There is some evidence to indicate a second layer above the normal E layer located at about 150 kilometers, and called the E2-layer.
The E layer has been observed to be subdivided into two or more layers, and these are then assigned the designation, E1, E2, etc. Patchy and intermittent clouds of fairly high ionization, known as sporadic E layers, also form in the same general region.
The earth axes may remain fixed or may move with the aircraft or other object.
Current patterns of quasi-circular form and extending over areas the size of whole continents have been identified and are known to be closely related to solar-induced variations in the extreme upper atmosphere.
A unit of angular drift, as of a gyro, equal to the rate of angular movement of the earth with respect to the stars, 15° per hour.
Spectroscopic observations reveal that earthlight is relatively richer in blue light than is direct sunlight; this condition results from the fact that an appreciable part of the total earth reflection is backward-scattered light which, in accordance with Rayleigh law, is relatively rich in the blue and poor in the red.
See anomaly.
1. Of any conic, the ratio of the length of the radius vector through a point on the conic to the distance of the point from the directrix.
2. Of an ellipse, the ratio of the distance between the center and focus of an ellipse to its semimajor axis. Also called numerical eccentricity.
The eccentricity e of an ellipse can be computed by the formula
3. Of an ellipse, the distance between the center and the focus. Also called linear eccentricity.
2. In radar, a pulse of reflected radio frequency energy; the appearance on a radar indicator of the energy returned from a target. Also called blip.
2. The apparent cutting off, wholly or partially, of the light from a luminous body by a dark body coming between it and the observer.
1. The first type of eclipse is exemplified by a lunar eclipse, the moon passing through the shadow cast by the earth; or by the passage of a satellite into the shadow cast by its planet; but when the satellite actually passes directly behind its planet, it may properly be termed an occultation.
2. The second type of eclipse is exemplified by a solar eclipse, caused by the moon passing between the sun and the earth. If the relative positions and distances are such that at a point on the earth the sun is completely obscured, the eclipse is total; if the distances are such that, when in line with the sun, the moon is surrounded by a ring of light, the eclipse is annular; and when the moon passes to one side of a straight line from sun to observer and shows a crescent of light, it is a partial eclipse.
The ecliptic is a great circle of the celestial sphere inclined at an angle of about 23° 27' to the celestial equator.
The points 90° from the ecliptic are the north and south ecliptic poles. Angular distance north or south of the ecliptic, analogous to latitude, is celestial latitude. Celestial longitude is measured eastward along the ecliptic from the vernal equinox through 360°.
Ideally the environment furnishes the sustenance for life, and the resulting waste products revert or cycle back into the environment to be used again for the continuous support of life.
2. A volume of space surrounding the Sun, extending from the orbit of Venus past the orbit of Mars, in which some biologists believe conditions are favorable for the development and maintenance of life.
,
is mean velocity. Also called fluctuation velocity. Over the same interval which defines the mean velocity, the average value of the eddy velocity is necessarily zero.
The value of the coefficient of eddy viscosity (an exchange coefficient) is of the order of 104 square centimeters per second, or 100,000 times the molecular kinematic viscosity.
by the equation:
2 / 4
The effective area of an ideal antenna is equal to its physical area S. In practice, A/S for microwave antennas is always less than one, a representative value for paraboloids being 0.6.
2. Same as scattering cross section.
For example, an earth satellite orbiting at 250 miles altitude remains within the ionosphere, but because the air particles are so sparse at this altitude as to cause no appreciable friction of deflection, the satellite may be considered to be outside the effective atmosphere. For movement of air vehicles the effective atmosphere ends at the aeropause (which see).
2. = optically effective atmosphere.
A fictitious exhaust velocity that would theoretically produce the observed value of jet thrust.
The effective exhaust velocity ce is determined by the equation
The ratio of the neutron flux in a nuclear reactor to that supplied by a neutron source.
This average takes into account delayed as well as prompt neutrons.
Under conditions of standard refraction the effective radius of the earth is 8.5 * 106 meters, or four-thirds the geometrical radius. If the effective radius is used in ray tracing diagrams, the rays may be drawn as though they were traveling in straight lines.
Effective temperature is always less than actual temperature.
2. In physiology, the temperature at which motionless, saturated air would induce, in a sedentary worker wearing ordinary indoor clothing, the same sensation of comfort as that induced by the actual conditions of temperature, humidity, and air movement. Compare sensible temperature, standard operative temperature, operative temperature.
