The Impacts of Two Types of El Ni（n）o on Global Ozone Variations in the Last Three Decades

The effects of E1Nifio Modoki events on global ozone concentrations are investigated from 1980 to 2010 E1 Nifio Modoki events cause a stronger Brewer-Dobson （BD） circulation which can transports more ozone-poor air from the troposphere to stratosphere, leading to a decrease of ozone inthe lower-middle stratosphere from 90~S to 90~N. These changes in ozone concentrations reduce stratospheric column ozone. The reduction in stratospheric column ozone during E1 Nifio Modoki events is more pronounced over the tropical eastern Pacific than over other tropical areas because transport of ozone-poor air from middle-high latitudes in both hemispheres to low latitudes is the strongest between 60°W and 120°W. Because of the decrease in stratospheric column ozone during E1 Nifio Modoki events more UV radiation reaches the tropical troposphere leading to significant increases in tropospheric column ozone An empirical orthogonal function （EOF） analysis of the time series from 1980 to 2010 of stratospheric and tropospheric ozone monthly anomalies reveals that： E1 Nifio Modoki events are associated with the primary EOF modes of both time series. We also found that E1 Nifio Modoki events can affect global ozone more significantly than canonical E1 Nifio events. These results imply that E1 Nifio Modoki is a key contributor to variations in global ozone from 1980 to 2010.     

Satellite Measurements of the Madden–Julian Oscillation in Wintertime Stratospheric Ozone over the Tibetan Plateau and East Asia

We investigate the Madden–Julian Oscillation(MJO) signal in wintertime stratospheric ozone over the Tibetan Plateau and East Asia using the harmonized dataset of satellite ozone profiles. Two different MJO indices — the all-season Real-Time multivariate MJO index(RMM) and outgoing longwave radiation-based MJO index(OMI) — are used to compare the MJOrelated ozone anomalies. The results show that there are pronounced eastward-propagating MJO-related stratospheric ozone anomalies(mainly within 20–200 h Pa) over the subtropics. The negative stratospheric ozone anomalies are over the Tibetan Plateau and East Asia in MJO phases 4–7, when MJO-related tropical deep convective anomalies move from the equatorial Indian Ocean towards the western Pacific Ocean. Compared with the results based on RMM, the MJO-related stratospheric column ozone anomalies based on OMI are stronger and one phase ahead. Further analysis suggests that different sampling errors, observation principles and retrieval algorithms may be responsible for the discrepancies among different satellite measurements. The MJO-related stratospheric ozone anomalies can be attributed to the MJO-related circulation anomalies,i.e., the uplifted tropopause and the northward shifted westerly jet in the upper troposphere. Compared to the result based on RMM, the upper tropospheric westerly jet may play a less important role in generating the stratospheric column ozone anomalies based on OMI. Our study indicates that the circulation-based MJO index(RMM) can better characterize the MJOrelated anomalies in tropopause pressure and thus the MJO influence on atmospheric trace gases in the upper troposphere and lower stratosphere, especially over subtropical East Asia.     

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.     

On the transfer of stratospheric ozone into the troposphere near the north pole

A series of nearly daily ozone vertical profiles obtained at station T-3 on Fletcher's Ice Island (85°N, 90°W) during the period January-March 1971 shows several significant ozone intrusions into the troposphere. These intrusions are not only associated with enhanced ozone amounts in the stratosphere but also require tropopause folding events to transport ozone into the troposphere. These folds in the Arctic tropopause appear to be capable of contributing significantly to the ozone budget of the Arctic troposphere during the late winter and spring seasons. The importance of tropopause folding for bringing ozone into the troposphere seen in the daily ozone profiles confirms the results found in the Arctic Gas and Aerosol Sampling Program aircraft flights.     

Comparison of Lower-Tropospheric Temperature Climatologies and Trends at Low and High Elevation Radiosonde Sites

