The Proceedings of the Eighth International Conference on Creationism (2018)

and layers of air above it cause the thermal circulation to break into three circulation patterns. The three circulation patterns are called the Hadley cell, the Ferrel cell and the polar cell as illustrated in Figure 2. The Hadley cell and polar cell behave as we would expect for a thermal circulation: cold surface air moving from the poles to the equator. This results in a cooling of the equator and a net heating of the poles as thermal energy is transported poleward. In addition, air converging at the equator from both poles forces warm humid air upward. Since temperatures decrease with altitude, water vapor in this rising air condenses into precipitation, thus releasing thermal energy high in the troposphere and transporting cool rain to the surface. This region of rising air near the equator, called the Intertropical Convergence Zone (ITCZ), produces a band of clouds that are easily observed in satellite imagery. In the mid-latitudes the Ferrel cell forms a reverse circulation where warm air at the surface is driven to the poles. The clash of warm air in the Ferrel cell and cold air in the Polar cell form the polar front, which is the source of severe weather and precipitation at the higher latitudes. Although this reverse circulation hinders the flow of cool, surface, polar air to the equator; instabilities in the polar front grow until cold polar air penetrates further towards the equator (trough) and warm tropical air extends further poleward (ridge). Low pressure systems along the polar front are also generated, which mix these two contrasting air masses. As a result, there is still a net flow of thermal energy poleward through the Ferrel cell. Since the Coriolis effect veers winds to the right in the Northern Hemisphere, winds do not blow in a north-south direction. High in the troposphere in the mid-latitudes the pressure gradient force is directed northward from the warm southerly air to the cold northerly air. Since there is very little interaction of this air with the surface, friction has a minimal effect. The Coriolis effect acts perpendicular to wind direction and is proportional to wind speed. Gollmer ◀ Post-Flood Ice Age precipitation ▶ 2018 ICC 697 Figure 1. Thermal circulation occurs when there is a difference in surface temperature. a) Air over the warm surface occupies more volume and extends to greater altitudes than air over the cold surface. This results in a pressure gradient force high in the atmosphere that drives air from the warm to the cold column of air. b) Once warm air is transported to the top of the cold column, the surface pressure over the warm surface decreases and over the cold surface increases. This results in a pressure gradient force that drives air horizontally from the cold surface to the warm surface. This circulation pattern is perpetuated as long as a temperature difference occurs at the surface. Figure 2 The global circulation pattern is a combined effect of a thermal circulation between the equator and poles, the Coriolis effect and surface friction. Both the Northern and Southern Hemispheres have a three cell circulation pattern. The Hadley cell is located closest to the equator and has winds that converge on the equator. This results in a rising band of air called the Intertropical Convergence Zone (ITCZ) and is identified from satellite images as a band of cloudiness and high precipitation. Due to the Coriolis effect the winds become easterlies as they converge near the equator. The Ferrel cell circulates opposite of what is expected from a thermal circulation, but is the result of instability generated by surface friction and the Coriolis effect. This cell has winds moving poleward from the sub-tropical high pressure located at the sinking portion of the Hadley and Ferrel cells. Surface winds in the mid-latitudes become westerlies as they approach the polar cell. The polar cell begins at the pole and has surface winds driving towards the equator. These winds are also easterlies and converge with the westerlies of the Ferrel cell. This convergence zone is called the polar front and air is forced to rise and become unstable. As a result, there is an increased probability of clouds and precipitation. Because the winds on each side of the polar front are from different directions, there is shear that produces instability in the front. As a result, the polar front can form undulations called ridges and troughs and generate low pressure storm systems.