Atmospheric Laboratory For Applications And Science Research Articles

Assessment of the Impact of Solar Spectral Irradiance on Near‐Infrared Clear‐Sky Atmospheric Absorption and Heating Rates

AbstractIn the near infrared (near IR), differences in both the absolute level and spectral resolution of available observation‐based solar spectral irradiances (SSI) are very significant. In this paper, a very high‐resolution line‐by‐line radiative transfer model has been used to investigate the effect of the differences in the absolute level of SSI on the clear‐sky total absorbed solar irradiance and solar heating rates in the near IR from 4,000 to 10,000 cm−1 (2.5–1 μm), for a midlatitude summer atmosphere. Absorption calculated using observed SSI from the surface, aircraft, and satellite are between 2 and 8% lower than that for the widely used ATmospheric Laboratory for Applications and Science (ATLAS) 3 spectrum. Tropospheric and stratospheric heating rates produce by these spectra are also lower than that produced by the ATLAS 3 spectrum by about 3–9% and 4–11%, respectively. However, there is a closer agreement between near IR absorbed irradiances and heating rates computed using two most recent observed spectra. That notwithstanding, it is recommended that the uncertainty in the choice of the SSI in near IR radiative transfer modeling should be quantified.

Solar irradiance reference spectra for two solar active levels

Two new composite solar irradiance reference spectra extending from 0.1 to 2400 nm are constructed using recent space measurements for two distinct time periods during solar cycle 22. For wavelengths above Lyman α, data were gathered from the instruments placed aboard three space platforms, the ATmospheric Laboratory for Applications and Science (ATLAS), the Upper Atmosphere Research Satellite (UARS) and the EUropean Retrieval Carrier (EURECA). Below Lyman α, data from an instrument flown on rockets are used. The two spectra obtained at the time of ATLAS 1 and 3 missions cover about half of the total solar cycle amplitude as gauged by the Mg II and F10.7 solar indices. The accuracy of the spectra varies from 40% in the X-ray to about 3% in the UV–visible, and near IR ranges. A comparison between the total solar irradiance obtained through integration of the reference spectra and their observed values at the time of the ATLAS missions shows agreements of the order of 1%.

The Solar Spectral Irradiance from 200 to 2400 nm as Measured by the SOLSPEC Spectrometer from the Atlas and Eureca Missions

The SOLar SPECtrum (SOLSPEC) and the SOlar SPectrum (SOSP) spectrometers are two twin instruments built to carry out solar spectral irradiance measurements. They are made of three spectrometers dedicated to observations in the ultraviolet, visible and infrared domains. SOLSPEC flew with the ATmospheric Laboratory for Applications and Science (ATLAS) while SOSP flew on the EUropean Retrieval CArrier (EURECA) missions. ATLAS 1 and 2 data being already published, this paper is mostly dedicated to the ATLAS 3 and EURECA data in the IR domain. Comparisons between the ATLAS data sets and the Upper Atmosphere Research Satellite (UARS) results are made. EURECA IR data are shown and compared with previous results. Our best UV, visible and IR spectra are finally merged into a single absolute solar irradiance spectrum covering the 200 to 2400 nm domain.

Polar vortex dynamics during spring and fall diagnosed using trace gas observations from the Atmospheric Trace Molecule Spectroscopy instrument

