Analysis of auroral electrojet magnetic indices

In this paper magnetic indices were extracted from World Data Center (WDC) for geomagnetism forsix years (2008 to 2013). The indices extracted are  AuroralElectrojet (AE), Auroral Upper (AU), Auroral Lower (AL) and Auroral Oval (AO). The indices daily values measured at 24 hours Universal Time (UT) were averaged to monthly values. Time series statistical analysis was carried out on the monthly averaged data using SPSS version 16.0 with expert modeler, to determine the level, trend and seasonal  variations of the indices.From the results obtained after the statistical analysis, it can be seen that the indices have seasonal patterns of which AE, AL and AO as March but AU has July. Also from the values of the coefficient of determination, R2, it can also be concluded that AE and AL can be better predicted from the models than AU and AO. From the results obtained, simple seasonal model for AE, AL, and AO, and winter’s additive for AU was determined. Using the values of R2, it can be seen that the models for AE and AL can be used to predict or make forecast of the behavior of the indices. It was also discovered that level (alpha) has more significant contributions in the behavior of the system than seasonal.Keywords: Magnetic indices, World Data Center, Auroral, Level, Trend, Season, Expert modeler

The effect of water solubles on Kelvin effects of the Maritime Polluted aerosols

In this work microphysical properties of Maritime Polluted aerosols wereextracted from Optical Properties of Aerosols and Clouds (OPAC) after varying the concentrations of water soluble at five different levels. The analytical expressions for the changes in the equilibrium relative humidity (RH), effective radii, effective hygroscopic growth, their magnitudes and fractional changes on the  effects of surface tension (the Kelvin effect) on the ambient aerosols were numerically  analyzed. The expressions were applied to two - one parameter models. It was  discovered that the increase in water soluble concentration caused decreased in the Kelvin effects which implies decrease in surface tension. The numerical analysis of the data showed that to the lowest order error.   Increase in the overestimation of the effective hygroscopic growth and decrease in the overestimation of the effective radii. On  the two models applied, we discovered that the fractional changes in hygroscopic growth increase in overestimation while there is decrease in  overestimation of fractional changes in effective radii. Finally, decrease in the underestimation of the fractional  changes in the equilibrium pressure it was discovered.Keywords: Kelvin effect, effective radius, effective hygroscopic growth, water soluble, ambient Relative Humidity, overestimation

Model prediction and climatology of aerosol optical depth (τ550) and angstrom exponent (α470-660) over three aerosol robotic network stations in Sub-Saharan Africa using moderate resolution imaging spectroradiometer data

The spatial and temporal variations of aerosol optical depth at 550 nm (τ550) and Angstrom exponent derived from 470 and 660 nm (α470-660) over Nairobi (NAI), Skukuza (SKU) and Ilorin (ILO) Aerosol Robotic Network (AERONET) stations in sub-Saharan Africa, as recorded by Moderate Resolution Imaging Spectroradiometer (MODIS) satellites for fifteen years (2000-2015), were examined in relation to their climatologies and prediction. The MODIS measurements of τ550 and α470-660 from aqua (MYD04) and terra (MOD04) satellites were used in this study. Retrievals of τ550 for both satellites were validated with AERONET τ550 for the same period. The validation results showed that they compare favourably over the three stations, but MOD04 performed better than MYD04 data in NAI and ILO for τ550. This shows that the τ550 of NAI and ILO are best captured using the MOD04 data while that of SKU is best with MYD04. It was also discovered that MODIS underestimated AERONET τ550 data over NAI and SKU. The most polluted station is ILO while the least polluted one is NAI. Similarly, the station with the highest concentration of absorbing aerosols is NAI and the least was observed in ILO. The aerosol climatology shows that the most polluted months in NAI, SKU and ILO are October, June and March respectively. On the other hand, February, November and March has the highest amount of scattering aerosols in the atmosphere for NAI, SKU and ILO respectively. The highest amount of absorbing aerosols was found, respectively, in the months of June, June and August. The generated time series (TS) models are all good, though a general underestimation of the parameters by the models was also observed. Keywords: Aerosol optical depth, Angstrom exponent, MODIS, Time series, sub-Saharan Afric

The Effect of Kelvin Effect on the Equilibrium Effective Radii and Hygroscopic Growth of Atmospheric Aerosols

In this paper we extracted microphysical properties of six types of atmospheric aerosols from Optical Properties of Aerosols and Clouds (OPAC) and numerically analyzed the analytical expressions for the changes in the equilibrium relative humidity (RH), effective radius, effective hygroscopic growth, the magnitudes and fractional changes in the effective radii  and the effective hygroscopic growth on the effects of surface tension (the Kelvin effect) on ambient atmospheric aerosols. The expressions were applied to two - one parameter models. We discovered from the analysis of the data extracted that, to the lowest order error, the change in the equilibrium RH, effective radii and effective hygroscopic growth depend on the compositions of the aerosols. From the two models used, we also discovered that the fractional changes in the ambient RH, effective radii and effective hygrosocopic growth, also depend on the aerosols compositions. Finally, we discovered that the magnitude of the Kelvin effect and its consequences on the atmospheric aerosols depend on the hygroscopicity of the aerosols. Keywords: Kelvin effect, effective radius, effective hygroscopic growth, atmospheric aerosols, ambient Relative Humidity

