Showing papers in "Journal of Applied Meteorology in 1988"
TL;DR: In this article, a new method for estimating both tropical convective precipitation and stratiform precipitation (produced under the anvils of mature and decaying convective systems) from satellite infrared data is described.
Abstract: This paper describes a new method of estimating both tropical convective precipitation and stratiform precipitation (produced under the anvils of mature and decaying convective systems) from satellite infrared data. The method, denoted CST (Convective-stratiform Technique) locates, in an array of infrared data, all local minima in the brightness temperature field (Tmin. After an empirical screening to eliminate cirrus, these points are assumed to be convective centers. Rainrate and rain area are assigned to each minimum point as a function of its Tmin, based on one-dimensional cloud model results. A stratiform rain algorithm, using a brightness temperature threshold based on the mode temperature of thunderstorm anvils, completes the convective/stratiform rain estimation. Individual CST rain fields wore spatially most similar to the radar for young, isolated storms, and most dissimilar in capturing linear features such as squall lines. Some convective features were missed, while others (generally ...
465 citations
TL;DR: In this article, a semi-empirical scheme is proposed which relates the nocturnal surface fluxes of sensible heat, latent heat, and momentum to routine weather data.
Abstract: In this paper a semiempirical scheme is proposed which relates the nocturnal surface fluxes of sensible heat, latent heat, and momentum to routine weather data. The main components of the surface radiation and energy balance over land are described on a half-hourly basis. Observations over a grass-covered surface at Cabauw are used to investigate topics proposed in the literature, and to develop new parameterizations. The input data of the scheme are total cloud cover, wind speed, air temperature, and specific humidity deficit at single heights in the atmospheric surface layer. A semiempirical expression is proposed for the estimation of the soil heat flux. Also the relation between the surface radiation temperature and the temperature at the level of the roughness length is described semiempirically. It is found that their difference is considerable, especially for low wind speeds. The output of the scheme is presented in terms of the main forcing terms. On average, the agreement of the model qu...
394 citations
TL;DR: In this paper, the morphology of microburst outflows observed in Colorado is described based on analysis of observation by Doppler radars and a surface meteorological network and the vertical and horizontal structure of the microburst life cycle is discussed.
Abstract: Intense, small-scale divergent outflows known as microbursts are held responsible for a number of aircraft accidents. This paper describes the morphology of microburst outflows observed in Colorado. Outflows are categorized into morphological types based on analysis of observation by Doppler radars and a surface meteorological network. Outflow life cycle is discussed, and the vertical and horizontal structure is described. Basic characteristics of microburst outflows are summarized from statistics compiled using both single and multiple Doppler analyses. The microburst outflows are classified into two types: individual microbursts and microburst lines. Examples of observations of each type are shown. Organization of microbursts into microburst lines results in much longer-lasting wind shear than exists with isolated microbursts. The greater lifetime of microburst lines, combined with the much larger area of divergence, can create a much greater potential for hazard to aircraft than is the case fo...
275 citations
TL;DR: In this article, a nonlinear multichannel sea surface temperature (MCSST) algorithm was proposed for estimating sea surface temperatures with satellite data, which is similar in form to the MCSST algorithm but with the gamma parameter having a specific two- or three-channel temperature dependence.
Abstract: The familiar linear multichannel sea surface temperature algorithms (MCSST) for estimating sea surface temperature with AVHRR satellite data describe the solution in terms of a constant gamma parameter multiplied by the measured brightness temperature difference of two of the window channels. A nonlinear algorithm is developed in this paper which is similar in form to the MCSST algorithm but with the gamma parameter having a specific two- or three-channel temperature dependence. Simulation studies show that the linear and nonlinear algorithms provide nearly identical accuracies for a wide range of atmospheric conditions if the satellite data are error free. When random or noncorrelative error sources are present in the multichannel AVHRR data, it is found that the nonlinear algorithms significantly reduce their effect upon the final solution relative to the linear MCSST solution. These results are verified with actual AVHRR data obtained in January-March 1982 and 1983. The algorithm estimates of ...
