Meteorological conditions and polar stratospheric clouds over Yakutsk in winter 2004/05

Regular observations of polar stratospheric clouds were started at a lidar stratospheric station in the city of Yakutsk. According to lidar measurements in the winter of 2004/05, thick aerosol layers in the lower stratosphere appeared over this region quite frequently. They were episodically observed as pearl clouds. In November 2004, polar stratospheric clouds were observed at the stratospheric temperatures that were much higher than those at which particles of the polar stratospheric clouds could condense. Analysis of air-mass trajectories that simultaneously passed over Yakutsk at different altitudes on the days of polar stratospheric cloud observations showed that clouds could be formed over the Norwegian Sea at altitudes of about 18–21 km, where the stratosphere was the coldest, and then were transported to Yakutsk by wind during 4–5 days.     

Observation of polar stratospheric clouds over Obninsk in December 2012

In late December 2012 a blocking anticyclone followed by the event of minor stratospheric warming, set in the troposphere over West Siberia and, after that, over the European part of Russia. As a result of the deformation of a polar stratospheric vortex, the temperature in the lower stratosphere over Obninsk dropped below the threshold of the formation of polar stratospheric clouds. The lidar measurements of temperature, ozone values, and aerosol characteristics in the middle atmosphere were carried out at the lidar station during this atmospheric event. In three cases, polar stratospheric clouds (PSCs) referred to NAT I_a type according to the sounding results, were registered at the height of about 20 km. No considerable decrease in the ozone concentration in the area of PSC formation was revealed in these measurements.     

A review of global stratospheric aerosol: Measurements, importance, life cycle, and local stratospheric aerosol

Stratospheric aerosol, noted after large volcanic eruptions since at least the late 1800s, were first measured in the late 1950s, with the modern continuous record beginning in the 1970s. Stratospheric aerosol, both volcanic and non-volcanic are sulfuric acid droplets with radii (concentrations) on the order of 0.1–0.5 µm (0.5–0.005 cm^− 3), increasing by factors of 2–4 (10–10³) after large volcanic eruptions. The source of the sulfur for the aerosol is either through direct injection from sulfur-rich volcanic eruptions, or from tropical injection of tropospheric air containing OCS, SO₂, and sulfate particles. The life cycle of non-volcanic stratospheric aerosol, consisting of photo-dissociation and oxidation of sulfur source gases, nucleation/condensation in the tropics, transport pole-ward and downward in the global planetary wave driven tropical pump, leads to a quasi steady state relative maximum in particle number concentration at around 20 km in the mid latitudes. Stratospheric aerosol have significant impacts on the Earth's radiation balance for several years following volcanic eruptions. Away from large eruptions, the direct radiation impact is small and well characterized; however, these particles also may play a role in the nucleation of near tropopause cirrus, and thus indirectly affect radiation. Stratospheric aerosol play a larger role in the chemical, particularly ozone, balance of the stratosphere. In the mid latitudes they interact with both nitrous oxides and chlorine reservoirs, thus indirectly affecting ozone. In the polar regions they provide condensation sites for polar stratospheric clouds which then provide the surfaces necessary to convert inactive to active chlorine leading to polar ozone loss. Until the mid 1990s the modern record has been dominated by three large sulfur-rich eruptions: Fuego (1974), El Chichón (1982) and Pinatubo (1991), thus definitive conclusions concerning the trend of non-volcanic stratospheric aerosol could only recently be made. Although anthropogenic emissions of SO₂ have changed somewhat over the past 30 years, the measurements during volcanically quiescent periods indicate no long term trend in non-volcanic stratospheric aerosol.     

基于CloudSat资料对中国低纬度陆地区域卷云物理特征的研究

利用2008年9月—2016年8月的CloudSat卫星资料对发生在我国低纬度陆地区域(5°~36.5°N,78°~124°E)的卷云物理特征进行统计分析,并分别讨论东部沿海、中部、西部3个子区域的卷云物理特征的季节变化。结果表明:卷云的整层发生率西部地区整体低于中部与东部沿海地区。3个子区域整层发生率均在夏季最高、冬季最低。卷云的主要发生高度在5.04~18.71 km,垂直分布中卷云发生率的最大值出现在春季中部地区,为15.34%,高度为9.83 km。冰水路径最大值出现在夏季的东部沿海,液水路径最大值在秋季的西部地区。冰水含量、冰粒数浓度、冰粒有效半径的主要分布高度与卷云的发生高度一致,液水含量、液滴数浓度、液滴有效半径的主要分布高度在5.04~9.35 km。3个子区域卷云冰水含量、冰粒数浓度、冰粒有效半径垂直分布中大多集中在中上部;液水含量垂直分布主要集中在分布高度的中下部。四季卷云雷达反射率因子的最大值在-19.89~-16.78 dBZ,分布高度在7.19~10.55 km。     

