Classification and Long-term Trends of Seasons in Tokyo Determined from Air Temperature

Abstract

　Temperature rise associated with climate change has been reported, however how have the seasons changed associated with the change? This report presents classification and long-term trends of seasons determined by temperature in Tokyo by a new method which does not depend on the absolute value of temperature. “Seasons determined by temperature” have six seasons and set step-wise changes in temperature as seasonal dates, therefore the seasons reflect only temperature aspects of climatological seasons. Seasonal dates determined by temperature are combination of dates which minimize the square errors of fitting to a transition of temperature statistical model that temperature is constant in each season. Comparison reveals that there is a clear deference between seasons determined by temperature and conventional seasons based on a condition of whether patterns all over Japan. The annual seasons determined by temperature from 1964 to 2013 reveals that the starting date of late summer moves back and that the length of summer is prolonged in Tokyo. The trend of seasons determined by temperature shows changes in annual transition of temperature independent from the temperature rise.