Abstract
Abstract. The interrelated geographic and temporal variability seen in more than seven years of tropical and subtropical upper tropospheric (215 hPa) ozone, carbon monoxide and cloud ice water content (IWC) observations by the Aura Microwave Limb Sounder (MLS) are presented. Observed ozone abundances and their variability (geographic and temporal) agree to within 10–15 ppbv with records from sonde observations. MLS complements these (and other) observations with global coverage and simultaneous measurements of related parameters. Previously-reported phenomena such as the ozone "wave one" feature are clearly seen in the MLS observations, as is a double peak in ozone abundance over tropical East Africa, with enhanced abundances in both May to June and September to November. While repeatable seasonal cycles are seen in many regions, they are often accompanied by significant interannual variability. Ozone seasonal cycles in the southern tropics and subtropics tend to be more distinct (i.e., annually repeatable) than in the northern. By contrast, carbon monoxide shows distinct seasonal cycles in many northern subtropical regions, notably from India to the Eastern Pacific. Deep convection (as indicated by large values of IWC) is typically associated with reductions in upper tropospheric ozone. Convection over polluted regions is seen to significantly enhance upper tropospheric carbon monoxide. While some regions show statistically significant correlations among ozone, carbon monoxide and IWC, simple correlations fall well short of accounting for the observed variability. The observed interrelated variations and metrics of annual and interannual variability described here represent a new resource for validation of atmospheric chemistry models.
Highlights
Upper tropospheric ozone (O3) abundances are influenced by a variety of chemical and dynamical processes
This paper presents the first seven years of Microwave Limb Sounder (MLS) tropical and subtropical upper tropospheric O3, ice water content (IWC) and carbon monoxide (CO) observations, discusses the perspective they provide on previously reported phenomena, and identifies some behavior not previously reported
This study considers the MLS O3, IWC and CO profiles produced by the “Version 3.3” (v3.3 hereafter) data processing algorithms (Livesey et al, 2011)
Summary
Upper tropospheric ozone (O3) abundances are influenced by a variety of chemical and dynamical processes. Air transported up from the continental lower troposphere is often rich in ozone precursors: nitrogen oxides (NOx, which may be enhanced by emissions from lightning directly in the upper troposphere), carbon monoxide (CO), and volatile organic compounds. Lofting of these species can subsequently lead to increases in upper tropospheric ozone We present findings from seven years of nearcontinuous upper tropospheric ozone observations from the Microwave Limb Sounder (MLS) instrument (Waters et al, 2006) on NASA’s Aura satellite.
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