1. The Mediterranean Israeli Dust Experiment (MEIDEX) Joachim H. Joseph, Zev Levin, Yuri Mekler, Adam Devir, Eliezer Ganor, Peter Israelevich, Edmund Klodzh, Tamir G. Reisin, Yoav Yair Department of Geophysics and Planetary Sciences, Tel- Aviv University, Tel- Aviv 69978, Israel. ABSTRACT A remote sensing experiment will be carried out on a future flight of NASA’s Space Shuttle as part of the Hitchhiker Program. The aim is to investigate the geographical variation of the optical, physical, chemical and mineralogical properties of desert aerosol particles, including the location and temporal variation of its sinks, sources and transport. The prime location of the experiment is the Mediterranean area and its immediate surroundings. The MEIDEX experiment on the space shuttle includes measurements of light scattering by desert aerosol particles in six different wavelength intervals from the near UV to the Solar IR. The wavelengths include two used by the TOMS instruments as well as four of those installed on MODIS. A CCD radiometric camera (Xybion) will observe a volume of atmosphere containing desert aerosol over both land and sea and illuminated by solar radiation. The observation of this volume of air by our instrument will simulate simultaneously both the TOMS and MODIS experiments. A wide-angle white-light video camera will make possible the observation of a large area around the instrument field of view and the identification of the presence of a desert aerosol plume. The supporting ground- based and airborne measurements both include optical observations, direct sampling of aerosol size spectra as well as collecting aerosols for subsequent chemical analysis of bulk and individual particles. Numerical simulations of the transport of dust plumes will be conducted in order to determine the evolution of the dust trajectories and to understand the atmosphere - aerosol interactions. The co-location and simultaneity of shuttle, aircraft and ground-based correlated data will make possible the validation of remotely observed sequence of measurements. OVERVIEW Mineral dust particles make up a large fraction of the natural aerosol population and should be studied on a global as well as on a regional scale. The Mediterranean region is an excellent place to study the optical, chemical and physical properties of dust aerosols and to follow their physical and chemical transformation as they pass over the sea. MEIDEX is designed to conduct radiometric measurements of dust storms over the Mediterranean Sea supplemented with in situ airborne and ground measurements. Investigation of global aerosols is needed for a better understanding of their direct and indirect effects on climate. This improved understanding will help to better parameterize the role of aerosols in climate models and in models of clouds and rain formation. The experiment will enable to perform an inter-calibration with and validation of other existing satellite data. The data collected will be an important addition to the global database on desert aerosols. The MEIDEX experiment data acquisition scheme. Radiometric measurements of the dust plume will be augmented by simultaneous observations from ground based stations and an airborne laboratory. Top: Monthly average of dust events in the Eastern Mediterranean. Bottom: Daily shuttle passes (51 0 orbital inclination) over the Mediterranean. Yellow arrows show typical trajectories of dust transport in the Eastern Mediterranean. Dust storm over the Dead Sea, Israel. Photomicrograph of a dust sample and its chemical composition. Shuttle-borne XYBION radiometric camera equipped with six narrow-band filters. The central wavelengths (CW) of the filters are chosen to simulate two TOMS and four MODIS spectral channels. Dust over the Mediterranean region, photographed from the NOAA/AVHRR (false colors).