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- Author or Editor: James K. Luers x
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Abstract
A technique was developed to calculate the radiosonde temperature error as a function of altitude under different environmental conditions. The environmental conditions analyzed include the surface (or cloud) temperature, the atmospheric gaseous constituents, the aerosol and thermodynamic structure of the atmosphere, the solar elevation angle, the solar albedo, the rise rate of the balloon, and the atmospheric density.
The technique was validated by comparing calculated results with data from flights of experimental radiosondes containing the NWS radiosonde's rod thermistor and three other thermistors with different radiative coatings. The experimental measurements were compared with that predicted by the modeling technique. Comparisons were made between eight flights: four at night, three daylight, and one twilight, which occurred during all seasons of the year and under various surface conditions. The comparisons showed good agreement. For the flights analyzed the temperature error at nighttime was small, below 20 km, and increased negatively above this altitude. At 30 km the error generally exceeded −1°K. During the daytime the temperature error was positive and sometimes took on its maximum value as low as 20 km. At altitudes near 30 km and above, the error often decreased due to influences of an increasing atmospheric temperature. Results from this study suggest that the radiosonde temperature error is likely to differ at different latitudes and solar elevation angles because of differing radiative fluxes to the thermistor and because of differing atmospheric temperature profiles.
Abstract
A technique was developed to calculate the radiosonde temperature error as a function of altitude under different environmental conditions. The environmental conditions analyzed include the surface (or cloud) temperature, the atmospheric gaseous constituents, the aerosol and thermodynamic structure of the atmosphere, the solar elevation angle, the solar albedo, the rise rate of the balloon, and the atmospheric density.
The technique was validated by comparing calculated results with data from flights of experimental radiosondes containing the NWS radiosonde's rod thermistor and three other thermistors with different radiative coatings. The experimental measurements were compared with that predicted by the modeling technique. Comparisons were made between eight flights: four at night, three daylight, and one twilight, which occurred during all seasons of the year and under various surface conditions. The comparisons showed good agreement. For the flights analyzed the temperature error at nighttime was small, below 20 km, and increased negatively above this altitude. At 30 km the error generally exceeded −1°K. During the daytime the temperature error was positive and sometimes took on its maximum value as low as 20 km. At altitudes near 30 km and above, the error often decreased due to influences of an increasing atmospheric temperature. Results from this study suggest that the radiosonde temperature error is likely to differ at different latitudes and solar elevation angles because of differing radiative fluxes to the thermistor and because of differing atmospheric temperature profiles.
Abstract
The new F-Thermocap sensor used on the Vaisala RS90 radiosonde is a miniaturized capacitive sensor designed to decrease the solar radiation error and the time lag error that exists with the Thermocap sensor used on the RS80 radiosonde. The heating and response characteristics of the F-Thermocap sensor were evaluated by developing a heat balance model, RS90COR, that calculates the temperature of the sensor relative to the air temperature in various flight environments. The temperature of the F-Thermocap sensor was found to be essentially identical to that of the atmosphere in all nighttime environments. In daytime conditions solar heating of the sensor increases its temperature to slightly above that of the ambient air. The daytime error increases with altitude but remains less than 0.5°C to an altitude of 35 km. The time lag error of the miniaturized sensor is insignificant. The RS90COR modeling results were validated by using model-predicted errors to correct RS90 and RS80 temperature profiles from sondes flown on the same balloon. The corrected profiles agreed, except for a temperature bias of 0.1°–0.3°C that results from a calibration or electronics error in one or both of the sondes. A new source of temperature error in daytime flights of RS80, RS90, and VIZ radiosondes has been discovered that relates to the orientation of the sensor with respect to the impinging solar radiation. This orientation error is smallest in the RS90 sensor.
Abstract
The new F-Thermocap sensor used on the Vaisala RS90 radiosonde is a miniaturized capacitive sensor designed to decrease the solar radiation error and the time lag error that exists with the Thermocap sensor used on the RS80 radiosonde. The heating and response characteristics of the F-Thermocap sensor were evaluated by developing a heat balance model, RS90COR, that calculates the temperature of the sensor relative to the air temperature in various flight environments. The temperature of the F-Thermocap sensor was found to be essentially identical to that of the atmosphere in all nighttime environments. In daytime conditions solar heating of the sensor increases its temperature to slightly above that of the ambient air. The daytime error increases with altitude but remains less than 0.5°C to an altitude of 35 km. The time lag error of the miniaturized sensor is insignificant. The RS90COR modeling results were validated by using model-predicted errors to correct RS90 and RS80 temperature profiles from sondes flown on the same balloon. The corrected profiles agreed, except for a temperature bias of 0.1°–0.3°C that results from a calibration or electronics error in one or both of the sondes. A new source of temperature error in daytime flights of RS80, RS90, and VIZ radiosondes has been discovered that relates to the orientation of the sensor with respect to the impinging solar radiation. This orientation error is smallest in the RS90 sensor.
