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New methods for retrieving tropospheric ozone column depth and absorbing aerosol (smoke and dust) from the Earth Probe-Total Ozone Mapping Spectrometer (EP/TOMS) are used to follow pollution and to determine interannual variability and trends. During intense fires over Indonesia (August to November 1997), ozone plumes, decoupled from the smoke below, extended as far as India. This ozone overlay a regional ozone increase triggered by atmospheric responses to the El Niño and Indian Ocean Dipole. Tropospheric ozone and smoke aerosol measurements from the Nimbus 7 TOMS instrument show El Niño signals but no tropospheric ozone trend in the 1980s. Offsets between smoke and ozone seasonal maxima point to multiple factors determining tropical tropospheric ozone variability.

The seasonal tropospheric ozone maximum in the tropical South Atlantic, first recognized from satellite observations [Fishman et al., 1986, 1991], gave rise to the IGAC/STARE/SAFARI 1992/TRACE A campaigns (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Southern African Atmospheric Research Initiative/Transport and Atmospheric Chemistry Near the Equator‐Atlantic) in September and October 1992. Along with a new TOMS‐based method for deriving tropospheric column ozone, we used the TRACE A/SAFARI 1992 data set to put together a regional picture of the O3 distribution during this period. Sondes and aircraft profiling showed a troposphere with layers of high O3 (≥90 ppbv) all the way to the tropopause. These features extend in a band from 0° to 25°S, over the SE Indian Ocean, Africa, the Atlantic, and eastern South America. A combination of trajectory and photochemical modeling (the Goddard (GSFC) isentropic trajectory and tropospheric point model, respectively) shows a strong connection between regions of high ozone and concentrated biomass burning, the latter identified using satellite‐derived fire counts [Justice et al., this issue]. Back trajectories from a high‐O3 tropical Atlantic region (column ozone at Ascension averaged 50 Dobson units (DU)) and forward trajectories from fire‐rich and convectively active areas show that the Atlantic and southern Africa are supplied with O3 and O3‐forming trace gases by midlevel easterlies and/or recirculating air from Africa, with lesser contributions from South American burning and urban pollution. Limited sampling in the mixed layer over Namibia shows possible biogenic sources of NO. High‐level westerlies from Brazil (following deep convective transport of ozone precursors to the upper troposphere) dominate the upper tropospheric O3 budget over Natal, Ascension, and Okaukuejo (Namibia), although most enhanced O3 (75% or more) equatorward of 10°S was from Africa. Deep convection may be responsible for the timing of the seasonal tropospheric O3 maximum: Natal and Ascension show a 1‐ to 2‐month lag relative to the period of maximum burning [cf. Baldy et al., this issue; Olson et al., this issue]. Photochemical model calculations constrained with TRACE A and SAFARI airborne observations of O3 and O3 precursors (NOx, CO, hydrocarbons) show robust ozone formation (up to 15 ppbv O3/d or several DU/d) in a widespread, persistent, and well‐mixed layer to 4 km. Slower but still positive net O3 formation took place throughout the tropical upper troposphere [cf. Pickering et al., this issue (a); Jacob et al., this issue]. Thus whether it is faster rates of O3 formation in source regions with higher turnover rates or slower O3 production in long‐lived stable layers ubiquitous in the TRACE A region, 10–30 DU tropospheric O3 above a ∼25‐DU background can be accounted for. In summary, the O3 maximum studied in October 1992 was caused by a coincidence of abundant O3 precursors from biomass fires, a long residence time of stable air parcels over the eas...

Details are presented concerning the derivation of new, standard, effective ozone absorption coefficients for use with Dobson ozone spectrophotometers. The work was performed under auspices of the World Meteorological Organization (WMO) Global Ozone Research and Monitoring Program, with the goal of improving and standardizing ozone measurements throughout the world. The new coefficients, based on the laboratory measurements of Bass and Paur (1985), were sanctioned for use worldwide, beginning January 1, 1992, by the WMO Executive Panel on Environmental Pollution and Atmospheric Chemistry. The new coefficients, together with use of slightly improved Rayleigh molecular scattering coefficients also adopted as standard, yield total ozone amounts 2.6% smaller than values obtained during July 1, 1957 to December 31, 1991, derived from the use of Vigroux (1953, 1967) ozone absorption coefficients. Information is provided also on correcting ozone data obtained in the past to the new ozone absorption coefficient scale. 1. INTRODUCTION Early Dobson ozone spectrophotometer observations were processed using ozone absorption coefficients based on the laboratory data of Ny and Choong [1933]. At the beginning of the International Geophysical Year (IGY) (July 1, 1957), new absorption coefficients were adopted for use [Dobson, 1957a], employing the laboratory values of Vigroux [1953]. Pre-IGY Dobson spectrophotometer ozone values were converted to the Vigroux [1953] scale by multiplying them by 1.36. Because the Vigroux [1953] coefficients (Table 1) gave inconsistent ozone values from observations on different combinations of wavelengths (e.g., CD-wavelength and ABwavelength observations yielded 10% less and 13% more ozone, respectively, than did AD-wavelength observations), the Vigroux AD-wavelength ozone absorption coefficients were adopted as standard. Based on a redetermination of the ozone absorption coefficients by Vigroux [1967] and an examination of the coefficients by G.M.B. Dobson in light of atmospheric observations made in Canada, the United Kingdom and elsewhere, a modified set of ozone absorption coefficients (Table 2) was derived [World Meteorological Organization (WMO), 1968] which gave highly consistent ozone amounts from observations made on different wavelengths (Table 3). These modified coefficients, which preserved the original Vigroux AD-wavelengths coefficient as standard, were recommended for use by the International 1Now at by the WMO throughout the world beginning January 1, 1968 [WMO, 1968]. Rayleigh molecular scattering coefficients used with the ozone absorption coefficients in processing ozone data were derived from the Rayleigh-Cabanes formula [Dobson, 1957a]. Komhyr [1980] reexamined the Vigroux [1953] ozone absorption coefficients and concluded that the ADwavelengths coefficient of 1.388 cm -1, adopted as standard, may be too small, causing Dobson instrument ozone values to be overestimated by up to 5%. Discussion of the problem with A. Bass (U.S. Bureau of Standards, Gaithersburg, Maryland) promp...

The magnetometer instrument on the Solar Orbiter mission is designed to measure the magnetic field local to the spacecraft continuously for the entire mission duration. The need to characterise not only the background magnetic field but also its variations on scales from far above to well below the proton gyroscale result in challenging requirements on stability, precision, and noise, as well as magnetic and operational limitations on both the spacecraft and other instruments. The challenging vibration and thermal environment has led to significant development of the mechanical sensor design. The overall instrument design, performance, data products, and operational strategy are described.