Surface ozone measurements in the Venezuelan tropical savannah

A one-year set of surface ozone measurements in a four-station network located in the Venezuelan savannah is reported. The diurnal ozone variation is typical of continental stations with a maximum in the afternoon, when vertical turbulent mixing is strongest. The annual O₃ average concentration, based on the monthly averages of daily maxima, was 17±2 ppb, which is in good agreement with values reported for similar latitudes. The boundary-layer ozone levels did not fall below 8 ppb, in contrast with previous sporadic measurements made in tropical latitudes. No evidence was found that mesoscale O₃ downdrafts in the ITCZ in the South American continent are an important source of surface ozone. Finally, it is suggested that the relatively high ozone levels observed at the end of the dry season are probably of photochemical origin.     

Interannual variability and temporal variations of total column ozone in Visakhapatnam from ground based observations

Total column ozone (TCO) measured by the portable, handheld, multichannel Sun photometer (ozonometer-Microtops-II) at Visakhapatnam (17.43°N, 83.14°E; 51 m above mean sea level), India, which is a tropical urban station has been analysed in this study. The results showed the estimate of the annual and seasonal trends of TCO from the period February 2005 to December 2008. The linear regression technique was applied in Microtops II data to study the trend of TCO during 2005?C2008. It also provides statistics of mean and variability on temporal scale. The results showed increasing trend at Visakhapatnam an average of 1.88 DU per year (or 0.61% per year). However the maximum deviation in diurnal variability of TCO were 28 DU (9.19%) while the minimum deviation were ?36 DU (?11.8%) respectively, which is one of the unique result of this study. The range of the seasonal change represents 9.2% of the mean TCO value with maximum/minimum during March/December.     

Relationship between the interannual variations of total ozone in the Northern Hemisphere and the QBO of basic flow in the tropical stratosphere

The harmonic analyses of monthly mean total ozone in the atmosphere over the Northern Hemisphere for 26 years (1960-1985) are made by using the Fourier expansion. The analysed results show that there is obviously a quasi-biennial oscillation (QBO) in the interannual variations of the amplitudes of total ozone. Generally, the amplitudes of wavenumber 1 and 2 during the westerly of the equatorial QBO are larger than those during the easter-ly. In the early winter, the amplitude of wavenumber 1 during the easterly phase is larger, and in the late winter, it is larger during the westerly phase. These are in good agreement with the observational distributions.     

Chemical effect of carbonaceous aerosols on the diurnal cycle of MBL ozone at a tropical site: measurements and simulations

During late austral summer and winter 1998, black carbon (BC) aerosols were monitored with an Aethalometer at 2 sites of La Réunion Island (Indian Ocean): Saint‐Denis, the main city and Sainte‐Rose, a quite uninhabited region situated at the east coast. BC concentration data at Saint‐Denis show a marked diurnal cycle, which may be primarily attributed to traffic. The background data found at night‐time display average BC concentrations, ranging from about 80 to 250 ng/m³ whereas during the day, BC concentrations increase by a factor of at least 4. In comparison, BC concentrations vary in the range of 10 to 60 ng/m³ at Sainte‐Rose. Ozone concentration was also measured at Saint‐Denis using a Dasibi photometer and found to be at significant levels (means: 16.5–23 ppbv in April and 28.5–34 ppbv in September). A noticeable increase of ozone concentrations during the day points out the build‐up of pollutants enhancing photochemical transformations. However, during traffic pollution peaks, ozone concentration displays systematic depletion. The comparison of ozone and BC measurements at both seasons points to some possible effects of heterogeneous interaction of ozone and its precursors with BC particles. These interactions were also simulated with a 0D time‐dependent chemistry model using conditions of a polluted site. The measured ozone concentration characteristics (mean concentration and range of variation) are well simulated in the presence of BC. Our model results show that at La Réunion Island adsorption of ozone and its precursors onto BC aerosol particles could be one of the important steps determining ozone concentration characteristics, especially in absence of photochemistry during night‐time.     

Total ozone in the most humid monsoon region

Summary Simple analysis of about fifteen years of monthly total ozone data in the light of associated meteorological processes has been carried out in the tropical and subtropical regions of northern hemisphere. A well marked trough in total ozone has been observed in July and August over the most humid part of the region, which comes under the influence of monsoon circulation. It appears that the occurrence of the trough may be due to the lifting of air mass by the intense convective activity over areas of the low level convergence, which is fed normally from the equatorial belt. Also, the possible occurrence of stratospheric fountain due to the existence of the coldest air around the tropopause over the entire Southeast Asia and adjacent west Pacific ocean, may be playing some role to produce this feature.With 5 Figures     

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.     