Observations of rapid retreat of tropical mountain glaciers over the past two decades seem superficially at odds with observations of little or no warming of the tropical lower troposphere during this period. To better understand the nature of temperature and atmospheric freezing level variability in mountain regions, on seasonal to multidecadal time scales, this paper examines long-term surface and upper-air temperature observations from a global network of 26 pairs of radiosonde stations. Temperature data from high and low elevation stations are compared at four levels: the surface, the elevation of the mountain station surface, 1 km above the mountain station, and 2 km above the mountain station. Climatological temperature differences between mountain and low elevation sites show diurnal and seasonal structure, as well as latitudinal and elevational differences. Atmospheric freezing-level heights tend to decrease with increasing latitude, although maximum heights are found well north of the equator, over the Tibetan Plateau. Correlations of interannual anomalies of temperature between paired high and low elevation sites are relatively high at 1 or 2 km above the mountain station. But at the elevation of the station, or at the two surface elevations, correlations are lower, indicating decoupling of the boundary layer air from the free troposphere.Trends in temperature and freezing-level height are generally upward, both during 1979–2000 and during longer periods extending back to the late 1950s. However, some negative trends were found at extratropical locations. In many cases, statistically significant differences were found in trends at paired high and low elevation stations, with tropical pairs revealing more warming (and greater increases in freezing-level height) at mountain stations than at low elevations. This result is consistent with both the observed retreat of tropical glaciers and the minimal change in tropics-wide tropospheric temperatures over the past two decades.Overall, the analysis suggests that, on diurnal, seasonal, interannual, and multidecadal time scales, temperature variations at mountain locations differ significantly from those at relatively nearby (a few hundred kilometers) low elevation stations. These differences are greatest at the two surface levels, but can persist up to 2 km above the mountain site. Therefore, to determine the nature of climate variability at high elevation sites requires local observations, since large-scale patterns derived from low elevation observations may not be representative of the mountain regions. Conversely, temperature change in mountain regions should not be viewed as necessarily representative of global surface or tropospheric trends.     

Dynamical and Chemical Features of a Cutoff Low over Northeast China in July 2007: Results from Satellite Measurements and Reanalysis

The European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) meteorology and measurements from the Microwave Limb Sounder, High Resolution Dynamics Limb Sounder, and Ozone Monitoring Instrument onboard the Earth Observing System Aura satellite were applied to analyze the dynamical and chemical features of a cutoff low (COL) event over northeast China in early July 2007. The results showed the polar stratospheric origin of an upper-level warm-core cyclone at 100--300 hPa, associated with a funnel-shaped tropopause intruding into the mid-troposphere just above the COL center. The impacts of the stratospheric intrusion on both column ozone and ozone profiles were investigated using satellite measurements. When the intensity of the COL peaked on 10 July 2007, the total column ozone (TCO) increase reached a maximum (40--70 DU). This could be dynamically attributed to both the descent of the tropopause (～75%) and the downward transport of stratospheric ozone across the tropopause (～25%). Analysis of the tropospheric ozone profiles provided evidence for irreversible transport/mixing of ozone-rich stratospheric air across the tropopause near the upper-level front region ahead of the COL center. This ozone intrusion underwent downstream transport by the upper tropospheric winds, leading to further increase in TCO by 12--16 DU over broad regions extending from east China toward the northern Japan Sea via South Korea. Meteorological analysis also showed the precedence of the stratospheric intrusion ahead of the development of cyclones in the middle and lower troposphere.     

夏季风爆发前后中国区域对流层顶高度变化特征

利用2008—2014年全国高垂直分辨率的L波段探空资料,统计分析了东亚夏季风爆发前后我国不同区域对流层顶高度变化特征。研究表明:夏季风爆发后,对流层顶高值区向北推进,最大值位于青藏高原南部及其东南部地区;对流层顶高度的向南梯度和向东梯度大值区均由爆发前的30°~40°N北移至40°~50°N;受地面加热和垂直运动的影响,中国东北部和中东部在夏季风爆发后对流层升温,平流层-对流层过渡层降温,大气温度梯度增加,对流层顶上升,其中中国东北部在夏季风爆发前,大气温度廓线为双峰结构,易出现双对流层顶,第一对流层顶较低;中国南部整层大气温度廓线在夏季风爆发后略有增加,对流层顶有所下降。     

利用探空资料验证GOME卫星臭氧数据

利用1996年3月-2003年6月部分时段拉萨、西宁、北京3个站的臭氧探空资料验证了GOME（Global Ozone Monitoring Experiment）卫星臭氧廓线及对流层臭氧柱总量。对比结果表明:在对流层中下层,拉萨和西宁两地GOME与探空的平均偏差小于5%,北京地区平均偏差小于10%;在对流层上层/平流层下层,拉萨和西宁平均偏差小于10%,北京小于20%;在平流层中上层3个站的平均偏差均小于5%。在对流层上层/平流层下层区域,GOME与臭氧探空的平均偏差在北京明显高于拉萨和西宁。3个地区对流层柱总量的平均偏差都在10%以内,表明该资料可用于研究我国对流层臭氧总量的变化规律。同时段的GOME最低层（0~2.5km）月平均臭氧浓度对比结果显示,GOME结果同地面臭氧观测值有很好的相关性,GOME臭氧浓度反映了拉萨、瓦里关、临安地面臭氧浓度的主要变化特征。     

