Abstract
Abstract. The geographic and temporal variations in tropospheric and stratospheric ozone columns from individual swath measurements of the Ozone Monitoring Instrument (OMI), on the NASA Aura spacecraft, are reasonably well simulated by the University of California, Irvine (UCI) chemistry transport model (CTM) using 1°×1°×40-layer meteorological fields for the year 2005. From the CTM we find that high-frequency spatial variations in tropospheric column ozone (TCO), including around the jet streams, are not generally correlated with variations in stratospheric ozone column, but instead are collocated with folding events involving stratospheric-origin, high-ozone layers below the tropopause. The CTM fold events are verified in many cases with available ozone sondes. Using the OMI Level 2 profiles, and defining tropopause height from our CTM using the European Centre for Medium-Range Weather Forecasts (ECMWF) fields, we find that most of the variations in TCO near CTM folding events are also not correlated with those in stratospheric ozone column. A large fraction of the OMI TCO variance is accurately simulated by the CTM where the variance is significant, especially along the subtropical jets. The absolute tropospheric columns from OMI and CTM agree swath-by-swath, pixel-by-pixel within ±5 Dobson Units (DU) for most cases. Notable exceptions are in the tropics where neither the high ozone from biomass burning nor the low ozone in the convergence zones over the Pacific is found in the OMI observations, because of OMI's insensitivity to the lower troposphere. Another difference is identified with the OMI profiles near the southern subtropical jet. The CTM has a high bias in stratospheric column outside the tropics, due to problems previously identified with the stratospheric circulation in the 40-layer meteorological fields. Overall, we identify ozone folds with short-lived features in TCO that have scales of a few hundred kilometres as observed by OMI.
Highlights
Stratosphere-troposphere exchange (STE) plays an important role in determining the chemical composition in the atmosphere, bringing O3-rich stratospheric air into the troposphere (Danielsen, 1968), affecting the oxidative capacity of the atmosphere (Levy, 1972; Crutzen, 1973)
We identify STE O3 flux with many tropopause folds (TF) in our chemistry transport model (CTM) and show that these folds are observed as variations in tropospheric column ozone (TCO) on a daily global basis by the Aura Ozone Monitoring Instrument (OMI) satellite measurement
In the CTM, high ozone anomalies in the tropospheric column are correlated with TF events and occur most frequently near the subtropical jet streams, which is consistent with previous studies (Baray et al, 2000; Traub and Lelieveld, 2003)
Summary
Stratosphere-troposphere exchange (STE) plays an important role in determining the chemical composition in the atmosphere, bringing O3-rich stratospheric air into the troposphere (Danielsen, 1968), affecting the oxidative capacity of the atmosphere (Levy, 1972; Crutzen, 1973). Many studies have aimed at quantifying the STE flux (e.g., Danielsen, 1968; Holton et al, 1995; Appenzeller et al, 1996; Olsen et al, 2003; Sprenger et al, 2003; Stohl et al, 2003; Jaeger and Sprenger, 2009) This is a global problem that requires global observation and modelling. We identify STE O3 flux with many tropopause folds (TF) in our chemistry transport model (CTM) and show that these folds are observed as variations in tropospheric column ozone (TCO) on a daily global basis by the Aura Ozone Monitoring Instrument (OMI) satellite measurement. 2. Good consistency between the OMI and CTM TCO and total ozone is shown in Sect. We try to link TCO anomalies with STE O3 flux in Sect. 4 and find good correlation in the vicinity of subtropical jets, but not in high latitudes
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