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2004 Vol. 21, No. 2

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An Evaluation of the Effects of Cloud Parameterization in the R42L9 GCM
WU Tongwen, WANG Zaizhi, LIU Yimin, YU Rucong, WU Guoxiong
2004, 21(2): 153-162. doi: 10.1007/BF02915701
Cloud is one of the uncertainty factors influencing the performance of a general circulation model (GCM). Recently, the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics (LASG/IAP) has developed a new version of a GCM (R42L9). In this work, roles of cloud parameterization in the R42L9 are evaluated through a comparison between two 20year simulations using different cloud schemes. One scheme is that the cloud in the model is diagnosed from relative humidity and vertical velocity, and the other one is that diagnostic cloud is replaced by retrieved cloud amount from the International Satellite Cloud Climatology Project (ISCCP), combined with the amounts of high-, middle-, and low-cloud and heights of the cloud base and top from the NCEP. The boreal winter and summer seasonal means, as well as the annual mean, of the simulated top-of-atmosphere shortwave radiative flux, surface energy fluxes, and precipitation are analyzed in comparison with the observational estimates and NCEP reanalysis data. The results show that the scheme of diagnostic cloud parameterization greatly contributes to model biases of radiative budget and precipitation. When our derived cloud fractions are used to replace the diagnostic cloud amount, the top-of-atmosphere and surface radiation fields are better estimated as well as the spatial pattern of precipitation. The simulations of the regional precipitation, especially over the equatorial Indian Ocean in winter and the Asia-western Pacific region in summer, are obviously improved.
A Numerical Study of Tropospheric Ozone in the Springtime in East Asia
ZHANG Meigen, XU Yongfu, Itsushi UNO, Hajime AKIMOTO
2004, 21(2): 163-170. doi: 10.1007/BF02915702
The Models-3 Community Multi-scale Air Quality modeling system (CMAQ) coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to study the transport and photochemical transformation of tropospheric ozone in March 1998. The calculated mixing ratios of ozone and carbon monoxide are compared with ground level observations at three remote sites in Japan and it is found that the model reproduces the observed features very well. Examination of several high episodes of ozone and carbon monoxide indicates that these elevated levels are found in association with continental outflow,demonstrating the critical role of the rapid transport of carbon monoxide and other ozone precursors from the continental boundary layer. In comparison with available ozonesonde data, it is found that the model-calculated ozone concentrations are generally in good agreement with the measurements, and the stratospheric contribution to surface ozone mixing ratios is quite limited.
A New Perspective of the Physical Processes Associated with the Clear-Sky Greenhouse Effect over High Latitudes
Zuohao CAO, Ronald E.STEWART, M.K.YAU
2004, 21(2): 171-180. doi: 10.1007/BF02915703
The physical processes associated with the clear-sky greenhouse effect in the presence of water vapor are examined by including surface emissivity in the greenhouse effect formulation, and by introducing a new way to partition physical processes of the greenhouse effect. In this new framework, it is found that the clear-sky greenhouse effect is governed by three physical processes associated with (1) the temperature contrast between the surface and the atmosphere, (2) the interaction between the surface emissivity and the temperature contrast, and (3) the surface emissivity. The importance of the three physical processes is assessed by computing their vertical and spectral variations for the subarctic winter and summer standard atmosphere using the radiation model MODTRAN3 (Moderate Resolution Transmittance code Version 3). The results show that the process associated with the temperature contrast between the surface and the atmosphere dominates over the other two processes in magnitude. The magnitude of this process has substantial variations in the spectral region of 1250 to 1880 cm-1 and in the far infrared region. Due to the low-level temperature inversion over the subarctic winter, there exists a negative contribution to the greenhouse trapping. The seasonal variations are, however, dominated by the processes associated with the interaction between the surface emissivity and the temperature contrast as well as the surface emissivity itself. The magnitudes of these two physical processes contributing to the greenhouse trapping over the subarctic winter are about 7 to 10 times of those over the subarctic summer, whereas the magnitude of the processes associated with the temperature contrast in the subarctic summer is only about 2 times of that in the subarctic winter.