Effective temperature is used as a guide in air-conditioning practice, and, on the comfort chart (American Society of Heating and Air Conditioning Engineers) it appears as a family of curves which serves as one coordinate in defining comfort zones.
It is to be emphasized that this amount is a positive quantity, of the order of several tenths of a langley per minute, at all times of day (except under conditions of low overcast clouds). It typically attains its diurnal maximum during the midday hours when high soil temperatures create high rates of outgoing terrestrial radiation. (For this reason the synonym nocturnal radiation is apt to lead to slight confusion.) However, in daylight hours the effective terrestrial radiation is generally much smaller than the insolation, while at night it typically dominates the energy budget of the earth's surface.
) Of a device with respect to a physical quantity which may be stored, transferred, or transformed by the device, the ratio of the useful output of the quantity to its total input.
Unless specifically stated otherwise, the term efficiency means efficiency with respect to power.
2. A satellite, probe, or unmanned spacecraft, a boxlike unit, usually containing recording instruments or records of observed data, which may be ejected and returned to earth by a parachute or other deceleration device.
In Ekman's analysis (see Ekman spiral), the coefficient of eddy viscosity is assumed constant within this layer; subsequent calculations have relaxed this assumption.
Elastomers are used as pliable components, as in tires, seals, or gaskets.
In electromagnetics, the term dipole is often applied to two equal and opposite oscillating charges an infinitesimal distance apart; in this sense, it is synonymous with an electric-current element.
An electric field is a vector field in which magnitude of the vector is the electric-field strength and the vector is parallel to the lines of force.
2. = electric-field strength. See atmospheric electric field.
The electric-field strength of the atmosphere is commonly referred to as the atmospheric electric field.
A convenient unit of electrical distance is the light microsecond or approximately 983 feet (300 meters). In the use of this unit, electrical distance is numerically equal to transmission time in microseconds.
Electrical engines can be classified as electrothermal, electrostatic, or electromagnetic, depending on the nature of the accelerating device.
Microphones and earphones are electroacoustic transducer.
2. In a semiconductor device, an element that performs one or more of the functions of emitting or collecting electrons or holes, or of controlling their movements by an electric field.
3. In electron tubes, a conducting element that performs one or more of the functions of emitting, collecting or controlling, by an electromagnetic field, the movements of electrons or ions. See anode (electron tubes) and cathode.
In gas electroluminescence, light is emitted when the kinetic energy of electron or ions accelerated in an electric field is transferred to the atoms or molecules of the gas in which the discharge takes place.
Magnetoelectric pertains to electricity produced by or associated with magnetism.
The division of this continuum of wavelengths (or frequencies) into a number of named subportions is rather arbitrary and, with one or two exceptions, the boundaries of the several subportions are only vaguely defined. Nevertheless, to each of the commonly identified subportions there correspond characteristic types of physical systems capable of emitting radiation of those wavelengths. Thus, gamma rays are emitted from the nuclei of atoms as they undergo any of several types of nuclear rearrangements; visible light is emitted, for the most part, by atoms whose planetary electrons are undergoing transitions to lower energy states; infrared radiations are associated with characteristic molecular vibrations and rotations; and radio waves, broadly speaking, are emitted by virtue of the accelerations of free electrons as, for example, the moving electrons in a radio antenna wire.
2. The science dealing with the physical relations between electricity and magnetism.
The mass of the electron is approximately equal to 1/1836 that of a hydrogen atom; its theoretical rest mass (symbol me) is equal to 9.109 3897(54) * 10-31 kg and its rest energy is equal to 0.510 999 06(15) million electron-volt. The charge-to-mass ratio for the electron (symbol e/me) is 1.758796 cc½ / g½.
The term electron is usually reserved for the orbital or extranuclear particle, whereas the term beta particle refers to a nuclear electron.
*The numbers in bold type were taken from the 1987 publication of Fundamental Physical Constants: 1986 CODATA (Committee on Data for Science and Technology of the International Council of Scientific Unions) Recommended Values issued by the U. S. Department of Commerce, National Bureau of Standards.
"Digits in parentheses represent one standard deviation uncertainty in the final digits of the given value, based on a least-squares analysis with five variables and 17 degrees of freedom."
An avalanche cannot begin until the local electric field strength is high enough to accelerate a free electron to the minimum ionizing speed in the space and time interval corresponding to one mean free path of the electron, for upon collision, the electron usually loses its forward motion in the direction of the field.
A unit of energy equal to the energy required to move an electron through a potential difference of 1 volt. Often shortened to volt.
One electron volt equals 1.6020 * 10-9 joule.
