Global Meridional Circulation Research Articles

Meridional circulation and the lithium abundance gap in F stars

The effect of meridional circulation on the time evolution of superficial abundances of helium, lithium, and beryllium in F stars is calculated in detail. It is shown that, as long as the presence of convection zones is assumed not to modify global meridional circulation patterns, the maximum equatorial rotational velocity allowing the settling of Li and He decreases rapidly with T(eff), going from 50 km/s at 7250 K to only 5 km/s at 6400 K. It is also shown that, for stars of the age of the Hyades with T(eff) less than 7000 K and rotational velocities larger than about 25 km/s, meridional circulation is rapid enough to bring to the surface matter that originally was deep enough to have been depleted of its Li through nuclear burning. Observational tests are suggested to distinguish between this scenario and the gravitational settling model or turbulent diffusion model. It is shown how the Li/Be ratio varies in the presence of transport by meridional circulation. 48 references.

A SCHEME FOR EVALUATING THE MEAN MERIDIONAL CIRCULATION OF THE ATMOSPHERE

Based on the continuity of the atmosphere, a new scheme is developed to diagnose the atmospheric mean meridional circulations. ECMWF analyses four times per day of January 1982 were retrieved to evaluate the global mean meridional circulation. Investigations and calculations show that this new scheme produced more reasonable results in comparison with the traditional scheme. The existence of the double Hadley cell in the winter hemisphere is confirmed as well.