A reader wanted to know how Earth’s rotation affects the dynamics between solid earth and the gaseous atmosphere.
From our first breath until we die, the atmosphere has a profound effect on our lives.
Without this ocean of air, there would be no seas, lakes or rivers. There would be no rain for me to report nor sounds to listen too. There would only be scorching days and unbearably cold nights on a lifeless moonscape of a planet.
It’s unnerving to know that the atmosphere is relatively thin as compared to Earth’s circumference.
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Cut an apple in half, and its red skin would represent the thickness of the sky as compared to the white flesh representing the earth.
Move several miles above Earth’s surface, and you would suffocate. A realization of this condition could certainly make one an environmentalist.
Fortunately, the strong invisible force of gravity keeps our atmosphere safely in place, accelerating trillions of air molecules (78 percent nitrogen, 21 percent oxygen and the rest made up of argon, carbon dioxide and other trace gases) toward Earth’s surface and producing what we feel as air pressure.
A 1-square-inch column of air measured from the top of the atmosphere down to sea level would weigh about 14.7 pounds. One square foot would weigh 2,117 pounds. All the air surrounding the Earth would weigh about 5,600 trillion tons!
This weight would normally crush us like recycled aluminum cans at Cold Canyon Landfill. However, we don’t notice it because our bodies maintain an internal pressure that balances the external pressure.
But swift changes in elevation can cause us to detect atmospheric pressure changes. One local example can be found driving over the Cuesta Grade, which is 1,522 feet above sea level. Maybe you have felt your ears “pop.” This is caused by your inner ear trying to equalize the pressure from the outside air.
Uneven heating of Earth’s surface by the sun and changes in the jet stream — typically a tubular ribbon of high-speed winds flowing in wave-like patterns for thousands of miles from west to east some 18,000 to 40,000 feet up — produce areas of high and low pressure in our atmosphere. The jet stream more or less moves from west to east because of the earth’s rotation.
Air flows from areas of high pressure to low pressure, like air streaming out of a punctured tire, and gives rise to the winds our local kite surfers enjoy.
As Earth rotates under these winds, the wind flows in a curved path. The apparent force that causes this curved path is called Coriolis, name after French scientist Gaspard-Gustave Coriolis.
Generally, the wind turns to the right in the Northern Hemisphere and turns to the left in the Southern Hemisphere, except in the presence of hurricanes or other strong low-pressure centers. Is these areas, the pressure-gradient force produces the stunning counterclockwise pin-wheels cyclones that we see from satellite images.
Think of Coriolis force in this fashion. Earth rotates once on its axis every 24 hours. At the equator, you would move around Earth’s axis about 1,040 mph. This speed decreases as you go north or south away from the equator. At our latitude, it’s about 850 mph. Finally, when you reach the North Pole, it’s near zero mph. It takes a whole day to just turn once in place.
With large-scale weather systems that stretch hundreds of miles north to south across the surface of the Earth, the southern part of the system travels at a faster rate of speed than the part of the system to the north, covering a greater amount of real estate and appearing to turn to the right.
On smaller distances there’s not much effect. Don’t believe what you might have heard about Coriolis making the water in a sink rotate one way as it drains in one hemisphere, the other way in the other hemisphere.
This week’s forecast
A 1,028-millibar Eastern Pacific High is parked about 600 miles to the west-southwest of San Luis Obispo and will gradually weaken over the next 72 hours.
This morning will see a few areas of marine low clouds along our coastline and along Highway 101 from Atascadero northward through the Salinas Valley, but will clear later this morning.
Temperatures will warm into the low to mid-70s throughout San Luis Obispo County.
Rain will develop across Northern California and spread southward toward Monterey Bay late tonight into Monday, as a cold front moves onshore. This cold front will produce decreasing northwesterly winds and increasing clouds.
Fog, drizzle and maybe even a few sprinkles will develop Monday, especially along the coastline. In other words, Monday should be dreary and cooler. This system is expected to be relatively warm and snow levels will remain above 5,500 to 8,000 feet north to south.
A weak 1,011-millibar low-pressure system will approach the Central Coast later Tuesday, producing night and morning coastal low clouds and fog. As the system moves over the Central Coast on Wednesday, it’s expected to produce gentle southerly winds and mostly cloudy conditions with a few sprinkles or light rain showers.
A return to dry and warm weather along with strong- to gale-force northwesterly winds along the coastline is expected Thursday through next weekend.
Surf and sea report
Strong to gale-force (25- to 38-mph) northwesterly winds along the Central Coast will continue to generate 4- to 6-foot northwesterly (310-degree deep-water) sea and swell (with a 7- to 12-second period) through tonight.
A 3- to 5-foot northwesterly (285-degree deep-water) swell (with an 8- to 15-second period) will develop Monday, building to 4 to 6 feet (with an 8- to 13-second period) Tuesday. This swell will decrease to 2 to 4 feet Wednesday.
Another round of strong to gale force (25- to 38-mph) northwesterly winds later next week, will produce a 4- to 6-foot northwesterly (310-degree deep-water) sea and swell (with a 7- to 11-second period) late Thursday through next Sunday.
Arriving from the southern hemisphere:
A 1-foot southern hemisphere (205-degree deep-water) swell (with a 16- to 18-second period) will arrive along our coastline Monday, increasing to 2 to 4 feet (with a 15- to 17-second period) Tuesday and will continue at this height and period through Wednesday.
Seawater temperatures will range between 49 and 51 degrees through Friday.
A word of thanks
I want to personally thank those who came out Saturday to help us with the Earth Day project at Montaña de Oro State Park. It’s remarkable how much good can be accomplished by a motivated group of volunteers.
John Lindsey is a communications representative for PG&E. He is also a local weather expert and has lived along the Central Coast for more than 24 years. If you have a question, send him an e-mail at email@example.com.
CORRECTION: The 11th paragraph of this article was corrected to reflect that the jet stream moves west to east.