Shower Activity Research Articles

Automated Meteor Detection and the Leonid Shower

ABSTRACTA computer‐automated radio system for monitoring meteor activity is described. The receiver is tuned to the frequency of a television video carrier whose transmitter is located beyond the horizon. The system registers only a weak signal except when the ion trail from a meteor reflects additional power to the receiver. A sudden power increase alerts the computer to a possible meteor. Our system employs a unique method for distinguishing between meteors and false alerts due to lightning and other noise. Using the receiver's audio output, a meteor echo is identified by increased audio signal autocorrelation, whereas electrical noise is recognized by a decreased correlation. The system has now accumulated more than a year of observations. The data show clearly the expected diurnal variation in meteor count rate, as well as most of the stronger meteor showers. We have also obtained evidence of some new showers. Analysis of the data from 1997 November 15–20 reveals Leonid meteor shower activity with a peak at November 17.5 (±0.2) UT or solar longitude 235.°3 (±0.2). Leonid meteors are of current interest because the shower may be building toward a supermaximum or “meteor storm” in 1998 or 1999.

Perseid meteor stream : cross and longitudinal structures from radar observations

Abstract Results of 23 years of observations of the Perseid meteor shower by the Ondřejov meteor radar in the period 1958–1996 are presented. Activity profiles in four categories of echo durations differ slightly in the position of the activity peak and other characteristics of the central core in the range of solar longitudes (Eq.1950.0) 138.0° ⩽ L ○· ⩽ 140.5°. Maximum activity of the central core is allocated at L ○· = 139.17°±0.06° in accordance with previous studies. The variation ratio of the year-to-year shower activity along the stream within the above L ○· limits was found to be 2.2 : 1.

Safety assessment of enzyme-containing personal cleansing products: Exposure characterization and development of IgE antibody to enzymes after a 6-month use test

Enzyme-containing personal cleansing products were being considered for the consumer market. Although enzymes have been marketed safely for many years as ingredients in laundry products, their use in a personal cleansing application represented a new type of exposure for consumers that was not supported by the historical safety data. An exposure assessment and additional safety data would be needed before marketing to ensure consumer safety. The work in this paper was designed to evaluate the potential for inhalation exposure to the enzyme during use of this new product while showering. Then a clinical trial was conducted to determine whether or not the level, duration, and routes of exposure encountered during use of this product would induce a Type I sensitization response to the enzyme. Exposure was assessed during normal showering activities by collecting air samples with both high volume and personal samplers and quantitating enzyme levels with an ELISA. To assess the potential for sensitization, panelists were asked to use a prototype protease-containing bar product for all personal cleansing tasks and to keep a use diary reporting any associated symptoms. Physical and dermatologic examinations and skin prick tests with enzyme were conducted before the test commenced and at 2-month intervals. Exposure assessment results showed that airborne enzyme levels were primarily dependent on the concentration of the enzyme in the personal cleansing product. Mean values for total airborne enzyme protein ranged from 5.7 to 11.8 ng/m3 when enzyme concentration, time of use, and measurement technique remained constant. After 6 months of at-home product use, four of 61 test subjects using the enzyme-containing bar had positive skin prick test responses when tested with the enzyme. The skin prick test data were supplemented with serologic analyses, which detected IgE specific for the protease enzyme. None of these subjects showed any clinical symptoms indicative of allergic reaction. The ability of enzymes to induce development of allergic antibodies in this study led to the conclusion that this prototype enzyme-containing personal cleansing bar would represent an inappropriate use of enzymes in a consumer product application. The likelihood of both induction of an immunologic response and subsequent elicitation of allergy symptoms in a small but significant fraction of the user population was high. This finding resulted in the decision to halt further development of this prototype.

On the abundance of metal ions in the lower ionosphere

Height profiles of the metal ions Fe+, Mg+, Ca+, and Na+ in the lower ionosphere measured in situ in five rocket flights with a magnetic mass spectrometer are presented. The mean total column density of the ionized metals is within 4.4 ± 1.2 × 109 cm−2 in periods without special meteor shower activity. The column density increased by 1 order of magnitude during the Perseid meteor shower of August 12, 1976. The dominant metal ion in all five flights is Fe+. Its column density in the five flights is, in average, a factor 2.0 ± 0.6 larger than Mg+. A comparison of the column densities of Ni+, Al+, Ca+, Mg+, K+, and Na+, which were normalized to Fe+, to the corresponding ratios in carbonaceous chondrites type I (CI) showed a depletion in the abundance of aluminium (80%), calcium (65%), magnesium (55%), and nickel (35%). At heights above 95 km all metals under consideration should predominantly occur as ions, and no distinct mass fractionation between the different ionized metals is expected from the main loss process, the downward movement of the metal ion layers. The reduced abundance of Al, Ca, Mg, and Ni is therefore most likely an effect of a fractionation originating from partially melted micrometeorites and an associated partial evaporation retaining elements having a relatively high condensation temperature as compared to Fe, which is the case for Ni, Al, Ca, and Mg.

