11:15 AM - 11:30 AM
[AAS09-03] PV Inversion Analysis of the Impact of Upper Tropospheric Trough on the Development of the Heavy Rainfall Event occurred over Western Japan in July 2018
Keywords:Baiu season, heavy rainfall, piecewise PV inversion, upper tropospheric trough
In recent years, heavy rainfall events frequently have occurred during the Baiu season over the East Asia region. Especially, the heavy rainfall event occurred over western Japan in July 2018 spawned damaging floods and landslides. Some previous studies claimed that an upper tropospheric trough played an important role in forming the environment favorable for the well-organized rainfall systems. In this study, we used a piecewise quasi-geostrophic potential vorticity (QGPV) inversion technique to investigate the effects of the upper tropospheric trough on the development of heavy rainfall. The JRA-3Q reanalysis data were used for the present analysis.
First, we successfully extracted the QGPV anomaly corresponding to the upper tropospheric trough from the total QGPV fields during the heavy rainfall event by applying appropriate thresholds of QGPV and mixing ratio associated with the trough. After confirming the accuracy of the present QGPV inversion approach, we performed the piecewise inversion to the QGPV anomaly and obtained the geopotential and temperature anomalies corresponding to the trough. Subtracting these anomalies from the original atmospheric field, we created the field in which the trough was removed. We compared the original field, anomaly field, and trough-removed field, and examined the role of the trough in generating the heavy rainfall. Furthermore, we also obtained the dynamically induced vertical motion field associated with the trough by solving the quasi-geostrophic omega equation for those fields.
The analysis indicated that the geopotential anomaly associated with QGPV of the trough extended downward to the surface level and strengthened the moisture inflow to the Baiu frontal region. The trough enhanced the dynamical upward motion in the middle and upper troposphere to the east of the trough. Lower tropospheric upward motion, which was important for the vertical transport of moisture, was not associated with the upper-level trough but with the low-level mesoscale Baiu frontal depression. The trough could have influenced its development. In addition, the negative temperature anomaly associated with the trough led to a statically unstable condition as the trough approached. Such an unstable condition was favorable for the development of convective precipitation.
These results indicate that the upper tropospheric trough had an influence on the formation of heavy rainfall event in western Japan 2018. The proposed piecewise QGPV inversion method that separates geopotential and temperature anomalies corresponding to individual disturbances is a powerful tool for quantifying the contribution of each disturbance on the generation of heavy rainfalls.
First, we successfully extracted the QGPV anomaly corresponding to the upper tropospheric trough from the total QGPV fields during the heavy rainfall event by applying appropriate thresholds of QGPV and mixing ratio associated with the trough. After confirming the accuracy of the present QGPV inversion approach, we performed the piecewise inversion to the QGPV anomaly and obtained the geopotential and temperature anomalies corresponding to the trough. Subtracting these anomalies from the original atmospheric field, we created the field in which the trough was removed. We compared the original field, anomaly field, and trough-removed field, and examined the role of the trough in generating the heavy rainfall. Furthermore, we also obtained the dynamically induced vertical motion field associated with the trough by solving the quasi-geostrophic omega equation for those fields.
The analysis indicated that the geopotential anomaly associated with QGPV of the trough extended downward to the surface level and strengthened the moisture inflow to the Baiu frontal region. The trough enhanced the dynamical upward motion in the middle and upper troposphere to the east of the trough. Lower tropospheric upward motion, which was important for the vertical transport of moisture, was not associated with the upper-level trough but with the low-level mesoscale Baiu frontal depression. The trough could have influenced its development. In addition, the negative temperature anomaly associated with the trough led to a statically unstable condition as the trough approached. Such an unstable condition was favorable for the development of convective precipitation.
These results indicate that the upper tropospheric trough had an influence on the formation of heavy rainfall event in western Japan 2018. The proposed piecewise QGPV inversion method that separates geopotential and temperature anomalies corresponding to individual disturbances is a powerful tool for quantifying the contribution of each disturbance on the generation of heavy rainfalls.