Ocean Data Assimilation with Background Error Covariance Derived from OGCM Outputs
FU Weiwei, ZHOU Guangqing, WANG Huijun
2004, 21(2): 181-192. doi: 10.1007/BF02915704
The background error covariance plays an important role in modern data assimilation and analysis systems by determining the spatial spreading of information in the data. A novel method based on model output is proposed to estimate background error covariance for use in Optimum Interpolation. At every model level, anisotropic correlation scales are obtained that give a more detailed description of the spatial correlation structure. Furthermore, the impact of the background field itself is included in the background error covariance. The methodology of the estimation is presented and the structure of the covariance is examined. The results of 20-year assimilation experiments are compared with observations from TOGATAO (The Tropical Ocean-Global Atmosphere-Tropical Atmosphere Ocean) array and other analysis data.
The Characteristics of Climate Change over the Tibetan Plateau in the Last 40 Years and the Detection of Climatic Jumps
NIU Tao, CHEN Longxun, ZHOU Zijiang
2004, 21(2): 193-203. doi: 10.1007/BF02915705
Through analyzing the yearly average data obtained from 123 regular meteorological observatories located in the Tibetan Plateau (T-P), this article studies the characteristics of climate change in T-P in the last 40 years. From the distribution of the linear trend, it can be concluded that the southeastern part of T-P becomes warmer and wetter, with an obvious increase of rainfall. The same characteristics arc found in the southwestern part of T-P, but the shift is smaller. In the middle of T-P, temperature and humidity obviously increase with the center of the increase in Bangoin-Amdo. The south of the Tarim Basin also exhibits the same tendency. The reason for this area being humid is that it gets less sunshine and milder wind. The northeastern part of T-P turns warmer and drier. Qaidam Basin and its western and southern areas are the center of this shift, in which the living environment is deteriorating. Analyzing the characteristics of the regional average time series, it can be found that in the mid-1970s, a significant sudden change occurred to annual rainfall, yearly average snow-accumulation days and surface pressure in the eastern part of T-P. In the mid-1980s, another evident climatic jump happened to yearly average temperature, total cloud amount, surface pressure, relative humidity, and sunshine duration in the same area. That is, in the mid 1980s, the plateau experienced a climatic jump that is featured by the increase of temperature, snow-accumulation days, relative humidity, surface pressure, and by the decrease of sunshine duration and total cloud amount. The sudden climatic change of temperature in T-P is later than that of the global-mean temperature. From this paper it can be seen that in the middle of the 1980s, a climatic jump from warm-dry to warm-wet occurred in T-P.
Summertime Surface N2O Concentration Observed on Fildes Peninsula Antarctica: Correlation with Total Atmospheric O3 and Solar Activity
ZHU Renbin, SUN Liguang, YIN Xuebin, LIU Xiaodong, XING Guangxi
2004, 21(2): 204-210. doi: 10.1007/BF02915706
Three-year summertime surface atmospheric N2O concentrations were observed for the first time on the Fildes Peninsula, maritime Antarctica, and the relationships among the N2O concentration, total atmospheric O3 amount, and sunspot number were analyzed. Solar activity had an important effect on surface N2O concentration and total O3 amount, and increases of sunspot number were followed by decreases in the N2O concentration and total O3 amount. A corresponding relationship exists between the N2O concentration and total atmospheric O3, and ozone destruction was preceded by N2O reduction.We propose that the extended solar activity in the Antarctic summer reduces the stratospheric N2O by converting it into NOx, increases the diffusion of N2O from the troposphere to the stratosphere, decreases the surface atmospheric N2O, and depletes O3 via the chemical reaction between O3 and NOx. Our observation results are consistent with the theory of solar activity regarding the formation of the Antarctic O3 hole.
Intercomparison of Nox,SO2,O3,and Aromatic Hydrocarbons Measured by a Commercial DOAS System and Traditional Point Monitoring Techniques
XIE Pinhua, LIU Wenqing, FU Qiang, WANG Ruibin, LIU Jianguo, WEI Qingnong
2004, 21(2): 211-219. doi: 10.1007/BF02915707
A field-based intercomparison study of a commercial Differential Optical Absorption Spectroscopy (DOAS) instrument (OPSIS AB, Sweden) and different point-sample monitoring techniques (PM, based on an air monitoring station, an air monitoring vehicle, and various chemical methods) was conducted in Beijing from October 1999 to January 2000. The mixing ratios of six trace gases including NO, NO2, SO2,O3, benzene, and toluene were monitored continuously during the four months. A good agreement between the DOAS and PM data was found for NO2 and SO2. However, the concentrations of benzene, toluene,and NO obtained by DOAS were significantly lower than those measured by the point monitors. The ozone levels monitored by the DOAS were generally higher than those measured by point monitors. These results may be attributed to a strong vertical gradient of the NO-O3-NO2 system and of the aromatics at the measurement site. Since the exact data evaluation algorithm is not revealed by the manufacturer of the DOAS system, the error in the DOAS analysis can also not be excluded.
