Polar vortex evolution during the 2002 Antarctic major warming as observed by the Odin satellite

Abstract

In September 2002 the Antarctic polar vortex split in two under the influence of a sudden warming. During this event, the Odin satellite was able to measure both ozone (O3) and chlorine monoxide (ClO), a key constituent responsible for the so-called “ozone hole”, together with nitrous oxide (N2O), a dynamical tracer, and nitric acid (HNO3) and nitrogen dioxide (NO2), tracers of denitrification. The submillimeter radiometer (SMR) microwave instrument and the Optical Spectrograph and Infrared Imager System (OSIRIS) UV-visible light spectrometer (VIS) and IR instrument on board Odin have sounded the polar vortex during three different periods: before (19–20 September), during (24–25 September), and after (1–2 and 4–5 October) the vortex split. Odin observations coupled with the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) chemical transport model at and above 500 K isentropic surfaces (heights above 18 km) reveal that on 19–20 September the Antarctic vortex was dynamically stable and chemically nominal: denitrified, with a nearly complete chlorine activation, and a 70% O3 loss at 500 K. On 25–26 September the unusual morphology of the vortex is monitored by the N2O observations. The measured ClO decay is consistent with other observations performed in 2002 and in the past. The vortex split episode is followed by a nearly complete deactivation of the ClO radicals on 1–2 October, leading to the end of the chemical O3 loss, while HNO3 and NO2 fields start increasing. This acceleration of the chlorine deactivation results from the warming of the Antarctic vortex in 2002, putting an early end to the polar stratospheric cloud season. The model simulation suggests that the vortex elongation toward regions of strong solar irradiance also favored the rapid reformation of ClONO2. The observed dynamical and chemical evolution of the 2002 polar vortex is qualitatively well reproduced by REPROBUS. Quantitative differences are mainly attributable to the too weak amounts of HNO3 in the model, which do not produce enough NO2 in presence of sunlight to deactivate chlorine as fast as observed by Odin

HOCl chemistry in the Antarctic Stratospheric Vortex 2002, as observed with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS)

“…The single profile precision (total error) in the lower stratosphere is estimated at 19-31% (29-36%) at an altitude resolution of 4 km. ClO mixing ratios measured by MIPAS before 20 September and from 25 September onwards are in agreement with measurements by the Submillimeter Radiometer (SMR) on the Odin satellite (Ricaud et al, 2005). Unfortunately, no SMR measurements have been published for the 22-24 September period.…”

On the ability of chemical transport models to simulate the vertical structure of the N<sub>2</sub>O, NO<sub>2</sub> and HNO<sub>3</sub> species in the mid-latitude stratosphere

“…Ricaud et al, 2005). A next step of our work is to make comparisons at a global scale and for long time series using satellite data such as those of ODIN and ENVISAT.…”

“…Lefèvre et al, 1998;Wetzel et al, 2002;Stowasser et al, 2003;Ricaud et al, 2005) mid-latitudes during summer time are overestimated by the KASIMA model below 30 km . Comparisons between Reprobus and the Odin satellite measurements have shown that the model overestimated the N 2 O amounts observed by Odin/SMR at mid-latitudes in mid-September 2002 (Ricaud et al, 2005). Similar disagreements are observed with preliminary measurements of the MIPAS instrument on board the ENVISAT satellite for the same period (R. Runhke, personal communication).…”

“…The transport of too large quantities of the N 2 O precursor species at mid-latitudes stated above can result in a too weak production of NO y after its transport from tropical latitudes (e.g. Ricaud et al, 2005) which explains the low values for the upper part of the profile in Fig. 4.…”

“…Similar disagreements are observed with preliminary measurements of the MIPAS instrument on board the ENVISAT satellite for the same period (R. Runhke, personal communication). This notorious problem appears to be related to a too strong vertical transport above the Equator when using ECMWF operational analysis winds which provide too large quantities of N 2 O in the tropical middle stratosphere (Ricaud et al, 2005). Then these amounts reach mid-latitudes by the Brewer-Dobson circulation and quasi-horizontal transport from the tropical latitudes (Holton et al, 1995).…”