The impact of cut-off lows on ozone in the upper troposphere and lower stratosphere over Changchun from ozonesonde observations

In situ measurements of the vertical structure of ozone were made in Changchun(43.53?N, 125.13?E), China, by the Institute of Atmosphere Physics, in the summers of 2010–13. Analysis of the 89 validated ozone profiles shows the variation of ozone concentration in the upper troposphere and lower stratosphere(UTLS) caused by cut-off lows(COLs) over Changchun. During the COL events, an increase of the ozone concentration and a lower height of the tropopause are observed.Backward simulations with a trajectory model show that the ozone-rich airmass brought by the COL is from Siberia. A case study proves that stratosphere–troposphere exchange(STE) occurs in the COL. The ozone-rich air mass transported from the stratosphere to the troposphere first becomes unstable, then loses its high ozone concentration. This process usually happens during the decay stage of COLs. In order to understand the influence of COLs on the ozone in the UTLS, statistical analysis of the ozone profiles within COLs, and other profiles, are employed. The results indicate that the ozone concentrations of the in-COL profiles are significantly higher than those of the other profiles between ±4 km around the tropopause. The COLs induce an increase in UTLS column ozone by 32% on average. Meanwhile, the COLs depress the lapse-rate tropopause(LRT)/dynamical tropopause height by 1.4/1.7 km and cause the atmosphere above the tropopause to be less stable. The influence of COLs is durable because the increased ozone concentration lasts at least one day after the COL has passed over Changchun. Furthermore, the relative coefficient between LRT height and lower stratosphere(LS) column ozone is-0.62,which implies a positive correlation between COL strength and LS ozone concentration.     

Sodar observations of the nocturnal boundary layer at Kharagpur, India

Sodar has been installed at Kharagpur (22.2 ° N, 87.3 ° E) as a part of the MONTBLEX-90 experiment and data were collected during the monsoon period. The variation of the nocturnal boundary layer (NBL) during the monsoon period is discussed. The height corresponding to the low-level wind maximum in the sodar wind profile during night time is identified as the NBL height. Mean monthly winds for July and August, plotted as time-height cross sections, reveal the height of the ground-based stable layer. The average NBL heights in the months of July and August are found to be 324 m and 296 m respectively. It is observed that the NBL height is relatively high in the month of July (active phase of monsoon) compared to that during August (weak phase). The months of July (total rainfall = 901 mm) and August (total rainfall = 134 mm) are associated with cloudy and relatively clear sky conditions. This indicates that clouds (through their effect on longwave cooling to space) play an important role in determining the NBL height during the monsoon.     

Influence of local sources on rainwater chemistry over Pune region,India

Rainwater samples were collected at five locations in the Pune region, an urban area in the south-west part of India, during 2006–2009. These locations; viz., Swargate (Traffic), Bhosari (Industrial), Pashan, Sangvi (Urban) and Sinhagad (Rural and High Altitude), represent different environments in this region. The study based on chemical analyses of these samples reveals that, on average, rainwater was alkaline at all the locations with pH values of 6.7, 6.16, 5.94, 6.04 and 5.92, respectively. Higher pH value of rainwater at the traffic location than those at the other locations is due mainly to the abundance of Ca²⁺ caused by vehicle-driven road-side dust. The maximum SO₄^2? and NO₃^? concentrations were found at Bhosari and Swargate respectively caused by local industrial and vehicular emissions. The average Fractional acidity over Pune area is 0.024, indicating about 98% acidity is neutralized by alkaline constituents. Factor analysis of the results indicated the influence of various sources, such as anthropogenic, soil dust, sea salt and biomass burning.     

