亚洲夏季风的年际和年代际变化及其未来预测

本文是对我们近五年在亚洲夏季风年代际与年际变率及其未来预测方面研究的一个综述.主要包括下列三个问题:(1)根据123年中国夏季降水资料和印度学者的分析,检测出亚洲夏季风具有明显的年代际尺度减弱,这种年代际变化使中国东部(包括东亚)和南亚夏季降水的格局在过去60年中发生了明显变化.在东亚,从1970年代后期开始,主要异常雨带有不断南移的趋势,结果造成了南涝北旱的降水分布,这主要受到60～80年年代际振荡的影响.青藏高原前冬和春季积雪的年代际减少与热带中东太平洋海表温度的年代际增加是东亚降水型改变的主要原因,这是通过减弱亚洲地区夏季海陆温差与夏季风强度而实现的.未来亚洲夏季风的预测表明,东亚夏季风和南亚夏季风对气候变暖有十分不同的响应.东亚夏季风在本世纪将增强,雨带北推,尤其在2040年代之后;而南亚夏季风环流将继续减弱.这种不同的变化是由于两者对高低层海陆热力差异的不同响应造成.(2)年际尺度的变率在亚洲夏季风区主要表现为2年与4～7年的振荡.本文着重分析了2年振荡(TBO)形成的过程、机理及其对东亚降水的影响.对TBO-海洋机理进行了具体的改进,说明了东亚夏季风降水深受TBO影响的原因,尤其是阐明了长江型(YRV) TBO和淮河型(HRV) TBO的特征及其形成的循环过程.(3)在总结亚洲夏季风时期遥相关型的基础上,本文提出了季节内和年际尺度的低空遥相关型:即西北太平洋季风的遥相关型与印度“南支”和“北支”遥相关型.它们基本上反映了沿低空夏季风强风速带Rossby波群速度传播的结果.据此可以根据西北太平洋和印度夏季风的变化分别预测中国梅雨和华北雨季来临和降水异常.最后研究还表明,在本世纪亚洲夏季风可能更显著地受到人类活动造成的全球变暖的影响,未来的亚洲夏季风活动是人类排放的CO2引起的全球变暖与自然变化(海洋和陆面过程(积雪))共同作用的结果.     

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.     

Evaluation of surface ozone measurements during 2000–2005 at a rural area in the upper Spanish plateau

This paper presents the main experimental results of surface ozone concentrations measured at a rural area in Northern Spain from February 2000 to December 2005. Daily and seasonal variation of ozone has been analysed. The peak concentration levels are obtained in the afternoon, mean value around 88 μg m⁻³, with extreme average values of 59 μg m⁻³ in January and 113 μg m⁻³ in July. Small differences are found in the mean and median of the ozone levels from April to August, when spring and summer maxima are observed. Despite the great inter-annual ozone variability obtained, most air quality indicators showed a positive trend. Further analysis of the monthly mean ozone concentrations of the main percentiles have also been performed using a harmonic model. The upward trend was 6.2 ± 1.7 μg m⁻³ for the 98th percentile. To interpret the main features of the annual cycle and describe the ozone peaks, the influence of meteorological factors is studied. In summer, ozone production is governed by local processes, air temperature being the major controlling factor. However, the origin of the spring maximum is not so well identified.     

Conversion rates of surface HOx radicals in Beijing City

Surface OH radical concentration in Beijing City was measured by impregnated filter trapping technique-high performance liquid chromatography (IFT-HPLC). The observed concentration of OH radical showed obvious diurnal and seasonal variations, with maximum readings at noon or afternoon, ∼80×10⁶OH/cm³ in summer and ∼20×10⁶-40×10⁶OH/cm³ in fall. On the basis of measured data, the reaction rates related to the photochemical process of HO_X (OH+HO₂) were derived and characteristics of atmospheric chemical processes in the city were analyzed. The results showed that conversion rates of atmospheric OH and HO₂ in the summer of Beijing City were about 700×10⁶ molecule/(cm³·s) and 600×10⁶molecule/(cm³·s), respectively. And the net production of OH in the air of the city mainly originate from the photolysis of the gaseous HNO₂, and the main sink of OH were the photochemical reactions with VOCs, NO₂, HCHO and CO. It was different from the clean area. Foundation item: Under the auspices of the National Natural Science Foundation of China (No. 40075026) Biography: REN xin-rong (1973 -), male, a native of Zhejiang Province, Ph. D., now a postdoctorship in Pennsylvania State University, USA, specialized in the reaction kinetics of atmospheric environment. E-mail: ren@essc.psu.edu     

Phosphorus and nitrate run‐off in hill pasture and forest catchments,Taita, New Zealand

Abstract

Phosphorus and nitrogen were measured in stream run‐off from the four catchments of the Taita Experimental Basin (41° 11′ S, 174° 58′ E). The land is used as exotic conifer forest, native forest, and hill pasture. Multiple regression analysis was used to estimate chemical losses per unit area in floods and at low flows.

At low flows, the hill pasture (fertilised with lime at 630 kg·ba^?1·y^?1, and superphosphate at 380 kg·ha^?1·y^?1) tended to lose more phosphorus and nitrate than the forested land, but differences were small, and not always significant. During large floods, the hill pasture (No. 5 Catchment) lost about 3 times as much reactive phosphate and 2–5 times as much total phosphorus as the forested land, and 130–190 times as much nitrate as land in the Exotic Forest and Native Forest 2 Catchments. Nitrate losses from land in the No. 4 Catchment (mainly native forest) were as high as those from the hill pasture, so high nitrate loss is not associated solely with agriculture.

