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.     

Possible mechanism of ozone depletion on ice crystals in the polar stratosphere

Developed is a new mechanism of photochemical reactions taking account of the dipole interaction between the molecules and the ??sharp?? inhomogeneities of electrified ice crystals in polar stratospheric clouds. This mechanism enables to explain the ozone depression formation during the winter-spring period in the polar stratosphere.     

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.     

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.     

Validation of a limited area model over Dome C, Antarctic Plateau, during winter

The limited area model MAR (Modèle Atmosphérique Régional) is validated over the Antarctic Plateau for the period 2004–2006, focussing on Dome C during the cold season. MAR simulations are made by initializing the model once and by forcing it through its lateral and top boundaries by the ECMWF operational analyses. Model outputs compare favourably with observations from automatic weather station (AWS), radiometers and atmospheric soundings. MAR is able to simulate the succession of cold and warm events which occur at Dome C during winter. Larger longwave downwelling fluxes (LWD) are responsible for higher surface air temperatures and weaker surface inversions during winter. Warm events are better simulated when the small Antarctic precipitating snow particles are taken into account in radiative transfer computations. MAR stratosphere cools during the cold season, with the coldest temperatures occurring in conjunction with warm events at the surface. The decrease of saturation specific humidity associated with these coldest temperatures is responsible for the formation of polar stratospheric clouds (PSCs) especially in August-September. PSCs then contribute to the surface warming by increasing the surface downwelling longwave flux.     

Denitrification through PSC formation: A 1-D model incorporating temperature oscillations

A one-dimensional model of polar stratospheric cloud (PSC) formation and evolution during the polar winter, incorporating both HNO₃ and H₂O condensation, has been developed to investigate the interactions between Type I and Type II PSCs and the effects of these clouds on the stratospheric composition. Model simulations for various meteorological conditions and the results of extensive sensitivity tests are presented. Temperature oscillations, which have been included in the model, are shown to have an important influence on the characteristics and effects of the PSCs. The predicted proportions of the PSCs are consistent with observations of number, size, and optical effects, such as depolarization. Denitrification of stratospheric air by 35–88% is shown to occur in the presence of both Type I and Type II PSCs, with comparable nitrate removal in both types of clouds. Dehydration by Type II clouds simultaneously removes similar percentages of water vapour, up to 79% at lower altitudes. Altough dehydration is insensitive to most of the parameter variations except the minimum temperature, the process of denitrification, especially the proportion removed by Type I PSCs, is highly variable.     

Nitrosyl and Nitryl Chloride Formation in H2SO4/HNO3/H2O/HCl Solutions at 200 K

Infrared spectroscopy has been used to measure the vapor pressure of chlorine containing species generated from H2SO4/HNO3/H2O/HCl solutions at 200 K. The vapor pressure was observed to be a function of solution composition. Two solution compositions were investigated. One solution remained a liquid whereas the second solution was a mixed liquid and solid phase (an ice slurry). The liquid solution had a composition of 64.6 wt.% H2SO4/4.8 wt.% HNO3/30.1 wt.% H2O/0.5 wt.% HCl and produced only vapor phase HCl. The ice slurry solution had a composition of 76.6 wt.% H2SO4/3.0 wt.% HNO3/20.1 wt.% H2O/0.3 wt.% HCl and produced HCl, ClNO, and ClNO2 vapor phase components. The sulfuric acid, nitric acid, and water content of these solutions are representative of those present in polar stratospheric clouds (PSCs), however the HCl concentrations are much higher than present within these clouds. The partitioning of chlorine between vapor phase HCl (50%) and ClNO/ClNO2 (50%) for the ice slurry solution suggests a possible mechanism of halogen activation within PSCs. A reaction mechanism to model the observed chemistry is proposed.     

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.     

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.     

Trajectory Studies of Polar Stratospheric Cloud Lidar Observations at Sodankylä (Finland) During SESAME: Comparison with Box Model Results of Particle Evolution

Polar stratospheric clouds (PSC) were observed with the multi-wavelength lidar of the MOANA project (Modelling and Observations of Aerosols in the Northern Atmosphere) during SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment). The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distribution of the droplets along the trajectory were calculated using a micro-physical box model. Backscatter ratios calculated from the size distributions are in broad agreement with the lidar data, giving confidence in current understanding of the evolution of ternary solution (H2SO4, HNO3 and H2O) droplets.Results from two soundings are shown which bear on the problem of the formation of solid particles. In the first, solid particles were detected. The air mass had cooled to the frost point 12 hours earlier. In the second no solid particles were detected although the air temperature was below the nitric acid trihydrate existence point, and had decreased by 12K in the previous 14 hours.     

