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2012 Vol. 29, No. 5

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Eighth National Report to IUGG by China National Committee for IAMAS
Characteristics, Processes, and Causes of the Spatio-temporal Variabilities of the East Asian Monsoon System
HUANG Ronghui, CHEN Jilong, WANG Lin, LIN Zhongda
2012, 29(5): 910-942. doi: 10.1007/s00376-012-2015-x
Recent advances in the study of the characteristics, processes, and causes of spatio-temporal variabilities of the East Asian monsoon (EAM) system are reviewed in this paper. The understanding of the EAM system has improved in many aspects: the basic characteristics of horizontal and vertical structures, the annual cycle of the East Asian summer monsoon (EASM) system and the East Asian winter monsoon (EAWM) system, the characteristics of the spatio-temporal variabilities of the EASM system and the EAWM system, and especially the multiple modes of the EAM system and their spatio-temporal variabilities. Some new results have also been achieved in understanding the atmosphere--ocean interaction and atmosphere--land interaction processes that affect the variability of the EAM system. Based on recent studies, the EAM system can be seen as more than a circulation system, it can be viewed as an atmosphere--ocean--land coupled system, namely, the EAM climate system. In addition, further progress has been made in diagnosing the internal physical mechanisms of EAM climate system variability, especially regarding the characteristics and properties of the East Asia-Pacific (EAP) teleconnection over East Asia and the North Pacific, the Silk Road teleconnection along the westerly jet stream in the upper troposphere over the Asian continent, and the dynamical effects of quasi-stationary planetary wave activity on EAM system variability. At the end of the paper, some scientific problems regarding understanding the EAM system variability are proposed for further study.
Progress in Climate Prediction and Weather Forecast Operations in China
2012, 29(5): 943-957. doi: 10.1007/s00376-012-1194-9
The current status of weather forecasting and climate prediction, and the main progress China has made in recent years, are summarized in this paper. The characteristics and requirements of modern weather forecast operations are described briefly, and the significance of Numerical Weather Prediction (NWP) for future development is emphasized. The objectives and critical tasks for seamless short-term climate prediction that covers the extended-range (15--30 days), monthly, seasonal, annual, interannual and interdecadal timescales, are proposed.
Recent Progress in Studies of Climate Change in China
REN Guoyu, DING Yihui, ZHAO Zongci, ZHENG Jingyun, WU Tongwen, TANG Guoli, XU Ying
2012, 29(5): 958-977. doi: 10.1007/s00376-012-1200-2
An overview of basic research on climate change in recent years in China is presented. In the past 100 years in China, average annual mean surface air temperature (SAT) has increased at a rate ranging from 0.03o(10 yr)-1 to 0.12o (10 yr)-1. This warming is more evident in northern China and is more significant in winter and spring. In the past 50 years in China, at least 27% of the average annual warming has been caused by urbanization. Overall, no significant trends have been detected in annual and/or summer precipitation in China on a whole for the past 100 years or 50 years. Both increases and decreases in frequencies of major extreme climate events have been observed for the past 50 years. The frequencies of extreme temperature events have generally displayed a consistent pattern of change across the country, while the frequencies of extreme precipitation events have shown only regionally and seasonally significant trends. The frequency of tropical cyclone landfall decreased slightly, but the frequency of sand/dust storms decreased significantly. Proxy records indicate that the annual mean SAT in the past a few decades is the highest in the past 400--500 years in China, but it may not have exceeded the highest level of the Medieval Warm Period (1000--1300 AD). Proxy records also indicate that droughts and floods in eastern China have been characterized by continuously abnormal rainfall periods, with the frequencies of extreme droughts and floods in the 20th century most likely being near the average levels of the past 2000 years. The attribution studies suggest that increasing greenhouse gas (GHG) concentrations in the atmosphere are likely to be a main factor for the observed surface warming nationwide. The Yangtze River and Huaihe River basins underwent a cooling trend in summer over the past 50 years, which might have been caused by increased aerosol concentrations and cloud cover. However, natural climate variability might have been a main driver for the mean and extreme precipitation variations observed over the past century. Climate models generally perform well in simulating the variations of annual mean SAT in China. They have also been used to project future changes in SAT under varied GHG emission scenarios. Large uncertainties have remained in these model-based projections, however, especially for the projected trends of regional precipitation and extreme climate events.
