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- Author or Editor: C. L. Parsons x
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Abstract
A technique is presented whereby the presence of swell can be determined from satellites in orbit. Utilizing an empirical model developed during JONSWAP, a parameter is derived that is shown to be related to the percentage swell present as reported by National Weather Service hindcasters. Only data presently available from existing satellite radar altimeters are needed to map those areas of the oceans dominated by swell.
Abstract
A technique is presented whereby the presence of swell can be determined from satellites in orbit. Utilizing an empirical model developed during JONSWAP, a parameter is derived that is shown to be related to the percentage swell present as reported by National Weather Service hindcasters. Only data presently available from existing satellite radar altimeters are needed to map those areas of the oceans dominated by swell.
Abstract
The pressure sensors on balloon-borne sondes relate the sonde measurements to height above the earth's surface through the hypsometric equation. It is crucial that sondes used to explore the vertical structure of the atmosphere do not contribute significant height errors to their measurements of atmospheric constituent concentrations and properties. To describe quantitatively the magnitude of the error introduced by the pressure sensor, a series of radiosonde flights was conducted at Wallops Island, Virginia. In most cases, each flight consisted of two sondes attached to a single balloon; each flight was tracked by a highly accurate C-band radar. For the first 19 radiosondes, the standard aneroid cell-baroswitch assembly used by the National Weather Service was the pressure sensor. The last 26 radiosondes were equipped with a premium grade aneroid cell-baroswitch assembly sensor and with a hypsometer. Analysis has revealed that both aneroid cell-baroswitch sensors become increasingly inaccurate with altitude. At 35 km altitude, the standard deviation of the sonde sensor-radar differences was found to be 1.838 and 0.742 km, respectively, for the standard and premium sensors. On the other hand, the hypsometer-radar differences are not strongly dependent upon altitude, and the standard deviation of the differences at 34 km was found to be 0.276 km.
Abstract
The pressure sensors on balloon-borne sondes relate the sonde measurements to height above the earth's surface through the hypsometric equation. It is crucial that sondes used to explore the vertical structure of the atmosphere do not contribute significant height errors to their measurements of atmospheric constituent concentrations and properties. To describe quantitatively the magnitude of the error introduced by the pressure sensor, a series of radiosonde flights was conducted at Wallops Island, Virginia. In most cases, each flight consisted of two sondes attached to a single balloon; each flight was tracked by a highly accurate C-band radar. For the first 19 radiosondes, the standard aneroid cell-baroswitch assembly used by the National Weather Service was the pressure sensor. The last 26 radiosondes were equipped with a premium grade aneroid cell-baroswitch assembly sensor and with a hypsometer. Analysis has revealed that both aneroid cell-baroswitch sensors become increasingly inaccurate with altitude. At 35 km altitude, the standard deviation of the sonde sensor-radar differences was found to be 1.838 and 0.742 km, respectively, for the standard and premium sensors. On the other hand, the hypsometer-radar differences are not strongly dependent upon altitude, and the standard deviation of the differences at 34 km was found to be 0.276 km.
Abstract
Five ground-based total ozone spectrophotometers were intercompared at Wallops Island, Virginia between October 1979 and January 1981. The tests were conducted to evaluate the stability and accuracy of each instrument over an extended time period. Acceptable performance regarding these two characteristics is essential if an instrument is to be useful in field measurements and network monitoring of the atmospheric total ozone content. The Dobson spectrophotometer was used as the standard of comparison for the Brewer grating spectrophotometer, the USSR M-83 ozonometer, the Canterbury filter photometer, and the SenTran filter photometer. The grating instrument was found to be potentially the equal of the Dobson but was subject to unreliable performance by its rather sophisticated electronic components. The filter photometers performed acceptably for short periods but filter aging and eventual degradation rendered both units unusable before the end of the intercomparison. Finally, the M-83 results were found to be in acceptable agreement with the Dobson throughout the period when certain qualifications are invoked. The accuracy of a single M-83 ozone measurement may be low. Averages tend to improve its agreement with the Dobson. Airmass dependencies appear to be appropriately accounted for, but zenith cloudy measurements are too high by ∼30%.
Abstract
Five ground-based total ozone spectrophotometers were intercompared at Wallops Island, Virginia between October 1979 and January 1981. The tests were conducted to evaluate the stability and accuracy of each instrument over an extended time period. Acceptable performance regarding these two characteristics is essential if an instrument is to be useful in field measurements and network monitoring of the atmospheric total ozone content. The Dobson spectrophotometer was used as the standard of comparison for the Brewer grating spectrophotometer, the USSR M-83 ozonometer, the Canterbury filter photometer, and the SenTran filter photometer. The grating instrument was found to be potentially the equal of the Dobson but was subject to unreliable performance by its rather sophisticated electronic components. The filter photometers performed acceptably for short periods but filter aging and eventual degradation rendered both units unusable before the end of the intercomparison. Finally, the M-83 results were found to be in acceptable agreement with the Dobson throughout the period when certain qualifications are invoked. The accuracy of a single M-83 ozone measurement may be low. Averages tend to improve its agreement with the Dobson. Airmass dependencies appear to be appropriately accounted for, but zenith cloudy measurements are too high by ∼30%.