Parallel Computing of a Variational Data Assimilation Model for GPS/MET Observation Using the Ray-Tracing Method
ZHANG Xin, LIU Yuewei, WANG Bin, JI Zhongzhen
2004, 21(2): 220-226. doi: 10.1007/BF02915708
The Spectral Statistical Interpolation (SSI) analysis system of NCEP is used to assimilate meteorological data from the Global Positioning Satellite System (GPS/MET) refraction angles with the variational technique. Verified by radiosonde, including GPS/MET observations into the analysis makes an overall improvement to the analysis variables of temperature, winds, and water vapor. However, the variational model with the ray-tracing method is quite expensive for numerical weather prediction and climate research. For example, about 4 000 GPS/MET refraction angles need to be assimilated to produce an ideal global analysis. Just one iteration of minimization will take more than 24 hours CPU time on the NCEP's Gray C90 computer. Although efforts have been taken to reduce the computational cost, it is still prohibitive for operational data assimilation. In this paper, a parallel version of the three-dimensional variational data assimilation model of GPS/MET occultation measurement suitable for massive parallel processors architectures is developed. The divide-and-conquer strategy is used to achieve parallelism and is implemented by message passing. The authors present the principles for the code's design and examine the performance on the state-of-the-art parallel computers in China. The results show that this parallel model scales favorably as the number of processors is increased. With the Memory-IO technique implemented by the author, the wall clock time per iteration used for assimilating 1420 refraction angles is reduced from 45 s to 12 s using 1420 processors. This suggests that the new parallelized code has the potential to be useful in numerical weather prediction (NWP) and climate studies.
Numerical Simulation of Global Temperature Change during the 20th Century with the IAP/LASG GOALS Model
MA Xiaoyan, GUO Yufu, SHI Guangyu, YU Yongqiang
2004, 21(2): 227-235. doi: 10.1007/BF02915709
The IAP/LASG GOALS coupled model is used to simulate the climate change during the 20th century using historical greenhouse gases concentrations, the mass mixing ratio of sulfate aerosols simulated by a CTM model, and reconstruction of solar variability spanning the period 1900 to 1997. Four simulations,including a control simulation and three forcing simulations, are conducted. Comparison with the observational record for the period indicates that the three forcing experiments simulate reasonable temporal and spatial distributions of the temperature change. The global warming during the 20th century is caused mainly by increasing greenhouse gas concentration especially since the late 1980s; sulfate aerosols offset a portion of the global warming and the reduction of global temperature is up to about 0.11°C over the century; additionally, the effect of solar variability is not negligible in the simulation of climate change over the 20th century.
Mean Climatic Characteristics in High Northern Latitudes in an Ocean-Sea Ice-Atmosphere Coupled Model
LIU Xiying, ZHANG Xuehong, YU Yongqiang, YU Rucong
2004, 21(2): 236-244. doi: 10.1007/BF02915710
Emphasizing the model's ability in mean climate reproduction in high northern latitudes, results from an ocean-sea ice-atmosphere coupled model are analyzed. It is shown that the coupled model can simulate the main characteristics of annual mean global sea surface temperature and sea level pressure well, but the extent of ice coverage produced in the Southern Hemisphere is not large enough. The main distribution characteristics of simulated sea level pressure and temperature at 850 hPa in high northern latitudes agree well with their counterparts in the NCEP reanalysis dataset, and the model can reproduce the Arctic Oscillation (AO) mode successfully. The simulated seasonal variation of sea ice in the Northern Hemisphere is rational and its main distribution features in winter agree well with those from observations.But the ice concentration in the sea ice edge area close to the Eurasian continent in the inner Arctic Ocean is much larger than the observation. There are significant interannual variation signals in the simulated sea ice concentration in winter in high northern latitudes and the most significant area lies in the Greenland Sea, followed by the Barents Sea. All of these features agree well with the results from observations.
