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Propagation of radiosonde pressure sensor errors to ozonesonde measurements

Author(s): R. M. Stauffer | G. A. Morris | A. M. Thompson | E. Joseph | G. J. R. Coetzee

Journal: Atmospheric Measurement Techniques Discussions
ISSN 1867-8610

Volume: 6;
Issue: 4;
Start page: 7771;
Date: 2013;
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Several previous studies highlight pressure (or equivalently, pressure altitude) discrepancies between the radiosonde pressure sensor and that derived from a GPS flown with the radiosonde. The offsets vary during the ascent both in absolute and percent pressure differences. To investigate this, a total of 501 radiosonde/ozonesonde launches from the Southern Hemisphere subtropics to northern mid-latitudes are considered, with launches between 2006–2013 from both historical and campaign-based intensive stations. Three types of electrochemical concentration cell (ECC) ozonesonde manufacturers (Science Pump Corporation; SPC and ENSCI/Droplet Measurement Technologies; DMT) and five series of radiosondes from two manufacturers (International Met Systems: iMet, iMet-P, iMet-S, and Vaisala: RS80 and RS92) are analyzed to determine the magnitude of the pressure offset and the effects these offsets have on the calculation of ECC ozone (O3) mixing ratio profiles (O3MR) from the ozonesonde-measured partial pressure. Approximately half of all offsets are > ±0.7 hPa in the free troposphere, with nearly a quarter > ±1.0 hPa at 26 km, where the 1.0 hPa error represents ~5% of the total atmospheric pressure. Pressure offsets have negligible effects on O3MR below 20 km (98% of launches lie within ±5% O3MR error at 20 km). Ozone mixing ratio errors in the 7–15 hPa layer (29–32 km), a region critical for detection of long-term O3 trends, can approach greater than ±10% (>25% of launches that reach 30 km exceed this threshold). Comparisons of total column O3 yield average differences of +1.6 DU (−1.1 to +4.9 DU 10th to 90th percentiles) when the O3 is integrated to burst with addition of the McPeters and Labow (2012) above-burst O3 column climatology. Total column differences are reduced to an average of +0.1 DU (−1.1 to +2.2 DU) when the O3 profile is integrated to 10 hPa with subsequent addition of the O3 climatology above 10 hPa. The RS92 radiosondes are clearly distinguishable in performance from other radiosondes, with average 26 km errors of +0.32 hPa (−0.09 to +0.54 hPa 10th to 90th percentiles) or −1.31% (−2.19 to +0.37%) O3MR error. Conversely, iMet-P radiosondes had average 26 km errors of −1.49 hPa (−2.33 to −0.82 hPa) or +6.71% (+3.61 to +11.0%) O3MR error. Based on our analysis, we suggest that ozonesondes always be coupled with a GPS-enabled radiosonde and that pressure-dependent variables, such as O3MR, be recalculated/reprocessed using the GPS-measured altitude, particularly when 26 km pressure offsets exceed ±1.0 hPa/±5%.
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