利用扫描式红外亮温仪对天空云量的试验观测

利用中国科学院大气物理研究所中层大气与全球环境探测实验室自主开发研制的全自动扫描式天空红外亮温仪,于2007年4-8月在北京市气象局南郊观象台进行了试验观测.利用获得的天空红外亮温数据和南郊观象台(54511站)实时地面气象数据,进行了天空云量的计算.将整点前30 min内观测的云量的平均值作为与观象台观测对应的整点观测云量,分不同情况与观象台目视观测结果进行了对比分析.结果表明:(1)对于中低云,两种观测的云量比较一致,但如果在此期间云消散或增加很快,则差别较大.其主要原因是观测的时间和方式不同所造成的.(2)对于以卷云为主的天空情况,特别是高层薄卷云的情况,两种观测的云量差别较大.原因是受到目前试验所使用的红外传感器低温测量范围的限制(-50℃),以及判定云的阈值算法目前还只对于中低云比较适用,对于卷云的判断能力比较薄弱.(3)对于天空情况比较复杂,以及能见度不好的情况(气象站目视云量记录为10-),两种观测的云量差别也很大.其差别既受到仪器性能的影响,也与观测员视力与经验有关.仪器受到最低测量温度的限制,反演算法也有其不确定性,而观测员在低能见度时的观测局限性亦是一个重要原因.利用SIRIS-1进行云量和云底高度观测的优点是时间分辨率高,且全天时自动化,但对于卷云的判断还较薄弱.     

Analytical studies on the variations of the antarctic ozone layer

The Antarctic ozone hole which was discovered in the mid 1980s has caused much attention from the scientists and politicians throughout the world.For the formation of the Antarctic ozone hole, most scientists believe that the man-made chemical materials such as CFCs etc. are main cause. On the other hand, the electrochemistry-dynamics theory presented by Wei (Guang Ming Daily Dec. 11, 1990) two years ago has also caused some attention.In the paper the data of ozone, solar activity meteorology over Antarctica have been used for statistical analyti-cal studies. Our results present some new evidence to support Wei's theory. However the influence of the human activ-ities can never be slighted.     

Spatial variations of sea-level rise and impacts: An application of DIVA

Due to complexities of creating sea-level rise scenarios, impacts of climate-induced sea-level rise are often produced from a limited number of models assuming a global uniform rise in sea level. A greater number of models, including those with a pattern reflecting regional variations would help to assure reliability and a range of projections, indicating where models agree and disagree. This paper determines how nine new patterned-scaled sea-level rise scenarios (plus the uniform and patterned ensemble mean rises) influence global and regional coastal impacts (wetland loss, dry land loss due to erosion and the expected number of people flooded per year by extreme sea levels). The DIVA coastal impacts model was used under an A1B scenario, and assumed defences were not upgraded as conditions evolved. For seven out of nine climate models, impacts occurred at a proportional rate to global sea-level rise. For the remaining two models, higher than average rise in sea level was projected in northern latitudes or around populated coasts thus skewing global impact projections compared with the ensemble global mean. Regional variability in impacts were compared using the ensemble mean uniform and patterned scenarios: The largest relative difference in impacts occurred around the Mediterranean coast, and the largest absolute differences around low-lying populated coasts, such as south, south-east and east Asia. Uniform projections of sea-level rise impacts remain a useful method to determine global impacts, but improved regional scale models of sea-level rise, particularly around semi-enclosed seas and densely populated low-lying coasts will provide improved regional impact projections and a characterisation of their uncertainties.     

Long-term measurements of surface ozone in the German Democratic Republic

The ozone concentration near the earth's surface has been measured at some stations in the GDR for more than 30 yr using the wet chemical method. Even at rural stations the ozone data show a significant linear increase by about 1–3% yr^–1. The ozone increase being stronger in summer than in winter is assumed to be due to photochemical ozone production from increasing anthropogenic emissions of trace gases that are transported over long distances. A weaker ozone increase by only about 0.2% per year was observed in the free troposphere (5.5 km) from balloon-soundings at Lindenberg within the period 1975–1984. If the ozone trends continue, the ozone concentration near the surface and its seasonal amplitude will have doubled around the turn of the century as compared to the mid-fifties.     

