Showing papers in "Journal of Applied Meteorology in 1975"
TL;DR: In this article, the authors measured the albedo and soil water content of a drying bare soil and found that the relation is relatively independent of season and is a linear function of the soil water contents of a very thin surface layer.
Abstract: Simple albedo measurement may prove useful for sensing surface soil water content and as a research tool in the study of evaporation of water from soil. Intensive concurrent measurements of the albedo and soil water content of a drying bare soil indicate that albedo, normalized for sun zenith angle effects, is a linear function of the soil water content of a very thin surface layer (less than 0.2 cm thick) over a sizeable volumetric water content range (0.00 to 0.18 for an Avondale loam). Albedo is also well correlated with the average soil water content of greater soil thicknesses. Measurements to a depth of 10 cm indicate that the relation is relatively independent of season.
390 citations
TL;DR: In this paper, the Rand two-level general circulation model has been integrated to compute ground surface (bare land) temperature by solving: 1) the interface heat balance equation without soil heat flux; 2) a prognostic equation which includes the heat capacity of the soil as well as an explicit formulation for soil heat flow.
Abstract: The Rand two-level general circulation model has been integrated to compute ground surface (bare land) temperature by solving: 1) the interface heat balance equation without soil heat flux; 2) the interface heat balance equation by including parameterized soil heat flux; and 3) a prognostic equation which includes the heat capacity of the soil as well as an explicit formulation for soil heat flux. The integrations were performed for 48 hours for the month of January. A comparison of results shows that the most realistic distribution of the ground surface temperature with respect to the amplitude, diurnal range, and the phase relationship between the ground temperature, solar radiation, and soil heat flux is given by the solution of the prognostic equation.
346 citations
TL;DR: In this paper, the exact equations describing the variation with relative humidity of the equilibrium size of aqueous solution droplets were developed and an expression was obtained for the size distribution of a chemically homogeneous aerosol as a function of relative humidity.
Abstract: Approximations to the exact equations describing the variation with relative humidity of the equilibrium size of aqueous solution droplets are developed. For relative humidities between 81 and 99.5%, and for droplets formed by particles composed of greater than 60% by mass of any one of nine common electrolytes and having a dry radius in the range of 0.05 to 3.0 μm, the approximation formulas presented are accurate to within 5%. Using these formulas, an expression is obtained for the size distribution of a chemically homogeneous aerosol as a function of relative humidity.
280 citations
TL;DR: In this article, a versatile algorithm to generate weather-like spectra of any desired shape is described, and applications are briefly discussed, and a variety of weather-related applications are discussed.
Abstract: A versatile algorithm to generate weatherlike spectra of any desired shape is described, and applications are briefly discussed.
235 citations
TL;DR: In this paper, the distribution functions of the total amount of precipitation and the largest daily precipitation occurring in an n-day period were derived for the Markov chain-exponential model.
Abstract: General expressions are derived for the distribution functions of the total amount of precipitation and the largest daily precipitation occurring in an n-day period. Two special cases are considered: (i) the probability of occurrence of precipitation on any day in an n-day period is a constant (binomial counting process) and (ii) the probability of occurrence of precipitation on any day depends on whether the previous day was wet or dry (Markov chain counting process). The distribution function for daily precipitation was assumed to be exponential. Analytic expressions are derived for the distribution functions for total precipitation or precipitation greater than a threshold. For the numerical example chosen, the Markov chain-exponential model is slightly superior to the binomial-exponential model. This stochastic model seems to have several advantages over present approaches.
205 citations
TL;DR: In this article, the authors used a single calibration factor (the simple average ratio of gage-observed and radar-inferred rainfall at all input gages without regard to the spatial variation among ratios) to adjust the radar data.
Abstract: Estimates of precipitation are improved when raingage observations are used to calibrate quantitative radar data as well as to estimate precipitation in areas without radar data. Estimated areal precipitation depth errors for nine rainfalls over a 3000 km2 watershed averaged 13 and 14% (1.5 and 1.8 mm) when the radar was calibrated by networks of raingages having densities of one gage per 900 and 1600 km2. Areal precipitation estimates derived from rainfalls observed at the gages alone produced errors of 21 and 24% (2.5 and 3.0 mm). Adjusting the radar data by a single calibration factor (the simple average ratio of gage-observed and radar-inferred rainfall at all input gages without regard to the spatial variation among ratios) resulted in error reduction to 18% (2.1 mm). Radar data added to gage observations also increased the explained variance in point rainfall estimates above that from gages alone, from 53 to 77% and 46 to 72% for the above gage densities.
