Abstract
Abstract. The atmospheric water tracer (AWT) method is implemented in the Community Atmosphere Model version 5.1 (CAM5.1) to quantitatively identify the contributions of various source regions to precipitation and water vapour over East Asia. Compared to other source apportionment methods, the AWT method was developed based on detailed physical parameterisations, and can therefore trace the behaviour of atmospheric water substances directly and exactly. According to the simulation, the northern Indian Ocean (NIO) is the dominant oceanic moisture source region for precipitation over the Yangtze River valley (YRV) and southern China (SCN) in summer, while the north-western Pacific (NWP) dominates during other seasons. Evaporation over the South China Sea (SCS) is responsible for only 2.7–3.7 % of summer precipitation over the YRV and SCN. In addition, the Indo-China Peninsula is an important terrestrial moisture source region (annual contribution of ∼ 10 %). The overall relative contribution of each source region to the water vapour amount is similar to the corresponding contribution to precipitation over the YRV and SCN. A case study for the SCS shows that only a small part ( ≤ 5.5 %) of water vapour originates from local evaporation, whereas much more water vapour is supplied by the NWP and NIO. In addition, because evaporation from the SCS represents only a small contribution to the water vapour over the YRV and SCN in summer, the SCS mainly acts as a water vapour transport pathway where moisture from the NIO and NWP meet.
Highlights
Water vapour is one of the most important components of the atmosphere, affecting global climate and weather patterns (Held and Soden, 2000)
CAM5.1 generally shows a bias towards relatively high precipitation in the tropics of the summer hemisphere, the precipitation pattern and amount over Eurasia and its adjacent areas is captured well by CAM5.1
An Eulerian tagged atmospheric water tracer (AWT) method was implemented in CAM5.1, which provides the capacity to separately trace the behaviour of atmospheric water substances originating from various moisture source regions and to quantify their contributions to atmospheric water over an arbitrary region
Summary
Water vapour is one of the most important components of the atmosphere, affecting global climate and weather patterns (Held and Soden, 2000). Source apportionment methods have been developed to identify atmospheric moisture source regions These methods generally can be divided into three types, namely analytical models, isotopes, and numerical (Lagrangian and Eulerian) atmospheric water tracers (AWTs) (Gimeno et al, 2012). Chen et al (2013) suggested that the ECS, the SCS, the Indian peninsula and BOB, and the AS were the four major moisture source regions for summer water vapour over the Yangtze River valley (YRV) during 2004–2009. Previous studies have pointed out that analytical models need simplifying assumptions, isotope data reflect more than just the water cycle, the Lagrangian methods lack cloud processes, and sensitivity experiments contain non-linearities, limiting diagnostic studies of moisture sources.
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