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The Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) aboard the Canadian satellite SCISAT (launched in August 2003) was designed to investigate the composition of the upper troposphere, stratosphere, and mesosphere. ACE-FTS utilizes solar occultation to measure temperature and pressure as well as vertical profiles of over thirty chemical species including O3, H2O, CH4, N2O, CO, NO, NO2, N2O5, HNO3, HCl, ClONO2, CCl3F, CCl2F2, and HF. Global coverage for each species is obtained approximately over a three month period and measurements are made with a vertical resolution of typically 3–4 km. A quality-controlled climatology has been created for each of these 14 baseline species, where individual profiles are averaged over the period of February 2004 to February 2009. Measurements used are from the ACE-FTS version 2.2 data set including updates for O3 and N2O5. The climatological fields are provided on a monthly and three-monthly basis (DJF, MAM, JJA, SON) at 5 degree latitude and equivalent latitude spacing and on 28 pressure surfaces (26 of which are defined by the Stratospheric Processes And their Role in Climate (SPARC) Chemistry-Climate Model Validation Activity). The ACE-FTS climatological data set is available through the ACE website.

The Atmospheric Chemistry Experiment (ACE), or SCISAT mission, is a Canadian science satellite designed to investigate the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere. The ACE mission payload consists of two science instruments: a high-resolution infrared Fourier-Transform Spectrometer (FTS) and an ultraviolet/visible/near-infrared spectrometer. These instruments primarily function in occultation mode. However, during the dark portion of the orbit, the Earth passes between the Sun and the satellite. In this configuration, the ACE-FTS has the opportunity to acquire some nadir-view spectra of the Earth. Since the ACE-FTS was designed to view a hot source (i.e., the Sun) at high resolution using a single scan, it was necessary to determine if the ACE-FTS could also provide nadir spectra of the relatively cold atmosphere and surface with sufficient signal-to-noise ratio (SNR). As part of the pre-launch test program, laboratory measurements ...

Satellite-based limb occultation measurements are well suited for the detection and mapping of polar stratospheric clouds (PSCs) and cirrus clouds. PSCs are of fundamental importance for the formation of the Antarctic ozone hole that occurs every year since the early 1980s in Southern Hemisphere spring. Despite progress in the observation, modeling and understanding of PSCs in recent years, there are still important questions which remain to be resolved, e.g. PSC microphysics, composition, formation mechanisms and long-term changes in occurrence. In addition, it has recently become clear that cirrus clouds significantly affect the global energy balance and climate, due to their influence on atmospheric thermal structure. Since 2002, two major space missions using the occultation method have been put into orbit: the European stellar occultation spectrometer GOMOS on board ENVISAT and the Canadian solar occultation instruments ACE-FTS/MAESTRO on board SCISAT-I. PSCs and cirrus clouds are detected both by ACE and GOMOS. The results of an intercomparison between retrieved aerosol extinction, PSCs and cirrus clouds are the subject of this paper. The cloud data are also used to examine the evolution of PSCs over the Antarctic vortex and the latitudinal variation of tropical cirrus for the years 2004 and 2005.

[1] Derived Meteorological Products (DMPs, including potential temperature, potential vorticity (PV), equivalent latitude (EqL), horizontal winds and tropopause locations) from several meteorological analyses have been produced for the locations and times of measurements taken by several solar occultation instruments and the Aura Microwave Limb Sounder (MLS). MLS and solar occultation data are analyzed using DMPs to illustrate sampling issues that may affect interpretation and comparison of data sets with diverse sampling patterns and to provide guidance regarding the kinds of studies that benefit most from analyzing satellite data in relation to meteorological conditions using the DMPs. Using EqL or PV as a vortex-centered coordinate does not alleviate all sampling problems, including those in studies using “vortex averages” of solar occultation data and in analyses of localized features (such as polar stratospheric clouds) and other fields that do not correlate well with PV. Using DMPs to view measurements with respect to their air mass characteristics is particularly valuable in studies of transport of long-lived trace gases, polar processing in the winter lower stratosphere, and distributions and transport of O3 and other trace gases from the upper troposphere through the lower stratosphere. The comparisons shown here demonstrate good agreement between MLS and solar occultation data for O3, N2O, H2O, HNO3, and HCl; small biases are attributable to sampling effects or are consistent with detailed validation results presented elsewhere in this special section. The DMPs are valuable for many scientific studies and to facilitate validation of noncoincident measurements.