Weather and Climate Effects of the Tibetan Plateau
DUAN Anmin, WU Guoxiong, LIU Yimin, MA Yaoming, ZHAO Ping
2012, 29(5): 978-992. doi: 10.1007/s00376-012-1220-y
Progress in observation experiments and studies concerning the effects of the Tibetan Plateau (TP) on weather and climate during the last 5 years are reviewed. The mesoscale topography over the TP plays an important role in generating and enhancing mesoscale disturbances. These disturbances increase the surface sensible heat (SH) flux over the TP and propagate eastward to enhance convection and precipitation in the valley of Yangtze River. Some new evidence from both observations and numerical simulations shows that the southwesterly flow, which lies on the southeastern flank of the TP, is highly correlated with the SH of the southeastern TP in seasonal and interannual variability. The mechanical and thermal forcing of the TP is an important climatic cause of the spring persistent rains over southeastern China. Moreover, the thermodynamic processes over the TP can influence the atmospheric circulation and climate over North America and Europe by stimulating the large-scale teleconnections such as the Asian-Pacific oscillation and can affect the atmospheric circulation over the southern Indian Ocean. Estimating the trend in the atmospheric heat source over the TP shows that, in contrast to the strong surface and troposphere warming, the SH over the TP has undergone a significant decreasing trend since the mid-1980s. Despite the fact that {\it in situ} latent heating presents a weak increasing trend, the springtime atmospheric heat source over the TP is losing its strength. This gives rise to reduced precipitation along the southern and eastern slopes of the TP and to increased rainfall over northeastern India and the Bay of Bengal.
Progresses in the Atmospheric Electricity Researches in China during 2006--2010
QIE Xiushu
2012, 29(5): 993-1005. doi: 10.1007/s00376-011-1195-0
Atmospheric electricity is composed of a wide range of electric phenomena in the troposphere, stratosphere, and even lower ionosphere. Research progress on atmospheric electricity in the past 5 years in China are briefly reviewed here. This research area has been greatly expanded through rocket-triggered lightning experiments and the increased use of high spatio-temporal resolution techniques for the detection and location of lightning. The main results described in this review are summarized in the following five aspects: (1) processes and parameters inferred from rocket-triggered lightning, (2) lightning physics and effects (observations and theoretical study), (3) lightning activities associated with different thunderstorms, (4) charge structure of thunderstorms (observations and simulation), and (5) the VHF/UHF lightning location techniques and discharge channel mapping.
A Review of Atmospheric Chemistry Research in China: Photochemical Smog, Haze Pollution, and Gas-Aerosol Interactions
MA Jianzhong, XU Xiaobin, ZHAO Chunsheng, YAN Peng
2012, 29(5): 1006-1026. doi: 10.1007/s00376-012-1188-7
In this paper we present a review of atmospheric chemistry research in China over the period 2006--2010, focusing on tropospheric ozone, aerosol chemistry, and the interactions between trace gases and aerosols in the polluted areas of China. Over the past decade, China has suffered severe photochemical smog and haze pollution, especially in North China, the Yangtze River Delta, and the Pearl River Delta. Much scientific work on atmospheric chemistry and physics has been done to address this large-scale, complex environmental problem. Intensive field experiments, satellite data analyses, and model simulations have shown that air pollution is significantly changing the chemical and physical characters of the natural atmosphere over these parts of China. In addition to strong emissions of primary pollutants, photochemical and heterogeneous reactions play key roles in the formation of complex pollution. More in-depth research is recommended to reveal the formation mechanism of photochemical smog and haze pollution and their climatic effects at the urban, regional, and global scales.
