Clear Nights Research Articles

Estimates of clear night sky emissivity in the Negev Highlands, Israel

A simple method was introduced to estimate the atmospheric emissivity of clear night skies based on the water temperature variation inside an open shallow pond. The method used the pond as an absorber of atmospheric radiation by measuring the water evaporation rate from the pond to ambient air and then calculating the heat loss inside the pond due to the radiative heat exchange between the pond and sky dome. An empirical correlation for the calculations of clear night sky emissivity in the Negev Highlands, Israel, was found. It showed that the emissivity of clear night sky in the Negev Highlands is slightly lower than that expected by Berdahl et al. and Clark's correlations under the climatic conditions during the period of measurements.

Laser "firefly" clustering: A new concept in atmospheric probing

Profiling the chemical and particulate composition of the atmosphere is of growing importance as awareness of the role of pollution monitoring increases and deliberate contamination by hostile elements becomes a sad reality. Low cost, flexible, safe and mobile solutions are sought. In this letter, we propose an innovative concept of distributed probes in which miniature, low power lasers are deployed in situ at the altitude of interest. We term these laser transmitters "fireflies". The emitted light is at eye safety levels and is modulated by orthogonally coded signals, which make it possible to distinguish between the transmitters. The light is scattered by the aerosols and molecules in the locality of the firefly and received on the ground. Analysis of the received signals makes it possible to obtain a spatial map of the atmospheric constituents without having to perform mechanical scanning. It is shown that signal-to-noise ratios (SNRs) of above 10 dB can be achieved when using more than 1700 fireflies at an altitude of 1 km for a midlatitude summer clear night scenario. At half the altitude, 350 fireflies suffice to achieve the same SNR for the same environment.

Initial results of a rocket-based study of gravity wave effects on photoionization in the middle atmosphere

During May, 2002, two Nike Orion sounding rocket payloads were launched from NASA Wallops Flight Facility, Virginia, to explore the effects of gravity waves on the electrodynamics of the mesosphere. This effort extended earlier work that focused on observed correlations between mesospheric temperatures and conductivities. One result of that work was the postulation of subvisible “ice” particles throughout the mesosphere. Because the preferential size of the aerosols depends on the temperature (and therefore also on gravity wave activity), the present effort investigated the influences of thunderstorm-produced gravity waves on the aerosols. Although the extremely small size of these particles makes direct optical observation of them impossible, in situ observations of their ionization by UV radiation was used to show the electrodynamic effects of temperature variations in the lower mesosphere and upper stratosphere. One rocket flight occurred on a clear night with no nearby tropospheric source mechanisms, and the other flight occurred after the passage of a strong thunderstorm system in the vicinity of the rocket range. The effects of gravity waves generatged by the thunderstorms in the lower mesosphere were also observed by an inflatable falling sphere and ground-based observations of the OH layer.

Observation of mesospheric waves with an all-sky camera in Korean Peninsula

We have carried out all-sky imaging of OH Meinel and 01557.7 run airglow layers in the period of July, 2001 through March, 2002 at Mt. Bohyun, Korea (36.2° N, 128.9° E). The all-sky camera consists of a 37 mm/F4.5 fisheye lens with a 180° field of view, 4 inch diameter narrow band filters and a back-illuminated 1024 × 1024 CCD. Mesospheric wavelike activities were recorded only for 6.4 % of a total of 243 hours of clear moonless nights, which is much fewer than other studies in Japan and North America. We, however, cannot exclude the possibility that our observation has missed frequent wave activity during summer -observed in other sites due to cloudy weather: We detected 12 events of small wave packets, known as the ripple type wave and 10 events of horizon-to-horizon waves, known as the band type wave. The ripple type waves occur for less time but more often than the band type waves. We find that the ripple type waves can be classified into three different kinds in terms of their local environments: (1) ripples generated from a propagating band type wave, (2) ripples associated with a band type wave crest, and (3) ripples in isolation. We discuss different causes for the three kinds of the ripples. The characteristics of observed band type waves are consistent with internal gravity waves, as other studies noted. No southward propagation of band type waves was observed in our dataset.

