Mesoscale predictability of mei-yu heavy rainfall |
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| Authors: | Jianyong Liu Zhe-Min Tan |
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| Institution: | Key Lab of Mesoscale Severe Weather/MOE, and School of Atmospheric Sciences,
Nanjing University, Nanjing 210093;Key Lab of Mesoscale Severe Weather/MOE, and School of Atmospheric Sciences,
Nanjing University, Nanjing 210093 |
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| Abstract: | Recently reported results indicate that small amplitude and small scale initial errors grow
rapidly and subsequently contaminate short-term deterministic mesoscale forecasts. This rapid error growth
is dependent on not only moist convection but also the flow regime. In this study, the mesoscale
predictability and error growth of mei-yu heavy rainfall is investigated by simulating a particular
precipitation event along the mei-yu front on 4--6 July 2003 in eastern China.
Due to the multi-scale character of the mei-yu front and scale interactions, the error growth of
mei-yu heavy rainfall forecasts is markedly different from that in middle-latitude moist baroclinic
systems. The optimal growth of the errors has a relatively wide spectrum, though it gradually
migrates with time from small scale to mesoscale. During the whole period of this heavy rainfall
event, the error growth has three different stages, which similar to the evolution of 6-hour
accumulated precipitation. Multi-step error growth manifests as an increase of the amplitude of
errors, the horizontal scale of the errors, or both. The vertical profile of forecast errors in
the developing convective system indicates two peaks, which correspond with convective instability
and the moist physics. The error growth for the mei-yu heavy rainfall is concentrated inside the
mei-yu front, and related to moist convective instability and scale interaction. |
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| Keywords: | mesoscale predictability error growth scale interaction mei-yu front precipitation |
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