中国东部地区SO2, SO4=和HNO3(g)干沉降速度的季节变化

使用中国东部及其邻近地区各主要台站１９９２年全年００点和１２点（ＧＭＴ）地面及探空资料，由中尺度气象预报模式ＭＭ４产生中国东部地区地面以上大约４０ｍ高度（最低模式层）处二维温度、湿度和风场，使用污染物干沉降模块及该地区下垫面类型资料，计算出了该地区ＳＯ２，ＳＯ＝４和ＨＮＯ３（ｇ）全年干沉降速度的区域分布和季节变化。结果表明，由于受气象条件和下垫面类型的综合影响，３种污染物的干沉降速度有明显的变化。对ＳＯ２，全年区域平均极小值为０．０８８ｃｍ／ｓ，极大值为１．２７５ｃｍ／ｓ，平均值为０．４３０ｃｍ／ｓ；对ＳＯ＝４，分别为０．０１４ｃｍ／ｓ，０．２８７ｃｍ／ｓ和０．１１８ｃｍ／ｓ；对ＨＮＯ３（ｇ），分别为０．０６０ｃｍ／ｓ，５．２５０ｃｍ／ｓ和１．１２３ｃｍ／ｓ。ＳＯ２干沉降速度极大值分布在巴丹吉林沙漠和腾格里沙漠一带，对ＳＯ＝４和ＨＮＯ３（ｇ），除在上述沙漠地带有一极大值区域外，在靠近四川的云贵高原尚有另一极大区。对１９９２年全年来说，ＳＯ２和ＨＮＯ３（ｇ）干沉降速度极大值均出现在七月份，分别为０．５５２ｃｍ／ｓ和１．５１８ｃｍ／ｓ；而对ＳＯ＝４，干沉降速度极大值出现在九月份，其值为０．０９６ｃｍ／ｓ。这些值     

Nitrosyl and Nitryl Chloride Formation in H2SO4/HNO3/H2O/HCl Solutions at 200 K

Infrared spectroscopy has been used to measure the vapor pressure of chlorine containing species generated from H2SO4/HNO3/H2O/HCl solutions at 200 K. The vapor pressure was observed to be a function of solution composition. Two solution compositions were investigated. One solution remained a liquid whereas the second solution was a mixed liquid and solid phase (an ice slurry). The liquid solution had a composition of 64.6 wt.% H2SO4/4.8 wt.% HNO3/30.1 wt.% H2O/0.5 wt.% HCl and produced only vapor phase HCl. The ice slurry solution had a composition of 76.6 wt.% H2SO4/3.0 wt.% HNO3/20.1 wt.% H2O/0.3 wt.% HCl and produced HCl, ClNO, and ClNO2 vapor phase components. The sulfuric acid, nitric acid, and water content of these solutions are representative of those present in polar stratospheric clouds (PSCs), however the HCl concentrations are much higher than present within these clouds. The partitioning of chlorine between vapor phase HCl (50%) and ClNO/ClNO2 (50%) for the ice slurry solution suggests a possible mechanism of halogen activation within PSCs. A reaction mechanism to model the observed chemistry is proposed.     

The Soil Moisture and Net Primary Production Affected by CO_2 and Climate Change Using a Coupled Model

In this paper, a coupled model was used to estimate the responses of soil moisture and net primary production of vegetation （NPP） to increasing atmospheric CO2 concentration and climate change. The analysis uses three experiments simulated by the second-generation Earth System Model （CanESM2） of the Canadian Centre for Climate Modelling and Analysis （CCCma）, which are part of the phase 5 of the Coupled Model Intercomparison Project （CMIP5）. The authors focus on the magnitude and evolution of responses in soil moisture and NPP using simulations modeled by CanESM, in which the individual effects of increasing CO2 concentration and climate change and their combined effect are separately accounted for. When considering only the single effect of climate change, the soil moisture and NPP have a linear trend of 0.03 kg m^-2 yr^-1 and-0.14 gC m^- 2 yr^-2, respec- tively. However, such a reduction in the global NPP results from the decrease of NPP at lower latitudes and in the Southern Hemisphere, although increased NPP has been shown in high northern latitudes. The largest negative trend is located in the Amazon basin at -1.79 gC m^-2 yr^-2. For the individual effect of increasing CO2 concentration, both soil moisture and NPP show increases, with an elevated linear trend of 0.02 kg m^-2 yr^-1 and 0.84 gC m^-2 yr^-2, respectively. Most regions show an increasing NPP, except Alaska. For the combined effect of increasing atmospheric CO2 and climate change, the increased soil moisture and NPP exhibit a linear trend of 0.04 kg m^2 yr^-1 and 0.83 gC m^2 yr^-2 at a global scale. In the Amazon basin, the higher reduction in soil moisture is illustrated by the model, with a linear trend of-0.39 kg m^-2 yr^-1, for the combined effect. Such a change in soil moisture is caused by a weakened Walker circulation simulated by this coupled model, compared with the single effect of increasing CO2 concentration （experiment M2）, and a consequence of the reduction in NPP is also shown in this area, with a linear trend of-     

