NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> change over China and its influences

A 3-D chemical transport model (OSLO CTM2) is used to investigate the impact of the increase of NOx emission over China. The model is capable to reproduce basically the seasonal variation of surface NOx and ozone over eastern China. NOx emission data and observations reveal that NOx over eastern China increases quite quickly with the economic development of China. Model results indicate that NOx concentration over eastern China increasingly rises with the increase of NOx emission over China, and accelerates to increase in winter. When the NOx emission increases from 1995 to its double, the ratio of NO2/NOx abruptly drops in winter over northern China. Ozone at the surface decreases in winter with the continual enhancement of the NOx level over eastern China, but increases over southern China in summertime. It is noticeable that peak ozone over northern China increases in summer although mean ozone changes little. In summer, ozone increases in the free troposphere dominantly below 500 hPa.Moreover, the increases of total ozone over eastern China are proportional to the increases of NOx emission.In a word, the model results suggest that the relationship between NOx and ozone at the surface would change with NOx increase.     

Numerical Simulation Study on the Impacts of Tropospheric O_3 and CO_2 Concentration Changes on Winter Wheat. Part Ⅱ: Simulation Results and Analyses

With the rapid development of industrialization and urbanization, the enrichment of tropospheric ozone and carbon dioxide concentration at striking rates has caused effects on biosphere, especially on crops. It is generally accepted that the increase of CO2 concentration will have obverse effects on plant productivity while ozone is reported as the air pollutant most damaging to agricultural crops and other plants. The Model of Carbon and Nitrogen Biogeochemistry in Agroecosystems (DNDC) was adapted to evaluate simultaneously impacts of climate change on winter wheat. Growth development and yield formation of winter wheat under different O3 and CO2 concentration conditions are simulated with the improved DNDC model whose structure has been described in another paper. Through adjusting the DNDC model applicability, winter wheat growth and development in Gucheng Station were simulated well in 1993 and 1999, which is in favor of modifying the model further. The model was validated against experiment observation, including development stage data, leaf area index, each organ biomass, and total aboveground biomass. Sensitivity tests demonstrated that the simulated results in development stage and biomass were sensitive to temperature change. The main conclusions of the paper are the following: 1) The growth and yield of winter wheat under CO2 concentration of 500 ppmv, 700 ppmv and the current ozone concentration are simulated respectively by the model. The results are well fitted with the observed data of OTCs experiments. The results show that increase of CO2 concentration may improve the growth of winter wheat and elevate the yield. 2) The growth and yield of winter wheat under O3 concentration of 50 ppbv, 100 ppbv, 200 ppbv and the based concentration CO2 are simulated respectively by the model. The simulated curves of stem, leaf, and spike organs growth as well as leaf area index are well accounted with the observed data. The results reveal that ozone has negative effects on the growth and yield of winter wheat. Ozone accelerates the process of leaf senescence and causes yield loss. Under very high ozone concentration, crops are damaged dramatically and even dead. 3) At last, by the model possible effects of air temperature change and combined effects of O3 and CO2 are estimated respectively. The results show that doubled CO2 concentration may alleviate negative effect of O3 on biomass and yield of winter wheat when ozone concentration is about 70-80 ppbv. The obverse effects of CO2 are less than the adverse effects of O3 when the concentration of ozone is up to 100 ppbv. Future work should determine whether it can be applied to other species by adjusting the values of related parameters, and whether the model can be adapted to predict ozone effects on crops in farmland environment.     

RELATIONSHIP BETWEEN THE SEASONAL TRANSITION OF EAST ASIAN MONSOON CIRCULATION AND ASIAN-PACIFIC THERMAL FIELD AND POSSIBLE MECHANISMS

