Long-term variation of Asian dust and related climate factors

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dust-transport model. Simulation results were examined using visibility-based observations by Chinese and Japanese Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Nino/Southern Oscillation (ENSO) affects the dust transport path. Analyses of average dust transport flux at 130°E clarified variation of the transport path between La Nina years and El Nino years.