17:15 〜 19:15
[AAS04-P03] Comparison of two approaches for estimating vertical air motion in next-generation satellite radar observations
キーワード：鉛直流、MUレーダー、ドップラー手法、Δt手法
INCUS (Investigation of Convective Updrafts) and PMM (Precipitation Measuring Mission) are planned as the next-generation satellite precipitation radar observation missions. In the INCUS project, three small satellites equipped with precipitation radar will fly in formation, and observe the development of precipitation clouds by measuring the time difference of radar reflectivity (called “the Δt approach”). The PMM will measure the vertical Doppler velocity of precipitation particles using the first spaceborne Ku-band Doppler radar.
The ultimate goal of both the Δt approach and the Doppler approach is to estimate the vertical air motions, which cannot be directly observed. To evaluate these two approaches, we used the Middle and Upper Atmosphere (MU) radar and a vertical pointing X-band Doppler radar at Shigaraki, Japan. The MU radar is one of the atmospheric radars that can observe vertical air motion within precipitating clouds, while the vertical pointing X-band radar can observe radar reflectivity and vertical Doppler velocity of precipitation particles. Here, we focused on an isolated cumulonimbus cloud that developed and disappeared over Shigaraki, which we believe is suitable for adopting the Δt approach.
First, we attempted to estimate vertical air motions by the Δt approach using the data from the vertical pointing X-band Doppler radar. According to Dolan et al. (2023), no study has yet been conducted on the relationship between vertical velocity and time difference of radar reflectivity. To evaluate it, we calculated the correlation between the vertical velocity observed by the MU radar and the time difference of radar reflectivity divided by Δt (= 30s, 90s, 120s) . We found that high correlations were obtained near the echo tops in the developing stage, but not in other areas and stages.
Second, we attempted to estimate vertical air motions by the Doppler approach following Maki et al. (1998). The terminal velocity of precipitation particles is estimated from radar reflectivity data, assuming the type (raindrops, snowflakes, and hail), and vertical air motion is calculated by subtracting terminal velocity from the observed Doppler data. We found that the correlation between the vertical air motions observed by MU radar and the vertical air motions estimated using the Doppler approach with X-band radar data was high, about 0.8, if the type of precipitation particles was hail when the temperature was below 0℃ and raindrops when the temperature was over 0℃. Based on these results, it can be seen that the Doppler approach is better than that with the Δt approach to estimate vertical air motions.
The ultimate goal of both the Δt approach and the Doppler approach is to estimate the vertical air motions, which cannot be directly observed. To evaluate these two approaches, we used the Middle and Upper Atmosphere (MU) radar and a vertical pointing X-band Doppler radar at Shigaraki, Japan. The MU radar is one of the atmospheric radars that can observe vertical air motion within precipitating clouds, while the vertical pointing X-band radar can observe radar reflectivity and vertical Doppler velocity of precipitation particles. Here, we focused on an isolated cumulonimbus cloud that developed and disappeared over Shigaraki, which we believe is suitable for adopting the Δt approach.
First, we attempted to estimate vertical air motions by the Δt approach using the data from the vertical pointing X-band Doppler radar. According to Dolan et al. (2023), no study has yet been conducted on the relationship between vertical velocity and time difference of radar reflectivity. To evaluate it, we calculated the correlation between the vertical velocity observed by the MU radar and the time difference of radar reflectivity divided by Δt (= 30s, 90s, 120s) . We found that high correlations were obtained near the echo tops in the developing stage, but not in other areas and stages.
Second, we attempted to estimate vertical air motions by the Doppler approach following Maki et al. (1998). The terminal velocity of precipitation particles is estimated from radar reflectivity data, assuming the type (raindrops, snowflakes, and hail), and vertical air motion is calculated by subtracting terminal velocity from the observed Doppler data. We found that the correlation between the vertical air motions observed by MU radar and the vertical air motions estimated using the Doppler approach with X-band radar data was high, about 0.8, if the type of precipitation particles was hail when the temperature was below 0℃ and raindrops when the temperature was over 0℃. Based on these results, it can be seen that the Doppler approach is better than that with the Δt approach to estimate vertical air motions.