The NCEP/NCAR reanalysis, CMAP rainfall and Hadley Centre sea surface temperature (SST) datasets are used to investigate the relationship between the seasonal transition of East Asian monsoon and Asian-Pacific thermal contrast, together with the possible causes. Based on the 250 hPa air temperature over two selected key areas, the Asian-Pacific thermal difference (APTD) index is calculated. Results show that the APTD index is highly consistent with the Asian-Pacific Oscillation (APO) index defined by Zhao et al., in terms of different key areas in different seasons. Moreover, the time point of the seasonal transition of the Asian-Pacific thermal contrast can be well determined by the APTD index, indicative of seasonal variation in East Asian atmospheric circulation from winter to summer. The transition characteristic of the circulation can be summarized as follows. The continental cold high at lower tropospheric level moves eastward to the East China Sea and decreases rapidly in intensity, while the low-level northerlies turn to southerlies. At middle tropospheric level, the East Asia major trough is reduced and moves eastward. Furthermore, the subtropical high strengthens and appears near Philippines. The South Asia high shifts from the east of Philippines to the west of Indochina Peninsula, and the prevailing southerlies change into northerlies in upper troposphere. Meanwhile, both the westerly and easterly jets both jump to the north. The seasonal transition of atmospheric circulation is closely related to the thermal contrast, and the possible mechanism can be concluded as follows. Under the background of the APTD seasonal transition, the southerly wind appears firstly at lower troposphere, which triggers the ascending motion via changing vertical shear of meridional winds. The resultant latent heating accelerates the transition of heating pattern from winter to summer. The summer heating pattern can further promote the adjustment of circulation, which favors the formation and strengthening of the low-level southerly and upper-level northerly winds. As a result, the meridional circulation of the East Asian subtropical monsoon is established through a positive feedback between the circulation and thermal fields. Moreover, the time point of this seasonal transition has a significant positive correlation with the SST anomalies over the tropical central-eastern Pacific Ocean, providing a basis for the short-term climate prediction.     

Numerical Simulation of Long-Term Climate Change in East Asia

A 10-yr regional climate simulation was performed using the fifth-generation PSU/NCAR Mesoscale Model Version 3 (MM5V3) driven by large-scale NCEP/NCAR reanalyses. Simulations of winter and summer mean regional climate features were examined against observations. The results showed that the model could well simulate the 10-yr winter and summer mean circulation, temperature, and moisture transport at middle and low levels. The simulated winter and summer mean sea level pressure agreed with the NCAR/NCEP reanalysis data. The model could well simulate the distribution and intensity of winter mean precipitation rates as well as the distribution of summer mean precipitation rates, but it overestimated the summer mean precipitation over North China. The model's ability to simulate the regional climate change in winter was superior to that in summer. In addition, the model could simulate the inter-annual variation of seasonal precipitation and surface air temperature. Geopotential heights and temperature at middle and high levels between simulations and observations exhibited high anomaly correlation coefficients. The model also showed large variability to simulate the regional climate change associated with the El Nino events. The MM5V3 well simulated the anomalies of summer mean precipitation in 1992 and 1995, while it demonstrated much less ability to simulate that in 1998. Generally speaking, the MM5V3 is capable of simulating the regional climate change, and could be used for long-term regional climate simulation.     

Analysis on the 10-yr Simulation of the Meiyu Precipitation and Its Associated Circulation with the GAMIL Model

The major features of Meiyu precipitation and associated circulation systems simulated by the grid-point atmospheric model of IAP LASG (GAMIL) with Zhang-McFarlane and Tiedtke cumulus parameterization schemes are examined in this paper. The results show that the model with both schemes can reproduce the heavy precipitation center over the Yangtze-Huai River Basin (YHRB) during the Meiyu period. The horizontal and vertical structures of the circulation systems during the Meiyu period are also well simulated,such as the intensive meridional gradients of moisture and μse (pseudo-equivalent temperature), the strong low-level southwesterly flow in the lower troposphere over East China, the location of the westerly jet stream in the upper troposphere, the strong ascending motion in heavy precipitation zone, and compensation downward motion on the northern and southern sides of the heavy precipitation belt. However, obvious discrepancies occur in the simulated temperature field in the mid-lower troposphere,especially with the Zhang-McFarlane scheme. In addition, the simulated Meiyu period (onset and duration) is found to be associated with the temperature difference in the lower atmosphere over the land and ocean, and with the cumulus parameterization schemes. The land-sea thermal contrast (LSTC) simulated by the Zhang-McFarlane scheme increases faster than that in the reanalysis from April to July, and changes from negative to positive at the end of May. Consequently, the simulated Meiyu onset begins in May, one month earlier than the observation. On the other hand, since the LSTC simulated by the Tiedtke scheme is in agreement with the reanalysis during June and July, the simulated Meiyu period is similar to the observation. The different LSTCs simulated by the GAMIL model with the two cumulus parameterization schemes may affect the Meiyu period simulations. Therefore, it is necessary to refine the cumulus parameterization scheme in order to improve the Meiyu precipitation simulation by the GAMIL model.     

