Category Weather & Climate

          A Sundial shows the time of day by casting a shadow across its face. With the needle — the gnomon — of the sundial pointing north—south, the shadow indicates the time as the Sun passes through the sky from sunrise to sunset.

          When the earth rotates about its axis, the sun appears to “move” across the sky, causing objects to cast shadows. A sundial contains a gnomon, or a thin rod, that casts a shadow onto a platform etched with different times. As the sun changes relative positions over the course of a day, the rod’s shadows change as well, thus reflecting the change in time.

          If a sundial works based upon a rod’s shadow, then why can’t a simple stick in the ground work? As a result of the tilt of the earth’s axis, the visible movement of the sun changes daily.

          This can be accounted for in several ways. In a normal horizontal sundial, the base platform is kept steady, while the gnomon is moved to reflect the changes due to the earth’s axis tilt.

          Another method achieves the same effect by aligning the platform with the latitude and the gnomon perpendicular; mathematically, this is just the projection of the gnomon onto the platform.

          Sundials must be corrected across the span of a time zone. Every zone has a “reference longitude,” and with every degree of longitude away from the reference, the sundial is off by an additional 4 minutes.

          Thus, equation of time correction is employed in order to maintain a uniform time across the zone.

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          The number of hours of sunshine in a day is recorded on an instrument called a parheliometer. A solid glass ball focuses the Sun’s rays on to a strip of card. The intensified rays leave scorch marks on the card, moving along as the Sun moves through the sky. The longer the marks, the longer the period of sunshine.

         A sunshine recorder is a device that records the amount of sunshine at a given location or region at any time. The results provide information about the weather and climate as well as the temperature of a geographical area. This information is useful in meteorology, science, agriculture, tourism and other fields. It has also been called a heliograph.

          There are two basic types of sunshine recorders. One type uses the sun itself as a time-scale for the sunshine readings. The other type uses some form of clock for the time scale.

          Older recorders required a human observer to interpret the results; recorded results might differ among observers. Modern sunshine recorders use electronics and computers for precise data that do not depend on a human interpreter. Newer recorders can also measure the global and diffuse radiation.

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          Sometimes, intense amounts of electromagnetic energy are released from the Sun in the form of solar wind, or flares. The Earth is protected from solar wind — essentially an extremely hot gas — by its magnetic field, which stretches out into space. The particles of solar winds are known to affect satellites and even cause power blackouts on Earth. Scientists are still investigating the possible long-term effects of this activity on the Earth’s climate.

          Mt. Washington, New Hampshire is the windiest location in the United States, with an average wind speed of 35 mph. At this speed, trees start to sway and it becomes difficult to walk. Barrow Island, Australia has the highest wind speed ever recorded on Earth at 253 mph. This is strong enough to blow the roofs off of most buildings and uproot trees and shrubs. That is a pretty strong wind. But this is a drop in the bucket compared to the wind on the Sun.

          Solar wind is more than 4000 times as strong as the wind speed recorded on Barrow Island. Additionally, it reaches temperatures of around 1 million degrees Celsius, almost 15,000 times the hottest recorded temperature on Earth.

         The solar wind refers to the steady stream of highly charged particles that continually blow off the Sun in all directions. It is caused by the solar corona expanding into space. The corona is the outer atmosphere of the Sun. You can see it as a glowing halo around the Sun during a solar eclipse.

          The corona is so hot that the Sun’s gravity cannot hold it in. Instead, it streams off the Sun as protons and electrons shooting through space at speeds of around 400 km/s (about 1 million miles per hour). At that speed, you could travel from New York to Los Angeles in 10 seconds!

          The solar wind causes the Sun to lose more than 1 million tons of mass per second. That may seem like a really big number, but consider this: The Earth’s mass is about 6.5 sextillion tons. If you write that out it would be 6,500,000,000,000,000,000,000 tons. The Sun’s mass is 333,000 times that of Earth. If you think about it like that, 1 million tons per second isn’t actually that much.

          The solar wind escapes from coronal holes, which are generally found at the Sun’s poles. A coronal hole is an area in the corona that is thinner and less dense than the surrounding areas. It appears as a dark spot on the Sun’s surface since it is also a cooler temperature than the surrounding corona.

