Percent Cloud Cover Research Articles

Cloud statistics measured with the infrared cloud imager (ICI)

The Infrared Cloud Imager (ICI) is a ground-based thermal infrared imaging system that measures spatial cloud statistics with a 320/spl times/240-pixel uncooled microbolometer detector array. Clouds are identified from the residual radiance that remains after water vapor emission is removed from radiometrically calibrated sky images (the water vapor correction relies on measurements of precipitable water vapor and near-surface air temperature). Cloud amount, the percentage of an ICI image containing clouds, is presented for data from Atmospheric Radiation Measurement (ARM) sites at Barrow, AK in February-April 2002, Lamont, OK in February-April 2003, and Barrow, AK in March-April 2004. In Oklahoma, the percent cloud cover determined from full ICI images was slightly higher than that found from a single-pixel time series, suggesting that cloudiness may be under sampled by vertically viewing lidars or radars under highly variable conditions. Full-image and single-pixel statistics agreed more closely for Arctic clouds, which tend to be uniform for long periods of time. Good agreement is found in comparing cloud amount from ICI and active remote sensors during day and night, but much worse agreement is found between ICI and the ARM Whole Sky Imager during nighttime relative to daytime, indicating the importance of the diurnally consistent ICI measurements.

Frequency and magnitude of active‐layer detachment failures in discontinuous and continuous permafrost, northern Canada

AbstractActive‐layer detachment failures triggered weeks to months after forest fire in the central Mackenzie Valley (65°N, discontinuous permafrost zone) are compared to others generated almost immediately by summer meteorological conditions on the Fosheim Peninsula, Ellesmere Island (80°N, continuous permafrost zone). Preferred long‐axis orientations in both zones vary in relation to valley geometry and ground ice distribution: differential insolation plays no direct role in detachment failure distribution. Rates of geomorphic work over periods of one to two centuries are of the same order of magnitude. Threshold meteorological conditions for initiating failures on the Fosheim Peninsula can be incorporated into a surface heating index, but pre‐conditioning of the active layer remains important because rapid thaw does not always initiate activity. Slope pre‐conditioning does not occur at the fire‐affected sites because the failure zone is within formerly perennially frozen ground. Long‐term rates of unit vertical transport at the most active site on the Fosheim Peninsula are similar to those due to debris flow and slushflow in a nearby mountain range. The frequency of potential triggering events at the Ellesmere Island sites is expected to increase if summer climate warms, providing low percentage cloud cover is maintained during periods of high air temperatures. Copyright © 2005 John Wiley & Sons, Ltd.

Effect of clouds on UV and total irradiance at Paradise Bay, Antarctic Peninsula, from a summer 2000 campaign

¶The analysis of ground-based measurements of solar erythemal ultraviolet (UV) irradiance with a Solar Light 501 biometer, and total (300–3000 nm) irradiance with an Eppley B&W pyranometer at the Argentine Antarctic Base “Almirante Brown”, Paradise Bay (64.9° S, 62.9° W, 10 m a.s.l.) is presented. Measurement period extends from February 16 to March 28 2000. A relatively high mean albedo and a very clean atmosphere characterise the place. Sky conditions were of generally high cloud cover percentage. Clear-sky irradiance for each day was estimated with model calculations, and the effect of the cloudiness was studied through the ratio of measured to clear-sky value (r). Two particular cases were analysed: overcast sky without precipitation and overcast sky with rain or slight snowfall, the last one presenting frequently dense fog. Total irradiance was more attenuated than UV by the homogeneous cloudiness, obtaining mean r values of 0.54 for erythemal irradiance and 0.30 for total irradiance in the first case (without precipitation) and 0.27 and 0.17 respectively in the second case (with precipitation). Mean r values for the complete period were 0.58 for erythemal irradiance and 0.43 for total irradiance. Erythemal and total daily insolations reduce quickly at this epoch due to the increase of the noon solar zenith angle and the decrease of daylight time. Additionally, they were strongly modulated by cloudiness. Measured maxima were 2.71 kJ/m2 and 18.42 MJ/m2 respectively. Measurements were compared with satellite data. TOMS-inferred erythemal daily insolation shows the typical underestimation with respect to ground measurements at regions of high mean albedo. Measured mean total daily insolation agrees with climatological satellite data for the months of the campaign.

Atmospheric methane transport near landfill sites.

