NUMERICAL SIMULATION OF OZONE DISTRIBUTIONS AND ITS VARIATION MECHANISM

A 2-D global chemistry-transport model is set up in this paper.The model simulates theatmospheric ozone distributions well with specified dynamical conditions.The analysis of ozonevariation mechanism shows that ozone is chemically in quasi-equilibrium except for the polar nightregion where the variation of ozone concentration is under the control of dynamical processes,thatthe oxygen atoms which produce ozone are mainly provided by the photolysis of O_2 in the upperstratosphere and by the photolysis of NO_2 in the lower stratosphere and the troposphere.and thatthe ozone is destroyed mainly by NO_x:the reactions between NO_x and O_3 and the odd oxygen cyclecontribute 80% to more than 90% of the ozone destruction.     

NUMERICAL SIMULATION OF THE SEASONAL VARIATION OF TROPOSPHERIC OZONE OVER CHINA

An updated version of the Regional Acid Deposition Model(RADM)driven by meteorologicalfields derived from Chinese Regional Climate Model(CRegCM)is used to simulate seasonal variationof tropospheric ozone over the eastern China.The results show that:(1)Peak O_3 concentration moves from south China to north China responding to the changing ofsolar perpendicular incidence point from south to north.When solar perpendicular incidence pointmoves from north to south,so does the peak O_3 concentration.(2)In the eastern China.the highest O_3 month-average concentration appears in July.thelowest in January and the medium in April and October.The pattern mainly depends on the solarradiation,the concentration of O_3 precursors NO_x and NMHC and the ratio of NMHC/NO_x.(3)Daily variations of O_3 over the eastern China are clear.Namely,O_3 concentrations rise withthe sun rising and the maximums appear at noon.then O_3 concentrations decrease.The highest dailyvariation range of O_3 appears in summer(40×10~(-9) in volume fraction)and the lowest in winter(20×10~(-9) in volume fraction).(4)Daily variations of O_3 over the western China are not clear.The daily variation range of O_3 isless than 10×10~(-9) in volume fraction.     

A NUMERICAL STUDY OF THE VARIATIONS AND DISTRIBUTIONS OF TROPOSPHERIC OZONE AND ITS PRECURSORS OVER CHINA*

By means of a three-dimensional meteorological model (MM5) and a chemical model,the distributions of tropospheric ozone and its precursors over China have been simulated in summer and winter time,16-18 August 1994 and 7-9 January 1995.The distribution of ozone over the Tibetan Plateau in summer time is deeply discussed.The simulated results indicate that thedistributions of surface ozone and NO_x are in good agreement with observed results,and human activities and photochemical reactions are the main factors controlling the surface ozone and NO_x concentrations.In addition,higher ozone concentrations are coincided with the air convergence,and the lower concentrations are related to the air divergence.In summer,over the Tibetan Plateau the strong flow convergence results in higher ozone concentrations in the lower troposphere:and the strong flow divergence results in lower ozone concentrations in the upper troposphere.In winter time ozone concentrations show large-scale characteristics controlled by westerly flow,and in the jet area they are lower than those outside the jet.     

NUMERICAL SIMULATION OF THE FORMATION MECHANISM OF THE ANTARCTIC OZONE HOLE

The global zonally averaged atmospheric chemistry model is developed in this paper.Theformation mechanism of the Antarctic ozone hole is numerically simulated using the model to checkthe viewpoints on the formation mechanism.The results show that:(1)The Antarctic ozone hole is a special phenomenon resulting from the heterogeneousreactions on the surface of the polar stratospheric cloud particles,under the special conditions oftemperature and circulation in Antarctic spring.The heterogeneous reactions reduce the NO_2concentration,resulting in the decrease of ozone production rate.The ozone content decreaseswhen its production is less than its destruction.This is the direct cause for the formation of theAntarctic ozone hole.(2)The impact of the polar vortex on the transport of trace species is not the determinativefactor in the formation of the Antarctic ozone hole.but makes the intensity of the ozone holechanged.(3)The solar cycles have negligible influence on the intensity of the Antarctic ozone holethrough photochemical reactions.     

