Aziza Bounhir

The OTP-model applied to the Aklim site database

Within the framework of the site prospection for the future European Extremely Large Telescope (E-ELT), a wide site characterization was achieved. Aklim site located at an altitude of 2350 m at the geographical coordinates: lat.= 30°07’38” N, long.= 8°18’31” W , in the Moroccan Middle Atlas Mountains, was one of the candidate sites chosen by the Framework Programme VI (FP6) of the European Union. To complete the fulfilled study ([19]; [21]), we have used the ModelOTP (model of optical turbulence profiles) established by [15] and improved by [6]. This model allows getting the built-in profiles of the optical turbulence under various conditions. In this paper, we present an overview of the Aklim database results, in the boundary layers and in the free atmosphere separately and we make a comparison with Cerro Pachon result [15].

Meteorological parameters analysis above Oukaimeden Observatory using NCEP/NCAR data

We present a characterization of meteorological parameters: Wind and direction speed, temperature, relative humidity and pressure. Data set is provided by the system of NCEP/NCAR Re-analysis. The statistical treatment of data will cover the years between 2003 and 2006 for the Observatory Oukaïmeden. An analysis of monthly, seasonal, and annual results is presented. We calculated the Richardson number for each month of the year. In addition, this paper describes a comparison between balloon-sounding made at different stations and coincident model-based meteorological analysis. The comparison allows the assessment reliability of the analysis in studied period.

Meteorological study of Aklim site in Morocco

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.

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

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).

Astronomical extinction over the ELT Moroccan sites from aerosol satellite data

Two Moroccan sites have been selected to be characterized for the ELT telescopes. Those sites are in the Atlas, between Oukaimeden (where the national observatory is situated) and the Canary Islands. For this preliminary study, we have used the Nimbus-7 TOMS aerosol index to derive the astronomical extinction. This work builds on the findings of an earlier study which established the link between these two parameters over the Canary Islands.

Effect of altitude on aerosol optical properties

The ELT project is currently under way in Europe and North America. Astronomical sites depend critically on sky transparency and on aerosol loadings. A quantitative survey of aerosol optical properties at candidate ELT sites is an essential part of the site selection process. There are basically two methods to characterize aerosol properties: ground based measurements and satellite measurements. In this paper we will establish a full climatology of two sites very close to each other, but at a difference of 2300m in altitude: Izana and Santa Cruz located in the Canary Islands. Both have sun photometers from the AERONET network. We also use the aerosol index determined from TOMS satellite data to determine how aerosol optical properties vary with altitude. We establish a correlation between the TOMS index and the aerosol optical thickness in both sites. Aerosol optical properties show very good correlation between Izana and Santa Cruz. As a result we establish a set of relationships helpful to characterize sites at elevated altitude from data of neighbouring sites at low altitude.

ELT SITE PROSPECT IN MOROCCO: AEROSOL CHARACTERIZATION

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.