Changes in Wind Speed and Extremes in Beijing during 1960--2008 Based on Homogenized Observations

Daily observations of wind speed at 12 stations in the Greater Beijing Area during 1960–2008 were homogenized using the Multiple Analysis of Series for Homogenization method. The linear trends in the regional mean annual and seasonal (winter, spring, summer and autumn) wind speed series were-0.26,-0.39,-0.30,-0.12 and-0.22 m s-1 (10 yr)-1 , respectively. Winter showed the greatest magnitude in declining wind speed, followed by spring, autumn and summer. The annual and seasonal frequencies of wind speed extremes (days) also decreased, more prominently for winter than for the other seasons. The declining trends in wind speed and extremes were formed mainly by some rapid declines during the 1970s and 1980s. The maximum declining trend in wind speed occurred at Chaoyang (CY), a station within the central business district (CBD) of Beijing with the highest level of urbanization. The declining trends were in general smaller in magnitude away from the city center, except for the winter case in which the maximum declining trend shifted northeastward to rural Miyun (MY). The influence of urbanization on the annual wind speed was estimated to be about-0.05 m s-1 (10 yr)-1 during 1960–2008, accounting for around one fifth of the regional mean declining trend. The annual and seasonal geostrophic wind speeds around Beijing, based on daily mean sea level pressure (MSLP) from the ERA-40 reanalysis dataset, also exhibited decreasing trends, coincident with the results from site observations. A comparative analysis of the MSLP fields between 1966–1975 and 1992–2001 suggested that the influences of both the winter and summer monsoons on Beijing were weaker in the more recent of the two decades. It is suggested that the bulk of wind in Beijing is influenced considerably by urbanization, while changes in strong winds or wind speed extremes are prone to large-scale climate change in the region.     

Spatiotemporal Variability of Surface Wind Speed during 1961–2017 in the Jing–Jin–Ji Region,China

Wind speed variations are influenced by both natural climate and human activities. It is important to understand the spatial and temporal distributions of wind speed and to analyze the cause of its changes. In this study, data from 26 meteorological stations in the Jing–Jin–Ji region of North China from 1961 to 2017 are analyzed by using the Mann–Kendall(MK) test. Over the study period, wind speed first decreased by-0.028 m s-1 yr-1(p 0.01) in1961–1991, and then increased by 0.002 m s1-yr1-(p 0.05) in 1992–2017. Wind speed was the highest in spring(2.98 m s-1), followed by winter, summer, and autumn. The largest wind speed changes for 1961–1991 and1992–2017 occurred in winter(-0.0392 and 0.0065 m s-1 yr1-, respectively); these values represented 36% and 58%of the annual wind speed changes. More than 90.4% of the wind speed was concentrated in the range of 1–5 m s-1,according to the variation in the number of days with wind speed of different grades. Specifically, the decrease in wind speed in 1961–1991 was due to the decrease in days with wind speed of 3–5 m s-1, while the increase in wind speed in 1992–2017 was mainly due to the increase in days with wind speed of 2–4 m s-1. In terms of driving factors,variations in wind speed were closely correlated with temperature and atmospheric pressure, whereas elevation and underlying surface also influenced these changes.     

Seasonal Variation of Columnar Aerosol Optical Properties in Yangtze River Delta in China

In order to understand the seasonal variation of aerosol optical properties in the Yangtze River Delta,5 years of measurements were conducted during September 2005 to December 2009 at Taihu,China.The monthly averages of aerosol optical depth were commonly >0.6;the maximum seasonal average(0.93) occurred in summer.The magnitude of the Angstr¨om exponent was found to be high throughout the year;the highest values occurred in autumn(1.33) and were the lowest in spring(1.08).The fine modes of volume size distribution showed the maxima(peaks) at a radius of ～0.15 μm in spring,autumn,and winter;at a radius of ～0.22 μm in summer.The coarse modes showed the maxima(peaks) at a radius of 2.9 μm in spring,summer,and autumn and at a radius of 3.8 μm in winter.The averages of single-scattering albedo were 0.92(spring),0.92(summer),0.91(autumn),and 0.88(winter).The averages of asymmetry factor were found to be larger in summer than during other seasons;they were taken as 0.66 at 440-1020 nm over Taihu.The real part of the refractive index showed a weak seasonal variation,with averages of 1.48(spring),1.43(summer),1.45(autumn),and 1.48(winter).The imaginary parts of the refractive index were higher in winter(0.013) than in spring(0.0076),summer(0.0092),and autumn(0.0091),indicating that the atmosphere in the winter had higher absorbtivity.     