中部日本域における夏季の短時間降雨に関する解析およびその熱的局地循環との関連性

The summer rain shower which develop in central Japan under otherwise fair-weather conditions during the summer of 1985 were investigated, making use of routine observational data from weather stations. According to the statistical analysis, the diurnal cycle of precipitation exhibited a distinct peak around 1800 LST, while little rainfall occurred from 0000 to 1200 LST. This distinct peak was associated with the summer rain shower developed over the heated land surface during the afternoon. The rain shower activity increased as the atmospheric static stability for dry (or moist) convection decreased, under conditions that the atmospheric precipitable water exceeded 40 mm. The rain shower was concentrated in the mountainous regions which consist of several mountain ranges having the horizontal scale of about 100 km. The areas where the rain shower was concentrated largely did not move with time. The degree of spatial concentration of the rain showers however was weaker under higher activity conditions of the rain showers. A thermally induced local circulation developed over central Japan during the daytime under fair weather and weak synoptic wind conditions from the spring to summer seasons. This circulation was strongly dependent on the topography, and converged in the mountainous regions. According to the previous study, the daytime thermally induced circulation contributes to an increase in the water vapor content over the mountainous regions through the moist air advection from the plain and basin regions, and the greatest amounts of water vapor are accumulated over the mountainous regions in the late afternoon when the horizontal scale of topography is close to 100 km. Specific humidity measured in the mountainous area displayed an afternoon maximum, exceeding that at the basin bottom in the afternoon. The increase in water vapor over the mountainous regions is expected to contribute to the development of cumulus clouds, which was confirmed by decreased sunshine duration during the late afternoon over the mountainous regions. These results suggest that summer rain showers are triggered over the mountainous regions by the thermally-induced local circulation.

Exposure in a household using gasoline-contaminated water.

Contamination of drinking water with petroleum products is an increasingly common problem. Physicians are often asked to advise patients about such exposures. This study assessed household exposure from gasoline-contaminated drinking water in a New England household. A sampling strategy was designed to estimate inhalation and ingestion exposure to benzene and three other aromatic hydrocarbons typically found in gasoline-contaminated water. The estimated inhaled doses of all agents were similar to the estimated ingested dose. Over half the inhaled dose of all four agents was associated with shower activities as was over half the estimated total dose by all routes of exposure. Under these conditions, discontinuing ingestion of water contaminated with these agents may decrease the dose of benzene by less than one third, whereas discontinuing both ingestion and showering may decrease the dose of benzene by over three quarters. This limited study suggests that routes of exposure other than ingestion are important and should receive attention in the regulatory and risk-assessment process.

Perseid meteor stream as observed in 1993

Presented are results of Perseid 1993 meteor shower from radar observation at Ondřejov observatory. Investigation of the shower activity profiles in four echo duration intervals proved the position of dominant peak at solar longitude L⊙ = 138.°8±0.°05 (epoch 1950.0) followed by series of secondary maxima positions of which depend on examined echo duration class. Extremely low value of the mass distribution indexs = 1.27 ± 0.01 near the maximum activity peak associated with high proportion of fragmenting particles leads to the suggestion that meteor particles concentrated in this filament are younger than those which form the other parts of the stream.

Lyrids 1994 observed by a forward scatter system

Radio observations of the Lyrid meteor shower obtained by a forward scatter radio system (Bologna-Lecce) in 1994 are analysed and discussed. The shower maximum appeared at solar longitude 31.0°(1950.0) and a distinct displacement between the maxima of the short-duration (< 1s) and long-duration (≥ 1s) echoes is observed. The shower has displayed a high activity, but no exceptional burst similar to that one observed in 1982, was recorded. It has been shown that the shower activity continues down to the smallest particle size of which existence in a meteoroid stream means their recent origin.

Single station identification of radar meteor shower activity: the June Librids in 1992

Single station identification of radar meteor shower activity: the June Librids in 1992

Routes of Chloroform Exposure and Body Burden from Showering with Chlorinated Tap Water

While there is an awareness of the need to quantify inhalation exposure from showers, the potential for dermal exposure to organic contaminants in showers has not been appreciated or explored. To establish routes of environmental exposure from showers, comparisons of the concentration of chloroform in exhaled breath after a normal shower with municipal tap water were made with those after an inhalation-only exposure. The postexposure chloroform breath concentrations ranged from 6.0-21 micrograms/m3 for normal showers and 2.4 to 10 micrograms/m3 for inhalation-only exposure, while the pre-exposure concentrations were all less than the minimum detection limit of 0.86 micrograms/m3. According to an F-test, the difference between the normal shower and the inhalation-only exposures was considered significant at a probability of p = 0.0001. Based on the difference, the mean internal dose due to dermal exposure was found to be approximately equal to that due to the inhalation exposure. The effect of the showering activities on the concentration of chloroform shower air was examined by comparing air concentrations during a normal shower with the air concentrations obtained when the shower was unoccupied. The F-test showed that there is no significant difference between the two sets of data.

