The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Mingteh Chang - One of the best experts on this subject based on the ideXlab platform.
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Field assessments on the accuracy of spherical Gauges in rainfall measurements
Hydrological Processes, 2005Co-Authors: Mingteh Chang, Lee HarrisonAbstract:In an effort to reduce wind effect on rainfall catch to a minimum level, Chang and Flannery (2001. Hydrological Processes15: 643–654) designed two spherical orifices to modify the standard Gauge and other Gauges in use today. Because of the spherical shape, the two orifices will catch rain with an effective diameter always equal to the actual diameter, regardless of wind speed and direction. This report covers the testing of spherical Gauges at two different locations, one at the City Landfill, Nacogdoches, TX, and the other at the NWS Forecast Office, Shreveport, LA. Based on 131 storms at Nacogdoches and 94 storms at Shreveport, observed between May 1998 and February 2001, the results showed: (1) spherical Gauges recorded an average 6–9% greater than standard Gauge and 3–4% less than Pit Gauge, only 1–2% less than reported in the original study; (2) the catch of spherical Gauges was not significantly affected by three Gauge heights at 0·91, 1·83, and 2·74 m above the ground, but catch by the standard Gauge decreased with increasing Gauge height; (3) improvements of the spherical Gauges were most significant for larger storms and for winds at higher speeds; (4) the spherical Gauge with cylinders recorded 1–2% more rainfall than the spherical Gauge with vanes; and (5) correlation coefficients between catch deficiencies and wind speed were low and weak because of the distance and height of the existing wind sensor. Owing to greater surface wetting and evaporation loss, the spherical Gauges may underestimate rainfall catch by standard Gauge for small storms (generally less than 5·0 mm), especially on hot summer afternoons and for smaller storms. However, the underestimates do not overshadow the merits of spherical Gauges, because the differences are too small to be of hydrologic significance. Using polyethylene or other synthesized materials to construct spherical orifices may improve the catch for small storms. The results of the study agreed with the previous claims that spherical Gauges are effective in reducing wind effects on rainfall measurements. The spherical Gauges could greatly improve the accuracy of hydrologic simulations and the efficiency on the designs and management of water resources. They are suitable for large-scale applications. Copyright © 2004 John Wiley & Sons, Ltd.
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Spherical Gauges for improving the accuracy of rainfall measurements
Hydrological Processes, 2001Co-Authors: Mingteh Chang, Lee A. FlanneryAbstract:Rain-Gauge catch efficiencies are affected by wind. Wind makes raindrops fall at an angle of inclination and the effective diameter of the rain Gauge orifice smaller than if raindrops fall into the Gauge vertically. Two spherical and two semi-spherical orifices were designed to modify standard Gauges and others in use today. The two spherical orifices catch rain with an effective diameter always equal to the actual diameter regardless of wind speed and direction. The semi-spherical orifices, used side-by-side with a standard Gauge, correct 50% of catch deficiencies made by the standard Gauge. Tests based on 115 storms show that the four new Gauges caught more rainfall than the standard Gauge, with an average catch increase ranging from 8% to 16%. Compared with the Pit Gauge, average deficiency in catch ranged from −1% (spherical rain Gauge orifice with cylinders) to 4%, whereas the deficiency for the standard Gauge was −10%. Percentage deficiencies of the new Gauges were positively affected by wind speed, raindrop inclination and rainfall intensity. Although the new Gauges tended to underestimate the standard Gauge in small storms (
Lee Harrison - One of the best experts on this subject based on the ideXlab platform.
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Field assessments on the accuracy of spherical Gauges in rainfall measurements
Hydrological Processes, 2005Co-Authors: Mingteh Chang, Lee HarrisonAbstract:In an effort to reduce wind effect on rainfall catch to a minimum level, Chang and Flannery (2001. Hydrological Processes15: 643–654) designed two spherical orifices to modify the standard Gauge and other Gauges in use today. Because of the spherical shape, the two orifices will catch rain with an effective diameter always equal to the actual diameter, regardless of wind speed and direction. This report covers the testing of spherical Gauges at two different locations, one at the City Landfill, Nacogdoches, TX, and the other at the NWS Forecast Office, Shreveport, LA. Based on 131 storms at Nacogdoches and 94 storms at Shreveport, observed between May 1998 and February 2001, the results showed: (1) spherical Gauges recorded an average 6–9% greater than standard Gauge and 3–4% less than Pit Gauge, only 1–2% less than reported in the original study; (2) the catch of spherical Gauges was not significantly affected by three Gauge heights at 0·91, 1·83, and 2·74 m above the ground, but catch by the standard Gauge decreased with increasing Gauge height; (3) improvements of the spherical Gauges were most significant for larger storms and for winds at higher speeds; (4) the spherical Gauge with cylinders recorded 1–2% more rainfall than the spherical Gauge with vanes; and (5) correlation coefficients between catch deficiencies and wind speed were low and weak because of the distance and height of the existing wind sensor. Owing to greater surface wetting and evaporation loss, the spherical Gauges may underestimate rainfall catch by standard Gauge for small storms (generally less than 5·0 mm), especially on hot summer afternoons and for smaller storms. However, the underestimates do not overshadow the merits of spherical Gauges, because the differences are too small to be of hydrologic significance. Using polyethylene or other synthesized materials to construct spherical orifices may improve the catch for small storms. The results of the study agreed with the previous claims that spherical Gauges are effective in reducing wind effects on rainfall measurements. The spherical Gauges could greatly improve the accuracy of hydrologic simulations and the efficiency on the designs and management of water resources. They are suitable for large-scale applications. Copyright © 2004 John Wiley & Sons, Ltd.