Analysis of Wind Power Assessment Based on the WRF Model

Assessing wind energy is a key step in selecting a site for a wind farm. The accuracy of the assessment is essential for the future operation of the wind farm. There are two main methods for assessing wind power： one is based on observational data and the other relies on mesoscale numerical weather prediction（NWP）. In this study, the wind power of the Liaoning coastal wind farm was evaluated using observations from an anemometer tower and simulations by the Weather Research and Forecasting（WRF） model, to see whether the WRF model can produce a valid assessment of the wind power and whether the downscaling process can provide a better evaluation. The paper presents long-term wind data analysis in terms of annual, seasonal, and diurnal variations at the wind farm, which is located on the east coast of Liaoning Province. The results showed that, in spring and summer, the wind speed, wind direction, wind power density, and other main indicators were consistent between the two methods. However, the values of these parameters from the WRF model were significantly higher than the observations from the anemometer tower. Therefore, the causes of the differences between the two methods were further analyzed. There was much more deviation in the original material, National Centers for Environmental Prediction（NCEP） final（FNL） Operational Global Analysis data, in autumn and winter than in spring and summer. As the region is vulnerable to cold-air outbreaks and windy weather in autumn and winter, and the model usually forecasted stronger high or low systems with a longer duration, the predicted wind speed from the WRF model was too large.     

Observation and Simulation of Near-Surface Wind and Its Variation with Topography in Urumqi,West China

Near-surface wind measurements obtained with five 100-m meteorology towers, 39 regional automatic stations, and simulations by the Weather Research and Forecasting(WRF) model were used to investigate the spatial structure of topography-driven flows in the complex urban terrain of Urumqi, China. The results showed that the wind directions were mainly northerly and southerly within the reach of 100 m above ground in the southern suburbs, urban area, and northern suburbs, which were consistent with the form of the Urumqi gorge. Strong winds were observed in southern suburbs, whereas the winds in the urban,northern suburbs, and northern rural areas were weak. Static wind occurred more frequently in the urban and northern rural areas than in the southern suburbs. In the southern suburbs, wind speed was relatively high throughout the year and did not show significant seasonal variations. The average annual wind speed in this region varied among 1.9–5.5, 1.1–3.6, 1.2–4.3, 1.2–4.3, and 1.1–3.5 m s~(-1) with in the reach of 100 m above ground at Yannanlijiao, Shuitashan, Liyushan, Hongguangshan, and Midong, respectively. The flow characteristics comprised more airflows around the mountain, where the convergence and divergence were dominated by the terrain in eastern and southwestern Urumqi. Further analysis showed that there was a significant mountain–valley wind in spring, summer, and autumn, which occurred more frequently in spring and summer for 10–11 h in urban and northern suburbs. During daytime, there was a northerly valley wind,whereas at night there was a southerly mountain wind. The conversion time from the mountain wind to the valley wind was during 0800–1000 LST(Local Standard Time), while the conversion from the valley wind to the mountain wind was during 1900–2100 LST. The influence of the mountain–valley wind in Urumqi City was most obvious at 850 h Pa, according to the WRF model.     

POSSIBLE RELATIONSHIP BETWEEN THE INTERANNUAL ANOMALY OF THE TROPICAL PACIFIC SEA SURFACE HEIGHT AND SUMMER PRECIPITATION IN CHINA

