Advanced Navy Aerosol Model Research Articles

Modeling the Aerosol Extinction in Marine and Coastal Areas

Sea salt aerosol (SSA) significantly affects the atmospheric albedo, the radiation balance of the Earth, and has consequences for global and regional climate. There is currently no reliable radiative large-scale aerosol model of the marine and coastal atmosphere. All these lead to uncertainties in radiation boxes, short-term weather forecasts, and climate models and to uncertainties in interpretation of the lidar return data obtained and at the development of new lidar systems. The MaexPro model is shown to calculate adequately the aerosol extinction coefficients $\varepsilon (\lambda)$ and the concentration of SSA particles for different wind regimes, fetches, and humidity. The calculated $\varepsilon (\lambda)$ profiles well agree with the experimental data and with calculations using Advanced Navy Aerosol Model (ANAM) and MODTRAN codes. A new approach in studying the influence of the meteorological parameters on spectral $\varepsilon (\lambda)$ gives a new explanation for previously obtained conflicting experimental data, namely, to the effect of decreasing transparency, manifested in the coastal zone, and makes it possible indirectly to account for the type of air mass (marine or coastal). It is shown that the particle size distribution functions and spectral $\varepsilon (\lambda)$ , calculated using the model with the input parameters corresponding most closely to the conditions of experiment, agree well with observations, using OLAF transmissometer, and calculations using MODTRAN code and the experimental results receiving the same conditions of observations (numerical or field). The results obtained are of interest both in the calculations of radiative characteristics of the atmosphere and in interpretation of the lidar return data and calibration signal when developing new lidar systems.

An Aerosol Model of the Marine and Coastal Atmospheric Surface Layer

We present a microphysical model for the surface layer marine and coastal atmospheric aerosols that is based on long-term observations of size distributions for 0.01–100 µm particles. The fundamental feature of the model is a parameterization of amplitudes and widths for aerosol modes of the aerosol size distribution function (ASDF) as functions of fetch and wind speed. The shape of ASDF and its dependence on meteorological parameters, height above sea level (H), fetch (X), wind speed (U) and relative humidity (RH), are investigated. At present, the model covers the ranges H = 0–25 m, U = 3–18 km s−1, X ≤ 120 km and RH = 40–98%. The latest version of the Marine Aerosol Extinction Profiles model (MaexPro) is described and applied to the computation and analysis of the spectral profiles of aerosol extinction coefficients α(λ) in the wavelength band λ = 0.2–12 µm. MaexPro is based on the aforementioned aerosol model assuming spherically shaped aerosol particles and the well-known Mie theory. The spectral profiles of α(λ) calculated by MaexPro are in good agreement with observational data and the numerical results obtained from the Navy Aerosol Model (NAM) and the Advanced Navy Aerosol Model (ANAM). Moreover, MaexPro was found to be an accurate and reliable tool for investigating the optical properties of atmospheric aerosols.

Visible and infrared extinction of atmospheric aerosol in the marine and coastal environment

The microphysical model Marine Aerosol Extinction Profiles (MaexPro) for surface layer marine and coastal atmospheric aerosols, which is based on long-term observations of size distributions for 0.01-100 μm particles, is presented. The fundamental feature of the model is a parameterization of amplitudes and widths for aerosol modes of the aerosol size distribution function (ASDF) as functions of fetch and wind speed. The shape of the ASDF and its dependence on meteorological parameters, altitudes above the sea level (H), fetch (X), wind speed (U), and relative humidity is investigated. The model is primarily to characterize aerosols for the near-surface layer (within 25 m). The model is also applicable to higher altitudes within the atmospheric boundary layer, where the change in the vertical profile of aerosol is not very large. In this case, it is only valid for "clean" marine environments, in the absence of air pollution or any other major sources of continental aerosols, such desert dust or smoke from biomass burning. The spectral profiles of the aerosol extinction coefficients calculated by MaexPro are in good agreement with observational data and the numerical results obtained by the well-known Navy Aerosol Model and Advanced Navy Aerosol Model codes. Moreover, MaexPro was found to be an accurate and reliable instrument for investigation of the optical properties of atmospheric aerosols.

Spatial variation of the aerosol concentration over a Mediterranean coastal zone and implication on the infrared extinction

The performance of electro-optical systems can be substantially affected by aerosol particles that scatter and absorb electromagnetic radiation. While molecular extinction can be calculated using propagation codes such as MODTRAN (Berk et al., 1989), the influence of aerosols is much less easy to account for. However, concentrations and optical properties of aerosol particles in the atmosphere are quite variable both in time and space. Very few relevant models for the aerosol size distributions have been published during the last decades. One of the most used is the Navy aerosol model (NAM, Gathman, 1983), which is currently being upgraded to the advanced Navy aerosol model (ANAM, van Eijk and Merritt, 2006). NAM and ANAM are dedicated to open ocean, while coastal areas induce specific processes (Piazzola et al., 2000, and Bendersky et al., 2004). To include coastal effects for the prediction of aerosol concentrations and their effects on the extinction, Piazzola et al. (2003) proposed the aerosol extinction code MEDEX. We deal with the extension of the predictions of MEDEX on a regional scale. To achieve it, MEDEX is forced by the regional mesoscale meteorological model RAMS (Cotton et al., 2003) to account for the fine details of the coastal orography. Simulations are then compared to aerosol size distributions recorded in the Mediterranean. The results show a nonhomogeneous spatial coverage of the aerosol concentrations over the northern Mediterranean. In addition, we show the least performance of the coupling for unsteady conditions of the wave field.