William G. Mankin

Airborne observations of SO2, HCl, and O3 in the stratospheric plume of the Pinatubo Volcano in July 1991

We have used a high resolution infrared spectrometer aboard the NASA Wallops Flight Facility Electra aircraft to measure the total column amount of SO2, O3, and HCl above the aircraft while flying over the Caribbean three weeks after the June 15 eruption of Mt. Pinatubo in the Philippines, South of 20°N latitude we observed columns of SO2 ranging from 2.0 × 1016 to 3.7 × 1016 molecules-cm−2. In addition, the column amount of HCl averaged 1.5 × 1015 molecules-cm−2 in the region of the plume. This may represent a small increase in HCl above the amount, estimated from our previous measurements, that would have been present had there been no volcanic eruption, but the increase is substantially less than that seen following the 1982 eruptions of El Chichon [Mankin and Coffey, 1984].

Increased Stratospheric Hydrogen Chloride in the El Chichón Cloud

Spectroscopic observations of the total column amount of hydrogen chloride above an altitude of 12 kilometers in the latitude range 20� to 40�N have been made both before and 3 to 6 months after the eruptions of El Chich�n Volcano in March and April 1982. In the region of the cloud of volcanic aerosols, the hydrogen chloride total column after the eruptions increased by approximately 40 percent, even after allowance is made for the global secular increase in hydrogen chloride of 5 percent per year. The column amounts of hydrogen fluoride show no such increase.

Spectroscopic Detection of Stratospheric Hydrogen Cyanide

A number of features have been identified as absorption lines of hydrogen cyanide in infrared spectra of stratospheric absorption obtained from a high-altitude aircraft. Column amounts of stratospheric hydrogen cyanide have been derived from spectra recorded on eight flights. The average vertical column amount above 12 kilometers is 7.1 � 0.8 x 1014 molecules per square centimeter, corresponding to an average mixing ratio of 170 parts per trillion by volume.

Network for the Detection of Stratospheric Change Fourier transform infrared intercomparison at Table Mountain Facility, November 1996

An intercomparison of four Fourier transform infrared (FTIR) spectrometers, operated side by side by Jet Propulsion Laboratory (JPL), National Center for Atmospheric Research, and National Physical Laboratory groups, using two different spectral fitting algorithms, was conducted at JPLs Table Mountain Facility (TMF) during November 1996. A “blind” comparison of retrieved vertical column amounts, of preselected trace gases in preselected microwindows (mw), and subsequent reanalysis of the results are described. The species analyzed are N2 (3 mw), HF (1 mw), HCl (1 mw), CH4 (1 mw), O3 (2 mw), N2O (2 mw), HNO3 (2 mw), and CO2 (1 mw). The column agreements from the “blind” phase were within 0.5–2%, except that for HNO3, HF, and O3 the disagreement of the results was up to 10%, 5%, and 4%, respectively. It was found that several systematic effects were neglected in the “blind” phase analysis. Taking these into account in the postanalysis reduced the disagreements to 0.5–1.0% for most cases, and to less than 4%, 3%, and 1% for HNO3, HF, and O3 respectively. It was concluded that zero off-sets caused by detector nonlinearity were the main cause of the large errors in HNO3 and other gases (i.e., CO2) retrieved from the HgCdTe spectra. At shorter wavelengths (i.e., HF) we conclude that incomplete modeling of the instrument line shapes (ILS) was the main cause of column differences larger than 1%.

The High-Resolution Dynamics Limb Sounder (HIRDLS) experiment on AURA

Space-based experiments have contributed much to our knowledge of the stratosphere in recent years. These observations have been characterized by large horizontal or vertical scales, leaving a range of unobserved phenomena at smaller scales. This is especially true at the tropopause, the boundary between the troposphere and stratosphere, where rapid changes in the vertical in temperature and composition have been unobserved on a global basis. The HIRDLS instrument has been designed to address these issues. HIRDLS is a 21 channel limb scanning infrared radiometer designed to make global measurements at smaller vertical and horizontal scales than have been previously observed, from pole to pole, at altitudes of 8-80 km. This paper will present an overview of the HIRDLS science and instrument, as well as the data retrieval process. It will serve as an introduction to the series of subsequent papers dealing with the calibration and other aspects of the experiment.