201 citations
TL;DR: In this paper, the influence of land surface roughness on large scale atmospheric circulation and rainfall was examined by comparing three sets of simulations made with a general circulation model in which the terrain roughness length, z(0), was reduced from 45 cm to 0.02 cm, which produced a twofold increase in the boundary layer wind speed, a two-fold decrease in the magnitude of the surface stress, and almost no change in the surface evaporation and surface heat flux.
Abstract: The influence of land surface roughness on the large scale atmospheric circulation and rainfall is examined by comparing three sets of simulations made with a general circulation model in which the land surface roughness length, z(0), was reduced from 45 cm to 0.02 cm. It is found that the reduced surface roughness produced a two-fold increase in the boundary layer wind speed, a two-fold decrease in the magnitude of the surface stress, and almost no change in the surface evaporation and surface sensible heat flux. It is suggested that the height of the earth's vegetation cover has a large influence on the boundary layer water vapor transport convergence and the rainfall distribution.
185 citations
TL;DR: In this paper, the extinction of the 10.8 and 12.6-micron bands of the IR window region, due to optically thin clouds, were found in the measurements made by both an airborne broadband IR radiometer and the IR interferometer spectrometer (IRIS) aboard the Nimbus-4 satellite.
Abstract: Spectral differences in the extinction of the 10.8- and 12.6-micron bands of the IR window region, due to optically thin clouds, were found in the measurements made by both an airborne broadband IR radiometer and the IR interferometer spectrometer (IRIS) aboard the Nimbus-4 satellite; the extinction at 12.6 microns was significantly larger than that at 10.8 microns; both water and ice particles in the clouds can account for such spectral difference in extinction. Multiple scattering radiative transfer calculations of IRIS data revealed this spectral feature about 100 to 20 km away from the high-altitude cold clouds; it is assumed that this feature is related to the spreading of cirrus clouds. Based on this assumption, mean seasonal maps of the distribution of thin cirrus clouds over the oceans were deduced from the IRIS data. The maps show that such clouds are often present over the convectively active areas, such as ITCZ, SPCZ, and the Bay of Bengal during the summer monsoon.
166 citations
TL;DR: In this article, a three-dimensional numerical local-scale model for the simulation of the microclimate near the ground surface of nonhomogeneous regions during radiative frost events was developed.
Abstract: Radiative frost is one of the most severe weather conditions that affects agricultural activities in many parts of the world. Since various protective methods to reduce frost impact are available, refinements of frost forecasting methodologies should provide economical benefits. In the present study, a three-dimensional numerical local-scale model for the simulation of the microclimate near the ground surface of nonhomogeneous regions during radiative frost events was developed. The model is based on the equations of motion, heat, humidity and continuity in the atmosphere and the equations of heat and moisture diffusion in the soil. Emphasis was given in establishing a refined formulation of energy budget equations for soil surface and plant canopy Additionally, an improved finite difference scheme procedure for approximating horizontal derivatives in a terrain-following coordinate system was introduced. The sensitivity of the model to various parameters that way affect the nocturnal minimum temp...
134 citations
TL;DR: In this article, an improved second-moment turbulence-closure model and a random particle kernel diffusion model are described and tested with the 1982 ASCOT data collected in Brush Creek, Colorado.
Abstract: An improved, second-moment turbulence-closure model and a random particle kernel diffusion model are described and tested with the 1982 ASCOT (Atmospheric Studies in Complex Terrain) data collected in Brush Creek, Colorado. Three improvements of the models are the nested grid capability, inclusion of terrain shadows and application of a kernel method for concentration estimation. The present models are unique in a sense that wind variances needed for the computation of transport and diffusion of airborne materials are obtained directly from the second-moment turbulence-closure model.
127 citations
TL;DR: In this article, a three dimensional diagnostic wind field model is shown to be capable of generating potential flow solutions associated with simple terrain features, achieved by modifying an initially uniform background wind to make the flow divergence free.
Abstract: A three dimensional diagnostic wind field model is shown to be capable of generating potential flow solutions associated with simple terrain features. This is achieved by modifying an initially uniform background wind to make the flow divergence free. Atmospheric stability effects can be incorporated by considering the relative degree of adjustment that is allowed between the horizontal and vertical components of the wind. A framework for developing a Froude-number-dependent expression for this ratio is proposed and evaluated by comparing modeled streamline deflections of flow past an ideal hill with results from wind tunnel and tow tank experiments.