2. Of or pertaining to electronics, i.e., to that branch of physics that treats of the emission, transmission, behavior, and effects of electrons, especially as applied by means of vacuum tubes, cathode-ray tubes, photoelectric cells, and the like, together with the associated electrical devices.
A crossed baseline interferometer system giving azimuth and elevation angles.
This system was designed as an acquisition aid for theodolites. The EMA equipment operates on the Dovap transponder frequency.
2. In chemistry, a substance which cannot be broken down by ordinary chemical means into simpler components.
3. In an electron tube, a constituent part of the tube that contributes directly to the electrical operation of the tube.
4. In a circuit, any electrical device (such an inductor, resistor, capacitor, generator, line, electron tube) with terminals at which it may be directly connected to other electrical devices.
5. In a semiconductor device, any integral part of the semiconductor device, any integral part of the semiconductor device that contributes to its operation.
6. = orbital element.
The celestial pole below the horizon is called depressed pole.
The orbits of planets, satellites, planetoids, and comets are ellipses, the primary being at one focus.
It is so named from the fact that it can be formed by revolving an ellipse about one of its axes.
An elliptically polarized wave is equivalent to two superposed plane polarized waves of simple sinusoidal form in which the displacements lie in perpendicular planes and are 90° apart in phase.
The amount by which a spheroid differs from a sphere or an ellipse differs from a circle, calculated by dividing the difference in the length of the axes by the length of the major axis. Also called compression. See flattening.
2. As a measure of elliptical polarization, the power ratio of the maximum to the minimum electric vectors of an elliptically polarized antenna.
The greatest elongation of such a body is its maximum angular distance from the sun before it starts back toward conjunction. The direction of the body east or west of the sun is usually specified, as greatest elongation east.
An electronic device which indicates the departure of a rocket from a predetermined trajectory.
2. With respect to electric propulsion and energy conversion, the sending out of charged particles from a surface causing the generation of these particles; e.g., emission of ions from an ionizing surface in ion engines.
Each radiating substance has a unique, characteristic emission spectrum, just as every medium of transmission has its individual absorption spectrum.
) A property of a material, measured as the emittance of a specimen of the material that is thick enough to be completely opaque and has an optically smooth surface.
) 1. The radiant flux per unit area emitted by a body.
2. The ratio of the emitted radiant flux per unit area of a sample to that of a blackbody radiator at the same temperature and under the same conditions.
Spectral emittance refers to emittance measured at a specified wavelength.
Because of the two common meanings of emittance, it should be defined when used unless the context allows no misinterpretation.
During transitions from one energy level to another, quanta of radiant energy are emitted or absorbed, their frequency depending on the difference between the energy levels.
Enhanced radiation is usually accompanied by many bursts.
The change in enthalpy measures the heat imparted to a system during a reversible isobaric process:
,
/)
In an adiabatic process, the entropy increases if the process is irreversible and remains unchanged if the process is reversible. Thus, since all natural processes are irreversible, it is said that in an isolated system the entropy is always increasing as the system tends toward equilibrium, a statement which may be considered a form of the second law of thermodynamics.
2. In communication theory, average information content.
2. The bounds within which a certain system can operate as a flight envelope, especially a graphic representation of these bounds showing interrelationships of operational parameters.
Environments are usually specified by a range of values, and may be either natural or artificial.
T
/ z or occasionally
T / p,
where p is pressure. See autoconvective
lapse rate, superadiabatic
lapse rate. The concept may be applied to other atmospheric variables (e.g., lapse rate of density) if these are specified. The environmental lapse rate is determined by the distribution of temperature in the vertical at a given time and place and should be carefully distinguished from the process lapse rate, which applies to an individual air parcel.
A publication giving similar information useful to a navigator is called an almanac.
This was the fundamental unit of time of the International System of Units of 1960: 1/31556925.9747 of the tropical year defined by the mean motion of the sun in longitude at the epoch 1900 January 0 day 12 hours. See ephemeris time.
See second for the definition of the latest unit of time in the SI system or look on the WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI).
The uniform measure of time defined by the laws of dynamics and determined in principle from the orbital motions of the planets, specifically the orbital motion of the earth as represented by Newcomb's Tables of the Sun. Compare universal time.
Beginning with the volume for 1960 the American Ephemeris and Nautical Almanac uses ephemeris time as the tabular argument in the fundamental ephemerides of the sun, moon, and planets.