By using NCEP GODAS monthly sea surface height(SSH) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of SSH are analyzed over the tropical Pacific,and correlations between SSH and summer rainfall are discussed.The results are shown as follows:(1) The tropical Pacific SSH takes on a "V" pattern in the climatic field with an eastward opening,and it is higher in the western part(in the northwestern part) than in the eastern part(in the southwestern part).The high-value areas are more stable in the northwest,and the value range(greater than 0.8 m) is larger in spring and summer than in autumn and winter.The high-value area in the southwestern part is the largest(smallest) and more northerly(southerly) in spring(summer).SSH is higher in spring and autumn than in summer and winter over the equatorial zone.(2) The interannual anomalies of the SSH are the strongest over the tropical western and southwestern Pacific and are stronger in winter and spring than in summer and autumn.The interannual anomalies are also strong over the equatorial middle and eastern Pacific.The distribution ranges are larger and the intensities are stronger in the autumn and winter.There is a close relationship between the SSH interannual anomalies and ENSO events in autumn,winter and spring.(3) When ENSO events take place in winter,according to the simultaneous relationship among the tropic Pacific SSH,850 hPa wind fields and the summer precipitation of China,it can be predicted that the precipitation will be significantly more than normal over the south of the Yangtze River,especially over Dongting Lake and Poyang Lake region,eastern Qinghai-Tibet Plateau,Yangtze-Huai River Valley,eastern part of Inner Mongolia and less than normal over the area of Great Band of Yellow River,North China and South China in successive summers.     

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.     

Difference in the Interdecadal Variability of Spring and Summer Sensible Heat Flux over Northwest China

The present study investigates the difference in interdecadal variability of the spring and summer sensible heat fluxes over Northwest China by using station observations from 1960 to 2000. It was found that the spring sensible heat flux over Northwest China was greater during the period from the late 1970s to the 1990s than during the period from the 1960s to the mid-1970s. The summer sensible heat flux was smaller in the late 1980s through the 1990s than it was in the 1970s through the early 1980s. Both the spring and summer land-air temperature differences over Northwest China displayed an obvious interdecadal increase in the late 1970s. Both the spring and summer surface wind speeds experienced an obvious interdecadal weakening in the late 1970s. The change in the surface wind speed played a more important role in the interdecadal variations in sensible heat flux during the summer, whereas the change in the land-air temperature difference was more important for the interdecadal variations in sensible heat flux in the spring. This difference was related to seasonal changes in the mean land-air temperature difference and the surface wind speed. Further analysis indicated that the increase in the spring land surface temperature in Northwest China was related to an increase in surface net radiation.     

STATISTICAL ANALYSIS OF LOW-LEVEL JET STREAMS IN NANJING AREA BASED ON WIND PROFILER DATA

In order to understand the activity characteristics of low-level jets in the Nanjing area, statistical analysis and comparative study are carried out on their monthly and diurnal variations, characteristics of their cores and accompanying weather conditions using wind profile data in 2005—2008 collected by two wind profilers. The results show that low-level jets have significant monthly and diurnal variations. They occur more frequently in spring and summer than in autumn and winter and are more active in early morning and at night, with the maximum wind speed usually occurring at midnight. The central part of the low-level jet occurs mainly at the height of less than 1400 meters, and the enhancement of central speed is beneficial to the appearance of precipitation. Meanwhile, when the low-level jet appears in summer, it helps cause heavy rain. The statistical results of the boundary wind profiler are well consistent with those of the tropospheric wind profiler. Two kinds of wind profilers also have the capability of continuously detecting the development of low-level jets.     

Aerosol spectra and new particle formation observed in various seasons in Nanjing

The aerosol number spectrum and gas pollutants were measured and the new particle formation （NPF） events were discussed in Nanjing. The results showed that the size distributions of aerosol number concen- trations exhibited distinct seasonal variations, implying the relations of particle sizes and their sources and sinks. The number concentrations of particles in the nuclei mode （10-30 nm）, Aitken mode （30-100 nm）, accumulation mode （100 -1000 nm） and coarse mode （〉1μm） varied in the order of summer 〉 spring 〉 autumn, summer 〉 autumn 〉 spring, autumn 〉 summer 〉 spring, and spring 〉 autumn 〉summer, re- spectively. The diurnal variation of total aerosol number concentrations showed three peaks in all observed periods, which corresponded to two rush hours and the photochemistry period at noon. In general, the NPF in summer occurred under the conditions of east winds and dominant air masses originating from marine areas with high relative humidity （50%-70%） and strong solar radiations （400 -700 W m-2）. In spring, the NPF were generally accompanied by low relative humidity （14%-30%） and strong solar radiations （400-600 W m-2）. The new particle growth rates （GR） were higher in the summertime in the range of 10- 16 nm h-1. In spring, the GR were 6.8-8.3 nm h-1. Under polluted air conditions, NPF events were seldom captured in autumn in Nanjing. During NPF periods, positive correlations between 10- 30 nm particles and 03 were detected, particularly in spring, indicating that NPF can be attributed to photochemical reactions.     

