Unusual coastal ocean cooling in the northern South China Sea by a katabatic cold jet associated with Typhoon Mujigea(2015)

This study deals with a unusual cooling event after Typhoon Mujigea passed over the northern South China Sea(SCS) in October 2015. We analyze the satellite sea surface temperature(SST) time series from October 3 to 18,2015 and find that the cooling process in the coastal ocean had two different stages. The first stage occurred immediately after typhoon passage on October 3, and reached a maximum SST drop of –2℃ on October 7 as the usual cold wake after typhoon. The second stage or the unusual extended cooling event occurred after 7d of the typhoon passage, and lasted for 5d from October 10 to 15. The maximum SST cooling was –4℃ and occurred after 12d of typhoon passage. The mechanism analysis results indicate that after landing and moving northwestward to the Yunnan-Guizhou Plateau(YGP), Typhoon Mujigea(2015) met the westerly wind front on October 5. The lowpressure and positive-vorticity disturbances to the front triggered meridional air flow and low-pressure trough,thus induced a katabatic cold jet downward from the Qinghai-Tibet Plateau(QTP) passing through the YGP to the northwestern SCS. The second cooling reached the maximum SST drop 4d later after the maximum air temperature drop of –9℃ on October 11. The simultaneous air temperature and SST observations at three coastal stations reveal that it is this katabatic cold jet intrusion to lead the unusual SST cooling event.

Interdecadal changes in the frequency of winter extreme cold events in North China during 1989–2021

全球变暖背景下,极端天气气候事件的变化受到关注.本文研究发现, 1989-2021年期间,华北地区极端冷日数在2003和2013年发生了年代际变化.极端冷日数先增加后减少. 2003-2012年,西伯利亚-乌拉尔高压偏强,极地西风急流偏弱,有利于冷空气南下入侵华北地区,华北极端冷日数偏多.而在1989-2002年和2013-2021年,情况相反.虽然三个时段华北极端冷日的强度没有显著差异,但与其相联系的冷空气强度变得更强, 2013-2021年冷空气中心区域往西北扩张到了贝加尔湖以西地区.

The Interactions of Two Cold Atmospheric Plasma Jets

This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electrode distance d, three different interaction modes, attraction, repulsion and combination, were observed. It is shown that the interaction modes of the two jets are principally affected by the electrodes, the gas flow rate, the plasma jets and the power supply frequency.

Development of a new atmospheric pressure cold plasma jet generator and application in sterilization

This paper reports that a new plasma generator at atmospheric pressure, which is composed of two homocentric cylindrical all-metal tubes, successfully generates a cold plasma jet. The inside tube electrode is connected to ground, the outside tube electrode is connected to a high-voltage power supply, and a dielectric layer is covered on the outside tube electrode. When the reactor is operated by low-frequency （6 kHz-20 kHz） AC supply in atmospheric pressure and argon is steadily fed as a discharge gas through inside tube electrode, a cold plasma jet is blown out into air and the plasma gas temperature is only 25-30℃. The electric character of the discharge is studied by using digital real-time oscilloscope （TDS 200-Series）, and the discharge is capacitive. Preliminary results are presented on the decontamination of E.colis bacteria and Bacillus subtilis bacteria by this plasma jet, and an optical emission analysis of the plasma jet is presented in this paper. The ozone concentration generated by the plasma jet is 1.0× 10^16cm^-3 which is acquired by using the ultraviolet absorption spectroscopy.

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study,a coaxial transmission line resonator is constructed,which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon,nitrogen,or even air,respectively.Although the different kinds of working gas induce the different discharge performance,their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods,and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 10^(18)m^(-3).The tail region of plasma jets all contain a large number of active particles,like NO,O,emitted photons,etc,but without O_(3).The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields,the ionization wave propulsion,and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets.The parameters of plasma jet could be modulated by adjusting microwave power,modulation pulse parameters(modulation frequency and duty ratio),gas type and its flow rate,according to the requirements of application scenarios.