Integration of Multi-source Measurements to Monitor Dust over North China：A Case Study

The aerosol optical depth （AOD） data from the Moderate Resolution Imaging Spectroradiometer （MODIS） aboard Satellite Aqua, along with the altitude-resolved aerosol subtypes product from the Cloud-Aerosol LIdar with Orthogonal Polarization （CALIOP）, as well as surface PM 10 measurements, were utilized to investigate the dust activities common in springtime of northern China. Specifically, a dust storm episode that occurred over the North China Plain （NCP） during 17-21 March 2010 was identified. The PM 10 concentration at Beijing （39.8 °N, 116.47 °E） reached the peak value of 283 μgm -3 on 20 March 2010 from the background value of 15 μg m-3 measured on 17 March 2010, then dropped to 176 μgm-3 on 21 March 2010. Analysis of the CALIOP aerosol subtypes product showed that numerous large dust plumes floated over northern China, downwind of main desert source regions, and were lifted to altitudes as high as 3.5 km during this time period. The MODIS AOD data provided spatial distributions of dust load, broadly consistent with ground-level PM 10 , especially in cloud free areas. However, inconsistency between the MODIS AOD and surface PM 10 measurements under cloudy conditions did exist, further highlighting the unique capability of the CALIOP lidar. CALIOP can penetrate the cloud layer to give unambiguous and altitude-resolved dust measurements, albeit a relatively long revisit period （16 days） and narrower swath （90 m）. A back trajectory simulation using the Hybrid Single-Particle Lagrangian Integrated Trajectory （HYSPLIT） model was performed, and it was found that the sand-dust storm originated from the Gobi Desert on 18 March 2010 travelled approxi-mately 1200-1500 km day-1 eastward and passed over the NCP on 19 March 2010, in good agreement with previous findings. In addition, the multi-sensor measurements integrated with the HYSPLIT model output formed a three-dimensional view of the transport pathway for this dust episode, indicating that this episode was largely associated with the desert source regions to the northwest of the NCP. The results imply the importance of integration of multi-sensor measurements for clarifying the overall structure of dust events over northern China.     

Case Study on the Impact of the Vortex in the Easterlies in the Tropical Upper Troposphere on the Western Pacific Subtropical Anticyclone

By employing the NCEP/NCAR reanalysis data （1000-10 hPa, 2.5°×2.5°）, the impact of the vortex in the easterlies （EV） over the tropical upper troposphere on the zonal movement of the western Pacific subtropical anticyclone （WPSA） during 19-25 June 2003 is analyzed in this paper. It is shown that the EV can extend from middle troposphere to the height of 50 hPa, reaching a maximum at 200 hPa. The vertical thermal distribution appears to be ＂warmer in the upper layer and colder in the lower layer＂. The WPSA retreats eastward abnormally when the EV and the vortex in the westerlies （WV） encounter around the same longitude while they move toward each other. It is also shown that the vorticity variation extends from the troposphere to the height of 50 hPa, with the most prominent change occurring at 200 hPa by the diagnostic analyses of the vertical vorticity equation. The WPSA appears to retreat abnormally eastward while the negative/positive vorticity change becomes stronger near the east/west side of the EV, and the areas with positive vorticity tendency both in the EV and WV join together into one belt along 130°E during the process of the EV and the WV moving toward each other. In the vorticity equation, the positive contribution caused by the horizontal advection term is the maximum, and the minimum is caused by theβ effect. It is also found that enhanced horizontal vorticity advection andβ effect, as well as the ＂barotropic development＂ resulted from the in-phase superposition of the southerly and the northerly winds in the easterlies and westerlies near 130~E, are in agreement with the WPSA eastward retreat.     