Abstract
The error in horizontal wind field measurements as computed from the trajectory of balloons with linear and quadratic rise rates (as functions of altitude) has been derived. Balloon trajectories through light, moderate and severe wind fields have been considered. Figures are presented which show the wind error vs altitude for various rise rates in each wind field, assuming linear smoothing of the trajectory data. The rise rate profile of the Jimsphere is analyzed as a special case. The results and figures presented are useful in determining the ultimate capability of rising balloon systems in general and for the Jimsphere system in particular for measuring wind from the surface to 18 km. Using the figures presented, one can estimate the wind accuracy that can be achieved by any type of rising balloon by knowing only its rise rate behavior vs altitude. In addition, the results can be used in balloon design to determine what rise rate function is needed to achieve specified wind accuracies. A table is presented which shows the, balloon radius for smooth and roughened spheres needed to achieve 2–20 m sec−1 rise rates at 10 and 14 km altitudes. The wind-following capability for balloons of each radius is determined. Even balloons of very large diameter are shown to provide excellent response to fine-scale wind fluctuations.
Abstract
The error in horizontal wind field measurements as computed from the trajectory of balloons with linear and quadratic rise rates (as functions of altitude) has been derived. Balloon trajectories through light, moderate and severe wind fields have been considered. Figures are presented which show the wind error vs altitude for various rise rates in each wind field, assuming linear smoothing of the trajectory data. The rise rate profile of the Jimsphere is analyzed as a special case. The results and figures presented are useful in determining the ultimate capability of rising balloon systems in general and for the Jimsphere system in particular for measuring wind from the surface to 18 km. Using the figures presented, one can estimate the wind accuracy that can be achieved by any type of rising balloon by knowing only its rise rate behavior vs altitude. In addition, the results can be used in balloon design to determine what rise rate function is needed to achieve specified wind accuracies. A table is presented which shows the, balloon radius for smooth and roughened spheres needed to achieve 2–20 m sec−1 rise rates at 10 and 14 km altitudes. The wind-following capability for balloons of each radius is determined. Even balloons of very large diameter are shown to provide excellent response to fine-scale wind fluctuations.
Abstract
Ten of the most common radiosondes used throughout the world since 1960 have been evaluated concerning potential use of their temperature data for climate studies. The VIZ; Space Data Corp.; Chinese GZZ; Japanese RS2-80; Russian RKZ, MARS, and A-22; and Vaisala RS80, RS 12/15, and RS18/21 radiosondes were evaluated by modeling the temperature of the sensing element relative to the temperature of the air in which it is immersed. The difference, designated as the temperature error, was calculated under various environmental conditions. Validation and sensitivity analysis studies were performed on each radiosonde model as a means of estimating the environmental parameters that influence the temperature error and the resulting accuracy of the day and nighttime temperature profiles. Environmental parameters to which some sondes were sensitive include cloud cover, surface temperature, solar angle, ambient temperature profile, blackbody temperature, and the ventilation velocity. The ventilation velocity was found to depend strongly on the position of the sensor in the balloon wake. It is believed that the results of these analyses provide the best guidelines available to anyone wishing to perform climate studies using radiosonde data.
The research work presented in this paper indicates that climate trends can currently be estimated with a subset of the worldwide upper-air data. Trends can be calculated for monthly averaged, nighttime soundings with some confidence for the Vaisala RS80 (models not using the RSN80 and RSN86 corrections), Vaisala RS 12/15, Vaisala RS 18/21, Chinese GZZ (below 25 km), Russian RKZ, Russian MARS, and Russian A-22 (below 20 km) radiosonde models. The analysis presented in this paper shows that all of the above radiosondes have small errors in individual radiosonde soundings at night (< ±1°C) and the errors of the monthly averaged data are estimated to be less than ±0.5°C, except for the A-22 (±0.8°C). In addition, temperature data from the Japanese RS-2-80, the Russian A-22 above 20 km, Vaisala RS80 (RSN80 and RSN86 corrections applied), and VIZ can be made suitable for climate analysis if the appropriate temperature correction models are used to correct the data.