Methane production rates that have been estimated by a biogas production model (MICROGEN) are combined with an air dispersion model in order to determine the spatial distribution of methane around landfill sites. By utilising dispersion models under extreme atmospheric conditions, a maximum methane concentration around the landfills can be determined. The factors that enhance the maximum methane concentrations, using the meteorological model CALMET in conjunction with the dispersion model CALPUFF, are found to be the wind speed and the percentage of cloud cover. The rates of temperature and pressure variation, as well as the land use category seem to have no effect on the maximum methane concentrations. A rapid reduction of methane concentration is observed a few metres away from the landfill centre while a slower reduction is observed at distances greater than 300 m from it. The performance of this methodology is evaluated by comparing measured concentrations with model predictions.

Mapping Hydrothermally Altered Rocks at Cuprite, Nevada, Using the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), a New Satellite-Imaging System

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is a 14-band multispectral instrument on board the Earth Observing System (EOS), TERRA. The three bands between 0.52 and 0.86 μ m and the six bands from 1.60 and 2.43 μ m, which have 15- and 30-m spatial resolution, respectively, were selected primarily for making remote mineralogical determinations. The Cuprite, Nevada, mining district comprises two hydrothermal alteration centers where Tertiary volcanic rocks have been hydrothermally altered mainly to bleached silicified rocks and opalized rocks, with a marginal zone of limonitic argillized rocks. Country rocks are mainly Cambrian phyllitic siltstone and limestone. Evaluation of an ASTER image of the Cuprite district shows that spectral reflectance differences in the nine bands in the 0.52 to 2.43 μ m region provide a basis for identifying and mapping mineralogical components which characterize the main hydrothermal alteration zones: opal is the spectrally dominant mineral in the silicified zone; whereas, alunite and kaolinite are dominant in the opalized zone. In addition, the distribution of unaltered country rocks was mapped because of the presence of spectrally dominant muscovite in the siltstone and calcite in limestone, and the tuffaceous rocks and playa deposits were distinguishable due to their relatively flat spectra and weak absorption features at 2.33 and 2.20 μ m, respectively. An Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) image of the study area was processed using a similar methodology used with the ASTER data. Comparison of the ASTER and AVIRIS results shows that the results are generally similar, but the higher spectral resolution of AVIRIS (224 bands) permits identification of more individual minerals, including certain polymorphs. However, ASTER has recorded images of more than 90 percent of the Earth’s land surface with less than 20 percent cloud cover, and these data are available at nominal or no cost. Landsat TM images have a similar spatial resolution to ASTER images, but TM has fewer bands, which limits its usefulness for making mineral determinations.

A PDF-Based Model for Boundary Layer Clouds. Part II: Model Results

A new single-column model for the cloudy boundary layer, described in a companion paper, is tested for a variety of regimes. To represent the subgrid-scale variability, the model uses a joint probability density function (PDF) of vertical velocity, temperature, and moisture content. Results from four different cases are presented and contrasted with large eddy simulations (LES). The cases include a clear convective layer based on the Wangara experiment, a trade wind cumulus layer from the Barbados Oceanographic and Meteorological Experiment (BOMEX), a case of cumulus clouds over land, and a nocturnal marine stratocumulus boundary layer. Results from the Wangara experiment show that the model is capable of realistically predicting the diurnal growth of a dry convective layer. Compared to the LES, the layer produced is slightly less well mixed and entrainment is somewhat slower. The cloud cover in the cloudy cases varied widely, ranging from a few percent cloud cover to nearly overcast. In each of the cloudy cases, the parameterization predicted cloud fractions that agree reasonably well with the LES. Typically, cloud fraction values tended to be somewhat smaller in the parameterization, and cloud bases and tops were slightly underestimated. Liquid water content was generally within 40% of the LES-predicted values for a range of values spanning almost two orders of magnitude. This was accomplished without the use of any case-specific adjustments.

Biases in Bird Strike Statistics Based on Pilot Reports

Collisions between birds and aircraft are a concern because they threaten human safety and result in costly repairs. Most data on bird strikes have been provided by pilots and may be incomplete or biased. To assess whether bird strike statistics derived from pilot reports are biased, we compared the number of pilot-reported bird strikes at a Hawaiian airport during 1990-94 to the number of bird strikes obtained from regular runway searches for dead birds. We documented 526 bird strikes, of which only 25% were reported by pilots. Pilot reporting rates (percentage of all strikes reported by pilots) varied by species involved, number of birds struck, season, time of day, location on the runway during the landing phase, and the bird's mass. Reporting rates were not, however, correlated to size of the bird. Pilot reporting rates were independent of wind speed, wind direction, and percent cloud cover, and reporting rates were similar during landings and takeoffs. We found that bird strike statistics derived from pilot reports were biased. A sole reliance on such data can lead to incorrect conclusions and may cause airports to select inappropriate measures and times to reduce bird strikes.

