Solar Backscatter Ultraviolet Research Articles

Quasi‐biennial oscillation and quasi‐biennial oscillation–annual beat in the tropical total column ozone: A two‐dimensional model simulation

The National Centers for Environmental Prediction–Department of Energy Reanalysis 2 data are used to calculate the monthly mean meridional circulation and eddy diffusivity from 1979 to 2002 for use in the California Institute of Technology–Jet Propulsion Laboratory two‐dimensional (2‐D) chemistry and transport model (CTM). This allows for an investigation of the impact of dynamics on the interannual variability of the tropical total column ozone for all years for which the Total Ozone Mapping Spectrometer and the Solar Backscatter Ultraviolet merged total ozone data are available. The first two empirical orthogonal functions (EOFs) of the deseasonalized and detrended stratospheric stream function capture 88% of the total variance on interannual timescales. The first EOF, accounting for over 70% of the interannual variance, is related to the quasi‐biennial oscillation (QBO) and its interaction with annual cycles, the QBO‐annual beat (QBO‐AB). The 2‐D CTM provides realistic simulations of the seasonal and interannual variability of ozone in the tropics. The equatorial ozone anomaly from the model is close to that derived from the observations. The phase and amplitude of the QBO are well captured by the model. The magnitude of the QBO signal is somewhat larger in the model than it is in the data. The QBO‐AB found in the simulated ozone agrees well with that in the observed data.

Monitoring of observation errors in the assimilation of satellite ozone data

Ozone observations from the Solar Backscatter UltraViolet/2 (SBUV/2) instruments and/or the Earth Probe Total Ozone Mapping Spectrometer (EP TOMS) have been assimilated in near‐real time at NASA's Data Assimilation Office (DAO) since January 2000. The ozone data assimilation system was used as a tool for detecting and characterizing changes in the observation errors. The forecast model captures the geophysical variability. A change in the observed‐minus‐forecast (O‐F) residuals, which are defined as differences between the incoming ozone observations and the collocated short‐term model forecast, indicates a change in the assimilation system. If the model and the statistical analysis scheme are stable, then it points to a modification in instrument characteristics or a retrieval algorithm. However, sometimes a change in the ozone O‐F residuals is caused by differences in the availability of the meteorological observations or modifications in the meteorological assimilation system whose winds are used to drive the ozone transport model. The O‐F residuals are routinely produced and monitored in the assimilation process. Using examples from the NOAA 14 and NOAA 16 SBUV/2 instruments, and the EP TOMS, we demonstrate that the monitoring of time series of O‐F residual statistics is an effective, sensitive, and robust method for identifying time‐dependent changes in the observation‐error characteristics of ozone. In addition, the data assimilation system was used to assist in the validation of updated calibration coefficients for the NOAA 14 SBUV/2 instrument. This assimilation‐based monitoring work is being extended to ozone data from instruments on new satellites: Environmental satellite (Envisat), Earth Observing System (EOS) Aqua, and EOS Aura.

Observations of solar spectral irradiance change during cycle 22 from NOAA‐9 Solar Backscattered Ultraviolet Model 2 (SBUV/2)

The NOAA‐9 Solar Backscatter Ultraviolet Model 2 (SBUV/2) instrument is one of a series of instruments providing daily solar spectral irradiance measurements in the middle and near ultraviolet since 1978. The SBUV/2 instruments are primarily designed to measure the stratospheric profile and total column amount of ozone, using the directional albedo as the input to the ozone retrieval algorithm. Almost all optical components are common to both radiance and irradiance measurements, whose ratio forms the directional albedo, so that most response changes cancel out. As a result, the SBUV/2 instrument does not require onboard monitoring of time‐dependent sensitivity changes for production of ozone data. We use vicarious comparisons with coincident Shuttle SBUV (SSBUV) solar irradiance measurements during 1989–1996, combined with observed calibration drift during the solar activity minimum in 1985–1986, to determine the long‐term instrument characterization for NOAA‐9 SBUV/2. This approach allows us to derive more accurate solar spectral irradiances for the period from March 1985 to May 1997, spanning two solar cycle minima with a single instrument. The NOAA‐9 irradiance data show an amplitude of approximately 9.3% at 200–205 nm for solar cycle 22. This is consistent with the result of ΔF200–205 = 8.3% for cycle 21 from Nimbus‐7 SBUV and ΔF200–205 = 10% for cycle 23 from UARS SUSIM. NOAA‐9 data at 245–250 nm show a solar cycle amplitude of ∼5.7%. The observed irradiance change at 200–205 nm between the minima of solar cycles 21 and 22 is not consistent with the UV irradiance change expected from the total solar irradiance trend suggested by Willson and Mordvinov [2003]. NOAA‐9 SBUV/2 data can be combined with data from other instruments to create a 25‐year record of solar UV irradiance.