Summary of Recent Climate Change Studies on the Carbon and Nitrogen Cycles in the Terrestrial Ecosystem and Ocean in China
XU Yongfu, HUANG Yao, LI Yangchun
2012, 29(5): 1027-1047. doi: 10.1007/s00376-012-1206-9
This article reviews recent advances over the past 4 years in the study of the carbon-nitrogen cycling and their relationship to climate change in China. The net carbon sink in the Chinese terrestrial ecosystem was 0.19--0.26 Pg C yr-1 for the 1980s and 1990s. Both natural wetlands and the rice-paddy regions emitted 1.76 Tg and 6.62 Tg of CH4 per year for the periods 1995--2004 and 2005--2009, respectively. China emitted ~1.1 Tg N2O-N yr-1 to the atmosphere in 2004. Land soil contained ~8.3 Pg N. The excess nitrogen stored in farmland of the Yangtze River basin reached 1.51 Tg N and 2.67 Tg N in 1980 and 1990, respectively. The outer Yangtze Estuary served as a moderate or significant sink of atmospheric CO2 except in autumn. Phytoplankton could take up carbon at a rate of 6.4×1011 kg yr-1 in the China Sea. The global ocean absorbed anthropogenic CO2 at the rates of 1.64 and 1.73 Pg C yr-1 for two simulations in the 1990s. Land net ecosystem production in China would increase until the mid-21st century then would decrease gradually under future climate change scenarios. This research should be strengthened in the future, including collection of more observation data, measurement of the soil organic carbon (SOC) loss and sequestration, evaluation of changes in SOC in deep soil layers, and the impacts of grassland management, carbon-nitrogen coupled effects, and development and improvement of various component models and of the coupled carbon ~cycle-climate model.
Progress in the Study of Nonlinear Atmospheric Dynamics and Predictability of Weather and Climate in China (2007--2011)
ZHOU Feifan, DING Ruiqiang, FENG Guolin, FU Zuntao, DUAN Wansuo
2012, 29(5): 1048-1062. doi: 10.1007/s00376-012-1204-y
Recent progress in the study of nonlinear atmospheric dynamics and related predictability of weather and climate in China (2007--2011) are briefly introduced in this article. Major achievements in the study of nonlinear atmospheric dynamics have been classified into two types: (1) progress based on the analysis of solutions of simplified control equations, such as the dynamics of NAO, the optimal precursors for blocking onset, and the behavior of nonlinear waves, and (2) progress based on data analyses, such as the nonlinear analyses of fluctuations and recording-breaking temperature events, the long-range correlation of extreme events, and new methods of detecting abrupt dynamical change. Major achievements in the study of predictability include the following: (1) the application of nonlinear local Lyapunov exponents (NLLE) to weather and climate predictability; (2) the application of condition nonlinear optimal perturbation (CNOP) to the studies of El Ni\~{n}o-Southern Oscillation (ENSO) predictions, ensemble forecasting, targeted observation, and sensitivity analysis of the ecosystem; and (3) new strategies proposed for predictability studies. The results of these studies have provided greater understanding of the dynamics and nonlinear mechanisms of atmospheric motion, and they represent new ideas for developing numerical models and improving the forecast skill of weather and climate events.
Responses of Grassland and Forest to Temperature and Precipitation Changes in Northeast China
PENG Jing, DONG Wenjie, YUAN Wenping, ZHANG Yong
2012, 29(5): 1063-1077. doi: 10.1007/s00376-012-1172-2
Using the Normalized Difference Vegetation Index (NDVI) as an indicator of vegetation growth, we explored the characteristics and differences in the response to drought of five vegetation biomes in Northeast China, including typical steppe, desert steppe, meadow steppe, deciduous coniferous forest and deciduous broad-leaved forest during the period 1982--2009. The results indicate that growing season precipitation may be the primary vegetation growth-limiting factor in grasslands. More than 70% of the temporal variations in NDVI can be explained by the amount of precipitation during the growing season in typical and desert steppes. During the same period, the mean temperature in the growing season could explain nearly 43% of the variations in the mean growing season NDVI and is therefore a dominant growth-limiting factor for forest ecosystems. Therefore, the NDVI trends differ largely due to differences in the vegetation growth-limiting factors of the different vegetation biomes. The NDVI responses to droughts vary in magnitude and direction and depend on the drought-affected areas of the five vegetation types. Specifically, the changes in NDVI are consistent with the variations in precipitation for grassland ecosystems. A lack of precipitation resulted in decreases in NDVI, thereby reducing vegetation growth in these regions. Conversely, increasing precipitation decreased the NDVI of forest ecosystems. The results also suggest that grasslands under arid and semi-arid environments may be more sensitive to drought than forests under humid environments. Among grassland ecosystems, desert steppe was most sensitive to drought, followed by typical steppe; meadow steppe was the least sensitive.
