J.J. Remedios

Measurements of the evolution of the Mt. Pinatubo aerosol cloud by ISAMS

Measurements by the Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) are being used to study the spatial and temporal evolution of the volcanic stratospheric aerosol from Mt. Pinatubo. The maximum opacity of the aerosol cloud moved from a position south of the Equator at an altitude of about 26 km in early October 1991, became located over the Equator by mid-January 1992, and descended in altitude to about 21 km by July 1992. Dispersal of the cloud was more rapid in the Southern Hemisphere and penetration to the southern polar region occurred earlier than transport to the corresponding northern polar area. The area weighted global mean stratospheric optical thickness between 15 km and 35 km at 12.1 μm remained at about 5.5×10−3 from November 1991 through to April 1992. The estimated aerosol mass loading is 19–26 megatonnes for this period and by the end of July 1992 it had declined to 15–21 megatonnes.

Spectral parameters of self- and hydrogen-broadened methane from 2000 to 9500 cm-1 for remote sounding of the atmosphere of Jupiter

Abstract Long-pathlength self- and H 2 -broadened absorption spectra of CH 4 have been recorded from 2000 to 9500 cm -1 at a resolution of 0.25 cm -1 . Thesespectra were obtained for a wide range of conditions relevant to the atmosphere of Jupiter, including nominal temperatures of 190, 240, and 296 K, pathlenghts from 64 to 512 m, and pressures from 0.2 to 700 torr, giving CH 4 column abundances from 0.016 to 530 m-amagat. A series of molecular band models were fitted to these spectra at 10 cm -1 resolution, showingthat the Goody and Malkmus random band models with the Voigt lineshape provided the best fits to the data. The Goody-Voigt model was subsequently used to calculate the level in the Jovian atmosphere that will be sounded by observations of CH 4 absorption, and estimates were made of the accuracy to be expected if this model were used to retrieve atmospheric parameters.

Infrared absorption by volcanic stratospheric aerosols observed by ISAMS

The Improved Stratospheric and Mesospheric Sounder (ISAMS) aboard the Upper Atmosphere Research Satellite (UARS) senses in 14 wideband channels in the infrared. The absorption by the Mt. Pinatubo aerosol cloud for nine of the channels was averaged over heights from 20 km to 30 km for a 60° latitude band centred on the Equator. The absorption spectrum for sulphuric acid-water aerosols was calculated for wavelengths from 4 μm to 17 μm and investigated as a function of the particle size distribution and the particle composition. The infrared spectrum is shown to be more sensitive to changes in particle composition than to drop size; the ISAMS results are consistent with drops composed of a 59% to 77% solution of sulphuric acid in water.

Observations of Middle Atmosphere CO from the UARS ISAMS during the Early Northern Winter 1991/92

Abstract Structure and kinematics of carbon monoxide in the upper stratosphere and lower mesosphere (10–0.03 hPa) are studied for the early northern winter 1991/92 using the Upper Atmosphere Research Satellite Improved Stratospheric and Mesospheric Sounder (ISAMS) measurements. The study is aided by data from a 6-week parameterized-chemistry run of the Goddard Space Flight Center 3D Chemistry and Transport Model (CTM), initialized on 8 December 1991. Generally, CO mixing ratios increase with height due to the increasing source contribution from CO2 photolysis. In the tropical upper stratosphere, however, a local maximum in CO mixing ratio occurs. A simple photochemical model is used to show that this feature results largely from methane oxidation. In the extratropics the photochemical lifetime of CO is long, and therefore its evolution is dictated by large-scale motion of air, evidenced by strong correlation with Ertel potential vorticity. This makes CO one of the few useful observable tracers at the stra...

Antarctic polar descent and planetary wave activity observed in ISAMS CO from April to July 1992

Antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesosphere are observed in ISAMS CO data from April to July 1992. CO-derived mean April-to-May upper stratosphere descent rates of 15 K/day (0.25 km/day) at 60°S and 20 K/day (0.33 km/day) at 80°S are compared with descent rates from diabatic trajectory analyses. At 60°S there is excellent agreement, while at 80°S the trajectory-derived descent is significantly larger in early April. Zonal wavenumber 1 enhancement of CO is observed on 9 and 28 May, coincident with enhanced wave 1 in UKMO geopotential height. The 9 May event extends from 40 to 70 km and shows westward phase tilt with height, while the 28 May event extends from 40 to 50 km and shows virtually no phase tilt with height.