北半球平流层极涡崩溃早晚的环流特征及其对5月南亚降水的影响

本文采用1979—2014年NCEP/NCAR月平均再分析资料、CMAP和GPCP月平均降水资料,分析了北半球平流层极涡崩溃早晚的环流特征及其与南亚降水的关系。结果表明,北半球平流层极涡崩溃时间存在明显的年际变化特征。极涡崩溃偏早(偏晚)年,自3月开始异常信号从平流层向下传播,之后的4月,从平流层到对流层高层极区温度异常偏高(偏低),极涡异常偏弱(偏强),极夜急流异常偏弱(偏强)。结果还表明,5月南亚降水异常与平流层极涡崩溃时间的早晚存在显著相关,5月南亚降水异常与平流层极涡崩溃早晚年平流层异常信号的下传有关。当平流层极涡崩溃偏晚年,4月平流层极区表现为位势高度异常偏低,而中纬度则位势高度场异常偏高,并伴随位势高度异常场的向下传播,5月该位势高度异常场下传至阿拉伯海北部大陆上空对流层顶,形成有利于降水的环流场,导致南亚降水偏多。反之,则相反。     

Chemistry–Climate Interactions of Stratospheric and Mesospheric Ozone in EMAC Long-Term Simulations with Different Boundary Conditions for CO2, CH4, N2O,and ODS

Abstract

To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO₂, CH₄, and N₂O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO₂, CH₄, N₂O, or ODS to the year 2000.

In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO₂ mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH₄, which also forms additional H₂O in the upper stratosphere and mesosphere. Increasing N₂O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere.

In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO₂ mixing ratios, followed by increasing CH₄. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NO_x and HO_x mixing ratios due to increased N₂O and CH₄ lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NO_x; in the mesosphere the intensified ozone destruction is caused by additional HO_x. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NO_x is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.     

Vertical profiles of Volcanic Aerosol and Polar Stratospheric Clouds Above Kiruna, Sweden: Winters 1993 and 1995

Vertical profiles of aerosol were measured in February 1993, and January - March 1995 using balloon-borne particle counters released from Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii 0.15 - 10.0 µm were measured in 8-12 size classes. The three flights in 1993 were within the polar vortex. Temperatures were below polar stratospheric cloud (PSC) threshold temperatures on one flight and a thin PSC was observed. The volcanic aerosol in the 1993 vortex was similar to that in 1992. In 1993, surface areas were 10 - 20 µm2 cm-3 and volumes 1 - 3 µm3 cm-3. In 1995 three of five flights were within the polar vortex. The volcanic aerosol had decreased to 3 - 7 µm2 cm-3 and 0.1 - 0.4 µm3 cm-3. The top of the volcanic aerosol layer in both years was near 500 K potential temperature (~20 km). A thick nitric acid and water PSC was observed in January 1995. In the thickest region of this PSC nearly all CN were observed to be activated, and surface areas of 5 - 10 µm2 cm-3 were calculated. The volumes observed in this PSC were closer to what would be expected for particles composed of nitric acid trihydrate than for ternary solution droplets. In 1993 the opposite was observed, the volumes in the thin PSC were closer to what would be expected for ternary solution droplets.     

Indo-Japanese lidar observations of the tropical middle atmosphere during 1998 and 1999

A state-of-the art Rayleigh and Mie backscattering lidar was set up at Gadanki (13.5N, 79.2E) in the Tropics in India. Using this system, regular observations of upper tropospheric clouds, aerosols at stratospheric heights and atmospheric temperatures in the range from 30 to 80 km were made. In this paper, the data collected during the period of 1998–99 were selected for systematic investigation and presentation. The Mie scattering lidar system is capable of measuring the degree of depolarization in the laser backscattering. Several tropical cirrus cloud structures have been identified with low to moderate ice content. Occasionally, thin sub-visible cirrus clouds in the vicinity of the tropical tropopause have also been detected. The aerosol measurements in the upper troposphere and lower stratosphere show low aerosol content with a vertical distribution up to 35 km altitude. Rayleigh-scattering lidar observations reveal that at the tropical site, temperature inversion occurs at mesospheric heights. Atmospheric waves have induced perturbations in the temperatures for several times at the upper stratospheric heights. A significant warming in the lower mesosphere associated with a consistent cooling in the upper stratospheric heights is observed particularly in the winter season during the events of sudden stratospheric warming (SSW).     

