Li Shuanglin

A review of seasonal climate prediction research in China

The ultimate goal of climate research is to produce climate predictions on various time scales. In China, efforts to predict the climate started in the 1930s. Experimental operational climate forecasts have been performed since the late 1950s, based on historical analog circulation patterns. However, due to the inherent complexity of climate variability, the forecasts produced at that time were fairly inaccurate. Only from the late 1980s has seasonal climate prediction experienced substantial progress, when the Tropical Ocean and Global Atmosphere project of the World Climate Research program (WCRP) was launched. This paper, following a brief description of the history of seasonal climate prediction research, provides an overview of these studies in China. Processes and factors associated with the climate variability and predictability are discussed based on the literature published by Chinese scientists. These studies in China mirror aspects of the climate research effort made in other parts of the world over the past several decades, and are particularly associated with monsoon research in East Asia. As the climate warms, climate extremes, their frequency, and intensity are projected to change, with a large possibility that they will increase. Thus, seasonal climate prediction is even more important for China in order to effectively mitigate disasters produced by climate extremes, such as frequent floods, droughts, and the heavy frozen rain events of South China.

Lead-Lag Connection of the Atlantic Multidecadal Oscillation (AMO) with East Asian Surface Air Temperatures in Instrumental Records

Abstract The authors analyzed the lead-lag connection of the Atlantic Multidecadal Oscillation (AMO) with East Asian surface air temperatures (EATs) using instrumental records, and compared the results with the Pacific Decadal Oscillation (PDO). The maximum correlation was found when EATs led the AMO by five to seven years (with a correlation coefficient of 0.72, whereas the correlation coefficient was –0.91 when the AMO led EATs by 24–28 years). This is different from the PDO, which mostly correlated with EATs when the PDO led EATs by 13–15 years (with a correlation coefficient of 0.67, whereas the correlation coefficient was –0.76 when EATs led the PDO by 24–26 years). The PDO led the AMO by 19–21 years (with a correlation coefficient of 0.71, whereas the correlation coefficient was –0.84 when the AMO led the PDO by 16–18 years). These results support a previous understanding that EATs positively correlate with the AMO, and imply that the observed East Asian warming trend may have been slowing down since the early 2010s.

Causes of recurring drought patterns in Xinjiang, China

2 Xinjiang Institute of Ecology and Geography, CAS, Urumqi 830011, China Abstract: Xinjiang Uygur Autonomous Region of China, with its unique topography and geographical location receives very less precipitation in summer as compared with other parts of China. The region is a land locked where moisture is supplied only by westerly winds from Atlantic Ocean as the moisture coming from Indian Ocean is mostly blocked by the Himalayas Range and the Tibetan plateau. In such a scenario, Xinjiang faces severe drought conditions offering significant challenges to water management. In this paper, we analyzed the drought periods in Xinjiang and discussed the various factors that might have influenced precipitation over the past forty-four years. For this purpose, we defined three periods of consecutive four years for high and low precipitation intensities. The average observed precipitation was 1.05 mm/day and 0.7 mm/day in summer (June-July-August) for the Tianshan Mountain region and Junggar Basin of Xinjiang, respectively. The drought conditions indicated that high sea level pressure, wind divergence and low con- vection were the prominent features that caused the droughts, which often do not allow the condensation process to coagulate the tiny water droplets into relatively large raindrops reducing the amount of precipi- tation in the region. The period of 1983−1986 is the lowest precipitation interval indicating the severe drought in the western Xinjiang (i.e western Tianshan Mountain region), for which, less moisture availability, strong divergence and less convection could be the most influencing factors.

