KOIKE, Makoto

Associate Professor
Atmospheric and Oceanic Science Group

Office: Sci.Bldg.No.1-845
TEL: +81-3-5841-4595
FAX: +81-3-5841-8316

Research Field

Atmospheric Environmental Science/Atmospheric Chemistry

Current Research

Atmospheric aerosols (suspended particles) affect global radiation budget and climate by scattering and absorbing solar radiation (direct effect) and affecting clouds (indirect effect). The goal of my research group is to understand aerosol impacts on radiation and clouds in the East Asia and Arctic by making ground-based and aircraft measurements as well as numerical modeling.
1. Aerosol – cloud interaction in AsiaIn the East Asia we have carried out a series of aircraft experiments and have successfully captured clear evidences that anthropogenic aerosols indeed affect cloud microphysical parameters. We further found that the strength of aerosol impacts is influenced by the warm Kuroshio ocean current because the warm sea surface temperature (SST) destabilized atmosphere. This study designates SST impacts on aerosol – cloud interaction that is potentially important for climate study.
2. Aerosols and clouds in the ArcticIn the Arctic, we have carried out the first continuous in situ measurements of cloud microphysical properties in Spitsbergen Island. We have revealed their seasonal variation and evaluated aerosol impacts. A simple air parcel model can reproduce the observed droplet concentrations from observed aerosols and this result provide a constraint for aerosol impacts on clouds. We also found that small size aerosols, which could be formed by new particle formation, can affect clouds. From these studies, we have provided basic features of microphysical properties of Arctic clouds for the first time.We have been also studying black carbon (BC) aerosols by making ground-based and aircraft measurements as well as numerical modeling. By making a network BC measurement in the Arctic, we have showed that previous observations overestimated BC mass concentrations. This study is considered to be an important contribution to the assessment of the Arctic Council.

Representative Publications

1. Koike, M., Ukita, J., Ström, J., Tunved, P., Shiobara, M., Vitale, Lupi, V., Baumgardner, A., D., Ritter, C., Hermansen, O., Yamada, K., and Pedersen, C. (2019). Year‐round in situ measurements of Arctic low‐level clouds: Microphysical properties and their relationships with aerosols. J. Geophys. Res. Atmos., 124, 1798-1822. https://doi. org/10.1029/2018JD029802
2. Koike, M., N. Asano, H. Nakamura, S. Sakai, T. M. Nagao, and T. Y. Nakajima, Modulations of aerosol impacts on cloud microphysics induced by the warm Kuroshio Current under the East Asian winter monsoon, J. Geophys. Res. Atmos., 121, doi:10.1002/2016JD025375, 2016.
3. Koike, M., N. Moteki, P. Khatri, T. Takamura, N. Takegawa, Y. Kondo, H. Hashioka, H. Matsui, A. Shimizu, and N. Sugimoto, Case study of absorption aerosol optical depth closure of black carbon over the East China Sea, J. Geophys. Res. Atmos., 118, doi:10.1002/2013JD020163, 2014.