The Roles of Water Vapor and Nitric Oxide in Determining Electron Densities in the D-Region

Abstract

Many of the basic problems connected with the formation and loss of ionization in the D-region of the ionosphere remain unanswered as yet, despite many years of intensive study. Until quite recently, there was little information on even such a basic quantity as the electron density profile of the normal undisturbed mid-latitude D-region, but marked improvements have been made in the techniques, both rocket-borne and ground-based, for measuring these profiles, and a fairly large number of apparently reliable profiles have been published for a variety of locations, seasons, local times, and solar zenith angles. Unfortunately, the key to understanding these profiles lies in the ion chemistry of the region, and accurate and reliable profiles of ion densities cannot yet be produced, though there have been major advances in the area of determining the relative ion composition through rocket-borne mass-spectrometer techniques. These measurements have shown that there is a large amount of complexity and detail in the ion composition that is not present in the much simpler E and F regions, and that many of the mysterious features of the behavior of the D-region electron-density profiles are probably closely related to the complexity of ion chemistry, which therefore must be understood in as great detail as possible.