Sun Jian-Qi

A Quick Report on a Dynamical Downscaling Simulation over China Using the Nested Model

Abstract This paper describes a dynamical downscaling simulation over China using the nested model system, which consists of the modified Weather Research and Forecasting Model (WRF) nested with the NCAR Community Atmosphere Model (CAM). Results show that dynamical downscaling is of great value in improving the model simulation of regional climatic characteristics. WRF simulates regional detailed temperature features better than CAM. With the spatial correlation coefficient between the observation and the simulation increasing from 0.54 for CAM to 0.79 for WRF, the improvement in precipitation simulation is more perceptible with WRF. Furthermore, the WRF simulation corrects the spatial bias of the precipitation in the CAM simulation.

Relationships between the North Pacific Oscillation and the typhoon/hurricane frequencies

Relationships between the North Pacific Oscillation (NPO) and the typhoon as well as hurricane frequencies are documented. The correlation between NPO index in June–July–August–September and the annual typhoon number in the western North Pacific is 0.37 for the period of 1949–1998. The NPO is correlated with the annual hurricane number in the tropical Atlantic at −0.28 for the same period. The variability of NPO is found to be concurrent with the changes of the magnitude of vertical zonal wind shear, sea-level pressure patterns, as well as the sea surface temperature, which are physically associated with the typhoons and hurricanes genesis. The NPO associated atmospheric circulation variability is analyzed to explain how NPO is linked with variability of the tropical atmospheric circulation in the western Pacific and the tropical Atlantic, via the atmospheric teleconnection.

Relationship between Arctic Oscillation and Pacific Decadal Oscillation on decadal timescale

The relationship between the Pacific Decadal Oscillation (PDO) and the Arctic Oscillation (AO) on decadal timescale in the extended winter (November–March) is investigated in this study. The results indicate that AO plays an important role in the low frequency variability of PDO. When AO leads PDO by 7–8 years, the lagging correlation between them becomes the strongest with correlation coefficient 0.77. The leading decadal variability of AO pro-vides a valuably precursory signal for predicting the variability of PDO. The results of regression and lagging correlation reveal the possible mechanism for the AO-PDO coupling: A strong AO would lead to an enhanced Aleutian Low that is linked to PDO by ocean-atmosphere interaction in the North Pacific, and vice versa.

Future Changes of Drought and Flood Events in China under a Global Warming Scenario

Abstract This study investigates the impact of global warming on drought/flood patterns in China at the end of the 21st century based on the simulations of 22 global climate models and a regional climate model (RegCM3) under the SRES (Special Report on Emissions Scenarios) A1B scenario. The standardized precipitation index (SPI), which has well performance in monitoring the drought/ flood characteristics (in terms of their intensity, duration, and spatial extent) in China, is used in this study. The projected results of 22 coupled models and the RegCM3 simulation are consistent. These models project a decrease in the frequency of droughts in most parts of northern China and a slight increase in the frequency in some parts of southern China. Considering China as a whole, the spatial extents of droughts are projected to be significantly reduced. In contrast, future flood events over most parts of China are projected to occur more frequently with stronger intensity and longer duration than those prevalent currently. Additionally, the spatial extents of flood events are projected to significantly increase.

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.

Possible Impact of the Boreal Spring Antarctic Oscillation on the North American Summer Monsoon

Abstract This study examined the relationship between the boreal spring (April-May) Antarctic Oscillation (AAO) and the North American summer monsoon (NASM) (July-September) for the period of 1979-2008. The results show that these two systems are closely related. When the spring AAO was stronger than normal, the NASM tended to be weaker, and there was less rain-fall over the monsoon region. The opposite NASM situation corresponded to a weaker spring AAO. Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM. It was found that the tropical Atlantic sea surface temperature (SST) plays an important role in the connection between the two phenomena. The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic. These SST anomalies can persist from spring to summer and can influence the Bermuda High, affecting water vapor transportation to the monsoon region. Through these processes, the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation. Thus, information about the boreal spring AAO is valuable for the prediction of the NASM.

How Large Precipitation Changes over Global Monsoon Regions by CMIP5 Models

Abstract Future changes in precipitation over global monsoon domains and their adjacent dry regions are investigated using present-day climate simulations (1986- 2005) and future climate simulations under the Representative Concentration Pathways (RCP4.5) scenario by the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. In the present-day climate simulations, high reproducibility of the extents of global monsoon domains and dry regions is observed from the multi-model ensemble (MME) result; the associated local summer precipitation variation and its interannual variability are also successfully reproduced. In the future, the global monsoon domains are projected to be expanded, while the dry regions are expected to initially increase and then decrease. The summer precipitation and its variability show significant increases over most global monsoon domains and obvious decreases over their adjacent dry regions. These results indicate that currently wet regions will become wetter and dry areas will be dryer under global warming conditions. Further analysis indicates that changes in summer precipitation over global monsoon and dry regions can be interpreted as moisture convergence changes associated with changes in horizontal moisture transport.

Possible Impact of the Summer North Atlantic Oscillation on Extreme Hot Events in China

Abstract This paper reveals that the summer North Atlantic Oscillation (SNAO) is closely related to the extreme hot event (EHE) variability in China during the period of 1979-2009, with a positive-phase (negative-phase) SNAO corresponding to less (more) EHEs in northern China. The summer circulation anomalies associated with the SNAO give further confirmation of the above relationship. In a positive-phase (negative-phase) SNAO year, there is an anomalous cyclone (anticyclone) over central East Asia, which can increase (decrease) the total cloud cover over this region. Such changes of the total cloud cover can then decrease (increase) the solar radiation reaching the surface, which is consequently un-favorable (favorable) to the formation of EHEs over northern China.

Drought Response to Air Temperature Change over China on the Centennial Scale

Abstract Climate data from the Climatic Research Unit (CRU) for the period 1901–2013 are used to investigate the drought response to air temperature change over China on the centennial scale. Drought is observed to have increased evidently across China, except for some regions in eastern China. This increase is much stronger in northern China compared to southern China, especially in Northwest and North China. These change characteristics of drought are closely associated with air temperature change, with the severe droughts in the major drought episodes of the last century generally coinciding with higher temperatures. The significantly increasing trend of drought in China based on observations only appears when considering the effects of air temperature change, which can explain ∼49% of droughts in observations and 30%–65% of droughts in Coupled Model Intercomparison Project Phase 5 (CMIP5) model simulations. Furthermore, the response of drought to air temperature change generally increases as the drought time scale increases. Furthermore, drought shows relatively high sensitivity in spring and early summer in China on the centennial scale.

High-Resolution Hindcast of Record-Breaking Rainfall in Beijing and Impact of Topography

Abstract In this paper, a hindcast study of the record-breaking rainfall event occurring in Beijing on 21 July 2012, is conducted by using the Weather Research and Forecasting (WRF) model forced by National Centers for Environmental Prediction (NCEP) Global Forecasting System (GFS) outputs, paired with an investigation of the impact of topography in this region. The results indicate that WRF can reasonably predict the salient features of orographic precipitation; the 24-h rainfall amount and spatial distribution compare reasonably well with the observations. The hindcast simulation also indicates that rainfall events can be predicted approximately 36 h ahead. When the topography is removed, the spatial distribution of rainfall changes remarkably, suggesting the importance of the topography in determining rainfall structure. These results also indicate that prediction of such city-scale heavy rainfall events would benefit from a high-resolution prediction system.