The signature of short-period gravity waves imaged in the OI [formula omitted] and near infrared OH nightglow emissions over Panhala

With the development of cooled CCD detector, it has become possible to detect the spatial and temporal variation of the small-scale structure in airglow emission more accurately. Using tilting filter photometers ( 630 nm and OH) and a CCD-based multi-channel all-sky imager, the night airglow observations were carried out from Kolhapur (16.8°N,74.2°E) and Panhala (17.0°N,74.2°E; height above mean sea level 3200 ft ), India, during the clear and moonless nights of January–February, 2001. The multi-wavelength airglow imaging enables us to study the horizontal structures of the small-scale gravity waves at various heights in the region of emissions and to investigate propagation of those waves in detail. Hydroxyl (OH) and OI 557.7 nm images on the night of February 18, 2001 showed row-like structures moving from north to south direction spanning over 500 km in the sky. The observed horizontal phase speed (∼50 m/ s) , wavelength (∼25 km) , wave period (∼8 min) of the atmospheric gravity waves have been determined from a set of sequential images of OI 557.7 nm (at 97 km ) and OH (at 86 km ) observed at Panhala. These are the first observation of the signature of atmospheric gravity waves using an all-sky imager in Indian region indicating perturbation in density in the mesospheric region (80– 100 km ). The possible sources of the waves to the extended region have been discussed.

Homing ability and sensitivity to the geomagnetic field in the alpine newt, Triturus alpestris

Triturus alpestris has been found to be adept at homing, and previous studies have found that its orientation behaviour during breeding migration can be explained, at least in part, by the use of olfactory cues from the breeding pond. Nonetheless, the use of chemical cues from the pond probably does not support a guidance strategy when the newts are far from the pond. Hence, T. alpestris may rely on other orientation cues. In this study, alpine newts were tested in a circular arena to determine the sensory cues used to locate breeding ponds. Animals were collected from a permanent pond situated in northern Spain, taken to the experimental site 9020 m distant, and tested for orientation under a variety of conditions (i.e., orientation under a clear night sky, orientation under dark conditions, and orientation under a clear night sky in the presence of an altered geomagnetic field). The possibility of a non-homing directional bias was also tested. Newts chose a compass course in the direction of their breeding pond only when the ambient geomagnetic field and the celestial cues were simultaneously available. Conversely, animals failed to orient only when celestial cues or the geomagnetic field were the sole orientation cues available.

Quantitative Evaluation of Water Deposited By Dew on Monuments

Samples of White and Green Carrara marble, and three types oflimestone and brick exposed in the field vertically and horizontally were used to evaluate condensationon monuments during clear sky nights. Experiments in a simulation chamber under controlledconditions led to a general equation for the actual amount of water deposited on a surface by dew.This is determined by: How much and for how long the surface temperature falls below the dew point,the moisture content in the air and the ventilation. On clear nights, the condensation on buildingstructures facing the sky may reach some 0.2 kg m-2 (or 0.2 mm), whereas condensation on verticalsurfaces is very small. Computation of the seasonal trend of night-time condensationshowed that the maximum amount of water condensed per night occurs in the autumn, with the moreabundant concentration of moisture in the air. The total amount of water condensed per month isfound to be a maximum in the summer-autumn period. Morning condensationfor the thermal inertia of monuments is also relevant, and has been calculated to reach the same order of magnitude as thenocturnal dew. A detailed analysis of the temperature and mixing ratio profiles near a condensingsurface has shown two different situations. In still air, the two profiles follow an exponentiallaw and the thermal and the concentration layers lie within a few tens of millimetres. Inthe presence of turbulence, the thickness of these two layers is dramatically reduced. In still air, infront of a vertical, chilly surface, the deposition rate of air pollutants by thermophoresis and/orStefan flow is increased by 3 or 4 times in comparison with a horizontal surface. In the presence ofturbulence, the thickness of the thermal and concentration layers was dramatically reduced, makingthese two kinds of deposition much faster.

