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A winter storm that crossed the continental United States in mid-February 1990 produced hazardous weather across a vast area of the nation. A wide range of severe weather was reported, including heavy snowfall; freezing rain and drizzle; thunderstorms with destructive winds, lightning, large hail, and tornadoes; prolonged heavy rain with subsequent flooding; frost damage to citrus orchards; and sustained destructive winds not associated with thunderstorms. Low-end preliminary estimates of impacts included 9 deaths, 27 injuries, and $120 million of property damage. At least 35 states and southeastern Canada were adversely affected. The storm occurred during the field operations of four independent atmospheric research projects that obtained special, detailed observations of it from the Rocky Mountains to the eastern Great Lakes.
A winter storm that crossed the continental United States in mid-February 1990 produced hazardous weather across a vast area of the nation. A wide range of severe weather was reported, including heavy snowfall; freezing rain and drizzle; thunderstorms with destructive winds, lightning, large hail, and tornadoes; prolonged heavy rain with subsequent flooding; frost damage to citrus orchards; and sustained destructive winds not associated with thunderstorms. Low-end preliminary estimates of impacts included 9 deaths, 27 injuries, and $120 million of property damage. At least 35 states and southeastern Canada were adversely affected. The storm occurred during the field operations of four independent atmospheric research projects that obtained special, detailed observations of it from the Rocky Mountains to the eastern Great Lakes.
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.
In May 2003 there was a very destructive extended outbreak of tornadoes across the central and eastern United States. More than a dozen tornadoes struck each day from 3 May to 11 May 2003. This outbreak caused 41 fatalities, 642 injuries, and approximately $829 million dollars of property damage. The outbreak set a record for most tornadoes ever reported in a week (334 between 4–10 May), and strong tornadoes (F2 or greater) occurred in an unbroken sequence of nine straight days. Fortunately, despite this being one of the largest extended outbreaks of tornadoes on record, it did not cause as many fatalities as in the few comparable past outbreaks, due in large measure to the warning efforts of National Weather Service, television, and private-company forecasters and the smaller number of violent (F4–F5) tornadoes. This event was also relatively predictable; the onset of the outbreak was forecast skillfully many days in advance.
An unusually persistent upper-level trough in the intermountain west and sustained low-level southerly winds through the southern Great Plains produced the extended period of tornado-favorable conditions. Three other extended outbreaks in the past 88 years were statistically comparable to this outbreak, and two short-duration events (Palm Sunday 1965 and the 1974 Superoutbreak) were comparable in the overall number of strong tornadoes. An analysis of tornado statistics and environmental conditions indicates that extended outbreaks of this character occur roughly every 10 to 100 years.
In May 2003 there was a very destructive extended outbreak of tornadoes across the central and eastern United States. More than a dozen tornadoes struck each day from 3 May to 11 May 2003. This outbreak caused 41 fatalities, 642 injuries, and approximately $829 million dollars of property damage. The outbreak set a record for most tornadoes ever reported in a week (334 between 4–10 May), and strong tornadoes (F2 or greater) occurred in an unbroken sequence of nine straight days. Fortunately, despite this being one of the largest extended outbreaks of tornadoes on record, it did not cause as many fatalities as in the few comparable past outbreaks, due in large measure to the warning efforts of National Weather Service, television, and private-company forecasters and the smaller number of violent (F4–F5) tornadoes. This event was also relatively predictable; the onset of the outbreak was forecast skillfully many days in advance.
An unusually persistent upper-level trough in the intermountain west and sustained low-level southerly winds through the southern Great Plains produced the extended period of tornado-favorable conditions. Three other extended outbreaks in the past 88 years were statistically comparable to this outbreak, and two short-duration events (Palm Sunday 1965 and the 1974 Superoutbreak) were comparable in the overall number of strong tornadoes. An analysis of tornado statistics and environmental conditions indicates that extended outbreaks of this character occur roughly every 10 to 100 years.
A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and long-term, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (Ka band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.
