1 Introduction

Oukaimeden is a potential site for an astronomical observatory in Morocco. Precise astronomical site-testing first requires a thorough preliminary study. The installation of astronomical equipment by groups such as IRIS (International Research of the Interior of the Sun), GONG (Global Oscillation Network Group) and FIP (Flux Integration Photometer) form the body of our meteorological database. We have selected the Canarian Observatories (Fig. 1) as an obvious comparison site with Oukaimeden because the Observatorio del Roque de los Muchachos (ORM) has been proven to be excellent for night-time observations (see, for example, McInnes & Walker 1974; McInnes 1981; Brandt & Wohl 1982; Murdin 1985; Mahoney et al. 1998; Muñoz-Tuñón et al. 1998). Assuming that both sites are driven by similar meteorological trends, we believe that Oukaimeden may also be a good candidate for astronomical research.

Figure 1: Oukaimeden and ORM site localization

Both French and Moroccan researchers have selected Oukaimeden as an astronomical observing site. Benkhaldoun (1994) has already presented the criteria for this choice; therefore, for the purpose of this paper, we will simply summarize the relevant points.

The first search for a Moroccan observatory site began with data analysis taken from the Moroccan National Center of Meteorology (Kadiri 1983). This climatological and geographical preliminary investigation limited the selection to mountains located in the northern and southern regions. The northern area revealed good logistic conditions but poor photometric data. In the south, logistical and meteorological reasons led us to exclude some areas. Finally, Oukaimeden located in the high Atlas Mountains, (longitude: 7^o 52' 52'' W, latitude: 31^o 12' 32'' N) and 2700 m above mean sea level, was pre-selected as a potentially excellent site for astronomical observations.

Oukaimeden dominates the plain of Marrakech (the nearest city), and is located on a peak overlooking a village also bearing the name Oukaimeden. To the south and south-east, the 4000 m summits act as a natural barrier against wind-borne dust from the nearby Sahara Desert. Therefore, Oukaimeden is the first natural obstacle that homogeneous, unperturbed air masses meet as they arrive from the Atlantic Ocean. This particularly advantageous situation gives Oukaimeden the benefit of extremely transparent skies and enables us to predict the low atmospheric turbulence that characterizes coastal sites (Benkhaldoun 1994).

Weather conditions are so favourable at Oukaimeden that several groups studying helioseismology have also proposed the installation and development of international observation networks there. Currently The IRIS network observing the full solar disc is installed at the site.

The ORM, on La Palma (Canary Islands) has also been extensively studied. For a precise location and general surface layer meteorology see (Muñoz-Tuñón et al. 1997; Mahoney et al. 1997, and references therein). In 1984, more than 14 European countries recognized the excellence of the Canary Island location and after signing formal agreements, set up the present ORM on an international basis. The 10 m segmented Gran Telescopio Canarias (GTC) is now being constructed at ORM, thereby increasing the Observatory's technological capabilities as well as assuring ORM's future as a renowned international observatory. In 1985, a special issue of Vistas in Astronomy (Murdin 1985) was dedicated to the Canarian Observatories to coincide with ORM's inauguration. This issue highlighted the characteristics which make the ORM a prime astronomical location.

During the last few years, spectacular progress has been made in the study of certain parameters that define atmospheric quality for astronomical observations. There have also been major breakthroughs in adaptive optics, high-resolution observational techniques, the modelling of orographical influences and dome and building design. At a recent conference entitled Site Properties of the Canarian Observatories astronomers reviewed and compiled new results concerning site-testing at the Canarian Observatories. The proceedings of this conference appeared in a special issue of New Astronomy Reviews (Muñoz-Tuñón 1998).

In this paper, we will present the surface layer meteorology of the Oukaimeden site gathered over more than two years of measurements. The results are given in Sect. 3. Section 4 describes the surface layer meteorology of the ORM based on CAMC data and in Sect. 5, we compare the potential of the Oukaimeden site for astronomical observing with the ORM.