Index of direction change of zonally averaged wind and change of season

In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.     

Maximum Wind Speed Changes over China

In this study,the maximum wind speed（WSmax） changes across China from 1956 to 2004 were analyzed based on observed station data,and the changes of WS max for 2046-2065 and 2080-2099 are projected using three global climate models（GFDL_CM2₀,CCCMA_CGCM3,and MRI_CGCM2） that have participated in the IPCC Fourth Assessment Report（AR4）.The observed annual and seasonal WS max and the frequency of gale days showed obvious declining trends.The annual WS max decreased by approximately 1.46 m s-1 per decade,and the number of gale days decreased by 3.0 days per decade from 1956 to 2004.The amplitudes of the annual and seasonal WS max decreases are larger than those of the annual and seasonal average wind speeds（WSavg）.The weakening of the East Asian winter and summer monsoons is the cause for the distinct decreases of both WS max and WS avg over the whole China.The decrease of WS max in the southeast coastal areas of China is related to the reduced intensity of cold waves in China and the decreasing number（and decreasing intensity） of land-falling typhoons originated in the Northwest Pacific Ocean.The global climate models GFDL_CM2₀,MRI_CGCM2,and EBGCM（the ensemble of above mentioned three global climate models） consistently suggest that the annual and seasonal WS max values will decrease during 2046-2065 and 2080-2099 relative to 1981-2000.The models also suggest that decreases in WS max for whole China during 2046-2065 and 2080-2099 are related to both the reduced intensity of cold waves and the reduced intensity of the winter monsoon,and the decrease in WS max in the southeast coastal areas of China is corresponding to the decreasing number of tropical cyclones over the Northwest Pacific Ocean in the summer during the same periods.     

ANALYSIS OF “BIMODAL PATTERN” STORM ACTIVITY CHARACTERISTICS OF THE BAY OF BENGAL

Storms that occur at the Bay of Bengal (BoB) are of a bimodal pattern, which is different from that of the other sea areas. By using the NCEP, SST and JTWC data, the causes of the bimodal pattern storm activity of the BoB are diagnosed and analyzed in this paper. The result shows that the seasonal variation of general atmosphere circulation in East Asia has a regulating and controlling impact on the BoB storm activity, and the “bimodal period” of the storm activity corresponds exactly to the seasonal conversion period of atmospheric circulation. The minor wind speed of shear spring and autumn contributed to the storm, which was a crucial factor for the generation and occurrence of the “bimodal pattern” storm activity in the BoB. The analysis on sea surface temperature (SST) shows that the SSTs of all the year around in the BoB area meet the conditions required for the generation of tropical cyclones (TCs). However, the SSTs in the central area of the bay are higher than that of the surrounding areas in spring and autumn, which facilitates the occurrence of a “two-peak” storm activity pattern. The genesis potential index (GPI) quantifies and reflects the environmental conditions for the generation of the BoB storms. For GPI, the intense low-level vortex disturbance in the troposphere and high-humidity atmosphere are the sufficient conditions for storms, while large maximum wind velocity of the ground vortex radius and small vertical wind shear are the necessary conditions of storms.     

Reliability Analyses of Anomalies of NCEP/NCAR Reanalyzed Wind Speed and Surface Air Temperature in Climate Change Research in China