Trace gases measured by the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during three Atmospheric Laboratory for Applications and Science (ATLAS) space‐shuttle missions, in March/April 1992 (AT‐1), April 1993 (AT‐2), and November 1994 (AT‐3) have been mapped into equivalent latitude/potential temperature (EqL/θ) coordinates. The asymmetry of the spring vortices results in coverage of subtropical to polar EqLs. EqL/θ fields of long‐lived tracers in spring in both hemispheres show the net effects of descent at high EqL throughout the winter, reflecting strong descent in the upper stratosphere, decreasing descent at lower altitudes, and evidence of greater descent at the edge of the lower stratospheric vortex than in the vortex center; these results are consistent with trajectory calculations examining the history of the air measured by ATMOS in the month prior to each mission. EqL/θ tracer fields, the derived fields CH4‐CH4* (CH4* is the expected CH4 calculated from a prescribed relationship with N2O for fall) and NOy−NOy* (analogous to CH4*), and parcel histories all indicate regions of strong mixing in the 1994 Southern Hemisphere (SH) spring vortex above 500 K, with the strongest mixing confined to the vortex edge region between 500 and 700 K, and mixing throughout the Northern Hemisphere (NH) spring vortex in 1993 below about 850 K. Parcel histories indicate mixing of extravortex air with air near the vortex edge below 500 K in the SH but not with air in the vortex core; they show extravortex air mixing well into the vortex above ∼450 K in the NH and into the vortex edge region below. The effects of severe denitrification are apparent in EqL/θ HNO3 in the SH lower stratospheric spring vortex. The morphology of HNO3 in the Arctic spring lower stratospheric vortex is consistent with the effects of descent. EqL/θ fields of ATMOS NOy−NOy* show decreases consistent with the effects of mixing throughout the NH lower stratospheric vortex. The EqL/θ‐mapped ATMOS data thus indicate no significant denitrification during the 1992–1993 NH winter. Examination of H2O+2CH4 shows that dehydration in SH spring 1994 extended up to ∼600 K; it also suggests the possibility of a small amount of dehydration in the NH 1993 spring vortex below ∼465 K. Ozone depletion is evident in the spring vortices in both hemispheres. Differences in autumn EqL/θ tracer fields between the missions reflect the fact that each succeeding mission took place ∼2 weeks later in the season, when the vortex had developed further. There was greater average descent and greater isolation of air in the developing vortex during each succeeding mission, consistent with progressively larger downward excursions of long‐lived tracer contours observed in the upper stratosphere at high EqL.

ATMOS/ATLAS 3 INFRARED PROFILE MEASUREMENTS OF TRACE GASES IN THE NOVEMBER 1994 TROPICAL AND SUBTROPICAL UPPER TROPOSPHERE

Vertical mixing ratio profiles of four relatively long-lives gases, HCN, C 2H 2, CO, and C 2H 6, have been retrieved from 0.01 cm -1 resolution infrared solar occultation spectra recorded between latitudes of 5.3°N and 31.4°N. The observations were obtained by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS) 3 shuttle flight, 3–12 November 1994. Elevated mixing ratios below the tropopause were measured for these gases during several of the occultations. The positive correlations obtained between the simultaneously measured mixing ratios suggest that the enhancements are likely the result of surface emissions, most likely biomass burning and/or urban industrial activities, followed by common injection via deep convective transport of the gases to the upper troposphere. The elevated levels of HCN may account for at least part of the “missing NO y ” in the upper troposphere. Comparisons of the observations with values measured during a recent aircraft campaign are presented.

Measurements of O3, H2O and ClO in the Middle Atmosphere Using the Millimeter‐Wave Atmospheric Sounder (MAS)

The Millimeter‐Wave Atmospheric Sounder (MAS) is a shuttle‐based limb‐sounding instrument designed for global spectroscopic studies of O3, and constituents important in O3 photochemistry, in the middle atmosphere. It is part of the NASA's Atmospheric Laboratory for Applications and Science (ATLAS) spacelab shuttle mission. This paper presents an overview of the instrument, operation, and data analysis. In addition, as an example of the results, we present zonal average retrievals for O3, H2O and ClO obtained in ATLAS 1. The MAS O3 and H2O measurements are shown to agree well with simultaneous observations made with the UARS MLS instrument.

On the assessment and uncertainty of atmospheric trace gas burden measurements with high resolution infrared solar occultation spectra from space by the ATMOS Experiment

The Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument is a high resolution Fourier transform spectrometer that measures atmospheric composition from low Earth orbit with infrared solar occultation sounding in the limb geometry. Following an initial flight in 1985, ATMOS participated in the Atmospheric Laboratory for Applications and Science (ATLAS) 1, 2, and 3 Space Shuttle missions in 1992, 1993, and 1994 yielding a total of 440 occultation measurements over a nine year period. The suite of more than thirty atmospheric trace gases profiled includes CO2, O3, N2O, CH4, H2O, NO, NO2, HNO3, HCl, HF, ClONO2, CCl3F, CCl2F2, CHF2Cl, and N2O5. The analysis method has been revised throughout the mission years culminating in the ‘version 2’ data set. The spectroscopic error analysis is described in the context of supporting the precision estimates reported with the profiles; in addition, systematic uncertainties assessed from the quality of the spectroscopic database are described and tabulated for comparisons with other experiments.