Intercontinental transport of tropospheric ozone: a study of its seasonal variability across the North Atlantic utilizing tropospheric ozone residuals and its relationship to the North Atlantic Oscillation

Abstract. Using the empirically-corrected tropospheric ozone residual (TOR) technique, which utilizes coincident observations of total ozone from the Total Ozone Mapping Spectrometer (TOMS) and stratospheric ozone profiles from the Solar Backscattered Ultraviolet (SBUV) instruments, the seasonal and regional distribution of tropospheric ozone across the North Atlantic from 1979-2000 is examined. Its relationship to the North Atlantic Oscillation (NAO) is also analyzed as a possible transport mechanism across the North Atlantic. Monthly climatologies of tropospheric ozone for five different regions across the North Atlantic exhibit strong seasonality. The correlation between these monthly climatologies of the TOR and ozonesonde profiles at nearby sites in both eastern North America and western Europe are highly significant (R values of +0.98 and +0.96 respectively) and help to validate the use of satellite retrievals of tropospheric ozone. Distinct springtime interannual variability over North Atlantic Region 5 (eastern North Atlantic-western Europe) is particularly evident and exhibits similar variability to the positive phase of the NAO (R=+0.61, r=<0.01). Positive phases of the NAO are indicative of a stronger Bermuda-Azores high and a stronger Icelandic low and thus faster more zonal flow across the North Atlantic from west to east. This flow regime appears to be causing the transport of tropospheric ozone across the North Atlantic and onto Europe. The consequence of such transport is the impact on a downwind region's ability to meet their ozone attainment goals. This link between the positive phase of the NAO and increased tropospheric ozone over Region 5 could be an important tool for prediction of such pollution outbreaks.

Temporal and spatial patterns of the interannual variability of total ozone in the tropics

The recently constructed gridded Merged Ozone Data (MOD) set, combining the monthly mean column abundances collected by the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet (SBUV and SBUV/2) instruments, provides a nearly continuous record from late 1978 to 2000 on a 5° × 10° latitude‐longitude grid. The precision of these measurements and their calibration allow very small signals, ∼1% of total column ozone, to be clearly seen. Using MOD, we have carried out an empirical orthogonal function (EOF) study of the temporal and spatial patterns of the interannual variability of total column ozone in the tropics. The first four EOFs of our study capture over 93% of the variance of the deseasonalized data. The leading two EOFs of our study, respectively accounting for 42% and 33% of the variance, display structures attributable to the quasi‐biennial oscillation (QBO), with influence from a decadal oscillation. The third EOF (15% of the variance) represents an interaction between the QBO and an annual cycle. The fourth EOF (3% of the variance) is related to the El Niño ‐ Southern Oscillation. This EOF decomposition is robust; nearly identical patterns occur in the decomposition of various equatorial latitude bands of MOD and similar patterns occur in the analysis of the deseasonalized TOMS data set, a shorter record with a more finely resolved spatial grid. For comparison, similar decompositions were performed for dynamical fields from the reanalysis product from the National Centers for Environmental Prediction and the National Center for Atmospheric Research. Using these analyses, we found possible connections between the deduced patterns in ozone and the climate variables.

Global distribution of total ozone and lower stratospheric temperature variations