On the seasonal sea surface temperature variations in the tropical Pacific

Summary In this paper, we investigated physical processes that control the seasonal variations of sea surface temperature in the tropical Pacific, using an intermediate ocean model. It is found that the westward propagation of sea surface temperature along the equator is attributed to dynamic response of the ocean to the wind (that consists of 3-dimensional temperature advection), whereas the northward propagation of sea surface temperature in the eastern Pacific results from the thermodynamic response of the ocean to the surface heat flux, primarily shortwave radiation that includes the effect of low-level stratus clouds. The remote response of the eastern Pacific sea surface temperature to seasonally varying wind in the western Pacific is of secondary importance, compared to the local wind forcing. The results suggest that the mechanism that controls the seasonal cycle of sea surface temperature is different from that associated with El Nino-Southern Oscillation.With 9 Figures     

Airborne measurements of the vertical flux of ozone in the boundary layer

A fast-response chemiluminescent ozone sensor was mounted in an aircraft instrumented for air motion and temperature measurements. Measurements of the vertical flux of ozone by the eddy correlation technique were obtained after correcting for time delay and pressure sensitivity in the ozone sensor output. The observations were taken over eastern Colorado for two days in April, one a morning and the other an afternoon flight. Since the correlation coefficient of ozone and vertical velocity is small compared to, for example, temperature and vertical velocity in the lower part of the convective boundary layer, an averaging length of the order of 100 km was required to obtain a reasonably accurate estimate of the ozone flux. The measured variance of ozone appeared to be too large, probably mainly due to random noise in the sensor output, although the possibility of the production of ozone fluctuations by chemical reactions cannot be dismissed entirely. Terms in the budget equation for ozone were estimated from the aircraft measurements and the divergence of the ozone flux was found to be large compared to the flux at the surface divided by the boundary-layer height.Part of this work was carried out while a visitor at Risø National Laboratory, Denmark.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

中层大气臭氧的全日盘掩日测量

本文研究了日盘张角对掩日测量的影响,引进了日盘光辐射空间变化特性这一先验信息,提出了从全日盘掩日测量反演中层大气臭氧含量的新方法.数值模拟试验指出,这一方法可以满意地给出25—65km高度范围内大气臭氧的垂直分布。当测量吸收比的均方根噪声为0.01时,其反演误差小于10％.利用这一方法,可以大大简化探测系统、降低测量对遥感平台的要求.     

地基GPS在暴雨预报中的应用进展

加密的地基GPS全球定位系统网具备监测中小尺度天气水汽变化的功能.利用对流层延迟与水汽之间的关系,可以建立地基GPS水汽反演方法以获取大气可降水汽总量PWV和斜路径水汽含量SWV,并通过层析算法得到三维水汽分布.PWV的时间变率、PWV水平梯度变率和区域PWV水汽辐合辐散量定量反映了水汽输送以及区域水汽增减,PWV时间序列的初始峰值在暴雨临近预报中有重要的指示意义,地基GPS网的PWV可以作为数值天气预报模式的重要资料.不同指向的SWV可以表征测站周围水汽的非均匀性质,SWV和三维水汽层析可有效用于中小尺度天气的湿度分析和降水的定量预测.结合掩星GPS和其他探测信息,GPS/MET可以在暴雨监测预报中发挥更重要的作用.     

基于局部阈值插值的地基云自动检测方法

地基云自动化观测是当前气象业务发展的迫切需求.目前的地基云检测算法仍主要是以阈值为基础,针对固定阈值和全局阈值算法在云检测精度方面存在的不足,利用晴朗天空下天空呈蓝色、云呈白色的属件,提出了一种基于局部阈值插值的地基云自动检测方法.该方法在对云图进行重采样后,对云图蓝、红波段进行归一化差值处理,再将处理后的结果图像按空间像素位置自动分成互不重叠、大小相等的均匀子块,对每一子区域采用一定的规则并结合改进的最大类间方差自适应阈值算法计算局部阈值,然后对每一子区域形成的阈值矩阵采用双线性插值算法进行插值处理,形成与原始云图大小相等的阈值曲面,利用此阈值曲面与云图蓝、红波段归一化差值处理结果进行比较,即可完成地基云的自动检测.与固定阈值和全局阈值算法相比,局部阈值插值算法对一些细碎的云和与背景反差不大的云获得了更好的检测效果.定量的评估结果表明,固定阈值方法在正确率和精确度上都要远远低于全局阈值和局部阈值方法,而文中提出的局部阈值算法在正确率和精确度上相比全局阈值算法又有较大提高.