Xueyuan Kuang

Centennial Variations of the Global Monsoon Precipitation in the Last Millennium: Results from ECHO-G Model

The authors investigate how the global monsoon (GM) precipitation responds to the external and anthropogenic forcing in the last millennium by analyzing a pair of control and forced millennium simulations with the ECHAM and the global Hamburg Ocean Primitive Equation (ECHO-G) coupled ocean‐atmosphere model. The forced run, which includes the solar, volcanic, and greenhouse gas forcing, captures the major modes of precipitation climatology comparably well when contrasted with those captured by the NCEP reanalysis. The strength of the modeled GM precipitation in the forced run exhibits a significant quasibicentennial oscillation. Over the past 1000 yr, the simulated GM precipitation was weak during the Little Ice Age (1450‐1850) with the three weakest periods occurring around 1460, 1685, and 1800, which fell in,

The Impact of the East Asian Subtropical Jet and Polar Front Jet on the Frequency of Spring Persistent Rainfall over Southern China in 1997–2011

AbstractSpring persistent rainfall (SPR) over southern China has great impact on its society and economics. A remarkable feature of the SPR is high frequency. However, SPR frequency obviously decreases over the period of 1997–2011. In this study, the possible causes have been investigated from the perspective of the individual and concurrent effects of the East Asian subtropical jet (EASJ) and East Asian polar front jet (EAPJ). A close relationship is detected between SPR frequency and EASJ intensity (but not EAPJ intensity). Associated with strong EASJ, abundant water vapor is transported to southern China by the southwesterly flow, which may trigger the SPR. Additionally, frequencies of both strong EASJ and weak EAPJ events are positively correlated with SPR frequency. Further investigation of the concurrent effect indicates a significant positive correlation between the frequencies of SPR and the strong EASJ–weak EAPJ configuration. Associated with this configuration, southwesterly flow strengthens in ...

Spatial differences in seasonal variation of the upper-tropospheric jet stream in the Northern Hemisphere and its thermal dynamic mechanism

NCEP/NCAR reanalysis daily data from 1951 to 2008 are used in this study to reveal the spatial-asymmetric features in the seasonal variation of the upper-tropospheric jet stream (UTJS) and its thermal dynamic forcing mechanism. The jet occurrence percentage distribution of the UTJS demonstrates a spiral-like pattern in winter, but it is quasi-annular in summer. The jet occurrence percentage in the Eastern Hemisphere is larger than that in the Western Hemisphere, and its maximum area is located further south. The polar front jet stream (PJS) and subtropical jet stream (SJS) can be distinguished over the Northern Africa and Asian regions, whereas only one jet stream can be observed over the Western Pacific and Atlantic Ocean. Furthermore, a single peak pattern is found in the seasonal variation of the SJS occurrence frequency with the highest jet occurrence appearing in winter and the lowest in summer, while a double peak pattern is observed in the seasonal variation of the PJS occurrence, i.e., the jet occurrence reaches its peaks in autumn and spring for the PJS. Based on the thermal wind theory, air temperature gradient and atmospheric baroclinicity are calculated and compared with the jet occurrence variation to explore the thermal dynamic forcing mechanism for the UTJS variation. In addition, synoptic-scale transports of eddy heat and momentum are also calculated. The results indicate that the SJS variation is primarily determined by the air temperature gradient and atmospheric baroclinicity, while the PJS variation is under great influence of the transport of eddy heat and momentum over Northern Africa and East Asia. The UTJS variation over the area from 140E to 70W cannot be well individually explained by the air temperature gradient and atmospheric baroclinicity. Further analysis indicates that UTJS variation over this area is largely under control of combined effect of the transport of eddy heat and momentum as well as the atmospheric baroclinicity.