Abstract. This study gives an overview of interannual variations of total ozone and 50 hPa temperature. It is based on newer and longer records from the 1979 to 2001 Total Ozone Monitoring Spectrometer (TOMS) and Solar Backscatter Ultraviolet (SBUV) instruments, and on US National Center for Environmental Prediction (NCEP) reanalyses. Multiple linear least squares regression is used to attribute variations to various natural and anthropogenic explanatory variables. Usually, maps of total ozone and 50 hPa temperature variations look very similar, reflecting a very close coupling between the two. As a rule of thumb, a 10 Dobson Unit (DU) change in total ozone corresponds to a 1 K change of 50 hPa temperature. Large variations come from the linear trend term, up to -30 DU or -1.5 K/decade, from terms related to polar vortex strength, up to 50 DU or 5 K (typical, minimum to maximum), from tropospheric meteorology, up to 30 DU or 3 K, or from the Quasi-Biennial Oscillation (QBO), up to 25 DU or 2.5 K. The 11-year solar cycle, up to 25 DU or 2.5 K, or El Niño/Southern Oscillation (ENSO), up to 10 DU or 1 K, are contributing smaller variations. Stratospheric aerosol after the 1991 Pinatubo eruption lead to warming up to 3 K at low latitudes and to ozone depletion up to 40 DU at high latitudes. Variations attributed to QBO, polar vortex strength, and to a lesser degree to ENSO, exhibit an inverse correlation between low latitudes and higher latitudes. Variations related to the solar cycle or 400 hPa temperature, however, have the same sign over most of the globe. Variations are usually zonally symmetric at low and mid-latitudes, but asymmetric at high latitudes. There, position and strength of the stratospheric anti-cyclones over the Aleutians and south of Australia appear to vary with the phases of solar cycle, QBO or ENSO.

Global distribution of tropospheric ozone from satellite measurements using the empirically corrected tropospheric ozone residual technique: Identification of the regional aspects of air pollution

Abstract. Using coincident observations of total ozone from the Total Ozone Mapping Spectrometer (TOMS) and stratospheric ozone profiles from the Solar Backscattered Ultraviolet (SBUV) instruments, detailed maps of tropospheric ozone have been derived on a daily basis over a time period spanning more than two decades. The resultant climatological seasonal depictions of the tropospheric ozone residual (TOR) show much more detail than an earlier analysis that had used coincident TOMS and Stratospheric Aerosol and Gas Experiment (SAGE) ozone profiles, although there are many similarities between the TOMS/SAGE TOR and the TOMS/SBUV TOR climatologies. In particular, both TOR seasonal depictions show large enhancements in the southern tropics and subtropics in austral spring and at northern temperate latitudes during the summer. The much greater detail in this new data set clearly defines the regional aspect of tropospheric ozone pollution in northeastern India, eastern United States, eastern China, and west and southern Africa. Being able to define monthly climatologies for each year of the data record provides enough temporal resolution to illustrate significant interannual variability in some of these regions.

Solar backscattered ultraviolet (SBUV) observations of polar mesospheric clouds (PMCs) over two solar cycles

Previous satellite measurements have provided nearly complete seasonal and geographic coverage of polar mesospheric clouds (PMCs), but previous data sets have not been able to evaluate changes in PMC behavior on decadal timescales. The Solar Backscattered Ultraviolet (SBUV) series of ozone measuring instruments have been flying continuously since 1978. While the instrument design is not optimized for PMC detection, the radiance data can be analyzed to examine the occurrence frequency and intensity of relatively bright PMCs. In this paper, we present PMC results from five SBUV and SBUV/2 instruments covering more than 23 years (1978–2002), starting just before the maximum of solar cycle 21 and extending through the maximum of solar cycle 23. The overlapping data sets from nearly identical instruments give an accurate picture of long‐term variations. Multiple linear regression fits are used to examine solar and secular correlations. PMC occurrence frequency is anticorrelated with solar Lyman alpha irradiance, with an approximate 0.5‐year phase lag in the Northern Hemisphere (Rsolar = −0.87) and no phase lag in the Southern Hemisphere (Rsolar = −0.65). The distribution of cloud brightness by season appears to be changing over time. When the PMC brightness for each season is characterized using an exponential cumulative distribution function, the exponent decreases in magnitude by a factor of 2 from 1978 to 2002 in the Southern Hemisphere (Rtime = +0.85). This implies an increase in the relative proportion of the brightest PMCs. The secular brightness trend is less significant in the Northern Hemisphere (Rtime = +0.58). We discuss possible origins for these changes.

