Randall Skelton

Atmospheric Chemistry Experiment (ACE): Mission overview

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths 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.

A global inventory of stratospheric chlorine in 2004

Total chlorine (CITOT) 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 ±.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.

A global inventory of stratospheric fluorine in 2004 based on Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements

[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.

Cloud detection in the upper troposphere‐lower stratosphere region via ACE imagers: A qualitative study

[1] Satellite-based limb occultation measurements are well suited for the detection and mapping of polar stratospheric clouds (PSCs) and cirrus clouds. Usually, cloud signatures are detected on aerosol extinction profiles. In this paper, ACE two-dimensional (2-D) imager data are used to show PSCs and cirrus clouds. Clouds can be clearly seen, with a good vertical and horizontal resolution (1 km), during sunset and sunrise. In addition, we discovered significant differences between stratospheric (PSCs) and tropospheric (cirrus) clouds. PSCs appear as ‘‘symmetric’’ layers, no horizontal or vertical ‘‘structure’’ is detected within the PSC, suggesting that PSCs are uniform clouds with a very large horizontal extent. On the other hand, cirrus cloud image geometry is not well-defined. In contrast to PSCs, cirrus clouds appear as irregular shaped clouds. These tropospheric clouds seem to have horizontal dimensions similar to the Sun on the image (25 km at the tangent point). The qualitative display of these different kinds of clouds, seen on the raw 2-D imager data, proves the ability of the imagers to be an efficient cloud detector in the upper troposphere-lower stratosphere (UTLS) region. Moreover, the structure of these clouds can be derived.

Fourier transform spectroscopy of chemiluminescence from the A′1Π–X1Σ+ system of SrO

Abstract The A′1Π–X1Σ+ near infrared system of strontium oxide (SrO) was observed at high spectral resolution by measuring the chemiluminescence from a Broida flow reactor using a Fourier transform spectrometer. In total, 32 bands from 88 SrO , 87 SrO , 86 SrO were measured within the 4000–10 000 cm −1 spectral region at a resolution of 0.03 cm −1 . Vibrational levels of the upper state were observed up to vA′=4, and more than 5600 rotational lines were assigned. Incorporating previously published high resolution data for the A1Σ+–X1Σ+ system, a global fit to both data sets yields improved Dunham constants for the ground state and for the lower vibrational levels (vA′=0, 1, and 2) of the A′1Π state. Because perturbations arising from interactions with the b3Σ+ and A1Σ+ states affect the higher vibrational levels of the A′1Π state more strongly, levels vA′=3 and 4 were represented by effective band constants in the fits. RKR potentials for the X1Σ+,A′1Π, and b3Σ+ states have been generated utilizing all the available data, Franck–Condon factors have been calculated for the A′1Π–X1Σ+ system, and A′1Π∼b3Σ+ and A′1Π∼A1Σ+ perturbations are discussed.