Abstract
Compared to recent years, the development of the Antarctic ozone hole in 2002 showed very unusual dynamical features. The midwinter polar vortex was one of the smallest observed during the ...past decade. Driven by planetary waves, the vortex showed a strong asymmetry in early spring. A large air mass separated in late September, leaving what was previously a small vortex even smaller. Furthermore, stratospheric temperatures exceeded the polar stratospheric cloud (PSC) threshold earlier than in previous years, leading to a decrease in halogen activation by heterogeneous surface reactions.
Ground-based observation of stratospheric trace gases in austral spring of 2001 and 2002 using passive Differential Optical Absorption Spectroscopy (DOAS) observations of zenith-scattered sunlight in the UV and visible wavelength region (320–650 nm) are presented. Using DOAS measurements of ozone, NO2, BrO, and OClO at two different Antarctic sites, Neumayer Station (70°S, 8°W) and Arrival Heights (78°S, 167°E), the chemical composition of the stratosphere is investigated under the unusual conditions of the 2002 ozone hole period and compared to the more typical observations of the previous year (2001).
Sudden loss of tropospheric ozone well above the boundary layer was observed on three occasions at two coastal sites in Antarctica in spring 1995. Back trajectories show that the air sampled the ...boundary layer near the northern edge of the sea ice (1000 km from the coast) between 3 and 5 days previously. Enhanced BrO observed over sea ice in spring suggests that such ozone loss is common offshore, hence it may cause a small climate effect whose sign would create positive feedback, if sea ice reduced during warming.
Validation of POAM III NO2 measurements Randall, C. E.; Lumpe, J. D.; Bevilacqua, R. M. ...
Journal of Geophysical Research - Atmospheres,
27 October 2002, Volume:
107, Issue:
D20
Journal Article
Peer reviewed
Open access
We describe the Polar Ozone and Aerosol Measurement (POAM) III NO2 measurements and associated errors and compare the POAM III data to correlative measurements obtained from satellite‐, balloon‐, and ...ground‐based instruments. POAM III NO2 densities are retrieved from 20 to 45 km, with a vertical resolution of about 1.5–2.5 km at altitudes below 40 km and increasing to more than 7 km at an altitude of 45 km. Predicted random errors are on the order of 5% in this altitude range. Sunspots and high aerosol extinction can cause errors in the NO2 retrievals but generally affect only about 10% of the data or less, depending on the altitude. The agreement between POAM III NO2 data and correlative observations is excellent, demonstrating that the POAM III measurements are reasonable in terms of their magnitude, profile structure, and temporal variations. The largest number of comparisons was made with the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite. On average, POAM and HALOE agree to within about 0.2 ppbv from 20 to 33 km or within about 6% at most of these altitudes, with no systematic bias. Differences increase to about 0.7 ppbv (17%, POAM higher than HALOE) by 40 km. This difference decreases to about 12% after accounting for a recently discovered error in the HALOE retrievals. Differences decrease above 40 km and are slightly negative (0.1–0.2 ppbv on average) at 45 km, the top edge of the valid POAM III NO2 altitude range. We conclude that the POAM III NO2 profiles from 20 to 45 km are appropriate for scientific analysis and for the validation of NO2 measurements from other instruments.
An algorithm has been developed to retrieve altitude information at different diurnal stages for trace gas species by combining direct-sun and zenith-sky UV-visible differential slant column density ...(DSCD) measurements. DSCDs are derived here using differential optical absorption spectroscopy. Combining the complementary zenith-sky measurements (sensitive to the stratosphere) with direct-sun measurements (sensitive to the troposphere) allows this vertical distinction. Trace gas species such as BrO and NO
2 have vertical profiles with strong diurnal dependence. Information about the diurnal variation is simultaneously retrieved with the altitude distribution of the trace gas. The retrieval is a formal optimal estimation profile retrieval, allowing a complete assessment of information content and errors.
The consistency of BrO column amounts derived from GOME spectra and from correlative ground-based and balloon measurements performed in 1998-1999 during the Third European Stratospheric Experiment on ...Ozone (THESEO) has been investigated. The study relies on UV-visible observations at several mid- and high latitude ground-based stations in both hemispheres, complemented by balloon-borne solar occultation profile measurements and 3D chemical transport model simulations. Previous investigations have reported GOME BrO columns systematically larger than those deduced from balloon, suggesting BrO being present, possibly ubiquitously, in the free troposphere. The robustness of this hypothesis has been further tested based on the presently available correlative data set. It is shown that when accounting for the BrO diurnal variation and the solar zenith angle dependency of the sensitivity of correlative data to the troposphere, measurements from all platforms are consistent with the presence of a tropospheric BrO background of 1–3 ×10
13 molec/cm
2 extending over mid- and high latitudes.
Emission of bromine from sea‐salt aerosol, frost flowers, ice leads, and snow results in the nearly complete removal of surface ozone during Arctic spring. Regions of enhanced total column BrO ...observed by satellites have traditionally been associated with these emissions. However, airborne measurements of BrO and O3 within the convective boundary layer (CBL) during the ARCTAS and ARCPAC field campaigns at times bear little relation to enhanced column BrO. We show that the locations of numerous satellite BrO “hotspots” during Arctic spring are consistent with observations of total column ozone and tropopause height, suggesting a stratospheric origin to these regions of elevated BrO. Tropospheric enhancements of BrO large enough to affect the column abundance are also observed, with important contributions originating from above the CBL. Closure of the budget for total column BrO, albeit with significant uncertainty, is achieved by summing observed tropospheric partial columns with calculated stratospheric partial columns provided that natural, short‐lived biogenic bromocarbons supply between 5 and 10 ppt of bromine to the Arctic lowermost stratosphere. Proper understanding of bromine and its effects on atmospheric composition requires accurate treatment of geographic variations in column BrO originating from both the stratosphere and troposphere.
Ozone depletion above Kiruna (67.9°N, 21.1°E), Sweden, was investigated using daily ozone and temperature measurements by ozonesondes between 1 February and 25 March 1997. Using UKMO Ertel's ...potential vorticity (EPV) and wind fields, three dynamically distinct regions were defined on a grid of isentropic surfaces viz.: the polar vortex boundary region characterized by steep EPV gradients, the area poleward of the boundary region (inside the polar vortex), and the area equatorward of the boundary region (outside the polar vortex). Due to dynamically induced displacements of the vortex, measurements were made in all three regions. By calculating the isentropic EPV at each measurement point and comparing it with the values defining the equatorward and poleward edges of the vortex boundary region, all ozone and temperature measurements could be binned according to their position relative to the vortex edge. Since the data outside the polar vortex were highly variable, mean ozone profiles and their standard deviations were calculated and compared only for the two other regions. To investigate whether differences between these mean profiles were indicative of ozone loss, the temporal evolution of ozone mixing ratios measured along several isentropic surfaces was examined, taking into account the diabatic descent of airmasses. Finally, ozone loss rates were calculated for six potential temperature surfaces and loss rates of up to 0.63ppm/month were found inside the Arctic vortex at surfaces descending from approximately 475 K (1 February) to 460 K (25 March).
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