A new millimeter-wave cloud radar (MMCR) has been designed to provide detailed, long-term observations of nonprecipitating and weakly precipitating clouds at Cloud and Radiation Testbed (CART) sites of the Department of Energy's Atmospheric Radiation Measurement (ARM) program. Scientific requirements included excellent sensitivity and vertical resolution to detect weak and thin multiple layers of ice and liquid water clouds over the sites and long-term, unattended operations in remote locales. In response to these requirements, the innovative radar design features a vertically pointing, single-polarization, Doppler system operating at 35 GHz (Ka band). It uses a low-peak-power transmitter for long-term reliability and high-gain antenna and pulse-compressed waveforms to maximize sensitivity and resolution. The radar uses the same kind of signal processor as that used in commercial wind profilers. The first MMCR began operations at the CART in northern Oklahoma in late 1996 and has operated continuously there for thousands of hours. It routinely provides remarkably detailed images of the ever-changing cloud structure and kinematics over this densely instrumented site. Examples of the data are presented. The radar measurements will greatly improve quantitative documentation of cloud conditions over the CART sites and will bolster ARM research to understand how clouds impact climate through their effects on radiative transfer. Millimeter-wave radars such as the MMCR also have potential applications in the fields of aviation weather, weather modification, and basic cloud physics research.
Abstract
The European Severe Storms Laboratory (ESSL) was founded in 2006 to advance the science and forecasting of severe convective storms in Europe. ESSL was a grassroots effort of individual scientists from various European countries. The purpose of this article is to describe the 10-yr history of ESSL and present a sampling of its successful activities. Specifically, ESSL developed and manages the only multinational database of severe weather reports in Europe: the European Severe Weather Database (ESWD). Despite efforts to eliminate biases, the ESWD still suffers from spatial inhomogeneities in data collection, which motivates ESSL’s research into modeling climatologies by combining ESWD data with reanalysis data. ESSL also established its ESSL Testbed to evaluate developmental forecast products and to provide training to forecasters. The testbed is organized in close collaboration with several of Europe’s national weather services. In addition, ESSL serves a central role among the European scientific and forecast communities for convective storms, specifically through its training activities and the series of European Conferences on Severe Storms. Finally, ESSL conducts wind and tornado damage assessments, highlighted by its recent survey of a violent tornado in northern Italy.
Abstract
The European Severe Storms Laboratory (ESSL) was founded in 2006 to advance the science and forecasting of severe convective storms in Europe. ESSL was a grassroots effort of individual scientists from various European countries. The purpose of this article is to describe the 10-yr history of ESSL and present a sampling of its successful activities. Specifically, ESSL developed and manages the only multinational database of severe weather reports in Europe: the European Severe Weather Database (ESWD). Despite efforts to eliminate biases, the ESWD still suffers from spatial inhomogeneities in data collection, which motivates ESSL’s research into modeling climatologies by combining ESWD data with reanalysis data. ESSL also established its ESSL Testbed to evaluate developmental forecast products and to provide training to forecasters. The testbed is organized in close collaboration with several of Europe’s national weather services. In addition, ESSL serves a central role among the European scientific and forecast communities for convective storms, specifically through its training activities and the series of European Conferences on Severe Storms. Finally, ESSL conducts wind and tornado damage assessments, highlighted by its recent survey of a violent tornado in northern Italy.
Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address several problems, including the cross-shore variability and turbulent structure of the marine boundary layer, the influence of the coast on the development of the marine layer and clouds, the ageostrophy of the flow, the dynamics of trapped events, the parameterization of surface fluxes, and the supercriticality of the marine layer.
Based in Monterey, California, the National Center for Atmospheric Research (NCAR) C-130 Hercules and the University of North Carolina Piper Seneca obtained a comprehensive set of measurements on the structure of the marine layer. The study focused on the effects of prominent topographic features on the wind. Downstream of capes and points, narrow bands of high winds are frequently encountered. The NCAR-designed Scanning Aerosol Backscatter Lidar (SABL) provided a unique opportunity to connect changes in the depth of the boundary layer with specific features in the dynamics of the flow field.
