Thursday, October 17, 2019

Atoms of metals and LIDAR Essay Example | Topics and Well Written Essays - 2000 words

Atoms of metals and LIDAR - Essay Example pag). LIDAR is a remote sensing technology that can measure distances or properties of a material by laser illumination (Sanderson n. pag.). Origin of metal atoms in the atmosphere Normally, meteoroids enter the Earth’s atmosphere between 11 to 72 kilometres per second. Friction between the meteor and air molecules in the upper atmosphere generates enough heat to disintegrate it to particles less than 1mm in diameter. These particles are deposited at an altitude of 70 to 140 km in the upper atmosphere (Von Zahn, Hoffner and McNeil, 149). McNeil, Lai and Murad acknowledged the fact that meteoric material is the most significant source of metal atoms in the upper atmosphere. However, the amount of metal atoms in the atmosphere differs from the amount present in the meteor itself. This is attributed to the process known as differential ablation. Differential ablation suggests that more volatile metals vaporize earlier than less volatile metal components in a meteorite. Comparison between sodium, magnesium, and calcium ablation revealed that sodium is the most volatile of the three elements. Thus, sodium ablates at a much higher altitude. On the other hand, calcium ablates at a much lower altitude. Therefore, the rate of conversion of elemental calcium into compounds in the lower atmosphere is the primary cause of calcium ion depletion (10899-10911). Aside from sodium, metallic atoms of potassium, lithium, calcium and iron make up the rest of the metal atom layer in the mesosphere. The discovery of other metal constituents started in 1973. Potassium ions detected through the use of ruby-laser-pumped dye laser components calibrated at 769.9 and 766.5 nanometres. Lithium ions were identified using a flashlamp-pumped dye laser calibrated at 670.8 nanometres with 800 millijoules output pulse energy. Calcium was detected with a dye laser calibrated at 422.7 nanometres (Abo 315). Thin layers of sodium, calcium and iron have been detected by LIDAR in the upper atmo sphere. These layers range from 100 metres to several kilometres thick and usually superimpose on a background layer 10 kilometres thick. Despite efforts to ascertain the origins of sporadic layers, no single scientific explanation was accepted (Clemesha 725). Chemical role of metal atoms in the atmosphere The formation of metal layers in the upper atmosphere has been instrumental in several vital atmospheric processes. Rapp and Thomas have confirmed the role of mesospheric metal layers in the formation of noctilucent clouds through the nucleation of ice particles in the upper atmosphere (715-744). Murphy, Thomson and Mahoney investigated the composition of aerosol particles in the stratosphere and discovered the existence of meteoric particles in stratospheric aerosol. Thus a link was suggested between mesospheric metal particles and the condensation of stratospheric sulphate aerosols (1664-1669). Atmospheric observation over the South Pole was initiated through LIDAR to measure th e seasonal variations of the mesospheric sodium and iron layer. The polar annual mean abundance is almost equal to mid-latitude readings while the mean centroid height is 100 metres higher for sodium and 450 metres higher for

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