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- Author or Editor: Lawrence D. Carey x
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Abstract
Three methodologies for correcting the radar reflectivity factor (Z H) in the presence of partial beam blockage are implemented, compared, and evaluated using a polarimetric radar dataset from the North American Monsoon Experiment (NAME) in northwestern Mexico. One methodology uses simulated interactions between radar beams and digital terrain maps, while the other two invoke the self-consistency of polarimetric radar measurands in rainfall, and the relative insensitivity of a specific differential phase to beam blockage. While the different methodologies often agree to within 1–2 dB, significant disagreements can occur in regions of sharp azimuthal gradients in beam blockage patterns, and in areas where the terrain-caused radar clutter map is complex. These disagreements may be mitigated by the use of additional radar data to develop the polarimetric correction techniques, by a more sophisticated terrain-beam interaction model, or by a higher-resolution digital terrain map. Intercomparisons between ground radar data and Tropical Rainfall Measuring Mission satellite overpasses suggest that all of the methodologies can correct mean Z H to within the expected uncertainty of such intercomparisons (1–1.5 dB). The polarimetric correction methods showed good results even in severely blocked regions (>10 dB reduction). The results suggest the possibility that all of the techniques may be valid approaches to correcting partial beam blockage, and within that context relative advantages and disadvantages of each technique are discussed. However, none of the techniques can correct radar data when weak echoes are reduced to noise by strong blocks, thus leading to biases in corrected Z H and rainfall climatologies.
Abstract
Three methodologies for correcting the radar reflectivity factor (Z H) in the presence of partial beam blockage are implemented, compared, and evaluated using a polarimetric radar dataset from the North American Monsoon Experiment (NAME) in northwestern Mexico. One methodology uses simulated interactions between radar beams and digital terrain maps, while the other two invoke the self-consistency of polarimetric radar measurands in rainfall, and the relative insensitivity of a specific differential phase to beam blockage. While the different methodologies often agree to within 1–2 dB, significant disagreements can occur in regions of sharp azimuthal gradients in beam blockage patterns, and in areas where the terrain-caused radar clutter map is complex. These disagreements may be mitigated by the use of additional radar data to develop the polarimetric correction techniques, by a more sophisticated terrain-beam interaction model, or by a higher-resolution digital terrain map. Intercomparisons between ground radar data and Tropical Rainfall Measuring Mission satellite overpasses suggest that all of the methodologies can correct mean Z H to within the expected uncertainty of such intercomparisons (1–1.5 dB). The polarimetric correction methods showed good results even in severely blocked regions (>10 dB reduction). The results suggest the possibility that all of the techniques may be valid approaches to correcting partial beam blockage, and within that context relative advantages and disadvantages of each technique are discussed. However, none of the techniques can correct radar data when weak echoes are reduced to noise by strong blocks, thus leading to biases in corrected Z H and rainfall climatologies.
Abstract
Lightning stroke data from both the World Wide Lightning Location Network (WWLLN) and the Earth Networks Total Lightning Network (ENTLN) were compared to lightning group data from the Lightning Imaging Sensor (LIS) from 1 January 2010 through 30 June 2011. The region of study, from 39°S to 39°N latitude, chosen based on the orbit of LIS, and 164°E east to 17°W longitude, chosen to approximate the possible Geostationary Lightning Mapper (GLM) longitude, was considered in its entirety and then divided into geographical subregions. Over this 18-month time period, WWLLN had an 11.0% entire region, 13.2% North American, 6.2% South American, 16.4% Atlantic Ocean, and 18.9% Pacific Ocean coincidence percent (CP) value. The ENTLN CP values were 28.5%, 63.3%, 2.2%, 3.0%, and 2.5%, respectively. During the 18 months, WWLLN CP values remained rather consistent but low and often higher over ocean than land; ENTLN CP values showed large spatial and temporal variability. With both networks, North America had less variability during summer months than winter months and higher CP values during winter months than summer months. The highest ENTLN CP values were found in the southeastern United States, especially in a semicircle that extended from central Oklahoma, through Texas, along the northern Gulf of Mexico, across southern Florida, and along the U.S. East Coast. There was no significant change in CP values over time; the lowest monthly North American ENTLN CP value was found in June 2011 at 48.1%, the last month analyzed. These findings are consistent with most ENTLN sensors being located in the United States.
Abstract
Lightning stroke data from both the World Wide Lightning Location Network (WWLLN) and the Earth Networks Total Lightning Network (ENTLN) were compared to lightning group data from the Lightning Imaging Sensor (LIS) from 1 January 2010 through 30 June 2011. The region of study, from 39°S to 39°N latitude, chosen based on the orbit of LIS, and 164°E east to 17°W longitude, chosen to approximate the possible Geostationary Lightning Mapper (GLM) longitude, was considered in its entirety and then divided into geographical subregions. Over this 18-month time period, WWLLN had an 11.0% entire region, 13.2% North American, 6.2% South American, 16.4% Atlantic Ocean, and 18.9% Pacific Ocean coincidence percent (CP) value. The ENTLN CP values were 28.5%, 63.3%, 2.2%, 3.0%, and 2.5%, respectively. During the 18 months, WWLLN CP values remained rather consistent but low and often higher over ocean than land; ENTLN CP values showed large spatial and temporal variability. With both networks, North America had less variability during summer months than winter months and higher CP values during winter months than summer months. The highest ENTLN CP values were found in the southeastern United States, especially in a semicircle that extended from central Oklahoma, through Texas, along the northern Gulf of Mexico, across southern Florida, and along the U.S. East Coast. There was no significant change in CP values over time; the lowest monthly North American ENTLN CP value was found in June 2011 at 48.1%, the last month analyzed. These findings are consistent with most ENTLN sensors being located in the United States.