Relationships between the Limit of Predictability and Initial Error in the Uncoupled and Coupled Lorenz Models
DING Ruiqiang, LI Jianping
2012, 29(5): 1078-1088. doi: 10.1007/s00376-012-1207-8
In this study, the relationship between the limit of predictability and initial error was investigated using two simple chaotic systems: the Lorenz model, which possesses a single characteristic time scale, and the coupled Lorenz model, which possesses two different characteristic time scales. The limit of predictability is defined here as the time at which the error reaches 95% of its saturation level; nonlinear behaviors of the error growth are therefore involved in the definition of the limit of predictability. Our results show that the logarithmic function performs well in describing the relationship between the limit of predictability and initial error in both models, although the coefficients in the logarithmic function were not constant across the examined range of initial errors. Compared with the Lorenz model, in the coupled Lorenz model---in which the slow dynamics and the fast dynamics interact with each other---there is a more complex relationship between the limit of predictability and initial error. The limit of predictability of the Lorenz model is unbounded as the initial error becomes infinitesimally small; therefore, the limit of predictability of the Lorenz model may be extended by reducing the amplitude of the initial error. In contrast, if there exists a fixed initial error in the fast dynamics of the coupled Lorenz model, the slow dynamics has an intrinsic finite limit of predictability that cannot be extended by reducing the amplitude of the initial error in the slow dynamics, and vice versa. The findings reported here reveal the possible existence of an intrinsic finite limit of predictability in a coupled system that possesses many scales of time or motion.
Satellite-Based Monitoring of Decadal Soil Salinization and Climate Effects in a Semi-arid Region of China
WANG Hesong, JIA Gensuo
2012, 29(5): 1089-1099. doi: 10.1007/s00376-012-1150-8
Soil salinization is a common phenomenon that affects both the environment and the socio-economy in arid and semi-arid regions; it is also an important aspect of land cover change. In this study, we integrated multi-sensor remote sensing data with a field survey to analyze processes of soil salinization in a semi-arid area in China from 1979 to 2009. Generally, the area of salt-affected soils increased by 0.28% per year with remarkable acceleration from 1999 to 2009 (0.42% increase per year). In contrast, the area of surface water bodies showed a decreasing trend (-0.08% per year) in the same period. Decreases in precipitation and increases in aridity due to annual (especially summer) warming provided a favorable condition for soil salinization. The relatively flat terrain favored waterlogging at the surface, and continuous drought facilitated upward movement of soil water and accumulation of surface saline and calcium. Meanwhile, land-use practices also played a crucial role in accelerating soil salinization. The conversion to cropland from natural vegetation greatly increased the demand for groundwater irrigation and aggravated the process of soil salinization. Furthermore, there are potential feedbacks of soil salinization to regional climate. The salinization of soils can limit the efficiency of plant water use as well as photosynthesis; therefore, it reduces the amount of carbon sequestrated by terrestrial ecosystem. Soil salinization also reduces the absorbed solar radiation by increasing land surface albedo. Such conversions of land cover significantly change the energy and water balance between land and atmosphere.