Effects of cryogenic cold air jet cutting on chip break in metal machining

The half-dry cutting employs cryogenic compressed air cooled down to (10 to 40) and a micro-dosage of lubricating oil, called cryogenic cold air jet cutting was studied. On the basis of a comparative experiment on dry and cryogenic cold air jet cuttings carried out for grade 45 steel, the effects of cryogenic cold air jet on the breaking of chips were discussed. The experimental results reveal that in the valid ranges of pressure and temperature, the cryogenic cold air jet widens the chip breaking areas effectively. When the cutting depth is not greater than 1 mm, the influence of chip breaking is much more significant. But different injecting angle of cold air has different influence on the chip-break. From the experiment, the optimized jet injecting angle, temperature effecting range and pressure working range of cold air are obtained. These results can offer a foundation for industrial manufacturing.

Influences of the inner diameter of the solid shielding tube on the characteristics of the radio-frequency cold atmospheric plasma jet

Active control of the local environment of the cold atmospheric plasma(CAP) jet is of great importance in actual applications since the CAP operates in an open atmosphere with the inevitable entrainment of the surrounding cold air. In this paper, the solid shielding effects of the cylindrical quartz tubes with different inner diameters on the characteristics of the CAP jets driven by a radio-frequency(RF) power supply are studied experimentally. The experimental results show that the total length of the shielded plasma jet can be increased significantly by an appropriate combination of the quartz tube inner diameter and that of the plasma generator nozzle exit with other parameters being unchanged. This phenomenon may be qualitatively attributed to the loss of diffusion of the charged particles in the radial direction under different inner diameters of the quartz tubes. Compared with the plasma free jet, the plasma shielding jet is produced with optimized parameters including longer plasma jet length, higher concentrations of chemically reactive species, higher rotational, vibrational, and electron excitation temperatures when the inner diameters of the solid shielding tube and the generator nozzle exit are the same. A maximum plasma jet length of 52.0 cm is obtained in contrast to that of 5.0 cm of the plasma free jet in this study. The experimental results indicate that the solid shielding effect provides a new method for the active control of the local environment of the RF-CAP jet operating in an open atmosphere.

Cold Plasma Jet Construction to Use in Medical, Biology and Polymer Applications

Cold atmospheric pressure plasma jets were capable of generating cold plasma plumes that were not confined by electrodes, which make them very enticing for biological, medical and polymer applications. During this work, experimental study of a low frequency, atmospheric plasma-jet discharge in nitrogen has been presented. The experimental operation of this device was conducted with commercially neon power supply. The discharge process operated by using nitrogen as input gas with different flow rates. The experimental results showed that the maximum plasma jet length of 7 mm was detected at 3 Kv input voltage corresponding to 14 l/min as a nitrogen flow rate. The effect of distance from nozzle, nitrogen flow rate and input voltage on the plasma temperature was examined. The gas temperature decreased continuously as the flow rate of nitrogen increasing from 2 l/min to 14 l/min at 3 Kv as a fixed input voltage.

2021年11月7—9日辽宁省极端雨雪天气分析

选用常规气象观测资料、人工加密观测资料和NCEP/NCAR格点资料,对2021年11月7—9日辽宁省极端雨雪天气进行诊断分析。结果表明:东北冷涡和地面气旋为此次极端雨雪天气的主要影响系统,对流层中低层辐合、高层辐散以及强的冷暖气流交汇,是产生极端雨雪天气的主要原因;高低空急流耦合和高空辐散抽吸作用,配合东北冷涡动力抬升作用,暖湿低空急流沿冷垫爬升,进一步加强了上升运动。暖湿急流为此次极端雨雪天气提供了充沛的水汽条件,暖湿急流的增强对应水汽辐合作用增强,配合低层冷垫和东北冷涡的动力抬升作用,对降雪有明显增幅作用;地面辐合线沿地形分布,触发了此次极端强降雪天气。地形阻挡导致地面冷空气堆积形成冷垫,是极端降雪天气发生的重要原因。温度层结差异是鞍山、岫岩雨雪相态差异的主要原因。具有冻结层特征的低层冷垫,为鞍山极端暴雪提供了有利的温度层结条件;融化层厚度和地面温度是岫岩出现冻雨的关键因素。