Numerical Modeling of the Influence of Physical and Chemical Factors on the Interannual Variability of Antarctic Ozone

The variability of Antarctic total column ozone in 1980–2018 is considered. The study analyzes trends in Antarctic total column ozone during the study period as well as the physical and chemical processes affecting the seasonal variability of total column ozone. The main attention is paid to the influence of dynamical processes on the stability of the Antarctic polar vortex, to the formation of polar stratospheric clouds, and to the influence of gas-phase and heterogeneous processes on the surface of polar stratospheric clouds and sulfate aerosol. The method of research is the analysis of the results of ground and satellite observations and numerical modeling of physical and chemical processes over the Antarctic using a global chemistry transport model with the dynamical parameters specified from reanalysis data.     

Interannual variations in total ozone fields at high latitudes of the Northern Hemisphere, November to March 1998–2005

Synoptic analysis of monthly and daily mean total ozone fields is carried out using ground-based (Roshydromet) and TOMS measurements. Large interannual changes in the evolution of the stratospheric polar vortex and the North Pacific anticyclone influence the formation and dynamics of the winter-spring ozone fields in the stratosphere of high northern latitudes. The analysis shows considerable variations in the direction of zonal ozone transport from the sector of ozone inflow from low latitudes and accumulation in the Far East depending on the winter polar stratosphere temperature and the quasi-biennial oscillation (QBO) phase. In years with the easterly QBO phase and the warm polar stratosphere, ozone at the end of winter is transported to northeastern Canada and Atlantic. In years with the easterly phase and cold polar stratosphere, ozone transport is directed to northern Eurasia. These characteristics will be verified on extensive observational data.     

Deuterium, Oxygen-18, and Tritium as Tracers for Water Vapour Transport in the Lower Stratosphere and Tropopause Region

Simultaneous measurements of the three rare isotopes Deuterium (D), Tritium (T), and Oxygen-18 (18O) in water vapour were made for the first time in the vicinity of the northern hemisphere tropopause. In contrast to expectation, high D/H and 18O/16O ratios, but relatively low T/H ratios, were found within the lowermost stratosphere. Since water vapour in the low-latitude upper troposphere shows a similar isotopic signature, we conclude that in the mid-latitudes considerable amounts of tropospheric water vapour are injected into the lowermost stratosphere, probably resulting in a hydration of the lower stratosphere. In addition, T can serve as tracer for precipitation of water containing stratospheric aerosol particles, because the T/H ratio in stratospheric water vapour is orders of magnitude higher than in the upper troposphere. Thus, even a small contribution of water of stratospheric origin should be detectable in the tropopause region. In our measurements performed in the Arctic we did not find isotopic evidence for sedimentation of PSC particles down to the tropopause. This may be caused by the low spatial and temporal coverage of our observations; however, it may also be due to the much weaker wintertime dehydration of the Arctic vortex compared to the Antarctic.     

平流层强、弱极涡事件的演变过程及其对我国冬季天气的影响

本文利用1979～2010年的NCEP再分析资料,通过北半球环状模NAM指数挑选出的强、弱极涡个例,分析了北半球平流层异常变化过程中行星波的演变以及与之相联系的我国天气的变化特征。结果表明,在强极涡事件前,行星波1波会被反射回对流层,极地波导减弱,低纬波导增强,中高纬地区的E-P通量矢量有着从平流层传播到对流层的趋势;强极涡事件后,极地波导增强,低纬波导减弱。在弱极涡事件前,中、高纬度行星波1波沿着极地波导的传播明显增强;弱极涡事件后,极地波导明显减弱。与此对应的我国天气也有明显变化,在强极涡事件前,我国大部分地区温度偏低,南方地区偏湿而新疆西北部和云南西部地区偏干;在强极涡事件后,东亚冬季风进一步增强,冷空气加强南下,南方地区可降水量减少,新疆西北部仍然偏干,而云南大部分地区可将水量增加。在弱极涡事件前,东亚冬季风显著增强,使我国气温偏冷,降水减少,而弱极涡事件后,我国气温明显回升,中、东部地区和新疆西北部地区降水明显增加。