Ph.D. Thesis

Holger Bremer: Measurements of dynamic tracers and ozone in the Arctic stratosphere

Abstract

The Airborne SUbmillimeter Radiometer ASUR is a passive heterodyne instrument using a superconducting detector with an instrumental frequency range from 604.3 GHz to 662.3 GHz. Operating onboard an aircraft to avoid absorption by tropospheric water vapor key species of the stratospheric ozone chemistry, like ClO, HCl, HNO₃, and HO₂, the dynamical tracers N₂O and CH₃Cl as well as water vapor, and ozone can be detected for a vertical altitude range from 15 km to 55 km. In the winter 1999/2000 the ASUR instrument participated in the THESEO 2000/SOLVE project onboard the NASA research aircraft DC-8. Three deployments were carried out in December 1999, January 2000, and March 2000 with 23 flights total. This last winter was one of the coldest in the last ten years with sufficiently low temperatures for PSC formation from December 1999 until March 2000. The ASUR ClO measurements show a high chlorine activation from January 2000 until the beginning of March 2000 with very low HCl values in the lower stratosphere.

To estimate the chemical ozone loss during winter chemical and dynamical effects have to be separated. Four different methods have been applied to take diabatic descent into account: isentropes of constant potential temperature, heating rates calculated from ozone measurements, measurements of the dynamical tracer N₂O, as well as correlation of ozone and N₂O across the vortex edge. Also within this study diabatic descent has been calculated from ASUR N₂O measurements and heating rate calculations, using ASUR ozone measurements. Finally the results have been compared to measurements performed by various instruments as well as the SLIMCAT model calculations.

An important result of these investigations is that the ozone loss estimated from heating rate calculations as well as from correlation with N₂O agree very good with each other. Both methods lead to a chemical loss between 30% and 40% in the lower stratosphere. Taking ASUR's lower vertical resolution into account, these results also agree very good with sonde measurements and model calculations.

The two other methods investigated, isentropes and correlations across the vortex edge tend to underestimate respectively overestimate the chemical ozone loss in the winter 1999/2000.