Why does earth have climate zones and seasons

Seasons are inverted in the Southern hemisphere. The Earth is an oblate spheroid sphere flattened at the Poles and as we move away from the Equator, it gets progressively colder, giving rise to climatic zones, from the torrid at the Equator, to the frigid at the Poles. What causes the seasons and climate zones of the earth and why? Sanjay Kamath. Mar 20, Explanation: The Earth revolves around the Sun in Related questions What's the Earth's "absolute" speed? How does density affect earth's layers?

A thinner layer of greenhouse gases causes them to lose heat rapidly. Because they protrude up into the atmosphere, mountain tops have less of this blanket above them, so they are colder. There are however some exceptions to this pattern of temperature decline with altitude: places where the mid-altitudes of a mountain arc warmer on average than the lowest altitudes.

This occurs where there are enclosed valleys between mountains, where there is not much wind. At night, cold air from the upper mountain slopes tends to drain as a fluid into the valley below, and accumulate.

Just above the level that this cold draining air tops up to, there is a warm mid-altitude belt that can have warmer-climate plants than the valley below Figure 1.

Mid-altitude warm belts like this often occur in the Austrian Alps, for example. How mid-altitude warm belts form. Cold air drains down as "rivers" from the upper slopes of the mountain, and fills up the valley below. Just above the top of the accumulated cold air, temperatures are warmer.

The general pattern of cooler temperatures at higher altitudes occurs not only on mountains, but through the atmosphere in general, essentially because of the same factor—a thinner blanket of greenhouse gases higher up. If air is rising up from the surface due to the sun's heating, it will tend to cool as it rises due to this same factor. Another thing that will tend to make it cool is that it expands as it rises into the thinner upper atmosphere—an expanding gas always takes up heat.

If the rising air is moist, the cooling may cause it to condense out water droplets as cloud, and then perhaps rain drops which will fall back down to earth. Differences in the amount of the sun's energy received by the surface drive a powerful global circulation pattern of winds and water currents. The most basic feature of this circulation, and a major driving force for almost everything else, is a broad belt of rising air along the equator. This is known as the intertropical convergence zone, or ITCZ for short.

The air within the ITCZ is rising by a process known as convection; intense tropical sunlight heats the land and ocean surface and the air above it warms and expands. Along most of this long belt, the expanding air rises up into the atmosphere as a plume, sucking in air sideways from near ground level to replace the air that has already risen up. Essentially the same process of convection occurs within a saucepan full of soup heated on a hot plate, or air warmed by a heater within a room; any fluid whether air or water can show convection if it is healed from below.

The difference with the ITCZ, though, is that it is convection occurring on an enormous scale. Because air is being sucked away upwards, this means that the air pressure at ground level is reduced so the ITCZ is a zone of low air pressure in the sense that it would be measured by a barometer at ground level.

What goes up has to come down, and the air that rises along the equator ends up cooling and sinking several hundred kilometers to the north or south of the equator. These two belts of sinking air press down on the ground from above, imposing higher pressure at the surface as they push downwards. The air that sinks down in these outer tropical high-pressure belts gets sucked back at ground level towards the equator, to replace the air that is rising up from being heated by the sun.

It would be easiest for these winds blowing back to the equator to take a simple north-south path; this after all is the shortest distance. But the earth is rotating, and in every 24 hour rotation the equator has a lot farther to travel round than the poles.

So, the closer you are to the equator, the faster you are traveling as the earth turns. When wind comes from a sliuhtlv hiaher latitude, it comes from a part of the earth that is rotating more slowly. As it nears the equator, it gets "left behind"—and the closer to the equator it gets, the more it lags behind. This lagging effect of differences in the earth's rotation speed with latitude is known as the "Coriolis effect", and any wind or ocean current that moves between different latitudes will be affected by it.

It also explains, for example, why hurricanes rotate. Air descends Air rises at zone Air descends further away of maximum further away heating from sun being directly overhead. Although it has been moving towards the equator, much of this wind does not get there bccausc the Coriolis cflcct turns it sideways. It ends up blowing westwards as two parallel belts of winds, one belt either side of the equator Figure 1.

