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8 - 2. Life gets almost all its energy from the sun. Solar energy does more than provide energy for life on Earth; it drives the wind and it drives the currents in the ocean. Earth's temperature relies on sunlight. Therefore, the sun not only provides life, but also the conditions in which life
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2. 8 - 2 Life gets almost all its energy from the sun. Solar energy does more than provide energy for life on Earth; it drives the wind and it drives the currents in the ocean. Earth’s temperature relies on sunlight. Therefore, the sun not only provides life, but also the conditions in which life exists.
Air and Sun
Air is a mixture of gases that surround us.
The four layers of the atmosphere include:
1. Troposphere – the lowest layer. This one concerns us most.
2. Stratosphere
3. Mesosphere
4. Thermosphere – the top layer which goes out into space.
3. 8 - 3 Air and Sun (continued) The amount of water vapor in the air relates to air temperature, density, and pressure.
As temperature rises, air pressure increases, and density decreases.
Adding water vapor decreases the density even more.
Warm air is less dense than cool air.
When a saturated or nearly saturated air mass cools, it has more water vapor in it than it can hold. The vapor condenses, forming rain when the temperature is above freezing or snow when temperature is below freezing.
Understanding air masses and the weather they create is important because:
1. These movements redistribute heat around the Earth.
2. Precipitation is the primary source of fresh water.
4. 8 - 4 The Earth’s Heat Balance About 50% of all the sunlight that reaches the atmosphere makes it to Earth’s surface.
To maintain balance with the heat from the sun, all the energy absorbed reradiates through various paths back into space as infrared radiation.
If this process were imbalanced with more heat coming in than leaving, the Earth would grow hotter and hotter until life perished.
Uneven Heating
Factors that cause the Earth to heat unevenly:
The Earth is round, the Earth’s axis is tilted, and the Earth’s orbit is elliptical hence the distance between the Earth and sun varies with time of year.
Uneven heating causes weather – in part due to convection.
Convection is vertical circular currents caused by temperature differences in a fluid such as air. Warm air becomes less dense and rises. Cool dense air comes in to replace it, which in turn warms and rises. This creates a circular airflow pattern.
5. 8 - 5 Deflection to the Right or Left The Coriolis effect is the tendency for the path of a moving object to deflect to the right in the Northern Hemisphere and to deflect to the left in the Southern Hemisphere.
The Earth’s Rotation
The Coriolis effect is caused by the Earth’s rotation relative to an object in motion over its surface.
Motion or lack of motion is relative to the place from which you observe it.
Standing on the equator relative to anyone on the Earth, you’re motionless.
Someone at a fixed point in space would say you’re moving. To that person, you are moving because the Earth is rotating.
Major Ocean Gyres: The Coriolis effect creates circular airflow and current patterns such as the major ocean gyres – in the Northern Hemisphere to the right and in the Southern Hemisphere to the left.
6. 8 - 6 The Coriolis Effect and the Wind The Coriolis effect deflects the air to the right in the Northern Hemisphere. This gives the air a circular flow pattern rather than a straight north-south pattern.
Atmospheric circulation cells are six distinct air masses (three in each hemisphere) with individual air flow patterns.
Of the six cells, the most important are the Hadley cells. These lie between the equator and approximately 30° north or south latitude.
Trade winds are caused by air rising at the equator and moving northward. The air becomes dense enough from cooling and moisture loss to sink. Most of the air descends and flows back toward the equator, deflecting westward as it flows.
Between 30° and 60° latitude are the Ferrel cells. They exist because some of the wind that descends from the Hadley cells doesn’t turn toward the equator. Instead it continues on toward the poles shifting to the right (Northern Hemisphere) as it moves. This is what causes the Westerlies, getting this name because they’re from the west.
7. 8 - 7 Intertropical Convergence Zones (ITCZ) The geographic equator is 0° latitude.
The meteorological (ITCZ) equator is an imaginary line marking the temperature equilibrium between the hemispheres that shifts north and south of the geographic equator with seasonal changes.
The ITCZ equator is important because atmospheric and ocean circulation are approximately symmetrical on either side of it – not at the geographic equator.
The Earth’s major deserts are found at 30° latitude. Here the downward vertical airflow brings dry air to the Earth’s surface. This leads to areas with little rainfall and significant evaporation.
Where oceans/seas are alongside deserts, the combination of high evaporation and low rainfall makes the salinity of these waters higher than average.
8. 8 - 8 Monsoons and Cyclones Monsoons are seasonal wind pattern changes caused by heating or cooling on the continents. Monsoons cause summers with significant rainfall and winters with very little.
Cyclones are large rotating storm systems of low pressure air with converging winds at the center. There are two main types: extratropical and tropical.
Extratropical cyclones occur where the Polar and Ferrel cells meet.
Tropical cyclones form within a single atmospheric cell.
In both cases, cyclones form when moist wind gets drawn into a low-pressure area, causing it to twist around on itself.
Cyclones appear to rotate the “wrong” way with respect to the Coriolis effect.
When a cyclone forms, the low pressure pulling the wind into the pattern is stronger than the Coriolis effect.
The winds that get drawn in and provide the cyclone energy are pulled away from the Coriolis effect. This imparts the “backwards” spin.
Cyclones help with the redistribution of heat that is important to all life on Earth.