华北局地大暴雨过程中多个β中尺度对流系统发生发展对比分析

利用常规地面高空观测、多普勒雷达、风廓线、VDRAS(Variational Doppler Radar Analysis System)和NCEP再分析资料,对2018年8月5—6日副热带高压(以下简称副高)控制下华北一次局地大暴雨过程中多个β中尺度对流系统触发和发展机制进行了分析。结果表明:这次大暴雨发生在副高控制下,处于高温、高湿气团中,大气层结极不稳定。暴雨由多个相继发展的中尺度对流系统造成,分别是太行山迎风坡上西南—东北向、华北平原地区保定一带南北向、保定至霸州附近西南—东北向和以雄安新区为中心东西向原地生消的准静止MCS-Ⅰ、MCS-Ⅱ、MCS-Ⅲ和MCS-Ⅳ,均属于β中尺度。在相似的环境中,不同中尺度对流系统触发机制有较大差异,太行山迎风坡上的MCS-Ⅰ是由近地层偏东暖湿气流在迎风坡与山风形成的辐合抬升触发;由辐射差异和前期强降水形成的局地冷池受MCS-Ⅰ影响再次加强后,其出流与环境风形成的两条地面辐合线分别触发了MCS-Ⅱ和MCS-Ⅲ,并组织对流沿辐合线呈带状发展;而超低空偏东风增强叠加冷池出流在地形抬升作用下促使沿山暖湿气团进一步抬升,使得原本消亡的MCS-Ⅰ再次重建。MCS-Ⅳ发展最旺盛、持续时间最长,是大暴雨中心的直接制造者,一方面MCS-Ⅱ与MCS-Ⅲ、MCS-Ⅰ与MCS-Ⅳ的两次合并过程,是MCS-Ⅳ增强、持久的重要原因;另一方面边界层偏东风急流为MCS-Ⅳ的发展提供了水汽和不稳定能量等有利条件,同时推动其左前方中尺度涡旋的发展,导致MCS-Ⅳ所在地的气旋性涡度大大增加,加强了以急流轴为中心的垂直次级环流发展,造成MCS-Ⅳ的发展维持,形成华北平原地区以雄安新区为中心的东西向大暴雨带。

介质管介电常数对大气压Ar冷等离子体射流特性的影响

通过二维流体模型,研究介质管的介电常数对大气压氩气冷等离子体射流放电性质的影响.结果表明,射流在介质管内外具有不同的放电性质.当射流在介质管内时,电离波沿着介质管内表面向管口传播,因而呈现环状结构,其传播速度先增加后减小.介电常数越大,环形结构的半径越小,电子密度越低,射流传播的速度也越小.当射流喷出管口后,射流的传播速度迅速提升,然后减小,介电常数越大,提升越快.随着射流的传播,环状结构不断收缩,最终消失.研究结果对大气压冷等离子体源的设计和优化具有一定的理论指导意义.

2023年麦收期河南省连阴雨的气候特征和可能成因

2023年麦收期河南省出现了罕见的连阴雨天气,降水和阴雨日数异常偏多,分别为自1961年以来的历史第五位和第二位。分析连阴雨的可能气候成因,主要结论如下:(1)造成连阴雨的环流形势为欧亚中高纬度西高东低,乌拉尔山高压脊持续发展并出现阶段性阻塞,东北冷涡活跃,冷空气能持续南下,西太平洋副热带高压(以下简称副高)偏北、偏强且异常偏西,来自副高西北侧边缘的暖湿气流和冷空气在河南省交汇。(2)副高偏强、偏北、偏西是由偏强、偏北、偏大、偏东的南亚高压和偏强、偏北的东亚副热带西风急流(以下简称西风急流)的引导所致,而东南亚对流层中高层的暖中心偏大、偏北和偏东且呈东西向带状分布,使南亚高压形成了上述的特征。暖中心和东北冷涡的共同作用,使东亚中高层的气温梯度增大,进而加强了西风急流。(3)2023年前期的La Ni1a事件有利于麦收期副高偏北,但不利于副高偏强和明显偏西。麦收期由于台风扰动由泰国湾至菲律宾群岛以东的热带西太平洋对流活跃释放的凝结潜热较多,以及麦收期前期的春季和麦收期伊朗高原至青藏高原的地面感热和潜热较强,使暖中心形成了上述的特征,进而决定了南亚高压和副高的特征。(4)2023年麦收期北大西洋海温偏高,以及北大西洋三极子为负位相,导致了乌拉尔山高压脊持续发展并出现阶段性阻塞,麦收期前期的春季和麦收期伏尔加河至贝加尔湖西北侧地面感热和潜热偏强,而下游贝加尔湖东南侧至鄂霍次克海地面感热和潜热偏弱一定程度上导致上述两区域分别出现了大范围的位势高度正距平和负距平。