176 citations
TL;DR: In this paper, a simple model for approximating the shapes of raindrops in terminal fall equilibrium is proposed, which can be represented approximately as oblate spheroids, which have axis ratios determined by the balance of surface and gravity forces at the equator.
Abstract: A simple model is proposed for approximating the shapes of raindrops in terminal fall equilibrium. The equilibrium figures of raindrops are complex, but they can be represented approximately as oblate spheroids, which have axis ratios determined by the balance of surface and gravity forces at the equator. The axis ratios and drop diameters predicted by the model correlate well with experimental and other theoretical results. Using empirical formulas for evaporation from ellipsoids and the results of the model, estimates of ventilation coefficients are made. It is found that drop deformation may cause a small diminution of ventilation coefficient compared with evaporation from an equivalent sphere.
159 citations
TL;DR: In this article, it is shown that when radar data are compared with instantaneous point rainfall rate, a random error and a bias are introduced by the smoothing, which could account for some of the difficulties in the hydrological use of radars.
Abstract: Spacial smoothing by the radar beam as well as post-detection integration reduce the variability of the distribution of rainfall rate in space. It is shown that when radar data are compared with instantaneous point rainfall rate a random error and a bias are introduced by the smoothing. This could account for some of the difficulties in the hydrological use of radars. It is shown that when raingage data are smoothed in time there is an optimum smoothing time interval such that the random error and the bias are reduced to a negligible level. A method is suggested for the optimum comparison of radar and raingage data and the possibility of a determination of Z-R relationships from such comparisons is discussed.
151 citations
TL;DR: In this paper, the boundary-layer free-convection similarity scaling was used to estimate the diffusion from a source near the ground into the daytime mixed layer. But this was applied only to chemically inert, non-buoyant pollutants having no interaction with the ground.
Abstract: The diffusion from a source near the ground into the daytime mixed layer has been deduced from laboratory measurements, making use of boundary-layer free-convection similarity scaling. A parameterization is presented which preserves this similarity scaling for intermediate and long-range diffusion, and which for short-range diffusion incorporates the effects of source height and of near-ground mechanically induced mixing. The parameterization can be applied in steady conditions to the pollution concentration downwind of a steady source, or in unsteady conditions to the concentration in an expanding cylindrical column advected within a multiple puff model. The parameterization applies only to chemically inert, nonbuoyant pollutants having no interaction with the ground.
149 citations
TL;DR: In this article, five techniques of estimating power spectrum mean frequency are examined: fast Fourier transform, covariance argument approximation, vector phase change, scalar phase change and time derivative form of covariance.
Abstract: Five techniques of estimating power spectrum mean frequency are examined. Performance is given in terms of estimate bias, accuracy, and noise immunity. Techniques examined are: 1) fast Fourier transform, 2) covariance argument approximation, 3) vector phase change, 4) scalar phase change, and 5) time derivative form of covariance. Estimator evaluation is made from numerical results obtained with a computer-simulated signal having a Gaussian spectral density which serves as the population with known parameters in the statistical analysis, and 2) real data from a pulsed Doppler radar. Both data sets consist of uniformly time-spaced digital samples of a complex signal. Absolute and relative performance of each estimator are noted, and numerical results are compared with theoretical calculations made by other investigators. Insofar as the pulsed Doppler meteorological return is represented by the signal type examined (narrow, symmetrical spectral densities), the covariance technique of mean frequency...
137 citations
TL;DR: In this article, a TIROS radiometer was used to measure the anisotropy of a specular component to reflect the reflection of solar radiation in spring snowcovers, which is of importance for interpreting albedo values and for reducing air-borne reflectance data taken under distinct nadir angles.