Empirical estimation of the effect of urban heat advection on the temperature series of De Bilt (The Netherlands)

AbstractThe influence of urban heat advection on the temperature time series of the Dutch GCOS station De Bilt has been studied empirically by comparing the hourly meteorological observations (1993–2000) with those of the nearby (7.5 km) rural station at Soesterberg. Station De Bilt is in the transition zone (TZ) between the urban and rural area, being surrounded by three towns, Utrecht, De Bilt and Zeist. The dependence of the hourly temperature differences between De Bilt and Soesterberg on wind direction has been examined as a function of season, day‐ and night‐time hours and cloud amount. Strong dependence on wind direction was apparent for clear nights, with the greatest effects (up to 1 °C on average) for wind coming from the towns. The magnitude of the effect decreased with increasing cloudiness. The analysis suggests that most of the structure in the wind direction dependence is caused by urban heat advection to the measuring site in De Bilt. The urban heat advection is studied in more detail with an additive statistical model. Because the urban areas around the site expanded in the past century, urban heat advection trends contaminate the long‐term trends in the temperature series (1897–present) of De Bilt. Based on the present work, we estimate that this effect may have raised the annual mean temperatures of De Bilt by 0.10 ± 0.06 °C during the 20th century, being almost the full value of the present‐day urban heat advection. The 0.10 ± 0.06 °C rise due to urban heat advection corresponds to about 10% of the observed temperature rise of about 1.0 °C in the last century. Copyright © 2003 Royal Meteorological Society

The Puzzling Optical Light Curve of the Polar QQ Vulpeculae

About 10.5 yr of V-band photometry of QQ Vul allows the examination of systematic changes in orbital light curve features of the system. The photometry is generally limited to one or two data points each clear night at a random orbital phase; however, the orbital light curve and its slower changes can be studied when the data are grouped into intervals of 1 to 2 months. We have isolated four main distinguishing behaviors in the optical light curve of the system. In type 1 the phased light curve has a single broad primary dip. In type 2 the primary dip retains its shape but becomes dimmer and is accompanied by a secondary dip about 0.5 phase units away. As part of the type 2 behavior there is a decrease in the overall brightness level of the phased light curve by ~0.5 mag. This correlation between the morphology of the orbital light curve and the brightness of the system is shown to hold not only for our new data but also for light curves obtained during 1982–1986. Type 3 behavior is an unresolved mixture of types 1 and 2, whereas type 4 appears to be an extreme bright case of type 1. We find a highly significant correlation between the depth of the secondary dip and the system brightness. The implications of this correlation in the context of one- or two-pole accretion are discussed.

Studies of equatorial F-region depletions and dynamics using multiple wavelength nightglow imaging

A charge coupled device based all-sky imaging system with 180° field of view has been operating at Kolhapur (16.8°N, 74.2°E, dip lat. 10.6°N) in India on clear moonless nights to study the dynamics of equatorial ionospheric irregularities by examining the images of three oxygen lines at OI 630, 557.7 and 777.4 nm . The all-sky camera offers broad and instantaneous coverage of the movement of large-scale size ionospheric irregularities (depletions or bubbles) over a region of 1800 km at about 300 km altitude. The location of the station is important as the single image at a given instant maps the irregularities over a large area extending from the geomagnetic equator to the equatorial ionization anomaly region. Several characteristics of irregularities discussed in this report were observed during ISTEP campaign periods conducted in March–April of 1998 and 1999. One example of the signature of simultaneous depletions observed in OI 630, 557.7 and 777.4 nm images is reported. Also, the signature of midnight temperature maximum (MTM) in OI 630 nm airglow has been presented. The tilt of the MTM structure with magnetic meridian was found to change during the course of its movement towards north. The eastward plasma drift speeds ranging from 0 to 289 m/ s computed from bubble movement matches well with the drift speeds computed from VHF scintillation experiments and Jicamarca radar observations.

Airborne Water Droplets in Mist or Fog 05 Affect Nocturnal Attacks in Asthmatic Children

