12:00 PM - 12:15 PM
[AAS10-12] Time Evolution of Precipitation Cells from the First Radar Echo Observed by X-band Phased Array Weather Radar
Keywords:X-band phased array weather radar, precipitation cell, time evolution, cell tracking, first radar echo
Cumulonimbus clouds develop rapidly during the summer season and produce localized heavy rainfall, increasing the risk of water-related disasters such as urban flooding and inundation. Early detection of precipitation particles in the sky in the early stage of cumulonimbus cloud development is vital from the perspective of disaster prevention to ensure lead time and improve the accuracy of localized heavy rainfall prediction. Conventional parabolic meteorological radars, which conduct three-dimensional observations at five-minute intervals, face limitations in continuously capturing rapidly developing cumulonimbus clouds in both temporal and spatial aspects. Phased Array Weather Radar (PAWR) significantly enhances temporal resolution, allowing continuous three-dimensional observations of cumulonimbus structures every 30 seconds.
This study focuses on the time evolution of precipitation cells from the first radar echo detected by meteorological radar and conducts a time-series analysis using observational data from an X-band PAWR. The observational data used in this study were obtained from the X-band PAWR operated by Japan Radio Co. Ltd., located at Chiba City (35°52’N, 140°23’E). This radar can observe a three-dimensional space within an 80 km radius and up to an altitude of 15 km, with a temporal resolution of 30 seconds and a spatial resolution of 250 m. To mitigate clutter effects from terrain and buildings and to avoid the spread of radar echoes, only data within a 60 km radius and above an altitude of 1 km were utilized. Additionally, XRAIN composite rainfall data were used to determine ground-level precipitation intensity.
In this study, a precipitation cell was defined as a contiguous region with a reflectivity of 20 dBZ or higher and a volume of at least 5 km³. The identified cells were automatically extracted and labeled, and their three-dimensional centroids were calculated. This process was conducted for each time step, and the movement distance of each cell centroid was determined by comparing results with the next time step (30 seconds later). If the centroid displacement was within 2.5 km, the cells were considered the same. Furthermore, cells with durations between 20 and 90 minutes were selected. The first radar echo was defined as the radar echo detected at the time when a cell was initially extracted during the tracking process.
For the time-series analysis, the following parameters were examined: (1) vertical reflectivity at the cell centroid, (2) surface rainfall intensity (XRAIN composite rainfall), (3) cell centroid altitude, (4) echo top height, (5) maximum accumulated reflectivity at each altitude, (6) voxel count, and (7) aspect ratio (vertical/horizontal). A case study was conducted on a precipitation cell observed on August 3, 2022, using this method.
At 16:40 JST, the first radar echo was detected at an altitude of approximately 3 km, and the cell persisted for 53 minutes. Eight minutes after the detection of the first radar echo, a region with reflectivity exceeding 40 dBZ was observed in the upper atmosphere, and 19 minutes later, intense rainfall of 80 mm/h was recorded at the surface. During this period, the cell centroid altitude gradually increased from 3 km to 6 km, while the voxel count increased sharply. The aspect ratio exceeded 1 between 5 and 10 minutes after the first radar echo, indicating that the precipitation cell rapidly developed in the vertical direction.
In the presentation, we will introduce additional cases and discuss the relationship between the time evolution of precipitation cells from the first radar echo and precipitation intensity.
This study focuses on the time evolution of precipitation cells from the first radar echo detected by meteorological radar and conducts a time-series analysis using observational data from an X-band PAWR. The observational data used in this study were obtained from the X-band PAWR operated by Japan Radio Co. Ltd., located at Chiba City (35°52’N, 140°23’E). This radar can observe a three-dimensional space within an 80 km radius and up to an altitude of 15 km, with a temporal resolution of 30 seconds and a spatial resolution of 250 m. To mitigate clutter effects from terrain and buildings and to avoid the spread of radar echoes, only data within a 60 km radius and above an altitude of 1 km were utilized. Additionally, XRAIN composite rainfall data were used to determine ground-level precipitation intensity.
In this study, a precipitation cell was defined as a contiguous region with a reflectivity of 20 dBZ or higher and a volume of at least 5 km³. The identified cells were automatically extracted and labeled, and their three-dimensional centroids were calculated. This process was conducted for each time step, and the movement distance of each cell centroid was determined by comparing results with the next time step (30 seconds later). If the centroid displacement was within 2.5 km, the cells were considered the same. Furthermore, cells with durations between 20 and 90 minutes were selected. The first radar echo was defined as the radar echo detected at the time when a cell was initially extracted during the tracking process.
For the time-series analysis, the following parameters were examined: (1) vertical reflectivity at the cell centroid, (2) surface rainfall intensity (XRAIN composite rainfall), (3) cell centroid altitude, (4) echo top height, (5) maximum accumulated reflectivity at each altitude, (6) voxel count, and (7) aspect ratio (vertical/horizontal). A case study was conducted on a precipitation cell observed on August 3, 2022, using this method.
At 16:40 JST, the first radar echo was detected at an altitude of approximately 3 km, and the cell persisted for 53 minutes. Eight minutes after the detection of the first radar echo, a region with reflectivity exceeding 40 dBZ was observed in the upper atmosphere, and 19 minutes later, intense rainfall of 80 mm/h was recorded at the surface. During this period, the cell centroid altitude gradually increased from 3 km to 6 km, while the voxel count increased sharply. The aspect ratio exceeded 1 between 5 and 10 minutes after the first radar echo, indicating that the precipitation cell rapidly developed in the vertical direction.
In the presentation, we will introduce additional cases and discuss the relationship between the time evolution of precipitation cells from the first radar echo and precipitation intensity.