Large-Scale Environmental Conditions Related to Midsummer Extreme Rainfall Events around Japan in the TRMM Region

Abstract

The precipitation characteristics of extreme events in August determined from 13 years of satellite data around Japan in the TRMM observation region and their relationship with large-scale environmental conditions are examined. Two types of extreme events, extreme rainfall and extreme convective events, are defined in each analysis grid box using maximum near-surface rainfall and maximum 40-dB Z echo-top height in each event, respectively. There are clear differences in precipitation characteristics between the two types of extreme events. Extreme rainfall events are more organized precipitation systems than the extreme convective events, with relatively lower echo-top heights and very low lightning activity. There are also clear differences in the related environmental conditions, where the environments related to the extreme rainfall events are somewhat convectively stable and very humid in almost the entire troposphere. These facts are consistent with our previous studies and reinforce the importance of warm-rain processes in extremely intense precipitation productions. The environments related to the extreme rainfall events exhibit a zonally extended moist anomaly in the free troposphere from southern China to the east of Japan, indicating that the excessive moisture transported from the west by a large-scale flow may partially play a role in producing environmental conditions favorable for extreme rainfall. On the other hand, the environments related to extreme convective events are not associated with free-tropospheric moisture inflow. The relationships with the tropical cyclones and upper-tropospheric dynamical fields are also examined, and are found to be clearly different between the extreme rainfall events and extreme convective events.

The Effects of an Upper-Tropospheric Trough on the Heavy Rainfall Event in July 2018 over Japan

“…Hamada and Takayabu (2018) statistically showed that extreme rainfall around Japan in summer time tends to be associated not with extremely tall convective systems with intense lightning activity, but rather with organized rainfall systems that build large areas of stratiform rainfall. The environment related to extreme rainfall events is relatively convectively stable and very humid throughout most of the troposphere, associated with the transport of excessive moisture from the west via large-scale flow (Hamada and Takayabu 2018). Bretherton et al (2004) showed that rainfall rapidly increases with an increase in column water vapor over the tropical ocean.…”

“…Rainfall from moderately high altitudes (7-9 km) is predominant both for convective and stratiform rainfall. These are characteristics of organized rainfall systems (e.g., Hamada and Takayabu 2018), which are maintained by mesoscale circulations (Houze et al 1989). The profile of temperature anomalies is very small and almost vertical in the layer below 550 hPa, indicating that the temperature stratification in the mid-to lower troposphere is nearly the same as the climatology (Fig.…”

Polarizing rain types linked to June drought in the Korean peninsula over last 20 years

“…These two types of heavy rain are similar concept with extreme rainfall and extreme convective events defined using maximum near‐surface rain rate and 40 dBZ echo‐top height from Hamada et al . () over the tropics and Hamada and Takayabu () around Japan. Since the humid environment prerequisite for the warm‐type heavy precipitation is established by large‐scale water vapour transport from the southwest and its convergence onto the monsoon frontal area where the rain forms (Sohn et al ., ), the monsoon circulation change, particularly associated with the development and evolution of the North Pacific high, should result in change in the rain type in Korea.…”

Response of precipitation extremes to warming: what have we learned from theory and idealized cloud-resolving simulations, and what remains to be learned?

“…The environmental conditions for each extremes also differ, in the manner that the convective systems are embedded in environments with large instability, while precipitation extremes are embedded in environments with deep moist layer in the troposphere, but the atmospheric stratification is relatively more stable. Hamada and Takayabu (2018) further explored the extreme convection and extreme rainfall in a region around Japan in midsummer. In their study, it was found that the extreme convection had smaller area size and was accompanied by much more frequent lightening, while extreme rainfall had relatively larger area size with larger stratiform ratio and much less lightening.…”

“…Parodi andEmanuel 2009, Bao andSherwood 2019), and atmospheric stability (e.g. Attema et al 2014, Hamada and Takayabu 2018), as well as microphysical processes including cloud-rain autoconversion and rain evaporation (e.g. Lutsko and Cronin 2018).…”