Masayuki Tanaka
1935-2025

Masayuki Tanaka, Prof. Emeritus of Tohoku University, passed away on Dec. 21, 2025, at the age of 90. Prof. Tanaka made significant contributions to the studies on atmospheric radiation and trace constituents. As early as 1971, he formulated a matrix operator method for solving the transfer of polarized radiation in the Earth’s atmosphere. Based on this method, he performed pioneering calculations of multiple scattering to evaluate the polarized radiation field caused by atmospheric molecules and particles. In 1972, using this rigorous calculation method, he quantified the change in the Earth’s albedo due to an increase of air pollution by aerosol particles, showing that the albedo change shifted from increase to decrease due to the larger absorption, quantified by the imaginary part of the complex refractive index of the aerosol particles. This was a world-leading contribution to our modern understanding of the climate effect of aerosols.

In 1973, at the young age of 37, he was appointed full professor of the Department of Geophysics in Tohoku University. While his predecessor, Prof. Giichi Yamamoto, who has significantly contributed to the establishment of the International Radiation Commission (IRC), developed a method for calculating the thermal-infrared radiative cooling rate of trace gases, Prof. Tanaka and his collaborators extended Yamamoto’s work to the solar spectral region considering multiple scattering effects. As a testbed for their computations, Tanaka and his group designed and built instrumentation for appropriate measurements, such as polar nephelometers and sun-sky photometers. They applied these instruments to quantify the optical and microphysical properties of aerosol and cloud particles, which has contributed to developments of modern global networks of sun-sky photometers, a variety of satellite remote sensing algorithms, and climate studies of radiative effects of aerosols and clouds. Other important achievements of Prof. Tanaka included high-precision measurements of the absorption coefficients of weak absorption bands of carbon dioxide, water vapor, and methane using a long-path gas absorption cell, and the establishment of a measurement system of the atmospheric carbon dioxide concentration with a high accuracy of 0.1 ppm. These activities led Tanaka and his collaborators and students to successful ground-based measurements around the globe including the polar regions and aircraft observations of the global distribution of carbon dioxide, which has contributed to improved assessments of global warming phenomena.

Prof. Tanaka also served as a director of the Meteorological Society of Japan and a visiting professor at the National Institute of Polar Research. He devoted himself to promoting national research programs and raising the next generation of researchers. In later years, he served as Dean of the Faculty of Science at Tohoku University and Vice President of Tohoku Institute of Technology, making significant contributions to university education. His publication includes introductory books of “A Warming Earth” and ” Introduction to Global Warming ” for general readers. For these achievements, he was awarded the Purple Ribbon Medal by the Japanese government in 1998.

We remember Professor Tanaka’s achievements and offer our condolences.