Using a Modified Soil-Plant-Atmosphere Scheme (MSPAS) to Simulate the Interaction between Land Surface Processes and Atmospheric Boundary Layer in Semi-Arid Regions
LIU Shuhua, YUE Xu, HU Fei, LIU Huizhi
2004, 21(2): 245-259. doi: 10.1007/BF02915711
This paper uses a Modified Soil-Plant-Atmosphere Scheme (MSPAS) to study the interaction between land surface and atmospheric boundary layer processes. The scheme is composed of two main parts:atmospheric boundary layer processes and land surface processes. Compared with SiB and BATS, which are famous for their detailed parameterizations of physical variables, this simplified model is more convenient and saves much more computation time. Though simple, the feasibility of the model is well proved in this paper. The numerical simulation results from MSPAS show good agreement with reality. The scheme is used to obtain reasonable simulations for diurnal variations of heat balance, potential temperature of boundary layer, and wind field, and spatial distributions of temperature, specific humidity, vertical velocity,turbulence kinetic energy, and turbulence exchange coefficient over desert and oasis. In addition, MSPAS is used to simulate the interaction between desert and oasis at night, and again it obtains reasonable results.This indicates that MSPAS can be used to study the interaction between land surface processes and the atmospheric boundary layer over various underlying surfaces and can be extended for regional climate and numerical weather prediction study.
Detecting and Adjusting Temporal Inhomogeneity in Chinese Mean Surface Air Temperature Data
LI Qingxiang, LIU Xiaoning, ZHANG Hongzheng, Thomas C. PETERSON, David R. EASTERLING
2004, 21(2): 260-268. doi: 10.1007/BF02915712
Adopting the Easterling-Peterson (EP) techniques and considering the reality of Chinese meteorological observations, this paper designed several tests and tested for inhomogeneities in all Chinese historical surface air temperature series from 1951 to 2001. The result shows that the time series have been widely impacted by inhomogeneities resulting from the relocation of stations and changes in local environment such as urbanization or some other factors. Among these factors, station relocations caused the largest magnitude of abrupt changes in the time series, and other factors also resulted in inhomogeneities to some extent. According to the amplitude of change of the difference series and the monthly distribution features of surface air temperatures, discontinuities identified by applying both the E-P technique and supported by China's station history records, or by comparison with other approaches, have been adjusted. Based on the above processing, the most significant temporal inhomogeneities were eliminated, and China's most homogeneous surface air temperature series has thus been created. Results show that the inhomogeneity testing captured well the most important change of the stations, and the adjusted dataset is more reliable than ever. This suggests that the adjusted temperature dataset has great value of decreasing the uncertaities in the study of observed climate change in China.
Modelling Air-Sea Fluxes during a Western Pacific Typhoon: Role of Sea Spray
LI Weibiao
2004, 21(2): 269-276. doi: 10.1007/BF02915713
It has long been recognized that the evolution of marine storms may be strongly affected by the flux transfer processes over the ocean. High winds in a storm can generate large amounts of spray, which can modify the transfer of momentum, heat, and moisture across the air-sea interface. However, the role of sea spray and air-sea processes in western Pacific typhoons has remained elusive. In this study, the impact of sea spray on air-sea fluxes and the evolution of a typhoon over the western Pacific is investigated using a coupled atmosphere-sea-spray modeling system. Through the case study of the recent Typhoon Fengshen from 2002, we found that: (1) Sea spray can cause a significant latent heat flux increase of up to 40% of the interracial fluxes in the typhoon; (2) Taking into account the effects of sea spray, the intensity of the modeled typhoon can be increased by 30% in the 10-m wind speed, which may greatly improve estimates of storm maximum intensity and, to some extent, improve the simulations of overall storm structure in the atmospheric model; (3) The effects of sea spray are mainly focused over the high wind regions around the storm center and are mainly felt in the lower part of the troposphere.
The Relationship between Nonconservative Schemes and Initial Values of Nonlinear Evolution Equations
LIN Wantao
2004, 21(2): 277-282. doi: 10.1007/BF02915714
For the nonconservative schemes of the nonlinear evolution equations, taking the one-dimensional shallow water wave equation as an example, the necessary conditions of computational stability are given.Based on numerical tests, the relationship between the nonlinear computational stability and the construction of difference schemes, as well as the form of initial values, is further discussed. It is proved through both theoretical analysis and numerical tests that if the construction of difference schemes is definite, the computational stability of nonconservative schemes is decided by the form of initial values.