Temperature stratification of the lower atmosphere over Moscow

Features of diurnal and annual cycles and of seasonal changes of temperature stratification in the lower 800-m air layer over Moscow are discussed on the basis of analysis of long-term data of acoustic (sodar) observations at Moscow State University (MSU). Of about 34 000 separate hours of height-time sweep of echo signal during 1988–2003, refined estimates are presented of occurrence frequencies of surface and elevated inversions, unstable stratification, etc., in Moscow. On the basis of long series of hourly sodar data and surface weather observations at MSU, special features of temperature stratification are considered under extremely low and high values of air temperature, wind speed, and relative humidity. A review is presented of existing data on temperature stratification in central Russia for the whole period of aerological observations; results of acoustic sounding are compared against the data obtained using other techniques.     

基于旋翼无人机观测的雾天和霾天VOCs垂直分布特征研究

为研究雾和霾天气下VOCs时空变化特征,于2020年11月19日—2021年1月15日在江苏省东海国家气象观测站进行为期58 d的外场观测试验。利用自主研发的多旋翼无人机捕获2次辐射雾和2次霾天气过程,获得气温、气压、相对湿度、风向、风速、VOCs、O₃等7种要素100多条垂直廓线。结果表明：时间上,霾过程夜间VOCs体积浓度(0.225～0.253 ppm(parts per million, 1 ppm=10^-6))明显高于白天(0.191～0.205 ppm),雾形成前体积浓度(0.121～0.239 ppm)显著高于雾过程(0.056～0.209 ppm)。雾过程中VOCs体积浓度与雾强度变化相反,雾层高度与VOCs体积浓度剧烈变化高度一致,雾层(<200 m)中VOCs体积浓度(0.172～0.178 ppm)明显减小,显著低于雾形成前(0.195～0.240 ppm),雾层以上浓度变化大,雾结束后1 h内保持雾过程中分布特点。雾对逆温层中的水溶性污染物有清除作用,VOCs体积浓度和O₃质量浓度均下降。     

A study of multiple stable layers in the nocturnal lower atmosphere

The structure of nocturnal inversions in the first 300 m of the atmosphere is analyzed using observational data from the Boulder Atmospheric Observatory (BAO) from March through June 1981. The temperature profiles show more than one inversion layer 41% of the time during the observational period. The vertical distributions of wind speed and moisture also show evidence of stratification during these multiple-layer events. The relation between the radiative cooling rate in time and height, including moisture, and the vertical structure of the multiple layers is calculated. The vertical distribution of eddy kinetic energy and the turbulent vertical fluxes of heat and momentum are also calculated. Turbulent structure in the elevated inversion layers is more complicated than that in the single-layer, stable nocturnal boundary layer. The total heat budget for a multiple-layer case is calculated, and turbulent cooling is found to be negligible relative to radiative cooling and to horizontal advection and/or horizontal divergence of heat flux.     

Sodar observations of the stable lower atmospheric boundary layer at Barrow,Alaska

Events in the stably stratified lower atmospheric boundary layer within the first several hundreds of meters at Barrow, Alaska were recorded from 27 March to 5 April 1990 using an acoustic sounder (sodar), a tethered balloon, radiosondes, and an instrumented meteorological tower. These events include ground-based and low-level inversion layers, gravity waves, breaking waves, and multiple-layer structures. Even though these events are commonly found in a stable boundary layer, it is perhaps surprising to find them in such a slowly changing environment and over a terrain that is essentially devoid of immediate orographic influence.Visiting Scientist at Wave Propagation Laboratory, NOAA/ERL 325 Broadway, Boulder, CO, 80303, U.S.A.     

Radiative destabilization of the nocturnal stable atmospheric boundary layer over the desert

Radiative destabilization of the nocturnal stable atmospheric boundary layer (NSABL) over homogeneous desert terrain is predicted by an analytical model based on a modified diffusion equation. The model applies late at night under calm, dry conditions when long-wave radiative transfer dominates the NSABL evolution. A three-layer structure for the NSABL is proposed: a shear sub-layer closest to the surface, a radiative sub-layer which contains the inversion top, and a coupling sub-layer which matches the NSABL with the residual layer aloft. A sub-sub-layer called the nocturnal internal boundary layer (NIBL) is nested within the radiative sub-layer and comprises the temperature maximum. The model can explain: (1) maximum cooling in the NIBL, (2) deepening of the NIBL, (3) radiative destabilization of the NSABL, and (4) possible surface warming before sunrise. An example from the Mohave Desert, USA is presented, and the observed temperature profile compares favorably with the model solution.     

