Ozone variability in the troposphere and the stratosphere from six years of IASI observations (2008-2013)
Abstract:In this study, we present daytime observations of ozone (O3) measured during 6 years (2008-2013) by the thermal infrared IASI remote sensor launched in October 2006 onboard the polar orbiting MetOp-A satellite. Thanks to its high spatiotemporal coverage along with its radiometric stability, IASI provides a unique dataset of vertically-resolved profiles for investigating global distributions, time series and climatology.
We analyze the time development of O3 by fitting constant, annual and semi-annual terms, solar flux and quasi biennial oscillation proxies to the IASI time series on a large spatial scale (20-degree latitudinal bands), separately in different layers over the stratosphere and the troposphere which help to distinguish the chemical and dynamical contributions to the O3 total columns variations. Based on the fitting procedure, the ozone time development estimation (“trends”) is also derived. Despite the short time period of available IASI dataset, statistically significant trends are measured in both the troposphere and the stratosphere. Significant positive trends are obtained in the upper stratosphere, in particular over the highest latitudes, which potentially point out a turnaround for stratospheric O3 recovery, and significant negative trends are observed over the mid-and high northern latitudes during summer which is possibly linked to the decreasing ozone precursor emissions. More specifically, ozone trends are also estimated in the troposphere on a regional scale over and downwind anthropogenic polluted areas. Finally, the influence of the stratosphere on the tropospheric variability as seen from IASI is also evaluated using simulations from global 3-D chemical transport models.