Category Science

WHAT ARE THE SEASONS IN TEMPERATE ZONES?

          Spring brings warmer weather. Flowers come into bloom, trees regain their leaves and blossom. Some sunshine will be accompanied by cool breezes and light showers of rain.

          In summer, the days are long and the land receives a lot of sunshine. Temperatures are high and trees and plants are green and leafy. Thunderstorms will bring rain.

          Temperatures drop during autumn, as the days begin to get shorter. Some places may experience violent storms at this time of year. Leaves go brown and fall from the trees.

          In winter, the days are short and the skies may be filled with dark, grey cloud. Many trees are bare, and the ground is often covered with frost, snow or ice.

          In geography, the temperate or tepid climates of Earth occur in the middle latitudes, which span between the tropics and the polar regions of Earth. In most climate classifications, temperate climates refer to the climate zone between 35 and 50 north and south latitudes (between the subarctic and subtropical climates).

          These zones generally have wider temperature ranges throughout the year and more distinct seasonal changes compared to tropical climates, where such variations are often small. They typically feature four distinct seasons, Summer the warmest, Autumn the transitioning season to Winter, the colder season, and Spring the transitioning season from winter back into summer. In the northern hemisphere, the year starts with winter, transitions in the first half year through spring into summer, which is in mid-year, then at the second half year through autumn into winter at year-end. In the southern hemisphere, the seasons are swapped, with summer between years and winter in mid-year.

          The temperate zones (latitudes from 23.5° to the polar circles at about 66.5°, north and south) are where the widest seasonal changes occur, with most climates found in it having some influence from both the tropics and the poles. The subtropics (latitudes from about 23.5° to 35°, north and south) have temperate climates that have the least seasonal change and the warmest in winter, while at the other end, Boreal climates located from 55 to 65 north latitude have the most seasonal changes and long and severe winters.

          In temperate climates, not only do latitudinal positions influence temperature changes, but sea currents, prevailing wind direction, continentally (how large a landmass is), and altitude also shape temperate climates.

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WHAT CAUSES THE SEASONS?

          As the Earth orbits the Sun, different parts of the planet face towards or away from it, receiving varying amounts of heat. The Earth is tilted at an angle and always tilts the same way. This means that when the Earth is on one side of the Sun, the Northern Hemisphere leans towards the Sun and experiences summer. At the same time, the Southern Hemisphere is leaning away from the Sun and is having winter weather. Six months later, the Earth is on the other side of the Sun and the situation is reversed. Spring begins in a hemisphere at the moment at which it starts to lean towards the Sun; Autumn starts when it begins to lean away from it.

           The seasons have nothing to do with how far the Earth is from the Sun.  If this were the case, it would be hotter in the northern hemisphere during January as opposed to July.  Instead, the seasons are caused by the Earth being tilted on its axis by an average of 23.5 degrees (Earth’s tilt on its axis actually varies from near 22 degrees to 24.5 degrees).  Here’s how it works:

          The Earth has an elliptical orbit around our Sun.  This being said, the Earth is at its closest point distance wise to the Sun in January (called the Perihelion) and the furthest in July (the Aphelion).  But this distance change is not great enough to cause any substantial difference in our climate.  This is why the Earth’s 23.5 degree tilt is all important in changing our seasons.  Near June 21st, the summer solstice, the Earth is tilted such that the Sun is positioned directly over the Tropic of Cancer at 23.5 degrees north latitude.  This situates the northern hemisphere in a more direct path of the Sun’s energy.  What this means is less sunlight gets scattered before reaching the ground because it has less distance to travel through the atmosphere.  In addition, the high sun angle produces long days.  The opposite is true in the southern hemisphere, where the low sun angle produces short days.  Furthermore, a large amount of the Sun’s energy is scattered before reaching the ground because the energy has to travel through more of the atmosphere.  Therefore near June 21st, the southern hemisphere is having its winter solstice because it “leans” away from the Sun.

          Advancing 90 days, the Earth is at the autumnal equinox on or about September 21st.  As the Earth revolves around the Sun, it gets positioned such that the Sun is directly over the equator.   Basically, the Sun’s energy is in balance between the northern and southern hemispheres.  The same holds true on the spring equinox near March 21st, as the Sun is once again directly over the equator. 

          Lastly, on the winter solstice near December 21st, the Sun is positioned directly over the Tropic of Capricorn at 23.5 degrees south latitude.  The southern hemisphere is therefore receiving the direct sunlight, with little scattering of the sun’s rays and a high sun angle producing long days.  The northern hemisphere is tipped away from the Sun, producing short days and a low sun angle.

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WHY IS IT COLD AT THE TOP OF A MOUNTAIN?

          Because the air is warmed by heat rising from the ground, the air temperature at the top of a mountain will always be lower than it is at the bottom.

          The lowering of temperature as you reach higher altitudes is due to the change in atmospheric pressure. You may be aware that the air around us is constantly exerting pressure on us due to there being lots of air above us weighing down on us. It sounds a bit strange to say that air weighs something but it does, we just don’t feel it because it is what we’re used to, just like gravity is constantly pulling us down.