多结构形式小通道液冷板散热性能对比研究

小通道冷板作为一种有效的热控装置,已被广泛应用于高热流密度电子器件的热管理领域。文中以通道特征尺寸为2 mm的串行、并行以及射流冲击/小通道混合液冷板为研究对象,旨在获取这3种结构形式冷板的极限散热能力和流动阻力损失的差异。研究结果表明:在相同冷却工质流量条件下,3种冷板的散热功率由大到小依次为串行通道、射流冲击/小通道混合液冷板、并行通道;串行通道冷板的板内阻力损失明显大于其余两者;在综合考虑压力损失和散热性能的基础上,根据不同热源热流密度条件选择合适的冷板结构,有望满足特定应用的需求。该研究可供小通道液冷板的设计和优化参考。

辽东半岛一次湿下击暴流过程分析

2020年9月11日辽东半岛南部发生了一次强对流天气,并出现了湿下击暴流,大连金州得胜站地面最大阵风达到21.7 m·s^(-1)。本文利用常规气象资料、大连多普勒天气雷达资料、欧洲中期天气预报中心第5代全球再分析资料和高分辨率中尺度数值模拟资料,对此次湿下击暴流天气过程的环流背景、对流风暴发生发展环境及其回波特征等进行分析。结果表明:(1)此次强对流天气发生在北上台风变性形成的高空冷涡东部西南风与东南风的切变线上,地面辐合线和低空急流是触发初始对流的直接系统,初始对流在高空辐散耦合作用下发展加强;对流系统西移登陆至地面冷池与其东部暖空气之间形成锋生带上,辐合抬升作用加强,促使对流系统组织化程度更高、强度更强。(2)高温、高湿、对流不稳定层结是对流系统发生发展的有利环境条件。强对流发生前,探空曲线“上干下湿”、呈“V”型分布,抬升凝结高度明显下降;湿下击暴流发生时,径向速度垂直分布为中层径向辐合、低层辐散;瞬时大风出现前后,大连多普勒天气雷达在高、低仰角均探测到超过45 dBZ强反射率因子缺口,高仰角强反射率因子缺口先于低仰角出现,通过监测高仰角强反射率因子的变化,对湿下击暴流有一定的预警作用。

LYZH型急冷箱数值模拟与结构优化

为适应加氢反应器大型化趋势,开发了集旋流、撞击及挡板分流等功能于一体的LYZH型急冷箱,其结构由上至下依次为旋流冷氢管、冷氢盘、喷射管和接液盘。采用CFD软件对LYZH型急冷箱进行数值模拟研究,结果表明LYZH型急冷箱具有优秀的传热性能及气液混合性能。为使LYZH型急冷箱的性能得到进一步提升,对其结构进行了优化,最优结构的旋流冷氢管中径为2218.9 mm、喷射管直径为526.9 mm以及接液盘到冷氢盘高度为175.4 mm。与原始结构相比,最优结构的传热性能提高7.61%,压力降降低14.4%,LYZH型急冷箱的综合性能得到较大改善。

宜昌市致洪中尺度极端降水成因分析

极端降水对河流防洪调控、水库蓄水泄洪等具有重要的影响,研究极端降水成因成为强化区域洪水资源管理的必要环节。基于多源观测资料和ERA5再分析资料,利用HYSPLIT后向轨迹模式和锋生强度诊断等方法,对2023年8月26日夜间宜昌市致洪中尺度极端降水成因进行分析。结果表明:①此次极端降水过程关键影响系统为低空急流、超低空急流、边界层冷空气和中尺度低涡。强降水可以分为中尺度低涡新生、低空急流发展,冷暖对峙、冷锋南下,低涡中心东移3个阶段。②此次过程中低层主要有4条暖湿输送通道,强降水区水汽通量超800 kg/(m·s),可降水量超70mm。③强降水时段低层相对涡度正值中心与垂直速度负值中心基本重合,加之锋生作用增强,强降水中心低层垂直速度达-7.1 Pa/s。④强降水时段,地形过渡带附近形成θ_(se)(假相当位温)能量锋区,垂直方向上出现高能舌,800 hPa附近中心强度达360 K以上。⑤中尺度地形形成了“西北冷干、东南暖湿”中尺度温湿锋区,并起到了阻挡抬升和触发作用,使强降水出现在山前喇叭口内。研究成果可为汛期区域洪水资源管理策略制定提供依据。

