Shaowu Wang

East Asian Winter Monsoon and Arctic Oscillation

In this study, the connection between Arctic Oscillation (AO) and variability of East Asian winter monsoon is investigated. Two indices are chosen to describe the winter monsoon. One is the intensity of the Siberian High, defined as the average SLP over the center region, and the other is the temperature of eastern China, averaged over 76 surface stations. These are two tightly related components, correlate at −0.62 for period 1951–99. Temperature drops by 0.64 degrees Celsius in association with a one standard deviation increase in Siberian High intensity. It is found that there are significant out-of-phase relationships between the AO and the East Asian winter monsoon. The correlation coefficient between the AO and the Siberian High intensity index is −0.48 for period 1958–98. AO is also significantly correlated with the temperature of eastern China at 0.34. However, when the linear trend is removed, the correlation between AO and temperature is no longer significant. But the strong connection between the AO and Siberian High, and between the Siberian High and temperature are still significant. These results reveal that the AO influences the East Asian winter monsoon through the impact on the Siberian High. Negative phase of the AO is concurrent with a stronger East Asian Trough and an anomalous anticyclonic flow over Urals at the middle troposphere (500hPa). Both the AO and the Eurasian pattern play important roles in changes of the Siberian High and/or East Asian winter monsoon. They account for 13.0% and 36.0% of the variance in the Siberian High respectively.

Impacts of ENSO on rainfall of global land and China

Based on the analysis of x2 test of global land rainfall time series, it is found that the mean global land annual rainfall reduce significantly when El Niño events occur, and increase evidently in La Niña years. The impacts of ENSO on the winter and autumn precipitation over eastern China are also notable. Usually, the rainfall of winter and autumn over southern China increases, and that over northern China decreases in El Niño years. The effects of ENSO on summer rainfall are not so significant as on autumn and winter rainfall in China. The summer precipitation of area to the north of the Yellow River often decreases in El Niño years. No evident relationship is found between ENSO and spring rainfall in China.

Antarctic oscillation : concept and applications

Based on the NCEP/NCAR reanalysis data set, empirical orthogonal function analysis and wrrelation analysis have been carried out. Antarctic osillation index (AOI) is defined as the difference between the zonal-mean monthly sea level pressure departures of 40°s and 65°s. Regional surface temperature and precipitation over the extratropical Southern Hemisphere have a close relationship with AO1.

Comparative Analysis of China Surface Air Temperature Series for the Past 100 Years

Abstract Temperature change plays a crucial role in global change sciences. In the past several decades, comprehensive findings have been achieved on temperature change in China for the past 100 years. Several time series have been created to illustrate the averaged surface air temperature for the country. The correlations of these series range from 0.73 to 0.97. It is also achieved in better data quality, wider spatial data coverage, improved homogeneity of time series, and enhanced reliability of findings. The results show an annual mean temperature increase by 0.78±0.27°C per 100 years in China for the period 1906–2005. After prolonging the period till 2007, it is found that 2007 is rated as the warmest year in the past 100 years. Although all the series, except one, reflect temperature changes in the eastern part of China before the 1930s, they represent the general temperature change in most parts of the country after the 1930s. Citation Tang, G., Y. Ding, S. Wang, et al., 2010: Comparative analysis of China surface air temperature series for the past 100 years. Adv. Clim. Change Res., 1, doi: 10.3724/SP.J.1248.2010.00011.

