Sunlight fluctuation

Diurnal and seasonal variations in solar intensity are, of course, of utmost importance to ecosystems. In the extreme polar regions there is no direct solar radiation at all for more than four months of the year, whereas near the equator the overall intensity of sunlight fluctuates less than 10% annually. The spectral energy distribution also varies with the season. For example, in July in the middle latitudes (ca. 40 ), the fraction of shorter-wave UV (290-315 nm) in the total solar radiation is more than three times higher than it is in December, due to the shorter path these easily scattered wavelengths have to traverse through the atmosphere. For similar reasons, shortwave UV is more intense at high elevations, particularly in the tropics where stratospheric ozone is less concentrated (Caldwell et al., 1980). 

Figure 22.4.8. The effect of sunlight fluctuations on the photothermal destruction of methyl ethyl ketone in the parabolic trough, photothermal reactor. MEK conversion, insolation level, and reactor temperature are plotted as a function of continuous outdoor illumination time.

The Phenomenon. In existing materials the electron density is not even constant inside a single phase. This is obvious for the liquid structure of amorphous regions. Nevertheless, even in crystalline phases lattice distortions and grain boundaries result in variations of the electron density about its mean value. In analogy to the sunlight scattered from the fluctuations of air density, X-rays are scattered from the fluctuations of electron density. 

You have probably identified factors such as vibration, dirt, sunlight, radiation, electric and magnetic fields and noise. Other factors, such as fluctuations in laboratory temperature and humidity, can have a more subtle effect. 

Worms work best at temperatures between 50 and 77°F (12-25°C). They will survive considerably lower temperatures, but their rate of producing compost will slow down. Keep a worm bin where temperatures do not fluctuate widely—out of direct sunlight in summer. Bring the bin into a garage or warm greenhouse in winter, or insulate it well before the cold weather starts. A worm bin with an integral drainage sump can be kept indoors, in a shed or porch, for example, and moved out in the summer. Other bins may need to be set on bare soil to absorb any excess liquid produced. 

Place the gas chromatograph away from drafts from air conditioning or heat vents, and, away from poorly insulated outside walls and direct sunlight, as all of these things can contribute to temperature fluctuations in the detector (and in the oven). 

The spectrophotometer should have a thermostat in situ during the experiment and be positioned away from the sun otherwise, the temperature of the spectrophotometer s inner electronics would increase, possibly introducing important errors in the optical density (OD) measurements. In addition, exposing the spectrophotometer to sunlight can induce continuous fluctuations in the OD, thus making any serious measurements impossible. 

Many of these problems can be avoided by hydrostatic testing before the entire system is assembled. Other important preventatives include adequate shelter for the system so that it is not exposed to extreme temperature fluctuations. Direct sunlight, for instance, will heat system components, then as the sun sets they will cool. This daily cycle can loosen the connec-... 

The total radiation from the Sun is continually changing, with variations of <0.2% from one month to the next. The timing and nature of these shorter-term fluctuations are consistent with the Sun s 27-day period of rotation. They occur because brighter or darker areas on the solar surface alter the amount of sunlight received at the Earth. This rotational variation of total solar radiation (see top panel in Figure 23.7) is superimposed on the 11-year sunspot cycle, which had an amplitude of about lWm-2 (0.1%) in the two most recent cycles (Haigh, 1996). The 11-year sunspot cycle is clearly evident in the second panel from the top of Figure 23.7. 

It is important to mention that effect of temperature is less important on absorption than on fluorescence spectra. However, it is better to keep the spectrophotometer thermostated along the experiment. Also, one should avoid placing the spectrophotometers in front of the sun. The sun will heat the electronics of the spectrophotometer inducing important errors in the optical density measurements. Also, exposing the spectrophotometer to the sunlight can induce continuous fluctuations in the optical density making impossible any serious measurement. 

Testing allows isolation of the individual parameters, a useful feature if the application involves a complex and varied environment or if the behavior of the prototype is not predictable. Accelerated simulation of in-service conditions is often feasible by applying environmental factors that are most influential in product lifetime, such as stresses, strains, temperature, and humidity fluctuations sunlight exposure and attack by solvents. 

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