On the use of HF as a reference for the comparison of stratospheric observations and models

Hydrogen fluoride (HF) is often used as a simple reference for other column observations of chemically active stratospheric species. However, seasonal and shorter timescale variations in column HF make its use as a reference more complicated. In this paper we characterize the expected magnitude of these variations in HF, and variations of ratio quantities involving HF, using a two-dimensional (2-D) photochemical model and two versions of a three-dimensional (3-D) transport model. The 2-D model predicts that the column ratios HNO3/HF and HCl/HF increase from midlatitudes to the tropics, although this is very sensitive to HCl and HNO3 abundances in the tropical upper troposphere. Seasonal variations in vertical motion modifys the predicted ratios; for example, wintertime descent at high latitudes decreases HCl/HF. The ratio HNO3/HF at high latitudes is strongly modified by seasonal variations in the chemical partitioning of the odd nitrogen (NOy) species. We compare these model predictions with ground-based Fourier transform infrared spectroscopy (FTIR) observations of HF along with HCl, ClONO2 and HNO3 obtained at eight northern hemisphere sites between October 1994 and July 1995. We investigate quantitatively how HF can be used as a tracer to follow the evolution of observations at a single station and to intercompare results from different stations or with photochemical models. The magnitude of the 3-D model HF column agrees well with the observations, except on some occasions at high latitudes, giving indirect support for the important role of COF2 in the stratospheric inorganic fluorine budget. The observed day-to-day variability in the column ratios HCl/HF and HNO3/HF is much larger at high latitudes. This variability is reproduced in the 3-D models and is due to horizontal motion. Short timescale vertical displacement of the species profiles is estimated to have a small effect on the column ratios. In particular, we analyze the usefulness of the observed column ratio (ClONO2 + HCl)/HF as an indicator for chlorine activation. Current measurement uncertainties limit the degree of activation which can be unambiguously detected using this observed quantity, but we can determine that chlorine-activated air was observed above Aberdeen (58°N) on 6 days in late January 1995.

Ground-based infrared solar spectroscopic measurements of carbon monoxide during 1994 Measurement of Air Pollution From Space flights

Results of the comparison of carbon monoxide ground-based infrared solar spectroscopic measurements with data obtained during 1994 Measurement of Air Pollution From Space (MAPS) flights are presented. Spectroscopic measurements were performed correlatively with April and October MAPS flights by nine research groups from Belgium, Canada, Germany, Japan, New Zealand, Russia, and the United States. Characterization of the techniques and error analysis were performed. The role of the CO a priori profile used in the retrieval was estimated. In most cases an agreement between spectroscopic and MAPS data is within estimated MAPS accuracy of _+ 10%.

Balloon Intercomparison Campaigns: Results of remote sensing measurements of HCl

All of the techniques used to measure stratospheric HCl during the two BIC campaigns involved high resolution infrared spectroscopy. The balloon-borne instruments included five different spectrometers, three operating in the solar absorption mode and two in emission (at distinctly different wavelengths). Ground-based and aircraft correlative measurements were made close to the balloon locations, again by near-infrared spectroscopy.Within this set of results, comparisons between different techniques (absorption vs emission) viewing the same airmass (i.e., on the same gondola) were possible, as were comparisons between the same technique used on different gondolas spaced closely in time and location. The final results yield a mean profile of concentration of HC1 between 18 and 40 km altitude; an envelope of ±15% centered on this profile encompasses all of the results within one standard deviation of their individual mean values. The absolute accuracy of the final profile is estimated to be no worse than 10%. It is concluded also that the measurement techniques for HCl have reached a level of performance where a precision of 10% to 15% can be confidently expected.

Airborne Fourier Transform Spectroscopy of the Upper Atmosphere

High resolution infrared spectroscopy is a very useful technique for remote sensing of atmospheric constituents. From an aircraft it is possible to use emission or absorption spectroscopy to measure total quantities of constituents above the aircraft or profiles at altitudes below the flight. The adaptation of a commercial high resolution (0.06 cm-1) Fourier transform infrared spectrometer for use in absorption spectroscopy on a jet aircraft is described, emphasizing methods of dealing with the difficulties of the aircraft environment. Atmospheric constituents with concentrations less than one part per billion can be measured.

Fourier transform method for calculating the transmittance of inhomogeneous atmospheres.

For spectral lines with combined Doppler and pressure broadening, the Fourier transform of the line shape is calculated analytically in an isothermal layer in which both the pressure and absorber concentrations vary along the line of sight. Use of the Cooley-Tukey fast Fourier transform algorithm allows efficient computation of the optical depth of such layers containing a large number of absorption lines of the same shape. The computation time is almost independent of the number of absorption lines. In many cases, this method allows increased speed and accuracy compared with conventional line-by-line methods.