Radar observations of asteroid 1986 JK

The asteroid 1986 JK was observed with a 3.5 cm-wavelength radar in May and June, 1986, at less than 0.029 AU; its radar echo power circular polarization ratio indicates single backscattering from smooth surface elements. A working model constructed for the asteroid in light of these radar data postulates a 1-2 km object whose shape has little elongation and some polar flattening. Orbital and physical characteristics are rather cometlike. The radar astrometric data obtained are noted to be extremely powerful for orbit-improvement, so that a search ephemeris whose uncertainty is an order-of-magnitude smaller than that based on relevant optical data alone can be prepared by combining optical and radar data.

Measurements of atmospheric sea salt concentrations in Hawaii using a Tala kite

An inexpensive and convenient method to sample sea salt concentrations in the lowest few hundred meters of the atmosphere was tested in Hawaii. The string to a Tala kite flying at about 150 m was intersected by thin steel wires on which sea salt collected during one hour long flights. Measurements were taken at two beaches and inland of one of them. Sampled concentrations compared well with same day aircraft and tower measurements. A surf zone upwind of one of the beaches produced surface concentrations as high as 250 μg m -3 , while the other beach without such a zone had less than 35 μg m -3 . The high concentrations at the surf beach extended above 145 m. Concentrations at 100 m correlated best to wind speed at this level and less so to previous two-day mean upwind surf condition, cloudiness and shower activity. Simultaneous measurements at and inland of the surf beach showed the effects of boundary layer mixing with a much more uniformly decreasing concentration profile as opposed to a steep decrease up to about 40 m at the beach. DOI: 10.1111/j.1600-0889.1989.tb00136.x

Debris from Comets: The Evolution of Meteor Streams

AbstractThe evolution of meteor streams is controlled basically by: (a) the initial velocities with which the particles were ejected from the parent body; (b) gravitational perturbations by the planets; (c) radiation forces; and (d) collisions. This review focuses mainly on recent numerical modelling dealing with (b) and (a).Ejection velocities spread the particles around the orbit, closing the ring in a few tens of revolutions. The greater ejection velocities of smaller particles cause more rapid dispersion both around the orbit and in the cross section.A determination of the effects of gravitational perturbations must take into account the distributed properties of the stream. The stream’s evolution is dependent on the short-term impulse nature of planetary perturbations, as well as on long-term secular effects. The combined effects produce complex stream cross-sections as in the ribbon-like form of the Halley stream (Orionid and η Aquarid showers) or as in the changes in the annual position of peak shower activity shown by the Quadrantids. Perturbations may cause the orbit of a parent body to sweep rapidly across the orbit of the Earth. But the associated particle stream may not be lost as a meteor shower because it tends to become dispersed in a manner that ensures a continuing supply of particles in Earth-crossing orbits. The nodes of the observed meteoroid orbits may show very little motion compared with the rapid motion of the nodes of the orbit of the parent object.Radiation effects contribute to size separation of particles. Very small particles are blown out of the stream or spiral in toward the sun because of Poynting–Robertson drag. Older meteor streams usually show a predominance of large particles.

The Grahamstown all-sky meteor radar

Abstract A coherent-wave meteor radar system which has been in operation at Grahamstown since April 1986 is described, and some results obtained to date briefly reviewed. The radar is of the monostatic type, operating at a fixed frequency near 28 MHz, square-wave modulated at 500 Hz. The effective antenna pattern, produced by an array of simple half-wave dipoles, consists of two oppositely directed broad beams which provide coverage of all azimuths. The direction of arrival and doppler shift of each meteor echo is determined, enabling wind motions in the meteor region to be deduced. 8, 12 and 24 hr periodicities are present at most times, superimposed on a nearly eastward prevailing wind. A “2-day” oscillation was strongly present in the meridional wind early in 1987. Observations of meteor shower activity are also presented, with some emphasis on the Comet Halley stream. Plans for future improvements to the system are briefly discussed.