The dehydration of air in the tropical tropopause layer (TTL) and mechanisms for the entry of water vapor into the stratosphere are investigated by an analysis of ACE-FTS profiles of temperature, water vapor, and the ratio [HDO]/[H2O] expressed in δD notation. Month-to-month comparisons indicate greater seasonal variability than interannual variability between 25°S–25°N, thus comparisons are made between February, April, August, and October averages for the years 2004 and 2005 combined. The data indicate a pattern of seasonal variability which is clearer in the Northern Hemisphere tropics and a relationship between minimum temperature, minimum water vapor, and maximum HDO depletion, which exists beyond the estimated uncertainty in these values. The range of values observed for HDO depletion and comparisons to modeled Rayleigh distillation curves indicate an important contribution from convection in addition to gradual dehydration. Multiple factors including the shape of the δD profiles suggest that a likely mechanism for the convective influence is the lofting of ice particles in the tropical troposphere.

[1] The Atmospheric Chemistry Experiment (ACE) onboard the Canadian Space Agency’s SCISAT-1 satellite has been in orbit since August of 2003. Its broad objective is to study the problem of stratospheric ozone depletion, particularly in the Arctic. The main instruments are two spectrometers, one an infrared Fourier Transform Spectrometer and the other a dual optical spectrophotometer sensitive in the UV and visible. Also included are two filtered imagers used to measure altitude profiles of atmospheric extinction and detect thin clouds. The nominal center wavelengths of the filters are 525 nm for the visible (VIS) imager and 1020 nm for the near-infrared (NIR) imager. With the decommissioning of other satellite instruments used to monitor global aerosols [i.e., Stratospheric Aerosol and Gas Experiment II (SAGE II), SAGE III, Polar Ozone and Aerosol Measurement (POAM) III, Halogen Occultation Experiment (HALOE)], the imagers provide much needed continuity in this data record. The data product from the imagers is still, however, in a preliminary state. Funding restrictions in the prelaunch period were responsible for an incomplete characterization of the imagers’ optics and electronics and prevented corrections being made for the problems found during testing. Postlaunch data analysis to correct for image artifacts is ongoing. A comparison with coincidental measurements from SAGE II shows that systematic errors from the preliminary analysis are within 5 and 20% for the VIS and NIR imagers, respectively, for uninverted profiles of optical depth. Despite the preliminary nature of the imager results, a paper describing the imagers and the initial operational data processing code is timely because the data are already being used.

[1] Total fluorine (FTOT) in the stratosphere has been determined using Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements of HF, COF2, COClF, CF4, CCl3F (CFC-11), CCl2F2 (CFC-12), CHClF2 (HCFC-22), CCl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), CH2FCF3 (HFC-134a), and SF6. The retrieval of HFC-134a (CH2FCF3) from spaceborne measurements had not been carried out prior to this work. Measurements of these species have been supplemented by data from models to extend the altitude range of the profiles and have also been complemented by estimates of 15 minor fluorine species. Using these data, separate fluorine budgets were determined in five latitude zones (60–82N, 30–60N, 30S–30N, 30–60S, and 60–82S) by averaging over the period of February 2004 to January 2005 inclusive, when possible. Stratospheric FTOT profiles in each latitude zone are nearly linear, with mean stratospheric FTOT values ranging from 2.50 to 2.59 ppbv (with a 1s precision of 0.04–0.07 ppbv and an estimated accuracy of 0.15 ppbv) for each zone. The highest mean FTOT value occurred in the tropics, which is qualitatively consistent with increasing levels of stratospheric fluorine and the mean stratospheric circulation pattern.

