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Christopher G. Piecuch, Ichiro Fukumori, Rui M. Ponte, and Ou Wang

Abstract

The nature of ocean bottom pressure () variability is considered on large spatial scales and long temporal scales. Monthly gridded estimates from the Gravity Recovery and Climate Experiment (GRACE) Release-05 and the new version 4 bidecadal ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO) are used. Estimates of from GRACE and ECCO are generally in good agreement, providing an independent measure of the quality of both products. Diagnostic fields from the state estimate are used to compute barotropic (depth independent) and baroclinic (depth dependent) components. The relative roles of baroclinic and barotropic processes are found to vary with latitude and time scale: variations in at higher latitudes and shorter periods are affected by barotropic processes, whereas fluctuations at lower latitudes and longer periods can be influenced by baroclinic effects, broadly consistent with theoretical scaling arguments. Wind-driven Rossby waves and coupling of baroclinic and barotropic modes due to flow–topography interactions appear to be important influences on the baroclinic variability. Decadal simulations of monthly variability based on purely barotropic frameworks are expected to be in error by about 30% on average ( in the tropical ocean and at higher latitudes). Results have implications for applying GRACE observations to problems such as estimating transports of the Antarctic Circumpolar Current.

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Xue-Fa Wen, Xuhui Lee, Xiao-Min Sun, Jian-Lin Wang, Ya-Kun Tang, Sheng-Gong Li, and Gui-Rui Yu

Abstract

The δ 18O and δD of atmospheric water vapor are important tracers in hydrological and ecological studies. Isotope ratio infrared spectroscopy (IRIS) provides an in situ technology for measuring δ 18O and δD in ambient conditions. An intercomparison experiment was carried out with four commercial IRIS analyzers to characterize their performance and transferability of calibration methods. Over a 15-day atmospheric measurement, during which the water vapor concentration ranged from 14 to 27 mol mol−1 and the isotopic ratios spanned about 90‰ and 13‰ for δD and δ 18O, respectively, these analyzers tracked the natural variability in ambient conditions very well and achieved an average difference between one another within 2‰ for δD and within 0.1‰ for δ 18O after calibration at appropriate frequencies. Two of the calibration methods (discrete liquid water injection and continuous dripping) agreed with each other within the tolerance thresholds of 2‰ for δD and 0.1‰ for δ 18O. The Rayleigh distillation technique appeared to be acceptable as a calibration standard for δD but not for δ 18O. The δD measurements were less prone to concentration dependence errors than the δ 18O measurements. The concentration dependence underscores the importance of using a calibration procedure at multiple mixing ratios to bracket the range of natural variability.

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