Meso-γ-scale convective systems observed by a 443-MHz wind-profiling radar with RASS in the Okinawa subtropical region

Abstract

a b s t r a c tWe observed a meso-g-scale convective system in July 2007 using a 443-MHz wind profiler radar (WPR) with a radio acoustic sounding system (RASS) at the NICT Ogimi observatory in Okinawa, Japan. We analyzed the virtual temperature, T v , the Brunt-Vaisala frequency squared, N 2 , and three components of wind velocity profiles from the WPR-RASS data. We also employed a non-hydrostatic meso-scale (NHM) numerical model. Although the island of Okinawa was covered with a Pacific highpressure system from 21-26 July, the atmospheric condition was convectively unstable below about 5 km. A number of convective clouds generally appeared from 11:00-18:00 in local time (i.e., Japan Standard Time; JST) with a typical horizontal scale of 10 km and temporal scale of 40-60 min. We focused on the convective system that passed over the Ogimi radar site on 23rd and 25th July. Just before rain occurred on these days, a low N 2 region extended upward to 2.0 km, and this characteristics is also commonly seen around a convective cloud in the NHM model. The cloud water content from the NHM model indicated that the cloud top height correlates with the low N 2 structure. Before the convective system was generated, N 2 decreased below an altitude of about 1 km, because air with low T v intruded at 1-3 km, and the surface temperature increased due to solar radiation. The sea-breeze from both the east and west coasts of Okinawa collided to force the convergence below 1 km. Thus, the synergetic effects of the low static stability and convergence seemed to trigger the generation of a convective system, which eventually grew to 11 km over the radar site.

Wet deposition of black carbon at a remote site in the East China Sea

“…According to back trajectory analysis at Cape Hedo [ Verma et al ., ], maritime air masses constituted about 80% of the air masses sampled at Cape Hedo. Summer precipitation over Okinawa Island is mainly associated with cloud systems developed by thermal convection [ Mikami et al ., ]. In summer and fall, typhoons and tropical cyclones frequently pass over the East China Sea (Figure c and Plate c), causing heavy precipitation [ Ueda et al ., ].…”

“…Summertime precipitation often comes from cloud systems developed by thermal convection [ Mikami et al ., ]. We therefore focused on data from summer.…”

ARPS Simulations of Convection during TOMACS

“…2007) for thermal geometric controls on surface air temperature. In addition, many observational studies were conducted for TMA to analyze two mesocyclones with the surface network and weather radar during TOMACS ; the urban canopy and winds (Kondo et al 2008); wind profiles, static stability, and convergence leading to the development of thunderstorms (Mikami et al 2011); multilayer winds and sea breezes measurements with the Doppler weather radar (Tsunematsu et al 2009); aerosols and sea breeze studies with the Doppler LIDAR (Iwai et al 2011); thermal and geometric studies on surface air temperature (Tomita et al 2007); effects of the Tokyo Bay sea surface temperature on urban temperature (Oda and Kanda 2009); climatology of synoptic winds and surface temperatures (Yoshikado 2013); and lee winds and rainfall in TMA (Inamura et al 2011). Further, many numerical simulations were conducted to study the impacts of land use and alteration on Tokyo surface temperature and sea breeze (Kusaka et al 2000), increased precipitation , energy balance and heat modeling (Ooka et al 2011), local heavy rainfall , Tokyo morphology (Adachi et al, 2014), and advanced data assimilation systems (Saito et al, 2017;Saito et al 2016;Kawabata et al 2011Kawabata et al , 2013Kawabata et al , 2014.…”

A Numerical Study on a Mesoscale Convective System over a Subtropical Island with 4D-Var Assimilation of GPS Slant Total Delays

“…They conducted impact tests with and without incorporating mountain effects and reported that similar MCSs were reproduced in both simulations; however, the sea-breeze circulation was somewhat stronger when the mountain effects were included. Mikami et al (2011) investigated the evolution of a small convective system over Okinawa by conducting a 1-km numerical simulation with wind profiler and radio acoustic sounding system (RASS) observations. They reported that the convective system developed when the sea-breeze circulation reduced the vertical atmospheric stability.…”

“…Although these various numerical simulations reproduced their target phenomena (MCS or convective system), Chang and Yoshizaki (1991) used a twodimensional model, whereas Minda et al (2010) and Mikami et al (2011) used high-performance numerical models but downscaled (so-called "cold start") initial conditions in their studies. From the viewpoint of weather forecasting, predicting the timing and location of an MCS or convective system is particularly important.…”