114 citations
TL;DR: In this paper, the authors present a case study for 6 March 1982 to examine its capability in a rapidly evolving weather pattern, in particular the bias errors in the retrievals and the dependence on first guesses.
Abstract: Vertical soundings of temperature and moisture derived from the GOES VISSR Atmospheric Sounder (VAS) measurements have been produced operationally since summer 1987 at the VAS Data Utilization Center (VDUC). The algorithm which was developed for the VDUC is described here in detail. Tunable features are identified, and their sensitivities are shown. The algorithm is used to process a case study for 6 March 1982 to examine its capability in a rapidly evolving weather pattern. Weaknesses are exposed, in particular the bias errors in the retrievals and the dependence on first guesses, but strengths are also evident, namely, the capacity to refine gradients and patterns in a manner which improves the first guesses.
110 citations
TL;DR: In this paper, a detailed study to determine the spatial and temporal behavior of the coastal and inland mixed layer in Israel was undertaken, and over 300 upper air measurements (minisonde and airplane) from the central and southern parts of Israel were compiled and analyzed utilizing a statistical methodology developed for this purpose.
Abstract: A detailed study to determine the spatial and temporal behavior of the coastal and inland mixed layer in Israel was undertaken. Over 300 upper air measurements (minisonde and airplane) from the central and southern parts of Israel were compiled and analyzed utilizing a statistical methodology developed for this purpose. The degree to which the upper air measurements taken at the permanent site at Beit Dagan represent five satellite sites in the central and southern part of the country was established. It was found that in cases of unstable atmospheric conditions accompanied by strong winds, the spatial correlation was higher than in cases of weak surface pressure gradients and stable atmospheric conditions. Significant differences in the mixing depth values were found for all synoptic categories at the permanent site, whereas the satellite sites exhibited significant differences only for the two most frequent summer synoptic conditions. The inland variance of the thickness of the mixed layer over...
TL;DR: In this paper, a retrieval method for estimating a mean column value of the upper tropospheric relative humidity (UTH) from radiance measurements in the 6.3 μm channel of the geostationary satellite METEOSAT is described.
Abstract: A retrieval method is described for estimating a mean column value of the upper tropospheric relative humidity (UTH) from radiance measurements in the 6.3 μm channel of the geostationary satellite METEOSAT. The physical retrieval method is based on an efficient radiative transfer scheme which uses the temperature forecast profiles from the European Centre for Medium Range Weather Forecasts (ECMWF) as ancillary data. Theoretical radiances for the given temperature profile and a set of fixed upper tropospheric humidities are employed to- relate the observed radiance to a mean humidity for a layer between 600 and 300 hPa. The retrieval is confined to areas with neither medium-nor high-level clouds. A calibration procedure of the 6.3 μm channel is described which uses the radiative transfer scheme with measured radiosonde profiles of temperature and humidity and collocated satellite measurements. An example of the UTH product and a comparison with radiosondes is presented. An estimate of the error of...
TL;DR: In this paper, the authors investigate the impact of time-dependent cloud microphysical structure on the transfer to space of passive microwave radiation at several frequencies across the EHF and lower SHF portions of the microwave spectrum in order to explore the feasibility of using multichannel passive-microwave retrieval techniques for the estimation of precipitation from space-based platforms.
Abstract: In a two-part study we investigate the impact of time-dependent cloud microphysical structure on the transfer to space of passive microwave radiation at several frequencies across the EHF and lower SHF portions of the microwave spectrum in order to explore the feasibility of using multichannel passive-microwave retrieval techniques for the estimation of precipitation from space-based platforms. A series of numerical sensitivity experiments have been conducted that were designed to quantify the impact of an evolving cumulus cloud in conjunction with a superimposed rain layer on the transfer to space of microwave radiation emitted and scattered from the cloud layers, rain layer and the underlying surface. The specification of cloud microphysics has been based on the results of a time-dependent two-dimensional numerical cumulus model developed by Hall (1980). An assortment of vertically homogeneous rain layers, described by the Marshall-Palmer rain drop distribution, has been inserted in the model a...