THE THREE-LEVEL GLOBAL ATMOSPHERIC GENERAL CIRCULATION MODEL:FORMULATION AND RESULTS

The“climate draft”often occurs in the coupling process of the atmospheric general circulation model (AGCM) andoceanic general circulation model (OGCM).One of the main methods to overcome the“climate draft”is to simulate theflow and temperature fields in the low-layer correctly.Therefore we designed a three-level AGCM including a planeta-ry boundary layer (PBL) and have run it seven model years to do climate simulation.The results show that the simulatedlower level air flow,surface air temperature and sea-level pressure in January and July,approximate to the climate av-erage fields,especially in Asian monsoon area.The simulated upper level flow and geopotential height are also in betteragreement with the observed fields.Moreover,the two westerly jets over the northern and southern sides of theQinghai-Xizang Plateau in winter,the disappearance of its southern subtropical jet during the seasonal transition fromspring to summer,the establishment of the two easterly jets near the equator and over the subtropical region during theseasonal transition,are also simulated well.In the mainland of China,the seasonal abrupt shift of the rainfall belt,suchas the Meiyu belt in South China during April to May,which jumps to the Changjiang River region in June,again jumpsback to the north China in July,and rapidly withdraws to the south in August,are simulated very well.Now we arecoupling this model to a global six-level OGCM and nesting a fine mesh (1°×1.25°)regional climate model over Chinaarea with it.     

Analysis of the simulated climatic characters of the South Asia High with a flexible coupled ocean-atmosphere GCM

The ability of a climate model to reproduce the climatic characters of the South Asia High （SAH） is assessed by analyzing the 110-yr output of a Flexible Coupled GCM, version 0 （FGCM-0）. Comparing the results of FGCM-0 with the NCEP/NCAR reanalysis data, the major findings show that FGCM-0 has better results in simulation of the geopotential height field at 100 hPa, and reproduces fairly the main atmospheric circulation centers. However, there are still some differences in the simulated results compared with the reanalysis data. The coupled model also successfully reproduces the mean seasonal variation of the SAH, that is, it moves from the Pacific Ocean to the Asian continent, remaining over the Tibetan Plateau from winter to summer, and then withdraws from the Tibetan Plateau to the Pacific Ocean from summer to winter. However, such observed relationships between the SAH positions and the summer precipitation patterns cannot be fairly reproduced in the FGCM-0.     

On the Nonlinear Response of Lower Stratospheric Ozone to External Forces---The Inclusion of BrOx and Radiation Processes

In this paper the bromine family and radiative effects are considered in an updated box model under the framework of ozone-temperature feedback,in order to further analyze the possible behavior of atmospheric ozone in the lower mid-latitude stratosphere.Results show that this updated photochemical system can present several different solutions,within a certain domain of parameters,with fixed-point and periodic states appearing in turn.The temperature feedback effect introduced in this box model has not changed the topology of the ozone system.This result presents nonlinear characteristics of the ozone system,and possible trends in the stratospheric atmosphere between complex chemistry and radiation processes.     

Differences between CMIP6 and CMIP5 Models in Simulating Climate over China and the East Asian Monsoon

We compare the ability of coupled global climate models from the phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6, respectively) in simulating the temperature and precipitation climatology and interannual variability over China for the period 1961–2005 and the climatological East Asian monsoon for the period1979–2005. All 92 models are able to simulate the geographical distribution of the above variables reasonably well.Compared with earlier CMIP5 models, current CMIP6 models have nationally weaker cold biases, a similar nationwide overestimation of precipitation and a weaker underestimation of the southeast–northwest precipitation gradient, a comparable overestimation of the spatial variability of the interannual variability, and a similar underestimation of the strength of winter monsoon over northern Asia. Pairwise comparison indicates that models have improved from CMIP5 to CMIP6 for climatological temperature and precipitation and winter monsoon but display little improvement for the interannual temperature and precipitation variability and summer monsoon. The ability of models relates to their horizontal resolutions in certain aspects. Both the multi-model arithmetic mean and median display similar skills and outperform most of the individual models in all considered aspects.     

Model analysis of seasonal variations in tropospheric ozone and carbon monoxide over East Asia

Temporal-spatial variations in tropospheric ozone concentrations over East Asia in the period from 1 January 2000 to 31 December 2004 were simulated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by the Regional Atmospheric Modeling System (RAMS). The simulated concentrations of ozone and carbon monoxide were compared with ground level observations at two remote sites, Ryori (39.03°N, 141.82°E) and Yonagunijima (24.47°N, 123.02°E). The co...     