ENSO Variability Simulated by a Coupled General Circulation Model:ECHAM5/MPI-OM

The accurate simulation of the equatorial sea surlhce temperature （SST） variability is crucial for a proper representation or prediction of the El Nino-Southern Os- cillation （ENSO）. This paper describes the tropical variability simulated by the Max Planck Institute （MPI） forr meteorology coupled atmosphere-ocean general circulation model （CGCM）. A control simulation with pre-industrial greenhouse gases is analyzed, and the simulation of key oceanic features, such as SST, is compared with observa- tions. Results from the 400-yr control simulation show that the model＇s ENSO variability is quite realistic in terms of structure, strength, and period. Also, two related features （the annual cycle of SST and the-phase locking of ENSO events）, which are significant in determining the model＇s performance of realistic ENSO prediction, are further validated to be well reproduced by the MPI cli mate model, which is an atmospheric model ECHAM5 （which fuses the EC tbr European Center and HAM for Hamburg） coupled to an MPI ocean model （MPI-OM）, ECHAMS/MPI-OM.     

Summer Asian-Pacific Oscillation and Its Relationship with Atmospheric Circulation and Monsoon Rainfall

Using the ERA-40 data and numerical simulations, this study investigated the teleconnection over the extratropical Asian-Pacific region and its relationship with the Asian monsoon rainfall and the climatological characteristics of tropical cyclones over the western North Pacific, and analyzed impacts of the Tibetan Plateau （TP） heating and Pacific sea surface temperature （SST） on the teleconnection. The Asian-Pacific oscillation （APO） is defined as a zonal seesaw of the tropospheric temperature in the midlatitudes of the Asian-Pacific region. When the troposphere is cooling in the midlatitudes of the Asian continent, it is warming in the midlatitudes of the central and eastern North Pacific; and vice versa. The APO also appears in the stratosphere, but with a reversed phase. Used as an index of the thermal contrast between Asia and the North Pacific, it provides a new way to explore interactions between the Asian and Pacific atmospheric circulations. The APO index exhibits the interannual and interdecadal variability. It shows a downward trend during 1958-2001, indicating a weakening of the thermal contrast, and shows a 5.5-yr oscillation period. The formation of the APO is associated with the zonal vertical circulation caused by a difference in the solar radiative heating between the Asian continent and the North Pacific. The numerical simulations further reveal that the summer TP heating enhances the local tropospheric temperature and upward motion, and then strengthens downward motion and decreases the tropospheric temperature over the central and eastern North Pacific. This leads to the formation of the APO. The Pacific decadal oscillation and El Nino/La Nina over the tropical eastern Pacific do not exert strong influences on the APO. When there is an anomaly in the summer APO, the South Asian high, the westerly jet over Eurasia, the tropical easterly jet over South Asia, and the subtropical high over the North Pacific change significantly, with anomalous Asian monsoon rainfall and tropical cyclon     

A Case Study on the Triggering of Thermal Convective Precipitation

Thermal convective precipitation （TCP） often occurs over mainland China in summer when the area is dominated by the western Pacific subtropical high （WPSH）. It is well known that the WPSH often brings about large scale subsidence, then why could deep moist convection occur and where does the water vapor come from？ In this paper, a deep convective precipitation case that happened on 2 August 2003 is studied in order to address these two questions. First, the characteristics of the TCP event are analyzed using the Tropical Rainfall Measuring Mission （TRMM） satellite data, automatic weather station observations, and the data from the US National Centers for Environmental Prediction （NCEP）. Second, water vapor sources are identified through examining surface evaporation, water vapor advection, and water vapor flux divergence calculated by using a regionally averaged water vapor budget equation. Furthermore, using an Advanced Regional Eta-coordinate Model （AREM）, contributions of sensible and latent heat fluxes to the TCP are compared through four sensitivity experiments. The results show that in the regions controlled by the WPSH, surface temperature rises rapidly after sunrise. Upon receiving enough sensible heat, the air goes up and leads to convergence in the lower atmosphere. Then the water vapor assembled from the surroundings and the ground surface is transported to the upper levels, and a favorable environment for the TCP forms. A model data diagnosis indicates that about half of precipitable water comes from the convergence of horizontal fluxes of water vapor, and the other half from surface evaporation, while little is from advection. Additional sensitivity experiments prove that both sensible and latent heating are essential for the onset of the TCP. The sensible heat flux triggers thermodynamic ascending motion, and the latent heat flux provides water vapor, but the contribution to TCP from the latter is a little smaller than that from the former.     