By means of varied statistical methods,such as normalized root mean square error(RMSE),correlation analysis,empirical orthogonal function(EOF)decomposition,etc.,the reliability of the varied seasonal anomalies of NCEP/NCAR reanalyzed wind speed and surface air temperature(SAT)data frequently used in the climate change research in China is studied.Results show that RMSEs of meteorological variables are smaller in eastern China than in western China,i.e.,the reliability of NCEP/NCAR reanalysis in eastern China is better than that in western China.This could be due to effects of the topography in the reanalysis model and the disposition of"dense-in-eastern-and-sparse-in-western"of meteorological stations in China. The RMSE of anomalies of reanalyzed wind speeds decreases with increasing height,further confirming the possible impact of topography on reliability of reanalysis.Results of correlation analysis inversely correspond to those of RMSE analysis,i.e.,if the RMSE is larger,the correlation between reanalyzed and observed data is worse,and vice versa.It is found from comparing the EOF eigenvectors of anomaly of reanalyzed and observed data that if a meteorological variable has smaller RMSE,the spatial patterns of corresponding EOF eigenvectors of anomaly of reanalyzed and observed data are similar and their time coefficients are significantly correlated,and vice versa.Therefore,the similarity of EOF modes and the consistency of their time coefficients can be used to objectively assess the reliability of the reanalysis.On the whole,the reliability of the reanalyzed wind speed is better in spring,summer,and autumn,but worse in winter;and for the reanalyzed SAT,it is the best in winter and the worst in summer.     

Modeling of the Second Indirect Effect of Anthropogenic Aerosols in East Asia

This study investigated the second indirect climatic effect of anthropogenic aerosols,including sulfate,organic carbon(OC) ,and black carbon(BC) ,over East Asia.The seasonal variation of the climatic response to the second indirect effect was also characterized.The simulation period for this study was 2006.Due to a decrease in autoconversion rate from cloud water to rain as a result of aerosols,the cloud liquid water path(LWP) ,and radiative flux(RF) at the top of the atmosphere(TOA) changed dramatically,increasing by 14.3 g m-2 and decreasing by-4.1 W m-2 in terms of domain and annual average.Both LWP and RF changed most in autumn. There were strong decreases in ground temperature in Southwest China,the middle reaches of the Yangtze River in spring and autumn,while maximum cooling of up to-1.5 K occurred in the Chongqing district.The regional and annual mean change in ground temperature reached-0.2 K over eastern China.In all seasons except summer,precipitation generally decreased in most areas north of the Yangtze River,whereas precipitation changed little in South China.Precipitation changed most in summer,with alternating bands of increasing(～40 mm) and decreasing(～40 mm) precipitation appearing in eastern China.Precipitation decreased by 1.5-40 mm over large areas of Northeast China and the Huabei Plain.The domain and annual mean change in precipitation was approximately-0.3 mm over eastern China.The maximum reduction in precipitation occurred in summer,with mean absolute and relative changes of-1.2 mm and-3.8%over eastern China.This study revealed considerable climate responses to the second indirect effect of aerosols over specific regions of China.     

Changes in Seasonal Cycle and Extremes in China during the Period 1960–2008

Recent trends in seasonal cycles in China are analyzed, based on a homogenized dataset of daily temperatures at 541 stations during the period 1960–2008. Several indices are defined for describing the key features of a seasonal cycle, including local winter/summer (LW/LS) periods and local spring/autumn phase (LSP/LAP). The Ensemble Empirical Mode Decomposition method is applied to determine the indices for each year. The LW period was found to have shortened by 2–6 d (10 yr)-1, mainly due to an earlier end to winter conditions, with the LW mean temperature having increased by 0.2°C–0.4°C (10 yr)?1, over almost all of China. Records of the most severe climate extremes changed less than more typical winter conditions did. The LS period was found to have lengthened by 2–4 d (10 yr)?1, due to progressively earlier onsets and delayed end dates of the locally defined hot period. The LS mean temperature increased by 0.1°C–0.2°C (10 yr)-1 in most of China, except for a region in southern China centered on the mid-lower reaches of the Yangtze River. In contrast to the winter cases, the warming trend in summer was more prominent in the most extreme records than in those of more typical summer conditions. The LSP was found to have advanced significantly by about 2 d (10 yr)-1 in most of China. Changes in the autumn phase were less prominent. Relatively rapid changes happened in the 1980s for most of the regional mean indices dealing with winter and in the 1990s for those dealing with summer.     

