The purpose of following project is to study the effect of dust aerosols on the radiative forcing which is directly related to the surface temperature. A single column radiative convective model is used for simulation purpose. A series of simulations have been performed by varying the amount of dust aerosols present in the atmosphere to study the trends in ground temperature, heating rate and radiative forcing for both its longwave and shortwave components. A case study for dust storm is also performed as dust storms are common in Arabian Peninsula. A sensitivity analyses is also performed to study the relationship of surface temperature minimum and maximum against aerosol concentration, single scattering albedo and asymmetry factor. These analyses are performed to get more insight into the role of dust aerosols on radiative forcing.

Recent emphasis on the prediction of temperature and concentration fields in the atmosphere has led to the investigation of accurate solution methods of the time-dependent conservation equations for mass, momentum, energy and species. Atmospheric radiation is the key component of this system. Therefore, atmospheric radiation models were developed in isolation from the climate models. The time-dependent multi-dimensional governing equations of atmospheric models must be solved in conjunction with the radiative transfer equation for accurate modeling of the atmosphere. In order to achieve this objective, a 1-D Radiative-Convective Model for Earth-Atmosphere System (RCM4EAS) was developed for clear and cloudy sky atmospheres. The radiative component of the code is Santa Barbara DISORT (Discrete Ordinate Radiative Transfer) Atmospheric Radiative Transfer (SBDART) integrated with exponential sum-fitting method as the radiative property estimation technique. The accuracy of SBDART was tested by comparing its predictions of radiative fluxes with those of Line-by-Line Radiative Transfer Model (LBLRTM) for 1-D longwave (3.33-100 &micro / m) clear sky atmosphere and a good agreement was obtained. A parametric study aiming at finding the optimum parameters to be used as input in SBDART regarding the wavelength increment and order of approximation was also carried out. Variable wavelength and eight streams were selected as optimum parameters for the accuracy and computational efficiency. The code was then coupled with a 1-D Radiative-Convective Model (RCM) to obtain the time dependent code, (RCM4EAS), which was applied to the investigation of the sensitivity of climate to changes in the CO2 concentration for clear and cloudy sky conditions. CO2 sensitivity analyses revealed that doubling the CO2 concentration in the earth&rsquo / s atmosphere from its present value (387 ppm) results in an increase in equilibrium surface temperature of 4.2 K in the clear sky atmosphere as opposed to 2.1 K in cloudy sky atmosphere with typical cloud physical parameters. It is worth noting that times required to reach equilibrium surface temperatures are approximately 2000 and 6000 days for clear and cloudy sky atmospheres, respectively and these temperature increases are calculated assuming that all the other parameters except CO2 concentration remain unchanged within these time periods. Therefore, it should be noted that these temperature increases reflect only the effect of CO2 doubling and excludes the effect of other forcings which might positively or negatively affect these temperature increases. Overall evaluation of the performance of the code developed in this thesis study indicates that it can be used with confidence in 1-D radiative-convective modeling of the earth-atmosphere systems.

Climate models are the primary tools used for understanding past climate variations and for future projections. The atmospheric radiation is the key component of these models. Accurate modeling of atmosphere necessitates reliable evaluation of the medium radiative properties and accurate solution of the radiative transfer equation in conjunction with the time-dependent multi-dimensional governing equations of atmospheric models. Due to difficulty in solving the equations of atmospheric and radiation models simultaneously, radiation equations have been solved when input data such as concentration, temperature etc. were made available upon solution of equations of atmospheric models. Generally, time step of conservation equations are 10-30 minutes but radiative transfer equation is called only once every 1-3 hours. However, there is inaccuracy due to the fixed radiation fluxes over the intervening time steps. To overcome this problem, the equations of atmospheric and radiation models have to be solved simultaneously and the solution methods have to be compatible. For this purpose, a radiative-convective model with radiation model based on method of lines (MOL) solution of discrete ordinate method (DOM) with wide band correlated-k (WBCK) was developed. To achieve this objective, a previously developed MOL solution of DOM with WBCK model was adapted to 1-D longwave clear sky atmosphere and its predictive accuracy and computational efficiency was examined on the test problem by using benchmark solution obtained from Line-by-line Radiative Transfer Model (LBLRTM). The radiation code was then coupled with radiative-convective model and the predictive accuracy of this model was examined for several coupling intervals. Comparisons reveal that as coupling interval increases, although the computation time of the model decreases, the predicted temperature profiles diverge from the one obtained when equations of radiative-convective model and the radiation model are solved simultaneously and percentage relative error in temperature increases an order of magnitude when coupling time between radiative-convective model and the radiation model increases from 2 to 10 hours. Therefore, it can be concluded that the equations of the radiation model have to be solved simultaneously with the equations of the climate model. Overall evaluation of the performance of the radiation model used in this study points out that it provides accurate and computationally efficient solutions and can be used with confidence in conjunction with the climate models for simultaneous solution of governing equations with radiation transfer equation.