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In Japan, a majority of heavy rainfall events are caused by quasi-stationary linear precipitation systems (QSLPSs), which persist for more than 5 hours near the same location. This study examines the performance of entraining convective available potential energy (E-CAPE), which considers effects of entraining environmental air during parcel ascent, in evaluating the environmental potential conducive to QSLPS occurrence. A composite analysis in which meteorological variables are superposed after rotating the coordinate system to match the direction of QSLPS, shows that a confined region of a maximum of E-CAPE exists at about 100 km upstream of the location of 3-hourly accumulated maximum precipitation (P3max), while a wider region of large CAPE is located further upstream. A comparison of E-CAPE between QSLPS and linear precipitation systems with shorter persistence (NQSLPS) demonstrates that significant differences in E-CAPE exist on both the left and right sides of the upstream region, while those in CAPE exist only on the left side of the upstream region. The differences in E-CAPE between QSLPS and NQSLPS are attributed to the combination of lapse rate and low- to mid-level moisture. A density plot showing the relationship between P3max and the upstream maxima of CAPE and E-CAPE also indicates that both values tend to be higher for QSLPSs than for NQSLPSs. Those results suggest that E-CAPE provides better information on the intensity of conditional instability for QSLPS occurrence compared to CAPE. A new parameter, named KT-index, is proposed. This index offers a simpler analytical formulation than E-CAPE while still providing a useful assessment of the environmental potential for QSLPS occurrence.
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