Altitude and atmosphere

Ambient temperature, altitude and atmospheric conditions at the place of installation of electrical equipment are considered to be the service conditions for the equipment to operate and perform its duties. All electrical equipment is designed for specific service conditions and variations may influence its performance. Below we analyse the influence of such non-standard service conditions on the performance of equipment and the required safeguards to achieve its required performance. 

A-6 Altitude and Atmospheric Pressures, 578 A-7 Vapor Pressure Curves, 579 A-8 Pressure Conversion Chart, 580 A-9 Vacuum Conversion, 581 A-10 Decimal and Millimeter Equivalents of Fractions, 582 A-11 Particle Size Measurement, 582 . A-12 Viscosity Conversions, 583 A-13 Viscosity Conversion, 584 A-14 Commercial Wrought Steel Pipe Data, 585 A-15 ... 

The value of the global irradiation (Eq. 7.3) varies widely with the time of day, the time of year, the latitude, the altitude, and atmospheric conditions. As indicated previously, the maximum solar irradiation incident on the earth s atmosphere averages 1366 W m-2. Because of scattering and absorption of solar irradiation by atmospheric gases (see Fig. 4-5), S on a cloudless day with the sun directly overhead in a dust-free sky is about 1000 W m-2 at sea level. 

Jones, L. A., and Condit, H. R., Sunlight and skylight as determinants of photographic exposure. I. Luminous density as determined by solar altitude and atmospheric conditions. 

Most small Hquid helium containers are unpressurized heat leak slowly bods away the Hquid, and the vapor is vented to the atmosphere. To prevent plugging of the vent lines with solidified air, check valves of some sort are included in the vent system. Containers used for air transportation are equipped with automatic venting valves that maintain a constant absolute pressure with the helium container in order to prevent Hquid flash losses at the lower pressures of flight altitudes and to prevent the inhalation of air as the pressure increases during the aircraft s descent. Improved super insulation has removed the need for Hquid nitrogen shielding from almost all small containers. 

Extracted from U.S. Standard Atmosphere, 1976, National Oceanic and Atmospheric Administration, National Aeronautics and Space Administration and tte U.S. Air Force, Washington, 1976. Z = geometric altitude, T = temperature, P = pressure, g = acceleration of gravity, M = molecular weight, a = velocity of sound, i = viscosity, k = thermal conductivity, X = mean free path, p = density, and H = geopotential altitude. The notation 1.79.—5 signifies 1.79 X 10 . ... 

Figure 12-23. Barometric and atmospheric pressure at altitudes. See the appendix for detailed tabular listing.

The composition of the earth s atmosphere differs from day to day, from altitude to altitude, and from place to place. The largest variation is in the concentration of water vapor. Water evaporates continually from the hydrosphere, from the soil, from leaves, from clothes drying, etc. At intervals, parts of the atmosphere become chilled until the dew point or frost point is reached and then any vapor in excess of the saturation amount is precipitated as rain or snow. 

The actual pressure exerted by the atmosphere varies with altitude and weather. The pressure of the atmosphere at the cruising height of a commercial jetliner (10 km) is only about 200 Torr (about 0.3 atm), and so airplane cabins must be pressurized. A very low pressure atmospheric region, such as an area of low pressure on the weather chart in Fig. 4.6, typically has a pressure of about 0.98 atm at sea level. A typical region of high pressure is about 1.03 atm. 

In order to estimate the extent of ozone depletion caused by a given release of CFCs, computer models of the atmosphere are employed. These models incorporate information on atmospheric motions and on the rates of over a hundred chemical and photochemical reactions. The results of measurements of the various trace species in the atmosphere are then used to test the models. Because of the complexity of atmospheric transport, the calculations were carried out initially with one-dimensional models, averaging the motions and the concentrations of chemical species over latitude and longitude, leaving only their dependency on altitude and time. More recently, two-dimensional models have been developed, in which the averaging is over longitude only. 

