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Abstract
A system is described for the measurement of the atmospheric flux of water vapor near the surface, using a quartz-crystal oscillator as humidity sensor (as described by Gjessing et al.) and based on the Fluxatron technique. Results from a field test give an energy balance recovery ratio (LE + H)/(R − G) = 1.00 ± 0.04.
Abstract
A system is described for the measurement of the atmospheric flux of water vapor near the surface, using a quartz-crystal oscillator as humidity sensor (as described by Gjessing et al.) and based on the Fluxatron technique. Results from a field test give an energy balance recovery ratio (LE + H)/(R − G) = 1.00 ± 0.04.
Abstract
Lightning has been observed from above cloud top by using satellites, balloons, rockets, and high-altitude airplanes, each of which provides a unique perspective and holds the potential for gaining new understanding of lightning phenomena. During the 1980s extensive optical observations of lightning have been made from a NASA U-2 airplane with a goal toward placing a lightning sensor in geostationary orbit. Analysis of these U-2 measurements suggest that most of the light generated within a cloud escapes, and that the optical energy of lightning measured from above clouds is not significantly different than the measurements made from below of discharges to ground. Near-infrared optical measurements were made of nearly 1300 optical pulses produced by 79 lightning flashes. The median source estimate of peak flash radiance is approximately 108 W with a dynamic range of less than three orders of magnitude. Of these 79 flashes, 90 percent produced peak radiant energy densities of 4.7 μJ m−2 sr−1 or greater, relative to the full field of view of the instrument. The median pulse rise time and full width at half maximum are 240 and 370 μs, respectively. We interpret these slow optical rise times and broad pulse widths as primarily a result of multiple scattering within the cloud. The spectral characteristics in the near-infrared of the neutral emission lines observed from above clouds are found to be very similar to ground-based measurements.
Abstract
Lightning has been observed from above cloud top by using satellites, balloons, rockets, and high-altitude airplanes, each of which provides a unique perspective and holds the potential for gaining new understanding of lightning phenomena. During the 1980s extensive optical observations of lightning have been made from a NASA U-2 airplane with a goal toward placing a lightning sensor in geostationary orbit. Analysis of these U-2 measurements suggest that most of the light generated within a cloud escapes, and that the optical energy of lightning measured from above clouds is not significantly different than the measurements made from below of discharges to ground. Near-infrared optical measurements were made of nearly 1300 optical pulses produced by 79 lightning flashes. The median source estimate of peak flash radiance is approximately 108 W with a dynamic range of less than three orders of magnitude. Of these 79 flashes, 90 percent produced peak radiant energy densities of 4.7 μJ m−2 sr−1 or greater, relative to the full field of view of the instrument. The median pulse rise time and full width at half maximum are 240 and 370 μs, respectively. We interpret these slow optical rise times and broad pulse widths as primarily a result of multiple scattering within the cloud. The spectral characteristics in the near-infrared of the neutral emission lines observed from above clouds are found to be very similar to ground-based measurements.
The present lack of a lower atmosphere research satellite program for the 1980s has prompted consideration of the Space Shuttle/Spacelab system as a means of flying sensor complements geared toward specific research problems, as well as continued instrument development. Three specific examples of possible science questions related to precipitation are discussed: 1) spatial structure of mesoscale cloud and precipitation systems, 2) lightning and storm development, and 3) cyclone intensification over oceanic regions. Examples of space sensors available to provide measurements needed in addressing these questions are also presented. Distinctive aspects of low-earth orbit experiments would be high resolution, multispectral sensing of atmospheric phenomena by complements of instruments, and more efficient sensor development through reflights of specific hardware packages.
The present lack of a lower atmosphere research satellite program for the 1980s has prompted consideration of the Space Shuttle/Spacelab system as a means of flying sensor complements geared toward specific research problems, as well as continued instrument development. Three specific examples of possible science questions related to precipitation are discussed: 1) spatial structure of mesoscale cloud and precipitation systems, 2) lightning and storm development, and 3) cyclone intensification over oceanic regions. Examples of space sensors available to provide measurements needed in addressing these questions are also presented. Distinctive aspects of low-earth orbit experiments would be high resolution, multispectral sensing of atmospheric phenomena by complements of instruments, and more efficient sensor development through reflights of specific hardware packages.
