Energy budgets on the interactions between the mean and eddy flows during a persistent heavy rainfall event over the Yangtze River valley in summer 2010

In this study, a persistent heavy rainfall event (PHRE) that lasted for around 9 days (from 0000 UTC 17 to 0000 UTC 26 June 2010) and caused accumulated precipitation above 600 mm over the Yangtze River valley, was reasonably reproduced by the advanced research WRF model. Based on the simulation, a set of energy budget equations that divided the real meteorological field into the mean and eddy flows were calculated so as to understand the interactions between the precipitation-related eddy flows and their background circulations (BCs). The results indicated that the precipitation-related eddy flows interacted with their BCs intensely during the PHRE. At different layers, the energy cycles showed distinct characteristics. In the upper troposphere, downscaled energy cascade processes appeared, which favored the maintenance of upper-level eddy flows; whereas, a baroclinic energy conversion, which reduced the upper-level jet, also occurred. In the middle troposphere, significant upscaled energy cascade processes, which reflect the eddy flows' reactionary effects on their BCs, appeared. These effects cannot be ignored with respect to the BCs' evolution, and the reactionary effects were stronger in the dynamical field than in the thermodynamical field. In the lower troposphere, a long-lived quasi-stationary lower-level shear line was the direct trigger for the PHRE. The corresponding eddy flows were sustained mainly through the baroclinic energy conversion associated with convection activities. Alongside this, the downscaled energy cascade processes of kinetic energy, which reflect the direct influences of BCs on the precipitation-related eddy flows, were also favorable. A downscaled energy cascade of exergy also appeared in the lower troposphere, which favored the precipitation-related eddy flow indirectly via the baroclinic energy conversion.