高光谱分辨率激光雷达同时测量大气风和气溶胶光学性质的模拟研究

提出一套高光谱分辨率激光雷达(HSRL)系统,用于同时测量大气风和气溶胶的光学性质.该HSRL系统中使用碘分子滤波器分离分子和气溶胶后向散射,同时利用双边缘检测技术测量大气风场引起的多普勒频移.文中选用合理的HSRL参数和大气模型数据,模拟和分析了HSRL的测量性能.系统夜晚运行时,可测量20 km以下的大气风速和气溶胶,风速误差小于2 m s-1,气溶胶的后向散射系数相对误差小于30%.在白天工作时,相同误差下的可探测高度为10 km.模拟分析结果表明,该HSRL雷达有较大的应用前景,对天气和气象研究等有重要意义.     

Cloud-base distribution and cirrus properties based on micropulse lidar measurements at a site in southeastern China

The cloud fraction(CF) and cloud-base heights(CBHs), and cirrus properties, over a site in southeastern China from June 2008 to May 2009, are examined by a ground-based lidar. Results show that clouds occupied the sky 41% of the time.Significant seasonal variations in CF were found with a maximum/minimum during winter/summer and similar magnitudes of CF in spring and autumn. A distinct diurnal cycle in the overall mean CF was seen. Total, daytime, and nighttime annual mean CBHs were 3.05 ± 2.73 km, 2.46 ± 2.08 km, and 3.51 ± 3.07 km, respectively. The lowest/highest CBH occurred around noon/midnight. Cirrus clouds were present ～36.2% of the time at night with the percentage increased in summer and decreased in spring. Annual mean values for cirrus geometrical properties were 8.89 ± 1.65 km, 9.80 ± 1.70 km, 10.73 ± 1.86 km and 1.83 ± 0.91 km for the base, mid-cloud, top height, and the thickness, respectively. Seasonal variations in cirrus geometrical properties show a maximum/minimum in summer/winter for all cirrus geometrical parameters. The mean cirrus lidar ratio for all cirrus cases in our study was ～ 25 ± 17 sr, with a smooth seasonal trend. The cirrus optical depth ranged from 0.001 to 2.475, with a mean of 0.34 ± 0.33. Sub-visual, thin, and dense cirrus were observed in ～12%, 43%, and 45%of the cases, respectively. More frequent, thicker cirrus clouds occurred in summer than in any other season. The properties of cirrus cloud over the site are compared with other lidar-based retrievals of midlatitude cirrus cloud properties.     

Ice Nucleation of Cirrus Clouds Related to the Transported Dust Layer Observed by Ground-Based Lidars over Wuhan,China

Cirrus clouds related to transported dust layers were identified on 22 occasions with ground-based polarization lidar from December 2012 to February 2018 over Wuhan (30.5°N, 114.4°E), China. All the events occurred in spring and winter. Cirrus clouds were mostly located above 7.6 km on top of the aloft dust layers. In-cloud relative humidity with respect to ice (RH_i) derived from water vapor Raman lidar as well as from ERA5 reanalysis data were used as criteria to determine the possible ice nucleation regimes. Corresponding to the two typical cases shown, the observed events can be classified into two categories: (1) category A (3 cases), in-cloud peak RH_i ≥ 150%, indicating competition between heterogeneous nucleation and homogeneous nucleation; and (2) category B (19 cases), in-cloud peak RH_i < 150%, revealing that only heterogeneous nucleation was involved. Heterogeneous nucleation generally took place during instances of cirrus cloud formation in the upper troposphere when advected dust particles were present. Although accompanying cloud-top temperatures ranged from –51.9°C to –30.4°C, dust-related heterogeneous nucleation contributed to primary ice nucleation in cirrus clouds by providing ice nucleating particle concentrations on the order of 10^?3 L^?1 to 10² L^?1. Heterogeneous nucleation and subsequent crystal growth reduced the ambient RH_i to be less than 150% by consuming water vapor and thus completely inhibited homogeneous nucleation.     