南半球臭氧变化气候效应的数值模拟

采用一个陆气耦合的９层谱模式模拟了南半球臭氧减少所产生的气候效应。数值试验结果表明,南半球臭氧的减少不仅对南半球温度场的 大气环流有影响,而且对北半球的温度场结构和大气环汉也有一定的影响。其气候效应具有全球性。南半球臭氧减少总体上可以使平流层中层以上大气降温、平流层低层增温、对流层顶附近降温。此外,在北半球冬半年期间,南半球臭氧的减少可使南北半球的副热带西风急流都减弱,极锋急流都增强;在北半球夏半     

中国地区对流层臭氧变化和分布的数值研究

利用三维中尺度非静力模式ＭＭ５和化学模式,对１９９４年８月１６～１８日,１９９５年１月７～９日冬夏两个不同时期中国大陆大气对流层臭氧及其前体物质的分布进行了数值模拟。同时深入地分析了青藏高原地区夏季对流层臭氧的分布。模拟结果地面臭氧和ＮＯｘ的分布与观测结果基本一致,人类活动和光化过程是决定地面臭氧和ＮＯｘ的主要因子。对流层臭氧浓度的分布与气流的辐合辐散存在较好的对应关系,辐合区臭氧浓度较高,辐散区臭氧浓度较低。夏季,青藏高原中低空存在很强的辐合气流,使周边臭氧向高原辐合;而高原高空,受南亚高压控制存在很强的反气旋环流,臭氧由高原向周边辐散。冬季,受西风气流控制,臭氧分布表征大尺度特征。西风急流区臭氧浓度偏低,而急流两侧臭氧浓度偏高。     

A NUMERICAL STUDY OF THE VARIATIONS AND DISTRIBUTIONS OF TROPOSPHERIC OZONE AND ITS PRECURSORS OVER CHINA

By means of a three-dimensional meteorological model(MM5)and a chemical model,thedistributions of tropospheric ozone and its precursors over China have been simulated in summerand winter time,16—18 August 1994 and 7—9 January 1995.The distribution of ozone over theTibetan Plateau in summer time is deeply discussed.The simulated results indicate that thedistributions of surface ozone and NO_x are in good agreement with observed results,and humanactivities and photochemical reactions are the main factors controlling the surface ozone and NO_xconcentrations.In addition,higher ozone concentrations are coincided with the air convergence,and the lower concentrations are related to the air divergence.In summer,over the TibetanPlateau the strong flow convergence results in higher ozone concentrations in the lowertroposphere:and the strong flow divergence results in lower ozone concentrations in the uppertroposphere.In winter time ozone concentrations show Iarge-scale characteristics controlled bywesterly flow,and in the jet area they are lower than those outside the jet.     

NUMERICAL SIMULATION OF THE INFLUENCE OFO3,CO2 AND SPECTRUM VARIATION ON THE PHOTOSYNTHESIS OF CROP CANOPY*

Coupled the photosynthesis with transpiration and adjustment of stoma,a dynamic ecological model for simulating the canopy photosynthesis of winter wheat was established by scaling up from the biochemical scale to canopy scale,in which the effects of O₃,CO₂ and solar spectrum on crop photosynthesis were fully considered.Validation of the model against the data measured with CI-301PS portable photosynthesis analyzer showed that the leaf photosynthesis model passed the correlation significance test and had a fairly high accuracy.Numerical analysis showed that the canopy photosynthesis rate would be reduced by 29% if the O₃ concentration increases from 0 ppbv to 200 ppbv,whereas the canopy photosynthesis rate would increase by about 37% while the CO₂ concentration increases from 330 ppmv to 660 ppmv,and the canopy photosynthesis rate would be reduced by 27%0 or so under the condition that the spectrum coefficient changed from 0.5 to 0.4.If the O₃ concentration reached 200 ppbv at noon on the typical sunny day with higher radiation,the canopy photosynthesis will be reduced slightly in the suburb area where the pollution is serious and the photochemical fog is easy to be formed,contrast with that in the clear region and regardless of the climate change,due to the fact that the positive effect of CO₂ on crop photosynthesis can not compensate the negative effect of O₃ on crop photosynthesis.The canopy photosynthesis will be reduced by 35% or so than the BASE value at present,when the spectrum of photosynthetic active radiation(PAR) reduces to 0.4 or so.     

DISTRIBUTIONS AND VARIATIONS OF SURFACE OZONE IN CHANGSHU, YANGTZE DELTA REGION*

Through one and half year continuous in-situ measurements,the distributions and variations of surface ozone and its precursors at a typical mixed agricultural and metropolitan area-Changshu,Yangtze Delta region,were studied.The preliminary analysis on the concentration levels and variations of surface ozone indicated the obvious seasonal and diurnal cycles during the experiment.The hourly averaged concentrations of surface ozone were high,in about 17% of total valid hours the surface ozone concentration exceeded 50 ppb,and in 22 days the hourly averaged ozone concentration was greater than 100 ppb.There were about 40% of the days in that the daily maximum 8-hour ozone concentration was greater than 50 ppb.The days with daily maximum 8-hour ozone concentration greater than 80 ppb were about 33 days that accounted for about 8% of the observational days.The variations of 5-day moving averaged ozone concentrations depended both on the weather conditions and on the changes of ozone in background atmosphere.Photochemical process had the significant impacts on ozone productions.     