2021年1月与2024年1月我国东部极端寒潮发生原因及机制探讨

伴随全球变暖和有卫星观测记录以来北极秋季海冰密集度的下降,近几年,东亚地区极端降温事件频繁发生。基于北极涛动指数、北极海冰密集度及温度、位势高度和风场等大气环流数据,研究2021年1月和2024年1月我国极端寒潮的时空变化特征及其原因机制。2021年1月1日至9日,2024年1月17日至24日,我国东部地区(115°00′~120°00′E,20°00′~37°30′N)均出现极端寒潮,最低温异常分别达到-9.028℃和-7.574℃,降温中心分别集中在蒙古高原南部和秦岭北部。2021年1月我国东部地区平均气温降至-3.8℃,达到21世纪以来的次低温纪录。本文基于美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)的再分析资料,得出西风带的异常减弱致使西风带对高纬度冷空气的阻拦作用减弱。2021年、2024年寒潮爆发时位于西伯利亚、太平洋西北部的高压中心和华北地区低压中心均出现显著增强,导致位于西伯利亚的冷空气的南移,致使我国东部地区出现寒潮现象。2024年1月极端寒潮现象显示于气温经验正交分解(Empirical Orthogonal Function,EOF)的第一模态(29.33%),而EOF分解的第二模态(14.92%)显示2021年出现降温现象。回归分析表明北极涛动指数和北极海冰的下降与1月我国东部地区气温之间存在较强的关系,北极涛动负相位及北极海冰的减少也是促使北极冷空气南下的重要因素。异常强劲的北风、减弱的西风急流及对应高压中心的移动共同作用导致了极地寒流入侵我国大陆地区,是造成2021年1月和2024年1月我国大陆地区极端天气事件的主要原因之一。

Preparation of novel Ni-Ir/γ-Al_2O_3 catalyst via high-frequency cold plasma direct reduction process

The novel Ni-Ir/γ-Al2O3 catalyst, denoted as NIA-P, was prepared by high-frequency cold plasma direct reduction method under ambient conditions without thermal treatment, and the conventional sample, denoted as NIA-CR, was prepared by impregnation, thermal calcination, and then by H2 reduction method. The effects of reduction methods on the catalysts for ammonia decomposition were studied, and they were characterized by XRD, N2 adsorption, XPS, and H2-TPD. It was found that the plasma-reduced NIA-P sample showed a better catalytic performance, over which ammonia conversion was 68.9%, at T = 450℃, P = 1 atm, and GHSV = 30, 000 h^-1. It was 31.7% higher than that of the conventional NIA-CR sample. XRD results showed that the crystallite size decreased for the sample with plasma reduction, and the dispersion of active components was improved. There were more active components on the surface of the NIA-P sample from the XPS results. This effect resulted in the higher activity for decomposition of ammonia. Meanwhile, the plasma process significantly decreased the time of preparing catalyst.

Pulsed cold plasma-induced blood coagulation and its pilot application in stanching bleeding during rat hepatectomy

This paper presents plasma-induced blood coagulation and its pilot application in rat hepatectomy by using a home-made pulsed cold plasma jet. Experiments were conducted on blood coagulation in vitro, the influence of plasma on tissue in vivo, and the pilot application of rat hepatectomy. Experimental results show that the cold plasma can lead to rapid blood coagulation. Compared with the control sample, the plasma-induced agglomerated layer of blood is thicker and denser, and is mostly composed of broken platelets. When the surface of the liver was treated by plasma, the influence of the plasma can penetrate into the liver to a depth of about 500 μm. During the rat hepatectomy, cold plasma was proved to be effective for stanching bleeding on incision. No obvious bleeding was found in the abdominal cavities of all six rats 48 h after the hepatectomy. This implies that cold plasma can be an effective modality to control bleeding during surgical operation.

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons

Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air.The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes.The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons.Moreover,for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave,the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas,frequencies of pulsed modulator,duty cycles of pulsed microwave,peak values of input microwave power,and even by using different materials of dielectric tubes.In addition,the emission spectrum,the plume temperature,and other plasma parameters are measured,which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.