Abstract: Spring snowcovers exhibit a substantial contribution of a specular component to their reflection of solar radiation. This anisotropy can be measured with radiometers with small aperture, here with a TIROS radiometer. Indicatrices thus determined are dependent on solar angle. They are of importance for interpreting albedo values and for reducing air- or spaceborne reflectance data taken under distinct nadir angles.
TL;DR: In this article, urban and rural airport surface weather observations in a 13-year period of rapid city growth are used to document city effects on absolute and relative humidity in a dry climate at fairly high latitudes.
Abstract: Urban and rural airport surface weather observations in a 13-year period of rapid city growth are used to document city effects on absolute and relative humidity in a dry climate at fairly high latitudes The city is found to be dry at all hours (relative humidity) and dry by day but moist at night (absolute humidity) in all but winter months Some but not all of the major features of the humidity differences conform to those found by Ackerman for Chicago In winter, relative and absolute humidities are high in the city at all hours because of vertical mixing and combustion sources Maximum differences in absolute humidity at night occur in March and August The former is attributed primarily to urban snowmelt on occasions when rural temperatures are below freezing The August peak occurs near sunrise and is attributed mainly to rural dewfall The times of maximum cooling and maximum absolute humidity in the city on clear hights in summer are strongly dependent on wind speed For this reason it i
TL;DR: In this article, the authors describe and compare various methods for calculating radar reflectivity factors in numerical cloud models that use bulk methods to characterize the precipitation processes, and use simplified equations for calculating reflectivity factor for both dry and wet hail.
Abstract: This paper describes and compares various methods for calculating radar reflectivity factors in numerical cloud models that use bulk methods to characterize the precipitation processes. Equations sensitive to changes in the parameters of the particle size distributions are favored because they allow simulation of phenomena causing such changes. Marshall-Palmer-type functions are established to represent hailstone size distributions because the previously available distributions lead to implausibly large reflectivity factors. Simplified equations are developed for calculating reflectivity factors for both dry and wet hail. Some examples are given of the use of the various equations in numerical cloud models.
TL;DR: In this paper, a two-dimensional, non-steady model of the flow over an infinitely wide, warm, rough city is presented, which consists of two layers, a lower analytical constant-flux layer, and an upper finite-difference transition layer, in which the vorticity and heat conduction equations are solved.
Abstract: A two-dimensional, non-steady model of the flow over an infinitely wide, warm, rough city is presented. The model consists of two layers, a lower analytical constant-flux layer, and an upper finite-difference transition layer, in which the vorticity and heat conduction equations are solved. The atmosphere is assumed to be Boussinesq, hydrostatic and slab symmetric, while all motions are assumed to be adiabatic. Finite-difference solutions are obtained over a variable, interlaced grid, with the use of a time-splitting technique, in conjunction with the donor cell method of differencing the advection terms. Simulations were carried out reproducing the daytime flow of a neutral atmosphere over a rough city, and the nighttime flow of stable atmosphere over a rough, warm city. Comparisons are presented to show that the model is capable of reproducing many of the observed characteristics of the urban boundary layer.
TL;DR: In this article, the authors compared gage and radar methods of convective rain measurement in the context of the continuing multiple cloud seeding experiment of the Experimental Meteorology Laboratory (EML).
Abstract: Gage and radar methods of convective rain measurement are compared in the context of the continuing multiple cloud seeding experiment of the Experimental Meteorology Laboratory. An optimal system, combining the best features of both, is recommended.The nature of the Florida convective rainfall to be measured is documented using measurements from a dense raingage mesonet (about 3 km2 per gage over 570 km2) that was operated for a total of 93 days in 1971 and 1973, and the gaging requirements for detection and measurement of 24 h rainfalls in the mesonet are determined using the full complement of gages as the standard. For the measurement of areal convective rainfall greater than 0.25 mm within a factor of 2 on 90, 70 and 50% of the days, gage densities of 31, 91 and 208 km2 per gage, respectively, are required.Radar performance in estimating convective rainfall over south Florida is determined using two collocated, calibrated 10 cm radars (UM/10-cm of the University of Miami and WSR-57 of the Nat...
TL;DR: In this article, a multicellular hailstorm consisting of four hail cells with a duration of 2-3 min each was measured and the size distributions were well approximated by an exponential law, the mean distribution was given by NH (D) = 12 exp (−0.42D).