Methoxy formation in the reaction of CH3O2 radicals with NO

Formation of methoxy (CH₃O) radicals in the reaction (1) CH₃O₂+NOCH₃O+NO₂ at 298 K has been observed directly using time resolved LIF. The branching ratio % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeqOXdyMaae% 4qaiaabIeadaWgaaWcbaGaae4maaqabaGccaqGpbGaaeiiaiaabIca% ieqacaWF9aGaa8hiaiaa-nbicaWFGaGaeuiLdqKaai4waiaaboeaca% qGibWaaSbaaSqaaiaabodaaeqaaOGaae4taiaac2facaWFVaGaeuiL% dqKaai4waiaaboeacaqGibWaaSbaaSqaaiaabodaaeqaaOGaae4tam% aaBaaaleaacaqGYaaabeaakiaac2facaqGPaaaaa!4E31!\[\phi {\rm{CH}}_{\rm{3}} {\rm{O (}} = -- \Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}]/\Delta [{\rm{CH}}_{\rm{3}} {\rm{O}}_{\rm{2}} ]{\rm{)}}\] has been determined by quantitative cw-UV-laser absorption at 257 nm of CH₃O₂ and CH₃ONO, the product of the consecutive methoxy trapping reaction (2) % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaae4qaiaabI% eadaWgaaWcbaGaae4maaqabaGccaqGpbacbeGaa83kaiaa-bcaieaa% caGFobGaa43taiaa+bcacaGFOaGaa83kaiaa+1eacaGFPaGaa4hiai% abgkziUkaabccacaqGdbGaaeisamaaBaaaleaacaqGZaaabeaakiaa% b+eacaqGGaGaaeOtaiaab+eacaqGGaGaa4hkaiaa-TcacaGFnbGaa4% xkaiaa+5cacaGFGaGaa4hiaiabeA8aMnaaBaaajqwaacqaaiaaboea% caqGibWaaSbaaKazcaiabaGaae4maaqabaqcKfaGaiaab+eaaSqaba% aaaa!55AC!\[{\rm{CH}}_{\rm{3}} {\rm{O}} + NO ( + M) \to {\rm{ CH}}_{\rm{3}} {\rm{O NO }}( + M). \phi _{{\rm{CH}}_{\rm{3}} {\rm{O}}} \] is found to be (1.0±0.2). The rate constant k ₁ is (7±2) 10^-12 cm³/molecule · s in good agreement with previous results.     

新标准下空气质量预报指导产品对比检验

为了解和掌握上级指导产品对石家庄市空气质量预报的适用性,进一步提高石家庄市空气质量预报的准确性,利用国家气象中心(NMC)、北京区域气象中心(BJ)和河北省气象局(HB)空气质量预报产品,对石家庄市夏季4种主要污染物PM_(2.5)、PM_(10)、O_3和SO_2的预报进行了对比检验,结果表明:1)NMC对4种污染物的预报效果均逊于HB和BJ的,对PM_(10)、PM_(2.5)和SO_2的预报值明显较实况偏大,尤其在发生重污染天气时,对PM_(10)和PM_(2.5)的空报率高达90%以上;2)HB对PM_(10)和SO_2的预报效果好于BJ的,对SO_2的预报值与实况值均在一个等级范围内,发生重污染天气时,对PM_(10)的预报效果好于BJ的,预报值更接近于实况,但对重污染向优、良转折天气的预报值偏高;3)BJ预报PM_(2.5)和O_3的效果好于HB的,对O_3的0级误差级别预报准确率高达90.5%,对PM_(2.5)优到轻度污染等级的预报效果较好,但对重污染天气的预报值低于实况。     

