No abstract

[1] A detailed assessment of radiosonde water vapor measurement accuracy throughout the tropospheric column is needed for assessing the impact of observational error on applications that use the radiosonde data as input, such as forecast modeling, radiative transfer calculations, remote sensor retrieval validation, climate trend studies, and development of climatologies and cloud and radiation parameterizations. Six operational radiosonde types were flown together in various combinations with a reference-quality hygrometer during the Atmospheric Infrared Sounder (AIRS) Water Vapor ExperimentGround (AWEX-G), while simultaneous measurements were acquired from Raman lidar and microwave radiometers. This study determines the mean accuracy and variability of the radiosonde water vapor measurements relative to simultaneous measurements from the University of Colorado (CU) Cryogenic Frostpoint Hygrometer (CFH), a referencequality standard of known absolute accuracy. The accuracy and performance characteristics of the following radiosonde types are evaluated: Vaisala RS80-H, RS90, and RS92; Sippican Mark IIa; Modem GL98; and the Meteolabor Snow White hygrometer. A validated correction for sensor time lag error is found to improve the accuracy and reduce the variability of upper tropospheric water vapor measurements from the Vaisala radiosondes. The AWEX data set is also used to derive and validate a new empirical correction that improves the mean calibration accuracy of Vaisala measurements by an amount that depends on the temperature, relative humidity, and sensor type. Fully corrected Vaisala radiosonde measurements are found to be suitably accurate for AIRS validation throughout the troposphere, whereas the other radiosonde types are suitably accurate under only a subset of tropospheric conditions. Although this study focuses on the accuracy of nighttime radiosonde measurements, comparison of Vaisala RS90 measurements to water vapor retrievals from a microwave radiometer reveals a 6-8% dry bias in daytime RS90 measurements that is caused by solar heating of the sensor. An AWEX-like data set of daytime measurements is highly desirable to complete the accuracy assessment, ideally from a tropical location where the full range of tropospheric temperatures can be sampled.

No abstract

Abstract. We present the results of two independent analyses of trends in the vertical distribution of ozone. For most of the ozonesonde stations we use data that were recently reevaluated and reprocessed to improve their quality and internal consistency. The two analyses give similar results for trends in ozone. We attribute differences in results primarily to differences in data selection criteria, rather than in statistical trend models. We find significant decreases

[1] A balloon flight to compare 18 ozonesondes with an ozone photometer and with ozone column measurements from Dobson and Brewer spectrophotometers was completed in April 2004. The core experiment consisted of 12 electrochemical concentration cell ozonesondes, 6 from Science Pump Corporation (SP) and 6 from ENSCI Corporation (ES), prepared with cathode solution concentrations of 0.5% KI (half buffer) and 1.0% KI (full buffer). Auxiliary ozonesondes consisted of two electrochemical concentration cell sondes with 2.0% KI (no buffer), two reconditioned sondes, and two Japanese-KC96 sondes. Precision of each group of similarly prepared ozonesondes was <2-3%. The six ozonesondes prepared according to the manufacturer's recommendations (SP, 1.0% KI, ES 0.5% KI) overestimated the photometer measurements by 5-10% in the stratosphere, but provided ozone columns in good agreement with the ground-based spectrophotometer measurements. This is consistent with the difference ($5%) in ozone photometer and column measurements observed during the experiment. Using cathode cell concentrations of 1.0% KI for ES sondes caused overestimates of the photometer by 10-15% and of ozone column by 5-10%. In contrast, 0.5% KI in SP sondes led to good agreement with the photometer, but underestimates of ozone column. The KC96 sondes underestimated the photometer measurements by about 5-15% at air pressures above 30 hPa. Agreement was within 5% at lower pressures. Diluting the solution concentration and the buffers from 1.0% to 0.5% KI causes an approximately linear pressure-dependent decrease in ozone for both SP and ES sondes, ratio (0.5 KI/1.0 KI) = 0.9 + 0.024 * log 10 (Pressure).

No abstract

Daily ozonesondes were launched from 14 North American sites during August 2006, providing the best set of free tropospheric ozone measurements ever gathered across the continent in a single season. The data reveal a distinct upper tropospheric ozone maximum above eastern North America and centered over the southeastern USA. Recurring each year, the location and strength of the ozone maximum is influenced by the summertime upper tropospheric anticyclone that traps convectively lofted ozone, ozone precursors and lightning NOx above the southeastern USA. The North American summer monsoon that flows northward along the Rocky Mountains is embedded within the western side of the anticyclone and also marks the westernmost extent of the ozone maximum. Removing the influence from stratospheric intrusions, median ozone mixing ratios (78 ppbv) in the upper troposphere (>6 km) above Alabama, near the center of the anticyclone, were nearly twice the level above the U.S. west coast. Simulations by an atmospheric chemistry general circulation model indicate lightning NOx emissions led to the production of 25–30 ppbv of ozone at 250 hPa above the southern United States during the study period. On the regional scale the ozone enhancement above the southeastern United States produced a positive all‐sky adjusted radiative forcing up to 0.50 W m−2.

The Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit/Humidity Sounder for Brazil (AIRS/AMSU/HSB) instrument suite onboard Aqua observes infrared and microwave radiances twice daily over most of the planet. AIRS offers unprecedented radiometric accuracy and signal to noise throughout the thermal infrared. Observations from the combined suite of AIRS, AMSU, and HSB are processed into retrievals of atmospheric parameters such as temperature, water vapor, and trace gases under all but the cloudiest conditions. A more limited retrieval set based on the microwave radiances is obtained under heavy cloud cover. Before measurements and retrievals from AIRS/AMSU/HSB instruments can be fully utilized they must be compared with the best possible in situ and other ancillary "truth" observations. Validation is the process of estimating the measurement and retrieval uncertainties through comparison with a set of correlative data of known uncertainties. The ultimate goal of the validation effort is retrieved product uncertainties constrained to those of radiosondes: tropospheric rms uncertainties of 1.0 C over a 1-km layer for temperature, and 10% over 2-km layers for water vapor. This paper describes the data sources and approaches to be used for validation of the AIRS/AMSU/HSB instrument suite, including validation of the forward models necessary for calculating observed radiances, validation of the observed radiances themselves, and validation of products retrieved from the observed radiances. Constraint of the AIRS product uncertainties to within the claimed specification of 1 K/1 km over well-instrumented regions is feasible within 12 months of launch, but global validation of all AIRS/AMSU/HSB products may require considerably more time due to the novelty and complexity of this dataset and the sparsity of some types of correlative observations.