A. P. Cracknell

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.

Advanced thermal inertia modelling

Abstract This paper presents a simple and operational thermal inertia model by using the phase angle information of the diurnal temperature change. The model which is developed in this paper is based on our first-order approximation operational thermal inertia model. We use a second-order approximation for the boundary conditions and a second-order approximation for the surface temperature series expression. The importance of this work is that from our model real thermal inertia (as distinct from apparent thermal inertia) can be computed directly. The model requires only one field measurement parameter for the calculation of real thermal inertia; this is the time of maximum temperature in the daytime and this parameter is easily obtained from a meteorological station. For the regions having vegetative cover, the thermal inertia value is the weighted thermal inertia values of vegetated cover and soil ground.

Operational bi-angle approach to retrieve the Earth surface albedo from AVHRR data in the visible band

Abstract The inference of surface spectral reflectance using visible observations is complicated mainly because of scattering effects. In the present paper we attempt a solution to the problem of retrieval of surface reflectance from satellite radiance measurements based on a solution of the radiative transfer equation. We have developed an operational method which relies on multiple view angle observations or multiple solar zenith angle observations of the surface to accomplish part of this task in a routine manner. This approach may be used for ERS-2 ATSR visible bands because there will be two view angle observations for the same area at essentially the same time. This approach can also be used with NOAA satellite AVHRR data by assuming that the distribution of the aerosol does not vary too rapidly as a function of time. Usually it is better to select the AVHRR data from around noon and at dusk in the same day. This approach requires that the visibility of the area should be more than 5 km for multiple...

New features observed in the 11-year solar cycle

The number of sunspots is characterized by a long-term temporal variation, reaching its maximum or its minimum approximately every 11 years (the solar cycle). This variation, in turn, has an effect in terms of variation in the global climate. Since 1979, the use of satellite-borne radiometers has enabled accurate measurements of total solar irradiance (TSI). For instance, the sunspot numbers that are scaled to correspond to Nimbus-7 TSI observations for 1979–1993 show little long-term trend. However, while the observations of different extremes of the solar cycle, which are available from 1749, seem irregular in time and magnitude and difficult to quantify, they appear to have a strong correlation between them when they are sorted pairwise according to their size rather than sequentially in time. A similar relation holds among the solar cycle lengths (periods) and the solar cycle extremes, which, in parallel, obey a linear relation that is reminiscent of the Gutenberg–Richter seismic law. This can be used for a probabilistic approach to forecast solar parameters that are connected to global climate. Based on the reasonable assumption that the basic parameters like extremes and length of the 11-year solar cycle are associated with the energy oscillating between the dipolar and quadrupolar phases of the cycle, it is concluded that these parameters obey a power-law distribution similar to that of the Gutenberg–Richter seismic law. The question of whether solar activity is deterministically chaotic is also investigated by exploring the behaviour of the main characteristics of the 11-year solar cycle. This is done by constructing return maps of solar cycle strength and duration, which seem to take the familiar up–down U shape, implying both non-linearity and re-injection. The results suggest that there might exist a coupling between two or three different non-linear deterministic dynamical systems on the Sun, depending on which variable of the solar cycle is being considered.

Retrieval of land and sea surface temperature using NOAA-11 AVHRR· data in north-eastern Brazil

Abstract The split-window method is investigated and a simple airborne atmospheric correction model for thermal data is proposed. Analysis shows that the atmospheric transmittance has a quadratic behaviour with the water vapour content in the first few kilometres of a wet atmosphere. The effect of the emissivity is evaluated for the retrieval of surface temperature using data from NOAA-11 AVHRR channels 4 and 5 for two extreme atmospheres. The results indicate that a spectral emissivity variation (Δe) in channels 4 and 5 of ±0.01 is not as important for a wet atmosphere as for a dry atmosphere. The split-window algorithm developed in this work has its parameters dependent on the atmospheric state and the values of these parameters are determined by using radiosonde profiles. Data from eighty-five radiosondes have been used to determine and check the local seasonal equatorial split-window parameters. The results of surface temperature retrieval show that the local seasonal equatorial and daily split-window...

Airborne lidar bathymetry

Abstract Through an extensive literature review the results of previous lidar investigations in Australia, Canada, Sweden, the U.S.A. and West Germany have been evaluated. Based on these findings estimates are given for the anticipated depth capability, measurement accuracy and operational constraints for a laser system in U.K. waters. Consideration is also given to the possibility of deploying a depth-sounding lidar for non-bathymetric purposes such as depth-resolved turbidity mapping.

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.

Ozone depletion over Scotland as derived from Nimbus-7 TOMS measurements

Abstract The TOMS (Total Ozone Mapping Spectrometer) flown on the Nimbus-7 satellite has been measuring the total ozone concentration over the globe since November 1978. Recent investigations based on TOMS data have shown that in the latitude belt 40–70° N the spring ozone depletion rate reaches the value of —0·8 per cent per year. This paper reports trends derived from the TOMS reprocessed total ozone data for the case of Dundee (56·5°N, 3°W) from January 1979 to January 1992. The depletion rate of the mean monthly total ozone concentration over this 13-year period shows a strong variation from more than —15 per cent in December and January to about +0·5 per cent in February and June, while the overall mean is about —7 per cent.

New evidence for ozone depletion over Athens, Greece

The seasonal total column ozone (TOZ) trends derived from satellite and ground-based instrumentation between June 1991-July 1999 at Athens, Greece, appear to be opposite to those of the period November 1978-May 1991. In the post-Pinatubo period large negative trends in TOZ during summertime combined with the large positive trends in TOZ during fall-winter period result in a decrease of the annual peak-to-trough differences from those of the pre-Pinatubo period.

The present status of the total ozone depletion over Greece and Scotland: a comparison between Mediterranean and more northerly latitudes

Abstract Results showing ozone concentrations over Athens and over Dundee, determined from satellite remote sensing measurements, are reported along with the results of ground-based ozone measurements in Athens and ground-based solar ultraviolet measurements in Dundee. The spatial variation of ozone concentrations within Greece is also discussed.