Vertical structure of tropical mesoscale convective systems: observations using VHF radar and cloud resolving model simulations

This study examines the time–height variation and structure of a tropical mesoscale convective system (TMCS). Convection experiments using VHF (53 MHz) radar aimed at improving the understanding of the vertical structure of TMCS occurred over Gadanki (13.5°N, 79.2°E), India during 21–22 June 2000 has been selected for the study. The time–height variations of reflectivity and vertical velocity exhibits four distinct patterns and have been used to classify four subjectively identified types of echoes; viz., formative, mature, transition zone and stratiform regions associated with TMCS. Average vertical velocity profiles were distinctive for each region. The mean vertical motion is upward at all levels in the troposphere during the formative phase. The vertical motion in the mature region is downward in the lower troposphere and upward in the middle and upper troposphere. The maximum upward motion is found in the middle troposphere and secondary maxima near the tropopause level. The transition zone is characterized by strong downdraft in the lower troposphere with local pockets of updrafts in the middle and upper troposphere. The magnitude of the mean vertical motion is considerably reduced in the stratiform region and is downward in the lower troposphere and upward in the upper troposphere. Time–height variation of reflectivity has been analyzed separately for each region. The observed diminished echo zone and tropopause break/weakening during the mature phase and two enhanced reflectivity zone in the stratiform region is also observed. A Cloud System Resolving Model (CSRM) simulation of the same event has been carried out. The CSRM simulations were able to capture the structure of the storm and are consistent with the observations. The model output in conjunction with observations has been used to validate the hypothesis.     

夏季亚洲季风区对流层向平流层输送的源区、路径及其时间尺度的模拟研究

基于NCEP/NCAR分析资料和拉格朗日轨迹输送模式FLEXPART, 通过气块轨迹计算, 对2005年夏季亚洲季风区对流层向平流层输送 (Troposphere to Stratosphere Transport, 简称TST) 的近地层源区、 输送路径及其时间尺度问题进行了一些初步探讨。结果表明: (1) 夏季亚洲季风区TST两个主要的边界层源区, 一个是热带西太平洋地区; 另一个是青藏高原南部、 孟加拉湾以及印度半岛中北部等地区, 上述两个区域与夏季强对流的分布相一致。在对流层顶高度附近 (约16 km高度), 两个近地层源区的垂直输送贡献相当。但进一步分析发现, 穿越对流层顶高度的质量输送只有约10％能够进入20～22 km高度的平流层中, 且主要源于以青藏高原南侧为代表的南亚季风区 (约贡献75%), 这进一步强调了青藏高原及其周边区域在全球TST过程中的重要地位。 (2) 轨迹分析显示, 夏季亚洲季风区对流层进入平流层的 “入口区” 主要在 (25°N～35°N, 90°E～110°E) 区域的青藏高原及其周边区域。TST路径受对流层上层南亚高压闭合环流、 北半球副热带西风急流和赤道东风急流的共同控制。 (3) 亚洲季风区TST两个主要的过程, 一个是和夏季湿对流抬升直接联系的快速输送过程, 它可以使近地层大气在1～2天内输送到平流层中, 贡献了整个TST的10%～30%; 另一个是大气辐射加热所致的大尺度垂直输送, 该输送是一个相对的慢过程, 时间尺度一般为5～30天。此结果意味着, 源于地表的短生命周期的大气污染物可通过光化学反应过程对该区域平流层臭氧及其他大气痕量成分平衡产生重要影响。     

Formation of the Summertime Ozone Valley over the Tibetan Plateau: The Asian Summer Monsoon and Air Column Variations