TL;DR: In this paper, the optical-pulse characteristics of intracloud (IC) and cloud-to-ground (CG) lightning flashes were investigated using a U2 aircraft flying above clouds at the same time that ground-based lightning measurements were carried out.
Abstract: The optical-pulse characteristics of intracloud (IC) and cloud-to-ground (CG) lightning flashes were investigated. The time-resolved optical waveforms at 777.4 nm and electric-field changes produced by lightning flashes were measured aboard a U2 aircraft flying above clouds at the same time that ground-based lightning measurements were carried out. The pulse shapes and intensities of IC and CG flashes, as viewed from above cloud, were found to exhibit remarkably similar waveshapes, radiances, and radiant energy densities. The median radiance at cloud top was found to be about 0.007 W/sq m per sr, and the median energy density about 0.000003 J/sq m per sr.
TL;DR: In this article, sampling errors of area-time averaged rain rate due to temporal sampling by satellites were estimated by accounting for varying visiting intervals and varying fractions of averaging area on each visit as a function of the latitude of the grid box for a range of satellite orbital parameters.
Abstract: In a parameter study of satellite orbits, sampling errors of area-time averaged rain rate due to temporal sampling by satellites were estimated. The sampling characteristics were studied by accounting for the varying visiting intervals and varying fractions of averaging area on each visit as a function of the latitude of the grid box for a range of satellite orbital parameters. The sampling errors were estimated by a simple model based on the first-order Markov process of the time series of area averaged rain rates. For a satellite of nominal Tropical Rainfall Measuring Mission (Thiele, 1987) carrying an ideal scanning microwave radiometer for precipitation measurements, it is found that sampling error would be about 8 to 12 pct of estimated monthly mean rates over a grid box of 5 X 5 degrees. It is suggested that an observation system based on a low inclination satellite combined with a sunsynchronous satellite simultaneously might be the best candidate for making precipitation measurements from space.
TL;DR: In this paper, a complete but budget investigation was carried out in summer at a site in Adelie Land, some 100 km from the edge of the Antarctic ice sheet, where the mean daily values of snow heat flux were negative, as the snow cover was warmed during the observational period.
Abstract: A complete but budget investigation was carried out in summer at a site in Adelie Land, some 100 km from the edge of the Antarctic ice sheet. For an average day, the all wave radiation budget based on the fluxes toward the surface being positive was positive for about 11 h, which is a short time considering that the sun was above the horizon between 22 and 24 h a day during the observational period. It is a result of the high albedo, which, on average, was found to be about 83%. Furthermore, with increasing cloudiness, a more positive radiation budget was found, which is in contrast to most studies at lower latitudes. The heat flux in and out of the snow cover was small, and showed a typical sinusoidal diurnal variation. The mean daily values of snow heat flux were negative, as the snow cover was warmed during the observational period. The latent heat flux was negative, on the average, as sublimation took place for most of the time. Deposition was observed only on a few nights. The sensible heat ...
TL;DR: In this article, a computerized method developed by Rosenfeld was used to track the three-dimensional structure of the rainshafts of about 3000 summer afternoon convective rain cells in the semi-arid region of central South Africa.
Abstract: A computerized method developed by Rosenfeld (1987) is used to track the three-dimensional structure of the rainshafts of about 3000 summer afternoon convective rain cells in the semiarid region of central South Africa. By assuming a fixed relationship between the radar reflectivity factor and the rain intensity, time- and area-integrated rain volumes of each individual rainshaft are obtained at the cloudbase level and at a lower level. These results are used to obtain the cumulative fractional evaporation of the falling rain. This permits the cumulative evaporation of the falling rain to be obtained in a quantitative way as a function of the fall distance from the cloud base level and the rain intensity at the cloud base.
TL;DR: In this paper, a comprehensive examination of the evolution and vertical distribution of supercooled liquid water in Sierra Nevada winter storms was completed as part of the Sierra Cooperative Pilot Project (SCP).