In order to determine how to achieve orders of magnitude improvement in spatial and temporal resolution and in sensitivity of satellite lightning sensors, better quantitative measurements of the characteristics of the optical emissions from lightning as observed from above tops of thunderclouds are required. A number of sensors have been developed and integrated into an instrument package and flown aboard a NASA U-2 aircraft. The objectives have been to acquire optical lightning data needed for designing the lightning mapper sensor, and to study lightning physics and the correlation of lightning activity with storm characteristics. The instrumentation and observations of the program are reviewed and their significance for future research is discussed.
In order to determine how to achieve orders of magnitude improvement in spatial and temporal resolution and in sensitivity of satellite lightning sensors, better quantitative measurements of the characteristics of the optical emissions from lightning as observed from above tops of thunderclouds are required. A number of sensors have been developed and integrated into an instrument package and flown aboard a NASA U-2 aircraft. The objectives have been to acquire optical lightning data needed for designing the lightning mapper sensor, and to study lightning physics and the correlation of lightning activity with storm characteristics. The instrumentation and observations of the program are reviewed and their significance for future research is discussed.
Abstract
Lightning data from the U.S. National Lightning Detection Network (NLDN) are used to perform preliminary validation of the satellite-based Optical Transient Detector (OTD). Sensor precision, accuracy, detection efficiency, and biases of the deployed instrument are considered. The sensor is estimated to have, on average, about 20–40-km spatial and better than 100-ms temporal accuracy. The detection efficiency for cloud-to-ground lightning is about 46%–69%. It is most likely slightly higher for intracloud lightning. There are only marginal day/night biases in the dataset, although 55- or 110-day averaging is required to remove the sampling-based diurnal lightning cycle bias.
Abstract
Lightning data from the U.S. National Lightning Detection Network (NLDN) are used to perform preliminary validation of the satellite-based Optical Transient Detector (OTD). Sensor precision, accuracy, detection efficiency, and biases of the deployed instrument are considered. The sensor is estimated to have, on average, about 20–40-km spatial and better than 100-ms temporal accuracy. The detection efficiency for cloud-to-ground lightning is about 46%–69%. It is most likely slightly higher for intracloud lightning. There are only marginal day/night biases in the dataset, although 55- or 110-day averaging is required to remove the sampling-based diurnal lightning cycle bias.
In the fall of 1992 a lightning direction finder network was deployed in the western Pacific Ocean in the area of Papua New Guinea. Direction finders were installed on Kapingamarangi Atoll and near the towns of Rabaul and Kavieng, Papua New Guinea. The instruments were modified to detect cloud-to-ground lightning out to a distance of 900 km. Data were collected from cloud-to-ground lightning flashes for the period 26 November 1992–15 January 1994. The analyses are presented for the period 1 January 1993–31 December 1993. In addition, a waveform recorder was located at Kavieng to record both cloud-to-ground lightning and intracloud lightning in order to provide an estimate of the complete lightning activity. The data from these instruments are to be analyzed in conjunction with the data from ship and airborne radars, in-cloud microphysics, and electrical measurements from both the ER-2 and DC-8. The waveform instrumentation operated from approximately mid-January through February 1993. Over 150 000 waveforms were recorded.
During the year, January–December 1993, the cloud-to-ground lightning location network recorded 857 000 first strokes of which 5.6% were of positive polarity. During the same period, 437 000 subsequent strokes were recorded. The peak annual flash density was measured to be 2.0 flashes km−2 centered on the western coastline of the island of New Britain, just southwest of Rabaul. The annual peak lightning flash density over the Intensive Flux Array of Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment was 0.1 flashes km−2, or more than an order of magnitude less than that measured near land. The diurnal lightning frequency peaked at 1600 UTC (0200 LT), perhaps in coincidence with the nighttime land-breeze convergence along the coast of New Britain. Median monthly negative peak currents are in the 20–30-kA range, with first stroke peak currents typically exceeding subsequent peak currents. Median monthly positive peak currents are typically 30 kA with one month (June) having a value of 60 kA.
