Abstract
Abstract. We present global distributions of carbon monoxide (CO) from the upper troposphere to the mesosphere observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat. Vertically resolved volume mixing ratio profiles have been retrieved from 4.7 μm limb emission spectra under consideration of non-local thermodynamic equilibrium. The precision of individual CO profiles is typically 5–30 ppbv (15–40% for altitudes greater than 40 km and lower than 15 km and 30–90% within 15–40 km). Estimated systematic errors are in the order of 8–15%. Below 60 km, the vertical resolution is 4–7 km. The data set which covers 54 days from September 2003 to March 2004 has been derived with an improved retrieval version including (i) the retrieval of log(vmr), (ii) the consideration of illumination-dependent vibrational population gradients along the instrument's line of sight, and (iii) joint-fitted vmr horizontal gradients in latitudinal and longitudinal directions. A detailed analysis of spatially resolved CO distributions during the 2003/2004 Northern Hemisphere major warming event demonstrate the potential of MIPAS CO observations to obtain new information on transport processes during dynamical active episodes, particularly on those acting in the vertical. From the temporal evolution of zonally averaged CO abundances, we derived extraordinary polar winter descent velocities of 1200 m per day inside the recovered polar vortex in January 2004. Middle stratospheric CO abundances show a well established correlation with the chemical source CH4, particularly in the tropics. In the upper troposphere, a moderate CO decrease from September 2003 to March 2004 was observed. Upper tropospheric CO observations provide a detailed picture of long-range transport of polluted air masses and uplift events. MIPAS observations taken on 9–11 September 2003 confirm the trapping of convective outflow of polluted CO-rich air from Southeast Asia into the Asian monsoon anticyclone, which has been described in previous studies. Upper tropospheric CO plumes, observed by MIPAS on this day, were predominantly located in the Northern Hemisphere. Most of these plumes could be related to Southeast Asian pollution by means of backward trajectory calculations. During 20–22 October, southern hemispheric biomass burning was the most likely source of the major CO plumes observed over the Southern Atlantic and Indian Ocean.
Highlights
Carbon monoxide (CO) is a key trace species in the lower and middle atmosphere
The regularization strength scaling profile was chosen iteratively by means of test retrievals such that the impact of the a priori profile on the retrieved CO abundances is negligible below 65 km, while the retrieval precision generally stays below 80%
KM,esaopspphreorxicimairamtealsyses 1000 K highewr etrheaonbsebrevefdordeowtnheto wapaprromxiimngat.elyM10i0d0-lKa.titude air masses with lowOCn O16aDbeucnemdabenrc, ethsewvoerrteexowbasseervveendstorovnegretrhsehipftoedletoup to altitudesawloarerfdad3sy5Nt0oh0rethNKAo,rmpthearPritocialceaurneldagirmolynida-itlna2tt5ith0ue0deK2a0(irs–ep4eo0Fo◦irgEisn. s9Ce–O1c2tfio,lurlepd(see Fig. 11).perTrhigehtvpoarnteelxs),. nIonwconlotrcaasttetod thoeveCrONdoecrrtehasAe mat epro-lar ica’s East coalsati,tuhdaesd, CshOruanbuknednanccoesnisnicdrearasebdlysiginnifisciaznetl.y iWnsihdielethe it remained very strong and conserved a high content of mesospheric air with CO vmrs around 1–2 ppmv at altitudes around 1500 K, a vortex weakening occurred in the upper stratosphere leading to a local minimum in the vortex CO abundances around 2000 K (Fig. 12, middle left panel)
Summary
Carbon monoxide (CO) is a key trace species in the lower and middle atmosphere. CO is produced at the surface by incomplete combustion processes related to industry, traffic, or biomass burning. Due to the over-sampled retrieval grid compared to the tangent height spacing, the retrieval is regularized by a Tikhonov-type constraint which adds to the objective function of the least squares fit a penalty keeping the differences of mixing ratios at adjacent altitudes reasonably small (Tikhonov, 1963; Steck, 2002) This is achieved by using a smoothness constraint matrix of the type γ LT1 L1 where γ is a scaling profile and L1 is a first order finite differences operator. The currently available V3O CO 9+10 data set, used in this study, includes retrieved CO profiles obtained from MIPAS measurements taken in the standard observation mode at full spectral resolution on 54 days between 9 September 2003 and 25 March 2004 (see Table 1). When all the data above 70◦ N are filtered out, the differences were found to be further reduced
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