Abstract: A comprehensive examination of the evolution and vertical distribution of supercooled liquid water in Sierra Nevada winter storms was completed as part of the Sierra Cooperative Pilot Project. Measurements of supercooled water in 63 storms, which affected the area from the 1983/84 through the 1986/87 winter field seasons, were made with a dual-channel microwave radiometer located near the Sierra Nevada crestline. The analyses were carried out in two parts. In the first part, winter storms were grouped into two general categories according to the prevailing flow and resultant storm trajectory. The two storm types consisted of those propagating in zonal flow and those in meridional flow. A complete description of the storm typing is provided. Storms in zonal flow were either developing, occluding, or dissipating during the time they affected the Sierra Nevada. The stage of evolution of the storm dictated the characteristics of supercooled water observed during the storm's passage over the Sierra Ne...
TL;DR: In this article, the seasonal dynamics of biospheric carbon sources and sinks to be used as an input to global atmospheric CO2 studies and models is discussed. And the results are compared with those from other models.
Abstract: The estimation of the seasonal dynamics of biospheric-carbon sources and sinks to be used as an input to global atmospheric CO2 studies and models is discussed. An ecological biosphere model is given and the advantages of the model are examined. Monthly maps of estimated biospheric carbon source and sink regions and estimates of total carbon fluxes are presented for an equilibrium terrestrial biosphere. The results are compared with those from other models. It is suggested that, despite maximum variations of atmospheric CO2 in boreal latitudes, the enormous contributions of tropical wet-dry regions to global atmospheric CO2 seasonality can not be ignored.
TL;DR: In this paper, the vertical fluxes of particles, momentum, heat and water vapor were measured over a partially snow covered field in central Pennsylvania during December 1985, where the PMS ASASP-300 and CSASP100-HV optical counters were used as sensors to measure particle-number fluxes.
Abstract: Eddy correlation measurements of the vertical fluxes of particles, momentum, heat and water vapor, were conducted over a partially snow covered field in central Pennsylvania during December 1985. The PMS ASASP-300 and CSASP-100-HV optical counters were used as sensors to measure particle-number fluxes. Overall, average dry deposition velocities for 28 half-hour runs were found to be 0.034 ± 0.014 and 0.021 ± 0.005 cm s−1 for particles in two size ranges, 0.15–30 and 0.5–1.0 μm, respectively. The average deposition velocity was close to results from prior wind-tunnel and theoretical investigations. These results were also comparable with those reported by other authors over grass. Relatively large sampling rates reduced the effects of counting noise on deposition measurements of 0.5–;1.0 μm particles. Small correlation coefficients between vertical velocity and the particle concentration were found even after corrections for the effects of counting noise. The normalized average surface deposition ...
TL;DR: In this article, the time-dependent role of cloud liquid water in conjunction with its vertical heterogeneities on top-of-atmosphere (TOA) passive microwave brightness temperatures is investigated.
Abstract: The time-dependent role of cloud liquid water in conjunction with its vertical heterogeneities on top-of-atmosphere (TOA) passive microwave brightness temperatures is investigated. A cloud simulation is used to specify the microphysical structure of an evolving cumulus cloud growing toward the rain stage. A one-dimensional multistream solution to the radiative transfer equation is used to study the upwelling radiation at the top of the atmosphere arising from the combined effect of cloud, rain, and ice hydrometeors. Calculations are provided at six window frequencies and one H2O resonance band within the EHF/SHF microwave spectrum. Vertically detailed transmission functions are used to help delineate the principal radiative interactions that control TOA brightness temperatures. Brightness temperatures are then associated with a selection of microphysical situations that reveal how an evolving cloud medium attenuates rainfall and surface radiation. The investigation is primarily designed to study ...
TL;DR: The structural characteristics of stratocumulus cloud fields off the coast of southern California are investigated using Landsat Multispectral Scanner imagery as mentioned in this paper, and it was found that stratocummulus clouds are bifractal in nature with fractal dimension of d of about 1.2 for cells with diameter D smaller than 0.5 km and d of approximately 1.5 for cells having D greater than 0.5 km.