          There is a direct relationship between temperature and pressure. If you increase the pressure of a system then the temperature will get higher. This is why bicycle pumps can get hot after use. Decrease the pressure and the temperature goes down as can be experienced letting the air out of a balloon very quickly, the balloon gets cold.
As you go higher up, the pressure gets less and less due to there being less air above you weighing down on you, therefore the temperature goes down too.

         If heat rises, then why is it so cold at the top of a mountain? Heat does indeed rise. More specifically, a mass of air that is warmer than the air around it expands, becomes less dense, and will therefore float atop the cooler air. This is true at any altitude, and if this were the only factor at play, one would expect the atmosphere to get uniformly hotter with altitude, like the second floor of a house.

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WHAT ARE THERMALS?

          Rising currents of warm air are called thermals. They are useful to glider pilots, who use them to help lift their craft into the air. Thermals can form over “hot spots” on the ground, such as a freshly ploughed field. Some large birds make use of thermals to circle in the air.

          The warmer air nearer to the surface expands, becoming less dense than the surrounding air. The lighter air rises and cools due to its expansion in the lower pressure at higher altitudes. It stops rising when it has cooled to the same temperature as the surrounding air.

          Associated with a thermal is a downward flow surrounding the thermal column. The downward-moving exterior is caused by colder air being displaced at the top of the thermal.

          The size and strength of thermals are influenced by the properties of the lower atmosphere (the troposphere). Generally, when the air is cold, bubbles of warm air are formed by the ground heating the air above it and can rise like a hot air balloon. The air is then referred to as unstable. If there is a warm layer of air higher up, an inversion can prevent thermals from rising high and the air is said to be stable.

 

 

          Thermals are often indicated by the presence of visible cumulus clouds at the top of the thermal. When a steady wind is present, thermals and their respective cumulus clouds can align in rows oriented with wind direction, sometimes referred to as “cloud streets” by soaring and glider pilots. Cumulus clouds are formed by the rising air in a thermal as it ascends and cools, until the water vapor in the air begins to condense into visible droplets. The condensing water releases latent heat energy allowing the air to rise higher. Very unstable air can reach the level of free convection (LFC) and, thus rise to great heights condensing large quantities of water and so forming showers or even thunderstorms. The latter are dangerous to any aircraft.

          Thermals are one of the many sources of lift used by soaring birds and gliders to soar.

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WHAT ARE CONVECTION CURRENTS?

         Where cool air lies above a warm area of land, the air will be heated. As the air warms up, it expands, becomes less dense (its molecules become less tightly packed) and it begins to rise. The surrounding cooler air replaces the rising warm air. As the warm air rises, it cools down and its density increases. These currents of warm and cold air are called convection currents.

           A convection current is a process which involves the movement of energy from one place to another. It is also called to as convection heat transfer. What is the reason that makes you feel hotter when placing hands above a campfire or when sitting next to it? Or, why is the movement of liquid so rapid when water is boiled in a pot? These things happen as a result of the Convection Currents.

          The convection currents tend to move a fluid or gas particles from one place to another. These are created as a result of the differences occurring within the densities and temperature of a specific gas or a fluid. Convection is one among the forms of heat transfers, of which the other two are radiation and conduction. Convection process only happens in the fluids i.e. in liquids and gases. This happens due to the reason that molecules within liquids or gases are free to move.

          The heat energy can be transferred by the process of convection by the difference occurring in temperature between the two parts of the fluid. Due to this temperature difference, the hot fluids tend to rise, whereas cold fluids tend to sink. This creates a current within the fluid called as Convection current.

          The mantle within the earth’s surface flows due to convection currents. These currents are mainly caused by a very hot material present in the deepest part of the mantle which rises upwards, then cools, sinks, again and again, repeating the same process of heating and rising.

          Hence Convection Current is defined as “a process of continuous heating up of liquids or gases by the process called as Convection. “

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WHAT IS ALBEDO?

            THE RELATIVE “shininess” of the Earth’s surface in a certain area will affect the local temperature — this is called albedo. Icy, snowy areas reflect most of the radiation of the Sun and remain cold. Forests and areas of bare soil absorb the radiation and tend to stay warm.

            Albedo can be defined as a way of quantifying how much radiation is reflected from the surface. It is a comparison between the reflection radiations from the surface to the amount of radiation that hits it. This term also refers to the quantity of radiation generated by electromagnetic rays which consequently reflects away.

Seasonal Effects on Albedo

Summer

            To understand albedo better, we look at two scenarios. One, if you walk barefoot on the black soil during summer, you will feel a lot of heat and can even get burnt because the surface is absorbing and retaining more heat. Another person walking on white soil during the same season will not be burnt. This is basically because white surface tends to reflect more heat and absorb very little of it. Equally, if you touch a black car in summer it will feel much hotter than touching a white car. This is because black absorbs and retains heat while white car surface will reflect back the solar rays.

Winter

            During this season, it is generally wet with either water or ice. Water reflects approximately 6% of the light and absorbs the rest. Ice, on the other hand, reflects 50% to 60% of the incoming solar heat, thereby remaining cooler. A snow-covered area reflects a lot of radiation, which is why skiers having a risk of getting sunburns while on the slopes. Albedo diminishes when the snow-covered places start to warm up.

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