中高层大气物理学第一章Scaleheight标高.ppt

LOGO 2011 PHYSICS OF THE MIDDLE AND UPPER ATMOSPHERE中高层大气物理学Scale height What is … Middle and upper atmosphere (physics)? Structure pressure, temperature, density (electron) Profile(剖面), distribution with altitude Processes Ionization(电离) and dissociation(离解) by radiations from sun and cosmos Chemical reactions Diffusion Wind, drift and waves Applications Ionosphere, magnetosphere… Orbit decay 五十年代以前人们曾猜测金星表面的环境也与地球相似,只不过可能更湿更热,从而覆盖着大片的沼泽和森林。 直到1970年金星7号首次在金星的夜半球着陆后,才确切得知其表面温度难以置信地竟高达460oC,表面大气压强至少为地球的90倍,金星7号也只坚持正常工作了23分钟。 Composition of atmosphere (below 100 km) Atmosphere as an ideal gas Ideal gas low Pressure Mass density, Universal gas constant, R0 Molecular mass (per mole), M Another form Boltzmann constant, k Number density, n (m-3) Avogadro’s number Velocity Normalized velocity distribution in thermal equilibriumMaxwell-Boltzmann distribution law Average speed Root mean square velocity The most probable speed Temperature and velocity For a mixture of gases in thermal equilibrium Kinetic energies must be For particles of different species in atmosphere So the lighter gas has a higher root mean square velocity for the same temperature. Terrestrial Gravity Acceleration due to gravity, g In terms of local altitude z, Earth’s radius Re and sea level value g0 With a centrifugal force, g is no longer directed towards the center of earth (except at equator and poles) a g Ω φ Hydrostatic (barometric equation) z z+dz z p+dp p g Consider a small mass element of air at a height z above the ground Assumption Ideal gas Constant g and T (isothermal) Static equilibrium of forces Scale height Scale height Integrating to get the pressure at any height Assume H is constant p = p0 at a reference height z0 Scale height p, ?, n Pressure Mass density Number density The scale height varies between 5.0 and 8.3 km in the region of below 100 km. T, m, g “thickness” of the atmosphere Total number of all particles above a unit area fro