The 1994 northern midlatitude budget of stratospheric chlorine derived from ATMOS/ATLAS‐3 observations

Volume mixing ratio (VMR) profiles of the chlorine‐bearing gases HCl, ClONO2, CCl3F, CCl2F2, CHClF2, CCl4, and CH3Cl have been measured between 3 and 49° northern‐ and 65 to 72° southern latitudes with the Atmospheric Trace MOlecule Spectroscopy (ATMOS) instrument during the ATmospheric Laboratory for Applications and Science (ATLAS)‐3 shuttle mission of 3 to 12 November 1994. A subset of these profiles obtained between 20 and 49°N at sunset, combined with ClO profiles measured by the Millimeter‐wave Atmospheric Sounder (MAS) also from aboard ATLAS‐3, measurements by balloon for HOCl, CH3CCl3 and C2Cl3F3, and model calculations for COClF indicates that the mean burden of chlorine, ClTOT, was equal to (3.53±0.10) ppbv (parts per billion by volume), 1‐sigma, throughout the stratosphere at the time of the ATLAS 3 mission. This is some 37% larger than the mean 2.58 ppbv value measured by ATMOS within the same latitude zone during the Spacelab 3 flight of 29 April to 6 May 1985, consitent with an exponential growth rate of the chlorine loading in the stratosphere equal to 3.3%/yr or a linear increase of 0.10 ppbv/yr over the Spring‐1985 to Fall‐1994 time period. These findings are in agreement with both the burden and increase of the main anthropogenic Cl‐bearing source gases at the surface during the 1980s, confirming that the stratospheric chlorine loading is primarily of anthropogenic origin.

Increase of stratospheric carbon tetrafluoride (CF4) based on ATMOS observations from space

Stratospheric volume mixing ratio profiles of carbon tetrafluoride, CF4, obtained with the Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument during the ATLAS (Atmospheric Laboratory for Applications and Science) −3 mission of 1994 are reported. Overall the profiles are nearly constant over the altitude range 20 to 50 km, indicative of the very long lifetime of CF4 in the atmosphere. In comparison to the stratospheric values of CF4 inferred from the ATMOS/Spacelab 3 mission of 1985, the 1994 concentrations are consistent with an exponential increase of (1.6±0.6) %/yr. This increase is discussed with regard to previous results and likely sources of CF4 at the ground. Further, it is shown that simultaneous measurements of N2O and CF4 provide a means of constraining the lower limit of the atmospheric lifetime of CF4 at least 2,300 years, two sigma.

Remote sensing of the Earth’s atmosphere from space with high-resolution Fourier-transform spectroscopy: development and methodology of data processing for the Atmospheric Trace Molecule Spectroscopy experiment

The methodology of spectroscopic remote sensing with high-resolution Fourier-transform spectra obtained from low Earth orbit by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment is discussed. During the course of the Atmospheric Laboratory for Applications and Science (ATLAS) shuttle missions (1992-1994) a flexible, yet reproducible, retrieval strategy was developed that culminated in the near-real-time processing of telemetry data into vertical profiles of atmospheric composition during the ATLAS-3 mission. The development, evolution, robustness, and validation of the measurements are presented and assessed with a summary comparison of trace-gas observations within the Antarctic polar vortex in November 1994.

Validation of the UARS solar ultraviolet irradiances: Comparison with the ATLAS 1 and 2 measurements

