Changes In Atmospheric Turbidity Research Articles

Secular Changes in Atmospheric Turbidity over Iraq and a Possible Link to Military Activity

We examine satellite-derived aerosol optical depth (AOD) data during the period 2000–2018 over the Middle East to evaluate the contribution of anthropogenic pollution. We focus on Iraq, where US troops were present for nearly nine years. We begin with a plausibility argument linking anthropogenic influence and AOD signature. We then calculate the percent change in AOD every two years. To pinpoint the causes for changes in AOD on a spatial basis, we distinguish between synoptically “calm” periods and those with vigorous synoptic activity. This was done on high-resolution 10 km AOD retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (Terra satellite). We found spatiotemporal variability in the intensity of the AOD and its standard deviation along the dust-storm corridor during three studied periods: before Operation Iraqi Freedom (OIF) (1 March 2000–19 March 2003), during OIF (20 March 2003–1 September 2010), and Operation New Dawn (OND; 1 September 2010–18 December 2011), and after the US troops’ withdrawal (19 December 2011–31 December 2018). Pixels of military camps and bases, major roads and areas of conflict, and their corresponding AOD values, were selected to study possible effects. We found that winter, with its higher frequency of days with synoptically “calm” conditions compared to spring and summer, was the best season to quantitatively estimate the impact of these ground-based sources. Surprisingly, an anthropogenic impact on the AOD signature was also visible during vigorous synoptic activity. Meteorological conditions that favor detection of these effects using space imagery are discussed, where the effects are more salient than in surrounding regions with similar meteorological conditions. This exceeds expectations when considering synoptic variations alone.

Sunshine duration and global radiation trends in Italy (1959–2013): To what extent do they agree?

AbstractTwo Italian homogenized data sets of sunshine duration (SD) and global radiation (Eg↓) relative anomalies are used to investigate to what extent these two variables agree with respect to their temporal evolution. They are compared for northern and southern Italy over the period 1959–2013. Both under all‐sky and clear‐sky conditions, the SD records tend to show a shorter and less intense decrease until the 1980s (“global dimming”) with respect to the Eg↓ ones, while there is a better agreement in the subsequent period when both variables increase (“brightening period”). To investigate whether such behavior can be explained by a different sensitivity of SD and Eg↓ to atmospheric turbidity variations, the observed clear‐sky trends are compared to those estimated by a model based both on Lambert‐Beer's law and on a simple estimation of diffuse radiation. Results show that most of the differences observed in the trends of the clear‐sky SD and Eg↓ records can be explained considering a realistic pattern of atmospheric turbidity in the 1959–2013 period. The only exception concerns winter and autumn in northern Italy where clear‐sky SD does not decrease in the dimming period as much as it would be expected on the basis of the corresponding increase in atmospheric turbidity. One reason for this discrepancy could be the influence of other variables like relative humidity. This case study highlights that changes in atmospheric turbidity have to be kept in mind when SD is used to investigate the multidecadal evolution of Eg↓.

A new approach to the real-time assessment of the clear-sky direct normal irradiance

In a context of sustainable development, interest for concentrating solar power and concentrating photovoltaic technologies is growing rapidly. One of the most challenging topics is to improve solar resource assessment and forecasting in order to optimize power plant operation. Since clear sky defines the nominal operating conditions of the plants, improving their management requires the use in real-time of clear-sky direct normal irradiance (DNI) models. Typically, accuracy is best achieved by considering water vapor and aerosol concentrations in the atmosphere separately. However, measuring such physical quantities is not easy and requires a weather station close to the considered site. When these data are not available, the attenuating effects can be modeled by atmospheric turbidity factors which can be obtained from DNI under clear-sky conditions. So, the main purpose of the present paper is to propose an efficient approach to assess the clear-sky DNI in real time. This approach combines an existing empirical model, proposed by Ineichen and Perez, with a new methodology for the computation of atmospheric turbidity. It takes advantage of the fact that changes in atmospheric turbidity are relatively small throughout the day in comparison to changes in DNI, even when the sky is free of clouds. In the present study, we considered data from two experimental sites (Golden, in the USA, and Perpignan, in France) and used a wavelet-based multi-resolution analysis as a clear-sky DNI detection tool. In addition, we compared the proposed approach with several combinations of empirical models and ways of computing atmospheric turbidity. The first model is a polynomial of the cosine of the solar zenith angle, whereas the two other models use atmospheric turbidity as an additional input. Regarding its calculation, monthly and daily mean values have been considered. Moreover, we defined a procedure in order to evaluate the accuracy of all the considered approaches. This procedure allows changes in DNI caused by clouds to be simulated using a noisy signal applied to clear-sky periods. In both sites, our approach to the real-time assessment of the clear-sky DNI outperforms the other approaches. In the worst case, the mean absolute error is reduced by 8 W m−2 in comparison to the approaches based on monthly mean values of atmospheric turbidity, and reduced by about 30 W m−2 when taking the polynomial-based model as a reference.