The effect of mineral nuclei modes in the particle distributions of Sahara mineral dust aerosols

In this work, the aerosols optical depth (AOD) of Sahara aerosols were extracted from Optical Properties of Aerosols and Clouds (OPAC) software package (4.0)at eight relative humidities RHs (00,50, 70, 80, 90, 95, 98,and 99)% and ultraviolet to visible wavelengths (0.25 to 0.9) μm. The mixture or composition of Sahara aerosols are water, mineral nuclei mode nonspherical, mineral accumulation mode nonspherical and mineral coarse mode nonspherical. The number concentrations of mineral nuclei modes nonspherical were varied. The angstrom exponent (α) which is normally used to analyze the type of particle and size distributions using inverse law was applied at all RHs. The inverse law was linearized by using natural logarithm and also into the second order polynomial with the natural log. From the linear part α were determined and analyzed while in quadratic part α2 (known as curvature)were also analyzed. It was observed that α is less than 1.0 signified coarse mode particles and increases with the increase in the concentration of nuclei mode particles and RHs. The α2 which gives additional information of particle mode distributions is positive at the RHs between 0 to 95%, this shows bimodal type of size distributions and negative at 98 and 99% which shows monomode type of size distributions with the dominance of coarse mode particles. With the increased in nuclei mode and RHs, it was clearly shown that from the figures 1 to 5 values of AOD is high at shorter wavelengths and decreases towards longer wavelengths indicating the loading of fine and coarse mode particles into the atmosphere. Keywords: Angstrom exponent, aerosols optical depth, curvature, wavelengths, relative humidit

Parametrisation of effective hygroscopic growths, kelvin effects and water activities of atmospheric aerosols

In this paper the effective hygroscopic growths of atmospheric aerosols and effective radii using microphysical properties of atmospheric aerosols are extracted from Optical Properties of Aerosols and Cloud (OPAC) at seven relative humidity (50%,70%,80%,90%,95%,98% and 99%). The microphysical properties extracted were radii of the individual aerosols and the volume mix ratios as functions of relative humidity (RH). The effective hygroscopic growths and effective raii were parameterized and the modified Kholer equation was used to determine the hygroscopicity, water activities, kelvin effects, and humidification factors. It was observed that the data fitted the models very well. The highest valuefor Kelvin effectat 50% RH (keff = 1.351) was found in maritime tropical and lowest value at 50% RH (keff=0.977) found in maritime clean also for Kelvin effect at 99% RH the highest value was found in maritime tropical (keff=1.201) and the lowest at 99% RH (keff=0.988) was found in maritime clean and for water activities at 50% RH the highest value was found in continental clean (αw = 1.534) and the lowest value of water activity at 50% RH was found in maritime tropical (αw = 0.354) and also the highest value of water activity at 99% RH (αw = 2.098) was found in continental clean and the lowest water activity value at 99% was found in maritime tropical (αw = 0.7049)

Assesment and comparison of modis aod and ae product over Ilorin Aeronet station using the statistical analysis of empirical orthogonal function (EOF)

In this Paper, Empirical Orthogonal Function (EOF) was used to assess the MODIS C006 LV2 aerosol AOD and AE products, and compared the data with AERONET AOD and AE observations. The data were taken from an AERONET station at Ilorin, Nigeria which were obtained from (MAPSS) and were averaged monthly using Microsoft excel spread sheets. The data period for the two satellite data were from Dec 2004 to May 2015 It was observed from the graphical representation that the seasonal variation of AOD peaks during the dry season from Dec to Feb and reaches minimum during summer in August 2008.The comparisons showed both underestimations in MODIS AOD and considerable overestimations in the AE. On the EOF analysis it was observed that a good correlation between MODIS & AERONET AOD are observed on the correlation matrices in all the data. Lower correlation is only observed at Ilorin AERONET wavelength at 470nm (ILA470) with Ilorin 660nm (ILM660).On the total variance explained table for MODIS and AERONET AOD, it was observed that out of the 6 components put into the EOF, only one component was extracted with a very high percentage of 81.57% For MODIS and AERONET AE,two components were observed with a percentage of 83.95% These show that the level of similarities is very high for MODIS and AERONET AOD,and little variation was observed for MODIS and AERONET AE.Keywords: Aerosol optical depth, Angstrom exponent, Empirical orthogonal function,AERONET nd MODIS Satellite data