The measurements of the solar ultraviolet spectral irradiance made by the two Upper Atmosphere Research Satellite (UARS) solar instruments, Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) and SOLar STellar Irradiance Comparison Experiment (SOLSTICE), are compared with same‐day measurements by two solar instruments on the shuttle ATmospheric Laboratory for Applications and Science (ATLAS) missions, ATLAS SUSIM and Shuttle Solar Backscatter UltraViolet (SSBUV) experiment. These measurements from the four instruments agree to within the 2σ uncertainty of any one instrument, which is 5 to 10% for all wavelengths above 160 nm and for strong emission features below 160 nm. Additionally, the long‐term relative accuracy of the two UARS data sets is better than the original 2% goal, especially at wavelengths greater than 160 nm. This level of agreement is credited to accurate preflight calibrations coupled with comprehensive inflight calibrations to track instrument degradation. Two solar irradiance spectra, 119 to 410 nm, are presented; the first combines observations from UARS SUSIM and UARS SOLSTICE taken on March 29, 1992, during the ATLAS 1 mission, and the second combines spectra for April 15, 1993, during the ATLAS 2 mission. The ATLAS 1 mission coincided with the initial decline from the maximum of solar cycle 22 when solar activity was relatively high. The ATLAS 2 mission occurred somewhat later during the declining phase of the solar cycle 22 when solar activity was more moderate.

Imaging of artificial aurora in the upper atmosphere

We use continuum (white light) and filtered (427.8 nm) images from the Atmospheric Emissions Photometric Imaging (AEPI) experiment on the Atmospheric Laboratory for Applications and Science (ATLAS) 1 shuttle mission to investigate the shape and evolution of artificial auroral patches generated by the Space Experiments with Particle Accelerators (SEPAC) electron beam experiment. Auroral patches generated by this beam experiment are complex and differ in the white light and filtered images. In the white light images, the auroral patch consists of a relatively large, diffuse, and somewhat symmetric head and a tail that is directed approximately opposite the spacecraft velocity vector. From the growth of the tail during a beam pulse, the distance from the imager to the emissions is estimated to be about 200 km, consistent with expectations from a simple model of auroral emissions in the atmosphere. In addition to the auroral patch, an intense, diffuse, and variable background glow filling essentially the entire field of view of the white light imager is seen during the beam pulses. This background glow may be caused by low‐energy electrons very near the shuttle. This glow is absent in the filtered images, in which the shape of the auroral patch differed, consisting of a relatively large, diffuse, but more asymmetric head, a tail, and a smaller and less intense spot below the head. Curvature of the magnetic field and spacecraft motion during the 1‐s filtered images allows an estimate of the relative distance from the shuttle to the head, tail, and small spot. This shape is consistent with head emissions generated relatively near the spacecraft (nearest few kilometers), tail emissions somewhat farther away, and finally the small spot emissions generated the farthest away in the lower atmosphere where the natural auroras would be created. In addition, the shape of these patches in the filtered images suggests that the risetime for the head and tail emissions in the filtered images appears to be longer than that for the small spot emission. The differences between the white light images and the filtered images are consistent with the difference between the emission parent state lifetimes and the energy requirement for the emission production. The white light images contain emissions with long lifetimes, and these emissions which are produced near the observer are swept out of the field of view because they are left behind by the shuttle. This gives a bias toward emissions generated farther from the orbiter. The filtered images contain only the very fast produced N2+ emission with a substantial component generated near the orbiter and with an inverse square law attenuated auroral spot in the lower atmosphere. The presence of the tail and the apparent risetime in the near‐field emission suggest that there is a buildup and decay time associated with the hot plasma created by the electron beam.

H2SO4 photolysis: A source of sulfur dioxide in the upper stratosphere

Numerous absorption lines of stratospheric sulfur dioxide (SO2) have been identified in solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Atmospheric Laboratory for Applications and Science (ATLAS)‐1 shuttle mission (March 24‐April 2, 1992). Based on their analysis, a volume mixing ratio profile of SO2 increasing from (13 ± 4) p.p.t.v. (parts per 10−12 by volume) at 16 mbar (∼ 28 km) to 455 ± 90 p.p.t.v. at 0.63 mbar (∼ 52 km) has been measured with no significant profile differences between 20°N and 60°S latitude. The increase in the SO2 mixing ratios with altitude indicates the presence of a source of SO2 in the upper stratosphere. Profiles retrieved from ATMOS spectra recorded during shuttle flights in April‐May 1985 and April 1993 show similar vertical distributions but lower concentrations. Two‐dimensional model calculations with SO2 assumed as the end product of H2SO4 photolysis produce SO2 profiles consistent with the ATMOS measurements to within about a factor of 2.

