Walter G. Planet

Ozone trends deduced from combined Nimbus 7 SBUV and NOAA 11 SBUV/2 data

The long-term time series of global ozone from the Nimbus-7 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°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 TOMS (through April 1993) and SBUV total ozone time series show small negative trends in the equatorial region, though they are not statistically significant at the 2-σ level.

Northern hemisphere total ozone values from 1989–1993 determined with the NOAA‐11 Solar Backscatter Ultraviolet (SBUV/2) instrument

Determinations of global total ozone amounts have been made from recently reprocessed measurements with the SBUV/2 on the NOAA-11 environmental satellite since January 1989. This data set employs a new algorithm and an updated calibration. Comparisons with total ozone amounts derived from a significant subset of the global network of Dobson spectrophotometers shows a 0.3% bias between the satellite and ground measurements for the period January 1989-May 1993. Comparisons with the data from individual stations exhibit differing degrees of agreement which could be due to the matchup procedures and also to the uncertainties in the Dobson data. The SBUV/2 data set discussed here traces the Northern Hemisphere total ozone from 1989 to the present, showing a marked decrease from the average of those years starting in the summer of 1992 and continuing into 1993, with an apparent returning to more normal levels in late 1993. 17 refs., 21 figs.

Temperature-dependent intensities and widths of N2-broadened CO2 lines at 15 μm from tunable laser measurements

Abstract Intensities and half-widths of individual lines in the 15 μm bands of 12C16O2 have been determined over the temperature range 200–325 K in an extension of work previously reported. Measurements were made on dilute Co2-N2 mixtures with a tunable IR diode laser spectrometer on the Q-branches of the 0110-0000 and the 0220-0110 transitions. Measured intensities are consistently lower than those available in the literature, which were derived from measurements using other than diode laser techniques. Measured half-widths follow the general relationship bL0(T) = bL0(T0)[T0/T]n, where n shows considerable variations for the two tr ansitions. The results presented here include an improved analysis of half-width data previously discussed by the authors and also additional data obtained over a broader temperature range.

Approximate separation of volcanic and 11-year signals in the SBUV-SBUV/2 total ozone record over the 1979-1995 Period

The combined Nimbus 7 SBUV, NOAA 11, and preliminary NOAA 9 SBUV/2 monthly zonal mean total ozone data set, extending from January 1979 to December 1995, is analyzed with a multiple regression statistical model that includes a term to describe the direct effect of volcanic aerosols on total ozone. Outside of polar regions, which are not included in this analysis, the volcanic regression coefficients in the northern hemisphere are negative (consistent with heterogeneous chemical losses of ozone on volcanic sulfate aerosols) and reach their maximum values between 40°N - 60°N latitude. Although inclusion of the aerosol term in the statistical model introduces some additional uncertainty to the derived solar response, statistically significant values of the solar coefficients are found in northern and southern subtropical regions throughout the year, with maximum amplitudes of ∼2.5% at 30° latitude in both hemispheres during winter. We conclude that the 11-year signal in the SBUV-SBUV/2 total ozone record is approximately separable from volcanic aerosol effects.

Temperature dependence of intensities and widths of N2-broadened lines in the 15 μm CO2 band from tunable laser measurements

Abstract Intensities and nitrogen-broadened widths of several low-J lines in the Q-branch of the 15 μm band of CO2 have been determined over the temperature range 200–300 K. Measurements were made with a tunable infra-red diode laser spectrometer having a spectral resolution ∼ 10-4 cm-1. Measured intensities are uniformly about 7% lower than available calculations which were based on previous measurements of band intensity. Measured line widths are higher than available calculations and generally followed the relation b L 0 (T)=b L 0 (T 0 )(T 0 |T) n with n = 0.74 (standard deviation 0.08).

Accuracy of total ozone retrieval from NOAA SBUV/2 measurements: Impact of instrument performance

The National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) has been collecting and evaluating the solar backscattered ultraviolet (SBUV/2) instrument data from NOAA 9 and NOAA 11 spacecraft since March 1985. Over 5 years (March 1985 to October 1990) of NOAA 9 (version 5.0) and over 4 years (January 1989 to June 1993) of NOAA 11 (version 6.0) reprocessed data are now available to the scientific community to study geophysical phenomena involving ozone. This paper examines the impact of the instrument performance on total ozone retrieval from the two instruments. We estimate that at the end of October 1990 the total postlaunch error for NOAA 9 due to instrument alone is -2.2%. A significant fraction of this error (-1.9%) is due to diffuser degradation which is not accounted for in the version 5 reprocessing. The estimate for NOAA 11 total postlaunch instrument error, at the end of June 1993, is -0.4%.