Abstract
The dual-polarization weather radar on the Kwajalein Atoll in the Republic of the Marshall Islands (KPOL) is one of the only full-time (24/7) operational S-band dual-polarimetric (DP) radars in the tropics. Through the use of KPOL DP and disdrometer measurements from Kwajalein, quality control (QC) and reflectivity calibration techniques were developed and adapted for use. Data studies in light rain show that KPOL DP measurements are of sufficient quality for these applications. While the methodology for the development of such applications is well documented, the tuning of specific algorithms to the particular regime and observed raindrop size distributions requires a comprehensive testing and adjustment period. Presented are algorithm descriptions and results from five case studies in which QC and absolute reflectivity calibration were performed and assessed. Also described is a unique approach for calibrating the differential reflectivity field when vertically pointing observations are not available. Results show the following: 1) DP-based QC provides superior results compared to the legacy Tropical Rainfall Measuring Mission (TRMM) QC algorithm (based on height and reflectivity thresholds), and 2) absolute reflectivity calibration can be performed using observations of light rain via a published differential phase–based integration technique; results are within ±1 dB compared to independent measurements. Future extension of these algorithms to upgraded Weather Surveillance Radar-1988 Doppler (WSR-88D) polarization diverse radars will benefit National Aeronautics and Space Administration’s (NASA’s) Precipitation Measurement Missions (PMM) validation programs.
Abstract
The dual-polarization weather radar on the Kwajalein Atoll in the Republic of the Marshall Islands (KPOL) is one of the only full-time (24/7) operational S-band dual-polarimetric (DP) radars in the tropics. Through the use of KPOL DP and disdrometer measurements from Kwajalein, quality control (QC) and reflectivity calibration techniques were developed and adapted for use. Data studies in light rain show that KPOL DP measurements are of sufficient quality for these applications. While the methodology for the development of such applications is well documented, the tuning of specific algorithms to the particular regime and observed raindrop size distributions requires a comprehensive testing and adjustment period. Presented are algorithm descriptions and results from five case studies in which QC and absolute reflectivity calibration were performed and assessed. Also described is a unique approach for calibrating the differential reflectivity field when vertically pointing observations are not available. Results show the following: 1) DP-based QC provides superior results compared to the legacy Tropical Rainfall Measuring Mission (TRMM) QC algorithm (based on height and reflectivity thresholds), and 2) absolute reflectivity calibration can be performed using observations of light rain via a published differential phase–based integration technique; results are within ±1 dB compared to independent measurements. Future extension of these algorithms to upgraded Weather Surveillance Radar-1988 Doppler (WSR-88D) polarization diverse radars will benefit National Aeronautics and Space Administration’s (NASA’s) Precipitation Measurement Missions (PMM) validation programs.
The RELAMPAGO Lightning Mapping Array: Overview and Initial Comparison with the Geostationary Lightning MapperAbstract
During November 2018–April 2019, an 11-station very high frequency (VHF) Lightning Mapping Array (LMA) was deployed to Córdoba Province, Argentina. The purpose of the LMA was validation of the Geostationary Lightning Mapper (GLM), but the deployment was coordinated with two field campaigns. The LMA observed 2.9 million flashes (≥ five sources) during 163 days, and level-1 (VHF locations), level-2 (flashes classified), and level-3 (gridded products) datasets have been made public. The network’s performance allows scientifically useful analysis within 100 km when at least seven stations were active. Careful analysis beyond 100 km is also possible. The LMA dataset includes many examples of intense storms with extremely high flash rates (>1 s−1), electrical discharges in overshooting tops (OTs), as well as anomalously charged thunderstorms with low-altitude lightning. The modal flash altitude was 10 km, but many flashes occurred at very high altitude (15–20 km). There were also anomalous and stratiform flashes near 5–7 km in altitude. Most flashes were small (<50 km2 area). Comparisons with GLM on 14 and 20 December 2018 indicated that GLM most successfully detected larger flashes (i.e., more than 100 VHF sources), with detection efficiency (DE) up to 90%. However, GLM DE was reduced for flashes that were smaller or that occurred lower in the cloud (e.g., near 6-km altitude). GLM DE also was reduced during a period of OT electrical discharges. Overall, GLM DE was a strong function of thunderstorm evolution and the dominant characteristics of the lightning it produced.
Abstract
During November 2018–April 2019, an 11-station very high frequency (VHF) Lightning Mapping Array (LMA) was deployed to Córdoba Province, Argentina. The purpose of the LMA was validation of the Geostationary Lightning Mapper (GLM), but the deployment was coordinated with two field campaigns. The LMA observed 2.9 million flashes (≥ five sources) during 163 days, and level-1 (VHF locations), level-2 (flashes classified), and level-3 (gridded products) datasets have been made public. The network’s performance allows scientifically useful analysis within 100 km when at least seven stations were active. Careful analysis beyond 100 km is also possible. The LMA dataset includes many examples of intense storms with extremely high flash rates (>1 s−1), electrical discharges in overshooting tops (OTs), as well as anomalously charged thunderstorms with low-altitude lightning. The modal flash altitude was 10 km, but many flashes occurred at very high altitude (15–20 km). There were also anomalous and stratiform flashes near 5–7 km in altitude. Most flashes were small (<50 km2 area). Comparisons with GLM on 14 and 20 December 2018 indicated that GLM most successfully detected larger flashes (i.e., more than 100 VHF sources), with detection efficiency (DE) up to 90%. However, GLM DE was reduced for flashes that were smaller or that occurred lower in the cloud (e.g., near 6-km altitude). GLM DE also was reduced during a period of OT electrical discharges. Overall, GLM DE was a strong function of thunderstorm evolution and the dominant characteristics of the lightning it produced.
