Browsing by Author "Few, Arthur A."
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Item Atmospheric conduction current: observations with a new method of measurement(1975) Burke, Hsiao-hua Kuo; Few, Arthur A.Atmospheric electric field intensity, air conductivity, air-earth current density and air space charge density are the four closely related parameters of atmospheric electricity. The normal field intensity, about I3 volts/m near ground, decreases with altitude and also varies with cloud conditions and space charge concentrations. The conductivity of air, approximately 3 x 1 ohm m near ground, increases with altitude and change*with aerosol content, humidity and other local conditions. The average conduction current density, on the other hand, stays more stable and is about 2 pA/m for all altitudes. During fair weather conditions, the directions of both the field and the current are downward from air to the ground ( traditionally referred to as the positive direction). Prior to our new method of measuring the atmospheric conduction current, there has been no direct measurement above ground. The instrument consists of an aluminum hemisphere pair suspended above the ground with the measuring electronics and the transmitter enclosed in the spherical structure. The upper hemisphere receives the positive component of the air-earth conduction current and the lower hemisphere the negative. The sum of the two is measured and the data are transmitted to a recorder. This is a direct and, therefore, more accurate method for measuring the air-earth current above the earth's surface. This method also avoids possible electrode effects and convection currents, which could not be distinguished from the conduction current, that are problems in the case of direct ground measurement. The electronic design employed here also includes compensation for the displacement current and temperature drifts. Experiments including testing Ohm's Law, the enhancement factor and effects of a mercury lamp light (UV-visible) were performed in the laboratory before detecting the air-earth conduction current. The instrument reads current densities from -5 pA/m to +5 pA/m with sensitivity up to .2 pA/m. Data for 13 weeks were collected. The results are divided into two categories: fair weather and disturbed weather conditions. Diurnal variations, seasonal trends, sunrise and fog effects are extensively discussed under fair weather conditions. During disturbed weather, the effects of low rain and thunder clouds are discussed. Observations indicate that charge separation occurs inside these clouds even when lightning activity is not observed. The charge concentrations within overcast clouds sufficient to reverse the normal atmospheric electric field direction are calculated. Negative current readings after rain and thunder storms are observed and discussed. From these results the air-earth charge balance theory is also modified. This experiment shows that simultaneous measurements of field intensity, current density, conductivity and space charge density at different locations are also required in order to draw more quantitative and accurate conclusions.Item Design and evaluation of a balloon-borne electric field sensor(1976) Christian, H. J. (Hugh J.); Few, Arthur A.A balloon-borne instrument has been developed which has the capability of making absolute measurements of the vector electric field inside thunderstorms and under fair weather conditions. Known as the Balloon Electric Field Sensor (BEFS), this device consists of a super-pressure spherical balloon and the associated electronics package which is mounted inside the balloon. The balloon, which has its surface divided into four conducting regions (in the shape of lunes), serves as both the measuring platform and the sensing element. Because of spherical symmetry and the absence of protrusions, calibration procedures are simplified, unknown field distortion factors are eliminated and corona problems are minimized. The BEFS measures the vertical and horizontal components of the ambient field in a total of three modes. By correlating these modes it is possible to separate the true field from various distorting effects.Item Design and preliminary evaluation of a baloon-borne instrument for measuring atmospheric electrical profiles(1979) Weinheimer, Andrew John; Few, Arthur A.; Reiff, Patricia H.; Freeman, John W.A balloon-borne instrument has been developed for the purpose of making fair weather atmospheric electrical measurements. The instrument named Balloon Electrical Environment Profiling System (BEEPS), is similar in principle to balloons flown previously into thunderstorms by our group at Rice. It has the capability of measuring the height profiles of the vector electric field, the vertical component of the conduction current, and the polar conductivities. The balloon is designed to make measurements up through the lower polar stratosphere (14 km), and the first two flights of BEEPS were made from Barrow, Alaska, (71°N, 157°W) in conjunction with a solar magnetic sector boundary crossing, with a flight on either side of the boundary. These flights are part of an effort to measure the electrical response of the atmosphere, as a function of altitude, to the solar sector structure. Knowledge gained from flights such as these may prove valuable to developing an understanding of the role atmospheric electricity may play in those aspects of the sun-weather problem that involve the solar sector structure.Item Digital analysis of narrow band imagery of the Cygnus loop(1983) Hester, John Jeffrey; Dufour, Reginald J.; Clayton, Donald W.; Few, Arthur A.Digital analysis of narrow passband direct imagery of a field in the southeast part of the Cygnus Loop SNR is presented. Calibrated surface brightness and spectral line ratio maps involving emission lines from six different ionic species are shown. The detailed morphology of the remnant and correlations between various line ratios are discussed in the context of recent shock model calculations. The spatial structure is categorized on the basis of the presence or absence of features in images isolating different emission lines, and the correlation or lack thereof between these features and features in the maps of spectral line ratios such as [ III] 57/Ha. For a common type of structure, features present in line ratio maps are not associated with surface brightness features. These same structures also demonstrate spectral behavior consistent with that predicted by steadyflow shock calculations, indicating the presence of steady-flow shocks with velocities from <= 6 km/sec to ≈ 12 km/sec. Differences in the morphologies