Backscatter Ultraviolet Data Research Articles

A comparison of 40 years of SBUV measurements of column ozone with data from the Dobson/Brewer network

AbstractTotal column ozone data from the Nimbus‐4 Backscatter UltraViolet (BUV) instrument, Nimbus‐7 Solar Backscatter Ultraviolet (SBUV) instrument, as well as from seven NOAA SBUV/2 instruments have been newly reprocessed with the Version 8.6 ozone retrieval algorithm. This yields a coherent data set that, unlike the Total Ozone Mapping Spectrometer ozone record, has no data gaps or significant time periods with large uncertainties due to calibration issues from 1979 to the present. The column ozone data from the first 3 years of the BUV record (1970–1972) is of high quality and can be used to extend the satellite ozone record back over 40 years. With the new algorithm, an improved total column ozone value is calculated by summing up the profile information as opposed to a single direct column measurement, and the algorithm is optimized for the detection of long‐term trends. The results from this processing of these data have been systematically compared to total ozone data from Brewer and Dobson spectrophotometers for many individual ground stations as a function of time, satellite solar zenith angle, and latitude. The time series comparisons show an agreement within ± 1% over the past 40 years with the bias approaching zero over the last decade. The aerosols associated with the eruption of Mt Pinatubo in 1991 produced an underestimation of ozone for our retrievals at high slant columns while the near‐nadir values were relatively unaffected. There is very little systematic offset between the satellite and ground‐based measurements as a function of latitude with the Nimbus‐4 BUV data (1970–1976) showing the largest offsets. The comparisons as a function of satellite solar zenith angle show consistent behavior for all instruments. Comparisons with ozonesonde data show good agreement in the integrated column up to 25 hPa with differences of no more than 5%.

Seasonal persistence of ozone and zonal wind anomalies in the equatorial stratosphere

Analysis of the variability of equatorial ozone profiles in the Satellite Aerosol and Gas Experiment‐corrected Solar Backscatter Ultraviolet data set demonstrates a strong seasonal persistence of interannual ozone anomalies, revealing a seasonal dependence to equatorial ozone variability. In the lower stratosphere (40–25 hPa) and in the upper stratosphere (6–4 hPa), ozone anomalies persist from approximately November until June of the following year, while ozone anomalies in the layer between 16 and 10 hPa persist from June to December. Analysis of zonal wind fields in the lower stratosphere and temperature fields in the upper stratosphere reveals a similar seasonal persistence of the zonal wind and temperature anomalies associated with the quasi‐biennial oscillation (QBO). Thus, the persistence of interannual ozone anomalies in the lower and upper equatorial stratosphere, which are mainly associated with the well‐known QBO ozone signal through the QBO‐induced meridional circulation, is related to a newly identified seasonal persistence of the QBO itself. The upper stratospheric QBO ozone signal is argued to arise from a combination of QBO‐induced temperature and NOx perturbations, with the former dominating at 5 hPa and the latter at 10 hPa. Ozone anomalies in the transition zone between dynamical and photochemical control of ozone (16–10 hPa) are less influenced by the QBO signal and show a quite different seasonal persistence compared to the regions above and below.

A composite Mg II index spanning from 1978 to 2003

The Mg II core‐to‐wing ratio is a measure of solar chromospheric variability. The Mg II Index, formed by combining various Mg II core‐to‐wing data sets, has been used in EUV, UV, and total solar irradiance models. It is one of the longest records of solar variability reaching back nearly 25 years. We present a single, continuous time series of the Mg II core‐to‐wing ratio extending from November 1978 to the present. The Mg II core‐to‐wing ratio is a measurement that is well suited to the creating of a single time series despite the fact that the seven different instruments measuring the solar flux near 280 nm have different spectral resolutions and sample rates. The Upper Atmosphere Research Satellite (UARS) Solar Ultraviolet Spectral Irradiance Monitor (SUSIM), UARS Solar Stellar Irradiance Comparison Experiment (SOLSTICE), ERS‐2/Global Ozone Monitoring Experiment (GOME) and five NOAA solar backscatter ultraviolet data sets were used. Initially, the best data sets were selected to create a time series spanning from 1978 to the present. Then the gaps in the record were filled with data from various other Mg II data sets. Where no alternate data were available, a cubic spline function was used to bridge the missing data. In some cases the data gaps were too long for reasonable spline fits (more than 5 days), and for these gaps the F10.7 cm flux data were scaled to fill the gaps. Thus a continuous, uninterrupted time series of the Mg II core‐to‐wing ratio was created. The final Mg II time series is compared with other solar activity indices, such as the F10.7, He I 1083, and Sunspot number, to look for trends in the Mg II data.