Diurnal Flight Activity of Diadegma insulare (Hymenoptera: Ichneumonidae), a Parasitoid of the Diamondback Moth (Lepidoptera: Plutellidae), in the Field

We studied the diurnal flight activity of Diadeg>ma insulare (Cresson) at the Collins Road Entomology Research Farm Michigan State University during the summers of 1992 and 1993. Foraging activity was measured using sticky traps placed within the broccoli canopy and by direct visual observation. Flight activity of D. insulare males was positively correlated with light intensity, whereas activity of females was positively correlated with light intensity, temperature, and wind speed. Relative humidity, percentage cloud cover, and time of day did not influence D. insulare catch. There was no significant difference between male and female catch. The patterns of males' and females' flight activity throughout the day were significantly different from a uniform distribution except on 14 and 22 August 1993 for males and 14 August for females. Activity generally began between 0800 and 1000 hours, peaked between 1100 to 1300 hours, and stopped by 2100 hours. There was no significant correlation between the numbers of males and females caught on the same trap, suggesting that an increase in numbers of females does not attract more males. Males were caught more frequently than females in September of both years, suggesting that males were more abundant or active at the end of the season. The total numbers caught (both sexes) at different times of the day in sticky traps were generally proportional to the numbers of parasitoid visually observed. The numbers of D. insulare caught were positively correlated with the numbers of diamondback moth larvae per plant. This information could be useful for developing a model that can predict the peak diurnal activity of D. insulare in the field which would help with decisions on whether pesticides should be sprayed.

The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

Abstract. The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

The influence of cloud structure and droplet concentration on the reflectance of shortwave radiation

<strong class="journal-contentHeaderColor">Abstract.</strong> The effects of cloud shadowing, channelling, cloud side illumination and droplet concentration are investigated with regard to the reflection of shortwave solar radiation. Using simple geometric clouds, coupled with a Monte Carlo model the transmission properties of idealized cloud layers are found. The clouds are illuminated with direct solar radiation from above. The main conclusion reached is that the distribution of the cloud has a very large influence on the reflectivity of a cloud layer. In particular, if the cloud contains vertical gaps through the cloud layer in which the liquid water content is zero, then, smaller more numerous gaps are more influential on the radiation than fewer, larger gaps with equal cloud fraction. At very low solar zenith angles channelling of the radiation reduces the reflection expected on the basis of the percentage cloud cover. At high solar zenith angles the illumination of the cloud edges significantly increases the reflection despite the shadowing of one cloud by another when the width of the gaps is small. The impact of droplet concentration upon the reflection of cloud layers is also investigated. It is found that at low solar zenith angles where channelling is important, the lower concentrations increase the transmission. Conversely, when cloud edge illumination is dominant the cloud distribution is found to be more important for the higher concentrations.

Home ranges of female cunner, Tautogolabrus adspersus (Labridae), as determined by ultrasonic telemetry

A fixed hydrophone array tracking system was used to study the use of space by sexually mature female cunner, Tautogolabrus adspersus (Walbaum, 1792). Ultrasonic transmitters attached externally through the dorsal musculature of eight females ranging in length from 194 to 250 mm provided 107 days of tracking data. Home-range areas varied from 300 to 2353 m2. Females utilized space disproportionately within their home-range boundaries, spending 60% of the time in 24–32% of their home-range area. Home ranges were significantly larger in the afternoon than in the morning and exhibited significant seasonal variation in size. Home-range size was not influenced by the state of the tide, and percent cloud cover and seawater temperature, individually, accounted for &lt; 3.3% of the variance in home-range sizes. Changing energy requirements associated with spawning and overwintering torpor appeared to play a more important role than reproductive behaviour per se in determining home-range size.