Changes in the frequencies of record‐breaking temperature events in China and its association with East Asian Winter Monsoon variability

The daily maximum and minimum temperatures observed at the 1897 meteorological stations of China over the past 60 years (1951–2010) are analyzed in this study to examine the interdecadal variation of frequency for record-breaking event (RBE) of temperature in the context of global warming. The results indicate that the frequency of record-breaking high temperature in the first decade of the 21st century is the highest in the three decades from the 1980s to the 2000s, implying a distinct warming trend. Meanwhile, frequencies of record-breaking low temperature in the 1990s and the beginning of the 21st century are also significant. In particular, the RBEs of low temperature occurred over most of China in the 1990s but concentrated in northern China during the 2000s. To understand why the record low temperatures in northern China are repeatedly broken in the 2000s, the related East Asian Winter Monsoon (EAWM) variability is investigated. The empirical orthogonal function analysis of surface air temperature reveals that the northern mode of the EAWM variability, which is highly associated with the Arctic Oscillation (AO) activities at both interdecadal and interannual timescales, has been intensifying since late 1990s. Corresponding to the intensification of the northern mode of the EAWM variability and the negative phase of AO in the 2000s, the Siberian High and East Asian trough intensify while the polar-front jet stream strengthens and the subtropical westerly jet stream abnormally shifts northward. As a result, anomalously strong cold air masses, originated from Siberia, intrude into East Asia but are blocked by the enhanced northward subtropical westerly jet and cannot reach low-latitude area. Therefore, the extremely strong cold air masses are amassed in mid-high latitudes of East Asia, resulting in RBEs of low temperature in this area.

Recent Winter Precipitation Changes over Eastern China in Different Warming Periods and the Associated East Asian Jets and Oceanic Conditions

AbstractGlobal-mean surface temperature has experienced fast warming during 1985–98 but stabilized during 1999–2013, especially in boreal winter. Climate changes over East Asia between the two warming periods and the associated mechanisms have not been fully understood. Analyses of observation and reanalysis data show that winter precipitation has decreased (increased) over southern (northeastern) China from 1985–98 to 1999–2013. Winds at 300 hPa over East Asia strengthened during 1999–2013 around 30°–47.5°N but weakened to the north and south of it. This change pattern caused the East Asian polar front jet (EAPJ) and the East Asian subtropical jet (EASJ) to shift, respectively, equatorward and poleward during 1999–2013. Associated with these jet displacements, the Siberian high enhanced and the East Asian trough shifted westward. The enhanced Siberian high strengthened the East Asian winter monsoon and weakened southwesterly winds over the South China Sea, leading to precipitation decreases over southern...

Application of back propagation neural network in paleoclimate

Studies of paleoclimate variations in local regions are seriously restricted by the low resolution and uncertainties of the simulated data at present. In order to apply large-scale modeling data to paleoclimate research in local regions, an effective downscaling model based on three-layer back propagation neural network (BPNN) is developed. Observational and ECHO-G simulated data are employed to train and test the BPNN model. With proper training and validation, BPNN model exhibits its ability to paleoclimate estimation, it is applied to reconstruct monthly (January and July) and annual mean temperature and precipitation in Anhui-Hubei region during the last millennium. The results indicate that BPNN model extracts useful climatic information from observation and simulation and provides fairly accurate paleoclimate estimation. This downscaling method is a successful trial of applying BPNN in local area of paleoclimate modeling, in the meantime, it improves the capacity of researching on paleoclimate variability in local regions using large-scale modeling data.

Regionality of record-breaking low temperature events in China and its associated circulation

Extreme cold events frequently occur around the world in recent several years and arouse widespread concern. In this study, 17 record-breaking event processes (RBEPs) of low temperature during 1981–2012 are identified by using daily minimum temperature at 1897 meteorological stations in China. These RBEPs are classified into two types based on the occurring area at northern or southern China to compositely examine the associated circulations. Although the correspondence between Arctic oscillation (AO) and RBEPs is not linearly stable, there still exist relationship between them, i.e. under AO negative phase the RBEPs tend to occur at northern China, nor the southern part, where the RBEPs prefer to happen under AO positive phase. In the RBEPs occurring at southern China, the continent high pressure over Mongolia area is extremely intensified and the East Asian polar front jet stream is enhanced accompanied with strong synoptic-scale eddy kinetic energy transports. Correspondingly, the cold air masses break out and unobstructed southward intrude to low latitudes, causing severe cooling effect in southern China. In the RBEPs occurring at northern China, however, the extremely intensified high pressure over northern Siberian area, combining with the northward enhanced subtropical jet stream, lead to the cold air mass accumulation and blockage at mid-latitudes and therefore RBEPs of low temperature at this area. Further study implies that interdecadal change of the AO phase and differences of synoptic-scale eddy activity might synthetically attribute to the different regional preference of those RBEPs of low temperature that are mostly located at southern China in 1990s but concentrated in northern China in 2000s.