Positive polar conductivity was measured by an ER-2 flight from 40°N geomagnetic latitude to 28°S geomagnetic latitude. The measurements show that the air conductivity is about a factor of 0.6 lower in the Tropics than in the midlatitudes. Consequently, a tropical storm will produce higher field values aloft for the same rate of electrical current generation. An ER-2 overflight of tropical cyclone Oliver on 7 February 1993 measured electric fields and 85-GHz brightness temperatures. The measurements reveal electrification in the eye wall cloud region with ice, but no lightning was observed.
In the fall of 1992 a lightning direction finder network was deployed in the western Pacific Ocean in the area of Papua New Guinea. Direction finders were installed on Kapingamarangi Atoll and near the towns of Rabaul and Kavieng, Papua New Guinea. The instruments were modified to detect cloud-to-ground lightning out to a distance of 900 km. Data were collected from cloud-to-ground lightning flashes for the period 26 November 1992–15 January 1994. The analyses are presented for the period 1 January 1993–31 December 1993. In addition, a waveform recorder was located at Kavieng to record both cloud-to-ground lightning and intracloud lightning in order to provide an estimate of the complete lightning activity. The data from these instruments are to be analyzed in conjunction with the data from ship and airborne radars, in-cloud microphysics, and electrical measurements from both the ER-2 and DC-8. The waveform instrumentation operated from approximately mid-January through February 1993. Over 150 000 waveforms were recorded.
During the year, January–December 1993, the cloud-to-ground lightning location network recorded 857 000 first strokes of which 5.6% were of positive polarity. During the same period, 437 000 subsequent strokes were recorded. The peak annual flash density was measured to be 2.0 flashes km−2 centered on the western coastline of the island of New Britain, just southwest of Rabaul. The annual peak lightning flash density over the Intensive Flux Array of Tropical Oceans Global Atmosphere Coupled Ocean–Atmosphere Response Experiment was 0.1 flashes km−2, or more than an order of magnitude less than that measured near land. The diurnal lightning frequency peaked at 1600 UTC (0200 LT), perhaps in coincidence with the nighttime land-breeze convergence along the coast of New Britain. Median monthly negative peak currents are in the 20–30-kA range, with first stroke peak currents typically exceeding subsequent peak currents. Median monthly positive peak currents are typically 30 kA with one month (June) having a value of 60 kA.
Positive polar conductivity was measured by an ER-2 flight from 40°N geomagnetic latitude to 28°S geomagnetic latitude. The measurements show that the air conductivity is about a factor of 0.6 lower in the Tropics than in the midlatitudes. Consequently, a tropical storm will produce higher field values aloft for the same rate of electrical current generation. An ER-2 overflight of tropical cyclone Oliver on 7 February 1993 measured electric fields and 85-GHz brightness temperatures. The measurements reveal electrification in the eye wall cloud region with ice, but no lightning was observed.
Abstract
The GOES-16 mesoscale domain sector (MDS) scans with 1-min intervals are used in this study to analyze a severe thunderstorm case that occurred in southeastern Brazil. The main objective is to evaluate the GOES-16 MDS rapid scans against the operational full-disk scans with lower temporal resolution for nowcasting. Data from a C-band radar, observed sounding, and a ground-based lightning network are also used in the analysis. A group of thunderstorms formed in the afternoon of 29 November 2017 in an environment of moderate convective available potential energy (CAPE) and deep-layer shear. The storms presented supercell characteristics and intense lightning activity with peak rates in excess of 150 flashes per 5 min. The satellite-derived trends with 1-min interval were skillful in detecting thunderstorm intensification, mainly in the developing stage. The decrease in cloud-top 10.35-μm brightness temperature was accompanied by increases in ice mass flux, concentration of small ice particles at cloud top, and storm depth. In the mature stage, there is no evident trend in the satellite-derived parameters that could indicate storm intensification, but the cluster area expands suggesting cloud-top divergence. The 1-min rapid scans indicate greater lead time to severe weather relative to 10- and 15-min-resolution imagery, but also presented numerous false alarms (indication of severe weather but no occurrence) due to oscillations in the satellite-derived parameters. The parameters calculated every 5 min presented better skill than 10 and 15 min and fewer false alarms than 1 min.