On the growth of nitric and sulfuric acid aerosol particles under stratospheric conditions

We present a theory for the formation of frozen aerosol particles in the Antarctic stratosphere, the coldest region of the Earth's stratosphere. The theory is applied specifically to the formation of polar stratospheric clouds. We suggest that the condensed ices are composed primarily of nitric acid and water with small admixtures of other compounds such as H₂SO₄ and HCl in solid solution. Our assumed particle formation mechanism is in agreement with the magnitude and seasonal behavior of the optical extinctions observed in the winter polar stratosphere. Physical chemistry and thermodynamic considerations suggest that at temperatures between about 200 and 185 K, stratospheric particulates are composed primarily of frozen nitric acid solutions with a composition near that of the trihydrate. Available data suggest the particles are amorphous solid solutions and not in the crystalline hydrate form. At lower temperatures (i.e., below the forst point of pure water) cirrus-like ice clouds can form.     

The APE-THESEO Tropical Campaign: An Overview

The APE-THESEO campaign was held from 15 February to 15 March 1999 from the Seychelles in the western Indian Ocean. APE-THESEO stands for Airborne Platform for Earth observation — (contribution to) the Third European Stratospheric Experiment on Ozone. The campaign aimed to study processes controlling the low water content of the stratosphere, including the mechanisms of cloud formation in the tropical tropopause region, and transport processes, studied using measurements of long-lived trace gases and ozone.Two aircraft were used: the high-altitude research aircraft, M-55 Geophysica, which can fly up to 21 km, and the Falcon of the Deutsches Zentrum für Luft- und Raumfahrt, a tropospheric aircraft. Seven flights were performed, including the first simultaneous in situ and remote sensing of sub-visible cirrus clouds, the first interception of sub-visible cirrus using in-flight guidance from a path-finding aircraft, and guided descent of a high-altitude research aircraft into the anvil cloud at the top of a tropical cyclone. In this paper we describe the payload used, the objectives for each flight, and the meteorological conditions encountered. First results show that a new type of cloud, which we have dubbed ultra-thin tropical tropopause cloud (UTTC), has been observed frequently, and observed to cover areas of 10⁵ km². The frequent coincidence of the tropopause and hygropause implies that the western Indian Ocean played an important role in the dehydration of the lower tropical stratosphere during the season of the mission. UTTCs, sub-visible cirrus, and visible cirrus, have all been implicated in the observed dehydration. Tracer measurements indicate little mixing of stratospheric air into the upper tropical troposphere.     

A climatological study of polar stratospheric clouds (1989–1997) from LIDAR measurements over Dumont d'Urville (Antarctica)

Backscatter lidar data from the French Antarctic base in Dumont d'Urville (66.40°S, 140.01°E), including aerosol background and observations of polar stratospheric clouds (PSCs), have been collected since 1989. In the present work we present a climatological study of PSCs, using a data base consisting of almost 90 observations. The seasonal evolution of PSCs, their optical classification, and their relationship with the observation temperature were studied. The first PSC was observed on day number 175 (15 June) and the last on day number 260 (7 September). The characteristic mid‐cloud altitude decreases through the season at a rate of 2.5 km/month. Type Ia, Ib, and II PSCs — identified by their optical properties — have been observed. External mixtures of these types have also been observed. These observations have been related to the local temperature measured by radiosondes. The relationship between PSC type and the period of the winter season was also investigated. Mixed (solid and liquid) type I clouds are mostly observed at the beginning of the winter. Type II clouds are observed only during the coldest period around midwinter, although temperatures below the frost point begin earlier and persist longer than this. Type Ia, solid‐particle, clouds are observed mostly at the end of the winter.     

Characteristics of cirrus clouds and its radiative properties based on lidar observation over Chung-Li, Taiwan

In this paper, characterization of cirrus clouds are made by using data from ground based polarization lidar and radiosonde measurements over Chung-Li (24.58°N, 121.10°E), Taiwan for a period of 1999–2006. During this period, the occurrence of cirrus clouds is about 37% of the total measurement nights over the lidar site. Analysis of the measurement gives the statistical characteristics about the macrophysical properties such as occurrence height, ambient temperature, and its geometrical thickness while the microphysical properties are interpreted in terms of extinction coefficient, optical depth, effective lidar ratio and depolarization ratio. The effective lidar ratio has been retrieved by using the simulation technique of backscattered lidar signals. The effect of multiple scattering has been taken into the account by a model calculation. Summer (Jun–Aug) shows the maximum appearances of cirrus due to its formation mechanism. It is shown that tropopause cirrus clouds may occur with a probability of about 24%. These clouds are usually optically thin and having laminar in structure with some cases resembling the characteristics similar to that of polar stratospheric clouds (PSCs). The radiative properties of the cirrus clouds are also discussed in detail by the empirical equations with results show a positive feedback on any climate change.     