An integral part of the experiment was the use of numerical models as forecast and diagnostic tools. The Naval Research Laboratory's Coupled Ocean Atmosphere Model System (COAMPS) provided high-resolution forecasts of the wind field in the vicinity of capes and points, which aided the deployment of the aircraft. Subsequently, this model and the MIUU (University of Uppsala) numerical model were used to support the analysis of the field data.
These are some of the most comprehensive measurements of the topographically forced marine layer that have been collected. SABL proved to be an exceptionally useful tool to resolve the small-scale structure of the boundary layer and, combined with in situ turbulence measurements, provides new insight into the structure of the marine atmosphere. Measurements were made sufficiently far offshore to distinguish between the coastal and open ocean effects. COAMPS proved to be an excellent forecast tool and both it and the MIUU model are integral parts of the ongoing analysis. The results highlight the large spatial variability that occurs directly in response to topographic effects. Routine measurements are insufficient to resolve this variability. Numerical weather prediction model boundary conditions cannot properly define the forecast system and often underestimate the wind speed and surface wave conditions in the nearshore region.
This study was a collaborative effort between the National Science Foundation, the Office of Naval Research, the Naval Research Laboratory, and the National Oceanographic and Atmospheric Administration.
Some of the highlights of an experiment designed to study coastal atmospheric phenomena along the California coast (Coastal Waves 1996 experiment) are described. This study was designed to address several problems, including the cross-shore variability and turbulent structure of the marine boundary layer, the influence of the coast on the development of the marine layer and clouds, the ageostrophy of the flow, the dynamics of trapped events, the parameterization of surface fluxes, and the supercriticality of the marine layer.
Based in Monterey, California, the National Center for Atmospheric Research (NCAR) C-130 Hercules and the University of North Carolina Piper Seneca obtained a comprehensive set of measurements on the structure of the marine layer. The study focused on the effects of prominent topographic features on the wind. Downstream of capes and points, narrow bands of high winds are frequently encountered. The NCAR-designed Scanning Aerosol Backscatter Lidar (SABL) provided a unique opportunity to connect changes in the depth of the boundary layer with specific features in the dynamics of the flow field.
An integral part of the experiment was the use of numerical models as forecast and diagnostic tools. The Naval Research Laboratory's Coupled Ocean Atmosphere Model System (COAMPS) provided high-resolution forecasts of the wind field in the vicinity of capes and points, which aided the deployment of the aircraft. Subsequently, this model and the MIUU (University of Uppsala) numerical model were used to support the analysis of the field data.
These are some of the most comprehensive measurements of the topographically forced marine layer that have been collected. SABL proved to be an exceptionally useful tool to resolve the small-scale structure of the boundary layer and, combined with in situ turbulence measurements, provides new insight into the structure of the marine atmosphere. Measurements were made sufficiently far offshore to distinguish between the coastal and open ocean effects. COAMPS proved to be an excellent forecast tool and both it and the MIUU model are integral parts of the ongoing analysis. The results highlight the large spatial variability that occurs directly in response to topographic effects. Routine measurements are insufficient to resolve this variability. Numerical weather prediction model boundary conditions cannot properly define the forecast system and often underestimate the wind speed and surface wave conditions in the nearshore region.
This study was a collaborative effort between the National Science Foundation, the Office of Naval Research, the Naval Research Laboratory, and the National Oceanographic and Atmospheric Administration.
The Lightning Mapper Sensor is proposed as an instrument for use on a geosynchronous satellite in the late 1980s to monitor lightning activity continuously over broad areas of the earth. The system was suggested in response to a variety of needs and the resulting data will provide important research information for such fields of geoscience as magnetospheric and ionospheric physics, atmospheric electricity, atmospheric chemistry, and storm physics. The research applications of Lightning Mapper Sensor data and related research programs are explored and sensor requirements are discussed.
The Lightning Mapper Sensor is proposed as an instrument for use on a geosynchronous satellite in the late 1980s to monitor lightning activity continuously over broad areas of the earth. The system was suggested in response to a variety of needs and the resulting data will provide important research information for such fields of geoscience as magnetospheric and ionospheric physics, atmospheric electricity, atmospheric chemistry, and storm physics. The research applications of Lightning Mapper Sensor data and related research programs are explored and sensor requirements are discussed.
