Hadley circulation

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Hadley circulation

The Hadley circulation is a thermally driven atmospheric circulation system centered on the equator and tropical areas of the earth. In essence, the warmer, tropical air rises and releases the stored heat and moves toward the colder, denser polar regions. As it enters the subtropics, the air masses cool, sinks, and flows back to the topics, creating a closed circulation loop in both the northern and southern hemispheres. The Hadley circulation, like many other atmospheric systems can be divided in subparts or zones.

The rising branch or zone is sometimes referred to as the Intertropical Convergence Zone, or ITCZ. It is approximately 200 to 300 kilometers in width, and exists where the trade winds from the northern and southern hemispheres converge near the equator. These trade winds, which move from east to west across the tropical region, are influenced not only by the temperature and pressure gradients caused by the ITCZ, but also by the Coriolis effect. The Coriolis effect is brought about by the rotational energies of earth.

This rotation causes the curved nature of the trade winds. The most pervasive influence of this effect for the atmosphere and oceans is the relatively steady flow that is characterized by a balancing effect between the temperature and pressure gradient force, and the Coriolis force (Phillips, 2000). Radiocarbon dating is used by geologist, archeologists, and other scientists to try and accurately determine the age before the present day of articles such as pottery, faunal or floral remains, and other geological or archeological significant fossils and artifacts.

Radiocarbon dating is a specific form of radiometric dating. Radiometric dating is a form of determining the age of a particular object through the use of radioactive nuclides, and their mathematical relationship to their stable, or daughter nuclides. In the case of radiocarbon dating, the ratio between carbon-14, a radioactive isotope of carbon, and carbon-12, the stable daughter isotope is measured. It is assumed that none of the daughter nuclide existed at the start, and that a portion of carbon-14 was absorbed into the plant or animal during its life span.

Since the half life, or amount of time it takes for 1/2 of the carbon-14 to radioactively decay into carbon-12 is known, as well as the decay rate content, the age of the specimen can be calculated using careful measurements of the isotopic ratio of the element and mathematic calculations. Of course, things in nature are rarely as straight forward. There are quite a number of ways that radiocarbon dating can be affected, one of which involves the earth magnetism. Fluctuations in the earth’s magnetic field can lead to variations in the production rate of carbon-14 in the atmosphere (Faure, 1998).

Since the amount of carbon-14 isn’t a constant process, it is necessary to calibrate the measurement tools used to determine the amount of radionuclide to take into account the probable amount of carbon-14 production based on the hypothesized fluctuations of the magnetic fields. If the ratio of 234U/238U has remained constant throughout time, then the ratio between the amounts of 234U/238U precipitated into the coral skeletal structure must be proportional to the material dissolved back into the sea water.

Therefore, the two ratios (234U/238U in sea water verses 234U/238U in coral skeleton) must be directly proportional to each other, based on the information provided. Based on this information, for every 1 mole of 238U that degrades into the daughter product, then 1. 15 moles of U234 degrades as well. Based on this information, the amount of U234 would decrease at a rate of 1. 15 times that of 238U. If the ratio between the two isotopes in the sea water was degrading in a closed system, then eventually the concentration of U238 would be greater in relation to the amount of U234.

However, the precipitation and dissolution of coral skeletal material indicate that the system is not closed. Therefore, to maintain the U234/U238 in the sea water as a constant, then the amount of U238 must be selectively precipitated from the sea water into the coral skeletal structure (Faure, 2005). Based on the dissolution rates, and the decay rates of U234 versus U238, the best time frame for the use of this radiometric dating method is over one million years.

The El Nino Southern Oscillation is a coupled oceanic and atmospheric event in which warmer, nutrient lacking water upwards towards the surface water along the coast of South America in the Pacific Ocean. This causes the corresponding air mass to be warmed, and trade winds, and the currents pull the warmer water and atmosphere to the west towards Japan, Australia, and finally the Indian Ocean. As it migrates, the air and water cools, becomes denser, and increases in nutrient value.

It sinks along the western portion of the Pacific ocean, and the cycle begins anew. Because of its cyclic nature, both farmers and fishermen have recognized the El Nino Southern Oscillation and the effects that it has brought to the region. During the winter months, when the El Nino causes the warmer, nutrient lacking water to rise along the South American coast, fishermen notice that marine life and fishing become scarce. In the agricultural side of things, the weather conditions along the coasts of South America become more draught like.

In addition, increased precipitation in the western portion of the Pacific Ocean leads to greater flooding and monsoon conditions (D’Aleo, 2002). While fluctuations caused by ENSO have become somewhat predictable, an increase in the strength of the event would most likely cause an increase in the intensity and variations seen. Stronger storms along the western part of the Pacific ocean, and a longer time of scarcity of marine life and precipitation during the winter months in South America are common.

A stronger El Nino event would most likely cause increased storm activity in other areas of the world. The ITCZ is a zone of low pressure associated with the Hadley circulation system. During the summer months, it is located to the north of the equator. However, as the North Atlantic region gets colder, the potential for the southern migration of the ITCZ increases. Because of its nature, the ITCZ is characterized by increased precipitation, cloud cover and lower pressure, the potential migration into the southern hemisphere would have a number of effects on the weather patterns in the tropical areas.

The first thing that would undoubtedly change with the migration of the ITCZ is that the overall temperature and pressure gradients in the atmosphere would be altered. Normally the atmospheric temperature gradients in the tropical regions are relatively high at the equator and slowly decrease in temperature as the air masses moved towards the polar region. The introduction of the ITCZ into the southern tropical region will cause an increase in the overall cloud cover of the area because of the drastic change in pressure gradient.

This in turn would lead to an overall lower temperature in the region, which would slightly alter the temperature gradient in the tropical area. The increased cloud cover and the changes in the pressure/temperature dynamics would undoubtedly cause an overall increase in precipitation. Eventually, however, a new dynamic equilibrium would be established within the Hadley circulation system. The ITCZ is a low pressure portion of the circulation system, and a migratory shift southward would cause the Hadley circulation system to shift south as well.

References D’Aleo, Joseph and Pamela G. Grube. (2002) The Oryx Resource Guide to El Nino and La Nina, Westport, Connecticut, Oryx Press Faure, Gunter and Theresa Mensing (2005) Isotopes Principles and Applications Third Edition Hoboken, New Jersey John Wiley and Sons, Incorporated. Faure, Gunter (1998) Principles and Applications of Geochemistry Second Edition Upper Saddle River, New Jersey Prentice Hall Phillips, Norman (2000) “An Explication of the Coriolis Effect” Bulletin of American Meteorological Society pgs 299-303


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  • University/College: University of Chicago

  • Type of paper: Thesis/Dissertation Chapter

  • Date: 22 October 2016

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