Spatial analysis of ground-based infrared cloudy sky images

In the development and analysis of sophisticated IR detection and recognition systems it is necessary to have a priori knowledge of the background clutter. The spatial power spectrum and the spatial autocorrelation functions are used to analyze the spatial structure of ground-based infrared cloudy sky images. The experimental results obtained for ground-based IR cloudy sky images do not fit the analytical model of the Wiener spectrum that is frequently used to describe natural clutter sources in the infrared. The spatial structure of ground-based cloudy sky IR images was found to be dependent on the percentage cloud cover in the image. A corrected model is developed that relates the spatial structure of cloudy sky images to the percentage cloud cover in the image.

Satellite-derived estimates of primary production on the northwest Atlantic continental shelf

Synoptic estimation of rates of primary production from remote observation of ocean color is essential for determination of the ocean's role in global carbon cycles. Models having a physiological and optical basis have been developed to predict water-column primary production, normalized to water-column biomass, as a linear function of sea-surface irradiance. Such a model is applied using 41 successive images of sea-surface chlorophyll concentration derived from the Coastal Zone Color Scanner (CZCS) and covering the northeast coast of the U.S. and Canada in the spring of 1979. The CZCS level III data set for the northwest Atlantic continental shelf includes estimates of surface chlorophyll concentration and percent cloud cover on a 10 km grid. Linear regression techniques are used to calibrate the CZCS chlorophyll estimates with ship measurements and to convert percent cloud cover into sea-surface irradiance; such satellite-derived irradiance estimates are significant predictors of irradiances recorded at the earth's surface. The satellite-derived primary production values have been composited as monthly images. The enhanced production of the spring bloom is evident in areas corresponding to major fisheries such as Georges Bank and offshore Yarmouth, Nova Scotia, while the lower production in the Gulf Stream and an associated warm-core ring can be seen farther to the south. Bottom topography seems to have a major influence on rates of primary production, particularly in waters shallower than 100 m. The relative error estimated for these calculations of primary production is approximately 75%.

Interaction between Net Shortwave Flux and Sea Surface Temperature

Abstract Ocean surface shortwave irradiance estimates, From GOES satellite data computed using the model of Gautier and Frouin (1985), are compared to in situ measurements from research vessels and buoys during the frontal air-sea interaction experiment (FASINEX). They reveal that the satellite method overestimates percentage cloudiness during fractional cloud cover and large satellite viewing angles. An empirical relationship, based on physical constraints, is developed to correct for the overestimation of percentage cloud cover under these conditions. Subsequent comparisons of the corrected satellite estimates with in situ measurements show a root-mean-square difference of 10% of the daily mean values, with a mean difference between satellite and in situ data of 1–10 W m−2. From fields of corrected satellite estimates a cloudiness parameter, called the equivalent cloud amount, is used to examine the influences and feedbacks between the clouds and the sea surface temperatures (SST's). Correlations betwee...

Cloud cover distribution in Indonesia

Abstract Indonesian spatio-temporal cloud cover distribution was quantified to allow planners to forecast probabilities for remote sensing data acquisition. The original data consisted of four randomly chosen Geostationary Meteorological Satellite displays per month from 1981 to 1985, which were analysed with a microcomputer after a 1 °15'pixel size digitization. Iterative interactive factorial analyses combined with a parallelepiped classifier clustered data by grouping pixels with similar profiles. For all classes, pixel profiles were linearly combined to provide a small number of classes with high pixel-class correlations. A 0–7 correlation threshold led to 18 classes for all land areas. Statistics of Landsat and SPOT images, grouped by class, were used to verify, calibrate and improve class profiles. This led to quantified temporal profiles of probability of acquiring remotely-sensed data with a given cloud cover percentage for any Indonesian land and marine area.

Natural variance in pH As a complication in detecting acidification of lakes

Natural variance in the pH of three dilute lakes in the Flat Tops Wilderness Area, Colorado, complicates the detection of acidification. Variations in pH during July–September of 1983 were: 0.95 (Ned Wilson Lake), 1.36 (Upper Island Lake), and 1.53 (Oyster Lake). Mean diurnal variations in pH during 1983 were: 0.37 (Ned Wilson Lake), 0.54 (Upper Island Lake), and 0.39 (Oyster Lake). Replicate pH measurements indicate that pH can be measured with a mean variance due to measurement error of ± 0.005. Regression analysis indicates that samples collected on the same day of different years may differ because of time of day and percentage of cloud cover. Differences in wind duration and intensity and primary productivity also may cause the pH to differ between years. Such differences can be either random or systematic. Comparisons of pH among 3 yr of data from Ned Wilson Lake indicate that natural variations in pH are much larger than variations in Colorado Lakes previously attributed to acidification by precipitation.