Improved calibration of NOAA-9 and NOAA-11 SBUV/2 total ozone data using in-flight validation methods

The Solar Backscattered Ultraviolet (SBUV)/2 instrument on-board the National Oceanic and Atmospheric Administration (NOAA)-9 satellite monitored global total ozone and its vertical distribution from 1985 to 1998. The instrument's diffuser reflectivity calibration system failed early in the mission and an alternative calibration procedure with a time extrapolation was used for an initial processing (Version 6.1 data). The total ozone data shows a +3% drift from 1992 to 1998 as well as large seasonal variations with respect to ground based and other satellite data. Using two internal data validation techniques the total ozone data quality is significantly improved. One method, the 'D-pair Method', which is analogous to the method used for the Nimbus 7 SBUV, corrects the diffuser reflectivity calibration and eliminates the drift in total ozone for NOAA-9. The D-pair Method applied to NOAA-11 SBUV/2 data from 1989 to 1994 shows good agreement with the NOAA-11 on-board diffuser reflectivity calibration system. The second validation method, the 'PMT System Method', is a new method that corrects the Photomultiplier Tube System Nonlinearity Characterization in Range 3 thereby reducing the seasonal variation in total ozone. The PMT System Method corrects both the NOAA-9 and NOAA-11 data.

Determination of NOAA-11 SBUV/2 radiance sensitivity drift based on measurements of polar ice cap radiance

The Solar Backscattered Ultraviolet model 2 (SBUV/2) instrument on the National Oceanic and Atmospheric Administration (NOAA-11) satellite has measured global total ozone and its altitude profile in the stratosphere since 1989. For the ozone measurement, its monochromator scans 12 discrete wavelengths from 252-340 nm. An onboard calibration system malfunctioned in late 1994. This necessitated the development of alternative methods of characterizing sensor sensitivity change. Assuming that the seasonal variation of surface reflectivity is the same from year to year, we used radiance measurements at 340 nm over the polar snow and ice to determine long-term instrument sensitivity drift at 340 nm. The spectral dependence of sensor sensitivity change in 1993 was used as an initial estimate for the current calibration. We then refined the calibration at 313, 318 and 331 nm for the total ozone retrieval, using the D-pair validation analysis. The estimated uncertainty in the extended calibration is less than 1%. The updated calibration has been used for NOAA-11 SBUV/2 operation. The resulting NOAA-11 SBUV/2 total ozone data were compared with ozone data from the Earth Probe Total Ozone Mapping Spectrometers (TOMS). The two agree with each other to better than 2%.

A discussion of upper stratospheric ozone asymmetries and SAGE trends

A chemical box model constrained by Upper Atmosphere Research Satellite (UARS) measurements of CH4, H2O, NOx, and temperature in 1992–1994 has been used in an attempt to simulate ozone trend measurements from the Stratospheric Aerosol and Gas Experiment (SAGE) at 43 km, 45° latitude and their hemispheric differences. The model is successful in simulating the seasonal cycle in ozone mixing ratios observed by the Microwave Limb Sounder (MLS) and the Solar Backscattered Ultraviolet (SBUV) instrument including the 15% larger values in the Southern Hemisphere at the wintertime ozone maximum. The model indicates that this hemispheric asymmetry is associated with hemispheric temperature differences of approximately 10°K; in contrast, hemispheric differences in methane and the resulting effects on ClOx make only a small contribution to this ozone asymmetry. The model predicts that, based on observed Cly increases, the ozone decrease in the Southern Hemisphere should have exceeded that in the Northern Hemisphere by approximately 1%/decade. This is consistent with an observed ozone hemispheric trend difference of 1.7 ± 2.1%/decade (1σ) for 1979–1997 and −0.8 ± 2.8%/decade for 1985–1997 from SAGE I and SAGE II (version 6.1) measurements. These trend differences are caused by hemispheric differences in temperature in early winter and in CH4 in late winter. The model, based on changes in Cly but not in other specified parameters, calculates a larger downtrend of ozone than is observed by SAGE II in 1985–1997 by approximately 3.1 ± 1.4%/decade (1σ), but it qualitatively simulates the observed ozone trend variations over the period 1979–1997. The amplitude of the model calculated downtrend would be reduced by approximately 1%/decade for a methane increase of 1%/yr. Observed temperature decreases of approximately 0.1°K/yr would have decreased the magnitudes of the calculated ozone downtrends on pressure surfaces by approximately 1%/decade but could have affected SAGE trends by a small amount in the opposite direction because of associated geopotential height changes.