Modeled Influence of East Asian Black Carbon on Inter-Decadal Shifts in East China Summer Rainfall

Abstract Two inter-decadal shifts in East China summer rainfall during the last three decades of the 20th century have been identified. One shift occurred in the late 1970s and featured more rainfall in the Yangtze River valley and prolonged drought in North China. The other shift occurred in the early 1990s and featured increased rainfall in South China. The role of black carbon (BC) aerosol in the first shift event is controversial, and it has not been documented for the second event. In this study, the authors used Geophysical Fluid Dynamics Laboratory’s (GFDL’s) atmospheric general circulation model known as Atmosphere and Land Model (AM2.1), which has been shown to capture East Asian climate variability well, to investigate these issues by conducting sensitive experiments with or without historical BC in East Asia. The results suggest that the model reproduces the first shift well, including intensified rainfall in the Yangtze River and weakened monsoonal circulation. However, the model captures only a fraction of the observed variations for the second shift event. Thus, the role of BC in modulating the two shift events is different, and its impact is relatively less important for the early 1990s event.

Intercomparison of the South Asian High in NCEP1, NCEP2, and ERA-40 Reanalyses and in Station Observations

Abstract The South Asian Highs (SAHs) at 100 hPa over China in the three reanalysis datasets NCEP1, NCEP2, and ERA-40 are evaluated by using station observation data. The results demonstrate a substantial discrepancy even between the reanalyses. First, the data of the three reanalyses generally underestimate the intensity of the SAH in the China domain. Second, there are interdecadal changes in the SAH, with highs in the 1960s and 1980s and lows in the 1970s, 1990s, and 2000s. This interdecadal variation of the SAH can be well depicted with NCEP1 data, but the high in the 1980s is missed by ERA-40. The NCEP2 corresponds well with NCEP1 and captures the decreasing trend after 1979. Furthermore, the NCEP1 reanalysis overestimates the interdecadal changes of SAH, while ERA-40 underestimates the interdecadal changes. This work suggests that much caution should be exerted when the reanalysis datasets are adopted to study the interdecadal variability of SAH.

Projecting the Summer Climate of Mainland China in the Middle 21st Century： Will the Droughts in North China Persist？

Abstract Since no consensus has been reached in previous studies about how the summer climate in China will evolve in the first half of the 21st century, this issue is addressed here through sensitivity experiments by forcing an atmospheric general circulation model (AGCM), the Geophysical Fluid Dynamics Laboratory (GFDL)s Atmospheric Model Version 2.0 (AM2) with projected sea surface temperature (SST) trend. A total of two SST trends from the Intergovernmental Panels on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A1B are used. The two trends are from two coupled climate system models, the National Center for Atmospheric Research (NCAR) Community Climate System Model Version 3.0 (CCSM3) and the GFDL Climate Model Version 2.0 (CM2), respectively. Results consistently suggest a substantial warming and drying trend over much of China, with a surface air temperature in-crease of 1.0-2.0°C and a 10%-20% decrease in rainfall. Exceptions are the areas from northwestern China to western North China as well as the southern Tibetan Plateau, which are projected to be wetter with a rainfall anomaly percentage increase of 10%-50%. The drying in eastern North China has not been documented to date but appears to be reasonable. Physically, it is attributed to anomalous northeasterly winds at the rear of a low-level cyclone over the South China Sea, the Philippines and the subtropical western North Pacific. These conditions, which govern the climate of eastern China, are forced by the northward shift of convection over warm waters due to additional warming.

Relationships between the Oxygen Isotopes in East Asian Stalagmites and Large-Scale Atmospheric and Oceanic Modes

Abstract The stalagmite δ18O record is known to be associated with the climate, but the specifics of the relationship remain unclear. It may not represent variation in air temperature or precipitation, but instead reflect integral changes of monsoon circulation, especially water vapor sources (the so-called “circulation effect”). Since large-scale atmospheric-oceanic modes such as the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and North Atlantic Oscillation (NAO) exert significant effects on Asian monsoon, in this paper the authors investigate the relationships of the East Asian stalagmite δ18O record with these modes. The last three centuries form the focus of our study, for which the authors use reconstructed as well as instrumental data. Considering the impacts of human activity, our analysis is conducted with respect to two periods—the pre- and post-industrial periods. The results show significant lead-lag connections: a positive correlation peaks when the PDO leads East Asian stalagmite δ18O by 3 years, which is persistent over the past 300 years; while the relationships of the AMO and NAO with the East Asian stalagmite δ18O record show significant differences in the post-industrial relative to the pre-industrial period. This implies that the East Asian stalagmite δ18O record may primarily reflect the PDO signal.

