We work on the formation of atmospheric large-scale (thousands of kilometers or more) circulation and climate variability. We pursue understanding of their mechanisms involving air-sea interactions and predictability. Our study contributes to answer how the phenomenon organizes into a characteristic structure, dominates in a particular season (or throughout a year), and varies in a specific time scale. Specifically, I have studied atmospheric teleconnection patterns that affect East Asian summer climate, to reveal their dynamical mechanisms, impacts on regional climate, seasonal predictability, natural inter-decadal modulations and possible future modulations due to the global warming. I also work on global and regional climate variability that occurs as part of anthropogenic climate changes and natural climate variability. Our scope of future researches is beyond these topics. We carry out statistical analyses and dynamical diagnosis of observational data and modeling studies based on various simplified dynamical models and more sophisticated general circulation models of atmosphere and ocean-atmosphere coupled system.