The ESO strategy for short listing ELT candidate sites is reviewed: it uses a specially designed tool to allow the simultaneous use of existing databases with various relevant parameters.

Site considerations for ELTs

Aerosol columnar characterization in Morocco: ELT prospect.

Candidate sites of the future European Extremely Large Telescopes (E-ELT) need to be assessed and analytically compared in their observing characteristics. In the site selection process, meteorological, photometric and seeing qualities have to be studied and measured carefully. Aklim site in Morocco is one among four candidates in the ELT project. In this paper, we present meteorological studies of the Aklim site over eleven years. The meteorological parameters include wind speed and direction, relative humidity, air temperature, cloud cover and water vapour content. Most of these data are taken from the National Center for Environmental Prediction/National Center for Atmospheric Research NCEP/NCAR Reanalysis. The meteorological analysis covers the vertical profile as well as surface layer meteorology. Furthermore, in extensive literature, it has been demonstrated that the global circulation of atmospheric wind at 200 mb can be used as a criterion to establish the suitability for the development of adaptive optics techniques. By using the NOAA NCEP/NCAR reanalysis database, we analyse the monthly average wind velocity at 200 mb for eleven years period and compare with famous observatories.

Meteorological study of Aklim site in Morocco

The aim of this paper is to characterize the aerosol loadings, their optical and microphysical properties over Morocco, by
use of the AERONET network and satellite data. Three AERONET stations in Morocco; Saada, Ras_El_Ain and Dakhla
are considered in this work. The aerosol parameters studied are the aerosol optical thickness, the Angstrom parameter,
the size distribution, the single scattering albedo and the refraction index. An inter-comparison with satellite data has
been achieved. The most popular satellite products, TOMS (Earth Probe and OMI), MODIS and MISR have been
considered. It comes out from this study that the mean aerosol optical thickness (550 nm) vary from 0.22 to 0.3, with a
peak in summer time of 0.56 for Dakhla, 0.42 for Ras_El_Ain and 0.35 for Saada. The Angstrom parameter mean is 0.6
for Dakhla and 0.75 for Saada and Ras_El_Ain with a summer minimum of 0.32 for Dakhla and 0.55 for Saada and
Ras_El_Ain. The size distribution is bimodal with a predominance of the coarse mode except for Saada in winter and
autumn. This region depicts desert dust predominant environment with a single scattering albedo varying from 0.72 to
0.96. Saada and Ras_El_Ain being at 52 km apart, their coincident daily AOT correlate with a correlation coefficient;
R=0.93. Concerning the correlation between satellite data and AERONET AOT, TOMS EP has a correlation coefficient
of 0.53 for Saada (all data), 0.68 for Dakhla (all data). TOMS OMI correlation coefficient is 0.68 for Saada (all data) and
0.71 for Ras_El_Ain (year 2006). MISR (level 3 data) correlation coefficient is 0.77 for Saada (all data) and 0.85 for
Dakhla (all data). MODIS (level 3) correlation coefficient is 0.86 for Saada (all data) and 0.92 for Dakhla (all data).
Level 2 MODIS correlation coefficient is 0.69 for Saada (year 2006), 0.86 for Ras_El_Ain (year 2006) and 0.97 for
Dakhla (year 2003).

Aerosol characterization of Morocco with AERONET and intercomparison with satellite data: TOMS, MODIS, and MISR

In order to prospect for good astronomical sites in Morocco, we make a preliminary study in terms of aerosol characterization. For that purpose we use AERONET data and the Aerosol Index provided by Earth Probe platform. After establishing a good correlation between the aerosol optical thickness (AOT) and the aerosol index (AI) in three sites located in the area of interest, we try to extrapolate to areas where AERONET data are not available. The studied areas are: Marrakech, Dakhla located in Morocco, and Izana in the Canary Islands. 
These areas exhibit a predominance of desert dust aerosol particles. The altitude seems to be the predominant factor influencing the distribution of the aerosol optical thickness during the year. A full characterization of these sites makes possible a determination of the aerosol optical thickness of neighbouring areas.

Site considerations for ELTs

Citations

Aerosol columnar characterization in Morocco: ELT prospect.

Meteorological study of Aklim site in Morocco

Aerosol characterization of Morocco with AERONET and intercomparison with satellite data: TOMS, MODIS, and MISR

Elt site prospect in morocco: aerosol characterization

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