The relationship between solar radiation and sunshine duration is studied for 132 stations in East Asia. Regression coefficientsa andb in the modified Angstrom formulaQ/Qa = a + b n/N are found to be systematically distributed in the area with low values ofa and high values ofb in the winter maximum/summer minimum regime ofQ/Qa andn/N, and high values ofa and low values ofb in the winter minimum/summer maximum regime ofQ/Qa andn/N. This shows that the distribution of regression coefficients is more closely related to the local seasonal radiation climate controlled by the prevailing winter monsoon, Bain, and the terrain features rather than to latitude or meann/N.