Estimation of daily average values of the Ångström turbidity coefficient β using a Corrected Yang Hybrid Model

This paper aims to test a method for estimating daily values of atmospheric turbidity from non-specialized data, such as those obtained from agro-meteorological stations. This method allows estimating the spatial and temporal evolution of aerosols concentration in more places than just those in which direct measurements are available. The method is based on the Corrected Yang Hybrid Model (CYHM). The data used in the determination of errors between measured and estimated values of the daily Ångström turbidity coefficient β were recorded in Valencia, Spain, during 2009 and 2011. These data were global solar irradiance, direct solar irradiance, temperature, relative humidity and Aerosol Optical Depth (AOD) measured at an AERONET station. The errors are shown as a function of daily clearness index Kt, observing that as Kt decreased, the error of estimate β increased. Taking into account that the nominal error of the apparatus used to measure AOD has the same order of magnitude as the calculated errors and that most of the terms involved in the measurement of atmospheric transmittance phenomena have been estimated, the method produces results that are acceptable for general purposes. The method was applied to historical meteorological data recorded in Bogotá, Colombia. The daily values of atmospheric turbidity were estimated for 1983 and 1997, showing little changes in atmospheric turbidity between those years.

Atmospheric Turbidity Estimation from Hourly Global Solar Radiation Data under Cloudless Skies

We estimated monthly atmospheric turbidity from hourly observation data of global solar radiation under cloudless skies at 67 stations all over Japan. Using an empirical formula for calculating global solar radiation, we determined atmospheric turbidity as the best-fit parameter. The estimated turbidity is consistent with the observation by the Japan Meteorological Agency. Sub-nationwide increases in atmospheric turbidity, caused by forest fires or Asian dust events, are detected in time series. Some temporal changes in atmospheric turbidity are also found in a small area. Such local phenomena are hardly detectable by sparse distribution of the stations for direct solar radiation observation. The accuracy of the global solar radiation estimation can be improved by considering the seasonal variation of the turbidity. Since Angstrom’s turbidity coefficient is directly linked with the volumetric aerosol content, the present method is useful for monitoring the spatial distribution of aerosols. In addition, the present method using the densely distributed observation network of global solar radiation has an advantage in compensating for the sparseness of the current atmospheric turbidity observation in Japan.

Photosynthetically active components of global solar radiation: Measurements and model computations

A three-year(1980–82) record of global solar radiation measurements made at Corvallis, Oregon, U.S.A. (44°34′N, 123°14′W; 65.5 m) has been utilized to determine the distribution of radiant energy in broad spectral intervals in the visible (0.385–0.695 μm) region of the spectrum which is often referred to as the photosynthetically active radiation or PAR band. The mean values of the ratios borne by the daily irradiation in the spectral intervals 0.385–0.530 μm and 0.630–0.695 μm, which cover most of the action spectra of plant photochemistry, to the daily total (0.295–2.8 μm) global irradiation are found to be 0.222 (standard deviation: 0.030) and 0.086 (standard deviation: 0.013) respectively; the corresponding ratios in the PAR band and in the spectral interval 0.530–0.630 km are 0.457 (standard deviation: 0.029) and 0.149 (standard deviation: 0.021). These irradiation ratios exhibit seasonal variations, attributable to changes in local air mass climatology, and dependence on sky conditions, with slightly larger values being observed under “cloudy” skies. The mean value of 0.457 that we have obtained for the irradiation ratio in the PAR band compares favorably with the values reported in the literature for different locations over a wide geographical area. There is reasonable correspondence between the observed irradiation ratios and the computed values in a cloud-free model of a turbid atmosphere.. The sensitivity of the broad-band spectral energy distribution of the global solar radiation to changes in atmospheric turbidity, precipitable water, ozone and surface albedo has been examined in the light of these model computations.

High cloud increases in recent years

Summary Changes in cloud amounts will disturb the existing complex balance of radiative energy. An increase in high cloud would reduce the initial input of energy into the atmosphere, and this study is directed to examine the high cloud amounts during the periods 1950–54 and 1966–70. Using information from Albuquerque, Denver and Lander increases of 25, 68 and 57 % in amount, respectively, are shown. Even at a Pacific island an increase of 152% is noted while three stations in the Sudan average 47% increases. Eight stations in western Chad, well removed from major airlines, showed only an 11 % increase. This investigation suggests that the increases may be due to long‐term changes in atmospheric turbidity, perhaps aggravated by jet aircraft contrails.

Atmospheric turbidity and CCl 3F concentrations in rural Southern England and Southern Ireland

The seasonal changes in atmospheric turbidity in rural Southern England and Southern Ireland have been observed and are compared with wind direction and with the concentration of CCl 3F a material whose origins are unequivocally anthropogenic. The observations suggest that the dense summertime aerosol is probably an end product of the atmospheric photochemistry of air pollutants and that Continental Europe is the principal source.