Abstract
Abstract. This study evaluates the agreement between ozone profiles derived from the ground-based differential absorption lidar (DIAL), satellite-borne Aura Microwave Limb Sounder (MLS), and 3-D chemical transport model (CTM) simulations such as the Model for Interdisciplinary Research on Climate (MIROC-CTM) over the Atmospheric Observatory of Southern Patagonia (Observatorio Atmosférico de la Patagonia Austral, OAPA; 51.6° S, 69.3° W) in Río Gallegos, Argentina, from September to November 2009. In this austral spring, measurements were performed in the vicinity of the polar vortex and inside it on some occasions; they revealed the variability in the potential vorticity (PV) of measured air masses. Comparisons between DIAL and MLS were performed between 6 and 100 hPa with 500 km and 24 h coincidence criteria. The results show a good agreement between DIAL and MLS with mean differences of ±0.1 ppmv (MLS − DIAL, n = 180) between 6 and 56 hPa. MIROC-CTM also agrees with DIAL, with mean differences of ±0.3 ppmv (MIROC-CTM − DIAL, n = 23) between 10 and 56 hPa. Both comparisons provide mean differences of 0.5 ppmv (MLS) to 0.8–0.9 ppmv (MIROC-CTM) at the 83–100 hPa levels. DIAL tends to underestimate ozone values at this lower altitude region. Between 6 and 8 hPa, the MIROC-CTM ozone value is 0.4–0.6 ppmv (5–8 %) smaller than those from DIAL. Applying the scaled PV (sPV) criterion for matching pairs in the DIAL–MLS comparison, the variability in the difference decreases 21–47 % between 10 and 56 hPa. However, the mean differences are small for all pressure levels, except 6 hPa. Because ground measurement sites in the Southern Hemisphere (SH) are very sparse at mid- to high latitudes, i.e., 35–60° S, the OAPA site is important for evaluating the bias and long-term stability of satellite instruments. The good performance of this DIAL system will be useful for such purposes in the future.
Highlights
Ozone-depleting substances have been decreasing due to the Montreal Protocol and its subsequent adjustments and amendments
Ground-based differential absorption lidar (DIAL) measurements were performed at OAPA in Río Gallegos (51.6◦ S, 69.3◦ W), Argentina, from September to November 2009, when a long-lasting southern polar vortex, and accompanying ozone depletion, occurred over the area for the first time since 1979
The mean differences between DIAL and Microwave Limb Sounder (MLS) are within ±0.1 ppmv (±3 %) from 6 to 56 hPa, showing good agreement regardless of the large scaled PV (sPV) variability between each matching pair
Summary
Ozone-depleting substances have been decreasing due to the Montreal Protocol and its subsequent adjustments and amendments. Stratospheric ozone (O3) is expected to increase in the future. The last WMO/UNEP ozone assessment concluded that increasing O3 has been observed in the upper stratosphere around 42 km, or 2 hPa, in altitude (WMO, 2014). Positive trends have been evaluated for both the tropics and 35–60◦ latitude bands of both hemispheres above 5 hPa levels from 2000 to 2016. The trend is still not statistically significant below 10 hPa levels. Steinbrecht et al (2017) found 0.7 ± 0.9 and −0.2 ± 1.4 % per decade changes at 10 and 70 hPa, respectively, for 35–60◦ S. The satellite measurement has an advantage for estimating longterm trends because of its global coverage on a daily basis. Its drift, i.e., the long-term measurement stability, should be quantitatively assessed with independent instruments. Ground-based ozone lidar is a potential candidate for such purposes and can be used to estimate drift (e.g., Nair et al, 2011, 2012; Eckert et al, 2014; Hubert et al, 2016)
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