute de gouttelettes sur de la glace dans des conditions variées. Une goutte de 20 mg à 20° C, tombant de 75 cm de hauteur libère la charge de 3,6·10^–13 Coul. Tandis que l'effet ne dépend que peu de la température de la goutte, il est fortement réduit si la température de la glace s'abaisse, car la goutte se congèle alors aussitôt. Des essais avec des variations de la hauteur de chute et de la masse des gouttes ont en outre montré que la charge libéréQ est en première approximation proportionelle à la seule énergie cinétiqueW de la goutte:Q=2,75·10^–16 Coul/erg·W pour une goutte à 20° C tombant sur de la glace à 0° C. On discute l'application de la formule à des gouttelettes nuageuses. Des mesures faites avec de l'eau non pure confirment le fait connu que la charge libérée diminue alors.

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