Presentation on theme: "General Structure and Properties of the Earth’s Atmosphere *global circulation *atmospheric radiation *weather patterns *atmospheric composition Dr Tony."— Presentation transcript:
General Structure and Properties of the Earth’s Atmosphere *global circulation *atmospheric radiation *weather patterns *atmospheric composition Dr Tony Cox ERCA 2004 -Lecture 1
Coriolis Force - This is a force which is caused by the rotation of the earth and acts perpendicular to the direction of motion. It results from the change in radius of rotation with latitude and the need to conserve angular momentum, by developing zonal motion, I.e. in the direction of the earths rotation. The hypothetical force producing this motion perpendicular to the initial direction of transport is called the Coriolis force. The horizontal component of the Coriolis force is directed perpendicular to the horizontal velocity vector: to the right in the N.Hemisphere and to the left in the S.Hemisphere. The Coriolis force has the magnitude: F c = 2ΩV h sin (Ω = angular velocity; V h = horizontal velocity; = latitude) The force is thus a minimum at the equator and maximum at the poles. The Coriolis and the horizontal pressure force tend to balance each other, see examples above for cyclonic and anticyclonic pressure systems
The majority of the minor constituents of the troposphere originate from emissions from the Earth's surface. Natural emissions are primarily biogenic although volcanism accounts for significant amounts of atmospheric sulphur. Man made emissions result from energy production, industrial activity and agricultural practices. It frequently occurs that the chemical transformation of one minor constituent in the atmosphere creates one or more products which may themselves have significant roles in the overall chemical system. Knowledge of atmospheric degradation pathways is therefore important for understanding the behaviour of many minor constituents, gases and aerosols. Several important trace species enter the troposphere from the stratosphere. Most notable is O 3 which plays a central role in tropospheric chemistry. Other species include HNO 3 and HCl which result from stratospheric NOx and ClOx chemistry.
Lifetimes and Atmospheric Concentrations The atmospheric concentration of a particular gas emitted to the atmosphere is determined by its emission rate, and its atmospheric lifetime. For well mixed gases (those with lifetimes of ~ several months or greater), the time evolution of concentration can be represented by a simple box model. [A] is the concentration of the gas of interest, emitted into the atmosphere at rate R.
Measurements of surface concentrations of atmospheric CH 3 CCl 3 Emissions regulated under Montreal Protocol k r = 6.8x10 -15 s -1 OH + CH 3 CCl 3 products k II = k r [OH] mean [OH] = 9.2x10 5 molecule cm -3 1/2 ~ 5 yr i.e. k II = 0.20 yr -1