A coolable long path absorption cell for laboratory spectroscopic studies of gases

Abstract A long path absorption cell (Long White Cell) which has been designed and built for laboratory spectroscopic studies of gases found in terrestrial and planetary atmospheres is described. Factors influencing the design and construction are discussed, including aspects of the optical, mechanical, cryogenic, vacuum, gas handling and safety systems, and the pressure and temperature monitoring systems. The practical capabilities of the cell include absorber pathlengths up to 512 m, gas sample pressures up to 5 bar and temperatures between 190 and 300 K, and the suitability for use with corrosive and flammable gases. The performance of the cell is discussed in relation to spectroscopic measurements of mixtures of gaseous methane and hydrogen.

The effect of sample emission on measurements of spectral parameters using a fourier transform absorption spectrometer

Radiative transfer within an interferometric spectrometer is discussed in relation to measurements of infrared transmittance spectra of gases. It is shown that for certain types of interferometric spectrometers, radiation from sources other than the spectrometer source must be considered, including the gas sample itself, if significant errors in measurement of line strengths and line widths are to be avoided. The validity of the radiative transfer theory is demonstrated by applying it to spectra of an evacuated gas cell, recorded over a range of temperatures, and thereby deriving a temperature independent emissivity for the cell windows. The error introduced into measurements of spectral line strengths and line widths is discussed with reference to experimental values of these parameters obtained for lines in the v2 band of H2O using a Bomem DA 3.002 spectrometer. Ways in which the effects of radiation from the gas cell and its contents can be minimised or eliminated are discussed, including an experimental procedure involving measurements with two different temperatures of the spectrometer source.

Properties of Northern Hemisphere Polar Stratospheric Clouds and Volcanic Aerosol in 1991/92 from UARS/ISAMS Satellite Measurements

Abstract Observations of polar stratospheric clouds by the Improved Stratospheric and Mesospheric Sounder (ISAMS) experiment on the Upper Atmospheric Research Satellite (UARS) have revealed new details of their global properties and behavior. These include the vertical and horizontal spatial distributions of Arctic and Antarctic polar stratospheric clouds (PSCs) as a function of time and air temperature, their optical thicknesses and estimated densities, their spectral properties, and their inferred composition. In particular, ISAMS spectral data allows different PSC types to be distinguished from each other and from volcanic aerosol by their compositional differences. Northern PSCs during the 1991/92 season are found to be more ephemeral and more compact than reported in previous years and to differ markedly in scale from those in the Southern Hemisphere, which cause the Antarctic ozone hole by activating stratospheric chlorine chemistry. There were only two episodes of dense PSC formation in the 1991/92...

Experimental spectral line parameters in the 1-0 band of nitric oxide

Abstract Laboratory Fourier transform absorption spectroscopy has been used to obtain new measurements of spectral line parameters in the P and R branches of the two allowed 1-0 subbands of NO. Parameters measured are the self-broadened widths and absolute strengths at room temperature and the N2-broadened widths over the temperature range 213–296 K. From these data a band-strength at 296 K (4.45 ∗ 10−17 cm−1/mol cm−2) and an average temperature exponent of N2-broadened linewidths (−0.71) have been derived. The J dependence of the temperature exponent was examined and found to be insignificant compared to experimental error.

Stratospheric and mesospheric observations with ISAMS

Abstract The scientific objectives of the Improved Stratospheric and Mesospheric Sounder (ISAMS) experiment involve the measurement of global temperature and composition profiles from an instrument on the Upper Atmosphere Research Satellite (UARS). This paper discusses these objectives in the light of the data acquired during the first ten months of the mission. Interesting interim results include detailed observations of a stratospheric sudden warming and a nitrogen dioxide (NO2) “Noxon cliff”, enhanced thermospheric nitric oxide (NO) production during a solar flare, strongly increased concentrations of carbon monoxide (CO) over the winter poles, non-LTE behaviour of mesospheric water vapour (H2O), and unexpected transport properties of volcanic aerosol, and the long-lived tracers methane (CH4) and nitrous oxide (N2O).