Summary

The Air Mass Transformation Experiment (AMTEX) was organized and implemented by the Japanese as a Global Atmospheric Research Program (GARP) Subprogram on air-surface interaction at a time and location of large transfer of energy from the sea to the atmosphere. The field phase was conducted over the East China Sea within a 300 km hexagonal array of observation stations centered at Okinawa during the last two weeks of February in both 1974 and 1975. This area is an excellent location for the study of air mass modification due to large air-sea temperature differences that occur during winter.

Besides Japan, Australia, Canada, and the United States also participated in this international experiment that investigated the processes by which heat, moisture, and momentum are transferred from the ocean surface through the boundary layer and into the overlying free atmosphere in a region of large temperature contrast between the warm, northward flowing Kuroshio (Japan Current) and relatively cold, southward-flowing continental air. The resulting transfer of energy from the ocean fuels the development of atmospheric disturbances on several interacting scales: individual cumulus clouds (1-10 km), clusters of clouds organized into meso-scale patterns (10-100 km), medium-scale cyclonic disturbances (~ 1000 km), and large planetary-scale disturbances (> 3000 km). In the area around the Southwest Islands, meso- and medium-scale disturbances develop most frequently, but in practice, few operational observations are available. Many disturbances which develop in this area move eastwards and seriously influence the weather over Japan.