2019年4月广州白云机场持续暴雨前对流层顶和平流层异常信号分析

利用欧洲中心ERA5再分析资料和广州白云机场自动观测系统降水资料,分析2019年4月白云机场持续暴雨前对流层顶和平流层的信号特征。分析发现,2019年4月中下旬,广州白云机场出现了3次持续时间长、降水量大的持续性暴雨过程,降水较往年同期显著偏多。研究结果表明,3次持续暴雨发生前,对流层顶高度出现了下降,平流层高位涡冷空气入侵,机场上空位涡升高;在环流场中,中低纬地区对流层顶和平流层东风偏强,向北和向下传播,广州白云机场终端区在暴雨发生前西风持续下传;广州白云机场上空暴雨发生前对流层顶至平流层位势高度正异常。暴雨发生前,平流层冷空气高位涡移入、对流层顶下降、西风的下传均有利于持续性暴雨的生成。     

A 1-D model of the formation and evolution of Polar Stratospheric Clouds

A 1-D model of the formation and seasonal evolution of Polar Stratospheric Clouds (PSCs) is described. The model considers PSCs of types 1 and 2 in the vertical range from 8 to 30 km and utilizes real temperature data. The micro-physical processes included in the model are the heterogeneous nucleation and condensation (or evaporation), while sedimentation, gas diffusion and vertical wind velocity are the processes responsible for transport. Model simulations have been compared with PSC data obtained by lidar at the South Pole: results for the winter 1990 are discussed. The different contribution of type 1 and type 2 PSCs to the measured backscattering coefficient has been evidenced. In the simulations, layers of NAT particles form when low values of the backscattering coefficient are measured; similarly, ice particles form when sharper and rapidly changeable structures with higher values of the backscattering coefficient are observed. Significant results on the condensation and depletion of HNO₃ and H₂O are presented. Water vapor profiles measured during winter 1990 are reproduced quite well.     

Beryllium-7 Deposition and Its Relation to Sulfate Deposition

Deposition of ⁷Be, a cosmogenic radionuclide, was observed at the Meteorological Research Institute in Tsukuba, Japan from 1986 to 1993 and compared with those of several chemical species observed in Tsukuba over the same period. We found a correlation between the monthly depositions of ⁷ Be and SO ₄ ² -, a major acidic species. The correlation was especially strong for late spring and fall, when both species had high depositional fluxes. This correlation was also observed in precipitation samples collected daily in 1992 at the same site. The cause of this correlation is discussed in connection with the fact that the stratospheric aerosol is composed largely of SO ₄ ² -. ⁷ Be is produced in the upper atmosphere, and detection of ⁷Be, especially in spring and fall in Japan, can be regarded as detection of stratospheric aerosol. However, we conclude that the bulk of the SO ₄ ² - observed did not have a stratospheric or an upper tropospheric origin. The correlation, therefore, may present a new question regarding acidic deposition: Why does the deposition of stratospheric aerosol in Japan coincide with that of nss-SO ₄ ² - originally from anthropogenic sources on the Earth's surface?     

Groundbased Doas UV/visible measurements at Kiruna (Sweden) during the sesame winters 1993/94 and 1994/95.

Zenith sky observations of O3, NO2, OClO and BrO are reported, which were performed at Kiruna (67.9°N, 21.1°E) within the SESAME winters 1993/1994 and 1994/95. For both winters large total amounts of OClO were observed inside the polar vortex at twilight, indicating the degree and the temporal variation of the halogen activation of the polar stratosphere. Occasionally OClO could also be observed outside the polar vortex, most likely due to export of halogen activated vortex air masses into the ambient stratosphere. BrO could also be detected in winter 1994/95, with the largest slant column amounts (5·1014/cm2) occuring in the polar vortex in mid-winter. Similar abundances of stratospheric BrO were observed at dusk and dawn, for both, air masses inside and outside the vortex. This observation is in reasonable agreement with previous studies on stratospheric BrO (observations and models) of Wahner et al. (1992), Arpag et al. (1994), Krug et al. (1996), and Lary et al. (1996a,b), but partly in disagreement with those of Solomon et al. (1989), Fish et al. (1995), and Sessler et al. (1996).     