of the remnant as viewed in different emission lines and gradients in spectral line ratios are interpreted as a continuous transition with distance behind the blast wave from non-steady-flow shocks with velocities >= 13 km/sec to steady-flow shocks with velocities ≈ 6 km/sec .Item Jovian meteorology from Voyager 1: A diagnostic assessment of zonal thermal winds from Iris data(1980) Allison, Michael David; Chamberlain, Joseph W.; Few, Arthur A.; Talbot, Raymond J.The Voyager 1 near-encounter infrared data for Jupiter's atmosphere yield a measure of the temperature as a function of latitude and pressure level. These measurements are applied to the computation of the zonal thermal wind field above the cloud deck. The results are compared with the imaging measurements of the zonal winds at the cloud level and tentatively suggest that the thermal field is correlated with the jet stream system and in the sense required to reduce the strength of the jets with height. The possible dynamical implications of certain discrepancies in this picture are discussed. Also the variation of the standard deviation of the tropospheric temperature with latitude is discussed as a possible diagnostic indicator, of meridional momentum flux.Item Lightning location in a Colorado thunderstorm(1977) MacGorman, D. R.; Few, Arthur A.The method of acoustically reconstructing lightning channels from thunder recorded with a small array of microphones (having a base line of about 5 m) is relatively slow (about 7 hours per lightning flash). We examine another method, which we have called thunder ranging, that does not provide as many points on the lightning channel but is considerably faster (about 2 hours per lightning flash). In this technique, the ranges of a source of a thunder pulse, .1-2 sec long, (also called a clap) to three, noncollinear microphones, separated by distances on the order of 1 km, are measured manually from an analogue oscillogram. From these ranges, the coordinates of the channel segment generating the pulse can be calculated. We discuss the sources and typical magnitudes of errors in this calculation. In the 1972 Colorado experiment, from which our data was taken, the error in the calculated location of a channel segment is typically within 15% of its range. We plot the location of twenty lightning flashes occurring between 18:7 MDT and 18:3 MDT in a multi-cell storm on 25 July 1972. These plots are superimposed on radar reflectivity contours in order to study ways in which lightning and storm structure are related. As in earlier acoustic studies (e,g Teer and Few,1974), the lightning channels are predominantly horizontal. They occur in a relatively thin layer; 4-5% of the calculated locations are between 4 km and 5 km above the ground; 7-8% are between 3.5 km and 5.5 km. The narrower layer is completely above the ° C isotherm in the cloud. Two other conclusions are tentative, since they are based on fewer observations, (1) The lightning channels seem to avoid regions of heavy rainfall 1.4 mm hr^-1, as determined by 1-cm radar) and often extend long distances into regions from which the echo is less than 3 dBZ. (2) Lightning is roughly aligned, having two possible correlations with the storm: the channels often parallel radar reflectivity contours, and they point from the region around the array spread toward regions into which a radar contour is expanding.Item The photoklystron(1980) Simons, Sedgwick Lewis; Freeman, John W.; Dufour, Reginald J.; Few, Arthur A.The photoklystron is a photoelectric vacuum tube designed to convert broadband light energy directly into monochromatic high frequency AC power. It requires a DC reflecting voltage (which draws no power) and the first model works best with a DC accelerating voltage (which represents an additional input energy) but has been shown to operate with only light energy. With the accelerating voltage, frequencies from 4 to over 2 MHz. have been produced, and electrical efficiencies near 2% have been measured. Computer analysis of the electron trajectories revealed that unlike a reflex klystron the photoklystron works by extracting the kinetic energy of the electrons over a period of several cycles. For net energy output the accelerating and reflecting voltages are adjusted so that the electron trajectories have a period which is a multiple of the period of the RF output desired. Any electrons which are improperly phased are quickly eliminated by collision with the photocathode or repeller. Conditions for optimum interaction of the electrons with the RF field have been investigated both analytically and numerically using a Tektronix 452 computer. Although some aspects of the photoklystron are not fully understood at this time, it has been shown to be a fundamentally new and simple oscillator, offering a wide variety of applications.Item The use of air ion mobility spectrum analysis to determine air pollution(1974) Arnold, Jon Alan; Few, Arthur A.The objective of the Investigation was to determine If air ion concentrations could be used to determine the concentrations of air pollutants. A coaxial-conical, converging channel ion mobility chamber was constructed and a series of extensive measurements were made. A regression analysis was used to determine if the ion concentrations were correlated to the air pollutant concentrations. Some degree of correlation was found for two air pollutants. The potential use of air ion measurements to determine air quality still remains to be proven.Item Two balloon-borne experiments to measure electric field structure inside thunderstorms(1978) Weber, Mark Edward; Few, Arthur A.Two balloon borne instruments, capable of making in situ electrical measurements, have been flown into active thunderclouds. The Balloon Electric Field Sensor is a spherical field mill which measures the full vector electric field by making use of its simple relatioship to the surface density of induced charge on a conducting sphere. Analysis of data obtained in a flight on August 12,1976 is well under way and results are presented here. A simple device, compatible in every way with the standard meteorological radiosonde has been developed to measure the vertical electric field component within thunderclouds. This "Coronasonde" measures the corona current induced in a pair of antennae extending above and below the radiosonde box as an indication of the field which is inducing this current. Four flights, made in August of 1977, have produced data of interest. In particular, speculation on the possibility that a "screening layer" of charge at the cloud-air boundary contributed to the corona profile from two of these flights is presented.