Fig. 17-1 The global climate system, (a) Energy fluxes, including incoming solar radiation, reflected radiation, emitted longwave radiation (from an effective altitude of ca. 6 km), and atmospheric and oceanic heat flux toward the polar regions, (b) The atmospheric circulation corresponding to part (a). Refer back to Fig. 7-4 and associated text for a discussion of the general circulation.

At sea level, atmospheric pressure supports a mercury column approximately 760 mm in height. Changes in altitude and weather cause fluctuations in atmospheric pressure. Nevertheless, at sea level the height of the mercury column seldom varies by more than 10 mm, except under extreme conditions, such as in the eye of a hurricane, when the mercury in a barometer may fall below 740 mm. 

The gravitation of the earth attracts the gaseous components of the air, which exert a force, known as atmospheric pressure, on the surface of the planet. The pressure on any particular place on the earth s surface depends on the amount of air above the place. It follows that the atmospheric pressure decreases at high altitudes, increases at low altitudes and below sea level, and is also affected by changes in weather. Measuring the atmospheric pressure is usually done with physical instruments known as barometers (see Fig. 83). 

The hydrosphere (the Greek prefix hydro means water) is the great mass of water that surrounds the crust of the earth. Water is one of a few substances that, at the temperatures normal on the surface of the earth (which range between about -50 and 50°C), exists in three different states liquid, gas, and solid. Liquid water makes up the oceans, seas, and lakes, flows in rivers, and underground streams. Solid water (ice) occurs in the polar masses, in glaciers, and at high altitudes, and gaseous water (moisture) is part of the atmosphere (O Toole 1995). Liquid and solid water cover over 70% of the surface of the earth. 

The final column presents the radius of 50% mortality from fallout 1 hour after the explosion. Of all of the threats described, fallout is the hardest to predict because of the influence of local, regional, or even global weather patterns. The mushroom cloud can rise into the atmosphere as far as 80,000 feet, where wind and rain influence the time and location for fallout to occur.2 Individuals several miles from ground zero and well outside any radius presented in Table 5.1 can receive significant or even lethal radiation doses from fallout. However, while the air blast, thermal burns, and initial radiation are threats in all directions, fallout is a threat downwind from ground zero. Wind speed and direction vary at different altitudes, and it is safest to assume that fallout is a potential threat in all directions from ground zero. Individuals outside the blast zone generally will have several minutes to an hour or more to seek shelter before fallout arrives. 

The 8 N- and 8 0-values of atmospheric N2O today, range from 6.4 to 7.0%c and 43 to 45.5%c (Sowers 2001). Terrestrial emissions have generally lower 8-values than marine sources. The 8 N and 8 0-values of stratospheric N2O gradually increase with altitude due to preferential photodissociation of the lighter isotopes (Rahn and Wahlen 1997). Oxygen isotope values of atmospheric nitrous oxide exhibit a mass-independent component (Cliff and Thiemens 1997 Clifif et al. 1999), which increases with altitude and distance from the source. The responsible process has not been discovered so far. First isotope measurements of N2O from the Vostok ice core by Sowers (2001) indicate large and 0 variations with time (8 N from 10 to 25%c and 8 0 from 30 to 50%c), which have been interpreted to result from in situ N2O production via nitrification. 

The maximum concentration of ozone in the stratosphere (or the ozone layer) is about 9 ppm at an altitude of about 35 km. That is, the concentration of ozone in the so-called ozone layer is still very low. Transport of ozone in the atmosphere modifies ozone concentration levels at each altitude and latitude. It is emphasized that the steady-state concentration of O3 in the stratosphere is not the thermodynamic equilibrium concentration, but is established by kinetics of photochemical reactions. 

FIGURE 3.13 Approximate regions of maximum light absorption of solar radiation in the atmosphere by various atomic and molecular species as a function of altitude and wavelength with the sun overhead (from Friedman, 1960). 

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