These are the trade winds, so-called because in the days of sail, merchant vessels could rely on these winds to carrv them straight across an ocean. There is another related effect—the "Ekman spiral"—when a wind bent by the Coriolis effect blows over the rough surface of the earth, the friction of the earth's surface—which remember is rotating underneath it at a different speed— will drag the wind along with the rotating earth, canccling out the Coriolis cflcct Figure 1.

This causes the wind direction to change near the earth's surface, and is part of the reason why winds by the ground can be blowing in one direction, while the clouds up above arc being blown in a different direction. Between the air nearest the ground and the air way above, the wind will be blowing at an intermediate angle; it is "bent" around slightly.

The closer it gets to the surface the more bent off course it gets. There arc many other aspects to the circulation pattern of the world's atmosphere. For instance, there is another convection ccll of rising and sinking air just to the north of the outer tropical belt, and driven like a cog w heel by pushing against the cooling air that sinks back down there. A third convection cell sits over each of the poles. Outside the tropics, air lends to move mostly in the form of huge "blobs" hundreds of miles across.

These are known as "air masses". An air mass is formed when air stays still for days or weeks over a particular region, cooling off or heating up, and only later starts to drift away from where it formed. You might regard an air mass as resembling a big drop of treacle poured into a pan of water.

It tends to spread out sideways, and also mix sideways with what is around it. The collision zone between an air mass and the air that it is moving into is known as a "front". When a front passes over, you get a change in the weather, and often rain. But dragging of wind near surface changes its direction to follow the rotation of the part of the Earth it N. In a sense, the detailed patterns of moving individual air masses are controlled by thin belts of higher altitude winds at between 3 and 12 km altitude in the atmosphere at the edge of the polar regions, and also at lower latitudes where the air from the ITCZ starts descending.

These eastward-trending winds arc the jet streams. They "push around" the lower-level air masses like chcss picccs. There is the subtropical jet stream and the polar jetstream in each hemisphere. That makes four jet streams in all. The jet streams are fed by air rising up into them moving in a polewards direction, and they are propelled east by the Coriolis force because the air comes from the faster-rotating lower latitudes.

Just as the winds move through the atmosphere, there are currents in the oceans. These too transport an immense amount of heat from the equator towards the higher latitudes. For the most part, ocean currents only exist because winds blow them along, pushing the water by friction. But part of the reason winds blow is that there are temperature differences at the surface, and ocean currents sometimes bring about such contrasts in temperature especially if there is upwelling of cool water from below.

So the water moves because the wind blows across it, yet the wind may blow because of the very same temperature contrasts that are brought about by the water moving! Wind skimming across the surface will drive the top layer of water as a current in a particular direction, and if it moves towards or away from the equator the current will eventually gel bent round by the Coriolis effect.

So, for example, in each of the world's main ocean basins there are eastward-curving currents that travel out from the equator because of this mechanism see below. But below the surface of a current being bent by the Coriolis effect, the deeper part of the current is being dragged by contact with the still waters below it.

That dragging tends to move it along in the direction that the earth is rotating locally. So because of this dragging, this deeper water in the ocean ends up traveling in a slightly different direction. The deeper you go, the more the angle of the current is diverted by dragging against water below, and different layers in the ocean can be traveling in quite different directions.

This is the same Ekman spiral effect as occurs in the atmosphere. Winds blow fast but per volume of air they don't carry very much heat. The heat-carrying capacity of ocean water is much greater, but the ocean currents move much more slowly than the winds. In fact, both ocean currents and winds are important in transporting heat around the earth's surface. The most prominent feature of the world's ocean circulation are currents that run in big loops, known as gyres. They start off in the tropics moving west, and curve round eastwards in the higher latitude parts of each ocean basin, eventually coming back down to the tropics and completing a circle.

These gyres originate from the powerful trade winds that blow towards the west in the outer tropics. These climate zones are so dry because moisture is rapidly evaporated from the air and there is very little precipitation.

C: Temperate. In this zone, there are typically warm and humid summers with thunderstorms and mild winters. These regions have warm to cool summers and very cold winters.

E: Polar. If you classify the United States into climate zones using all of this information, it actually looks something like this:. This is an illustration of the climate zones within the United States. The extra climate zone, labeled "H" on this map, is a special zone called the highlands. The highlands climate zone is characterized by weather that differs from the surrounding area because of mountains. Credit: NOAA modified.