INFLUENCE OF SPRING EQUATORIAL EASTERN PACIFIC SSTA ON THE SEASONAL CHANGE FROM SPRING TO SUMMER OF EASTERN ASIAN CIRCULATION

Based on the analysis of NCEP height, wind and OLR data, the influence of spring equatorial eastern Pacific SSTA on the seasonal change from spring to summer of eastern Asian circulation has been investigated. Results show that related to the warm (cold) spring SSTA in the equatorial eastern Pacific, the anomalous anticyclone (cyclone) circulation emerges around the South China Sea and the Philippines, the strong (weak) west Pacific subtropical high locates to the west (east) of its normal position, which induces to the late (early) onset of the South China Sea monsoon. The numerical simulations have also shown that the remarkable influence of spring SSTA in the equatorial eastern Pacific on the spring seasonal change of eastern Asian circulation will last till summer.     

Typical Surface Seasonal Circulation in the Indian Ocean Derived from Argos Floats

This study investigates the surface circulation in the Indian Ocean using Argos float data over the period 1979-2011.The Argos observations manifest some new phenomena.The climatological annual mean circulation shows that the surface current becomes much stronger after turning around in shore in the western Indian Ocean.In the tropical Indian Ocean,the Great Whirl(GW) to the east of Somalia develops quickly in spring(April-May) as the monsoon reverses to move northward,becoming strongest in summer(June-September) and disappearing in autumn(October-November).The west end of the Agulhas retroflection can reach 18°E,and it exhibits a seasonal variation.At approximately 90°E,the Agulhas Return Current combines with the eastward South Atlantic Current and finally joins the Antarctic Circumpolar Current.     

A GCM Study on the Tropical Intraseasonal Oscillation

The ability of AGCM to simulate the tropical intraseasonal oscillation (ISO) has been studied using the output of global spectral model (ALGCM (R42L9)) of the Institute of Atmospheric Physics, Chinese Academy of Sciences, and the outoput is compared with the results from NCEP/NCAR reanalysis for the year 1978-1989. The model displays an evident periodic signal of the tropical ISO. Basic propagating characters of the tropical ISO are captured, and changes in phase speed between Eastern and Western Hemispheres are also well presented, and the simulation of eastward propagation is better than that of westward propagation. This model has increased the ability to simulate the strength of the tropical ISO, especially at 200 hPa, and basically simulates the horizontal structure of wind characterized by the convergence in low-level and divergence in upper-level. The vertical structure of the zonal wind is also well reproduced. Moreover, observed results show that the representing of seasonal preference to form strong ISO in winter and spring is related to ISO's interannual variability, but it is shown in this model with strong ISO in winter and summer and weak ISO in spring and autumn. Structures of some physical elements such as vertical velocity, divergence, specific humidity, etc., and the special distribution of ISO have also differences with these from NCEP reanalysis data, which make it clear to develop this model to simulate the structure and spatial distribution of the ISO.     

RESEARCH ON SURFACE O_3 WITH METEOROLOGICAL CONDITIONS UNDER ATMOSPHERIC BACKGROUND CONDITIONS IN NORTHEAST CHINA

Surface O_3 concentration and its precursors have been observed at Longfengshan station,Heilongjiang Province for a period of one year from August 13,1994 to July 30,1995.Relationship between surface O_3 and the meteorological conditions during this period is analyzed inthis study.Observation results show that diurnal variation of surface O_3 follows a pattern ofdouble-peaks with amplitude of 27—28 ppb under fine days in summer and autumn.Although thediurnal variation is small(14 ppb),it is still detectable when it is overcast.Diurnal variation of O_3is irregular under rainy days.Surface O_3 concentration rises when wind speed starts to increase at0800 BT(Beijing Time)from 0 to 6 m s~(-1)in autumn,winter and summer.Relative high surfaceO_3 concentration is noticed frequently when S,SSW,SW and WSW wind are encountered at thestation during all seasons.At 0800 BT and 1400 BT the surface O_3 concentration increases with theincrease of global radiation accordingly during fine days in winter,spring and autumn.During finedays average peak of O_3 concentration in summer is 20 ppb higher than that in winter while theaverage peak of global radiation in summer is almost twice as high as that in winter.The averagesurface O_3 concentration under fine days in autumn at Longfengshan station is 14 ppb lower incomparison to the observation results from Lin'an station where Lin'an is at about the samelongitude and lower latitude,with same environment,which is mainly caused by the difference ofglobal radiation due to different latitudes in these two areas(difference of average peak globalradiation about 100 W m~(-2)).