Northern Hemisphere Sudden Stratospheric Warming and Its Downward Impact in Four Chinese CMIP6 Models

Using the World Meteorological Organization definition and a threshold-based classification technique,simulations of vortex displacement and split sudden stratospheric warmings(SSWs)are evaluated for four Chinese models(BCC-CSM2-MR,FGOALS-f3-L,FGOALS-g3,and NESM3)from phase 6 of the Coupled Model Intercomparison Project(CMIP6)with the Japanese 55-year reanalysis(JRA-55)as a baseline.Compared with six or seven SSWs in a decade in JRA-55,three models underestimate the SSW frequency by~50%,while NESM3 doubles the SSW frequency.SSWs mainly appear in midwinter in JRA-55,but one-month climate drift is simulated in the models.The composite of splits is stronger than displacements in both the reanalysis and most models due to the longer pulse of positive eddy heat flux before onset of split SSWs.A wavenumber-1-like temperature anomaly pattern(cold Eurasia,warm North America)before onset of displacement SSWs is simulated,but cold anomalies are mainly confined to North America after displacement SSWs.Although the lower tropospheric temperature also displays a wavenumber-1-like pattern before split SSWs,most parts of Eurasia and North America are covered by cold anomalies after split SSWs in JRA-55.The models have different degrees of fidelity for the temperature anomaly pattern before split SSWs,but the wavenumber-2-like temperature anomaly pattern is well simulated after split SSWs.The center of the negative height anomalies in the Pacific sector before SSWs is sensitive to the SSW type in both JRA-55 and the models.A negative North Atlantic Oscillation is simulated after both types of SSWs in the models,although it is only observed for split SSWs.     

赤道东太平洋弯曲急流区质点轨迹及混沌运动机制

利用运动学模型 ,研究了弯曲急流控制参数为定常和发生周期扰动时的流体质点运动轨迹以及混沌现象的产生机制。发现弯曲急流控制参数为定常时 ,流体质点的运动为规则的周期运动 ;而控制参数发生扰动时 ,可以发生流体质点在不同特征区的穿行 ,流体质点的运动具有混沌特性。弯曲急流的相速、振幅发生周期扰动均可使流体质点的运动出现混沌特性。作者从运动学上对弯曲急流区的漂流浮标混沌特性给出了解释。     

Variability of Near-Ground Ozone Concentrations During Cold Front Passages – a Possible Effect of Tropopause Folding Events

The analysis of surface ozone variability requires besides chemicalstudies the consideration of meteorological conditions and dynamicprocesses. Our research focuses on the mechanisms in connection with coldfront passages. A statistical study and case studies of cold front passageswere carried out at six German ground-based sites during the year 1990.After the passage of cold fronts three typical developments of thenear-ground ozone concentrations could be identified. Usually the ozoneconcentrations decrease due to advection of clean air masses or due toenhanced cloudiness preventing the photochemical production of ozone,chemical destruction by nitrogenoxides, and heterogeneous chemistry. In somecases the concentrations increased by reason of downward mixing of ozoneenriched air intruded from the stratosphere into the troposphere bytropopause foldings. For a few cases no modification set in. The decreasewas mostly twice as strong as the increase. The latter was between 4 and 8ppb on the average. Special emphasis is given to the transport ofstratospheric ozone down to the ground. There is no direct evidence forstratospheric ozone at ground level, because it cant be distinguished fromthe tropospheric one, but from case studies circumstantial evidence is foundin favour of it. As an example of increasing ozone behind the passage ofcold fronts one case study typical of all other case studies is presented.It shows the characteristic properties of the corresponding fronts, whichare fast movement, a vertical split structure and strong convection.     