Abstract: Time-resolved hail and raindrop size distributions measured simultaneously during a multicellular hailstorm are presented. The time variation of the size distributions allowed a detailed analysis of the structure of the hailswath. It consisted of four hail cells with a duration of 2–3 min each. The number density of the hailstones increased and the mean diameter decreased during the lifetime of a cell. The contributions of liquid water and ice water content to the total water W were about equal; W was never larger than 5 g m−3. The size distributions were well approximated by an exponential law. The mean distribution is given by NH (D) = 12 exp (−0.42D). The distributions are compared with measurements and calculations of other authors and the differences are discussed.
TL;DR: For univariate or one-dimensional distributions the standard tables used for the Kolmogorov-Smirnov test are valid when testing whether a set of observations are from a completely specified distribution as discussed by the authors.
Abstract: For univariate or one-dimensional distributions the standard tables used for the Kolmogorov-Smirnov test are valid when testing whether a set of observations are from a completely specified distribution. If one or more parameters must be estimated from the sample, then the standard tables are no longer valid. Other tables must be used. Lilliefors indicates the conservative extent of the tests when parameters are estimated for the sample and used with the standard tables. He provides valid tables for the univariate normal, exponential, gamma, and extreme value distributions when one or more parameters must be estimated from the sample. For the multivariate normal distributions the only tables known to the author are those of Malkovich and Afifi. This note brings the problem to the attention of scientists who rely on the tools developed by statisticians to help them to use the appropriate tools correctly.
TL;DR: In this paper, the variance of a time average of a stationary time series is estimated by fitting a low-order autoregression to the data, allowing for diurnal and annual variability and serial correlation.
Abstract: The variance of a time average of a stationary time series depends on the spectral density near frequency zero rather than on the variance of the process. Equations are given for estimating the variance of a time average by fitting a low-order autoregression to the data. Details are given for selecting the order of the autoregression. An example is presented which uses an analysis of variance approach for testing for climatic trends, allowing for diurnal and annual variability and serial correlation.
TL;DR: In this paper, the authors estimate evaporation and transpiration from routine climatological observations using a conceptual model that requires no assumptions concerning the availability of water and demonstrate the versatility of this unorthodox approach by comparing model and water budget estimates for 118 river basins in Canada, Ireland and the southern United States.
Abstract: Evaporation and transpiration are estimated from routine climatological observations using a conceptual model that requires no assumptions concerning the availability of water. The versatility of this unorthodox approach is demonstrated by comparing model and water budget estimates for 118 river basins in Canada, Ireland and the southern United States.
TL;DR: In this paper, the authors describe field investigations, carried out from 1969 to 1974, of winter clouds and precipitation in the Cascade Mountains of Washington State, and physical evaluations of their modification by artificial seeding.
Abstract: This is the first of three papers describing field investigations, carried out from 1969 to 1974, of winter clouds and precipitation in the Cascade Mountains of Washington State, and physical evaluations of their modification by artificial seeding. The present paper describes airborne and ground observations of the natural clouds and precipitation.It has been observed that (i) in pre-frontal conditions ice particles dominate over water droplets above the −10°C level, but the ratio of ice to water is lower in post-frontal conditions; (ii) the passage of an occluded or warm front causes a sharp lowering of the diffusional growth layers of the ice crystals, so that particles reaching the ground change from unrimed crystals which grow at low temperatures to rimed crystals which form at higher temperatures; (iii) the maximum ice particle concentrations in the clouds are often several orders of magnitude greater than measurements of ice nuclei would suggest; (iv) the growth of precipitation particles b...
TL;DR: In this paper, Doppler-derived wind fields in a tornadic storm were synthesized from these data and the first three-dimensional display of wind field in a DoppLER-derived storm was presented.
Abstract: On 20 April 1974 a tornadic storm passed between the two NSSL Doppler radars spaced about 42 km apart. Both radars simultaneously collected Doppler data throughout the storm. Air motions synthesized from these data provide the first three-dimensional display of Doppler-derived wind fields in a tornadic storm. Cyclonic circulation, associated with the tornado, and regions of intense up- and down-drafts are clearly evident.