Preliminary results of solar constant observations with the SOLCON experiment on ATLAS-1

A brief description is given of the Solar Constant (SOLCAN) experiment on Atmospheric Laboratory for Applications and Science (ATLAS) 1, its scientific and technical objectives, as well as its measurement principle and its on board chronology of operations. A preliminary value of the solar constant during the third solar operation of the mission is also provided.

The ATLAS-1 mission

Atmospheric Laboratory for Applications and Science (ATLAS)-1 was launched on March 24, 1992, carrying an international payload of 14 investigations, and conducted a successful series of experiments and observations over the subsequent 9 days. The objectives included: measuring the solar irradiance at high precision; remote sensing of the composition of the stratosphere, mesosphere, and thermosphere using techniques for wavelengths from 300 A to 5 mm; and inducing auroras by means of 1.2 amp electron beams. A subset of these instruments will subsequently be flown in a series of shuttle missions at roughly 1-year intervals over an 11-year solar cycle. The frequent recalibration opportunities afforded by such a program allows the transfer of calibrations to longer duration orbiting observatories. The ATLAS-1 mission occurred at the same time as the Upper Atmosphere Research Satellite (UARS), TIROS-N, and ERB satellites were in operation, and correlative measurements were conducted with these. In all, the mission was most successful in achieving its objectives and a unique and important database was acquired, with many scientific firsts accomplished. This paper provides the mission overview for the series of papers that follow.

ATLAS Space Shuttle studies Earth's atmosphere and solar input

A shuttle‐based component of NASA's Mission to Planet Earth, the Atmospheric Laboratory for Applications and Science (ATLAS), completed its second mission making detailed measurements of Earth's middle atmosphere and solar input in April 1993. ATLAS‐1 was successfully conducted in spring 1992. In addition to the standard payload, this mission carried instruments that studied the upper atmosphere, magnetosphere, space plasma physics, and ultraviolet astronomy.The ATLAS‐1 mission obtained a large database on the middle and upper atmosphere, and access to much of the data is available through the investigator teams. The mission procured the first space‐based measurements of OH in the atmosphere; compared middle atmosphere trace species between 1985 and 1992; and tested critical ionization velocity theory.

ATMOS/ATLAS 1 measurements of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere

Vertical profiles of sulfur hexafluoride (SF6) in the lower stratosphere and upper troposphere have been retrieved from 0.0l‐cm−1 resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the ATLAS (Atmospheric Laboratory for Applications and Science) 1 shuttle mission of March 24 to April 2, 1992. Based on measurements of the unresolved absorption by the SF6 ν3 band Q branch at 947.9 cm−1, average SF6 volume mixing ratios and 1‐sigma uncertainties of 3.20 ± 0.54 parts per trillion by volume (pptv; 10−12 ppv) at 200 mbar (∼11.8 km) declining to 2.86 ± 0.29 pptv at 100 mbar (∼16.2 km) and 1.95 ± 0.50 pptv at 30 mbar (∼23.9 km) have been retrieved. The profiles show no obvious dependence with latitude over the range of the measurements (eight occultations spanning 28°S to 54°S). Assuming an exponential growth model and applying a correction for the interhemispheric concentration difference, an average SF6 rate of increase of 8.7 ± 2.2% per year, 2 sigma, between 12 and 18 km has been derived by fitting the present measurements, ATMOS measurements from the April‐May 1985 Spacelab 3 mission, and balloon‐borne IR measurements obtained in March 1981 and June 1988.

The ATLAS‐1 shuttle mission

A space shuttle mission scheduled for launch on March 23, 1992, carrying a payload of largely remote‐sensing instruments, will constitute an important element of the NASA's Mission to Planet Earth and the U.S. Global Change Research Program. The mission was planned in 1983 and was earlier known as the Earth Observations Mission (EOM), subsequently becoming the Atmospheric Laboratory for Applications and Science (ATLAS) in 1986.The ATLAS‐1 flight is intended to be the first in a series of shuttle flights that will monitor the radiant energy output of the Sun, look for potential responses of the Earth's atmosphere to changes in this energy source, and verity global change assessments. Emphasis is on the frequent recalibration opportunities afforded by such a program, which allow transfer of calibrations to other longer‐duration orbiting observatories, such as the National Atmospheric and Oceanic Administration TIROS‐N satellites