Losses of total phosphorus via the catchment streams were estimated as: No. 5 Catchment (hill pasture), 293 g·ha^?1·y^?1; Native Forest 2 Catchment, 201 g·ha^?1·y^?1; No. 4 Catchment, 124 g·ha^?1·y^?1; Exotic Forest Catchment, 71 g·ha^?1.y^?1. Nitrate‐N losses were estimated to have been 1356 g·ha^?1·y^?1, 11.5 g·ha^?1·y^?1, 1436 g·ha^?1·y^?1, and 44 g·ha^?1·y^?1 respectively. Phosphorus and nitrate concentrations were similar in the Exotic Forest and Native Forest 2 streams, but the Exotic Forest tended to lose smaller amounts because it yielded about 50% less water per unit area.

Over the 2‐y study, an estimated 47–70% of phosphorus losses and up to 83% nitrate losses occurred in large floods; 31% and 48% respectively were apparently lost from the hill pasture catchment in a single flood. Less than 20% of estimated phosphorus losses and as little as 1% of nitrate losses occurred at low flows.

Run‐off of phosphorus and nitrate was spasmodic, and this should be considered in assessing the impact of surface run‐off on the biology and chemistry of receiving waters.     

Application of hyperspectral remote sensing reflectance data to photochemical rate calculations in the Duplin River,a tidal river on the coast of Georgia,USA

Estuaries are photochemically dynamic environments with high carbon loads and relatively small areas. The small area poses problems for large-scale satellite-based remote sensing calculations, where the resolution is too coarse to distinguish land from water. Airborne remote sensing instruments have the potential to reveal the dynamics of these areas with fine-scale resolution. In June 2006, hyperspectral remote sensing imagery, using an AISA Eagle instrument, was collected over the tidal Duplin River, Georgia, USA. A dark-water updated version of the SeaUV algorithm was applied to the AISA remote sensing image to determine diffuse attenuation constants in the ultraviolet and calculate surface photochemical production rates of two inorganic products – carbon monoxide (CO) and carbon dioxide (CO₂). For an average day in June at the study site, the modeled photoproduction rates for CO₂ and CO averaged ~7 × 10^?1 nmol C/day/cm³ and ~3.5 × 10^?2 nmol C/day/cm³, respectively.     

珠江三角洲对流层气溶胶时空变化特征分析

利用AERONET资料对珠三角地区气溶胶物理性质特征进行分析,建立珠三角地区的气溶胶模型,在此基础上,根据RT3 辐射传输模型构建矢量查找表,采用多角度偏振方法从PARASOL L1B数据反演得到细模态气溶胶光学厚度(AOD),最后采用2007-2009年MODIS总的AOD产品和本文的细模态AOD三年的反演结果分析了珠三角地区气溶胶的时间变化和空间分布特征,为深入研究珠三角地区污染物的局地排放和输送提供了条件.结果表明:(1)珠三角地区对流层气溶胶呈双峰型对数正态分布,其中细粒子平均半径主要集中在0.05~0.1,标准方差以0.5、0.6为主,粗粒子平均半径以0.9、1.0为主,标准方差为0.6、0.7,复折射指数实部以1.4、1.5 居多,虚部以0、0.01为主,细粒子所占比例大于70%,珠三角气溶胶呈现出粗颗粒物和细颗粒物并存的特征;(2)PARASOL业务算法中的气溶胶模型在珠三角地区有较大的局限性,引入当地气溶胶模型使细模态AOD的反演精度较卫星产品有了很大提高,细模态AOD主要反映了珠三角地区二次污染的强度;(3)珠三角地区总AOD值春季较大,秋夏季次之,冬季较小,并呈现逐年较小的趋势;(4)珠三角地区细模态AOD也在逐年降低,2009年细模态AOD年均值比2007年低了0.02,在空间分布上,高值地区主要集中在广州、佛山、中山等城市.     

Photochemistry in the Arctic Free Troposphere: Ozone Budget and Its Dependence on Nitrogen Oxides and the Production Rate of Free Radicals

Local ozone production and loss rates for the arctic free troposphere (58–85° N, 1–6 km, February–May) during the TroposphericOzone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 kmlayer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NO_x mixing ratiosup to 300 pptv in February and for NO_x mixing ratios up to 500 pptv in May. These NO_x limits are an order of magnitude higher thanmedian NO_x levels observed, illustrating the strong dependence ofgross ozone production rates on NO_x mixing ratios for the majority of theobservations. The threshold NO_x mixing ratio needed for netpositive ozone production was also calculated to increase from NO_x 10pptv in February to 25 pptv in May, suggesting that the NO_x levels needed to sustain net ozone production are lower in winter than spring. This lower NO_x threshold explains how wintertime photochemical ozone production can impact the build-up of ozone over winter and early spring. There is also an altitude dependence as the threshold NO_x neededto produce net ozone shifts to higher values at lower altitudes. This partly explains the calculation of net ozone destruction for the 1–3 km layerand net ozone production for the 3–6 km layer throughout the campaign.