Modulation of the Aleutian–Icelandic Low Seesaw and Its Surface Impacts by the Atlantic Multidecadal Oscillation

Early studies suggested that the Aleutian–Icelandic low seesaw(AIS) features multidecadal variation. In this study, the multidecadal modulation of the AIS and associated surface climate by the Atlantic Multidecadal Oscillation(AMO) during late winter(February–March) is explored with observational data. It is shown that, in the cold phase of the AMO(AMO|-),a clear AIS is established, while this is not the case in the warm phase of the AMO(AMO|+). The surface climate over Eurasia is significantly influenced by the AMO's modulation of the Aleutian low(AL). For example, the weak AL in AMO|-displays warmer surface temperatures over the entire Far East and along the Russian Arctic coast and into Northern Europe,but only over the Russian Far East in AMO|+. Similarly, precipitation decreases over central Europe with the weak AL in AMO|-, but decreases over northern Europe and increases over southern Europe in AMO|+.The mechanism underlying the influence of AMO|-on the AIS can be described as follows: AMO|-weakens the upward component of the Eliassen–Palm flux along the polar waveguide by reducing atmospheric blocking occurrence over the Euro–Atlantic sector, and hence drives an enhanced stratospheric polar vortex. With the intensified polar night jet, the wave trains originating over the central North Pacific can propagate horizontally through North America and extend into the North Atlantic, favoring an eastward-extended Pacific–North America–Atlantic pattern, and resulting in a significant AIS at the surface during late winter.     

黄海绿潮分布年际变化特征分析

2008-2015年,连续8年在黄海海域暴发大规模绿潮,但因暴发时间、规模及漂移路径的不同,对沿海地区造成的环境影响和经济损失大不相同。本文利用EOS/MODIS卫星的多通道资料,采用NDVI算法获取绿潮信息,给出了2007年以来5-8月所有无云或少云晴朗天气下黄海海面绿潮的分布情况。黄海绿潮覆盖面积变化每年呈现单峰值分布,MODIS卫星在5月中旬至6月初首次发现绿潮,随后30~40 d内达到覆盖面积峰值,7月快速消退,8月上旬完全消失。2007年绿潮出现首年覆盖面积极低,发现绿潮时面积均未超过50 km2;2008年和2009年绿潮覆盖面积峰值分别为3 110 km2和4 075 km2,自此绿潮灾害成为新的海洋环境事件;2010-2012年绿潮暴发规模异常低值,各年覆盖面积峰值均未超过1 800 km2,但从2013年开始绿潮规模逐渐攀升,到2015年绿潮覆盖面积峰值达5 629 km2,持续可达98 d,覆盖面积和持续时间为历年之最。绿潮漂移路径可归纳分为3类:2008年和2011年绿潮主体先北向漂移越过34°30'N后,西北向垂直于岸线漂移,主要对连云港、日照和青岛造成较大影响;2009年和2012年绿潮主体先北向漂移越过35°N后,东北向平行于岸线漂移,故只有少许绿潮上岸;2010年、2013-2015年绿潮主体北向漂移至近岸后东北向沿岸漂移,对日照、青岛和荣成沿海造成大面积影响。所有年份绿潮影响范围均限于南黄海内,东侧边界最远未越过124.2°E。     

Vapour source and spatiotemporal variation of precipitation isotopes in Southwest Spain

The δ²H and δ¹⁸O composition of 77 precipitation samples collected between January 2014 and April 2019 from two sites across the Guadalquivir Basin, SW Spain, were analysed. The first site is located in an urban area of Seville at 100 km distance to the Atlantic coast and the second site is located in a dune area of the Doñana National Park a few kilometres from the coast. Sampling was performed within intervals of at least 14 days if rain occurred but frequently intervals were longer according to the rainfall incidence. Samples from both sites are available for the period February 2016 to June 2018 with six samples containing identical rain events at both locations. Precipitation weighted averages and local meteoric water lines produced by weighting and non-weighting regression methods are presented for its use in hydrological applications. Results show a remarkably high variability in δ²H and δ¹⁸O values and precipitation weighted average d-excess values of 11.8‰ and 13‰ at the sites Plaza de España and Doñana, respectively. Temperature and amount effects were found to be weak. A significant influence of secondary evaporation for single rainfall events during summer was identified by enriched isotopic signatures with reduced d-excess values plotting close or below the global meteoric water line. Backward trajectory analysis of 115 days with daily rainfall above 3 mm yield a predominant Atlantic Ocean vapour source with negligible Mediterranean influence and therefore, d-excess variability is attributed to the different ocean surface conditions of relative humidity and sea surface temperature. Parallel sampling indicate very similar isotopic signatures at both sites and point to the existence of thermal effects of the Plaza de España site in Seville city during the summer season.