Corrections to the Nimbus 7 solar backscatter ultraviolet data in the “nonsync” period (February 1987 to June 1990)

The solar backscatter ultraviolet (SBUV) radiance data in the period February 1987 to June 1990 were affected by chopper synchronization errors. The synchronization errors have been characterized and a method was developed for correcting the individual radiance measurements. The profile and total ozone values retrieved using the corrected radiance data have much less variance than the uncorrected data. The total and profile ozone values were compared with external ozone measurements, and no apparent bias was introduced by the correction method.

Ozone and temperature changes in the stratosphere following the eruption of Mount Pinatubo

Global variations in stratospheric ozone and lower stratospheric temperature are documented for the period 1991–1994, following the eruption of Mount Pinatubo in June 1991. Column ozone measurements are from the total ozone mapping spectrometer instruments on the Nimbus 7 and Meteor 3 satellites, together with solar backscattered ultraviolet data from NOAA 11; these satellite ozone data are validated by comparisons with ground‐based Dobson spectrophotometer measurements. Ozone profile data from the halogen occultation experiment and microwave limb sounder instruments on the upper atmosphere research satellite are also analyzed. Satellite temperature data are from the microwave sounding unit channel 4, representing a mean of the 150‐ to 50‐mbar layer. The ozone observations show substantial decreases in column ozone (of order 5–10%) over large regions of the globe; largest losses are observed in northern hemisphere middle‐high latitudes during winter‐spring of each year (largest in 1992–1993), over southern hemisphere high latitudes in spring 1993, and episodically over the tropics during 1991–1993. Temperatures are anomalously warm (by order 1 K) over 30°N‐S for 1 to 2 years following the eruption. Significant cold anomalies are also observed over the northern hemisphere polar cap during summer 1993, a result probably related to the decreased ozone levels throughout 1993.

A new self‐calibration method applied to TOMS and SBUV backscattered ultraviolet data to determine long‐term global ozone change

The currently archived (1989) total ozone mapping spectrometer (TOMS) and solar backscattered ultraviolet (SBUV) total ozone data (version 5) show a global average decrease of about 9.0% from November 1978 to November 1988. This large decrease disagrees with an approximate 3.5% decrease estimated from the ground‐based Dobson network. The primary source of disagreement was found to arise from an overestimate of reflectivity change and its incorrect wavelengths dependence for the diffuser plate used when measuring solar irradiance. Both of these factors have led to an overestimate of the rate of atmospheric ozone depletion by SBUV and TOMS. For total ozone measured by TOMS, a means has been found to use the measured radiance‐irradiance ratio from several wavelengths pairs to construct an internally self consistent calibration. The method uses the wavelength dependence of the sensitivity to calibration errors and the requirement that albedo ratios for each wavelength pair yield the same total ozone amounts. Smaller errors in determining spacecraft attitude, synchronization problems with the photon counting electronics, and sea glint contamination of boundary reflectivity data have been corrected or minimized. New climatological low‐ozone profiles have been incorporated into the TOMS algorithm that are appropriate for Antarctic ozone hole conditions and other low ozone cases. The combined corrections have led to a new determination of the global average total ozone trend (version 6) as a 2.9±1.3% decrease over 11 years (October 1978 to November 1989). Version 6 data are shown to be in agreement within error limits with the average of 39 ground‐based Dobson stations and with the world standard Dobson spectrometer 83 at Mauna Loa, Hawaii. The global average ozone trend from version 6 data shows the presence of varying short‐period trends (1979 to 1983, −0.33%/yr; 1983 to 1986, −0.91% yr, and 1986 to 1990, +0.16%/yr) that are partially masked in the original version 5 trends.

Simultaneous in situ measurements and diurnal variations of NO, NO2, O3, jNO2, CH4, H2O, and CO2 in the 40‐ to 26‐km region using an open path tunable diode laser spectrometer