The summertime ozone valley over the Tibetan Plateau is formed by two influences,the Asian summer monsoon(ASM) and air column variations.Total ozone over the Tibetan Plateau in summer was ～33 Dobson units(DU) lower than zonal mean values over the ocean at the same latitudes during the study period 2005-2009.Satellite observations of ozone profiles show that ozone concentrations over the ASM region have lower values in the upper troposphere and lower stratosphere(UTLS) than over the non-ASM region.This is caused by frequent convective transport of low-ozone air from the lower troposphere to the UTLS region combined with trapping by the South Asian High.This offset contributes to a ～20-DU deficit in the ozone column over the ASM region.In addition,along the same latitude,total ozone changes identically with variations of the terrain height,showing a high correlation with terrain heights over the ASM region,which includes both the Tibetan and Iranian plateaus.This is confirmed by the fact that the Tibetan and Iranian plateaus have very similar vertical distributions of ozone in the UTLS,but they have different terrain heights and different total-column ozone levels.These two factors(lower UTLS ozone and higher terrain height) imply 40 DU in the lower-ozone column,but the Tibetan Plateau ozone column is only ～33 DU lower than that over the non-ASM region.This fact suggests that the lower troposphere has higher ozone concentrations over the ASM region than elsewhere at the same latitude,contributing ～7 DU of total ozone,which is consistent with ozonesonde and satellite observations.     

Mean structure of the tropical tropopause and its variability over the Indian longitude sector

The mean spatiotemporal variations in tropopause parameters over the tropics (±35°, in latitude) in the Indian monsoon region are examined using the upper air data for an extended period obtained from radiosonde and Radio Occultation measurements. In general, the altitude of cold point tropopause (CPT) is a minimum near the equator and increases with latitude on either side. While CPT over the entire southern tropical latitudes and northern equatorial region is cooler (higher) during boreal winter and warmer (lower) during boreal summer, the annual pattern of CPT-temperature reverses in the northern hemispheric off-equatorial region. The temperature of lapse rate tropopause (LRT) is always negatively correlated with its altitude. While the annual variation of LRT-temperature in tropics is always positively correlated with CPT-temperature, the annual variation of LRT-altitude differs mainly in the off-equatorial regions. While the altitude of the convective tropopause is positively correlated with CPT-altitude over the latitude region 20°S–5°N, they are negatively correlated at the north of 10°N. In general, the tropical tropopause layer (TTL) is very thin (~3 km) near the equator and its thickness increases with latitude on either side of the equator to reach a peak value (of ~6 km) around ±30°. A pronounced decrease in TTL-thickness observed over the northern off-equatorial region during the ASM period can be attributed to the manifestation of very deep convection over the land near the Head Bay-of-Bengal region. The TTL-lapse-rate (γ_TTL) is large in the equatorial region and decreases with increase in latitude. While γ_TTL in the northern hemispheric off-equatorial region is low during winter, it increases and becomes comparable to that over equatorial region during the ASM period. The annual variations in CPT parameters as well as the TTL- thickness are significantly modulated by quasi-biennial oscillation and the El Niño Southern Oscillation.     

Effects of the Tibetan Plateau on total column ozone distribution

The relatively low total column ozone (TCO) above the Tibetan Plateau (TP) observed in summer is only partly due to the thinness of the atmospheric column. In this paper the effect of the TP on the TCO is further investigated using satellite data [Total Ozone Mapping Spectrometer (TOMS) ozone column and Stratospheric Aerosol and Gas Experiment II (SAGE II) ozone profiles], ECMWF ERA-40 reanalysis data and a 3-D chemistry-climate model (CCM). It is found that the low TCO over the TP is also closely related to large-scale uplift and descent of isentropic surfaces implied by seasonal and longitudinal variations in the tropopause height. The variations in tropopause height, with a maximum in summer, can be driven by various processes including convective activity, air expansion as well as the monsoon system. While previous studies have showed an important role of troposphere-to-stratosphere transport in contributing to the observed low ozone column over the TP, the mechanism revealed in this study is an alternative amendment to the causes of the TCO low over the TP. It is also found that the monsoon anticyclone circulation induces an isentropic transport of trace gases from high latitudes towards the TP in the lower stratosphere and hence modifies tracer distributions. For the vertical distribution of ozone, the modulation by the TP is most significant below ∼20 km, that is, in the upper troposphere and lower stratosphere (UTLS). The smaller differences in NO _x between Eastern TP and TP compared to large dynamically caused differences in ozone and methane imply the TCO low over the TP is mainly due to transport processes rather than chemistry.     