Abstract: The structural characteristics of stratocumulus cloud fields off the coast of southern California are investigated using Landsat Multispectral Scanner imagery. Twelve scenes in this area are examined along with three other stratocumulus scenes near San Francisco, over central Oregon, and in the Gulf of Mexico. Results from this initial study of stratocumulus clouds indicate that cloud-background threshold selection techniques based upon edge detection gradient assumptions are not appropriate for cloud segmentation and classification algorithms, cloud size distributions obey a power law, and cell horizontal aspect ratio increases with cell diameter. It was also found that stratocumulus clouds are bifractal in nature with fractal dimension of d of about 1.2 for cells with diameter D smaller than 0.5 km and d of about 1.5 for cells with D greater than 0.5 km; stratocumulus cloud fields appear to be homogeneous over regions of about 100 km x 100 km, a much smaller region than the 2.5-deg x 2.5-deg boxes to be used in the ISCCP regional averaging algorithms; and that structural properties of stratocumulus clouds observed off the coast of southern California are similar to those observed for stratocumulus clouds at three other locations.
TL;DR: In this paper, the authors analyzed 12 cirrus scenes to determine textural and structural features using LANDSAT imagery and found that convective-type cirrus clouds have high contrast measures and a rapid decrease of correlation at short distances, while stratiform clouds have low contrast measure and more gradual slopes; asymptotic values are good descriptors of general characteristics of cloud fields, while the slopes o...
Abstract: Twelve cirrus scenes are analyzed to determine textural and structural features using LANDSAT imagery. The main structural characteristics are: 1) cirrus cloud size distributions obey a power law, with larger cloud cells (D ⩾ 1.5 km) having smaller slopes than smaller cloud elements; 2) convective-type cirrus are fractal in nature with fractal dimensions of ≈ 1.4, while stratiform cirrus clouds show bifractal behavior, with larger clouds having smaller fractal dimensions (≈1.3); 3) stratiform cirrus cloud cells have significantly larger horizontal aspect ratio than do smaller cells; and 4) structural results are not sensitive to threshold selection. The main textural characteristics are: 1) convective cirrus clouds have high contrast measures and a rapid decrease of correlation at short distances, while stratiform cirrus clouds have low contrast measures and more gradual slopes; 2) asymptotic values are good descriptors of general characteristics (macrotexture) of cloud fields, while the slopes o...
TL;DR: In this paper, several airborne and ground-based silver iodide (AgI) seeding experiments were conducted over the Grand Mesa, Colorado, during a three-day period of northerly flow and shallow orographic cloud.
Abstract: During March 1986, several airborne and ground-based silver iodide (AgI) seeding experiments were conducted over the Grand Mesa, Colorado, during a three-day period of northerly flow and shallow orographic cloud. While little natural snowfall was observed during these experiments, supercooled liquid water formed over the windward slopes and evaporated to the lee of the mesa of many hours. Seeding-induced microphysical changes coincident with the AgI plumes were found in all eight experiments, (including two that employed ground-based seeding) by aircraft sampling about 500 m above the mesa top. Precipitation rates estimated from ice particle images at light levels suggested increases within the seeded volumes in all but one experiment. Surface precipitation increases were observed in three aircraft seeding experiments and one ground-based seeding experiment that coincided with the passage of AgI plumes aloft. Surface observations were not possible during the other ground-based seeding experiment,...
TL;DR: In this paper, an Nd:YAG lidar system was flown aboard NASA's ER-2 high altitude aircraft to provide the topography of clouds and local boundary layer depth.
Abstract: An Nd:YAG lidar system was flown aboard NASA's ER-2 high altitude aircraft. Observations of cloud top height were made with 70 m along-track and 7.5 m vertical-height resolution. The lidar data observed from an East Pacific stratocumulus cloud height deck revealed large cloud variability on 1-5 km scales. The cloud deck sloped upward from 700 to 1000 m in a northeast-southwest direction over a distance of 120 km. Vertical cloud top distributions were negatively skewed indicating flat-topped clouds. The dominant spectral peak of the cloud top variations was found at 4.5 km, which is 5 to 7 times the depth of the local boundary layer. No other peaks were significant in the average spectrum. The cloud layer was stable with respect to cloud top entrainment instability. The southwestern region of the study area was more prone to shear instability at cloud top than the northeastern region. The results of this study show that a lidar system is ideal to provide the topography of clouds and local boundary layer depth. This information is useful in the study of cloud top radiation and parameterization of clouds in numerical models.
TL;DR: In this article, six aircraft sampling flights were made in cloud over the target area of an earlier randomized exploratory cloud seeding experiment in the Bridger Range, Montana during January 1985.
