Space Weather and Climate

Abstract

The term Space Weather denotes variations of the Earth's environment on short terms. In analogy to meteorology, where the distinction between weather and climate is made, space climate denotes long term variations of the Earth's climate mainly caused by solar variations. 6.1 The Atmosphere's Response to Solar Irradiation 6.1.1 Introduction The penetration of solar radiation strongly depends on its wavelength, the larger the wavelength the deeper the penetration (see Fig. 6.1). The principal effects of solar radiation on the middle and upper atmosphere are summarized in table 6.1. In the second and the third column of that table the variation due to the solar activity cycle is given. From that table it follows that the amount of variation depends on the wavelength of the solar radiation becoming smaller at longer wavelengths. Above 300 nm it is very difficult to detect and can be measured only with satellite radiometric detectors. In addition to radiation, the Sun also emits the solar wind which consists of particles that interact with the geomagnetic field to form the Earth's magne-tosphere. We observe a large input of electrons and protons (causing the aurora) and ionospheric currents are produced causing joule heating. In principle these phenomena are concentrated at high geomagnetic latitudes; heating effects can spread equatorward by convection and conduction. The typical structure of the Earth's atmosphere was already shortly described. The boundaries of the various layers (Troposphere, Stratosphere, Mesosphere, Ionosphere) are called pauses (e.g. the Tropopause) and are defined by minima or maxima of the temperature profile. At 100 km the density is 10 −6 of its surface value. The temperature in the thermosphere is strongly dependent on solar activity. The major sources for heating at this layer are: 143