敦煌莫高窟大气颗粒物中水溶性离子变化及来源解析

为探明莫高窟大气颗粒物污染特征,采集了2014年4-12月第16窟及72窟外环境中大气颗粒物PM2.5和PM10~2.5样品,对比分析了样品中水溶性离子变化及影响因素,通过主成分分析法解析了其主要来源。结果表明:(1)窟区主风向为南风,起沙风频率仅为0.01%,不利于污染物的扩散;(2)窟外PM2.5和PM10~2.5、窟内PM2.5和PM10~2.5中水溶性离子总浓度分别为6.1±4.0μg·m^-3、12.2±9.1μg·m^-3、3.7±0.8μg·m^-3和7.5±1.6μg·m^-3,SO₄^2-、Ca²⁺、NO3^-、Na⁺及Cl^-是主要组成,SO42-、NO3-和Ca2+之和在窟外和窟内PM2.5和PM10~2.5中占总离子比例分别为79.24%,76.81%,80.61%及77.74%,二次离子主要来自固定污染源;(3)PM2.5与PM10~2.5中各离子浓度的比值在窟外、内分别为0.33~0.88、0.25~0.94,9种水溶性离子在不同粒径粒子中富集程度有所差异,3-5月的沙尘、7-9月的降雨、11月农村农作物秸秆燃烧及冬季取暖燃煤等对水溶性离子都有一定影响,窟内PM2.5中游客数量与NH4+和NO^3-有一定的相关性(R2=0.27、0.35)、PM10~2.5中游客数量与NH4+有一定的相关性(R2=0.31);(4)沙尘天气下窟外和窟内的PM2.5与PM10-2.5中Cl-、SO₄^2-、Na⁺、K+和Ca²⁺的浓度增加,窟区微环境主要受区域环境气象因素影响,建议极端沙尘天气关闭洞窟;(5)莫高窟大气环境呈碱性;(6)PM2.5和PM10~2.5主要来源于当地秸秆燃烧、二次污染源、土壤沙尘及干涸的大泉河。     

1961-200年中国各季降水趋势变化

Trends in six indices of precipitation in China for seasons during 1961-2007 were analyzed based on daily observations at 587 stations. The trends were estimated by using Sen＇s method with Mann-Kendall＇s test for quantifying the significance. The geographical patterns of trends in the seasonal indices of extremes were similar to those of total precipitation. For winter, both total and extreme precipitation increased over nearly all of China, except for a small part of northern China. Increasing trends in extreme precipitation also occurred at many stations in southwestern China for spring and the midlower reaches of the Yangtze River and southern China for summer. For autumn, precipitation decreased in eastern China, with an increasing length of maximum dry spell, implying a drying tendency for the post-rainy season. Wetting trends have prevailed in most of western China for all seasons. The well-known ＇flood in the south and drought in the north＇ trend exists in eastern China for summer, while a nearly opposite trend pattern exist for spring.     

Tides and Wind-Driven Circulation in the Tropical and Southern Atlantic Ocean:The BRAZCOAST System

The Brazilian coast is characterized by dif- ferent tidal regimes and distinct meteorological influ- ences. The northern part has larger tidal amplitudes and is permanently affected by trade winds and tropical distur- bances; the southern portion has smaller tidal amplitudes and is frequently influenced by extratropical cyclone ac- tivity. Besides these aspects, many features regarding current structure and behavior are also present, such as the equatorial system of currents, the subtropical gyre and the corresponding western boundary currents, and the Bra- zil-Malvinas confluence region. Within this context, ef- forts were made to develop the BRAZCOAST system, capable of describing the processes that determine the oceanic circulation from large to coastal scales. A cus- tomized version of the Princeton Ocean Model （POM） was implemented in a basin-scale domain covering the whole of the tropical and southern Atlantic Ocean, with 0.5° spatial resolution, as well as three nested grids with （1/12）° resolution covering the different parts of the Bra- zilian shelf, in a one-way procedure. POM was modified to include tidal potential generator terms and a par- tially-clamped boundary condition for tidal elevations. The coarse grid captured large-scale features, while the nested grids detailed local circulations affected by bathymetry and coastal restrictions. An interesting aspect at the coarse grid level was the relevance of the Weddell Sea to the location of the tidal amphidromic systems.     

