Featured So, Why All the Record Cold ? Introduction So, why is global warming making it so cold? Think of it like this (somewhat oversimplified, but essentially correct): first, cold air on earth is heavier than warm air, and the cold air tends to build up in the arctic (and Antarctic). Second, the air spins rapidly in a circle with the earth’s rotation. So, you’d think the air would just fly off into space like water from a lawn sprinkler. But it doesn’t because the air is tied to the earth by gravity. Think of a huge clump of cold arctic air (say 100 cubic miles, or so) like a tennis ball on a string (the force of gravity) that the earth is whirling around a circle at roughly 530 mph. The ball of cold air wants to get away, but it can’t because of the gravity string. The best it can do to get as far from the center as possible is to go southward towards the tropics and the equator where the distance from the center is greatest. (Everything, of course, is reversed for South Africa, South America and Australia. The cold Antarctic air ball goes northward.) Physics of Earth and Atmosphere But in order to go south, the polar air must overcome friction and push the warm tropical air out of the way. Which it does quite easily because it’s not polite and it’s much heavier. And the warmer the tropical air gets, the easier it is for the cold air balls to displace the lighter, warmer air. The centrifugal force experienced by the mass of air at each latitude acts perpendicular to the rotation axis of the earth and can be calculated by the formula, F = m(v)2/r. ( ) At 30o N latitude, the centrifugal force acts at an angle of 60o from the horizontal plane (surface of the earth). Conversely, at 60o N, the force acts at 30o from the horizontal plane. But at each location, the centrifugal force vector can be decomposed by trigonometric methods into two components, one force “horizontal,” (parallel to the surface of the earth) and one “vertical” (perpendicular to the surface). The horizontal force drives the mass of air south towards the tropics, the vertical force acts to reduce the apparent “weight” of the air mass by a small percentage (less than 1%). Fortunately for life on Earth, the gravi-tational force on the atmosphere is large enough everywhere to overwhelm the vertical component of centrifugal force. In fact, a tower of cold, dry, arctic air one mile square and 100 miles high has a mass of about one billion slugs (the unit of mass) and weighs almost 32,200,000,000 lbs! In contrast, the Path length at equator: 132,000,300 ft Velocity at equator: 1530 ft/sec Path length at 30o N: 114,269,150 ft Velocity at 30o N: 1320 ft/sec Path length at 60o N: 66,985,000 ft Velocity at 60o N: 775 ft/sec Diagram of the Earth with Radius at Latitude 60o N, 30o N and Equator ( ) centrifugal force on this air mass at the equator (all vertical) is only 104,200,000 lbs, much less than 1% of the weight. But the horizontal component at higher latitudes is quite sufficient to drive the air mass towards the tropics from either the north or the south polar region. For example, at 60o north latitude, the 100 cubic miles of air above would feel more than 45 million lbs. of horizontal force driving it southward from the centrifugal action of the spinning Earth (see the figure below). If there were no warm air in the way and no friction with objects and the surface of the Earth, this force would be enough to propel the air mass (100 cubic miles) to a speed of 175 ft/sec (120 mph) in one hour. But the cold air mass must overcome friction caused by surface elements (trees, mountains and the like), and must push the southern air out of the way. The warmer tropic air is a lightweight (less dense) and more polite compared to the heavyweight cold air from the north, and the rude northern air mass has little trouble shoving the warmer air out of the way and taking over the warm air’s territory. The displaced warm air can do nothing but retire upward (over the top of the cold air), northward and eastward (because the spinning Earth has it going that way) to the space formerly occupied by the invading cold air, losing in the process some of the heat that made it warm, to heat the land and water of the colder regions along the way. Thus, the Hadley, Ferrel and Polar circulation cells come into being in part through the whirling of the atmosphere by the rotating Earth. As the atmosphere grows warmer, and the temperature difference between the cold polar air and the warmer tropic and mid-latitude air increases, it becomes easier for polar air masses to displace the warmer air. And so, driven by the centrifugal action of the spinning Earth, the cold air masses plunge deeper and faster into the mid-latitudes and sub-tropics. Larger excursions in the jet-stream and more frequent sub-freezing temperatures in southern states are symptomatic of this imbalance. At times, the cold air ball gets so big, and displaces so much tropical air back to the poles that it’s warmer in Barrow, AK than it is in Chicago, IL., testifying to the rapid movement of warmer air from lower latitudes northward to the poles. So, How Does It All End? Some authorities are convinced that the present unstable condition of Earth’s atmosphere will eventually settle down at a warmer, more uniform temperature similar to the Jurassic period (Age of Dinosaurs). If so, the extreme temperature differences experienced today might disappear along with the Ferrel cells, icebergs and polar bears. Given this scenario, extreme weather events might be expected to go away, along with catastrophic forest fires, droughts and floods. But this outcome depends heavily on halting the increase in “greenhouse gases” and controlling the level of destabilizing pollutants such as SO2, ozone, “smoke” and other particulate matter. It is sad to contemplate this outcome, given that most coastal settlements will have to move well inland from their present location, or implement extreme measures to protect from rising sea levels in this “best case” scenario. In any event, it’s encouraging to think that our descendants might see Ginko Trees proliferate and Apatosauri populate the Earth, “but we’ll see what happens.” Horizontal and Vertical Components of Centrifugal Force on 100 Cubic Miles of Atmosphere at 60o and 30o N Latitude
Climate Change 