D. N. Turnbull

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.

Spectrometric and imaging measurements of a spectacular gravity wave event observed during the ALOHA‐93 Campaign

During the ALOHA-93 campaign coincident imaging and interferometric measurements of the near infrared and visible wavelength nightglow emissions were made from Haleakala Crater, Maui. On 10 October, 1993 a most unusual wave event was observed. This disturbance appeared as a sharp “front” followed by several conspicuous wave crests which progressed rapidly through the imagers field of view (180°). As the front passed overhead the interferometer detected a sudden jump in both the OH intensity (>50%) and its rotational temperature (∼20 K) with the temperature increase leading the intensity by almost 15 min. At the same time the imager registered a sharp decrease in the OI(557.7 nm) emission intensity. A description of this remarkable event follows.

Dynamical and chemical aspects of the mesospheric Na “wall” event on October 9,1993 during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA) campaign

On October 9, 1993, observations were made from the National Center for Atmospheric Research Electra aircraft during a flight from Maui, Hawaii, toward a low-pressure system NW of the island, a flight of 7 hours in total. The leading edge (wall) of a bright airglow layer was observed 900 km NW of Maui at 0815 UT, which was traveling at 75 m s−1 toward the SE, reaching Haleakala, Maui, about 3.25 hours later [see Swenson and Espy, 1995]. An intriguing feature associated with the event was the large increase in the mesospheric Na column density at the wall (∼180%). The enhancement was distributed over a broad region of altitude and was accompanied by significant perturbations in the Meinel (OH) and Na D line airglow emission intensities, as well as the temperature. This paper describes an investigation of the combined measurements from the aircraft and at Haleakala, including an analysis of the event using a gravity wave dynamic model. The modeled atmospheric variations associated with the leading edge of the “wall” wave are then applied to models of the neutral and ionic chemistry of sodium in order to establish whether the enhancement was caused by the release of atomic Na from a local reservoir species, as opposed to redistribution by horizontal convection. The most likely explanation for the Na release was the neutralization of Na+ ions in a sporadic E layer that was first transported downward by a large amplitude (≈10%) atmospheric gravity wave and then vertically mixed as the wave pushed the atmosphere into a super adiabatic state with associated convective instabilities and overturning.

Formation characteristics of sporadic Na layers observed simultaneously by lidar and airglow instruments during ALOHA-90

Sporadic Na (Nas) layers were observed by the airborne lidar during ALOHA-90 on the 22, 25 and 27 March flight missions. Perturbations in the O2 and OH nighttime airglow emission intensities and temperatures were also observed by instruments on the aircraft and at Haleakala Crater (20.8°N, 156.2°W) during these events. The most striking correlation between the airglow and lidar measurements occurred during the northbound flight leg of the 25 March mission. When the Nas layer formed at 90.7 km, while the Electra aircraft was between 750 and 500 km south of Haleakala, the O2 temperatures near 95 km above the Electra and Haleakala increased by approximately 45 K. The data for this night suggest a connection between Nas and a large-scale wave, and suggest that the wave is tidal in nature. The data also suggest that some Nas layers can form very quickly over large geographic areas. Fast chemical processes are required to generate the large amounts of atomic Na involved in some of these events.

Comparison of ALOHA‐93, ANLC‐93 and ALOHA‐90 observations of the hydroxyl rotational temperature and gravity wave activity

Hydroxyl airglow measurements during the ALOHA-93, ALOHA-90 and ANLC-93 campaigns are used to evaluate features of the temperature variation of the mesopause region. Each campaign shows a persistent pattern in the averaged local time variation of temperature with peak-to-peak amplitudes of 5 K to 15 K, suggestive of the presence of tidal modulation. The nightly temperature variance, after detrending to remove low frequency variations due to tides, is shown to be significantly less during the Hawaiian campaigns than during the ANLC-93 and other campaigns at sites where significant orographic excitation of waves might be expected.

Coincident Imaging and Spectrometric Observations of Zenith OH Nightglow Structure

During the ALOHA-90 campaign a novel comparative study was made between near infrared wave structure imaged in the zenith using a CCD camera and that detected at infrared wavelengths by a Fourier Transform Spectrometer. Coincident measurements were made briefly on several occasions and for an extended period on 31 March. The temporal variations imaged in the near infrared structure during this night almost completely matched those detected in the OH (3,1) band spectrometer data when similar viewing fields were compared. However, the image data also displayed small scale wave forms that were not resolved by the larger field instrument. These structures exhibited significant changes in brightness and position on a time scale much shorter than the local Brunt-Vaisala period indicating that very high resolution measurements are necessary to investigate short period (<20 min) upper atmospheric wave motions.

Temporal variations in the hydroxyl nightglow observed during ALOHA‐90

Ground-based observations of the hydroxyl nightglow were made with a Fourier transform spectrometer from Haleakala, Maui during the ALOHA-90 campaign. Vibrational level populations and rotational temperatures were obtained with a temporal resolution of 1 minute. Temperature precision was ±1 K. Highly correlated in-phase variations in temperature and population were seen on all nights. However, a long term trend in the vibrational population was not reflected in the temperature.

High latitude summer observations of the hydroxyl airglow

Abstract Spectra of the hydroxyl night airglow in the near infrared region were obtained under high latitude summer conditions at Poker Flat, Alaska, during August 1986. Rotational temperatures and relative populations have been deduced from the spectra for vibrational levels from 2 to 8. During the observing period the nightly average rotational temperature increased from 155 to 173 K, but the nightly variation of temperature generally did not exceed 10 K. On one night, a short period of nearly sinusoidal variation of both intensity and temperature was observed, with small phase shifts which varied with vibrational level. Correlation of intensity and temperature variation on two nights gave a value of ∼ 8 for Krassovskys parameter, η. Differences in the average rotational temperature as measured from bands arising from different vibrational levels were noted, but in general they did not exceed the possible calibration uncertainty.

Steller Brewer, ozonesonde, and DIAL measurements of Arctic O3 column over Eureka, N.W.T. during 1996 winter/spring

Ozone total column amounts derived from differential UV absorption of starlight measurements made using the new Stellar Brewer instrument are compared with simultaneous measurements using a DIAL system and ECC ozonesondes. Good agreement within the 2% error estimate of the Stellar Brewer is shown between the various methods after correction is made for a calibration offset error for the Stellar Brewer. All three methods identify a generally decreasing trend of total ozone column between day 15 and 75 of the 1996 spring season.