Abstract: During January 1985 six aircraft sampling flights were made in cloud over the target area of an earlier randomized exploratory cloud seeding experiment in the Bridger Range, Montana. One of the two diver iodide (AgI) generator sites used in the earlier experiment was operated well up the wed (windward) slope of the north-south oriented Main Ridge, Crosswind aircraft sampling was done to within 300 m above the secondary ridge target about 17 km downwind of the AgI generator. The AgI plume was detected over the target area on each of the six missions and was generally 5–8 km wide. Three of the missions detected supercooled liquid water (SLW) in the region of the AgI plume. The ice particle concentration (IPC) averaged about an order of magnitude higher in the seeded zone in these cases, and the estimated precipitation rate was greater, as compared with crosswind control zones. Most seeded ice particles were small hexagonal plates, appropriate for the prevailing temperatures and moisture conditions....
TL;DR: A series of wintertime airborne tracing experiments was examined to determine some characteristics of the plumes of silver iodide smoke released either from the ground or from an aircraft over the Grand Mesa of Colorado as discussed by the authors.
Abstract: A series of wintertime airborne tracing experiments was examined to determine some characteristics of the plumes of silver iodide smoke released either from the ground or from an aircraft over the Grand Mesa of Colorado. The plumes were identified in nearly every experiment by detecting the airborne AgI particles and often also by observing resulting ice particle plumes in essentially the same airspace. The lateral and vertical plume positions of Wound-released AgI from eight sites were determined for several wind, cloudiness and stability conditions. The instantaneous ground-released plume had a median spreading angle of 15° and meandered within a median angle of 38°. The median plume height above the crest exceeded 500 m. The lateral spreading rates of aircraft-released AgI were estimated at over 2 m s−1 for cloudy conditions and less in clear conditions. The implications for future cloud seeding strategies are discussed.
TL;DR: In this paper, the authors used the observed periodicity of cloud-free, visible and near-infrared data from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA-9 for a particular target can be efficiently used for deriving the monthly mean clear-sky planetary albedo.
Abstract: It is suggested that the observed periodicity of cloud-free, visible and near-infrared data from the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA-9 for a particular target can be efficiently used for deriving the monthly mean clear-sky planetary albedo. The broadband albedo is approximated by a linear combination of visible and near-infrared albedos. The new method of 9-day compositing distributes the clear-sky observations over the sun-target-sensor geometry combinations and weights them by the occurrence of each combination during a particular month. It is shown that the monthly mean clear-sky planetary albedo can be estimated solely from the visible and near-infrared data in a model-independent manner. The surface albedo is then obtained by applying a simple atmospheric correction to the derived clear-sky planetary albedo. A comparison of the results of the present method and those obtained by using the “minimum albedo” method indicates that the latter may lead to an underesti...
TL;DR: In this article, the thermodynamic model of Whiteman and McKee, as extended with Steinacker's concept of valley area-height relationships, simulated inversion breakup well when sensible heat flux was assumed to be about 6% of the extraterrestrial solar flux.
Abstract: The nocturnal potential temperature inversion in Switzerland's Dischma Valley on 11 August 1980 was destroyed during a 4½-h period following sunrise. The temperature inversion breakup was accomplished primarily by descent of the inversion top rather than upward growth of a convective boundary layer from the valley floor. The thermodynamic model of Whiteman and McKee, as extended with Steinacker's concept of valley area-height relationships, simulated inversion breakup well when sensible heat flux was assumed to be about 6% of the extraterrestrial solar flux. Observations in the valley support this value of sensible heat flux, which is lower than values observed in the drier Colorado valleys where the model was initially tested.
TL;DR: In this paper, rotary spectra were computed from wind data collected in the summers of 1978 and 1979 at six stations along the east Adriatic coast, and the spectra showed diurnal peaks associated with sea and land breezes.
Abstract: Rotary spectra were computed from wind data collected in the summers of 1978 and 1979 at six stations along the east Adriatic coast. The spectra showed diurnal peaks associated with sea and land breezes and their spatial variability is analyzed in this note. It appears that the energy of sea and land breezes diminishes with latitude. Moreover, the breezes generally turn clockwise, with the exception of the Senj station where a slight predominance of anticlockwise rotation occurs. It is suggested that the Senj breezes are modified by topographically induced flows.