Abstract
Ten of the most common radiosondes used throughout the world since 1960 have been evaluated concerning potential use of their temperature data for climate studies. The VIZ; Space Data Corp.; Chinese GZZ; Japanese RS2-80; Russian RKZ, MARS, and A-22; and Vaisala RS80, RS 12/15, and RS18/21 radiosondes were evaluated by modeling the temperature of the sensing element relative to the temperature of the air in which it is immersed. The difference, designated as the temperature error, was calculated under various environmental conditions. Validation and sensitivity analysis studies were performed on each radiosonde model as a means of estimating the environmental parameters that influence the temperature error and the resulting accuracy of the day and nighttime temperature profiles. Environmental parameters to which some sondes were sensitive include cloud cover, surface temperature, solar angle, ambient temperature profile, blackbody temperature, and the ventilation velocity. The ventilation velocity was found to depend strongly on the position of the sensor in the balloon wake. It is believed that the results of these analyses provide the best guidelines available to anyone wishing to perform climate studies using radiosonde data.
The research work presented in this paper indicates that climate trends can currently be estimated with a subset of the worldwide upper-air data. Trends can be calculated for monthly averaged, nighttime soundings with some confidence for the Vaisala RS80 (models not using the RSN80 and RSN86 corrections), Vaisala RS 12/15, Vaisala RS 18/21, Chinese GZZ (below 25 km), Russian RKZ, Russian MARS, and Russian A-22 (below 20 km) radiosonde models. The analysis presented in this paper shows that all of the above radiosondes have small errors in individual radiosonde soundings at night (< ±1°C) and the errors of the monthly averaged data are estimated to be less than ±0.5°C, except for the A-22 (±0.8°C). In addition, temperature data from the Japanese RS-2-80, the Russian A-22 above 20 km, Vaisala RS80 (RSN80 and RSN86 corrections applied), and VIZ can be made suitable for climate analysis if the appropriate temperature correction models are used to correct the data.
Abstract
The National Weather Service VIZ radiosonde and the Vaisala RS-80 radiosondes are used worldwide to obtain upper-air measurements of atmospheric temperature and moisture. The temperature measured by each sensor is not equal to the atmospheric temperature due to solar and infrared irradiation of the sensor, heat conduction to the sensor from its attachment points, and radiation emitted by the sensor. Presently, only the RS-80 radiosonde applies corrections to the sensor temperature to compensate for these heating sources, and this correction is only considered to be a function of solar angle and pressure.
Temperature correction models VIZCOR (VIZ sonde) and VAICOR (Vaisala RS-80 sonde) have been developed that derive the atmospheric temperature from the sensor temperature, taking into account all significant environmental processes that influence the beat transfer to the sensor. These models have been validated by comparing their corrected profiles with atmospheric temperature profiles derived from the NASA multithermistor radiosonde. All three radiosondes were flown on the same balloon during the potential reference radiosonde intercomparison. Excellent agreement has been found between all profiles up to an altitude of 30 km. Since the significant error sources in the VIZCOR, VAICOR, and multithermistor techniques are largely independent, agreement between all profiles implies that the corrected sensor profiles are providing an unbiased estimate of the true atmospheric temperature.
Abstract
The National Weather Service VIZ radiosonde and the Vaisala RS-80 radiosondes are used worldwide to obtain upper-air measurements of atmospheric temperature and moisture. The temperature measured by each sensor is not equal to the atmospheric temperature due to solar and infrared irradiation of the sensor, heat conduction to the sensor from its attachment points, and radiation emitted by the sensor. Presently, only the RS-80 radiosonde applies corrections to the sensor temperature to compensate for these heating sources, and this correction is only considered to be a function of solar angle and pressure.
Temperature correction models VIZCOR (VIZ sonde) and VAICOR (Vaisala RS-80 sonde) have been developed that derive the atmospheric temperature from the sensor temperature, taking into account all significant environmental processes that influence the beat transfer to the sensor. These models have been validated by comparing their corrected profiles with atmospheric temperature profiles derived from the NASA multithermistor radiosonde. All three radiosondes were flown on the same balloon during the potential reference radiosonde intercomparison. Excellent agreement has been found between all profiles up to an altitude of 30 km. Since the significant error sources in the VIZCOR, VAICOR, and multithermistor techniques are largely independent, agreement between all profiles implies that the corrected sensor profiles are providing an unbiased estimate of the true atmospheric temperature.