Uncertainty of global summer precipitation in the CMIP5 models: a comparison between high-resolution and low-resolution models

The uncertainty of global summer precipitation simulated by the 23 CMIP5 CGCMs and the possible impacts of model resolutions are investigated in this study. Large uncertainties exist over the tropical and subtropical regions, which can be mainly attributed to convective precipitation simulation. High-resolution models (HRMs) and low-resolution models (LRMs) are further investigated to demonstrate their different contributions to the uncertainties of the ensemble mean. It shows that the high-resolution model ensemble means (HMME) and low-resolution model ensemble mean (LMME) mitigate the biases between the MME and observation over most continents and oceans, respectively. The HMME simulates more precipitation than the LMME over most oceans, but less precipitation over some continents. The dominant precipitation category in the HRMs (LRMs) is the heavy precipitation (moderate precipitation) over the tropic regions. The combinations of convective and stratiform precipitation are also quite different: the HMME has much higher ratio of stratiform precipitation while the LMME has more convective precipitation. Finally, differences in precipitation between the HMME and LMME can be traced to their differences in the SST simulations via the local and remote air-sea interaction.

Can reanalysis datasets describe the persistent temperature and precipitation extremes over China

The persistent temperature and precipitation extremes may bring damage to the economy and human due to their intensity, duration and areal coverage. Understanding the quality of reanalysis datasets in descripting these extreme events is important for detection, attribution and model evaluation. In this study, the performances of two reanalysis datasets [the twentieth century reanalysis (20CR) and Interim ECMWF reanalysis (ERA-Interim)] in reproducing the persistent temperature and precipitation extremes in China are evaluated. For the persistent temperature extremes, the two datasets can better capture the intensity indices than the frequency indices. The increasing/decreasing trend of persistent warm/cold extremes has been reasonably detected by the two datasets, particularly in the northern part of China. The ERA-Interim better reproduces the climatology and tendency of persistent warm extremes, while the 20CR has better skill to depict the persistent cold extremes. For the persistent precipitation extremes, the two datasets have the ability to reproduce the maximum consecutive 5-day precipitation. The two datasets largely underestimate the maximum consecutive dry days over the northern part of China, while overestimate the maximum consecutive wet days over the southern part of China. For the response of the precipitation extremes against the temperature variations, the ERA-Interim has good ability to depict the relationship among persistent precipitation extremes, local persistent temperature extremes, and global temperature variations over specific regions.

Multi-scale analysis of warm extremes over China

Multi-scale features of warm extremes over China from 1961 to 2002 are evaluated using daily minimum and maximum temperature data. Different time scales of regional features of warm extremes are performed using rotated empirical orthogonal function (REOF) analysis and time scale departure methods. Clearly, significant differences are found in multi-scale of warm extremes. Significant increasing linear trends are detected in Northeast China, Inner Mongolia, northwestern part of Xinjiang, and southwestern China. However, in middle and lower reaches of Yangtze River, southern China and lower reaches of Yellow River basin, the linear trend is not remarkable, but the interannual pattern is the leading part, with several extreme peaks. The links with global temperature anomalies are studied, focusing in northeastern China and in middle and lower reaches of Yangtze River. It is found that the extreme indices show largest correlations with temperature anomalies in the Pacific Ocean. We detect that in northeastern and inland areas, high-related regions of frequency of warm extremes and the global temperature anomalies are broader, while the high-related area is smaller in the middle and lower reaches of the Yangtze River and the coastal regions.