春末夏初南亚高压的形成过程及其与ENSO事件的联系   总被引：2，自引：1，他引：1  

何金海  刘伯奇  吴国雄 《大气科学》2014,38(4):670-684

利用ERA-Interim再分析资料,分析了春末夏初南亚高压建立过程的气候特征和可能机制,并讨论了ENSO事件冷、暖位相对南亚高压建立过程年际变化的影响。结果表明,第24候,气候平均的南亚高压形成于中南半岛东南部的对流层高层,这与菲律宾群岛南部和中南半岛局地对流的加强有关。一方面,菲律宾群岛南部对流加强能够在其北部产生负涡度源,在高空热带东风急流的作用下,其下游的南海地区出现负涡度,相应地出现闭合的高空反气旋,南亚高压初步形成。另一方面,中南半岛局地对流令南亚高压中心加强发展,并使其最终位于中南半岛上空。春末夏初菲律宾群岛附近对流的经向摆动决定了南亚高压的形成位置,而中南半岛局地对流的强度则控制着南亚高压的加强北抬。由于菲律宾南部和中南半岛的局地对流都受ENSO事件影响,因此在ENSO事件的冷、暖位相下,南亚高压的形态和位置在其建立过程中差异明显。在暖事件发生后,热带对流在加里曼丹岛以东发展,南亚高压形成于苏门答腊群岛北部至泰国湾上空,此时中南半岛对流偏弱,限制了南亚高压的北抬发展;而在冷事件发生后,热带对流在菲律宾群岛中部加强,同时南亚高压形成于中南半岛中部上空,随后中南半岛对流迅速加强,令南亚高压明显西伸北抬。因此,ENSO事件的冷、暖位相对春末夏初南亚高压的形成位置有显著影响。  相似文献   

近红外波段凝结核性质对雨滴散射特性的影响   总被引：1，自引：0，他引：1  

刘西川  高太长  韩小冬 《气象科学》2010,30(1):42-47

用M ie散射理论,在已知大气气溶胶粒子的折射率基础上,计算并讨论大气气溶胶以及在其上凝结形成的雨滴的散射相函数、散射效率因子等散射特性。结果表明,对流层中气溶胶粒子的散射能力依次为水滴,冰晶,海洋性粒子,沙尘性粒子,水溶性粒子,煤烟。对于在可溶性核上凝结形成的雨滴,海洋性核的散射能力强于水溶性核的散射能力。由不可溶性核凝结形成雨滴的散射能力依次为煤烟核、冰晶核和沙尘性核。纯水雨滴的散射能力介于沙尘性核和冰晶核之间,强于海洋性核。该结论可以为光学测雨仪器在不同地区条件下的参数设置提供依据。  相似文献   

Condensation particle counting below 2 nm seed particle diameter and the transition from heterogeneous to homogeneous nucleation     

Paul M. Winkler  Aron Vrtala  Paul E. Wagner 《Atmospheric Research》2008,90(2-4):125-ICNAA07

Particle detection by condensation particle counters (CPCs) is ultimately limited by the onset of homogeneous nucleation. At vapour supersaturations around the homogeneous nucleation limit the diameter of critical clusters is typically about 2 nm. It is widely assumed that only particles larger than critical clusters can be activated by vapour condensation and the general detection limit of CPCs is therefore currently accepted to be around 2 nm particle diameter. Using an expansion type CPC with n-propanol as working fluid we investigated the transition from heterogeneous to homogeneous nucleation, clearly showing that particles are activated much before the onset of homogeneous nucleation, even at particle diameters as small as 1.4 nm. For particle diameters below 2 nm we have usually found condensation particle counting to be influenced by the simultaneous presence of ions as generated in a bipolar diffusion charger. In this paper we illustrate how the presence of ions influences particle number concentration measurement and how ions can be removed in order to obtain accurate seed particle number concentrations for particle diameters down to 1 nm.  相似文献   

Formation of disk- and bowl-shaped igneous Ca,Al-rich inclusions: Constraints from their morphology,textures, mineralogy and modelling     