Application of Direct Assimilation of ATOVS Microwave Radiances to Typhoon Track Prediction
ZHANG Hua, XUE Jishan, ZHU Guofu, ZHUANG Shiyu, WU Xuebao, ZHANG Fengying
2004, 21(2): 283-290. doi: 10.1007/BF02915715
In order to solve the difficult problem of typhoon track prediction due to the sparsity of conventional data over the tropical ocean, in this paper, the No. 0205 typhoon Rammasun of 4-6 July 2002 is studied and an experiment of the typhoon track prediction is made with the direct use of the Advanced TIROS-N Operational Vertical Sounder (ATOVS) microwave radiance data in three-dimensional variational data assimilation. The prediction result shows that the experiment with the ATOVS microwave radiance data can not only successfully predict the observed fact that typhoon Rammasun moves northward and turns right, but can also simulate the action of the fast movement of the typhoon, which cannot be simulated with only conventional radiosonde data. The skill of the typhoon track prediction with the ATOVS microwave radiance data is much better than that without the ATOVS data. The typhoon track prediction of the former scheme is consistent in time and in location with the observation. The direct assimilation of ATOVS microwave radiance data is an available way to solve the problem of the sparse observation data over the tropical ocean, and has great potential in being applied to typhoon track prediction.
Abrupt Climate Change around 4 ka BP: Role of the Thermohaline Circulation as Indicated by a GCM Experiment
WANG Shaowu, ZHOU Tianjun, CAI Jingning, ZHU Jinhong, XIE Zhihui, GONG Daoyi
2004, 21(2): 291-295. doi: 10.1007/BF02915716
A great deal of palaeoenvironmental and palaeoclimatic evidence suggests that a predominant temperature drop and an aridification occurred at ca. 4.0 ka BP. Palaeoclimate studies in China support this dedution. The collapse of ancient civilizations at ca. 4.0 ka BP in the Nile Valley and Mesopotamia has been attributed to climate-induced aridification. A widespread alternation of the ancient cultures was also found in China at ca. 4.0 ka BP in concert with the collapse of the civilizations in the Old World. Palaeoclimatic studies indicate that the abrupt climate change at 4.0 ka BP is one of the realizations of the cold phase in millennial scale climate oscillations, which may be related to the modulation of the Thermohaline Circulation (THC) over the Atlantic Ocean. Therefore, this study conducts a numerical experiment of a GCM with SST forcing to simulate the impact of the weakening of the THC. Results show a drop in temperature from North Europe, the northern middle East Asia, and northern East Asia and a significant reduction of precipitation in East Africa, the Middle East, the Indian Peninsula, and the Yellow River Valley. This seems to support the idea that coldness and aridification at ca. 4.0 ka BP was caused by the weakening of the THC.
On Spatiotemporal Series Analysis and Its Application to Predict the Regional Short Term Climate Process
WANG Geli, YANG Peicai, LU Daren
2004, 21(2): 296-299. doi: 10.1007/BF02915717
Based on the theory of reconstructing state space, a technique for spatiotemporal series prediction is presented. By means of this technique and NCEP/NCAR data of the monthly mean geopotential height anomaly of the 500-hPa isobaric surface in the Northern Hemisphere, a regional prediction experiment is also carried out. If using the correlation coefficient R between the observed field and the prediction field to measure the prediction accuracy, the averaged R given by 48 prediction samples reaches 21%, which corresponds to the current prediction level for the short range climate process.
A Comparison Analysis of Chemical Composition of Aerosols in the Dust and Non-Dust Periods in Beijing
ZHANG Renjian, XU Yongfu, HAN Zhiwei
2004, 21(2): 300-305. doi: 10.1007/BF02915718
Dust events occurred frequently in Beijing in recent years. In this work, 120 aerosol samples were collected in two typical dust events (21-22 March and 15 May) and a non-dust period in Beijing from March to May 2001. Samples were analyzed for major elemental components by the Proton Induced Xray Emission (PIXE) method. Results show that the enrichment factors of crustal elements such as Mg,Al, and Ti had little differences between the dust period and the non-dust period in Beijing, while the enrichment factors of other elements that have a relation to anthropogenic emissions were very low during the dust period. The results derived by using multivariate factor analysis from the observation data show that the sources such as soil dust, industry, and fuel combustion were among the major contributors to the particles in Beijing.