SBUV/2

Abstract: Solar irradiance data gathered with the Nimbus 7 spacecraft from 1978-1985 are compared with atmospheric MG 289-nm doublet emission line data to evaluate the possibility of using the rotational line data to calculate the total solar UV input. The satellite instrumentation is described, including the calibration equipment and procedures. The spacecraft records solar irradiance once per day and the remainder of the time records irradiance scattered by the atmosphere. The measured irradiances are converted to equivalent brightness temperatures, which can be interpolated for specific layers of the atmosphere. Sample daily data are provided to illustrate the correlation between variations in the Mg-II core radiation and the soalr UV irradiance. Techniques are defined for correcting for periodic variations in instrument performance to quantify long-term solar UV radiance variations. Using the atmospheric Mg-II doublet radiation for measuring soalr UV irradiance is concluded of value for characterizing the effects of solar radiation on the atmosphere.

Abstract: The long-term time series of global ozone from the Nimbus-7 Solar Backscatter Ultraviolet instrument (SBUV) (Nov. 1978-June 1990) are extended through June 1994 by using measurements from the NOAA-11 SBUV/2. The data sets are merged based upon comparisons during the 18-month overlap period in which both instruments were operational. During this period, the average offset between the two time series is less than 2% in total ozone, and less than 6% in Umkehr layers 1-10. A linear-regression trend model is applied to the extended time series to calculate updated trends as a function of latitude and altitude. Trends through June 1994 are 1.5-2% per decade less negative than through June 1990 in the tropical middle stratosphere (35-40 km) and in the upper stratosphere (45-50 km) at mid-latitudes. In the lower stratosphere, the trends are nearly 1.5% per decade more negative in the southern hemisphere tropical regions to 25 deg S, but remain relatively unchanged elsewhere. The seasonal structure of the total ozone trends is similar to past trend study results, but the magnitude of the seasonal trend can vary by 2% per decade depending on the length of the time series. Both Total Ozone Mapping Spectrometer (TOMS) (through April 1993) and SBUV total ozone time series show small negative trends in the equatorial region, though they are not statistically at the 2-sigma level.

Abstract: [1] Coincident ozone measurements by the Solar Backscattered Ultra Violet (SBUV) and Stratospheric Aerosol and Gas Experiment (SAGE) II instruments and by ozonesondes and the Umkehr method are used to estimate stratospheric ozone variability and standard uncertainties of these different measurements. Below 20 km over northern midlatitudes, estimated measurement uncertainties for SBUV(/2), sondes, and Umkehr are similar (∼8% for 0 to 20 km integrated ozone), although only sondes have a high vertical resolution there. From 20 to 28 km., the estimated uncertainties (4–6%) for all four measurement sources are substantially smaller than the ozone variability in winter (10–15%), but they are comparable in summer (∼5%). Above 28 km, sonde uncertainties are larger than or comparable to the ozone variability, and much larger than uncertainties of SBUV(/2), Umkehr, or SAGE II data. Umkehr measurement uncertainties at 24–32 km are about 5% and are lower than sonde uncertainties (7–13%) at these levels. SBUV(/2) data are used to evaluate differences between different types of ozonesondes, and to show that correction by total ozone measurements noticeably reduces ozonesonde uncertainties. The latitudinal dependence of ozone variability and instrument uncertainties is studied using pairs of collocated SBUV(/2) and SAGE II measurements. There is good correlation between these measurements over middle and high latitudes. Over the tropical region, the correlation coefficients are modest (about 0.5) but significant in all layers except at 28–31 km. It is noted that where ozone variability is comparable to instrument uncertainties, comparison with a climatology based on a large number of observations may provide better insight into instrument performance than intercomparison of a small number of quasi-coincident measurements.

Abstract: Total ozone and ozone profiles are currently being measured by solar backscatter ultraviolet (SBUV/2) instruments onboard NOAA polar orbiting spacecraft using the backscattered ultraviolet technique. The NOAA 11 SBUV/2 operational data set was reprocessed from January 1989 to May 1993 and is now called version 6. The version 6 data include an updated algorithm and revised prelaunch and postlaunch calibrations of the geometrical albedo observations used to derive ozone values. Only the calibration revisions are described in this paper. The postlaunch revisions remove time dependent errors in the ozone amounts due to instrument drift, while the revised prelaunch calibration corrects the absolute value of retrieved ozone. The prelaunch corrections are a result of calibration checks from in-orbit comparisons of ultraviolet geometric albedos measured by shuttle SBUV (SSBUV) and the NOAA 11 SBUV/2. Geometric albedo comparison data are further corrected using a radiative transfer code to account for the small difference in observing conditions between the two spacecraft. The postlaunch corrections rely on in-flight calibration and solar irradiance data to account for time dependent changes in instrument gain, thermal response, and instrument diffuser degradation over time. Comparison of data from three SSBUV flights, which occurred about one year apart, with concurrent SBUV/2 data provided an independent check of the time dependent change derived from the in-flight calibration data. Time independent corrections result in an increase of about 1% for total ozone, 5% for ozone at 1 mbar, and near 0% at 15 mbar. The time dependent corrections amount to an increase of 2% for total ozone, 10% for ozone near 1 mbar, and 3% at 15 mbar at the end of the current record in May 1993. Recent laboratory studies indicate that the absolute radiance calibrations may still be in error by a few percent which results in ozone profile values that are too low. The SBUV/2 total and ozone profile data are compared to the Nimbus SBUV data during the period when the data overlapped. Total ozone values agree to about 1%, while ozone profile differences range from −4% to +6%, depending on latitude and altitude, relative to SBUV. These differences are not statistically significant given the uncertainties of the two data sets.