《Chemie der Erde / Geochemistry》2019,79(4):125523

Calcium-aluminum-rich inclusions (CAIs) are the oldest Solar System solids dated that formed by evaporation, condensation, aggregation and, sometimes, melting processes near the protoSun, and were subsequently dispersed throughout the protoplanetary disk by still poorly-understood mechanism(s). Here we report on the discovery of disk- and bowl-shaped centimeter-sized igneous CAIs in CV (Vigarano type) carbonaceous chondrites. Igneous CAIs of these shapes are not expected for crystallization of melt droplets in a low gravity field of the protoplanetary disk. We have tested several models for the formation of disk- and bowl-shaped igneous CAIs including: collision, aerodynamic deformation and shock flattening. We conclude that these CAIs resulted from aerodynamic deformation of CAI-like melt droplets and propose the following multistage formation scenario: (1) nearly complete melting and acceleration of CAIs at <30 km/s in the CAI-forming region having approximately solar dust/gas ratio; (2) aerodynamic deformation, ablation, deceleration, solidification at ∼30–40 K/min, Wark-Lovering rims formation, and deceleration of the CAIs entering a dust-rich inner disk wall; (3) radial drift of the solidified deformed CAIs towards the Sun; (4) heating and partial melting of the deformed CAIs by solar radiation that preserve their morphology; (5) cooling and crystallization of CAIs at ∼2 K/h; (5) radial transport of CAIs from their formation region to the outer disk.  相似文献   

On Helmert’s methods of condensation   总被引：2，自引：0，他引：2  

B. Heck 《Journal of Geodesy》2003,77(3-4):155-170

Helmerts first and second method of condensation are reviewed and generalized in two respects: First, the point at which the effects of topographical and condensation masses are calculated may be situated on or outside the topographical surface; second, the depth of the condensation layer below the geoid is arbitrary. While the first extension permits the application of the generalized model to the evaluation of airborne and satellite data, the second one gives an additional degree of freedom which can be used to provide a smooth gravity field after reducing the observation data. The respective formulae are derived for the generalized condensation model in both planar and spherical approximation. A comparison of the planar and the spherical model shows some structural differences, which are primarily visible in the out-of-integral terms. Considering the respective formulae for the combined topographic–condensation reduction on the background of the density structure of the Earths lithosphere, the consequences for the residual gravity field are investigated; it is shown that the residual field after applying Helmerts second model of reduction is very rough, making this procedure unfavourable for downward continuation. Further considerations refer to the question of which sets of formulae should be used in geoid and quasigeoid determination. It is concluded that for high-precision applications the generalized spherical model, involving a depth of the condensation layer of between 20 and 30 km, should be superior to Helmerts second model of condensation, although it requires the direct calculation of the indirect effect, which is larger than in the case of Helmerts second method of condensation.  相似文献   

Observations of condensation growth determined by entity type mixing     

James W. Telford  Peter B. Wagner 《Pure and Applied Geophysics》1981,119(5):934-965

It has been speculated for many years that the development of the droplet spectra in cloud is probably influenced by mixing processes. Various theoretical attempts to broaden the droplet spectra by mixing parcels with different velocity histories has shown that that particular effect is small. Similarly, very simpleuniform entrainment procedures did not lead to cloud drop size spectra which were broad enough, although by producing cloud drop size distributions with a double mode these models did substantially improve the drop size spectra of earlier adiabatic models which only exhibited a single mode.Recently a model based on entraining entities representing moving parcels of cloud air within the cloud was detailed byTelford andChai (1980). This study showed that the mixing in of dry air at cumulus turrets could lead to vertical cycling of diluted parcels, and that this cycling, with continual entrainment across the parcel boundaries, will produce much larger drops, as well as smaller drops of all sizes, in the droplet spectra. The entity entrainment concept studied there appears to apply to the observations of stratus cloud discussed in this paper.This paper presents data taken in marine stratus off the California coast which give a particularly clear example of how such droplet spectra modification occurs in practice. Both large drops, and the spread of the spectra to smaller sizes, occur in relation to other variables in such a way as to be consistent with an entity entrainment explanation, with no other obvious possibility.In a marine stratus cloud just over 200 m thick and many tens of miles in extent we find clear evidence that dry air is mixing in at cloud tops. Strong vertical motion is to be found in the cloud, large sized drops are found in cloud parcels where the mixing gives lower droplet concentrations, and there is evidence that newly formed cloud parcels are warmer and contain many more smaller droplets.The observations show that immediately following entrainment of dry air drop diameters are not reduced appreciably, but, in the same parcels, drop concentrations have been reduced by a factor of ten or more. Further down in the cloud big drops, able to start growth by coalescence, are found associated with low total droplet concentrations.Overall, it seems likely from the consideration of these observations that the formation of the large drops which lead to precipitation processes in clouds depends critically on the mixing in of dry air at cloud tops, and very little on the size of the small drops resulting from the condensation nucleus counts. As a conclusion it appears reasonable to state that if entrainment occurs at cloud tops, then big drops will be formed!  相似文献   