Paleoclimate Modeling in China: A Review

This paper provides a review of paleoclimate modeling activities in China. Rather than attempt to cover all topics, we have chosen a few climatic intervals and events judged to be particularly informative to the international community. In historical climate simulations, changes in solar radiation and volcanic activity explain most parts of reconstructions over the last millennium prior to the industrial era, while atmospheric greenhouse gas concentrations play the most important role in the 20th century warming over China. There is a considerable model-data mismatch in the annual and boreal winter temperature change over China during the mid-Holocene [6000 years before present (ka BP)], while coupled models with an interactive ocean generally perform better than atmospheric models. For the Last Glacial Maximum (21 ka BP), climate models successfully reproduce the surface cooling trend over China but fail to reproduce its magnitude, with a better performance for coupled models. At that time, reconstructed vegetation and western Pacific sea surface temperatures could have significantly affected the East Asian climate, and environmental conditions on the Qinghai-Tibetan Plateau were most likely very different to the present day. During the late Marine Isotope Stage 3 (30–40 ka BP), orbital forcing and Northern Hemisphere glaciation, as well as vegetation change in China, were likely responsible for East Asian climate change. On the tectonic scale, the Qinghai-Tibetan Plateau uplift, the Tethys Sea retreat, and the South China Sea expansion played important roles in the formation of the East Asian monsoon-dominant environment pattern during the late Cenozoic.

The relationship between the thermohaline circulation and climate variability

The long-term integration with the Global Ocean-Atmosphere-Land System model of the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics(IAP), Chinese Academy of Sciences has been used in the investigations on the relationship between the thermohaline circulation and climate variability. The results show that the strength of the North Atlantic Thermohaline circulation (THC) is negatively correlated with the North Atlantic Oscillation (NAO). Based on this kind of relationship, and also the instrument-measured climate record such as air pressure and sea surface temperature, the activity of the thermohaline circulation during the 20th century has been evaluated. The inferred variations of the strength of the THC is that, during two multi-decadal periods of 1867–1903 and 1934–1972, the THC is estimated to have been running stronger, whereas during the two periods of 1904–1933 and 1973–1994, it appears to have been weaker.

The Extratropical Northern Hemisphere Temperature Reconstruction during the Last Millennium Based on a Novel Method

Large-scale climate history of the past millennium reconstructed solely from tree-ring data is prone to underestimate the amplitude of low-frequency variability. In this paper, we aimed at solving this problem by utilizing a novel method termed “MDVM”, which was a combination of the ensemble empirical mode decomposition (EEMD) and variance matching techniques. We compiled a set of 211 tree-ring records from the extratropical Northern Hemisphere (30–90°N) in an effort to develop a new reconstruction of the annual mean temperature by the MDVM method. Among these dataset, a number of 126 records were screened out to reconstruct temperature variability longer than decadal scale for the period 850–2000 AD. The MDVM reconstruction depicted significant low-frequency variability in the past millennium with evident Medieval Warm Period (MWP) over the interval 950–1150 AD and pronounced Little Ice Age (LIA) cumulating in 1450–1850 AD. In the context of 1150-year reconstruction, the accelerating warming in 20th century was likely unprecedented, and the coldest decades appeared in the 1640s, 1600s and 1580s, whereas the warmest decades occurred in the 1990s, 1940s and 1930s. Additionally, the MDVM reconstruction covaried broadly with changes in natural radiative forcing, and especially showed distinct footprints of multiple volcanic eruptions in the last millennium. Comparisons of our results with previous reconstructions and model simulations showed the efficiency of the MDVM method on capturing low-frequency variability, particularly much colder signals of the LIA relative to the reference period. Our results demonstrated that the MDVM method has advantages in studying large-scale and low-frequency climate signals using pure tree-ring data.

Reconstruction and analysis of time series of ENSO for the last 500 years

Abstract This paper reports the classification of ENSO into seven categories according to annual (March to February of next year) mean SST of Nino 3.4 and composite index (ΔI) for the period of 1861–2000. Categories +3, +2, and +1 denote very strong, strong and weak warm episodes (E), −3, −2, and −1 mean very strong, strong and weak cold episodes (A). Absolute SST anomalies are about 1.5°C, 1.0°C and 0.5°C respectively for the categories 3, 2, and 1 (or −3, −2, and −1). The normal years are expressed as category 0. Annual categories of ENSO are estimated on the basis of proxy data from AD 1501 to 1860. And a series of ENSO category is established for the period of 1501–2000 in conjunction with the observational data. Comparison of proxy data with observations for 1874–1973 indicates that about 80% of the El Nino years and La Nina years can be reconstructed from proxy data, and the reliability of the reconstruction is verified. Analysis of the power spectrum of the reconstructed ENSO series shows significa...