TL;DR: In this article, vertical profiles of the horizontal radial wind component in the lowest kilometer of the atmosphere have been measured remotely with lidar and wind speed determinations were made by observing the motion of naturally occurring aerosol density inhomogeneities.
Abstract: Vertical profiles of the horizontal radial wind component in the lowest kilometer of the atmosphere have been measured remotely with lidar. Wind speed determinations were made by observing the motion of naturally occurring aerosol density inhomogeneities. Lidar wind measurements compare favorably with simultaneous pilot balloon observations of the wind.
TL;DR: In this paper, the effect of different observation times on the mean daily temperature of a station was investigated. But the results showed deviations can be of such magnitude as to discourage comparison of station temperatures and temperature-derived quantities such as heating degree days and growing degree days unless observation times are the same or corrections are applied.
Abstract: The increased interest and application of heating degree days (HDD) and growing degree days (GDD) prompted this study into the effect of different observation times upon the mean daily temperature. The study was based upon three years of hourly air temperatures measured at St. Paul. These data were used to calculate 1) a true daily mean, 2) a mean of the maximum and minimum between successive midnights as observed at first order stations, and 3) a mean of the maximum and minimum observed at all other hours of the day to simulate cooperative station means. Comparisons of the annual and monthly mean temperatures showed deviations can be of such magnitude as to discourage comparison of station temperatures and temperature-derived quantities such as HDD and GDD unless observation times are the same or corrections are applied.
TL;DR: In this paper, extensive measurements were made of micrometeorological variables associated with eleven fogs in the Chemung River Valley near Elmira, N.Y. The formation of ground fog may be explained by radiational cooling of the surface and associated low-level heat exchange.
Abstract: Extensive measurements were made of micrometeorological variables associated with eleven fogs in the Chemung River Valley near Elmira, N.Y. Temperature was measured at five levels on a 17 m tower, dew point at three levels, wind speed and direction at two levels, and net radiation and vertical wind at one level. Visibility was measured at three locations, and dew deposition and evaporation at one location near the surface. Vertical temperature distributions were also measured using an aircraft. The microphysical variables are discussed in Part II of this paper. Consistent patterns of behavior of all micrometeorological variables were observed. The formation of ground fog may be explained by radiational cooling of the surface and associated low-level heat exchange. To explain observed temperature behavior (maximum cooling rate near 100 m in the 6 h preceeding fog) and the initial formation of a thin fog layer slightly below that level, it seems necessary to invoke Defant's model of valley circulat...
TL;DR: In this article, the photoelectric condensation nucleus counter of Pollak with convergent light beam has been compared with an electrical aerosol detector using monodisperse aerosols with particle diameters between 0.025 and 0.15 μm.
Abstract: The photoelectric condensation nucleus counter of Pollak with convergent light beam has been compared with an electrical aerosol detector using monodisperse aerosols with particle diameters between 0.025 and 0.15 μm, particle concentrations between 127 and 260,800 cm−3, and particles of two different chemical constituencies, e.g., NaCl and material volatilized from a heated nichrome wire. Very good agreement has been obtained. The discrepancy between these two methods was found to be less than 9% at concentration levels below 104 particles cm−2 and 17% at 2.5 × 105 particles cm−3. This discrepancy is well within the combined uncertainties in the two independent aerosol concentration measuring methods.
TL;DR: Eddy correlation instruments mounted above a plantation of Pinus radiato near Mt. Gambier, South Australia, have been operated during two periods of intensive effort, in May and October, 1972 as discussed by the authors.
Abstract: Eddy correlation instruments mounted above a plantation of Pinus radiato near Mt. Gambier, South Australia, have been operated during two periods of intensive effort, in May and October, 1972. Measurements of the Reynolds stress and of wind speed gradients show that the zero plane for momentum is located at about d = 0.8h (where h is the height of the trees), and that the roughness length of the surface is about 30% of the difference (h—d).Sensible heat fluxes and temperature gradients give a displacement length not significantly different from that applicable in the momentum case, but the roughness length for sensible heat transfer is smaller than that for momentum, by about a factor of 3.Advective effects are found to be important, particularly when the fetch across the canopy is less than about 0.8 km (corresponding in our case to an effective fetch/height ratio of between 100 and 200). Long-fetch cases allow an evaluation of the heat storage (S) in the canopy and in the air below the height o...