A gravitational ephemeris expresses the position of a celestial body as a function of ephemeris time; and, at any instant, the measure of ephemeris time is the value of the argument at which the ephemeris position is the same as the actual position at the instant. The ephemeris time at any instant is obtained from observation by directly comparing observed position of the sun, moon, and planets with gravitational ephemerides of their coordinates; observations of the moon are the most effective and expeditious for this purpose. An accurate determination, however, requires observations over a more or less extended period; in practice, it takes the form of determining the time correction
T that must be applied to universal time (U.T.) to obtain ephemeris time: T
The fundamental epoch from which ephemeris time is reckoned is the epoch that Newcomb designated as 1900 January 0, Greeenwich mean noon, but which actually is 1900 January 0 day 12 hours E.T.; the instant to which this designation is assigned is the instant near the beginning of the calendar year A.D. 1900 when the geometric mean longitude of the Sun referred to the mean equinox of data was 279 degrees 41 minutes 48.04 seconds. Ephemeris time is the measure of time in which Newcomb's Tables of the Sun agree with observation.
The primary unit of ephemeris time is the tropical year, defined by the mean motion of the sun in longitude at the epoch 1900 January 0 day 12 hours E.T.; its length in ephemeris days is determined by the coefficient of T in Newcomb's expression for the geometric mean longitude of the sun L referred to the mean equinox of date, given among the elements of the sun.
This instrument has been adopted by the U.S. Weather Bureau for station use.
For instrumentation of NOAA's Surface Radiation Research Branch see http://www.srrb.noaa.gov/instrument/instpage.htm
A large number of such equations have been devised to apply equally to gaseous and liquid phases throughout a wide range of temperatures and pressures. Of these, the simplest are the perfect gas law and Van der Waal equation.
The terrestrial equator is 90° from the earth's geographical poles; the celestial equator or equinoctial is 90 ° from the celestial poles; the galactic equator or galactic circle is 90° from the galactic poles. The astronomical equator is a line connecting points having 0° astronomical latitude; the geodetic equator connects points having 0° geodetic latitude. The expression terrestrial equator is sometimes applied to the astronomical equator. The geodetic equator is shown on charts. A fictitious equator is a reference line serving as the origin for measurement of fictitious latitude. A transverse or inverse equator is a meridian the plane of which is perpendicular to the axis of a transverse projection. An oblique equator is a great circle the plane of which is perpendicular to the axis of an oblique projection. A grid equator is a line perpendicular to a prime grid meridian at the origin. The magnetic equator or aclinic line is that line on the surface of the earth connecting all points at which the magnetic dip is zero. The geomagnetic equator is the great circle 90° from the geomagnetic poles of the earth.
In meteorology the reference is to water substance unless otherwise specified.
That point occupied on or about March 21, when the sun's declination changes from south to north, is called vernal equinox, March equinox, or first point of Aries; that point occupied on or about September 23, when the declination changes from north to south, is called autumnal equinox, September equinox, or first point of Libra.
Equinox is often used to mean vernal equinox, when referring to the origin of measurement of right ascension and celestial longitude.
2. That instant the sun occupies one of the equinoctial points.
2. The number of places required to express in binary notation a quantity in some other notation.
e = Ta, e (1000 / p)0.286
e is the equivalent potential temperature; Ta, e is the adiabatic equivalent temperature; and p is the pressure in millibars. This temperature is conservative with respect to dry-adiabatic and pseudoadiabatic processes.
2. Adiabatic equivalent temperature; The temperature that an air parcel would have after undergoing the following (physically unrealizable) process: dry-adiabatic expansion until saturated; pseudoadiabatic expansion until all moisture is precipitated out; dry-adiabatic compression to the initial pressure. This is the equivalent temperature as read from a thermodynamic chart and is always greater than the isobaric equivalent temperature:
The formula for equivalent width W is
where A is the fraction of incident radiation which is absorbed at
any wavelength, and 1
and 2 are wavelengths,
on opposite sides of the line or band, where the absorption has dropped to
zero. An equivalent-barotropic atmosphere is, accordingly, an atmosphere in which the wind does not change direction with height and consequently one in which the contours and isotherms (on isobaric surfaces, for example) are everywhere parallel. In such an atmosphere, the vertically averaged motions are presumably equivalent to those at some intermediate level, the equivalent-barotropic level. In terms of the motion at this level, assumed to be an isobaric surface, the behavior of the equivalent-barotropic model may be described by a single equation (the vorticity equation) in a single unknown (the height of the isobaric surface). See barotropic vorticity equation.
See constellation.
2. = terrestrial radiation.