A cohesive total ozone data set from the SBUV(/2) satellite system

The long‐term data collection of total ozone estimates from the Solar Backscatter Ultraviolet Ozone Sensors (SBUV and SBUV/2) began with the launch of SBUV on NASA's Nimbus‐7 spacecraft in 1978. Following this successful demonstration, the National Oceanic and Atmospheric Administration (NOAA) adopted the slightly modified SBUV/2 instruments for placement on the afternoon Polar‐Orbiting Operational Environmental Satellites (POES). The SBUV/2 instruments have flown on NOAA‐9, ‐11, ‐14, and ‐16 in the POES series, with NOAA‐16 launched in late 2000. Three more instruments are scheduled for launches in the next 6 years. While the absolute calibrations of individual instruments are good, they give total ozone accuracies of approximately 2%. However, without further adjustment, such interinstrument differences pose significant problems for atmospheric ozone trend analysis. In this paper we use the differences between total ozone estimates from the instruments during periods with overlapping coverage to account for these possible calibration biases. We use the NOAA‐9 SBUV/2 record as the reference standard because of the length of its record and the amount of overlap with other instruments' records. By applying adjustments to the other data sets based on these differences, a complete, unified data set is created for use in analysis of long‐term changes. The monthly‐averaged total ozone time series for 50°S to 50°N and the hemispheric subsets are compared to the results from two 2‐D chemistry models as a demonstration of the usefulness of the unified data sets.

Applications of satellite remote sensing in numerical weather and climate prediction

The year 2000 marks the 40 th anniversary of the launch of the first weather satellite. The images of cloud systems from the early satellites enabled forecasters to locate and monitor the movements of storms. Today's satellites provide a wealth of quantitative information about the constantly changing state of the Earth's atmosphere, ocean, and land surface. Significant strides are being made by operational centers around the world to effectively use these remotely-sensed observations in forecast models. The satellite measurements are used to initialize, provide boundary conditions for, and verify predictions of models. As an example of the state of the art, this paper reviews how satellite observations are used in the numerical weather and climate prediction models of the U.S. National Weather Service. The National Weather Service, National Centers for Environmental Prediction (NCEP), Environmental Modeling Center (EMC) develops regional and global weather prediction models, coupled ocean-atmosphere models for seasonal to interannual climate predictions, and a coastal ocean forecast model. A three dimensional variational data assimilation system is used to specify the initial conditions for the forecast models. Data from the following satellite instruments are currently used in one or more of these models: High Resolution Infrared Sounder (HIRS), Microwave Sounding Unit (MSU), Advanced Microwave Sounding Unit-A (AMSU-A), Geostationary Operational Environmental Satellites (GOES) sounder, GOES, METEOSAT, and Geostationary Meteorology Satellite (GMS) imagers, Advanced Very High Resolution Radiometer (AVHRR), Special Sensor Microwave/Imager (SSM/I), ESA Remote-sensing Satellite-2 (ERS-2) scatterometer, Solar Backscatter Ultraviolet Spectrometer/2 (SBUV/2), and Oceanic Topography Experiment (TOPEX) and ERS-2 altimeters.

Spectral solar UV irradiance data for cycle 21

The Nimbus 7 Solar Backscatter Ultraviolet (SBUV) instrument, which began taking data in November 1978, was the first instrument to make solar UV irradiance measurements covering both the minimum and maximum activity levels of a solar cycle. The currently archived irradiance data set was processed with an instrument characterization which fails to completely account for sensor degradation in the later part of the data record, thus limiting the accuracy of estimated long‐term solar activity variations and the scientific value of the data. In this paper, we describe an improved Nimbus 7 SBUV spectral irradiance data set, which utilizes a more accurate model for instrument sensitivity and treats other time‐dependent problems in the archived data. Estimated long‐term irradiance changes during solar cycle 21 are 8.3(±2.6)% at 205 nm, and 4.9(±1.8)% at 240 nm. The revised Nimbus 7 SBUV irradiance data are in good agreement with predictions of solar cycle variations from the Mg II index proxy model. These solar irradiance changes are also consistent with overlapping irradiance data from the declining phase of solar cycle 21 measured by the Solar Mesosphere Explorer (SME). The Nimbus 7 SBUV irradiance data represent the earliest component of a 20+ year continuous record of solar spectral UV activity.