TL;DR: In this paper, optical constants for water at far-infrared and submillimeter wavelengths were used to estimate water cloud and rain attenuation over the wavelength range between λ12 μm and λ2 cm.
Abstract: Newly determined optical constants for water at far-infrared and submillimeter wavelengths, as revealed by a recent survey, are used to estimate water cloud and rain attenuation over the wavelength range between λ12 μm and λ2 cm. For this purpose new analytic drop-size distribution models simulating fog, nimbostratus cloud and rain, corresponding to rainfall rates of 10 and 50 mm h−1, are set up. The corresponding volume extinction and absorption coefficients as computed according to polydisperse Mie scattering theory at specific wavelengths are listed in tables and presented graphically in plots for purposes of interpolation. It is found that cloud extinction may exceed 50 nepers per kilometer in the λ≲100 μm region, whereas for wavelengths longer than λ200 μm, under near-saturated conditions, water vapor absorption should be the dominant attenuator. The greatest attenuation by heavy rain may be expected around λ5 mm with a value of about 5 nepers per kilometer. The results also suggest that in ...
TL;DR: In this article, a transcendental equation for the Monin-Obukhov length L is presented based on Businger-Dyer surface layer formulations, parameterizations of the moisture flux, ground storage, and radiation terms in the surface energy budget; and the wind and temperature at 10 m above a surface characterized by a roughness length zo.
Abstract: A transcendental equation is presented for the Monin-Obukhov length L based upon (i) the Businger-Dyer surface layer formulations, (ii) parameterizations of the moisture flux, ground storage, and radiation terms in the surface energy budget; and (iii) the wind and temperature at 10 m above a surface characterized by a roughness length zo. The surface temperature, friction velocity and sensible heat flux are obtained from the computed value of L.
TL;DR: In this paper, the authors studied the volatility of the Los Angeles smog aerosol up to 250°C and simultaneously measured the scattering coefficient using a nephelometer and the change of size distribution by an optical counter.
Abstract: It has been shown by earlier studies on the formation of the Los Angeles smog aerosol, that a significant fraction of the particulate matter in the visible size range is made by secondary gas-particle conversion processes, and that it consists mainly of liquid matter. In this study the volatility was studied quantitatively by heating the smog aerosol up to 250°C and simultaneously measuring the scattering coefficient using a nephelometer and the change of size distribution by an optical counter. The thermal analyses revealed that 50–80% of the submicron aerosol mass is volatile at 220°C. Inspection of the shapes of thermo-nephelograms (bscat vs temperature) also revealed that photochemically formed aerosols have distinctly different thermo-nephelograms than those obtained on humid “hazy” days. Thus it is suggested that thermal analyses may at least in some instances provide the means of on-line monitoring the origin of the ambient aerosol.
TL;DR: In this article, a research program is in progress at Brookhaven National Laboratory to determine the nature of atmospheric diffusion from a representative oceanic site, to relate observed diffusion patterns to meteorological and oceanographic variables, and to develop models to describe such diffusion.
Abstract: A research program is in progress at Brookhaven National Laboratory to determine the nature of atmospheric diffusion from a representative oceanic site, to relate observed diffusion patterns to meteorological and oceanographic variables, and to develop models to describe such diffusion. The program was initiated in response to plans for construction of offshore nuclear power plants. Tracer experiments are conducted utilizing oil-fog smoke released from a boat stationed from 1 to 3 miles offshore during onshore flows. The smoke is photographed from above and from the side to document lateral and vertical spread. The crosswind concentration distribution is measured by vehicle- and boat-mounted densitometers during successive traverses across the plume. Wind, turbulence and temperature at several levels are measured on the beach by tower-mounted instruments. Temperature profiles at greater heights are measured by kytoon- and aircraft-borne sensors. Water temperatures are also measured. Winds aloft are determined by pibal ascents and turbulence at various altitudes is sampled by an aircraft-mounted variometer. Preliminary results show that diffusion is governed primarily by water and air temperature differences.