Our study objectives were to evaluate whether or not airborne water droplets in mist or fog affect the occurrence of nocturnal attacks of asthmatic children using a retrospective study. This study included 971 visits by children with bronchial asthma to the emergency department at nighttime (from 18:00 to 09:00) during a 3-year period (04 1, 1998–03 31, 2001). Meteorological data were checked at a local fire station and regional meteorological observatory. We divided nighttime into five 3-hour periods to evaluate the relationship between chronological changes in the frequency of the emergency department visits of asthmatic children and of meteorological conditions. In four of five periods of nighttime, multivariate analysis showed that mist or fog, average atmospheric temperature, and barometric pressure were related to the number of emergency department visits (n = 1096, r = 0.165–0.263, p<0.0001). We divided the year into four seasons to eliminate differences between atmospheric temperature and barometric pressure on clear nights and on misty or foggy nights; we also found the mean number of emergency department visits was higher on misty or foggy nights than on clear nights in each seasonal period (p<0.01). In addition, average atmospheric temperature on misty or foggy nights with the emergency department visits was higher than that on misty or foggy nights without any visits (p<0.01). Asthmatic children frequently visited the emergency department on misty or foggy nights, especially during midnight to dawn periods with high atmospheric temperature. Because a higher atmospheric temperature on misty or foggy nights indicates a larger saturated amount of airborne water droplets, our results suggest that mist and fog, in particular a saturated amount of airborne water droplets, may be a stimulus for bronchoconstriction.

C306 大気風観測のためのドップラーライダー

The multi-channel incoherent doppler lidar is currently developed under Communications Research Laboratory (CRL). This system is designed for the visualization of the stratospheric winds in clear nights. It consists of a stabilized Nd:YAG(SHG) laser, a 75cm collection mirror, Fabry-Perot interferometer and multi-ring photon detector. The preliminary observation was held at Koganei, Tokyo, and the result was compatible with the radiosonde data at Tateno/Hamamatsu between altitude 12km and 24km.

Baseball's All-Stars: Birthplace and Distribution

Paul M. Sommers (psommers@middlebury.edu) is a starry-eyed professor of economics at Middlebury College in Middlebury, Vermont. He is the author of Diamonds Are Forever, a Brookings Institution volume on baseball, not agents On Her Majesty's Secret Service. On clear nights, he searches the heavens for a cluster of stars in a constellation vaguely forming a baseball-shaped configuration. Maybe the astrology will be right and the Boston Red Sox will win a World Series, their first since the accursed trade.

Baseball's All-Stars: Birthplace and Distribution

Paul M. Sommers (psommers@middlebury.edu) is a starry-eyed professor of economics at Middlebury College in Middlebury, Vermont. He is the author of Diamonds Are Forever, a Brookings Institution volume on baseball, not agents On Her Majesty's Secret Service. On clear nights, he searches the heavens for a cluster of stars in a constellation vaguely forming a baseball-shaped configuration. Maybe the astrology will be right and the Boston Red Sox will win a World Series, their first since the accursed trade.

Photometric Study of the W Uma-Type Eclipsing Binary System GSC 4832.400

We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Stromgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve.

In the Core of the Night-Effects of Intermittent Mixing on a Horizontally Heterogeneous Surface

Intermittent breakdowns that accompany wind gusts at the surface are responsible for a large fraction of the turbulent exchange between the surface and the upper boundary layer in the core of clear nights. Vertical and horizontal structure of the breakdowns are investigated using data from a network of 26 stations in an area of 30 km × 30 km. Surface heterogeneity in the area includes complex terrain with different types of land cover. We treat the fine-scale landscape structure near sensors (‘sheltering’) as a separate component of heterogeneity. These features have important consequences on the spatial distribution of mean variables and surface fluxes. We found that breakdowns connect the surface layer to a higher level (level HC). Weak wind gusts below a threshold (approximately 1.5 m s-1) mix the air down to the colder ground, cooling the surface layer. On the other hand, wind gusts above this threshold promote mixing with upper levels, warming the surface layer. The spatial maximum of surface temperature over the network can be used as an estimate of the temperature at HC, allowing vertical gradients and stability to be approximated. Minimum temperature is a function of topography and sheltering. Appreciable surface fluxes at night occur primarily at high, open locations, and can be large enough there to influencearea-averaged values. Surface-fluxparameterizations currently used in mesoscale models were tested first by estimating fluxes at each station and aggregating, and then by formingarea-averages before estimating fluxes. Results show that these formulations underestimate the average surface fluxes over a region for most of the nights.

Brown dwarfs: stars that never made it

ONCE you have looked at the night sky on a clear night, it is not hard to realize why so much of our science and religion has its roots in the stars. Yet it took until 1850 for us to realize that fainter stars are not necessarily further away, nor brighter ones closer. In fact, stars that are brighter to the naked eye are probably further away. Even today the measurement of stellar distances is relatively difficult and is generally only done using dedicated telescopes.