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          Some Scientists believe that sunspot activity may have an effect on the Earth’s weather. Sunspots seem to occur in cycles of 11 years. Research has shown that major periods of drought have occurred roughly every 22 years, or two sunspot cycles. We have yet to discover the exact relationship between the two.

          A new study in the journal Science by a team of international of researchers led by the National Center for Atmospheric Research have found that the sunspot cycle has a big effect on the earth’s weather. The puzzle has been how fluctuations in the sun’s energy of about 0.1 percent over the course of the 11-year sunspot cycle could affect the weather? The press release describing the new study explains:

          The team first confirmed a theory that the slight increase in solar energy during the peak production of sunspots is absorbed by stratospheric ozone. The energy warms the air in the stratosphere over the tropics, where sunlight is most intense, while also stimulating the production of additional ozone there that absorbs even more solar energy. Since the stratosphere warms unevenly, with the most pronounced warming occurring at lower latitudes, stratospheric winds are altered and, through a chain of interconnected processes, end up strengthening tropical precipitation.

          At the same time, the increased sunlight at solar maximum causes a slight warming of ocean surface waters across the subtropical Pacific, where Sun-blocking clouds are normally scarce. That small amount of extra heat leads to more evaporation, producing additional water vapor. In turn, the moisture is carried by trade winds to the normally rainy areas of the western tropical Pacific, fueling heavier rains and reinforcing the effects of the stratospheric mechanism.

          The top-down influence of the stratosphere and the bottom-up influence of the ocean work together to intensify this loop and strengthen the trade winds. As more sunshine hits drier areas, these changes reinforce each other, leading to less clouds in the subtropics, allowing even more sunlight to reach the surface, and producing a positive feedback loop that further magnifies the climate response.

          These stratospheric and ocean responses during solar maximum keep the equatorial eastern Pacific even cooler and drier than usual, producing conditions similar to a La Nina event. However, the cooling of about 1-2 degrees Fahrenheit is focused farther east than in a typical La Nina, is only about half as strong, and is associated with different wind patterns in the stratosphere.

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          Light from the Sun is made up of several different colours, each of which has its own wavelength. The wavelength of the blue part of the Sun’s light is shorter than the size of an oxygen atom. When the blue light waves hit the oxygen atoms in the Earth’s atmosphere, they are scattered, making the sky appear blue. The light waves of other colours (with greater wavelengths than blue) are also affected, but blue waves are scattered more than most.

          To understand why the sky is blue, we need to consider the nature of sunlight and how it interacts with the gas molecules that make up our atmosphere. Sunlight, which appears white to the human eye, is a mixture of all the colors of the rainbow. For many purposes, sunlight can be thought of as an electromagnetic wave that causes the charged particles (electrons and protons) inside air molecules to oscillate up and down as the sunlight passes through the atmosphere. When this happens, the oscillating charges produce electromagnetic radiation at the same frequency as the incoming sunlight, but spread over all different directions. This redirecting of incoming sunlight by air molecules is called scattering.

          The blue component of the spectrum of visible light has shorter wavelengths and higher frequencies than the red component. Thus, as sunlight of all colors passes through air, the blue part causes charged particles to oscillate faster than does the red part. The faster the oscillation, the more scattered light is produced, so blue is scattered more strongly than red. For particles such as air molecules that are much smaller than the wavelengths of visible light the difference is dramatic. The acceleration of the charged particles is proportional to the square of the frequency, and the intensity of scattered light is proportional to the square of this acceleration. Scattered light intensity is therefore proportional to the fourth power of frequency. The result is that blue light is scattered into other directions almost 10 times as efficiently as red light.

          When we look at an arbitrary point in the sky, away from the sun, we see only the light that was redirected by the atmosphere into our line of sight. Because that occurs much more often for blue light than for red, the sky appears blue. Violet light is actually scattered even a bit more strongly than blue. More of the sunlight entering the atmosphere is blue than violet, however, and our eyes are somewhat more sensitive to blue light than to violet light, so the sky appears blue.