Saturday, December 14, 2019

The Magical Roaring Forties – Part II

Continued from the previous post regarding information about the winds and currents and how they drove Lehi to the Land of Promise.
    The Westerlies (anti-trades) and prevailing westerlies are the dominant west-to-east motion of the atmosphere, centered over the middle latitudes between 35º and 65º of both hemispheres (“Westerlies,” Glossary of Meteorology, AMS publisher, June 2010).
    These prevailing winds blow from the west toward the east in the middle latitudes between 35º and 65º, and originate from the high-pressure areas in the horse latitudes and trend towards the poles and steer extratropical cyclones, which is a synoptic scale low pressure weather system that has neither tropical nor polar characteristics, being connected with fronts and horizontal gradient in temperature and dew point. In fact, these tropical cyclones which cross the subtropical ridge axis into the westerlies recurve due to the increased westerly flow—one of the two bands of high atmospheric pressure belts which are formed by the subtropical highs.
Areas of extratropical cyclone formation worldwide, showing the southern Ocean and the Roaring Forties where these are located along the West Wind Drift

The descriptor "extratropical" refers to the fact that this type of cyclone generally occurs outside of the tropics, in the middle latitudes of the planet, where the Westerlies steer the system generally from west to east. These systems may also be described as "mid-latitude cyclones" due to their area of formation, or "post-tropical cyclones" where extratropical transition has occurred, and are often described as "depressions" or "lows" by weather forecasters and the general public.
    They are predominantly from the southwest in the Northern Hemisphere and from the northwest in the Southern Hemisphere. In addition, they are strongest in the winter hemisphere and times when the pressure is lower over the poles, while they are weakest in the summer hemisphere and when pressures are higher over the poles. An extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone, if it dwells over warm waters and develops central convection, which warms its core and causes temperature and dewpoint gradients near their centers to fade.
    The westerlies are particularly strong, especially in the Southern Hemisphere, in areas where land is absent, because land amplifies the flow pattern, making the current more north-south oriented, slowing the westerlies. The strongest westerly winds in the middle latitudes can come in the Roaring Forties, between 40º and 50º latitude. The westerlies play an important role in carrying the warm, equatorial waters and winds to the western coasts of continents, especially in the southern hemisphere because of its vast oceanic expanse.
    In addition, if the Earth always had the same face toward the sun in its orbit (tidal locking) known was synchronous rotation, that is, when the tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner—which, in case of the Earth and Sun, it is not. If it were, the Earth being tidally locked to the Sun, solar heating would cause winds across the mid-latitudes to blow in a poleward direction, away from the subtropical ridge. However, the Coriolis effect caused by the rotation of Earth causes winds to steer to the right of what would otherwise be expected across the Northern Hemisphere, and left of what would be expected in the Southern Hemisphere (Nathan Gasser, Solar Heating and Coriolis Forces, University of Tennessee Press, Knoxville, October 8, 2000).
    This is why winds across the Northern Hemisphere tend to blow from the southwest, but they tend to be from the northwest in the Southern Hemisphere. When pressures are lower over the poles, the strength of the westerlies increases, which has the effect of warming the mid-latitudes. This occurs when the Arctic oscillation—a ringlike (or "annular") pattern of sea-level pressure anomalies centered at the poles, which presence of continents and large landmasses disrupts the ringlike structure—is a weather phenomenon at the Arctic and Antarctic poles north or south of 20 degrees latitude. The index varies over time with no particular periodicity, and is characterized by non-seasonal sea-level pressure anomalies of one sign in the Arctic, balanced by anomalies of opposite sign centered very high and very low latitudes.
The West Wind Drift or Antarctic Circumpolar Current (Dk.Blue), is as much as 1250 miles wide based on ship-drift estimates of sea surface velocities that are available along major shipping routes

The Antarctic Circumpolar Current, or the West Wind Drift, flows from west to east around Antarctica, and is the dominant circulation feature of the Southern Ocean, and at approximately 125 Sverdrups the largest ocean current (Ryan Smith et al., The Antarctic CP Current,” Surface Currents in the Southern Ocean, Cooperative Institute for Marine and Atmospheric Studies, 2005).
    The point of all of this is to show how the current at the southern latitudes of the world, which runs unencumbered around the planet, is both faster than any other current as well as shorter because it is at the bottom of the circular sphere of the Earth. It would have been the safest route for an inexperienced crew, such as Lehi, and would have required the least amount of knowledge of weaving through islands, landing on an island to refresh supplies—which would have lasted on the far shorter time at sea.
    To have taken Lehi in any other direction from the southern shore of the Arabian Peninsula would have been longer in distance as well as longer in time. Because of the east of riding the Indian Ocean counter-clockwise running flow, taking Lehi down the western edge of the gyre to about 40º where a simple steering would have taken them into the Southern Ocean, where the only skill needed was to hang on a he winds and current took the ship across the southern Pacific Ocean toward South America. Of course, the wind-swept voyage there would have been overwhelmingly frightful to Laman and Lemuel and the sons of Ishmael and certainly would have overridden any thoughts about mutiny and taking over the ship, which would probably have happened if Lehi had been island-hopping across the Pacific as so many theorists claim.
The Southern Ocean is in one of the windiest parts of the planet, and its currents are driven mainly by the wind. The wind that blows over the surface of the ocean passes its energy to the water molecules in the ocean, giving the water more kinetic energy. Friction between the sea water and the bottom of the ocean cause the movement of the water or current to slow down. It is the balance between these two forces that stop the currents from getting faster and faster.
    As has been stated before, the northern edge of the Roaring Forties, i.e., in the low forties of latitude, the air and water is warmer because of the southward flow of equatorial waters. The Furious Fifties are colder, and the Screaming Sixties, where icebergs can form, is colder still. Beyond that is the Antarctic Current. It is also along these lower Roaring Forties (40º to 45º) that the underlying shelf of the South American continent moves water to the surface where it connects with the Humboldt (Peruvian) Current and flows northward along the western coast of Chile and Peru.
    The perfect method of getting Lehi from his Bountiful to the Lan of promise!
    It is imperative that we understand that we know exactly how the weather works, what drives the wind and ocean currents, and where they flow. This system was created by the Lord, and obviously used by him to send the Jaredites, Lehi, and Mulek to the Land of Promise. This was not a fluke, not a whim, not an unplanned event—it was directed specifically by the Lord as the scriptural record so clearly points out.

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