AAS has been accepted for Coverage by the Science Citation Index in 2009

In May 2008, ScienceWatch.com named Advances in Atmospheric Sciences a Rising Star among Geosciences journals. According to Essential Science IndicatorsSM from Thomson Reuters, the journal＇s cur-rent citation record includes 764 papers cited a total of 1,658 times between January 1, 1998 and February 29 2008.     

Results of a CLM4 Land Surface Simulation over China Using a Multisource Integrated Land Cover Dataset

In this study, the high-accuracy multisource integrated Chinese land cover （MICLCover） dataset was used in version 4 of the Community Land Model （CLM4） to assess how the new land cover information affected land surface simulation over China. Compared to the default land cover dataset in CLM4, the MICL data indicated lower values for bare soil （14.6% reduction）, nee- dleleaf tree （3.6%）, and broadleaf tree （1.9%）; higher values for shrub cover （1.8% increase）, grassland （9.9%）, cropland （5.0%）, glaciers （0.5%）, lakes （1.6%）, and wetland （1.1%）; and unchanged for urban areas. Two comparative CLM4 simulations were conducted for the 33-yr period from 1972 to 2004, one using the MICL dataset and the other using the default dataset. The results revealed that the MICL data produced a 0.3% lower mean annual surface albedo over China than the original data. The largest contributor to the reduced value was semiarid regions （2.1% reduction）. The MICL-data albedo value agreed more closely with observations （MODIS broad- band black-sky albedo products） over arid and semiarid regions than for the original data to some extent. The simulated average sensible heat flux over China increased by only 0.1 W m 2 owing to the reduced values in arid and semiarid regions, as opposed to increases in humid and semihumid regions, while an increased latent heat flux of I W m-2 was reflected in almost identical changes over the whole region. In addition, the mean annual runoff simulated by CLM4 using MICL data decreased by 6.8 mm yr-1, primarily due to large simulated decreases in humid regions.     

MM5 Simulations of the China Regional Climate During the LGM. Ⅱ： Influence of Change of Land Area,Vegetation, and Large-scale Circulation Background

Using a regional climate model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate the relative LGM climate response to changes of land-sea distribution, vegetation, and large-scale circulation background over China. Model results show that compared with the present climate, the fluctuations of sea-land distribution in eastern Asia during the LGM result in the temperature decrease in winter and increase in summer. It has significant impact on the temperature and precipitation in the east coastal region of China. The impact on precipitation in the east coastal region of China is the most significant one, with 25%-50% decrease in the total precipitation change during the LGM. On the other hand, the changes in sea-land distribution have less influence on the climate of inland and western part of China. During the LGM, significant changes in vegetation result in temperature alternating with winter increase and summer decrease, but differences in the annual mean temperature are minor. During the LGM, the global climate, i.e., the large-scale circulation background has changed significantly. These changes have significant influences on temperature and precipitation over China. They result in considerable temperature decreases in this area, and direct the primary patterns and characteristics of temperature changes. Results display that, northeastern China has the greatest temperature decrease, and the temperature decrease in the Tibetan Plateau is larger than in the eastern part of China located at the same latitude. Moreover, the change of large-scale circulation background also controls the pattern of precipitation change. Results also show that, most of the changes in precipitation over western and northeastern parts of China are the consequences of changing large-scale circulation background, of which 50%-75% of precipitation changes over northern and eastern China are the results of changes in large-scale circulation backgrou     

Analysis of Nonstationary Wind Fluctuations Using the Hilbert-Huang Transform

Climatological patterns in wind fluctuations on time scales of 1-10 h are analyzed at a meteorological mast at the Yangmeishan wind farm, Yunnan Province, China, using a 2-yr time series of 10-min wind speed ob- servations. For analyzing the spectral properties of non- stationary wind fluctuations in mountain terrain, the Hil- bert-Huang transform （HHT） is applied to investigate climatological patterns between wind variability and sev- eral variables including time of year, time of day, wind direction, and pressure tendency. Compared with that for offshore sites, the wind variability at Yangmeishan wind farm has a more distinct diurnal cycle, but the seasonal discrepancies and the differences according to directions are not distinct, and the synoptic influences on wind vari- ability are weaker. There is enhanced variability in spring and winter compared with summer and autumn. For flow from the main direction sector, the maximum wind vari- ability is observed in spring. And the severe wind fluctua- tions are more common when the pressure tendency is rising.     