Simultaneous in situ measurements of [NO], [NO2], [O3], jNO2, [CH4], [H2O], [CO2], pressure, and temperature in the 40 to 26‐km region of the stratosphere were made from Palestine, Texas (32°N), on October 16, 1986, using the Jet Propulsion Laboratory (JPL) Balloon‐borne Laser In Situ Sensor (BLISS) instrument, carrying a University of Denver jNO2 instrument piggyback. Using tunable diode laser absorption spectroscopy over a long path length, measurements were made as follows during a 21‐hour flight: daytime [NO], [NO2], [O3], and NO2 near 40 km; [NO], [NO2], and NO2 through the sunset transition near 40 km; postsunset measurements of the rate of decay of [NO2] into the night over the 35 to 29‐km range; nighttime measurements of [NO2], [O3], [CH4], [H2O], and [CO2] at 27 km; and [NO] after sunrise. The NO, NO2, O3, CH4, H2O, and CO2 concentration measurements generally show good agreement with previous observations, with a tendency for somewhat lower NO2 amounts. Measured O3 concentrations at 38 km agree well with comparable measurements from in situ UV photometers, but at 28 km they are lower by about 10% and agree more closely with solar backscattered ultraviolet data at this altitude. The observed change in [NO2] during the night over a 5‐km altitude range implies either lower [NO2] postsunset profiles, or significantly faster [NO2] decay than current model predictions using N2O5 chemistry. Measurements of [NO], [NO2], [H2O], and [CO2] from an October 1985 flight are included for comparison.

Interpretation of ozone temperature correlations: 1. Theory

Correlations between ozone and temperature are commonly used to investigate the photochemical and dynamical aspects of satellite‐derived ozone data. In this paper, the dynamical contributions to the ozone temperature correlations are examined using simple analytic and numerical models. It is shown that the phase differences between ozone and temperature waves caused by dynamical forcing can mimic the phase relationships predicted for photochemical equilibrium. Furthermore, the dynamical contribution to the phase relationship between ozone and temperature waves is routinely significant for chemistry time scales of ≃0.5 days and is potentially important for time scales as short as 2 hours during stratospheric warmings. The model results are highly relevant to the analysis of the limb infrared monitor of the stratosphere and solar backscatter ultraviolet data taken during the winter of 1979.

The temporal behavior of upper stratospheric ozone at low latitudes: Evidence from Nimbus 4 BUV data for short‐term responses to solar ultraviolet variability

Ozone mixing ratios at pressure levels near 2 mbar, derived from Nimbus 4 backscattered ultraviolet (BUV) profile data and averaged within 13 latitude zones between 65°N and 65°S, are studied for the period November 1970 to April 1972. In agreement with previous analyses the largest temporal variations are negatively correlated with changes in zonally averaged equivalent temperature measured simultaneously with the Nimbus 4 selective chopper radiometer. After approximately removing this component using a first‐order photochemical model, residual mixing ratios for latitudes ≲30° contain short‐term variations (periods ≲35 days; rms amplitude ∼1%) that are positively correlated with variations in the solar 10.7‐cm flux and in the 185–190 nm solar ultraviolet flux model of Lean et al. (1982). The correlation coefficients (R = 0.2–0.5; p> 0.95) are larger for each latitude zone when computed versus the ultraviolet flux model than when computed versus the 10.7‐cm flux, suggesting that photochemical responses of upper stratospheric ozone to solar ultraviolet variability at wavelengths near 200 nm are primarily responsible. At latitudes ≳40°, larger‐amplitude wintertime ozone fluctuations associated with planetary‐scale pressure waves become dominant and reduce the computed correlation coefficients to statistically insignificant levels. Linear regression analyses are performed to obtain estimates for the average percent change of ozone at low latitudes and on the considered time scale for given changes in 10.7‐cm flux and in the UV flux model.

An assessment of possible ozone‐solar cycle relationship inferred from NIMBUS 4 BUV data

The total ozone and the ozone mixing ratio at various pressure levels in the stratosphere measured from the NIMBUS 4 backscattered ultraviolet (BUV) experiment over a 7‐year period (1970–1977) comprise a very comprehensive data base available to study the possible effects of solar variability on stratospheric ozone. It is shown that with the decrease in solar activity from 1970 to 1976, the globally averaged ozone inferred from NIMBUS 4 data decreases from about 10–12% in the upper stratosphere to about 1–3% in the lower stratosphere. This systematic decrease at all pressure levels is modulated by a quasi‐periodic oscillation of about a 2‐year period. Both the systematic decrease and the quasi‐periodic oscillations in ozone seem to be correlated with the conventional indices of solar activity suggesting a solar UV‐ozone relationship. Despite this apparent correlation, it is difficult to account for the observed changes at various pressure levels with our current understanding of the photochemical models and the solar UV flux variations over a solar cycle. The agreement between the observed and the calculated profiles of ozone mixing ratio is considerably improved if the BUV data are corrected for the changes in the instrument sensitivity using Umkehr observations as a reference.

