Figure 4

(a) 500 hPa atmospheric circulation characteristics and distribution diagram of the volcanic dust curtain and aerosol layer in the mid-high latitudes of the Northern Hemisphere in December 1989; (b) schematic diagram of the atmospheric circulation characteristics of the 500 hPa layer from 30 to 90° N and distribution of the volcanic dust curtain and aerosol layer in January 1990; (c) atmospheric circulation characteristics of the 500 hPa layer from 30 to 90° N in March 1990; (d) potential height field anomaly distribution of the 500 hPa layer from 30 to 90° N in March 1990.