Analysis of the astroclimate
parameters associated with the
tropospheric conditions and their
time evolution at Roque de Los
Muchachos Observatory

Abstract

The early 1970's saw the start of a new era in astronomy with the rst approach to building large telescopes (2 to 5 meters class telescope) and locating them in the right places. The astronomical community started to evaluate these sites using the sky quality "seeing" parameters as one the major constraints to decide where to place the observatory in the world and where is the best location in the observatory. Taking a few words from one of the rst site testing works by Merle Walker (Walker,1971) that considered the Islands like as: Canary Islands, Hawaiian islands or Crete, a possible ideal place for Astronomy. "The best seeing occurs at sites on peaks near sea coasts having cold ocean currents oshore that reduce the height of the [temperature] inversion layer, and where the laminar air-flow set up over the ocean still persists".
(....) "Mountain peaks on (small) islands in warm oceans may be good sites, provided that the peaks are suciently high to place the observer above the inversion layer". It is in this new era when many engineers, physicist, meteorologists and astronomers started to search for new places and to develop new instruments to measure the sky quality. Please see the site testing report for La Palma from Mcinees (Mcinnes,1973).
Astronomy is now becoming more sophisticated, with new observatories and new adaptive optics instruments that can compensate the atmosphere to the difraction limit of the telescopes. The newer Adaptive Optics require more information about the optical parameters that aect image quality and it is also becoming more important to manage the technical and human resources in the observatory for high resolution observations. To obtain the information needed, a new set of instruments have been developed and used, such as: MASS-DIMM, DIMM, SCIDAR, SLODAR,Lusci, etc to mention only a few. They have been the main contributor to analyzing potential new sites for the future extremely large telescopes. They also provide new data for the analysis of the expected performances of the new generation of AO instruments for the TMT or E-ELT.
The purpose of this thesis is to establish the influence of the upper atmosphere, monitored using tropospheric wind speed and temperature, on the local sky conditions, measured by the refractive index parameter C2n and the astroclimate parameters (seeing, isoplanatic angle and coherence time), and their evolution through the years. The meteorological data used come from a launch site located about 150 km away from the observatory and which provides data for meterological forecasting agencies. It has been determined that the best yearly period for the seeing was the year 2005, which corresponds with the year with lower upper wind speed periods.
The use of these meteorological data and the good agreement found with the local sky conditions, provide the rst step to constructing a simple parametric optical turbulence model (Trinquet model) of the Observatory Roque de Los Muchachos.
This in turn opens the way to performing a nowcast of the astroclimate parameters and the refractive index parameter C2n using the meteorological forecasting data. It can also be used to help design the AO instrumentation capabilities at the ORM (and perhaps by extension elsewhere).
Due to the importance of the knowledge of the vertical C2n distribution and how this aacts the Laser Guide Star (LGS) AO observations, an instrument was
proposed based on the DIMM technique and using a range-gated CCD detector to measure the backscattered laser light at dierent altitudes. This can then produce a vertical distribution of the Fried parameter r0 and the seeing. A simple prototype was built but due to the lack of time and various faults the rst experiments could not full the proposed requirements. The preliminary prototype design and the initial on-sky results are provided in appendices of this thesis in order to suggest and support future work.