Monthly probabilities for acquiring remote sensed data of indonesia with cloud cover less than 10 , 20 and 30 percent

The Indonesian spatiotemporal cloud cover distribution was quantified with the aid of GMS, Landsat and SPOT data. Iterative interactive factorial analyses grouped pixels with similar profiles into 18 classes for all land areas. For each class, statistics of Landsat and SPOT images, grouped by class, were used to verify, calibrate and improve class profiles. This led to quantified temporal profiles of probability of acquiring remotely sensed data with 10 , 20 and 30 percent cloud cover, for any Indonesian land area.

Diel periodicity in density of Ephemeroptera nymphs on stream substrata and the relationship with drift and selected abiotic factors

The diel periodicity in density of Ephemeroptera nymphs on an undisturbed stream bottom was documented by direct observation. The study was conducted in a second-order Rocky Mountain foothill stream in Alberta. Observations were made for 24-h periods, twice during a new moon and twice during a full moon; the times of the dark and light periods were noted. Nocturnal observations were made using a red light. The abundance of drifting nymphs, incident light, percent cloud cover in the sky, and water temperature were recorded to determine if they were related to the observed diel periodicity on top of the substratum. The taxonomic groups of Ephemeroptera nymphs examined were Cinygmula, Heptageniidae (Cinygmula and Epeorus), Baetis, Baetis–Ameletus, Ameletus, Drunella coloradensis Dodds, and total fauna (all groups including minor taxa). In response to the artificial light used for observations, total fauna, Cinygmula, and Baetis nymphs were not affected by the light, and the nymphs were not found to be negatively phototactic. Total fauna and Heptageniidae nymphs exhibited a diel periodicity between 24-h periods; the Baetis–Ameletus group also had a diel periodicity. Cinygmula, Baetis, and D. coloradensis nymphs did not exhibit a diel periodicity. Most taxonomic groups were at greater densities on the top of the substratum in the dark period than in the light period. For small and large size classes of nymphs examined, only the small Heptageniidae and Baetis–Ameletus nymphs showed a diel periodicity in density. Drift of the common groups of nymphs was aperiodic and not statistically correlated with the diel density of nymphs on the substratum. In general, incident light, percent cloud cover, and water temperature were not correlated with the diel density of the taxonomic groups on the top of the substratum.

Natural History of the Brazilian Free-Tailed Bat in the San Luis Valley of Colorado

The natural history of Brazilian free-tailed bats, Tadarida brasiliensis mexicana (Saussure), in an atypical, predominantly male colony in south-central Colorado was investigated in 1982 and 1983. The colony inhabits the Orient Mine at the base of the Sangre de Cristo Mountains in the San Luis Valley. Iron ore was removed from the mine (elevation, 2,800–3,000 m) between 1881 and 1932. Colonization by free-tailed bats occurred no earlier than 1900 and most likely after the mine closed in 1932. The colony roosts in a cavernous underground stope in which ambient temperature varies from 6 to 12°C when bats are present from mid-June through October. At peak numbers, the colony consists of more than 100,000 bats. Outflights in both years lasted an average of nearly 1 h. Bats emerged earlier relative to sunset in late summer and autumn than in early summer. Timing of outflights was not affected by percent cloud cover. Outflights were dispersed in June and became more concentrated, often with serpentine components, later in the year. Capture samples taken with mist nets indicated that composition of the colony was 98% adult males until mid-August, when adult females and young-of-the-year became more common.

Stochastic nature of landsat MSS data

A multiple series generalization of the ARIMA models is used to model Landsat MSS scan lines as sequences of vectors, each vector having four elements (hands). The purpose of this work is to investigate if Landsat scan lines can be described by a general multiple series linear stochastic model and if the coefficients of such a model vary as a function of satellite system and target attributes. To accomplish this objective, an exploratory experimental design was set up incorporating six factors, four representing target attributes-location, cloud cover, row (within location), and column (within location)-and two factors representing system attributes-satellite number and detector bank. Each factor included in the design at two levels and, with two replicates per treatment, 2 7 or 128 scan lines were analyzed. The results of the analysis suggests that a multiple AR(4) model is an adequate representation across all scan lines. Further, the coefficients of the AR(4) model vary with location, particularly changes in physiography (slope regimes), and with percent cloud cover, but are insensitive to changes in system attributes.