Layersof the Earth’s Atmosphere
Definition:The atmosphere of the earth has four layers whose definition dependson air temperature (Hedin 765). The temperatures change as one movesfrom the earth’s surface into the upper layers. The variations intemperatures are caused by the changes in the chemical and physicalfeatures of the atmosphere with altitude (767). Thus, each layer hasunique chemical and physical features that cause the variations intemperatures. The other aspects that also changes throughout theatmospheric layers are the atmospheric pressure and water vapor loss.These changes are important for geophysicists to calculatemeasurements such as the radiowave loss due to gas compounds thatkeep changing in all the layers of the atmosphere. Therefore,according to temperature definition, there are four basic layers ofthe earth’s atmosphere: the troposphere, the stratosphere, themesosphere, and the thermosphere (Ahrens 12).
Thetroposphere covers about 8 to 16 kilometers from the earth’ssurface. The heights change according to specific temperature levelsin different climatic zones. The tropics have the greatest heightsbecause they have warm temperatures which cause vertical expansion ofair. Conversely, cold regions such as the temperate regions and thearctic circles have shorter distances in the troposphere because theair continually becomes thinner. Consequently, the depth of thetroposphere in the arctic regions is nearly half its depth in warmerregions such as the tropics and the equator regions. The averagedepth from the poles through the equator is 11 kilometers. Thegreater part of the earth’s land mass is in the troposphere. Allweather conditions happen in the troposphere.
Consideringthat the troposphere is close to the earth’s surface, most of itstemperature variations are influenced by terrestrial radiation.Terrestrial radiation is the background radiation that naturallyoccurs when the sun heats the surface of the earth followed theemission of heat waves by naturally existing radioactive materials.Examples of radioactive substances that radiate heat back to thetroposphere are radon, thorium, and uranium. Maximum temperaturesoccur close to the surface of the earth due to terrestrial radiation.In the troposphere, air temperatures drop uniformly with height atabout 6.40Cper 1000 meters of height (Hedin, et al 767). The phenomenon isreferred to as the environmental lapse rate. The environmental lapserate continues until the lowest temperature of the -56.5 0Cnear the tropopause, a transition zone that separates it withstratosphere.
Thestratosphere is the second layer different from the troposphere andseparated from it by the tropopause (Brasseur, Guy, and Susan 53). Ithas a fluctuating average altitude that ranges between 11 kilometersto 50 kilometers from the surface (53). The stratosphere is about19.9% of the total atmospheric mass (53). Very little weatheractivity occurs in the atmosphere. Thunderstorms from the top layersporadically break into the stratosphere (53). The stratosphere ishas unique phenomena called the polar jet stream and the subtropicaljet stream in its lower parts (54). Polar jets streams are fast windsthat blow in homogenous concentrations in a narrow band (54). Theypolar jet stream moves at a speed of between 110 and 185 kilometersper hour (55). The subtropical jet streams are similar to the polarjet streams except that former exists in higher altitudes within thestratosphere and moves in a rather slower speed than the latter.
In the first heights (about 9 kilometers) of the stratosphere closeto the tropopause, temperatures are constant. The phenomenon isreferred to as the isothermal layers because it does experiencetemperature changes with altitude. Temperatures in the isothermallayer of the stratosphere are high and constant due to the highconcentration of the ozone gas (Saastamoinen 250). Ozone gasmolecules exist throughout the earth’s atmosphere in varyingconcentrations (250). However, they exist in high concentration inthis region than any other layer. The ozone molecules actively absorbultraviolet radiation from the sun creating a concentration of heatwaves in the atmosphere hence, causing high temperature in thestratosphere (250).
Thestratosphere is a vital layer for living organisms because it trapsthe ultraviolet rays that have harmful effects (Holton 224). Forhumans ultraviolet can cause skin cancer. In plants, extreme levelsof ultraviolet rays can destroy the epithelial cells of leavesexposing, the inner cells to further destruction (225). Plantsexposed to harmful ultraviolet are likely to wither and causedesertification in regions. The depletion of the ozone layer hasbeen proven by geophysicists as one of the main causes of climatechange. The atoms and molecules of other gases in the stratospheresuch as oxygen and nitrogen absorb high-energy short-wave radiationfrom the sun and get ionized (227). The ionization creates an ionizedlayer that reflects radio waves hence, aiding in globaltelecommunication. For this reason, the stratosphere is sometimesreferred to as the ionosphere. Greenhouse gases emitted as productsof human activity deplete the ozone, therefore, exposing livingorganisms to the harmful effects of ultraviolet radiation (229). Insummary, there could be no life on the surface of the earth in theabsence of the ozone layer.
Bydefinition, the mesosphere is an area of the atmosphere situatedbetween the stratopause and the menopause. The mesosphere is thecoldest layer with about -900C.It is found at the height of 80 kilometers. Temperature in themesosphere rises with altitude.
Thelast layer is the thermosphere. The thermosphere is found at analtitude greater than 80 kilometers. This layer has the highesttemperatures than go can exceed 12000C(Saastamoinen 249). The high concentration of oxygen molecules in thethermosphere causes an intense absorption of solar radiation thatkeeps temperatures at the highest level in the atmosphere.Interestingly, the high temperatures in the thermosphere are notcaused by the heat but through radioactive emission from individualoxygen molecules that are separated in long distances. This explainswhy it is difficult to measure temperatures in the thermosphere usingthe thermometer. The thermometer depends on the conduction of kineticenergy from the molecules of a body mass to the expanding mercuryinside the thermometer. Kinetic heat transfer is not possible in thethermosphere because it would lose heat energy to molecules that emitradiation and then gain heat whenever there is contact with very hotoxygen gas molecules (Brasseur, Guy, and Susan 39).
Inconclusion, the layers of the earth’s atmosphere are largelydefined by the physical and chemical processes that occur in them.Temperature that primary originates from solar radiation influencesthe chemical and physical processes. The atmosphere is an importantpart of the earth whose research improved after the introduction ofpolar-orbiting and geostationary satellites, and remote sensingtechnology that is widely applied to observe and measure severalatmospheric elements in each layer. The instruments when placed inspace intercept radiation from the earth’s surface and theatmosphere in visible form as well as infrared radiation at differentwavelengths from which information is derived about differentphysical and chemical activities that define the four layers of theearth’s atmosphere.
Ahrens,C. Donald. Meteorology Today: An Introduction to Weather, Climate,and the Environment. 10th ed. Brooks/Cole, 2013. Digital file
Brasseur,Guy, and Susan Solomon. Aeronomyof the middle atmosphere: chemistry and physics of the stratosphereand mesosphere.Vol. 32. Springer Science & Business Media, 2006.
Hedin,Alan E., et al. "Revised global model of thermosphere windsusing satellite and ground‐basedobservations." Journalof Geophysical Research: Space Physics (1978–2012)96.A5 (1991): 765-768.
Holton,James R. "The dynamic meteorology of the stratosphere andmesosphere." Researchsupported by the National Science Foundation Boston, AmericanMeteorological Society (Meteorological Monograph. Volume 15, No. 37),1975. 224 p.Vol. 15. 1975.
Saastamoinen,J. "Atmospheric correction for the troposphere and stratospherein radio ranging satellites." Theuse of artificial satellites for geodesy(1972): 247-251.