Intensities and pressure-broadened widths of CO2 R-branch lines at 15 μm from tunable laser measurements

Abstract Intensities and half-widths of individual lines, over the temperature range 200–325°K in the 15 μm bands of 12C16O2, have been determined with a tunable diode laser spectrometer. Measurements were made on pure CO2 and on dilute CO2-in-N2 mixtures on the R-branches of the 0110-0000 and 0220-0110 transitions. Intensities are approximately equal to those listed in the AFGL compilation. The pressure-broadened half-widths follow the general relationship b L 0 (T) = b L 0 (T 0 ) [ T 0 T ] n where n varies considerably from line to line but is always greater than 1 2 .

Comparisons of observed ozone trends and solar effects in the stratosphere through examination of ground-based Umkehr and combined solar backscattered ultraviolet (SBUV) and SBUV 2 satellite data

Within the past year, two papers have been published which present updated profile ozone trends from the recently revised ground-based Umkehr record [Miller et al., 1995] and the combined Nimbus 7 solar backscattered ultraviolet (SBUV) and NOAA 11 SBUV 2 satellite data record [Hollandsworth et al., 1995]. In this paper we compare the ozone trends and responses to the 11-year solar cycle (represented by the F10.7 cm radio flux) derived from these two data sets for the period June 1977 to June 1991 (November 1978 to June 1991 for the satellite data). We consider data at northern midlatitudes (30°–50°N) at altitudes between 25 and 45 km derived from these two data sets. In particular, we investigate the effects of spatial sampling differences between the data sets on the derived signals. The trends derived from the two independent data sets are nearly identical at all levels except 35 km, where the Umkehr data indicate a somewhat more negative trend. The trend is approximately zero near 25 km but becomes more negative in the upper stratosphere, reaching nearly −7% per decade in the 40–45 km region. The upper stratospheric decreases are consistent with model results and are associated with the gas-phase chemical effect of chlorofluorocarbons CFCs and other ozone-destroying chemicals [World Meteorological Organization, 1995]. The ozone correlations in the two data sets with the F10.7 cm solar flux are similar, with near-zero solar-induced ozone variations in the 25–30 km region and statistically significant in-phase variations at higher altitudes. Estimates of the solar cycle in the ozone time series at 40–45 km from a regression model indicate variations of about 4.5% from solar cycle maximum to minimum. Analysis of the satellite overpass data at the Umkehr station locations shows that the average of the data from the 11 Umkehr stations is a good approximation for the 30°–50°N zonal mean.

Climate and global change: Characteristics of NOAA satellite data

The principal finding of an International Council of Scientific Unions ICSU)/Committee on Space Research (COSPAR) ad hoc group on Remote Sensing for Global Change [Rasool, 1987] was that “The current international operational satellite system, augmented with the technology developed by research missions and supported by validation experiments and a comprehensive data system, could provide the basis for a global change observing system.” The National Oceanic and Atmospheric Administrations environmental satellites represent a significant part of the international system. NOAA manages a NOAA series of polar orbiters and a Geostationary Operational Environmental Satellite (GOES) series of geostationary satellites. A NOAA satellite can view each point on the Earths surface every 12 hours, at approximately the same local time each overpass. An attempt is made to maintain two NOAA satellites in orbit at all times, a so-called afternoon “bird” with nominal observing times of 2 P.M. and 2 A.M. and a morning bird with observations at 7 A.M. and 7 P.M. A GOES satellite hovering over the equator views continuously the surface of the Earth within 60° Earth central angle of the subsatellite point. NOAA operates a two-GOES system, one nominally stationed at 75°W and the other at 135°W.

The 27 day solar UV response of stratospheric ozone: solar cycle 21 vs. solar cycle 22

Abstract A correlative study of ozone and the solar UV flux on the time scale of a solar rotation shows an anomalous response of ozone in the upper stratosphere during solar cycle 22. The study, which is based on the analysis of ozone and solar UV flux measured by the SBUV/2 spectrometer on NOAA 11 (January 1989–December 1990), shows a sharp transition from an in-phase relation between ozone and the solar UV flux below 2 mb to an almost out-of-phase relation above 1 mb. Such a phase change is not predicted by photochemical models and was not observed during solar cycle 21. The ozone measurements from the Nimbus-7 SBUV spectrometer from 1979 to 1984 showed an almost in-phase relation between ozone and the solar UV flux at these heights (in agreement with model predictions). Similar studies of ozone and temperature relations between 30 and 1 mb did not show significant changes from the solar cycle 21 to 22. The temperature oscillations appear to be primarily of dynamical origin, with no apparent correlation with solar UV flux.