Abstract
Using Dobson spectrophotometer measurements of total ozone as a comparison, an analysis of the Electrochemical Concentration Cell (ECC) ozonesonde's measurement accuracy is presented. Days of conjunctive ECC-Dobson observations (from 1970 to 1976 at Wallops Flight Center) provide a set of 123 pairs of total ozone values. Sample set statistics are generated with means and standard deviations of total ozone values and differences being noted. An in-depth study of factors such as time differences between associated observations, integration techniques used, assumptions used in calculating residual ozone and other possible sources of errors are examined. Short-period changes in total ozone using Dobson data during the observational period are also described.
Abstract
Using Dobson spectrophotometer measurements of total ozone as a comparison, an analysis of the Electrochemical Concentration Cell (ECC) ozonesonde's measurement accuracy is presented. Days of conjunctive ECC-Dobson observations (from 1970 to 1976 at Wallops Flight Center) provide a set of 123 pairs of total ozone values. Sample set statistics are generated with means and standard deviations of total ozone values and differences being noted. An in-depth study of factors such as time differences between associated observations, integration techniques used, assumptions used in calculating residual ozone and other possible sources of errors are examined. Short-period changes in total ozone using Dobson data during the observational period are also described.
Abstract
Inhomogeneities in U.S. radiosonde data that used the VIZ and Vaisala RS80 cannot be explained by radiation errors, which can be removed by the heat balance models. WMO intercomparision data, modeling results, temperature time series, and 1200 minus 0000 UTC temperature differences are examined to show that there appears to be an error in the U.S. RS80/RSN93 temperature correction software.
Radiosonde soundings taken at U.S. stations that launch Vaisala RS80 radiosondes, which are integrated within the National Weather Service (NWS) Microcomputer Automatic Radio-Theodolite (Micro-ART) system, should not be used in climate studies since there is a large systematic error of unknown origin in the temperature data. This paper is the first of two and is primarily concerned with the midtroposphere. The second paper discusses the large unexplained 0000 and 1200 UTC differences in the stratosphere.
Abstract
Inhomogeneities in U.S. radiosonde data that used the VIZ and Vaisala RS80 cannot be explained by radiation errors, which can be removed by the heat balance models. WMO intercomparision data, modeling results, temperature time series, and 1200 minus 0000 UTC temperature differences are examined to show that there appears to be an error in the U.S. RS80/RSN93 temperature correction software.
Radiosonde soundings taken at U.S. stations that launch Vaisala RS80 radiosondes, which are integrated within the National Weather Service (NWS) Microcomputer Automatic Radio-Theodolite (Micro-ART) system, should not be used in climate studies since there is a large systematic error of unknown origin in the temperature data. This paper is the first of two and is primarily concerned with the midtroposphere. The second paper discusses the large unexplained 0000 and 1200 UTC differences in the stratosphere.
CREATING CLIMATE REFERENCE DATASETS
CARDS Workshop on Adjusting Radiosonde Temperature Data for Climate Monitoring
Homogeneous upper-air temperature time series are necessary for climate change detection and attribution. About 20 participants met at the National Climatic Data Center in Asheville, North Carolina on 11–12 October 2000 to discuss methods of adjusting radiosonde data for inhomogeneities arising from instrument and other changes. Representatives of several research groups described their methods for identifying change points and adjusting temperature time series and compared the results of applying these methods to data from 12 radiosonde stations. The limited agreement among these results and the potential impact of these adjustments on upper-air trends estimates indicate a need for further work in this area and for greater attention to homogeneity issues in planning future changes in radiosonde observations.
Homogeneous upper-air temperature time series are necessary for climate change detection and attribution. About 20 participants met at the National Climatic Data Center in Asheville, North Carolina on 11–12 October 2000 to discuss methods of adjusting radiosonde data for inhomogeneities arising from instrument and other changes. Representatives of several research groups described their methods for identifying change points and adjusting temperature time series and compared the results of applying these methods to data from 12 radiosonde stations. The limited agreement among these results and the potential impact of these adjustments on upper-air trends estimates indicate a need for further work in this area and for greater attention to homogeneity issues in planning future changes in radiosonde observations.