Observations Of Nocturnal Drainage Flow In A Shallow Gully

The formation of cold air drainage flows in a shallow gully is studied during CASES-99 (Cooperative Atmosphere-Surface Exchange Study). Fast and slow response wind and temperature measurements were obtained on an instrumented 10-m tower located in the gully and from a network of thermistors and two-dimensional sonic anemometers, situated across the gully. Gully flow formed on clear nights even with significant synoptic flow. Large variations in surface temperature developed within an hour after sunset and in situ cooling was the dominant factor in wind sheltered locations. The depth of the drainage flow and the height of the down-gully wind speed maximum were found to be largest when the external wind speed above the gully flow is less than 2 m s-1. The shallow drainage current is restricted to a depth of a few metres, and is deepest when the stratification is stronger and the external flow is weaker. During the night the drainage flow breaks down, sometimes on several occasions, due to intermittent turbulence and downward fluxes of heat and momentum. The near surface temperature may increase by 6 ° C in less than 30 min due to the vertical convergence of downward heat flux. The mixing events are related to acceleration of the flow above the gully flow and decreased Richardson number. These warming events also lead to warming of the near surface soil and reduction of the upward soil heat flux. To examine the relative importance of different physical mechanisms that could contribute to the rapid warming, and to characterize the turbulence generated during the intermittent turbulent periods, the sensible heat budget is analyzed and the behaviour of different turbulent parameters is discussed.

Microclimatological characteristics of a miscanthus (Miscanthus cv. giganteus) stand during stable conditionsat night in the nonvegetative winter period

¶Microclimatological data obtained during a field experiment in the nongrowing winter period were used to study the microclimatologically stable night conditions of a 200 × 150 m miscanthus (Miscanthus cv. giganteus) stand and compared to open field conditions. The microclimatological pattern within the miscanthus canopy was characterized by long-wave radiative cooling of the plant stand and by an established temperature inversion within the canopy at calm nights. The results show that there are significant differences in air temperature and energy balance components between the open field and the miscanthus field during calm and clear nights. In general, net radiation difference during the cold and calm nights was relatively constant and about 20 W m−2 less negative in miscanthus (because of lower surface temperatures) than at the open field. Air temperature differences also remained fairly constant and were up to 3 °C lower than at the open field (at the height of 1 m). Through thermal inversion cold air accumulated in the lower parts of the canopy as shown by the vertical air temperature profiles. They showed a greater amplitude within the diurnal cycle in the miscanthus stand than in the open field. Through the onset of wind, temperature profiles changed rapidly and differences diminished. Vertical katabatic air drainage into the canopy layers was estimated indirectly by using the energy balance approach. It was calculated from the significant energy balance closure gap and showed a mean air exchange rate of up to 22 m3 m−2 h−1, related to a stand volume of 1 m2 area and 4 m height, during the mostly calm and clear nights, depending on the canopy net radiation and turbulent heat exchange forced by slight wind spells. Quantitative uncertainties in calculated cold air drainage which are introduced by the measurement method and certain assumptions in the calculations, were considered in a sensitivity analysis. In spite of these uncertainties evidence of katabatic cold air flow is given.

Geostatistical Analyses of Landsat Thematic Mapper–Derived Surface Temperature during Winter Nights

Abstract Geostatistical analyses were used to clarify the effects of the spatial structure of terrain on the spatial variability of satellite-derived surface temperatures on clear winter nights in central Japan. The clarification describes the mechanism for the formation of thermal belts found on mountain slopes. In addition to a digital elevation model on a fine scale, satellite images that were obtained by the Landsat Thematic Mapper on four different occasions were used. In the thermal belts, spatial interdependence between the surface temperatures and the digital elevations was different from that in other regions such as mountains and plains. Cross-variograms between these two attributes were represented by a double-exponential model comprising both short- and long-range structures. The cross-variograms with regard to the short-range structure depended on the kinds of heat sinks (i.e., atmosphere or surface) that control the cooling of surface air. When the sink was the upper cold part of the atmosph...