Frictional convergence at coastlines

The coastline generally represents a marked discontinuity in surface roughness. The resulting mechanical forcing leads to a secondary circulation in the boundary layer, and consequently to a vertical motion field that may have a strong influence on the weather in the coastal zone. In potentially unstable air masses, frictional convergence may cause a more-or-less stationary zone of heavy shower activity, for example. In this paper, we present a calculation of secondary flow patterns forced at a roughness discontinuity, as a function of the geostrophic wind. A neutral boundary layer is studied, with homogeneous conditions along the coastline (i.e., we study the circulation in a plane perpendicular to the coastline). The closure scheme for the turbulent mixing of momentum is based on a calculation of the eddy kinetic energy density (the I,E closure). The equations are solved on a grid stretched in both the vertical and horizontal directions, with largest resolution at the roughness discontinuity. Various relaxation techniques are combined to give an efficient calculation of the stationary flow fields. Upward motion turns out to be most pronounced when the geostrophic wind makes a small (˜20“) angle with the coastline (in a clockwise direction), and not when the geostrophic wind is perpendicular to the coastline, as is sometimes mentioned. The asymmetry relative to the normal to the coastline is due to the Coriolis acceleration, and not a nonlinear effect Nevertheless, nonlinear effects are important, because they create a tendency to frontogenesis in the case mentioned above. This is shown by a comparison of the linear and nonlinear solution. We finally present an example of heavy shower activity in the coastal zone of Belgium and The Netherlands, which is apparently due to frictional uplift and frontogenesis in a maritime polar air mass hitting the coastline at the critical angle referred to above. DOI: 10.1111/j.1600-0870.1986.tb00473.x

The seasonal structure of ionosonde Es parameters and meteoroid deposition rates

Abstract A comparison covering more than three decades is made between the seasonal variation of radar meteor influx and seasonal variations in the occurrence probabilities of ionosonde sporadic-E parameters ƒ 0 E s and ƒ b E s for different diurnal intervals at two Southern Hemisphere stations. The analyses show that for medium intensity 3Em type sporadic-E no clear correlation with major Southern Hemisphere meteor shower activity exists. This finding which does not support some earlier shorter period surveys suggests the need for further work into the aeronomy of Es source ions.

Synoptic and Regional Circulation Parameters Associated with the Degree of Convective Shower Activity in South Florida

Abstract Radar and synoptic data obtained during the Florida Area Cumulus Experiment have been used in an exploratory study to investigate the effects of synoptic and regional circulations on the development of convective activity in south Florida. The radar data were used to stratify the days into four groups according to their degree of shower coverage. Mean soundings and typical synoptic maps were constructed for each group. These products were then analyzed to identify and quantify the principal factors that are associated with the production of convective showers. In general, the overall differences in activity among the four groups are a result of the influence of large-scale regional and synoptic flow patterns on the underlying local mesoscale and sea-breeze circulations. This influence is reflected in the properties of the air mass in which the convection is developing, as well as in the additional large-scale dynamic effects that are provided.

Changes in the Frequency Distribution Characteristics of Ionosonde Es Parameters During Major Meteor Activity

The probability of occurrence of both 10 E, and Ib Es in excess of ionosonde limiting frequency has been examined for two Southern Hemisphere stations at periods of recurrent annual meteor shower activity and periods of no shower influx. The analyses show that marked changes occur in probabilities for high values of!o Es and Ib Es indicating structural modifications to Es layers.

The ecology of Rhizocarpon superficielle. I. The rock surface boundary-layer microclimate

The thermal environment of the crustaceous lichen Rhizocarpon superficiale (Schaer.) Vain, is documented for spring and summer conditions using selected data characteristic of a range of thallus hydration conditions. During extended rainfall periods hydrated thallus temperatures largely parallel air temperature, usually remaining below 10 °C. However, quite often periods of shower activity alternate rapidly with intervals of full solar isolation, particularly during summer thundershower activity. This can result in hydrated thallus temperatures, fluctuating from 5 to 20 °C within minutes. An equally wide range of hydrated thallus temperatures is also evident under spring snowmelt conditions. Under the high levels of convective cooling typical of the exposed habitat of Rhizocarpon superficiale, thallus temperatures under maximum solar radiation conditions in midsummer rarely rise above 32 °C. Under still conditions thallus temperatures rapidly reach a potentially stressful level of 45 °C and it is probable that strong convective cooling in summer plays an important role in the ecology of R. superficiale.

Why Not Raindrop Impressions?

ABSTRACT Field observations show that most raindrop impressions are produced during the last vestiges of shower activity when the rain has almost ceased to fall. These fewer number of raindrops impact upon portions of the mud surface that have the right degree of saturation to retain impressions. This accounts for the isolated nature of most modern and fossil raindrop impressions. While not all so-called raindrop impressions are considered to have formed due to the impact of raindrops, one can not eliminate their important role.