Spatial and temporal characteristics of aerosol optical depth over East Asia and their association with wind fields

Abstract

Abstract Rotated principal component analysis (PC) was performed on monthly Aerosol Optical Depth (AOD) from Moderate Resolution Imaging Spectroradiometer (MODIS) data over East Asia for the period of March 2000–January 2006. The first PC mode is a south–north dipole with a strong positive loading between 30–35°N and 130–150°E over middle latitude East Asia and a weaker negative loading in southern parts over East Asia. The first PC mode explains 32.44% of the total variance. By analysing time series of the PC1‐3, results show the PC‐1 and PC‐3 modes are important and both have distinct changes from the period 2000–2003 to 2004–2006; the former pattern (in middle latitudes over East Asia) is characterized in a decreasing linear trend and the latter (in eastern China) is in an increasing linear trend in the full 71 month evolution. Furthermore, based on the wavelet power spectrum analysis, it is found that the distinct changes of the monthly AOD in middle latitudes over East Asia (the PC‐1 pattern) are connected to the multi‐scale variations at intra‐seasonal (3–6 month) and annual (12 month) scales. While calculating the correlation of the PC‐1 with wind fields at 850 hPa from the NCEP/NCAR reanalysis dataset, it is shown that the PC‐1 is closely related to the U and V (horizontal) components over subtropical East Asia and western north Pacific, which well represents East Asian monsoon features. Finally, by comparing the PC‐1 pattern in May between 2003 and 2004, results show that the higher (lower) AOD in 2003 (2004) is associated with weaker (stronger) U component at 850 hPa in middle latitudes over East Asia. Copyright © 2008 Royal Meteorological Society