Airborne and lidar measurements of aerosol and cloud particles in the troposphere over Alert Canada in April 1986

As a component of the Canadian Arctic Haze Study, held coincident with the second Arctic Gas and Aerosol Sampling Program (AGASP II), vertical profiles of aerosol size distribution (0.17 m), light scattering parameters and cloud particle concentrations were obtained with an instrumented aircraft and ground-based lidar system during April 1986 at Alert. Northwest Territories. Average aerosol number concentrations range from about 200 cm^–3 over the Arctic ice cap to about 100 cm^–3 at 6 km. The aerosol size spectrum is virtually free of giant or coarse aerosol particles, and does not vary significantly with altitude. Most of the aerosol volume is concentrated in the 0.17–0.50 m size range, and the aerosol number concentration is found to be a good surrogate for the SO₄ ⁼ concentration of the Arctic haze aerosol. Comparison of the aircraft and lidar data show that, when iced crystal scattering is excluded, the aerosol light scattering coefficient and the lidar backscattering coefficient are proportional to the Arctic haze aerosol concentration. Ratios of scattering to backscattering, scattering to aerosol number concentration, and backscattering to aerosol number concentration are 15.3 steradians, 1.1×10^–13 m², and 4.8×10^–15 m² sr^–1, respectively. Aerosol scattering coefficients calculated from the measured size distributions using Mie scattering agree well with measured values. The calculations indicate the aerosol absorption optical depth over 6 km to range between 0.011 and 0.018. The presence of small numbers of ice crystals (10–20 crystals 1^–1 measured) increased light scattering by over a factor of ten.     

青藏高原及周边UTLS水汽时空特征的多源资料对比

利用Aura卫星微波临边观测仪(Microwave Limb Sounder,MLS)数据,评估了ERA-I、MERRA、JRA-55、CFSR和NCEP2等5套再分析资料的水汽数据在青藏高原及周边上对流层-下平流层(Upper Troposphere and Lower Stratosphere,UTLS)的质量,然后选取其中质量较好的两套水汽数据,分析它们对青藏高原及周边UTLS水汽的时空分布和演变的表征能力。结果表明,与MLS数据相比,5套再分析资料中在UTLS普遍偏湿,最大偏湿在上对流层215 hPa,约为165%,而在下平流层,ERA-I和MERRA与MLS的差异相对较小。总的来看,ERA-I和MERRA表征的水汽与MLS更为接近。进一步的对比表明,ERA-I和MERRA中青藏高原及周边水汽含量的时空分布与MLS较为接近,夏季能够表征青藏高原在纬向和经向上的水汽高值区,冬季能够表征对流层顶、西风急流中心附近的水汽梯度带,而且MERRA的结果要好于ERA-I。ERA-I、MERRA和MLS中青藏高原地区的水汽季节演变都表现为冬季1-2月水汽含量低,夏季7-8月水汽含量高,水汽的季节变化在200~300 hPa最大。MLS资料显示,在青藏高原地区对流层顶附近,存在随时间向上向极的水汽传输信号。相较而言,ERA-I对向上水汽传输信号的表征更好,而MERRA对下平流层(100 hPa)向极水汽传输信号的表征更好。     

Tree ring inferred summer temperature variations over the last millennium in western Himalaya, India

