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Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine - EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to s

The trend in stratospheric NO2 column at the NDACC (Network for the Detection of Atmospheric Composition Change) station of Jungfraujoch (46.5° N, 8.0° E) is assessed using ground-based FTIR and zenith-scattered visible sunlight SAOZ measurements over the period 1990 to 2009 as well as a composite satellite nadir data set constructed from ERS-2/GOME, ENVISAT/SCIAMACHY, and METOP-A/GOME-2 observations over the 1996–2009 period. To calculate the trends, a linear least squares regression model including explanatory variables for a linear trend, the mean annual cycle, the quasi-biennial oscillation (QBO), solar activity, and stratospheric aerosol loading is used. For the 1990–2009 period, statistically indistinguishable trends of -3.7 ± 1.1% decade-1 and -3.6 ± 0.9% decade-1 are derived for the SAOZ and FTIR NO2 column time series, respectively. SAOZ, FTIR, and satellite nadir data sets show a similar decrease over the 1996–2009 period, with trends of -2.4 ± 1.1% decade-1, -4.3 ± 1.4% decade-1, and -3.6 ± 2.2% decade-1, respectively. The fact that these declines are opposite in sign to the globally observed +2.5% decade-1 trend in N2O, suggests that factors other than N2O are driving the evolution of stratospheric NO2 at northern mid-latitudes. Possible causes of the decrease in stratospheric NO2 columns have been investigated. The most likely cause is a change in the NO2/NO partitioning in favor of NO, due to a possible stratospheric cooling and a decrease in stratospheric chlorine content, the latter being further confirmed by the negative trend in the ClONO2 column derived from FTIR observations at Jungfraujoch. Decreasing ClO concentrations slows the NO + ClO ¿ NO2 + Cl reaction and a stratospheric cooling slows the NO + O3 ¿ NO2 + O2 reaction, leaving more NOx in the form of NO. The slightly positive trends in ozone estimated from ground- and satellite-based data sets are also consistent with the decrease of NO2 through the NO2 + O3 ¿ NO3 + O2 reaction. Finally, we

info:eu-repo/semantics/published

In March 2002 the European Space Agency (ESA) launched the polar-orbiting environmental satellite Envisat. One of its nine instruments is the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument, which is a medium-resolution stellar occultation spectrometer measuring vertical profiles of ozone. In the first year after launch a large group of scientists performed additional measurements and validation activities to assess the quality of Envisat observations. In this paper, we present validation results of GOMOS ozone profiles from comparisons to microwave radiometer, balloon ozonesonde, and lidar measurements worldwide. Thirty-one instruments/launch sites at twenty-five stations ranging from the Arctic to the Antarctic joined in this activity. We identified 6747 collocated observations that were performed within an 800-km radius and a maximum 20-hour time difference of a satellite observation, for the period between 1 July 2002 and 1 April 2003. The GOMOS data analyzed here have been generated with a prototype processor that corresponds to version 4.02 of the operational GOMOS processor. The GOMOS data initially contained many obviously unrealistic values, most of which were successfully removed by imposing data quality criteria. Analyzing the effect of these criteria indicated, among other things, that for some specific stars, only less than 10% of their occultations yield an acceptable profile. The total number of useful collocated observations was reduced to 2502 because of GOMOS data unavailability, the imposed data quality criteria, and lack of altitude overlap. These collocated profiles were compared, and the results were analyzed for possible dependencies on several geophysical (e.g., latitude) and GOMOS observational (e.g., star characteristics) parameters. We find that GOMOS data quality is strongly dependent on the illumination of the limb through which the star is observed. Data measured under bright limb conditions, and to a certain extent a

The relaxation of the field cooled magnetisation of a multilayered 2D Cu(Mn) spin glass film has been investigated in a SQUID-magnetometer. The sample is cooled in a constant magnetic field (10 Oe) from a high temperature, where the magnetisation is at equilibrium, to a temperature below the freezing temperature, T(f). At constant temperature, the magnetisation is then found to increase with time at temperatures near T(f), showing an initial decrease followed by an increase at long time scales at intermediate temperatures and only decreases with time at lower temperatures. The behaviour, including the surprising downward relaxation away from the thermodynamic equilibrium magnetisation, is qualitatively interpreted in terms of a spin glass domain model., 20th International Conference on Low Temperature Physics, EUGENE, OR, AUG 04-11, 1993

Time-dependent dc-magnetization measurements on two-dimensional (2D) Cu(Mn) spin-glass films are reported. Results from the wait-time dependence of the relaxation of the zero-field-cooled magnetization combined with particular effects of temperature cyclings prior to the field application provide evidence for the existence of an overlap length in 2D spin glasses.

A new method that uses superstructures of Cu(Mn) spin glass films separated by metallic interlayers to probe the decay with thickness of the RKKY interaction within the interlayers is discussed., INTERNATIONAL CONF ON MAGNETISM, EDINBURGH, SCOTLAND, SEP 02-06, 1991

Utilizing zero-field cooled magnetization measurements the nonequilibrium dynamics in a 2D spin glass film is investigated. The experiments show that aging is an inherent property of 2D spin glass systems with qualitatively similar features as in 3D systems., INTERNATIONAL CONF ON MAGNETISM, EDINBURGH, SCOTLAND, SEP 02-06, 1991

Time-dependent susceptibility measurements have been performed on multilayered two-dimensional (2D) 40-angstrom-wide Cu0.865Mn0.135 spin-glass films, separated by Cu interlayers of width 10 < w(il) < 1200 angstrom. It is found that samples with w(il) < 30 angstrom display 3D dynamic behavior. For 30 < w(il) < 600 angstrom a gradual decoupling of the spin-glass layers occurs, and for w(il) greater-than-or-equal-to 600 angstrom typical 2D behavior is observed. The effect of a finite interlayer coupling on the dynamic susceptibility is a distinct crossover from 2D dynamic behavior at short observation times to 3D dynamic behavior at long times. A clear influence on the spin-glass dynamics is still observable for interlayer thicknesses of order 500 angstrom; i.e., multilayered spin-glass films are extremely sensitive probes of the effective range of Ruderman-Kittel-Kasuya-Yosida interaction mediated via metallic interlayers. The results also yield information on the relation between time scale and length scale in relaxation experiments, a fundamental concept of domain theories of the spin-glass phase.

19TH INTERNATIONAL CONF ON LOW TEMPERATURE PHYSICS ( LT-19 ), BRIGHTON, ENGLAND, AUG 16-22, 1990

34TH ANNUAL CONF ON MAGNETISM AND MAGNETIC MATERIALS, BOSTON, MA, NOV 28-DEC 01, 1989