我国地面O3、NOX、SO2背景值的观测研究

从1994年8月至1995年8月，在龙凤山、临安大气污染监测站和瓦里关大气本底基准观象台对O3、NOX及SO2首次进行了长期的连续观测。初步分析表明:3站地面O3的平均浓度、月际分布和日变化特征因地理环境、海拔高度和天气条件的不同，表现出明显的差异性。平均地面O3浓度，龙凤山为34.8×10-9,临安为39.1×10-9,瓦里关山为49.3×10-9,龙凤山和临安的月平均地面O3浓度分布较复杂，在6～7月和12月～1月较低，10月底～11月初较高。而在瓦里关山，月平均地面O3浓度变化较平稳，6月份最大，12月最小。龙凤山和临安地面O3平均日变化量较大，下午浓度最高，清晨最小；而瓦里关山地面O3平均日变化较小，上午浓度略低；NOX和SO2的分布具有明显的局地性特征，在龙凤山，临安和瓦里关山，3站的总平均浓度分别为2.7×10-9（NOX）和0.7×10-9(SO2),8.1×10-9(NOX)和16.1×10-9（SO2），0.04×10-9（NOX）和0.15×10-9（SO2）。     

The Unprecedented Freezing Disaster in January 2008 in Southern China and Its Possible Association with the Global Warming

The unprecedented disaster of low temperature and persistent rain, snow, and ice storms, causing widespread freezing in the Yangtze River Basin and southern China in January 2008, is not a local or regional event, but a part of the chain events of large-scale low temperature and snow storms in the same period in Asia. The severity and impacts of the southern China 2008 freezing disaster were the most significant among others. This disastrous event was characterized by three major features： （1） snowfall, freezing rain, and rainfall, the three forms of precipitation, coexisted with freezing rain being the dominant producer responsible for the disaster; （2） low temperature, rain and snow, and freezing rain exhibited extremely great intensity, with record-breaking measurements observed for eight meteorological variables based on the statistics made by China National Climate Center and the provincial meteorological services in the Yangtze River Basin and southern China; （3） the disastrous weathers persisted for an exceptionally long time period, unrecorded before in the meteorological observation history of China.
The southern China 2008 freezing disaster may be resulted from multiple different factors that superimpose on and interlink with one another at the right time and place. Among them, the La Nina situation is a climate background that provided conducive conditions for the intrusions of cold air into southern China; the persistent anomaly of the atmospheric circulation in Eurasia is the direct cause for a succession of cold air incursions into southern China; and the northward transport of warm and moist airflows from the Bay of Bengal and South China Sea finally warranted the formation of the freezing rain and snow storms and their prolonged dominance in the southern areas of China.
A preliminary discussion of a possible association of this disastrous event with the global warming is presented. This event may be viewed as a short-term regional perturbation to the global warming. There is no     

The Combined Effect of Initial Error and Model Error on ENSO Prediction Uncertainty Generated by the Zebiak-Cane Model

Initial errors and model errors are the source of prediction errors. In this study, the authors compute the conditional nonlinear optimal perturbation （CNOP）-type initial errors and nonlinear forcing singular vector （NFSV）- type tendency errors of the Zebiak-Cane model with respect to El Nifio events and analyze their combined effect on the prediction errors for E1 Nino events. The CNOP- type initial error （NFSV-type tendency error） represents the initial errors （model errors） that have the largest effect on prediction uncertainties for E1 Nifio events under the perfect model （perfect initial conditions） scenario. How- ever, when the CNOP-type initial errors and the NFSV- type tendency errors are simultaneously considered in the model, the prediction errors caused by them are not am- plified as the authors expected. Specifically, the predic- tion errors caused by the combined mode of CNOP-type initial errors and NFSV-type tendency errors are a little larger than those caused by the NFSV-type tendency er- rors. This fact emphasizes a need to investigate the opti- mal combined mode of initial errors and tendency errors that cause the largest prediction error for E1 Nifio events.