A New Approach for Classifying Two Types of El Nino Events

Abstract In recent decades, the typical El Niño events with the warmest SSTs in the tropical eastern Pacific have become less common, and a different of El Niño with the warmest SSTs in the central Pacific, which is flanked on the east and west by cooler SSTs, has become more frequent. The more recent type of El Niño was referred to as central Pacific El Niño, warm pool El Niño, or dateline El Niño, or the El Niño Modoki. Central Pacific El Niño links to a different tropical-to-extratropical teleconnection and exerts different impacts on climate, and several classification approaches have been proposed. In this study, a new classification approach is proposed, which is based on the linear combination (sum or difference) of the two leading Empirical Orthogonal Functions (EOFs) of tropical Pacific Ocean sea surface temperature anomaly (SSTA), and the typical El Niño index (TENI) and the central El Niño index (CENI) are able to be derived by projecting the observed SSTA onto these combinations. This classification not only reflects the characteristics of non-orthogonality between the two types of events but also yields one period peaking at approximate two to seven years. In particular, this classification can distinguish the different impacts of the two types of events on rainfall in the following summer in East China. The typical El Niño events tend to induce intensified rainfall in the Yangtze River valley, whereas the central Pacific El Niño tends to induce intensified rainfall in the Huaihe River valley. Thus, the present approach may be appropriate for studying the impact of different types of El Niño on the East Asian climate.

A New Method for Predicting the Decadal Component of Global SST

Abstract A simple approach that considers both internal decadal variability and the effect of anthropogenic forcing is developed to predict the decadal components of global sea surface temperatures (SSTs) for the three decades 2011–2040. The internal decadal component is derived by harmonic wave expansion analyses based on the quasi-periodic evolution of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), as obtained from observational SST datasets. Furthermore, the external decadal component induced by anthropogenic forcing is assessed with a second-order fit based on the ensemble of projected SSTs in the experiments with multiple coupled climate models associated with the third Coupled Model Intercomparison Project (CMIP3) under the Intergovernmental Panels on Climate Change (IPCC) Special Reports on Emissions Scenario (SRES) A1B. A validation for the years from 2002 to 2010 based on a comparison of the predicted and the observed SST and their spatial correlation, as well as the root mean square error (RMSE), suggests that the approach is reasonable overall. In addition, the predicted results over the 50°S– 50°N global band, the Indian Ocean, the western Pacific Ocean, the tropical eastern Pacific Ocean, and the North and the South Atlantic Ocean are presented.

Analysis of South Asian Monsoons within the Context of Increasing Regional Black Carbon Aerosols

Abstract South Asian monsoons were analyzed within the context of increasing emissions of black carbon (BC) aerosols using a global atmospheric general circulation model. The BC aerosols were allowed to increase only over the south Asian domain to analyze the impacts of regional black carbon over the climatological patterns of monsoons. The black carbon significantly absorbed the incoming short wave radiation in the atmosphere, a result that is consistent with previous studies. Pre-monsoon (March-April-May) rainfall showed positive anomalies, particularly for some coastal regions of India. The summer (June-July-August) rainfall anomalies were negative over the northern Himalayas, Myanmar, southern China, and most of the regions below 20°N due to the decrease in temperature gradients induced by the absorption of radiation by BC aerosols. The vertical wind speed anomalies indicated that these regions experienced less convection, which reduces the precipitation efficiency of the monsoon system in South Asia.