Brian J. Kerridge

Direct measurement of tropospheric ozone distributions from space

The role of ozone in absorbing ultraviolet solar radiation is well known. Ozone also makes a significant contribution to the radiative balance of the upper troposphere and lower stratosphere, such that changes in the distribution of ozone in these atmospheric regions will affect the radiative forcing of climate,. Furthermore, tropospheric ozone is the source of the hydroxyl radical which controls the abundance and distribution of many atmospheric constituents, including greenhouse gases such as methane and hydrochlorofluorocarbons. Tropospheric ozone is produced photochemically in situ and is also transported down from the stratosphere, but the relative importance of these two sources to its global budget is poorly understood. High-quality tropospheric and lower-stratospheric ozone profile measurements are available from sondes and lidar techniques, but their geographical sampling is very limited. Complementary satellite measurements of the global ozone distribution in this height region are therefore required to quantify ozones tropospheric budget and its participation in climate-forcing and tropospheric chemistry. Here we present direct measurements of tropospheric ozone concentrations from space, made by the European Space Agencys Global Ozone Monitoring Experiment. These results demonstrate the potential of satellite measurements to provide self-consistent tropospheric and stratospheric ozone distributions on a global scale.

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.

Non‐local thermodynamic equilibrium model for H2O 6.3 and 2.7‐μm bands in the middle atmosphere

A non-local thermodynamic equilibrium radiative transfer model is presented for the populations of H2O and O2(1) vibrational levels in the middle atmosphere. Radiative transfer in the H2O bands is treated using the Curtis matrix method, and an exhaustive review of the collisional processes and their rate constants affecting the populations of these levels has been carried out. The near resonant vibrational-vibrational coupling between H2O(010) and O2(1) is crucial for establishing their respective populations in the mesosphere. The population of H2O(010) starts departing from LTE significantly above about 65 km at night, this precise altitude being dependent on the temperature structure. At daytime, non-LTE begins at approximately the same height but is significantly enhanced with respect to nighttime. The principal additional daytime excitation processes are absorption of solar radiation by H2O at 2.7 and 6.3 μm in the upper mesosphere and lower thermosphere and excitation from the photodissociation of O3 through O2(1) in the lower mesosphere. A sensitivity study of the H2O and O2(1) vibrational temperatures to the atmospheric and model parameters has been carried out. A preliminary analysis of ISAMS/UARS measurements in the 6.9-μm H2O pressure-modulated (PM) and wideband (WB) channels is presented. The measurements show enhancements in the daytime radiances in both channels, as compared to the nighttime values, above about 55 km. The effect is larger in the WB channel. Comparisons with the model show that non-LTE excitation of the H2O (010) and (020) levels is responsible.

Evaluation of Global Ozone Monitoring Experiment (GOME) ozone profiles from nine different algorithms

An evaluation is made of ozone profiles retrieved from measurements of the nadir-viewing Global Ozone Monitoring Experiment (GOME) instrument. Currently four different approaches are used to retrieve ozone profile information from GOME measurements, which differ in the use of external information and a priori constraints. In total nine different algorithms will be evaluated exploiting the Optimal Estimation (Royal Netherlands Meteorological Institute, Rutherford Appleton Laboratory, University of Bremen, National Oceanic and Atmospheric Administration, Smithsonian Astrophysical Observatory), Phillips-Tikhonov Regularization (Space Research Organization Netherlands), Neural Network (Center for Solar Energy and Hydrogen Research, Tor Vergata University), and Data Assimilation (German Aerospace Center) approaches. Analysis tools are used to interpret data sets that provide averaging kernels. In the interpretation of these data, the focus is on the vertical resolution, the indicative altitude of the retrieved value, and the fraction of a priori information. The evaluation is completed with a comparison of the results to lidar data from the NDSC (Network for Detection of Stratospheric Change) stations in Andoya (Norway), Observatoire Haute Provence (France), Mauna Loa (USA), Lauder (New Zealand) and Dumont d’Urville (Antarctic) for the years 1997–1999. In total the comparison involves nearly 1000 ozone profiles, and allows the analysis of GOME data measured in different global regions and hence observational circumstances. The main conclusion of this paper is that unambiguous information on the ozone profile can at best be retrieved in the altitude range 15–48 km with a vertical resolution of 10 to 15 km, precision of 5–10%, and a bias up to 5% or 20% depending on the success of recalibration of the input spectra. The sensitivity of retrievals to ozone at lower altitudes varies from scheme to scheme and includes significant influence from a priori assumptions.

Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite

For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H2O, O3, HNO3, CH4, N2O, and NO2 have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.

Observations of V = 1–0 emission from thermospheric nitric oxide by ISAMS

The Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) has made global measurements of emission from the 1→0 band of nitric oxide (NO), using a limb viewing geometry in which the tangent point is scanned from 0 km to >150 km. Vertical profiles of atmospheric radiance often show a peak around 120 km altitude, due to the relatively high temperatures and densities of NO(v=1) found in the lower thermosphere. In this letter we report on some aspects of the radiance from NO(v=1), in particular observations of the lower thermosphere during periods of quiet and intense geomagnetic activity.

Validation of nitrogen dioxide measurements from the Improved Stratospheric and Mesospheric Sounder

Measurements of nitrogen dioxide (NO2) from the Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) are assessed. Channel 5 of the instrument was dedicated to observations of nitrogen dioxide and employed pressure-modulation and wideband radiometry to make measurements at 6.2 μm. This dual technique allows simultaneous determination of nitrogen dioxide mixing ratio and the aerosol extinction coefficient at this wavelength and therefore provides nitrogen dioxide data even in the presence of heavy aerosol loading. Approximately 180 days of data, in the period from September 1991 to July 1992, were obtained with, typically, over 2600 profiles per day for each retrieved species, covering an altitude range of 100–0.01 mbar. In this paper the version 10 data are assessed and a full error analysis is described. Comparisons with the Cryogenic Limb Array Etalon Spectrometer (CLAES) on UARS and the Limb Infrared Monitor of the Stratosphere (LIMS) on Nimbus 7 are also presented. It is concluded that the morphology of the retrieved ISAMS fields is robust and consistent with concurrent as well as previous infrared satellite measurements. Random errors are estimated to be of the order of 10% for nighttime and 15% for daytime NO2 near the maxima of the distributions, and systematic errors are estimated to be of a similar size. However, there remains an unresolved systematic difference of about a factor of 2 between ISAMS and CLAES. Both random and systematic errors are likely to be reduced in future versions of the processing.

New cryogenic heterodyne techniques applied in TELIS: the balloon-borne THz and submillimeter limb sounder for atmospheric research

We present a design concept for a new state-of-the-art balloon borne atmospheric monitor that will allow enhanced limb sounding of the Earths atmosphere within the submillimeter and far-infrared wavelength spectral range: TELIS, TErahertz and submm LImb Sounder. The instrument is being developed by a consortium of major European institutes that includes the Space Research Organization of the Netherlands (SRON), the Rutherford Appleton Laboratory (RAL) will utilize state-of-the-art superconducting heterodyne technology and is designed to be a compact, lightweight instrument cpaable of providing broad spectral coverage, high spectral resolution and long flight duration (~24 hours duration during a single flight campaign). The combination of high sensitivity and extensive flight duration will allow evaluation of the diurnal variation of key atmospheric constitutenets sucyh as OH, HO2, ClO, BrO togehter will onger lived constituents such as O3, HCL and N2O. Furthermore, TELIS will share a common balloon platform to that of the MIPAS-B Fourier Transform Spectrometer, developed by the Institute of Meteorology and Climate research of the over an extended spectral range. The combination of the TELIS and MIPAS instruments will provide atmospheric scientists with a very powerful observational tool. TELIS will serve as a testbed for new cryogenic heterodyne detection techniques, and as such it will act as a prelude to future spaceborne instruments planned by the European Space Agency (ESA).

Dinitrogen pentoxide measurements from the improved stratospheric and mesospheric sounder: Validation of preliminary results

The improved stratospheric and mesospheric sounder (ISAMS) on the Upper Atmosphere Research Satellite (UARS) made some of the first global measurements of dinitrogen pentoxide (N 2 O 5 ) in the 1991/1992 period. N 2 O 5 is a crucial part of the ozone photochemical cycle in the stratosphere, but measurements of its variability and distribution are difficult and hitherto have been rare, inhibiting adequate testing of dynamical-chemical models of the stratosphere. This paper describes the production and validation of the first set of ISAMS global N 2 O 5 data to be made publically available (version 10). It is concluded that the results represent a considerable improvement over those previously available and are ready for use in certain kinds of scientific work. There still exist problems regarding the treatment of stratospheric sulfate aerosol which further processing will hopefully resolve.

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).