The monsoons are often viewed as sea-breeze circulations driven by solar radiations and land-sea thermal contrast, and modified by compressibility and rotation effects. This highly idealized model is recently improved by considering a fully coupled land-ocean-atmosphere nature of the monsoon. In East Asia, the monsoons are further shaped by the unique geographical setting and weather dynamics. During the Meiyu season, a quasi-stationary monsoon front stretching thousands of kilometers wide perennially causes torrential rains and severe floods. This brings us to a few core questions: Where did all those water vapors come from when apparently local evaporation does not suffice to supply all of them? How can we understand the monsoons better from the perspective of moisture?

This thesis co...[ Read more ]

The monsoons are often viewed as sea-breeze circulations driven by solar radiations and land-sea thermal contrast, and modified by compressibility and rotation effects. This highly idealized model is recently improved by considering a fully coupled land-ocean-atmosphere nature of the monsoon. In East Asia, the monsoons are further shaped by the unique geographical setting and weather dynamics. During the Meiyu season, a quasi-stationary monsoon front stretching thousands of kilometers wide perennially causes torrential rains and severe floods. This brings us to a few core questions: Where did all those water vapors come from when apparently local evaporation does not suffice to supply all of them? How can we understand the monsoons better from the perspective of moisture?

This thesis contains four main chapters address the above questions. By backtracking the moisture two weeks before precipitation using a reanalysis-driven semi-Lagrangian model, we established a moisture source-receptor (SR) network for multiple regions in East Asia during the warm season. The network reveals an equal (or even greater) importance of non-local terrestrial sources compared to the oceanic sources. The network also demonstrates pronounced intraseasonal variabilities and is further shaped by the El Niño Southern Oscillation. Four main moisture corridors are found to sustain the heavy monsoon rainbands in East Asia. Interesting circumglobal wave trains attributable to the pathways are discovered at a two-week lead time. Applying a more sophisticated 3-D Lagrangian moisture tracking model on the global scale, we find that 62% of continental precipitation is sustained by terrestrial evaporation. The world’s leading moisture sources and a new concept of cascading moisture recycling are also proposed. The final study discovers a dual regime of MCSs closely tied to the monsoon annual cycle and reveals the prevailing environments for convective initiation under the two regimes.