J. Piazzola

The Advanced Navy Aerosol Model (ANAM): validation of small-particle modes

The image quality of electro-optical sensors in the (lower-altitude marine) atmosphere is limited by aerosols, which cause contrast reduction due to transmission losses and impact on the thermal signature of objects by scattering solar radiation. The Advanced Navy Aerosol Model (ANAM) aims at providing a quantitative estimate of the aerosol effects on the basis of standard meteorological parameters such as wind speed and relative humidity. For application in coastal regions, the ANAM includes non-marine aerosols that are governed by an ill-defined tuning parameter: the air mass parameter (AMP). The present paper proposes a new parameterization for assessing the effect of these non-marine particles on the propagation. The new parameterization utilizes the Ångström coefficient, which can be experimentally obtained with a sun photometer, and introduces new types of aerosols in ANAM. The new parameterization was tested against experimental validation data acquired at Porquerolles Island at the French Riviera. The limited test data suggested that the new parameterization is only partially efficient in capturing the aerosol signature of the coastal environment. Nevertheless, the new Ångström coefficient algorithm avoids using the ill-defined AMP, and may thus be useful to the ANAM community.

A world-wide comparison of aerosol data

A comparison of aerosol data acquired at five different sites around the globe is presented. All data has been acquired with the same instrumentation and representative size distributions for marine air masses at 10 m/s wind speed have been selected for comparison. Differences in the concentrations of larger and smaller aerosols at the various sites are explained in terms of fetch, trade winds, shielding, pollution, seawater temperature and phytoplankton bloom. The differences in size distribution induce significant differences in the extinction coefficients from the VIS to the LWIR at the various sites. Consequently, the transmission over a specific range also varies significantly. This suggests that a detailed analysis of the conditions at each site is necessary in order to understand the exact aerosol behavior and to correctly predict electro-optical propagation effects due to aerosols.

The POAEMM Project: Prediction of Spatial and Temporal Variation of Marine Aerosols in Coastal Area

The POAEMM project consists of developing a tool for predicting the spatial and temporal variation of aerosols particles in a marine coastal environment. This is achieved by coupling the MEDEX parametric model (MIO) and the fine mesh meteorological model AROME developed by Meteo France. The first step has been to do the semi-automation of the MIO experimental station. Based on semi-empirical formulations, MEDEX is then revised in order to take better account of oceanographic and meteorological conditions.

Effects of Surf Zone Sea-Spray Particles on Aerosol Concentration in Coastal Area

An experimental campaign has been conducted in Nov. 2007 in Duck, NC. Several sets of probes were used in various conditions, in order to measure either the marine aerosol vertical gradient and the flux emitted by the surf zone or the horizontal transport offshore. It was possible to find a new equation for the surf zone aerosol flux depending on the Wave Energy Dissipation (WED). The aerosol transport was simulated for offshore wind condition and compared to experimental data measured aboard a boat travelling along the offshore wind vector.

Transport of aerosols in the Mediterranean coastal zone

Aerosol particles in coastal areas result from a complex mixing between seaspray aerosols locally generated at the sea surface by breaking waves and a continental component arising from natural and/or anthropogenic sources. We present a study on the aerosol transport in a French Mediterranean coastal zone based on physico-chemical characterization of the particle size distributions measured on the island of Porquerolles. The results are analyzed using a 2D model, the MACMod model, dedicated to the aerosol transport at a local scale. A part of the analysis deals with the dispersion of organic compounds in the Marine Boundary Layer (MABL). This shows that, even at very short fetch, the seaspray particles represent a strong contribution of the aerosol size distributions measured in the coastal zone. In contrast, the low wind speed conditions correspond to air masses that are strongly impacted by pollution transported over the Mediterranean. Under higher wind speed conditions, aerosol number and mass concentrations of smaller sizes are lowered due to the dispersion of anthropogenic pollutants. However, the model simulations show that the lifetime of these submicronic particles in the atmosphere, which are characteristics of the anthropogenic influence in coastal areas, is rather large.