10:45 AM - 12:15 PM
[AAS03-P05] Downbursts and gust fronts associated with heavy precipitation over the Kanto Plain in a warm season.
Keywords:downburst, gust front, temperature
Downbursts (DB) is a gust phenomenon in which a downdraft from a developing cumulonimbus cloud diverges at the surface. DBs and cold pools associated with other severe convections often produce cold gusts, called gust fronts (GF). Strong turbulences due to DB and GF sometimes cause meteorological disasters, including aircraft accidents. To countermeasure this disaster, it is required to understand the time-space structures of DBs and GFs. DB development, structure, and size depending on the environmental conditions. In western Japan, DB occurs in various conditions, which may be associated with tropical cyclones. However, in eastern Japan, particularly in the Kanto Plain, DBs tend to occur in the afternoon in summer due to daytime surface heating. This study investigates the structures of DB and GF, focusing on the vertical structure in air temperature.
We used a ground-installed passive microwave radiometer (MWR). MWR-retrieved air temperature profiles at four stations were used. The air temperature profiles can be used from the surface to approximately 2 km at five minutes intervals, but future assessments may be required. We also used Japan Meteorological Agency (JMA) Automated Meteorological Data Acquisition System (AMeDAS) temperature, wind, and precipitation data to investigate the spatial structure of the GF. Also, we conducted numerical simulations with the Weather Research and Forecasting model (WRF). The horizontal resolution of the simulation is 1 km. Initial and boundary conditions are taken from the Final Analysis (FNL) developed by the National Center for Environmental Prediction (NCEP).
To understand the structure of the GF simply, we choose well-developed precipitation system and a relatively small influence of the synoptic scale system. We analyzed the DB of this pattern in the Kanto Plain in August 2018.
Here, we analyzed the case of August 27th, 2018, when well-developed daytime precipitation systems occurred over the western Kanto Plain (mainly in Tokyo and Saitama prefecture) because the duration of sunshine was 100% until noon. After 14:00, precipitation occurred in the west of the observation stations and moved eastward.
The surface air temperature (SAT) of AMeDAS observed a sudden 2 ℃ temperature drop before the precipitation system, which suggests a GF. We also examined the possible GF event by MWR. The temporal changes of the air temperature profile by MWR also showed the sudden air temperature drop near the surface to 1800 m. The air temperature drop was greater near the surface and smaller in the upper boundary layer. In addition, the air temperature increased 15 min after this drop. We also investigated the simulated results, which seemed to show a weaker signal, although we may reconsider the relationship between the simulated precipitation system and the GR traveling positions.
We used a ground-installed passive microwave radiometer (MWR). MWR-retrieved air temperature profiles at four stations were used. The air temperature profiles can be used from the surface to approximately 2 km at five minutes intervals, but future assessments may be required. We also used Japan Meteorological Agency (JMA) Automated Meteorological Data Acquisition System (AMeDAS) temperature, wind, and precipitation data to investigate the spatial structure of the GF. Also, we conducted numerical simulations with the Weather Research and Forecasting model (WRF). The horizontal resolution of the simulation is 1 km. Initial and boundary conditions are taken from the Final Analysis (FNL) developed by the National Center for Environmental Prediction (NCEP).
To understand the structure of the GF simply, we choose well-developed precipitation system and a relatively small influence of the synoptic scale system. We analyzed the DB of this pattern in the Kanto Plain in August 2018.
Here, we analyzed the case of August 27th, 2018, when well-developed daytime precipitation systems occurred over the western Kanto Plain (mainly in Tokyo and Saitama prefecture) because the duration of sunshine was 100% until noon. After 14:00, precipitation occurred in the west of the observation stations and moved eastward.
The surface air temperature (SAT) of AMeDAS observed a sudden 2 ℃ temperature drop before the precipitation system, which suggests a GF. We also examined the possible GF event by MWR. The temporal changes of the air temperature profile by MWR also showed the sudden air temperature drop near the surface to 1800 m. The air temperature drop was greater near the surface and smaller in the upper boundary layer. In addition, the air temperature increased 15 min after this drop. We also investigated the simulated results, which seemed to show a weaker signal, although we may reconsider the relationship between the simulated precipitation system and the GR traveling positions.