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 Now online (1)recycle ...and 214 guests Last 5 registered Oplandisks nothingstar N_loop yipe foxtrotromeo Browse members... |
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Solar radiation drives atmospheric circulation. Since solar radiation represents almost all the energy available to the earth, accounting for solar radiation and how it interacts with the atmosphere and the earth's surface is fundamental to understanding the earth's energy budget. Solar radiation reaches the earth's surface either by being transmitted directly through the atmosphere ("direct solar radiation"), or by being scattered or reflected to the surface ("diffuse sky radiation"). About 50 percent of solar (or shortwave) radiation is reflected back into space, while the remaining shortwave radiation at the top of the atmosphere is absorbed by the earth's surface and re-radiated as thermal infrared (or longwave) radiation. The intensity of solar radiation striking a horizontal surface is measured by a pyranometer. The instrument consists of a sensor enclosed in a transparent hemisphere that records the total amount of shortwave incoming solar radiation. That is, pyranometers measure "global" or "total" radiation: the sum of direct solar and diffuse sky radiation. Incoming (or "downwelling") longwave radiation is measured with a pyrgeometer. Outgoing ("upwelling") longwave radiation is measured in various ways, such as with pyrgeometers or with sensors that measure the temperature of the surface. |
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Thanks for the information. |
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My ulcer likes pie |
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The Principle Of Additive Synthesis The concept underlying additive synthesis is very simple, and I can best explain it by turning all the way back to Synth Secrets Part 1 (Sound On Sound May '99). In this, I showed that you could represent any waveform as a set of sine waves. For a simple harmonic oscillator, each of these sine waves has a frequency that is an integer multiple of the fundamental frequency, and we call these the 'harmonics' of the sound. Just to refresh our memory, let's take the most common synthesizer waveform -- the sawtooth wave -- as an example. Figure 1 shows an idealised sawtooth wave. You'll never see this in nature because the universe doesn't allow physical objects such as air molecules or the cones of a 4x12 cabinet to accelerate or move infinitely quickly. Unfortunately, this is what the ideal waveform requires as it moves instantaneously from its nadir to its zenith, but we're not going to worry about that. Now, you may recall that this waveform has a simple harmonic relationship, expressed as follows: every harmonic is present, and the amplitude of the nth harmonic is 1/n times that of the fundamental. We draw this as shown in Figure 2. It's important that you fully appreciate that, within limits, Figures 1 and 2 represent exactly the same thing. I have truncated the number of harmonics in Figure 2 to just nine whereas there should, in theory, be an infinite series, but neither my screen nor your copy of SOS is infinitely wide, so this will have to do. If you're worried that truncating the series so severely will ruin my argument, take a look at Figure 3. This is the waveform generated by the nine harmonics in Figure 2, and no others. It's remarkably close to the ideal sawtooth, don't you think? |
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figure 1, figure 2? figure 3? |
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That's better! |
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