一次对流层异常臭氧次峰的观测研究及其动力输送过程的分析

文中分析了 1996年 8月 1日发生在西宁 (36 .4 3°N ,10 1.4 5°E ,海拔 :2 2 96m)地区对流层异常臭氧次峰现象。观测资料揭示了高空低压槽东移是臭氧次峰的主要天气特征。三维后向轨迹计算表明 ,尽管代表臭氧次峰的气团可以追溯到中亚地区 ,但是明显的气团向下输送则发生在新疆、青海间的高空低压槽内。中尺度模拟进一步确认了对流层顶折叠和平流层向下输送是臭氧次峰出现的动力机制。臭氧次峰在对流层高度位置与准无辐散层有关     

北京地区对流层顶变化及其对上对流层/下平流层区域臭氧变化的影响

根据2001～2003年期间获得的大气臭氧探空资料,揭示了北京地区上空对流层顶高度的某些变化特征及其对上对流层(UT)和下平流层(LS)区域内大气臭氧含量变化的影响.结果显示:北京地区上空对流层顶高度的平均值约11.1 km,其变化范围为7.7～14.4 km,臭氧层顶始终处在对流层顶下方约0.9 km高度处.对流层顶高度变化与臭氧总量变化之间的关系相对较弱.通常情况下,LS中的臭氧积分量明显高于UT中的相应值,并且二者呈相反的季节变化特征.北京地区上空仲夏和初秋季节第一对流层顶出现的频数明显减少,在第一对流层顶消失的情况下,LS中的臭氧积分量明显减少,而UT中的臭氧积分量明显增加,臭氧量减少最多发生在200～100 hPa层次中,而臭氧量增幅最大的层次是400～250 hPa.     

Observation of a summer tropopause fold by ozonesonde at Changchun,China: Comparison with reanalysis and model simulation

Tropopause folds are one of the key mechanisms of stratosphere-troposphere exchange (STE) in extratropical regions, transporting ozone-rich stratospheric air into the middle and lower troposphere. Although there have been many studies of tropopause folds that have occurred over Europe and North America, a very limited amount of work has been carried out over northeastern Asia. Ozonesondes produced by the Institute of Atmospheric Physics were launched in Changchun (43.9°N, 125.2°E), Northeast China, in June 2013, and observed an ozone-enriched layer with thickness of 3 km and an ozone peak of 180 ppbv at 6 km in the troposphere. The circulation field from the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim) dataset shows that this ozone peak was caused by a tropopause fold associated with a jet stream at the eastern flank of the East Asian trough. By analyzing the ozone data from the ozone monitoring instrument and Weather Research and Forecasting model with Chemistry (WRF-Chem) simulations, it was found that a high ozone concentration tongue originating from the lower stratosphere at high latitude (near central Siberia) intruded into the middle troposphere over Changchun between 5 and 8 km on 12 June 2013. The high-resolution WRF-Chem simulation was capable of describing events such as the tropopause fold that occurred on the cyclonic shear side of the jet stream. In addition, the TRAJ3D trajectory model was used to trace the origin of measured secondary ozone peaks in the middle troposphere back, for example, to stratospheric intrusion through the tropopause fold.     

Lower/middle tropospheric ozone variability in Senegal during pre-monsoon and monsoon periods of summer 2008: observations and model results

During the summer (8 June through 3 September) of 2008, 9 ozone profiles are examined from Dakar, Senegal (14.75°N, 17.49°W) to investigate ozone (O₃) variability in the lower/middle troposphere during the pre-monsoon and monsoon periods. Results during June 2008 (pre-monsoon period) show a reduction in O₃ concentrations, especially in the 850–700 hPa layer with Saharan Air Layer (SAL) events. However, O₃ concentrations are increased in the 950–900 hPa layer where the peak of the inversion is found and presumably the highest dust concentrations. We also use the WRF-CHEM model to gain greater insights for observations of reduced O₃ concentrations during the monsoon periods. In the transition period between 26 June and 2 July in the lower troposphere (925–600 hPa), a significant increase in O₃ concentrations (10–20 ppb) occur which we suggest is caused by enhanced biogenic NO_X emissions from Sahelian soils following rain events on 28 June and 1 July. The results suggest that during the pre-monsoon period ozone concentrations in the lower troposphere are controlled by the SAL, reducing ozone concentrations through heterogeneous chemical processes. At the base of the SAL we also find elevated levels of ozone, which we attribute to biogenic sources of NO_X from Saharan dust that are released in the presence of moist conditions. Once the monsoon period commences, lower ozone concentrations are observed and modeled which we attribute to the dry deposition of ozone and episodes of ozone poor air that is horizontally transported into the Sahel from low latitudes by African Easterly Waves (AEWs).     