107 (ten million) erg s-1 (ergs per second) = 1 watt. Also, 1 Calorie = 4.2 x 1010 (42 billion) ergs.
See constellation.
An example of an erratic error is backlash in a gear train.
A quantity (equal in magnitude to the error) added to a calculated or observed value to obtain the true value is called a correction.
2. In a computer or data-processing system, any incorrect step, process, or result.
In addition to the mathematically usage, in the computer field the term is also commonly used to refer to machine malfunctions as machine errors and to human mistakes as human errors. It is frequently helpful to distinguish between these as follows: errors result from approximations used in numerical methods; mistakes result from incorrect programming, coding, data transcription, manual operation, etc.; malfunction result from failures in the operation of machine components such as gates, flip-flops, amplifiers, etc.
In radar use, error signals are obtained from selsyns and from automatic gain control circuits and are used to control a servo system so that the resultant motions tend to correct the error.
Several forms of erythema can be caused by undue exposure of the human body to weather elements. The most common is sunburn.
The escape tower is of such length as to protect the capsule from the heat of the escape rocket in case the rocket is used to separate the capsule from the booster vehicle during ascent. The tower is ultimately separated from the capsule if ascent is normal.
where G is the universal gravitational constant (see gravitation); m is the mass of the planet or star; and r is the radial distance from the center of the planet or star. Also called escape speed. Escape velocity from Earth is 7 miles/sec; from Mars it is 3.2 miles/sec; and from the Sun it is 390 miles/sec. In order for a celestial body to retain an atmosphere for long periods of time, the mean velocity of the atmospheric molecules must be considerably below the escape velocity.
Eulerian coordinates are to be distinguished from Lagrangian coordinates. The particular coordinate system used to identify points in space (Cartesian, cylindrical, spherical, etc.) is quite independent of whether the representation is Eulerian or Lagrangian.
In meteorology, evaporation usually is restricted in use to the change of water from liquid to gas, while sublimation is used for the change from solid to gas as well as from gas to solid.
According to the kinetic theory of gases, evaporation occurs when liquid molecules escape into the vapor phase as a result of the chance acquisition of above average, outward-directed, translational velocities at a time when they happen to lie within about one mean free path below the effective liquid surface. It is conventionally stated that evaporation into a gas ceases when the gas reaches saturation. In reality, net evaporation does cease, but only because the numbers of molecules escaping from and returning to the liquid are equal, that is, evaporation is counteracted by condensation.
Energy is lost by an evaporating liquid; and, when no heat is added externally, the liquid always cools. The heat thus removed is termed the latent heat of vaporization.
2. The number of molecules of a given substance evaporated per second per square centimeter from the free surface of the condensed phase.
Evection amounts to 1 degree 15 minutes in the moon's longitude at maximum.
The exchange-coefficient hypothesis states that the mean eddy flux per unit area of a conservative quantity (suitability expressed) is proportional to the gradient of the mean value of this quantity, that is,
/
dN)
2. The increase in the internal energy of an atomic or molecular system caused by a collision with another particle of greater energy.
For atoms in a discharge, excitation usually refers to increasing the energy level of a bound electron.
In the exosphere, the air density is so low that the mean free path of individual particles depends upon their direction with respect to the local vertical, being greatest for upward moving particles (see cone of escape, fringe region). It is only from the exosphere that atmospheric gases can, to any appreciable extent, escape into outer space.
2. Specifically, an explosion, sense 1, produced by combustion of a fuel and an oxidizer.
The distinction between an explosion, sense 2. and a detonation is that in an explosion the heat release rate and the number of molecules per unit volume increase with time more or less uniformly, whereas a detonation is propagated by an advancing shock front behind which exothermic reactions take place and thus is (spatially) nonuniform.
2. An atmosphere in which the density is given by
= o e-h/H
is density, o is density at the datum plane, h is altitude, and H is scale height.
A base line extension of the Dovap system to provide a coherent reference to the ground transmitter and all Dovap receivers located beyond line-of-sight to the ground transmitter.
The coherent reference is supplied by a cable and is multiplied up to the proper reference frequency.
is identified as
I dx x When so used, the extinction coefficient equals the sum of the medium's absorption coefficient and scattering coefficient, each computed as a weighted average over all wavelengths in the visible spectrum. As long as scattering effects are primary, as in the lower atmosphere, the value of the extinction coefficient is a function of the particle size of atmospheric suspensoids. It varies in order of magnitude from 10 per kilometer with very low visibility to 0.01 per kilometer in very clear air.
See frequency band.
See frequency band.