Lidar remote sounding of cirrus clouds and comparison of simulated fluxes with surface and METEOSAT observations

Three cirrus cloud cases have been remotely sounded near Paris by a ground-based backscatter lidar and broadband radiometers. Some cirrus properties (optical depth, emissivity, height) are derived from these measurements and used to compare radiative transfer calculations to surface and METEOSAT observations of broadband irradiances.For a useful comparison, the three cirrus cases were selected to have different morphologies and optical properties: June 29, 1993—thin cirrus cloud (thickness 1.5 km, optical depth 0.22); September 6, 1993—thick cirrus cloud (thickness 5 km, optical depth 2.7); and November 16, 1993—inhomogeneous and geometrically thick cirrus cloud (thickness 3.5–6.5 km) but optically thin (optical depth 0.82).At surface, the differences between measurements and model range from 1.5 to 4 Wm⁻² for longwave fluxes, and from 20 to 70 Wm⁻² for shortwave fluxes.At the top of the atmosphere, the differences between METEOSAT measurements and model are in fair agreement for longwave fluxes (up to 50 Wm⁻²). However, unexpected high differences are found for shortwave fluxes (up to 144 Wm⁻²) due to cirrus clouds heterogeneities and uncertainties in their microphysical properties and especially the occurrence of high reflectivity due to horizontally oriented ice crystals at the cloud top, which are not taken into account by the Model presently.     

中国及周边地区多层云垂直结构时空分布特征

利用CALIPSO激光雷达1km水平分辨率的云层产品,计算了中国及周边地区（0°~55°N,70°~140°E）多层云的出现概率,对不同高度多层云的水平分布及其季节变化特征进行了统计分析。结果表明:多层云的出现概率存在显著的区域差异,青藏高原和蒙古高原出现的概率较低,30°N以南的低纬度地区出现的概率较高;多层云系统中双层云占比最大,并且云层发生概率随着云层数的增多而减小;不同高度双层云和三层云的分布特征类似;多层云出现概率夏季最大,冬季最小,其中夏季双层云中“高云+高云”、“高云+中云”和三层云中“高云+高云+高云”、“高云+高云+中云”的配置在青藏高原主体的出现概率最大,而冬季单层云的低云、双层云中“高云+低云”及三层云中少量的“高云+高云+低云”配置在中国东北部海域、南海北部等30°N以北地区的出现概率高于其它季节。      

Lidar Measurements of Aerosols in the Tropical Atmosphere

Measurements of atmospheric aerosols and trace gases using the Laser radar (lidar) techniques, have been in pro-gress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18o32’N, 73o51’E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal va-riation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected me-teorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles ob-tained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol lay-ers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.     

HNO3 and PSC Measurements from the Transall: Sequestering of HNO3 in the Winter of 1994/95

In the winter of 1994/95 the TRANSALL research aircraft performed several flights in the region of the Arctic vortex during the period of low stratospheric temperatures. The results of simultaneous measurements of HNO3 column amounts by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) and of aerosol backscatter profiles by the Ozone Lidar EXperiment (OLEX) are presented for two typical flight scenarios across the polar vortex boundary on December 17, 1994 and January 11/12, 1995. On December 17 and January 12, the column amounts of gaseous HNO3 decreased significantly in regions with low stratospheric temperatures. This decrease was correlated with the extent of the polar stratospheric clouds. Depolarisation measurements showed that type Ib PSCs were observed primarily, but equilibrium calculations for H2SO4/HNO3/H2O aerosols seem to underestimate the observed HNO3 sequestering.     

