Monday, February 23, 2015

Determinants of Global Climate Patterns

by Antonio C. Antonio
February 7, 2015

Have you even been asked this innocent question: “Will climate change possibly bring snow to the Philippines?”  I would rather leave the answer to your fertile imagination.

There are two determinants of global climate patterns.  These are temperature and precipitation which are factors that determine climate.  Precipitation is defined as any form of water, liquid or solid, falling from the sky.  It includes rain, sleet, snow, hail and drizzle plus a few less common occurrences such as ice pellets, diamond dust and freezing rain.  On the other hand, temperature is the degree or intensity of heat present in a substance or object, especially as expressed according to a comparative scale and shown by thermometer or perceives by touch.

While precipitation and temperature are the determinants of climate, the following factors determine global climate:

THE SUN’S RAYS AND THE SPHERICAL EARTH – The sun’s rays does not reach the Earth uniformly.  The Earth is a sphere. The Earth’s surface is heated more at the equator than the poles because the sun’s rays strike the equator at right angles to the surface and maximum energy intensity is received.  At the poles, the sun’s rays are received at an oblique angle and are spread out over a much greater area, hence lower energy is received per unit area.  The obliqueness of the rays also means that they have to travel a longer distance through cloud cover and atmosphere.  This will further reduce the amount of energy actually heating the Earth’s surface.

ELLIPTICAL ORBIT AND THE EARTH’SROTATION AROUND THE SUN – The Earth rotates around the sun at the rate of 365.25 day/revolution.  The orbit of the Earth’s rotation around the sun is an ellipse.  At any given point in time, the Earth is located at a particular distance from the sun.  This distance determines the amount of energy received by the surface.  The Earth is nearest the sun at perihelion, observed ar abut January 3.  The aphelion, when the Earth is farthest the sun occurs at about July 4.  The average Earth-sun distance occurs about April 4 and October 5.  The amount of solar radiation intercepted by the Earth at perihelion is about 7% higher than aphelion.

GLOBAL TILT AND THE EARTH’S AXIS – As it rotates around the sun, the Earth is tilted on its axis at an angle of 23 degrees.  The tilt leads to uneven heating of the Earth and produces seasons and climate patterns around the globe.  Seasonal tilting of the Earth’s axis means that there is no sunlight at the poles during much of the winter.  In the tropical region, an almost uniform amount of solar energy is received by the surface.  Likewise, minimal variation in temperature is experienced in the tropics.  This is because the position of the tropical zone and the tilt of the Earth’s rotation are both at 23.5 degrees.  Temperature variation increases with increasing latitude from the equator.  In temperate region, there are four distinct season, therefore, winter, spring, summer, and autumn.  In the tropics, only two seasons are identified: dry and wet.

ATMOSPHERIC CIRCULATION – When the surface is heated, air above it is also heated, and it becomes light and rises up.  As warm air rises, it encounters lower atmospheric pressure and expands, spending some of its energy.  The decrease in the internal energy of the air parcel cools it at a rate of 10 degrees/1000 meters.  When it sinks, the air mass warms at the same rate.  The rate of decrease in temperature of the rising air mass is called the dry adiabatic lapse rate.  In most air, water vapour will condense as it cools and release latent heat to the surrounding air.  The heat released partially counteracts cooling of the air.  The adiabatic lapse rate for moist air is 6.0 degrees/1000 meters.  As the lighter warm air rises and is replaced by cooler heavier air, a vertical convection current develops, stirs the atmosphere and transport heat from one area to another.  Water vapour carries into the atmosphere by rising convection current transports large amounts of energy and plays an important role in the redistribution of heat from low to high altitudes and from the oceans to continental land masses.  If temperature is low enough, it will condense to form water droplets and precipitation will take place.  The heat released when water vapour condenses radiates into space.  The resulting cooler, drier air becomes denser, sinks, and creates an area of high pressure.  At this air mass flows across the Earth’s surface, it picks up heat and moisture and begins to rise again.  The resulting convection cells circulate air, heat, and moisture both vertically and from place to place in the troposphere, leading to different climates.  Mountains and other geographical barriers also affect the circulation of air and water.  As the moving air mass encounters a mountain barrier, air will be forced to rise following the slope of the mountain.  As the moisture-laden air mass from the windward side of the barrier rise, it cools and the water vapour condenses and falls as rain.  A cold air mass is heavy and will tend to sink but is forced to rise by the prevailing wind.  When the cold, dry air mass reaches the summit, it will descend on the leeward side of the mountain.  As it goes down, it warms up and picks up moisture along the way.  Warm air has a higher capacity to hold water.  Upon reaching the base of the mountain, it will have warmed up enough to again rise but it carries by the prevailing wind to another place where it will release water as precipitation, leaving the leeward side of the mountain barrier to be relatively dry.

PLACEMENT OF CONTINENTS AND OCEANS – The interior of a continent is usually drier that its coast simply because the interior is farther away from the major site of water evaporation.  Maritime (coastal) climates are also less variable than continental (interior) climates because the high heat capacity (amount of energy needed to change the temperature of 1 degree centigrade) of water compared to land, moderates coastal temperatures.

OCEAN CURRENT – Ocean current also plays a major role in transferring heat over the surface of the Earth.  In large ocean basins, cold water tends to move toward the tropics along the western coast of the U.S. continent.  The cold Humboldt current moving north along the coast of Chile and Peru is partly responsible for the presence of deserts along the west coast of South American rift to the equator.  Conversely, the warm Gulf Stream emanating from the Gulf of Mexico carries mild climate far to the north into western Europe.  Current also helps mix ocean waters and redistribute nutrients needed by aquatic organisms.  Along some steep, western coasts of continents, almost constant trade winds blow offshore, pushing surface water away from land.  This outgoing surface water is replaced by upwelling of nutrient-rich, cold bottom water.  Changes in prevailing winds can change the temperatures of surface waters, weaken or alter ocean currents, suppress upwelling and trigger weather changes over at least two-thirds of the globe.  (Source:  “Ecosystem Structure and Dynamics”: Medina, Zafaralla, Sierra, Cuevas, Macandog and Cervancia, 1999)

If and when the innocent question (therefore, “Will climate change possibly bring snow to the Philippines?”) is asked of you, you will now have more intelligent facts to use in answering it… the determinants of global climate patterns.

Just my little thoughts…

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