Abstract
The Observing System Research and Predictability Experiment (THORPEX) was a 10-yr, international research program organized by the World Meteorological Organization’s World Weather Research Program. THORPEX was motivated by the need to accelerate the rate of improvement in the accuracy of 1-day to 2-week forecasts of high-impact weather for the benefit of society, the economy, and the environment. THORPEX, which took place from 2005 to 2014, was the first major international program focusing on the advancement of global numerical weather prediction systems since the Global Atmospheric Research Program, which took place almost 40 years earlier, from 1967 through 1982. The scientific achievements of THORPEX were accomplished through bringing together scientists from operational centers, research laboratories, and the academic community to collaborate on research that would ultimately advance operational predictive skill. THORPEX included an unprecedented effort to make operational products readily accessible to the broader academic research community, with community efforts focused on problems where challenging science intersected with the potential to accelerate improvements in predictive skill. THORPEX also collaborated with other major programs to identify research areas of mutual interest, such as topics at the intersection of weather and climate. THORPEX research has 1) increased our knowledge of the global-to-regional influences on the initiation, evolution, and predictability of high-impact weather; 2) provided insight into how predictive skill depends on observing strategies and observing systems; 3) improved data assimilation and ensemble forecast systems; 4) advanced knowledge of high-impact weather associated with tropical and polar circulations and their interactions with midlatitude flows; and 5) expanded society’s use of weather information through applied and social science research.
Abstract
The Observing System Research and Predictability Experiment (THORPEX) was a 10-yr, international research program organized by the World Meteorological Organization’s World Weather Research Program. THORPEX was motivated by the need to accelerate the rate of improvement in the accuracy of 1-day to 2-week forecasts of high-impact weather for the benefit of society, the economy, and the environment. THORPEX, which took place from 2005 to 2014, was the first major international program focusing on the advancement of global numerical weather prediction systems since the Global Atmospheric Research Program, which took place almost 40 years earlier, from 1967 through 1982. The scientific achievements of THORPEX were accomplished through bringing together scientists from operational centers, research laboratories, and the academic community to collaborate on research that would ultimately advance operational predictive skill. THORPEX included an unprecedented effort to make operational products readily accessible to the broader academic research community, with community efforts focused on problems where challenging science intersected with the potential to accelerate improvements in predictive skill. THORPEX also collaborated with other major programs to identify research areas of mutual interest, such as topics at the intersection of weather and climate. THORPEX research has 1) increased our knowledge of the global-to-regional influences on the initiation, evolution, and predictability of high-impact weather; 2) provided insight into how predictive skill depends on observing strategies and observing systems; 3) improved data assimilation and ensemble forecast systems; 4) advanced knowledge of high-impact weather associated with tropical and polar circulations and their interactions with midlatitude flows; and 5) expanded society’s use of weather information through applied and social science research.
Abstract
The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at night.
To gain insight into nocturnal MCSs, their essential ingredients, and paths toward improving the relatively poor predictive skill of nocturnal convection in weather and climate models, a large, multiagency field campaign called Plains Elevated Convection At Night (PECAN) was conducted in 2015. PECAN employed three research aircraft, an unprecedented coordinated array of nine mobile scanning radars, a fixed S-band radar, a unique mesoscale network of lower-tropospheric profiling systems called the PECAN Integrated Sounding Array (PISA), and numerous mobile-mesonet surface weather stations. The rich PECAN dataset is expected to improve our understanding and prediction of continental nocturnal warm-season precipitation. This article provides a summary of the PECAN field experiment and preliminary findings.
Abstract
The central Great Plains region in North America has a nocturnal maximum in warm-season precipitation. Much of this precipitation comes from organized mesoscale convective systems (MCSs). This nocturnal maximum is counterintuitive in the sense that convective activity over the Great Plains is out of phase with the local generation of CAPE by solar heating of the surface. The lower troposphere in this nocturnal environment is typically characterized by a low-level jet (LLJ) just above a stable boundary layer (SBL), and convective available potential energy (CAPE) values that peak above the SBL, resulting in convection that may be elevated, with source air decoupled from the surface. Nocturnal MCS-induced cold pools often trigger undular bores and solitary waves within the SBL. A full understanding of the nocturnal precipitation maximum remains elusive, although it appears that bore-induced lifting and the LLJ may be instrumental to convection initiation and the maintenance of MCSs at night.
To gain insight into nocturnal MCSs, their essential ingredients, and paths toward improving the relatively poor predictive skill of nocturnal convection in weather and climate models, a large, multiagency field campaign called Plains Elevated Convection At Night (PECAN) was conducted in 2015. PECAN employed three research aircraft, an unprecedented coordinated array of nine mobile scanning radars, a fixed S-band radar, a unique mesoscale network of lower-tropospheric profiling systems called the PECAN Integrated Sounding Array (PISA), and numerous mobile-mesonet surface weather stations. The rich PECAN dataset is expected to improve our understanding and prediction of continental nocturnal warm-season precipitation. This article provides a summary of the PECAN field experiment and preliminary findings.