Total ozone determinations from National Oceanic and Atmospheric Administration operational solar backscattered ultraviolet 2 instrument observations: An update

Total ozone amounts have been derived from observations of the Solar Backscattered Ultraviolet 2 (SBUV/2) instruments on National Oceanic and Atmospheric Administration (NOAA) operational satellites since 1985. The data from the NOAA‐9 instrument for the period 1985–1997 have been reprocessed using instrument characterizations based on in‐orbit operation and comparisons with Shuttle Solar Backscattered Ultraviolet (SSBUV) observations. The data from the NOAA‐11 satellite for the period 1989–1994 have also been reprocessed using mainly internal spacecraft information. The data from the NOAA‐14 satellite for the period 1995–1998 have been reprocessed using complete instrument characterization. The NOAA‐11 and NOAA‐14 data for 1998 to the present, briefly discussed herein, are preliminary. The calibration adjustments used in the reprocessing of NOAA‐9, NOAA‐11, and NOAA‐14 total ozone data are internal, with the exception of those derived from SSBUV analysis, and are independent of Dobson and Total Ozone Mapping Spectrometer (TOMS) total ozone measurements. The reprocessed data have been validated with ground‐based Dobson spectrophotometer observations, and are compared to other sources of total column ozone amounts. The mean bias between NOAA‐9 data and Dobson data is 1.9%±0.6% over the 12‐year record with a trend of 0.1% per year. The mean bias between NOAA‐11 and Dobson data is 0.8%±0.2% with a near‐zero trend. The mean bias between NOAA‐14 and Dobson data is 1.5%±0.3% with a trend of 0.2% per year; the NOAA‐14 calibration and characterization data for the period 1998 to the present are not yet fully analyzed. The methods used in the validations are discussed here, as are some reasons for the results. Finally, a recommendation is made for the use of a relatively continuous total ozone data set.

The GEOS ozone data assimilation system: Specification of error statistics

A global three-dimensional ozone data assimilation system has been developed at the Data Assimilation Office of the NASA/Goddard Space Flight Center. The Total Ozone Mapping Spectrometer (TOMS) total ozone and the Solar Backscatter Ultraviolet (SBUV) or (SBUV/2) partial ozone profile observations are assimilated. The assimilation, into an off-line ozone transport model, is done using the global Physical-space Statistical Analysis Scheme (PSAS). This system became operational in December 1999. A detailed description of the statistical analysis scheme, and in particular, the forecast and observation error covariance models is given. A new global anisotropic horizontal forecast error correlation model accounts for a varying distribution of observations with latitude. Correlations are largest in the zonal direction in the tropics where data is sparse. Forecast error variance model is proportional to the ozone field. The forecast error covariance parameters were determined by maximum likelihood estimation. The error covariance models are validated using x squared statistics. The analyzed ozone fields in the winter 1992 are validated against independent observations from ozone sondes and HALOE. There is better than 10% agreement between mean Halogen Occultation Experiment (HALOE) and analysis fields between 70 and 0.2 hPa. The global root-mean-square (RMS) difference between TOMS observed and forecast values is less than 4%. The global RMS difference between SBUV observed and analyzed ozone between 50 and 3 hPa is less than 15%.

The GEOS ozone data assimilation system: Specification of error statistics

AbstractA global three‐dimensional ozone data assimilation system has been developed at the Data Assimilation Office of the NASA Goddard Space Flight Center. The Total Ozone Mapping Spectrometer (TOMS) total ozone data and the Solar Backscatter Ultraviolet/2 (SBUV/2) partial ozone profile observations are assimilated. The assimilation, into an off‐line ozone transport model, is done using the global Physical‐space Statistical Analysis Scheme. This system became operational in December 1999.A detailed description of the statistical analysis scheme and, in particular, of the forecast‐ and observation‐error covariance models is given. A new global anisotropic horizontal forecast‐error correlation model accounts for a varying distribution of observations with latitude. Correlations are largest in the zonal direction in the tropics where data are sparse. Forecast‐error variance is assumed to be proportional to the ozone field. The forecast‐error covariance parameters were determined by maximum‐likelihood estimation. The error covariance models are validated using χ2 statistics.The analysed ozone fields in the winter 1992 are validated against independent observations from ozone sondes and the Halogen Occultation Experiment (HALOE). The difference between the mean HALOE observations and the analysis fields is less than 10% at pressure levels between 70 and 0.2 hPa. The global root‐mean‐square difference between TOMS observed and forecast values is less than 4%. The global root‐mean‐square difference between SBUV observed and analysed ozone between 50 and 3 hPa is less than 15%.