Total chlorine (ClTOT) in the stratosphere has been determined using the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measurements of HCl, ClONO2, CH3Cl, Ccl4, Ccl3F (CFC-11), Ccl2F2 (CFC-12), CHClF2 (HCFC-22), Ccl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), COClF, and ClO supplemented by data from several other sources, including both measurements and models. Separate chlorine inventories were carried out in five latitude zones (60°–82°N, 30°–60°N, 30°S–30°N, 30°–60°S, and 60°–82°S), averaging the period of February 2004 to January 2005 inclusive, when possible, to deal with seasonal variations. The effect of diurnal variation was avoided by only using measurements taken at local sunset. Mean stratospheric ClTOT values of 3.65 ppbv were determined for both the northern and southern midlatitudes (with an estimated 1σ accuracy of ±0.13 ppbv and a precision of ±0.09 ppbv), accompanied by a slightly lower value in the tropics and slightly higher values at high latitudes. Stratospheric ClTOT profiles in all five latitude zones are nearly linear with a slight positive slope in ppbv/km. Both the observed slopes and pattern of latitudinal variation can be interpreted as evidence of the beginning of a decline in global stratospheric chlorine, which is qualitatively consistent with the mean stratospheric circulation pattern and time lag necessary for transport.

SCISAT-1, also known as the Atmospheric Chemistry Experiment, is a satellite mission for remote sensing of the Earth's atmosphere, launched on 12 August 2003. The primary instrument on the satellite is a 0.02 cm(-1) resolution Fourier-transform spectrometer operating in the mid-IR (750-4400 cm(-1)). We describe the approach developed for the retrieval of atmospheric temperature and pressure from the troposphere to the lower thermosphere as well as the strategy for the retrievals of volume-mixing ratio profiles of atmospheric species.

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earth's atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

[1] The ozone and nitrogen dioxide vertical number density profiles measured by the solar occultation Fourier transform spectrometer ACE-FTS and the UV-Vis stellar occultation instrument GOMOS are intercompared for 370 quasi-coincident observations. A good agreement is found for ozone, mostly better than 10% between 15 and 45 km. Also, there is no evidence for a systematic altitude registration error in the ACE-FTS profiles. A considerable ACE-FTS negative bias (50–100%) is found however for the nitrogen dioxide data that cannot be explained by the use of a local photochemical model.

[1] We report first comparisons of stratospheric column abundances of hydrogen chloride (HCl) and chlorine nitrate (ClONO2) derived from infrared solar spectra recorded in 2004 at selected northern latitudes by the spaceborne Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) and by Fourier transform infrared (FTIR) instruments at the NDSC (Network for Detection of Stratospheric Change)-affiliated sites of Thule (Greenland), Kiruna (Sweden), Jungfraujoch (Switzerland), and Egbert and Toronto (Canada). Overall, and within the respective uncertainties of the independent measurement approaches, the comparisons show that the ACE-FTS measurements produce very good stratospheric volume mixing ratio profiles. Their internal precision allows to identify characteristic distribution features associated with latitudinal, dynamical, seasonal and chemical changes occurring in the atmosphere.

[1] We present solar occultation measurements of H2O and CH4 by the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS). The data used here were selected from occultations spanning February to April 2004 from 0 to 79.8°N. The midlatitude volume mixing ratio (VMR) of potential water is determined as [H2O] + 2[CH4] and from [H2O] versus [CH4] correlations, then used to calculate the VMR of water vapor entering the stratosphere. We obtain 7.14 ± 0.23 ppm for potential water and 3.65 ± 0.29 ppm for water entering the stratosphere in 2004 for direct comparison with Atmospheric Trace Molecule Spectroscopy (ATMOS) data (1985–1994). We find a very small change in potential water and no change in water entering the stratosphere relative to the 1994 ATMOS data, indicating that increases observed by ATMOS and other instruments from that time period have not continued. This halt in stratospheric water vapor increases is consistent with recent water vapor measurements by other instruments.

The SCISAT-1 mission, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission to investigate the chemical and dynamical processes that control the distribution of ozone in the stratosphere and upper troposphere. The satellite is scheduled to launch in August 2003, carrying two main instruments: a high-resolution infrared Fourier transform spectrometer (ACE-FTS) and a dual grating UV-Vis-NIR spectrometer known as MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) both operating primarily in solar occultation mode. Aspects of the mission pertaining to work done by ACE science team members from the University of Waterloo will be described, such as: the ACE-FTS forward model for retrieval of temperature, pressure and VMR profiles; ACE-FTS instrument testing and results; and the ACE Database along with data storage and processing hardware.