Asia-Australia Dipole And Its Relationship With Climate Variability In The Asia-Australia Region

By EOF analyzing of upper troposphere geopotential height field of reanalysis data, there is a dipole in northern-southern over Asian-Australian monsoon region in the winter of northern hemisphere, which is defined as Asian-Australian Dipole (AAD) in this study, which diploe intensity define as index(AADI). The AAD not only reflects the activities of the north and south hemisphere weather system, but also reflects the force to atmospheric circulation from the thickness difference of air pressure in northern and southern hemisphere.The AADI has significant correlations with different Asian winter monsoon indexes, which are from different levels and reflects different subsystems of winter monsoon strength. It means the AADI has its reasonableness and representation as an intensity index of the winter monsoon. It also indicates that the winter monsoon system is a profound system, the monsoon system is not only forced by the temperature difference between land and sea, but also influenced by the thickness gradient in northern and southern hemispheres.Correlation and synthetic analysis illustrate that AADI is closely related to the Asian-Australian region weather and climate in northern hemisphere winter. In the years of strong AADI, the temperature in most areas in Asian-Australian region is lower than usual, and there will be less precipitation in west region in Eurasia and more precipitation in east Eurasia, and it will be on the contrary in weak AADI years, the East Asia major deep trough is stronger, the subtropical high is weaker and the Alaska ridge and the westerly jet are stronger than normal years. Enhanced meridional circulation between high and low latitude exists in the years of strong AADI. These relationships reflect the intrinsic link between the anomalies in the upper troposphere geopotential height and climate change in Asian-Australian region essentially.CMIP5 models can reproduce the signals of AAD and ENSO, but it has an overestimation of the correlations among the ENSO, AAD signal and the climate elements in Asian-Australian region. Both of the observational data and model results shows that the AAD signal was the main disturbing signal in the upper troposphere in Asian-Australian region and the main determiner of the temperature and precipitation in Asian-Australian region. Thus the AAD is not only the product of the force of sea surface temperature, but also forces by the difference in the upper troposphere in Asian-Australian region, and as the upper troposphere anomaly signal, the AAD contributes more to the climate variation in Asian-Australian region.Tibet Plateau snow that is the product of Asian-Australian monsoon region, but also the impact of the monsoon circulation important external forcing. By EOF method to analyze the spatial and temporal characteristics of different periods in winter and spring. It reveals that the the Tibetan Plateau snow sensitive area of the interannual variability changed significantly over time periods. Reflecting the Plateau snow mainly caused by the snowfall in the early winter. The sensitive area of the interannual variability is relatively stable in the whole winter, while it changes significantly in spring. As an intensity index of the winter monsoon, the AADI has significant correlation with the Tibet Plateau snow in winter-spring, models in CMIP5 has a certain deviation of the snow depth in Tibet Plateau, and because of the coarse resolution of the models and the ensemble average may smooth away some useful signal, so the relationship between AADI and winter-spring snow in Tibet Plateau has a greater difference comparing with the observation data.