Seasonal Variation of Climatological Bypassing Flows around the Tibetan Plateau
LI Qiang, ZHANG Renhe
2012, 29(5): 1100-1110. doi: 10.1007/s00376-012-1154-4
The present study investigated diagnostically the seasonal variation of the bypassing flows caused by the splitting effect of the Tibetan Plateau (TP). The relationships among the splitting bypassing flows around the TP to precipitation in China, the westerly jet stream, and the thermal status over the TP are revealed. The bypassing flows occur from the 1st to the 22nd pentad and from the 59th to the 73rd pentad, respectively, and they disappear from the 29th to the 58th pentad. They are strongest in winter from the 1st to the 22nd pentad and from the 59th to the 73rd pentad, respectively. During the rebuilding of the bypassing flows from mid-October to mid-February, they are the main cause of precipitation over southeastern China. The enhancement of the bypassing flow intensity in March can cause the precipitation to increase in the early stage of the persistent spring rain over southeastern China. From winter to summer, the seasonal transition of the bypassing flows in the lower troposphere precedes that of the westerly jet stream axis in the upper troposphere to the west of the TP by ~4 pentads, while from summer to winter lags by ~4 pentads. The seasonal variation of the thermal status over the TP plays an important role in the bypassing flows around the TP. The strengthening of the heating over the TP weakens the bypassing flows, and the increase in cooling over the TP is related to the rebuilding and strengthening of the bypassing flows.
Circulation Indices of the Aleutian Low Pressure System: Definitions and Relationships to Climate Anomalies in the Northern Hemisphere
WANG Panxing, Julian X. L. WANG, ZHI Hai, WANG Yukun, SUN Xiaojuan
2012, 29(5): 1111-1118. doi: 10.1007/s00376-012-1196-7
In this study, a group of indices were defined regarding intensity (P), area (S) and central position (λc, Φc) of the Aleutian low (AL) in the Northern Hemisphere in winter, using seasonal and monthly mean height field at 1000-hPa. These indices were calculated over 60 winter seasons from 1948/1949 to 2007/2008 using reanalysis data. Climatic and anomalous characteristics of the AL were analyzed based on these indices and relationships between the AL, and general circulations were explored using correlations between indices P, λc, and Pacific SST, as well as Northern Hemisphere temperature and precipitation. The main results are these: (1) AL is the strongest in January, when the center shifts to the south and west of its climatological position, and it is the weakest in December when the center shifts to the north and east. (2) AL intensity (P) is negatively correlated with its longitude (λc): a deeper low occurs toward the east and a shallower low occurs toward the west. On a decadal scale, the AL has been persistently strong and has shifted eastward since the 1970s, but reversal signs have been observed in recent years. (3) The AL is stronger and is located toward the east during strong El Nino winters and vice versa during strong La Nina years; this tendency is particularly evident after 1975. The AL is also strongly correlated with SST in the North Pacific. It intensifies and moves eastward with negative SST anomalies, and it weakens and moves westward with positive SST anomalies. (4) Maps of significance correlation between AL intensity and Northern Hemisphere temperature and rainfall resemble the PNA teleconnection pattern in mid-latitudes in the North Pacific and across North America. The AL and the Mongolian High are two permanent atmospheric pressure systems adjacent to each other during boreal winter over the middle and high latitudes in the Northern Hemisphere, but their relationships with the El Nino/La Nina events and with temperature and precipitation in the Northern Hemisphere are significantly different.
On the Differences and Climate Impacts of Early and Late Stratospheric Polar Vortex Breakup
LI Lin, LI Chongyin, PAN Jing, TAN Yanke
2012, 29(5): 1119-1128. doi: 10.1007/s00376-012-1012-4
The stratospheric polar vortex breakup (SPVB) is an important phenomenon closely related to the seasonal transition of stratospheric circulation. In this paper, 62-year NCEP/NCAR reanalysis data were employed to investigate the distinction between early and late SPVB. The results showed that the anomalous circulation signals extending from the stratosphere to the troposphere were reversed before and after early SPVB, while the stratospheric signals were consistent before and after the onset of late SPVB. Arctic Oscillation (AO) evolution during the life cycle of SPVB also demonstrated that the negative AO signal can propagate downward after early SPVB. Such downward AO signals could be identified in both geopotential height and temperature anomalies. After the AO signal reached the lower troposphere, it influenced the Aleutian Low and Siberian High in the troposphere, leading to a weak winter monsoon and large-scale warming at mid latitudes in Asia. Compared to early SPVB, downward propagation was not evident in late SPVB. The high-latitude tropospheric circulation in the Northern Hemisphere was affected by early SPVB, causing it to enter a summer circulation pattern earlier than in late SPVB years.