A comparative study on the growth of cloud drops by condensation using an air parcel model with and without entrainment     

In-Young Lee  H. R. Pruppacher 《Pure and Applied Geophysics》1977,115(3):523-545

During a study of the growth of cloud drops by condensation the evolution of cloud drop size spectra with height above cloud base was determined for maritime aerosols, and for continental aerosols containing aerosol particles of mixed composition. Air parcel models were used in which the parcel was either completely closed to mass and heat transfer (strictly adiabatic models), or open to heat transfer and to partial or complete mass transfer (entrainment models). It was found that adiabatic models and models which consider the entraining of air devoid of aerosol particles predict drop size distributions which are considerably narrower than those observed in non-precipitating cumulus clouds, and have only a single maximum. On the other hand, relative broad drop size distributions and distributions with a double maximum — as they are observed in atmospheric clouds — are predicted if the entrainment of both air and aerosol particles are considered in the condensation model. Our results support the findings ofWarner (1973) which were obtained for a purely maritime aerosol.  相似文献   

孟加拉湾季风爆发对南海季风爆发的影响Ⅱ:数值试验   总被引：3，自引：1，他引：3       下载免费PDF全文

刘屹岷  陈仲良  吴国雄 《气象学报》2003,61(1):10-19

通过数值试验研究了孟加拉湾季风爆发期间该地区旺盛的对流凝结加热对南海季风爆发和副热带高压“撤出”南海的影响,结果证明在孟加拉湾地区引入模拟的对流凝结潜热使该地区出现了强烈的上升运动,引起了孟加拉湾季风的爆发。同时由于对凝结加热的非对称Rossby响应,在南海北部导致西风出现和增强及垂直上升运动。因低层水汽平流的共同作用下,在南海北部引起了对流的发展。而正是南海北部的凝结加热促使南海地区温度经向梯度逆转,使副热带高压脊面的倾斜从冬季型转为夏季型,即低层的副热带高压减弱南移。最后当对流在南海地区发展起来时,副热带高压移出南海地区。  相似文献   

Turbulent mixing condensation nucleus counter     

Rashid Mavliev 《Atmospheric Research》2002,62(3-4)

The construction and operating principles of the Turbulent Mixing Condensation Nucleus Counter (TM CNC) are described. Estimations based on the semiempirical theory of turbulent jets and the classical theory of nucleation and growth show the possibility of detecting particles as small as 2.5 nm without the interference of homogeneous nucleation. This conclusion was confirmed experimentally during the International Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle Counters (Vienna, Austria). Number concentration, measured by the Turbulent Mixing CNC and other participating instruments, is found to be essentially equal.  相似文献   

Nolan–Pollak type CN counters in the Vienna aerosol workshop     

J. L. Gras  J. Podzimek  T. C. O'Connor  K. -H. Enderle 《Atmospheric Research》2002,62(3-4)

Three “standard” Nolan–Pollak (N–P) and a modified N–P design condensation nucleus (CN) counters were included in the Vienna Workshop on Intercomparison of Condensation Nuclei and Aerosol Particle counters. These counters came from diverse backgrounds, namely programs in USA, Europe and Australia. In this work, principles of the operation and previous history of calibration of the N–P expansion counter are briefly reviewed and comparisons between the particular counters used in the workshop are presented and discussed. Counting agreement was found to be very good between the N–P counters, typically better than ±12% for a range of aerosol sizes and compositions from a minimum diameter of 4 nm. The independently calibrated GIV CNC-440 (modified N–P type counter) also agreed well with the N–P counters. The minimum size sensitivity of the N–P counter was examined showing a lower detection limit for insoluble (Ag) particles of around 2.6±0.3 nm diameter.  相似文献