SIMULATION ON CLIMATIC VARIATION OF ARCTIC SEA ICE THROUGH AN ICE-OCEAN COUPLED MODEL*

An ocean model developed by the Institute of Marine Research and the University of Bergen in Norway (BOM) and a state-of-the-art sea ice model developed by NCAR (CSIM4) are coupled, Considering influences of 9 major rivers,forced by the NCEP reanalysis atmospheric fields and the Levitus surface salinity,the Arctic sea ice climatic variation from January 1949 to December.1999 was simulated through the coupled model.The comparison of simulated results and observations shows that:(1)the long-term ice concentration variation tendencies are in consistent with the observations in the divisional ocean regions;(2)simulated ice thickness horizontal distribution is reasonable.Simulated ice thickness has a decreasing tendency in the central Arctic,which agrees with the submarine observations.Simulated annually maximum ice thickness is highly related to observed fast-ice thickness off the Russian coast;and (3)sea ice area/volume fluxes through the Fram Strait are in accord with the satellite-derived data.Generally,the coupled model successfully simulated the Arctic Ocean sea ice climatic variation.     

A REGIONAL MODEL STUDY OF THE VARIATIONS AND DISTRIBUTIONS OF OZONE AND ITS PRECURSORS ON EASTERN ASIA AND WEST PACIFIC OCEAN REGIONS*

A simulated study of mechanism for variations and distributions of ozone and its precursors was made by using the three-dimensional regional Eulerian model.The results showed that the ozone production was controlled by NO_x,but there is a complicated nonlinear relation between them.The photochemical reactions controlled by solar radiation are the determinative factors affecting the variations of the surface ozone and its precursors.The relations of ozone and CO,PAN were studied.We compared the simulated and observed results during the PEM-WEST A in order to better understand the photochemical processes of ozone and its precursors.     

NUMERICAL SIMULATION OF FRONTOGENESIS FORCED BY DUST RADIATIVE HEATING*

In this paper,the frontogenesis forced by dust radiative heating and the radiative effects of an isolated duststorrn on a frontal circulation system are examined by means of two-and three-dimensional numerical models.Results indicate that as a duststorm breaks out,frontogenesis is caused in by dust radiative heating in the lower atmosphere.A marked isentropic potential temperature layer is formed in the middle troposphere.The low-level convergence occurs along the direction of the front movement.Atnight,dust radiative cooling results in frontolysis in the lower atmosphere.An obvious vertical circulation is forced by radiative heating of an isolated duststorm along the direction of the prevailing wind.It is stronger at day,weaker and reverse at night.The response of the horizontal wind field to dust radiative forcing is different at different levels.     

O3,CO2浓度及太阳光谱变化对作物光合作用影响的数值模拟研究

对光合作用 蒸腾作用 气孔调节进行耦合 ,从生物化学尺度扩展至冠层尺度 ,发展了一个冬小麦冠层光合作用生态动力模式 ,模式考虑了O3,CO2 和光谱变化对作物光合的综合影响。利用美国光合作用实测资料对模式进行验证 ,叶片模式通过了相关显著性检验并具有较高的准确度。数值分析表明 :当O3 浓度由 0× 10 -9V/V上升至2 0 0× 10 -9V/V时 ,冠层光合速率下降 2 9%左右 ;当CO2 浓度由 330× 10 -6V/V上升至 6 6 0× 10 -6V/V时 ,冠层光合速率增加大约 37% ;当光谱比例系数由目前的 0 .5下降至 0 .4时 ,冠层光合速率将下降 2 7%左右。对于污染严重、易发生光化学烟雾的城郊附近 ,在阳光强烈的典型晴天 ,中午O3 浓度达到 2 0 0× 10 -9V/V时 ,即使气候条件不发生改变 ,CO2 浓度对作物光合作用的正效应也不足以弥补O3 浓度升高所造成的负效应 ,冠层光合速率将比目前干洁地区略有下降 ,如果进一步考虑光合作用有效辐射光谱成分下降至 0 .4左右 ,冠层光合作用将比目前的BASE值下降 35 %左右。     

OBSERVATIONAL STUDY OF MERIDIONAL VARIATION OF UV-B RADIATION DURING VOYAGES TO THE ARCTIC AND ANTARCTIC REGIONS*

Based on 1999-2000 observations made by the first Arctic and sixteenth Antactic scientific voyages,a study is undertaken about the meridional surface UV-B (B band ultraviolet rays) variations in 75°N-70°S.It is mitigated as a function of latitudes and marked by lower radiation averaged over the Northern Hemisphere (NH) than over the Southern Hemisphere (SH),with its daily course basically similar to that of total radiation.Around polar summer noon hours (localtime) and where ice albedo is maximum,the strongest UV-B irradiance on the surface perpendicular to sun's beams as found at equatorial latitudes is measured sometimes.In the areas near Zhongshan Station the increase of surface UV-B radiation shows a close relation to the decrease of ozone in the higher atmosphere but it has a less intimate relation with its concentration at ground.     

