1.4 Charged Particles in the Atmospherebr /br /Only a tiny fraction of the atmosphere by mass, important role in many electromagnetic atmospheric phenonema. E.g. Aurora, the geomagnetic field, lightning etc.br /br /Several sources of charged particles:br /br /1) Ionizing solar radiation, above ~60kmbr /2) High energy rays, solar and cosmic, penetrate into the lower atmosphere, leaving trails of ionized particles (and cloud condensation nuclei).br /3) Radioactive decay in the crust and atmospherebr /4) Charge separation within clouds.br /br /1.4.1 The ionospherebr /Most of the free electrons are due to solar ionizing radiation and are thus located at about 60km. The densities there are sufficient to affect radio wave propagation (the atmosphere in this region is essentially – during daylight – a plasma of free electrons and ions, with the associated O and X modes, etc). This is also known as the Heaviside Layer.br /Solar flares modulate the ionizing radiation and thus the electron concentration and height distribution, affecting the reflection/absorption of radio waves and limiting long waqve radio communications during intense solar activity.br /br /1.4.2 The fair weather field.br /br /in the lowest ~20km, there is an approximately constant electrical field (120V/m, directed downwards) – during fair weather. A current flows, whoich would dissipate the charge quickly, where it not for the constant generation of charge by thunderstorms.br /br /1.4.3 The magnetospherebr /Above 500km, particles travel along magnetic field lines, with negligible interactions. The Earth’s magnetic field is roughly that of a dipole ~11 degrees from the axis of rotation, distorted by the solar wind. Magnetosphere acts as a shield from this stream of ionized particles.br /br /!.5 Temperature Distributionbr /br /The temperature of the lowest 10-20km of the atmosphere decreases with height at an average rate (lapse rate) of approximately 7 degrees/km. There is considerable variation, but rarely exceeds 10 degrees/km (as this would lead to dry convection that would quickly reduce the laspe rate back to 10degree/km), except near the ground.br /br /The troposphere accounts for ~80% of the mass and virtually all of the water vapor, clouds and precipitation.br /br /The tropopause marks the transition to the stratosphere. Here the concentrations of many species, such as vapor and ozone, as virtually discontinous (vapor vanishing and ozone appearing in the stratosphere). There is relatively little mixing across the tropopause. At this height, the temperature trend also reverses with temperature rising with height in this region.br /br /The stratosphere has relatively little vertical mixing. Updrafts are unable to penetrate far into the strongly stratified stratosphere before exhausting their buoyancy and turning into layered, flattened clouds.br /br /1.5.1 Climatological variabilitybr /br /The layered temperature profile exists at nearly all latitudes for all seasons, with considerable variability int he details. Tropospheric temperature on average, decreases as one moves away from the equator (and twice as fast in the winter hemisphere as summer). The tropical tropopause is both higher and colder than over the mid-latitudes and polar regions.