Maria N. Efstathiou

Long-range persistence in global Aerosol Index dynamics

Detrended fluctuation analysis (DFA) was applied to zonal mean daily Aerosol Index (AI) values derived from satellite observations during 1979–2003 to search for self‐similarity properties. The results show that the detrended and deseasonalized AI fluctuations in both hemispheres and globally obey persistent long‐range power‐law correlations for time scales longer than about 4 days and shorter than about 2 years. This suggests that the AI fluctuations in small time intervals are related to the AI fluctuations in longer time intervals in a power‐law fashion (when the time intervals vary from about 4 days to about 2 years). In other words, an anomaly in AI in one time frame continues into the next, exhibiting a power‐law evolution. The influence of the annual and semiannual cycles on the scaling behaviour of the AI time series in both hemispheres is discussed. A plausible mechanism for the time scale of about 2 years in AI time series could be the modulation of the Brewer–Dobson cell by the quasi‐biennial oscillation at the equatorial stratosphere in the zonal wind. The synoptic‐scale meteorological systems probably give rise to the time scale of about 4 days. These findings could prove useful in testing the results of existing models, which should be examined to determine if they demonstrate the scaling behaviour mentioned above.

On the seasonal variation of the surface ozone in Athens, Greece

Abstract An attempt has been made to examine the seasonal variation of the surface ozone mixing ratio in Athens, Greece during the periods 1901–1940 and 1987–1998. The first finding is that in July and August while the daytime surface ozone mixing ratio from the beginning until the end of the 20th century has increased by approximately 1.8 times, the nighttime surface ozone mixing ratio remained approximately at the same level. The second finding is that the increase in the mean daytime mixing ratio during the transition period from winter to summer is equal to the increase in the maximum daytime mixing ratios, whilst the enhancement of the nighttime surface ozone maxima is stronger than that of the nighttime mean surface ozone mixing ratio. Plausible explanation for this finding is given through mechanisms like long-range transport and photochemical processes occurring in the boundary layer, free troposphere and lower stratosphere.

On the longitude dependence of total ozone trends over middle-latitudes

It has recently been observed that the total ozone trends derived from certain geographical regions such as the Mediterranean and Athens (Greece) show similar values to those derived from the 40°N zonal averaged column ozone data. In this Letter, the total ozone concentration, collected by the Total Ozone Mapping Spectrometer (TOMS) flown on Nimbus-7 and Meteor-3 during the time-period January 1979-December 1993, as well as by Earth Probe during the time-period January 1997-May 2001, for the Mediterranean, Athens (Greece) and Srinagar (India), is analysed. Further, the harmonic analysis performed on total ozone time-series provides a proper tool to interpret the observed similarity in total ozone seasonal trends, which may probably be attributed to the effect of planetary waves on the ozone distribution.

An estimation of the surface solar ultraviolet irradiance during an extreme total ozone minimum

SummaryA simple theoretical algorithm has been employed to estimate the solar ultraviolet irradiance at Athens, Greece (38.7°N, 23.4°E) during, summertime 1993, a year of extreme total ozone minimum in the existing data record. This estimation has been performed by using total ozone measurements as derived by both ground-based and satellite instrumentation. The utilization of the present investigation will assist to the various assesments for the risk of human health from the biologically-effective doses of the solar ultraviolet radiation arrived at the earths surface during that time period.

On the altitude dependence of the temperature scaling behaviour at the global troposphere

Detrended fluctuation analysis is applied to the mean monthly temperature values, over different heights of the global troposphere, during 1980–2004, to search for self-similarity properties. The results show that the tropospheric temperature anomalies obey persistent long-range power-law correlations for time-scales longer than about four months and shorter than about six years. This suggests that the temperature fluctuations over small time periods (i.e. a few months) are related to those over longer time periods (i.e. a few years). In addition, the long-range power-law persistence in the global tropospheric temperature fluctuations becomes stronger as the altitude increases.

On the plausible association between environmental conditions and human eye damage.

The increase in solar ultraviolet radiation can have various direct and indirect effects on human health, like the incidence of ocular damage. Data of eye damage in residents of three suburban regions in Greece and in two groups of monks/nuns and fishermen are examined here. The statistics performed on these data provides new information about the plausible association between increased levels of solar ultraviolet radiation, air-pollution at ground level, and the development of ocular defects.

New features of land and sea surface temperature anomalies

Global mean land and sea surface temperature (LSST) anomalies were analysed statistically with detrended fluctuation analysis (DFA), for the period from January 1850 to August 2008, for both hemispheres, individually. Persistent long-range power-law correlations were revealed within the time series of the LSST anomalies, for all time lags between 4 months and 39 years. In addition, the derived ‘long memory’ in the time series of the LSST anomalies was examined to determine whether they are derived from their time evolution or from the distribution of their own values. The results obtained could be taken into consideration for the prediction of basic climate variables through the use of future climate modelling.

On the limits of the air pollution predictability: the case of the surface ozone at Athens, Greece

PurposeThe aim of this study is to investigate the potential effects of increased urbanization in the Athens city, Greece on the intrinsic features of the temporal fluctuations of the surface ozone concentration (SOC).MethodsThe detrended fluctuation analysis was applied to the mean monthly values of SOC derived from ground-based observations collected at the centre of Athens basin during 1901–1940 and 1987–2007.ResultsDespite the present-day SOC doubling in respect to SOC historic levels, its fluctuations exhibit long-range power-law persistence, with similar features in both time periods. This contributes to an improved understanding of our predictive powers and enables better environmental management and more efficient decision-making processes.ConclusionsThe extensive photochemistry enhancement observed in the Athens basin from the beginning of the twentieth century until the beginning of the twenty-first century seems not to have affected the long memory of SOC correlations. The strength of this memory stems from its temporal evolution and provides the limits of the air pollution predictability at various time scales.

Scaling effect in planetary waves over Antarctica

Detrended fluctuation analysis (DFA) was applied to the total ozone planetary waves 1 and 2 at the middle and high latitudes of the southern hemisphere that had been acquired by daily Total Ozone Mapping Spectrometer (TOMS) total ozone observations since 1979. The main aim of the analysis was to examine the ozone layer as a system invariant in a wide range of scales characterized by the fractal structure, and to search for the existence of long‐range correlations. The results show that fluctuations in the amplitude of wave 1 obey persistent long‐range power‐law correlations for time scales greater than about 4 days and less than about 3 months. This suggests that these fluctuations in small time intervals are closely related to the fluctuations in longer time intervals in a power‐law fashion (when the time intervals vary from about 4 days to about 3 months). Similar analysis applied to the amplitude of wave 2 revealed that this wave does not exhibit long‐range correlations.

The local and regional atmospheric oxidants at Athens (Greece)

In the present study, the investigation of the levels of the local and regional oxidants concentration at Athens, Greece, is attempted by analyzing the observations obtained at an urban and a rural station, during 2001–2011 and 2007–2011, respectively. A progressive increase of the daytime and nighttime average of [NO2]/[Ox] versus [NOx] is observed showing a larger proportion of Ox in the form of NO2 when the level of NOx increases. Similar results are observed when studying the variation of mean values of [NO2]/[NOx] versus [NOx]. The results obtained when compared with those that have earlier detected elsewhere, revealed similarities and discrepancies that are discussed in detail. The parameterized curves that are presented for the first time in this paper may be used by the air quality planners to track the trends in other cities also, and to understand what is or was driving them.