Recalculation of H-L alpha sky surveys: No need for anisotropic solar wind mass outflows? Comment

In a recently published paper, Scherer and Fahr (1995) claimed that the departures of sky L alpha emission measured by Prognoz 5 and 6 from an optically thin model can be attributed entirely to deficiencies ofthe optically thin approximation, and are not due to variations of solar wind ionization rate with latitude, as advocated since many years by our research group. They base their claim on the result of their new sophisticated model of L alpha radiation transport. It is shown here that their new model, in the simple case of isotropic solar wind, predicts a distribution of intensity in a simple geometry which is completely contradicted by the observations: they find a minimum of intensity near the upwind direction, where a maximum has been observed consistently by all La instruments. Therefore, their conclusion based on an erroneous model must be rejected.