We report the first millennium-long reconstruction of mean summer (May–June–July–August) temperature extending back to AD 940 derived from tree-ring width data of Himalayan pencil juniper (Juniperus polycarpos C. Koch) from the monsoon-shadow zone in the western Himalaya, India. Centennial-scale variations in the reconstruction reveal periods of protracted warmth encompassing the 11–15th centuries. A decreasing trend in mean summer temperature occurred since the 15th century with the 18–19th centuries being the coldest interval of the last millennium, coinciding with the expansion of glaciers in the western Himalaya. Since the late 19th century summer temperatures increased again. However, current warming may be underestimated due to a weakening in tree growth-temperature relationship noticeable in the latter part of the 20th century. Mean summer temperature over the western Himalaya shows a positive correlation with summer monsoon intensity over north central India. Low-frequency variations in mean summer temperature anomalies over northwestern India are consistent with tree-ring inferred aridity in western North America. These far-distance linkages reported here for the first time underscore the utility of long-term temperature records from the western Himalayan region in understanding global-scale climatic patterns.     

Temperature stratification of the atmospheric boundary layer over the Deccan Plateau,India, during the summer monsoon

The vertical and horizontal temperature structure of the atmospheric boundary layer (ABL) were studied using aircraft observations made in the lowest 2.4 km above ground level during the summer monsoon.The vertical temperature structure of the ABL in the region may be classified into the following four categories.Category The ABL consisted of two layers of thickness 700–900 m separated by a thin transition layer. The lapse rates in the former two layers were dry adiabatic.Category The lowest layer of the ABL of thickness 400–600 m was adiabatically stratified and the overlying layer was stable with gradients of potential temperature 4–5°C km^–1. The stable layer contained a thin adiabatic stratified layer of 200–300 m thickness at a height of 1.5 km.Category The lowest 200–400 m layer of the ABL was adiabatically stratified and the overlying layer was stable with potential temperature gradients of 5–6 °C km¹.Category The ABL was mainly stable with potential temperature gradients of 6 °C km^–1 or greater. Occasionally thin layers with adiabatic stratification were found embedded in the ABL.The temperature distribution of the horizontal temperature at 900 m was mainly normal. The high-frequency portion of the spectra lying between 0.05 and 0.16 Hz (corresponding to wave length 1 km to 300 m) oscillated around the –\2/3 power law line. The spectral curve showed a significant peak at 0.011 Hz having a wave-length of 5 km.Department of Geoscience, North Carolina State University, Raleigh, NC, 27650, U.S.A.     

Carbonaceous aerosols over Pune and Hyderabad (India) and influence of meteorological factors

Sampling of particulate matter with aerodynamic diameter cut off at 2.5 μm (PM_2.5) has been carried out over a semi urban site of Pune and an urban site of Hyderabad. Analysis of elemental Carbon (EC) and Organic Carbon (OC) present in PM_2.5 was carried out using advanced Desert Research Institute’s (DRI) Thermal/Optical Carbon Analyzer operated on IMPROVE_ A (Interagency Monitoring of Protected Visual Environments_ A) protocol. It is found that average concentration of EC and OC both at Pune and Hyderabad was highest during winter season and lowest during monsoon season. Winter high is mainly controlled by inversion, whereas monsoon low is due to rain-out and wash-out process. OC/EC ratio showed higher variation over Pune compared to that over Hyderabad in different seasons, indicating divergent sources of emission of OC and EC at Pune. Formation of Secondary Organic Carbon (SOC) has also been identified as one of the reasons for wide variation in OC/EC ratio value in different seasons over both the sites.     

Temperature stratification and altitude ozone variability in the low troposphere from acoustic and balloon sounding

Results of simultaneous balloon and acoustic sounding in the lower troposphere (in the surface layer up to 800 m) carried out in Velikie Luki in May–June 2002 jointly by the Moscow State University (MSU) and Central Aerological Observatory (CAO) are discussed. During the experiment, the tethered (captive) balloon for measuring air temperature and ozone partial pressure was ascended and descended 15 times. Simultaneously, gradient measurements were performed at a 4-m tower. During the intervals between ascents, the temperature stratification was determined by using the Ekho-1 sodar data. A dominating influence of temperature stratification and of some weather events on the ozone distribution with altitude is shown. In case of unstable stratification, its partial pressure is almost unchanged within the entire lower troposphere; in case of surface inversion, the ozone decrease is observed near the surface. In case of elevated inversion the ozone partial pressure is almost the same both below inversion and above it; in the layer of the inversion itself, it increases spasmodically with the altitude. Synoptic conditions largely influence the stratification regime: under conditions of the Arctic air mass, the thermal convection is observed more often and surface inversions are observed more rarely than when the local mass dominates. Artificial dynamic mixing can lead to the surface inversion dissipation in several minutes.     