Abstract
The GOES-16 mesoscale domain sector (MDS) scans with 1-min intervals are used in this study to analyze a severe thunderstorm case that occurred in southeastern Brazil. The main objective is to evaluate the GOES-16 MDS rapid scans against the operational full-disk scans with lower temporal resolution for nowcasting. Data from a C-band radar, observed sounding, and a ground-based lightning network are also used in the analysis. A group of thunderstorms formed in the afternoon of 29 November 2017 in an environment of moderate convective available potential energy (CAPE) and deep-layer shear. The storms presented supercell characteristics and intense lightning activity with peak rates in excess of 150 flashes per 5 min. The satellite-derived trends with 1-min interval were skillful in detecting thunderstorm intensification, mainly in the developing stage. The decrease in cloud-top 10.35-μm brightness temperature was accompanied by increases in ice mass flux, concentration of small ice particles at cloud top, and storm depth. In the mature stage, there is no evident trend in the satellite-derived parameters that could indicate storm intensification, but the cluster area expands suggesting cloud-top divergence. The 1-min rapid scans indicate greater lead time to severe weather relative to 10- and 15-min-resolution imagery, but also presented numerous false alarms (indication of severe weather but no occurrence) due to oscillations in the satellite-derived parameters. The parameters calculated every 5 min presented better skill than 10 and 15 min and fewer false alarms than 1 min.
Abstract
Two approaches are used to characterize how accurately the north Alabama Lightning Mapping Array (LMA) is able to locate lightning VHF sources in space and time. The first method uses a Monte Carlo computer simulation to estimate source retrieval errors. The simulation applies a VHF source retrieval algorithm that was recently developed at the NASA Marshall Space Flight Center (MSFC) and that is similar, but not identical to, the standard New Mexico Tech retrieval algorithm. The second method uses a purely theoretical technique (i.e., chi-squared Curvature Matrix Theory) to estimate retrieval errors. Both methods assume that the LMA system has an overall rms timing error of 50 ns, but all other possible errors (e.g., anomalous VHF noise sources) are neglected. The detailed spatial distributions of retrieval errors are provided. Even though the two methods are independent of one another, they nevertheless provide remarkably similar results. However, altitude error estimates derived from the two methods differ (the Monte Carlo result being taken as more accurate). Additionally, this study clarifies the mathematical retrieval process. In particular, the mathematical difference between the first-guess linear solution and the Marquardt-iterated solution is rigorously established thereby explaining why Marquardt iterations improve upon the linear solution.
Abstract
Two approaches are used to characterize how accurately the north Alabama Lightning Mapping Array (LMA) is able to locate lightning VHF sources in space and time. The first method uses a Monte Carlo computer simulation to estimate source retrieval errors. The simulation applies a VHF source retrieval algorithm that was recently developed at the NASA Marshall Space Flight Center (MSFC) and that is similar, but not identical to, the standard New Mexico Tech retrieval algorithm. The second method uses a purely theoretical technique (i.e., chi-squared Curvature Matrix Theory) to estimate retrieval errors. Both methods assume that the LMA system has an overall rms timing error of 50 ns, but all other possible errors (e.g., anomalous VHF noise sources) are neglected. The detailed spatial distributions of retrieval errors are provided. Even though the two methods are independent of one another, they nevertheless provide remarkably similar results. However, altitude error estimates derived from the two methods differ (the Monte Carlo result being taken as more accurate). Additionally, this study clarifies the mathematical retrieval process. In particular, the mathematical difference between the first-guess linear solution and the Marquardt-iterated solution is rigorously established thereby explaining why Marquardt iterations improve upon the linear solution.