Recent fluctuations of tropospheric temperature and water vapour content in the tropics

Summary During the last decades the average temperature of the tropical troposphere (200/850 hPa layer) has steadily increased, between 1965 and 1984 by about 0.8°C in the whole equatorial belt. Data series from a section of individual stations verify this trend as seasonally constant, but decreasing from the equator towards both hemispheres. Further evidence is presented by selected mountain stations and glacier retreat in all equatorial mountains.Above the equatorial Pacific, the same stations indicate an increase of moisture content in the middle troposphere (500/700 hPa layer) expressed in precipitable water as well as in relative humidity. This coincides with increasing sea surface temperature in the area around Indonesia and northern Australia. Above Africa the trend is (if real) quite patchy. Due to the short residence time of water vapour in the atmosphere the horizontal (zonal ) distances between its sources and sinks remain near 2000 km, which may explain, in addition to instrumental differences, large regional deviations.With 7 Figures     

Static Stability of the Troposphere Over the Southeastern Beaufort Sea–Amundsen Gulf Region of the Western Maritime Arctic

The characterization of the static stability of the troposphere over the western maritime Arctic remains limited in spite of its significance to both atmospheric thermodynamics and dynamics. Field observations of microwave radiometric temperature profiles from the International Polar Year, Circumpolar Flaw Lead System Study (late November 2007 to mid-July 2008) and the ArcticNet field campaign (mid-July to early November 2009) provided a unique opportunity to characterize the static stability of the troposphere over the southeastern Beaufort Sea–Amundsen Gulf region. Notably, the monthly median atmospheric boundary layer (<2000?m) static stability profile for April and the profile for May clearly revealed an inversion elevated above a thermal internal boundary layer, whereas the median summer static stability profiles had very strong surface-based inversions. These profiles have been linked to the seasonal evolution of sea-ice cover in Amundsen Gulf. The monthly static stability profiles for the free atmosphere (2000–10,000?m) revealed an annual cycle. The average static stability of the lower troposphere (2000–5000?m) had a minimum of 3.3?±?0.5?K?km^?1 in July and a maximum of 4.5?±?0.5?K?km^?1 in January and February. In the upper troposphere (>5000–8000?m), the average static stability had a minimum of 2.9?±?0.6?K?km^?1 in June and August and a maximum of 5.3?±?0.8?K?km^?1 in January. The monthly median heights of the tropopause also had an annual cycle. The maximum of 9750?m occurred in June, July, and August. The minimum tropopause height of 8000?m occurred in December, January, and March. The seasonal cycles of static stability in the free atmosphere and the seasonal cycle in the height of the tropopause can be attributed to regional as well as synoptic-scale forcing. This analysis will contribute to the understanding of the thermodynamics and dynamics of a data-sparse region of the Arctic by providing a “snapshot” of the state of the atmosphere through a composite annual cycle.     

The Role Of Halocarbons In The Climate Change Of The Troposphere And Stratosphere

Releases of halocarbons into the atmosphere over the last 50 years are among the factors that have contributed to changes in the Earth’s climate since pre-industrial times. Their individual and collective potential to contribute directly to surface climate change is usually gauged through calculation of their radiative efficiency, radiative forcing, and/or Global Warming Potential (GWP). For those halocarbons that contain chlorine and bromine, indirect effects on temperature via ozone layer depletion represent another way in which these gases affect climate. Further, halocarbons can also affect the temperature in the stratosphere. In this paper, we use a narrow-band radiative transfer model together with a range of climate models to examine the role of these gases on atmospheric temperatures in the stratosphere and troposphere. We evaluate in detail the halocarbon contributions to temperature changes at the tropical tropopause, and find that they have contributed a significant warming of ~0.4 K over the last 50 years, dominating the effect of the other well-mixed greenhouse gases at these levels. The fact that observed tropical temperatures have not warmed strongly suggests that other mechanisms may be countering this effect. In a climate model this warming of the tropopause layer is found to lead to a 6% smaller climate sensitivity for halocarbons on a globally averaged basis, compared to that for carbon dioxide changes. Using recent observations together with scenarios we also assess their past and predicted future direct and indirect roles on the evolution of surface temperature. We find that the indirect effect of stratospheric ozone depletion could have offset up to approximately half of the predicted past increases in surface temperature that would otherwise have occurred as a result of the direct effect of halocarbons. However, as ozone will likely recover in the next few decades, a slightly faster rate of warming should be expected from the net effect of halocarbons, and we find that together halocarbons could bring forward next century’s expected warming by ~20 years if future emissions projections are realized. In both the troposphere and stratosphere CFC-12 contributes most to the past temperature changes and the emissions projection considered suggest that HFC-134a could contribute most of the warming over the coming century.