Statistical interpolation of ozone measurements from satellite data (TOMS, SBUV and SAGE II) using the kriging method

Abstract. This study demonstrates that ordinary kriging in spherical coordinates using experimental semi-variograms provides highly usable results, especially near the pole in winter and/or where there could be data missing over large areas. In addition, kriging allows display of the spatial variability of daily ozone measurements at different pressure levels. Three satellite data sets were used: Total Ozone Mapping Spectrometer (TOMS) data, Solar Backscattered UltraViolet (SBUV), and the Stratospheric Aerosol and Gas Experiment (SAGE II) ozone profiles. Since SBUV is a nadir-viewing instrument, measurements are only taken along the sun-synchronous polar orbits of the satellite. SAGE II is a limb-viewing solar occultation instrument, and measurements have high vertical resolution but poor daily coverage. TOMS has wider coverage with equidistant distribution of data (resolution 1° × 1.25°) but provides no vertical information. Comparisons of the resulting SBUV-interpolated (column-integrated) ozone field with TOMS data are strongly in agreement, with a global correlation of close to 98%. Comparisons of SBUV-interpolated ozone profiles with daily SAGE II profiles are relatively good, and comparable to those found in the literature. The interpolated ozone layers at different pressure levels are shown.Key words: Atmospheric composition and structure (middle atmosphere - composition and chemistry) - Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Statistical interpolation of ozone measurements from satellite data (TOMS, SBUV and SAGE II) using the kriging method

This study demonstrates that ordinary kriging in spherical coordinates using experimental semi-variograms provides highly usable results, especially near the pole in winter and/or where there could be data missing over large areas. In addition, kriging allows display of the spatial variability of daily ozone measurements at different pressure levels. Three satellite data sets were used: Total Ozone Mapping Spectrometer (TOMS) data, Solar Backscattered UltraViolet (SBUV), and the Stratospheric Aerosol and Gas Experiment (SAGE II) ozone profiles. Since SBUV is a nadir-viewing instrument, measurements are only taken along the sun-synchronous polar orbits of the satellite. SAGE II is a limb-viewing solar occultation instrument, and measurements have high vertical resolution but poor daily coverage. TOMS has wider coverage with equidistant distribution of data (resolution 1° × 1.25°) but provides no vertical information. Comparisons of the resulting SBUV-interpolated (column-integrated) ozone field with TOMS data are strongly in agreement, with a global correlation of close to 98%. Comparisons of SBUV-interpolated ozone profiles with daily SAGE II profiles are relatively good, and comparable to those found in the literature. The interpolated ozone layers at different pressure levels are shown.Key words: Atmospheric composition and structure (middle atmosphere - composition and chemistry) - Meteorology and atmospheric dynamics (middle atmosphere dynamics)

Upper‐stratospheric ozone trends 1979–1998

Extensive analyses of ozone observations between 1978 and 1998 measured by Dobson Umkehr, Stratospheric Aerosol and Gas Experiment (SAGE) I and II, and Solar Backscattered Ultraviolet (SBUV) and (SBUV)/2 indicate continued significant ozone decline throughout the extratropical upper stratosphere from 30–45 km altitude. The maximum annual linear decline of −0.8±0.2 % yr−1 (2σ) occurs at 40 km and is well described in terms of a linear decline modulated by the 11‐year solar variation. The minimum decline of −0.1±0.1% yr−1 (2σ) occurs at 25 km in midlatitudes, with remarkable symmetry between the Northern and Southern Hemispheres at 40 km altitude. Midlatitude upper‐stratospheric zonal trends exhibit significant seasonal variation (±30% in the Northern Hemisphere, ±40% in the Southern Hemisphere) with the most negative trends of −1.2% yr−1 occurring in the winter. Significant seasonal trends of −0.7 to −0.9% yr−1 occur at 40 km in the tropics between April and September. Subjecting the statistical models used to calculate the ozone trends to intercomparison tests on a variety of common data sets yields results that indicate the standard deviation between trends estimated by 10 different statistical models is less than 0.1% yr−1 in the annual‐mean trend for SAGE data and less than 0.2% yr−1 in the most demanding conditions (seasons with irregular, sparse data) [World Meteorological Organization (WMO), 1998]. These consistent trend results between statistical models together with extensive consistency between the independent measurement‐system trend observations by Dobson Umkehr, SAGE I and II, and SBUV and SBUV/2 provide a high degree of confidence in the accuracy of the declining ozone amounts reported here. Additional details of ozone trend results from 1978 to 1996 (2 years shorter than reported here) along with lower‐stratospheric and tropospheric ozone trends, extensive intercomparisons to assess relative instrument drifts, and retrieval algorithm details are given by WMO [1998].