Some characteristics of ozone profiles above Hong Kong

Summary Analysis of ozonesonde data shows that in the lower troposphere above Hong Kong, there is a relative maximum with respect to height in all seasons except winter. In the upper troposphere, there is with respect to height a relative minimum in the seasonally averaged ozone mixing ratio in winter. Ozone mixing ratios in the upper troposphere in winter and spring can be significantly enhanced by stratospheric intrusions associated with the passage of cold fronts and upper cut-off lows.For Hong Kong, the seasonally averaged total ozone has the highest value in spring, and the lowest in winter. The seasonally averaged total tropospheric ozone also has the highest value in spring, but the lowest in summer. In a relative sense, total tropospheric ozone contributes most to the total ozone in spring and the least in summer.The phase of the total ozone anomaly above Hong Kong is influenced by the Quasi-Biennial Oscillation (QBO), with the positive anomaly associated with the easterly phase of QBO, and the negative anomaly the westerly phase.     

大气臭氧垂直分布变化的模拟研究

利用包括垂直平流、扩散和化学过程的一维平流层—对流层的大气化学模式，通过增加NOx的地面源，发现由于NOx地面源的增强，引起对流层下部臭氧浓度增加，夏季臭氧浓度的增加远大于冬季；通过扩散系数和垂直风速的敏感性试验比较，看出由平流层向对流层输送臭氧的过程中，平流过程的影响可能更重要。     

Ozone in the Marine Boundary Layer at Cape Grim: Model Simulation

A photochemical box model has been used to simulate the mixing ratio ofozone under conditions reflecting those encountered in the marine boundarylayer at Cape Grim, Tasmania, where a decade-long record of ozone mixingratio is available. The model is based on the proposition that ozone loss byphotolysis, atmospheric reaction with hydroperoxy and hydroxyl radicals, andsurface deposition is balanced by ozone gain via entrainment from the lowerfree troposphere with a small additional source in summer from photolysis ofnitrogen dioxide. This model simulates very well the observed ozone records,reproducing both the small diurnal cycle in ozone mixing ratio observedduring the summer months, and the factor of two seasonal ozone cycle showinga distinct winter maximum and summer minimum. The model result confirms thatunder the low-NO_x conditions of the clean marine boundarylayer net photochemical loss of ozone occurs at all times of year.     

Atmospheric Angular Momentum Transport and Balance in the AGCM-SAMIL

NCEP/NCAR reanalysis data and the spectral atmospheric general circulation Model (AGCM) of IAP/LASG (SAMIL) are employed to investigate the transport and balance of atmospheric angular momentum (AAM). It is demonstrated that SAMIL depicts the general features of the AAM transport and balance reasonably well. The AAM sources are in the tropics and sinks are in the mid-latitudes. The strongest meridional transport occurs in the upper troposphere. The atmosphere gains westerly momentum and transports it upward in the areas of surface easterlies, and downward into the areas of surface westerlies. Consequently, AAM balance is maintained. Systematic biases of the model compared to the reanalysis and observations are revealed. Possible mechanisms for these biases are investigated. In SAMIL, the friction torque in the tropics is stronger compared to the observations, which is probably due to the excessive precipitation along the Inter-tropical convergence zone (ITCZ) in the model, since the simulated Hadley circulation is much stronger than observed. In the winter half of the year, the transport center is in the lower troposphere in the SAMIL model, but it is in the upper troposphere in the reanalysis and observations. These discrepancies also suggest that simulations of convection and tropical precipitation need to be improved and that higher resolution is necessary for a quantitative simulation of AAM transport and balance. Results also demonstrate that the analysis of the transport and balance of atmospheric angular momentum is a powerful tool in diagnosing climate models for potential improvement.     

INTERCOMPARISON OF OZONE VERTICAL PROFILES BETWEEN ECC OZONESONDE AND BREWER UMKEHR MADE OVER QINGHAI PLATEAU OF CHINA*

From October 1995 to August 1996.a total of 50 ECC(electrochemical concentration cell) ozonesoundings were made in Xining(36.43°N,101.45°E,2296 m ASL)to study the distribution and seasonal characteristics of ozone profile,and intercompare the Brewer Umkehr ozone profiles obtained at Waliguan Baseline Station over the Qinghai Plateau.It was demonstrated that(1) Umkehr produced estimates of the ozone comparing with ECC profiles were accurate to better than 25% in the 20-38 km altitude range,and where 23-33 km region was the most accurate,within about 15% of the ECC ozonesonde:(2)higher differences between Brewer Umkehr and ECC ozonesonde occurred in the troposphere and lower stratosphere;and ozone amounts were overestimated in Umkehr layers 1,2 and 3,and were underestimated in Umkehr layers 6 and 7 by Brewer Umkehr method.     

