Ground-based measurements of O3, NO2, OClO, and BrO during the 1987 Antarctic ozone depletion event

Near-ultraviolet absorption spectroscopy in the wavelength range from 330 to 370 nm was used to measure O3, NO2, OClO, and BrO at McMurdo Station (78S) during 1987. Visible absorption measurements of O3, NO2, and OClO were also obtained using the wavelength range from about 403 to 453 nm. These data are described and compared to observations obtained in 1986. It is shown that comparisons of observations in the two wavelength ranges provide a sensitive measure of the altitude where the bulk of atmospheric absorption takes place

Near UV atmospheric absorption measurements from the DC-8 aircraft during the 1987 airborne Antarctic ozone experiment

During the Airborne Antarctic Ozone Experiment from 28 August to 30 September 1987 near UV zenith scattered sky measurements were made over Antarctic from the NASA DC-8 aircraft using a one third m spectrograph equipped with a diode-array detector. Scattered sky light data in the wavelength range 348 nm to 388 nm was spectrally analyzed for O3, NO2, OClO, and BrO column abundances. Slant column abudances of O3, NO2, OClO and BrO were determined, using a computer algorithm of non-linear and linear least square correlation of Antarctic scattered sky spectra to laboratory absorption cross section data. Using measured vertical electrochemical sonde ozone profiles from Palmer, Halley Bay, and the South Pole Stations the slant columns of O3 were converted into vertical column abundances. The vertical column amounts of NO2, OClO, and BrO were derived using vertical profiles calculated by a chemical model appropriate for Antarctica. NO2 vertical column abundances show steep latitudinal decrease with increasing latitude for all 13 flights carried out during the mission. In the regions where NO2 abudances are low, OClO and BrO were observed. The spatial and temporal vertical column abundances of these species are discussed in the context of the chemistry and dynamics in the antarctic polar vortex during the austral spring

Visible and near-ultraviolet spectroscopy at Thule AFB (76.5 N) from January 28 - February 15, 1988

Near-ultraviolet and visible spectrographs identical to those employed at McMurdo Station, Antarctica (77.8 S) during the austral spring seasons of 1986 and 1987 were used to study the stratosphere above Thule, Greenland (76.5 N) during early spring, 1988. Observations were carried out both at night using the direct moon as a light source, and during the day by collecting the scattered light from the zenith sky when solar zenith angles were less than about 94.5 degrees. Excellent meteorological conditions prevailed in the troposphere and stratosphere at Thule. Surface weather was extremely clear over most of the period, facilitating measurements of the direct light from the moon. The lower stratospheric arctic polar vortex was located very near Thule throughout the observing period, and temperature at the 30 mbar level were typically below -80 C above Thule, according to the National Meteorological Center daily analyses. Thus conditions were favorable for polar stratospheric cloud formation above Thule. Total column ozone abundances were about 350 to 400 Dobson units, and did not suggest a clear temporal trend over the observing period. Stratospheric nitrogen dioxide measurements were complicated by the presence of a large component of tropospheric pollution on many occasions. Stratospheric nitrogen dioxide could be identified on most days using the absorption in the scattered light from the zenith sky, which greatly enhances the stratospheric airmass while suppressing the tropospheric contribution. These measurements suggest that the total vertical column abundance of nitrogen dioxide present over Thule in February was extremely low, sometimes as low as 3 x 10 to the 14th per sq cm. The abundance of nitrogen dioxide increased systemically from about 3 x 10 to the 14th in late January to 1.0 x 10 to the 15th per sq cm in mid-February, perhaps because of photolysis of N2O5 in the upper part of the stratosphere, near 25 to 35 km

CRITIQUE OF THE METHODS OF ANALYZING SPECTRAL LINE POSITIONS

Author Institution: Aeronomy Laboratory, National Oceanic and Atmospheric Administration Environmental Research Laboratories Boulder; Department of Chemistry, Columbia UniversityMolecular constants can be determined from spectral data by (a) fitting the observed line positions with a set of calculated line positions given by the differences between the eigenvalues of numerically diagonalized Hamiltonians for the upper and lower states, and by (b) fitting the observed lines with a set of calculated term values and then subsequently fitting these term values with the eigenvalues of the Hamiltonians. It is shown that, in method (b), the resulting molecular constants and their associated uncertainties can be significantly in error if the relative uncertainties and correlations of the term values are not used in the subsequent fitting of these term values with the eigenvalues of a Hamiltonian. Moreover, it is shown that method (b) is equivalent to method (a) only if these uncertainties and correlations are indeed maintained in method (b). In addition, it is pointed out how a simultaneous fit to all of the recorded bands of a band system may mask the effects of systematic errors between the bands, leading to erroneously optimistic uncertainties for the resulting molecular constants. Method (a) is applied to the $O_{2} b^{1} \Sigma_{g}^{+} -X^{3} \Sigma_{g}^{-}$ Red Atmospheric bands. The discrepancies concerning the optical and microwave values for $B_{O}$ and $D_{O}$ of the $X^{3}\Sigma_{g}^{-}$ state are removed by a non-linear least-squares fit to all of the lines recorded by Babcock and Herzberg (Astrophys. J. 108, 167, 1948)

AN EXTENSION AND REANALYSIS OF THE b4∑gb^{4}\sum_{g} - a4Πa^{4}\Pi FIRST NEGATIVE BAND SYSTEM OF O2+O_{2}^{+}

Author Institution: National Oceanic and Atmospheric Administration, Aeronomy Laboratory; Department of Chemistry, Columbia University; Observatoire de Paris section d Astrophysqua, Columbia UniversityThe $O_{2}^{+}$ $b^{4}\sum_{g}$- - $a^{4}\Pi_{u}$ First Negative system has been extended to a new level of the upper state with the measurement of the (3,1) band. This new band and the previously measured bands of this system have been reduced to molecular constants by fitting each band separately and these results have been combined to yield a minimum-variance set of molecular constants for $v^{\prime} \leq 3$ and $v^{\prime\prime} \leq 6$. It was found that the ``anomalies” in the fine-structure splittings of the $^{4}\Pi_{u}$ state can be accounted for fully by the diagonal and off-diagonal elements of the phenomenological spin-spin Hamiltonian, rather than perturbations caused by two $^{2}\Pi$ states, as was previously thought. Particular attention has been paid to the correlation between the centrifugal distortion spin-orbit constant $A^\pi_{D}$ and the spin-rotation constant $\gamma^\pi$. A previously unnoticed possible perturbation in the $^{4}\Pi_{u}$ state also has been examined

RKR POTENTIAL FOR THE X1Σ+X^{1}\Sigma^{+} STATE OF CO

Author Institution: Wright-Patterson Air Force Base; Environmental Research Laboratories; Columbia UniversityEmploying the recent measurements of CO laser spectra and other precision absorption and emission data pertaining to this molecule, the RKR potential for the ${X}^{1}\Sigma^{1}$ state of the CO molecule was evaluated by two different approaches. The $r_{\max}$ and $r_{\min}$ values calculated agreed almost perfectly in these two sets of evaluations. Reasons will be advanced to show that the RKR potential developed is close to the true potential of the ground electronic state of CO