NUMERICAL SIMULATION STUDIES ON SHORT-RANGE CLIMATIC VARIATION

Several global and regional climatic models(including atmosphere models, ocean models and coupledatmosphere-ocean models)are improved and developed to simulate the predictability of short-range(i.e.monthly,sea-sonal,interannual)climate variability,based on the understanding of global and regional climatic characteristics andprocesses,and according to the theorem of climatological dynamics.The results of numerical experiment show that someare very encouraging,some others reveal problems existed.However,the model and data are being more and more ad-vanced.     

NUMERICAL SIMULATION ON THE RESPONSE OF LAND SURFACE TO SEVERE WEATHER*

A coupled model of RAMS3b(Regional Atmospheric Modeling System,Version 3b) and LSPM(a land surface process model),in which some basic hydrological processes such as precipitation,evapotranspiration.surface runoff,infiltration and bottom drainage are included,has been established.With the coupled model,we have simulated the response of soil to the sever eweather process which caused the disastrous flood in north italy during 4-7.November,1994,simultaneously compared with the observation and the original RAMS3b,which has a soil and vegetation parameterization scheme(hereafter,SVP) emphasizing on the surface energy fluxes,while some hydrological processes in the soil are not described clearly.The results show that the differences between coupling LSPM and SVP exist mainly in the response of soil to the precipitation.The soil in the SVP never saturates under the strong input of precipitation,while the newly coupled model seems better,the soil has been saturated for one day or more and causes strong surface runoff,which constitutes the flood.Further sensitivity experiments show that the surface hydrological processes are very sensitive to the initial soil moisture and soil type when we compared the results with a relatively dry case and sandy soil.The coupled model has potentiality for simulation on the interaction between regional climate and land surface hydrological processes,and the regional water resources research concerning desertification,drought and flood.     

MEASUREMENTS AND MODEL SIMULATIONS OF SURFACE OZONE VARIATIONS AT DIFFERENT BACKGROUND CONCENTRATIONS OF THE PRECURSORS*

Ozone photochemical production and loss in very different environments at Waliguan baseline station and Lin'an background station were simulated by using the measurement data and photochemical box model.The results show that net ozone photochemical production rate is negative,about 0.5 ppb/d,at Waliguan baseline sation,because of very low precursor concentrations.But at Lin'an background station,the net photochemical ozone production is positive,about 2-3 ppb/h.which is very closed with the measurement at Lin'an.That means ozone production was controlled by photochemical reactions at Lin'an background station,because of the higher precursor concentrations.The net destruction rate,at Waliguan Mt.,is not large,so that future increase in anthropogenic emission of reactive nitrogen will lead to larger production rates of steady-state O₃ concentration.     

中国低纬度地区大气臭氧总量的变化特征

分析研究了位于我国低纬地区不同经度的昆明与香港两个站点上空的臭氧分布与演变状况,得出了中国低纬度地区大气臭氧总量的时空演变特征.研究结果显示:(1)香港与昆明两地臭氧的时间变化特征极为相似;(2)整个中国低纬地区的大气臭氧的时间变化趋势是非常一致的,在空间上呈现出东高西低的特征;(3)我国低纬地区的大气臭氧总量在夏季出现极大值,在冬季出现极小值.计算结果还表明,昆明的臭氧总量要小于其所在纬圈的平均值.     

IMPACTS OF OZONE CONCENTRATION AND EXPOSURE TIME CHANGES ON RICE YIELDS*

The impacts of O₃ concentration change on rice yields for different lengths of exposure time are studied by means of the OTC-1 open-top chamber.The resuhs indicate that when O₃ concentration increased from 50 ppb to 200 ppb during the time period of 20 to 80 days in the experiment,the rice yield was reduced by 6.78% to 33.72%.Two main influencing factors for rice yields are the increased O₃ concentration and the extended exposure time.Using a logarithm function to simulate the impacts of O₃ concentration on rice yields is better than using a the Weibull function.     

VARIATION OF TOTAL OZONE IN LOWER LATITUDE AREA OF CHINA

By using the observational O3 data of Kunming and Hong Kong during the period of 1997 – 2001, the paper studies the distribution and variation of total ozone in low latitude region of China. The study shows that the characteristics of variation in Kunm…