Extremely low temperatures in the stratosphore and very low total ozone amount above northern and central Europe during winter 1989

On 1 February 1989, -83.5°C was recorded in 27.8 hPa over Hohenpeißenberg, the lowest temperature in the 22-year series. This was measured together with a very low total ozone amount of 266 DU. This may be compared with nearly twice this amount on 27 February 1989. The situation was very unusual: following an extremely cold winter in the Arctic stratosphere, the stratospheric cold pole was located over southern Scandinavia on 1 February in a very southerly position. The analyzed temperatures of -92 °C in 30 hPa were also unusual. Even though the low ozone amounts over Hohenpeißenberg were probably dynamically caused, an additional very small ozone decrease due to heterogeneous reactions in altitudes from 23–28 km, where the temperatures lie below -80 °C, cannot be ruled out. Extinction measurements by the orbitting SAGE II instrument indeed show polar stratospheric clouds over Europe near 50° N during the period 31 January–2 February. Also, polar stratospheric clouds were previously observed over Kiruna at similarly low temperatures and signs of a corresponding small ozone decrease were noted there.     

The impact of high altitude aircraft on the ozone layer in the stratosphere

The paper discusses the potential effects on the ozone layer of gases released by the engines of proposed high altitude supersonic aircraft. The major problem arises from the emissions of nitrogen oxides which have the potential to destroy significant quantities of ozone in the stratosphere. The magnitude of the perturbation is highly dependent on the cruise altitude of the aircraft. Furthermore, the depletion of ozone is substantially reduced when heterogeneous conversion of nitrogen oxides into nitric acid on sulfate aerosol particles is taken into account in the calculation. The sensitivity of the aerosol load on stratospheric ozone is investigated. First, the model indicates that the aerosol load induced by the SO₂ released by aircraft is increased by about 10–20% above the background aerosols at mid-high latitude of the Northern Hemisphere at 15 km for the NASA emission scenario A (the NASA emission scenarios are explained in Tables I to III). This increase in aerosol has small effects on stratospheric ozone. Second, when the aerosol load is increased following a volcanic eruption similar to the eruption of El Chichon (Mexico, April 1982), the ozone column in spring increases by as much as 9% in response to the injection of NO _x from the aircraft with the NASA emission scenario A. Finally, the modeled suggests that significant ozone depletion could result from the formation of additional polar stratospheric clouds produced by the injection of H₂O and HNO₃ by the aircraft engines.     

平流层准零风层统计特征及准两年周期振荡对其影响分析

根据形成机制的不同将平流层准零风层（Quasi-Zero Wind Layer,QZWL）划分为由平流层准两年周期振荡（Quasi-Biennial Oscillation,QBO）各高度处于不同位相形成的第一类QZWL和由于平流层低层经向温度梯度逆转而形成的第二类QZWL;利用ERA-40再分析资料分析了两类QZWL在不同季节中空间结构的变化规律,讨论了平流层QBO对两类QZWL年际变化产生的影响。研究结果表明：第一类QZWL集中出现在冬季赤道附近地区,第二类QZWL在夏季热带外地区和冬季20°N～40°N太平洋地区上空;QZWL夏季高度比冬季低约3 km,夏季QZWL出现高度比冬季稳定,约在50～70 hPa之间;由于受到QBO的直接影响,第一类QZWL出现的高度和纬度范围存在明显的年际变化,第二类QZWL受到QBO的影响主要体现在QBO西风位相年和东风位相年相比,冬季20°N～40°N范围内存在第二类QZWL的概率较高。     

The Spatial and Temporal Variability of Global Stratospheric Gravity Waves and Their Activity during Sudden Stratospheric Warming Revealed by COSMIC Measurements

This study investigates the spatial and temporal variability of global stratospheric gravity waves (GWs) and the characteristics of GW activity during sudden stratospheric warming (SSW) using the GPS radio occultation measurements from the COSMIC mission during September 2006 to May 2013. Corresponding to the COSMIC RO observational window and analysis method, GW potential energy (Ep) with vertical scales no shorter than ～2 km is resolved. It is found that the distributions of GW Ep over 20-30 km and 30-38 km show similar spatial and seasonal variations. The variations of GW Ep with altitude and latitude along the westerly wind are identified in different seasons over 60°-80°W. In the middle and high latitudes, seasonal cycles are distinct in the time-latitude and time-altitude distributions of GW activities, which show larger Ep in winters when westerly wind dominates and smaller Ep in summers when easterly wind dominates. The influence of quasi-biennial oscillation on GW activity is recognized in the tropics. GW Ep enhances closely following the occurrence of minor SSW events; while during major events, GW Ep may not enhance, and sometimes may even weaken, in the regions where reversals of zonal wind occur, probably caused by the filtering impact of the 0 m s-1 wind level on the GWs.