地球大气边界层结构和天文视宁度

STRUCTURE OF THE TERRESTRIAL ATMOSPHERIC BOUNDARY LAYER AND ASTRONOMICAL SEEING

依据声雷达资料和其他边界层资料讨论了大气边界层结构、地形等对视宁度的影响和有关选址问题．

Based on the recent study of the terrestrial atmospheric boundary layer with sodars,the relationship between the seeing quality contributed by lower atmosphere and the boundary structure is investigated.The echo patterns of sodar show that for a site close to waters the seeing is much better during on shore winds than off shore ones in clear days(see Fig.1),and the reverse is true for clear nights(Fig.2).For solar observations the prevailng wind in daytime is expected to be on shore.The typical inner boundary layer,which makes the seeing worse,can hardly take place above a small islet,which may be a preferable site for solar observations.Seeing may be affected by a katabatic or strong wind if it comes from a higher mountain far away from the observing site(about 10km or more,depending on the height).Fig 4 shows the katabatic wind from a mountain higher than the sodar site for about 600m and at a distance of about 14km.At night the top of inversion is kept at a height of 300 to 400m and the integral value of C 2 T is large.Fig.6 presents a pattem of strong wind in daytime in the same mountain area.It illustrates that the turbulence caused by strong wind grows with wind speed.When wind speed reaches 10m/s or more,the echo of turbulence is strong and may attain a height of 300 500m.Generally speaking,the seeing at an isolated high peak would be better on a hill,which has the same height but is located in a mountainous region.The seeing of a fixed site is affected by the surrounding topography and wind,and the details may be revealed with sodars.