Total Ozone Variations 1970-74 Using Backscattered Ultraviolet (BUV) and Ground-Based Observations

The most long-lived satellite set of ozone observations, to date, is that derived from the Backscatter Ultraviolet (BUV) ozone sensor on Nimbus 4 and extends from April 1970 through 1976. Unfortunately, this experiment suffered spacecraft power limitations which limited the spatial and temporal coverage and also appears to have suffered from long-term drifts which may be associated with changes in the instrument characteristics or the incident solar flux. Techniques have been developed to account for these problems, and this paper presents results of the BUV total ozone variations and compares them with those from ground-based observations, specifically the computations of Angell and Korshover (1978). After adjustments for the spatial gaps and comparison with concurrent Dobson ground-based observations, no significant trend was found in the BUV data over the years 1970-74. This finding is in contrast to a general decrease of about 2% during the same period appearing in the data of Angell and Korshover. The difference in these results is discussed in terms of the geographic sampling and the methods of hemispheric integration.

Absorption coefficients of ozone for the backscatter UV experiment

Band-averaged absorption coefficients for the wavelength channels of the backscatter ultraviolet (BUV) experiment are computed using the laboratory ozone absorption measurements of several experimenters. For the major ozone-determining channels on the BUV (3125 and 3175 A) the various coefficients ranged from +/-11 to +/-4%, respectively, about the range midpoint. These percentage uncertainties in the band absorption coefficients lead to similar percentage uncertainties in the absolute value of derived total ozone because of the reciprocal relationship between the two. Derived total-ozone ratios of the BUV A:B pairs, the Dobson AD:CD double pairs, and the BUV B:Dobson AD are estimated for the different sets of coefficients based on the ratios experimentally observed in the BUV and Dobson data. The Inn and Tanaka measurements lead to the most consistent results. Band-averaged coefficients for the BUV-profiling wavelengths are also computed.

Seasonal and interannual variations in total ozone Revealed by the Nimbus 4 Backscattered Ultraviolet Experiment

The first 2 years of backscattered ultraviolet (BUV) ozone data from the Nimbus 4 spacecraft have been processed to a more refined level. The seasonal variations of total ozone for the period April 1970 to April 1972 are described using daily means for 10° latitude zones and a time‐latitude cross section. In addition, the BUV data are compared with analyzed Dobson data and with infrared interferometer spectrometer data also obtained from the Nimbus 4 spacecraft. A harmonic analysis was performed on the daily zonal means. Amplitudes, days of peak ozone values, and percentage of variance have been computed for the annual and semiannual waves and for higher harmonics of an annual period for the 2 years. Asymmetries are found in the annual waves in the two hemispheres, with a subtle interannual difference which may be due to changes in the general circulation. A significant semiannual component is detected in the tropics for the first year. This component appears to result from influences of the annual waves in the two hemispheres. A search for shorter periods using the harmonic analysis revealed no periodicity whose amplitude was higher than the noise level.

Ozone profiles and chemical loss rates in the tropical stratosphere deduced from backscatter ultraviolet measurements

Analysis of data obtained by the backscatter ultraviolet (BUV) experiment on the Atmosphere Explorer E satellite has provided equatorial ozone mixing ratio profiles for equinox and solstice conditions. The combination of these results with a pure oxygen chemical model yields the rate of odd oxygen loss due to the sum of the odd hydrogen, nitrogen, and chlorine cycles. Use of recent mid‐latitude stratospheric measurements of HOx, NOx, and ClOx with the BUV data provides an independent calculation of the catalytic loss. Below 45 km the agreement between the two sets of loss rates is satisfactory. At higher altitudes the odd hydrogen cycle provides far more Ox loss than can be tolerated by the BUV measurements if the photodissociation of O2 is the only source and has the currently accepted magnitude. The results suggest either a tropical HOx concentration smaller than is now believed or the presence of a very large source of odd oxygen in the upper stratosphere and lower mesosphere.

Ozone Abundances in the Lower Mesosphere Deduced from Backscattered Solar Radiances

Backscatter ultraviolet data obtained by the Explorer E satellite imply very large ozone column abundances above 56 km in the tropics during mid-day. The number of molecules in a vertical column decays by a factor of 2-3 after the solar zenith angle exceeds 75 deg in the evening. An increase of similar magnitude occurs after sunrise. Such behavior implies the presence of a greater source of odd oxygen than is included in current photochemical theories. Ozone profiles deduced between altitudes of 50 and 62 km when the solar zenith angle exceeds 80 deg are in reasonable agreement with past rocket results.