Lee A. Flannery - One of the best experts on this subject based on the ideXlab platform.
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Spherical Gauges for improving the accuracy of rainfall measurements
Hydrological Processes, 2001Co-Authors: Mingteh Chang, Lee A. FlanneryAbstract:Rain-Gauge catch efficiencies are affected by wind. Wind makes raindrops fall at an angle of inclination and the effective diameter of the rain Gauge orifice smaller than if raindrops fall into the Gauge vertically. Two spherical and two semi-spherical orifices were designed to modify standard Gauges and others in use today. The two spherical orifices catch rain with an effective diameter always equal to the actual diameter regardless of wind speed and direction. The semi-spherical orifices, used side-by-side with a standard Gauge, correct 50% of catch deficiencies made by the standard Gauge. Tests based on 115 storms show that the four new Gauges caught more rainfall than the standard Gauge, with an average catch increase ranging from 8% to 16%. Compared with the Pit Gauge, average deficiency in catch ranged from −1% (spherical rain Gauge orifice with cylinders) to 4%, whereas the deficiency for the standard Gauge was −10%. Percentage deficiencies of the new Gauges were positively affected by wind speed, raindrop inclination and rainfall intensity. Although the new Gauges tended to underestimate the standard Gauge in small storms (
Claude E Duchon - One of the best experts on this subject based on the ideXlab platform.
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Observing the May 2015 Record Rainfall at Norman, Oklahoma, Using Various Methods
Journal of Hydrometeorology, 2017Co-Authors: Claude E Duchon, Christopher A. Fiebrich, Bradley G. IllstonAbstract:AbstractThe May 2015 record rainfall that occurred across Oklahoma was the result of a large number of high-intensity rain events. A unique set of observations from Gauges in the Oklahoma Mesonet, the NWS Cooperative Observer (COOP) network, the Community Collaborative Rain, Hail and Snow (CoCoRaHS) network, an experimental Pit Gauge system, and NWS radar was available that covered an area in and around Norman, Oklahoma. This paper documents the performance of the various Gauges throughout the course of the month. Key findings are 1) observations from all methods significantly exceeded the 200-yr return interval; 2) a weighing-bucket Gauge at ground level recorded amounts up to 4.5% higher than a similarly located ground-level tipping-bucket Gauge and up to 8.2% higher than a nearby aboveground tipping-bucket Gauge; 3) a manual COOP Gauge recorded nearly identical (within 1.2%) observations as compared to an automated tipping-bucket Gauge at a collocated Mesonet station; and 4) observations from 26 CoCoRa...
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comparative rainfall observations from Pit and aboveground rain Gauges with and without wind shields
Water Resources Research, 2001Co-Authors: Claude E Duchon, Gavin R EssenbergAbstract:A study of rain Gauge observations was initiated in 1995 to assess the magnitude of undercatch due to wind and the effect of reducing undercatch using an Alter-type wind shield. The observation site was near the Norman, Oklahoma, airport with good exposure in all directions. The experimental setup comprised three tipping-bucket rain Gauges, three weighing-bucket rain Gauges, and anemometers at 1 and 2 m. For each type of Gauge, one was placed in a Pit with its orifice at ground level, and the other two were placed above ground, one with an Alter shield and one without. One-minute rainfall accumulations and wind speed averages were obtained from 101 rainfall events over 30 months. The results show that for typical rainfall events, the undercatch of the unshielded tipping-bucket rain Gauges was 4% relative to the tipping-bucket Pit Gauge. The comparable figure for the unshielded weighing-bucket Gauge was 5%. Both Alter-shielded Gauges showed less than a 1% reduction in undercatch relative to the unshielded Gauges for typical rainfall events. We discuss the sources of errors that can be expected in similar rain Gauge measurements when the Gauges are properly maintained.
Gavin R Essenberg - One of the best experts on this subject based on the ideXlab platform.
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comparative rainfall observations from Pit and aboveground rain Gauges with and without wind shields
Water Resources Research, 2001Co-Authors: Claude E Duchon, Gavin R EssenbergAbstract:A study of rain Gauge observations was initiated in 1995 to assess the magnitude of undercatch due to wind and the effect of reducing undercatch using an Alter-type wind shield. The observation site was near the Norman, Oklahoma, airport with good exposure in all directions. The experimental setup comprised three tipping-bucket rain Gauges, three weighing-bucket rain Gauges, and anemometers at 1 and 2 m. For each type of Gauge, one was placed in a Pit with its orifice at ground level, and the other two were placed above ground, one with an Alter shield and one without. One-minute rainfall accumulations and wind speed averages were obtained from 101 rainfall events over 30 months. The results show that for typical rainfall events, the undercatch of the unshielded tipping-bucket rain Gauges was 4% relative to the tipping-bucket Pit Gauge. The comparable figure for the unshielded weighing-bucket Gauge was 5%. Both Alter-shielded Gauges showed less than a 1% reduction in undercatch relative to the unshielded Gauges for typical rainfall events. We discuss the sources of errors that can be expected in similar rain Gauge measurements when the Gauges are properly maintained.