On geoengineering with sulphate aerosols in the tropical upper troposphere and lower stratosphere

This paper is in response to the Editorial Essay by Crutzen and the Editorial Comment by Cicerone in the August 2006 issue of Climatic Change. We reprise the evidence from atmospheric nuclear weapon testing in the 1950s and 1960s which is salient to the mooted maintenance of an artificial sulphate aerosol layer in the lower stratosphere, including a hitherto and now posthumous unpublished analysis of the ¹⁸⁵W Hardtack data. We also review recent investigations by ourselves, which have considerable bearing on some relevant questions concerning meteorological dynamics, aerosol chemistry and physics and the photodissociation of stratospheric sulphuric acid.     

A comparison of ABL heights inferred routinely from lidar and radiosondes at noontime

The height of the atmospheric boundary layer (ABL) obtained with lidar and radiosondes is compared for a data set of 43 noon (12.00 GMT) cases in 1984. The data were selected to represent the synoptic circulation types appropriately. Lidar vertical profiles at 1064 nm were used to obtain three estimates for the ABL height (h _lid), based on the first gradient in the back-scatter profile, namely, at the beginning, middle and top of the gradient. The boundary-layer height obtained with the radiosondes (h _s) was determined with the dry-parcel-intersection method in unstable conditions. As a first guess for near-neutral and stable conditions, the height of the first significant level in the potential temperature profile was taken. Overall, the boundary-layer thickness estimates agree surprisingly well (regression lineh _lidb=h_s:cc.=0.93 and the standard error=121 m). However, in 10% of the cases, the lidar estimate was significantly lower (difference>400 m) than the routinely inferredh _s. These outliers are discussed separately. For stable conditions, an estimate of ABL height (h _N) is also made based on the friction velocity and the Brunt-Väisälä frequency. The agreement betweenh _Nandh _lidbis good. Discrepancies between the two methods are caused by:

1. rapid growth of the boundary layer arround the measurement time;
2. the presence of a deep entrainment layer leading to a large zone in which quantities are not well mixed;
3. a large systematic error of 100–200 m in the estimate of boundary-layer height obtained from the radiosonde due to the way that profiles are recorded, as a series of significant points.

     

2008年冬季北京上空上对流层/下平流层臭氧的异常特征

利用国产GPSO3臭氧探空系统观测的大气臭氧探空资料和NCEP再分析资料,结合对天气形势、大气环流背景、高空位涡变化及对流层顶高度扰动的分析,深入研究了2008年冬季北京地区10~14 km高度范围内持续出现的臭氧次峰值及大气臭氧含量异常现象。结果表明:在2008年我国南方雪灾这一特殊时期,引起臭氧垂直分布持续出现次峰值现象及臭氧含量异常的主要原因是平流层空气强烈下沉运动及其与对流层的交换作用,而引起这种下沉运动及平流层-对流层交换则是由于该阶段特殊的天气背景,乌拉尔阻塞高压长时间维持,贝加尔湖到巴尔喀什湖一带横槽稳定存在,里海以东切断低压长期维持,造成冷空气长时间、稳定地南下影响北京上空臭氧的垂直分布。加之副热带急流的出现,北京正处于其入口区左侧,其上空有强烈的辐合下沉运动,有利于平流层空气向下输送。此次臭氧次峰值及臭氧含量异常的现象很好地说明,在冷空气天气过程的影响下,北京地区上空的平流层空气运动及其与对流层的交换十分活跃。