Effects of atmospheric river landfalls on the cold season precipitation in California

Effects of atmospheric river (AR) landfalls in the California coast on the cold-season precipitation in California are examined for the cold seasons of 10 water years (WYs) 2001–2010 using observed data and regional modeling in conjunction with AR-landfall inventory based on visual inspections of precipitable water vapor (PWV) from remote sensing and reanalysis. The PWV in the SSM/I and SSMIS retrievals and the ERA-Interim reanalysis shows 95 AR-landfall days in the California coast that are almost evenly split between the northern and southern coasts across 37.5N. The CPC/NCEP gridded daily precipitation analysis shows that 10–30% of the cold-season precipitation totals in California have occurred during these AR landfalls. The analysis also reveals that the percentage of precipitation and the precipitation intensity during AR landfalls in California are characterized by strong north-to-south gradient. This north–south contrast in the AR precipitation is reversed for the non-AR precipitation in the coastal range. The frequency of AR landfalls and the cold-season precipitation totals in the Sierra Nevada region are only marginally correlated. Instead, AR landfalls are closely related with the occurrence of heavy precipitation events. The freezing-level altitudes are systematically higher for AR wet days than non-AR wet days indicating warmer low-troposphere during AR storms. Cold season simulations for the 10 WYs 2001–2010 show that the Weather Research and Forecast (WRF) model can reasonably simulate important features in both the seasonal and AR precipitation totals. The daily pattern correlation coefficients between the simulated and ERA-Interim upper-air fields exceed 0.9 for most of the period. This suggests that the simulated temporal variations in the atmospheric circulation agree reasonably with the reanalysis over seasonal time scales, characteristics critical for reliable simulations of regional scale hydrologic cycle. The simulated seasonal and AR precipitation totals also agree reasonably with the CPC/NCEP precipitation analysis. The most notable model errors include the overestimation (underestimation) of the season-total and AR precipitation in the northern (southern) California region. The differences in the freezing-level altitudes during the AR- and non-AR wet days in the simulation agree with those from the ERA-Interim reanalysis. The freezing level altitudes are systematically overestimated in the simulations, suggesting warm biases in the low troposphere. Overall, WRF appears to perform reasonably in simulating the key features in the cold season precipitation related with AR landfalls, an important capability for assessing the impact of global climate variations and change on future hydrology in California.     

Numerical Simulation Study on the Impacts of Tropospheric O3 and CO2 Concentration Changes on Winter Wheat. Part II: Simulation Results and Analyses

With the rapid development of industrialization and urbanization, the enrichment of tropospheric ozone and carbon dioxide concentration at striking rates has caused effects on biosphere, especially on crops. It is generally accepted that the increase of CO2 concentration will have obverse effects on plant productivity while ozone is reported as the air pollutant most damaging to agricultural crops and other plants. The Model of Carbon and Nitrogen Biogeochemistry in Agroecosystems (DNDC) was adapted to evaluate simultaneously impacts of climate change on winter wheat. Growth development and yield formation of winter wheat under different O3 and CO2 concentration conditions are simulated with the improved DNDC model whose structure has been described in another paper. Through adjusting the DNDC model applicability, winter wheat growth and development in Gucheng Station were simulated well in 1993 and 1999, which is in favor of modifying the model further. The model was validated against experiment observation, including development stage data, leaf area index, each organ biomass, and total aboveground biomass. Sensitivity tests demonstrated that the simulated results in development stage and biomass were sensitive to temperature change. The main conclusions of the paper are the following: 1) The growth and yield of winter wheat under CO2 concentration of 500 ppmv, 700 ppmv and the current ozone concentration are simulated respectively by the model. The results are well fitted with the observed data of OTCs experiments. The results show that increase of CO2 concentration may improve the growth of winter wheat and elevate the yield. 2) The growth and yield of winter wheat under O3 concentration of 50 ppbv, 100 ppbv, 200 ppbv and the based concentration CO2 are simulated respectively by the model. The simulated curves of stem, leaf, and spike organs growth as well as leaf area index are well accounted with the observed data. The results reveal that ozone has negative e ects on the growth and yield of winter wheat. Ozone accelerates the process of leaf senescence and causes yield loss. Under very high ozone concentration, crops are damaged dramatically and even dead. 3) At last, by the model possible effects of air temperature change and combined effects of O3 and CO2 are estimated respectively. The results show that doubled CO2 concentration may alleviate negative effect of O3 on biomass and yield of winter wheat when ozone concentration is about 70-80 ppbv. The obverse effects of CO2 are less than the adverse effects of O3 when the concentration of ozone is up to 100 ppbv. Future work should determine whether it can be applied to other species by adjusting the values of related parameters, and whether the model can be adapted to predict ozone e ects on crops in farmland environment.