Showing papers in "Journal of Applied Meteorology in 1977"
TL;DR: In this article, the authors developed a non-buoyant mathematical model of air flow within vegetative canopies, consisting of equations for mean horizontal momentum, Reynolds stress, and for the three components of turbulent kinetic energy with closure achieved by parameterizing the higher order terms.
Abstract: The equations of motion were used to develop a one-dimensional, nonbuoyant mathematical model of air flow within vegetative canopies. The model consists of equations for mean horizontal momentum, Reynolds stress, and for the three components of turbulent kinetic energy with closure achieved by parameterizing the higher order terms. This eliminates the need to model the Reynolds stress directly using an eddy viscosity. The closure schemes rely upon a prescribed length scale and have been used elsewhere in modeling the atmospheric boundary layer free of vegetation. The equations were solved numerically using specified boundary conditions. Using a profile of plant area density for a crop of corn (Zea mays L.) the model predicted mean wind velocity, Reynolds stress and turbulent intensities for the region from the soil surface to twice the canopy height that compare well with experimental measurements (Shaw et al., 1974a,b). The model is believed to overestimate the intensity of turbulence generated ...
588 citations
TL;DR: In this article, a compromise between maximum path-averaged rainfall rate sensitivity and minimum sensing errors may be achieved by the use of one-way methods between the transmitter and the receiver, with a wavelength of 1.5 to 2.0 cm.
Abstract: At a wavelength of about 0.9 cm, microwave attenuation is demonstrated to be linearly related to rainfall rate and independent of drop size distribution and temperature. In addition, practical methods for measuring path- and area-averaged rainfall rate are reviewed. A compromise between maximum path-averaged rainfall rate sensitivity and minimum sensing errors may be achieved by the use of one-way methods between the transmitter and the receiver, with a wavelength of 1.5 to 2.0 cm. Corrections for nonspherical drops and for multiple scattering are also discussed.
570 citations
TL;DR: In this article, the authors investigated the energy exchanges occurring within an urban canyon and investigated not only the energy balances of each of the canyon component surfaces (walls and floor), but also the balance of canyon system and of the air volume contained therein.
Abstract: This study investigates the energy exchanges occurring within an urban canyon. It considers not only the energy balances of each of the canyon component surfaces (walls and floor), but also the balance of the canyon system and of the air volume contained therein. The results are based on measurements conducted in a specially instrumented canyon during a period of fine anticyclonic summer weather in Vancouver, B.C. The timing and magnitude of the energy regime of the individual canyon surfaces are shown to be very different from each other, each being strongly affected by the influence of the canyon geometry on the radiation exchanges. The diurnal course of the canyon system energy balance is relatively smooth and symmetric. By day the canyon system radiative surplus is mainly dissipated by turbulent transfer, and the remaining 25–30% is stored in the canyon materials. In contrast, the nocturnal radiative deficit is almost entirely balanced by the release of subsurface heat storage. Advective cont...
432 citations
TL;DR: In this article, a theoretical model for calculating microwave radiative transfer in raining atmospheres is developed and compared with microwave brightness temperatures at a wavelength of 1.55 cm measured on the Nimbus-5 satellite and rain rates derived from WSR-57 radar measurements.
Abstract: A theoretical model for calculating microwave radiative transfer in raining atmospheres is developed. These calculations are compared with microwave brightness temperatures at a wavelength of 1.55 cm measured on the Nimbus-5 satellite and rain rates derived from WSR-57 meteorological radar measurements. A specially designed ground based verification experiment was also performed wherein upward viewing microwave brightness temperature measurements at wavelengths of 1.55 cm and 0.81 cm were compared with directly measured rain rates.
370 citations
TL;DR: In this article, a probabilistic model for the sequence of daily amounts of precipitation is proposed, which is a generalization of the commonly used Markov chain model for occurrence of precipitation.
Abstract: A probabilistic model for the sequence of daily amounts of precipitation is proposed. This model is a generalization of the commonly used Markov chain model for the occurrence of precipitation. Methods are given for computing the distribution of the maximum amount of daily precipitation and the distribution of the total amount of precipitation. The application of this model is illustrated by an example, using State College, Pennsylvania, precipitation data.
334 citations
TL;DR: The polynomial procedure is demonstrated to be highly accurate, more economic of computational time requirements than other procedures, and more economic than other methods currently in use.
Abstract: A procedure for computing saturation vapor by means of a polynomial approximation is presented and evaluated against other methods currently in use. The polynomial procedure is demonstrated to be highly accurate and more economic of computational time requirements than other procedures.
319 citations
TL;DR: In this paper, the authors present a framework for discussion of various estimators, uses the framework to make the case for a particular estimator, and then examines possible shortcomings of other estimators which appear in the literature.
Abstract: Doubt exists among atmospheric scientists about current estimates of local and regional effects of urbanization on climate, but not generally about the existence of these urban effects. This paper presents a framework for discussion of various estimators, uses the framework to make the case for a particular estimator, and then uses the framework to examine possible shortcomings of other estimators which appear in the literature. The measure recommended consists of differences between observations, from urban and pre-urban periods, first stratified by synoptic weather type. The measures whose shortcomings are examined are 1) contemporaneous urban-rural differences, 2) contemporaneous upwind-downwind differences, 3) contemporaneous urban-regional ratios, 4) time trends of differences and ratios and 5) contemporaneous weekday-weekend differences. The paper is designated as a “problem analysis” because its goal is general facilitation of discussion about the problem of empirical estimation of urban e...
295 citations
Abstract: It is noted that wind profiles measured in forest and crop canopies normally contain a secondary maximum or a region of very small shear beneath the level of greatest foliage density. One-dimensional models utilizing a turbulent transport coefficient cannot predict a reversed velocity gradient and, as a result, profile analyses normally imply coefficients that are unrealistic or nonsensical. Examination of the equation for the local rate of change of Reynolds stress u′w′ shows that the velocity gradient can reverse in sign if the divergence of the turbulent transport of stress is of opposite sign and exceeds in magnitude the pressure-velocity gradient correlation. Direct measurements of the turbulent transport of u′w′ in corn (Zea mays L.) indicate that its value is considerably larger than in the air layers above and show that stress is transported downward from the upper parts of the vegetation. A one-dimensional model of canopy flow which solves the equations for momentum, Reynolds stress and ...
178 citations
TL;DR: In this article, standard climatological observations made between 1971 and 1974 at Moisant Airport, New Orleans, were organized into a calendar of eight synoptic weather types identified from the daily surface weather maps of the United States.
Abstract: Standard climatological observations made between 1971 and 1974 at Moisant Airport, New Orleans, have been organized into a calendar of eight synoptic weather types identified from the daily surface weather maps of the United States. The hourly data have been reorganized into tables representing monthly frequencies of weather types, mean properties at 0600 and 1500 CST, and relationships to precipitation. The climatic calendar and associated climatic properties by weather types represent climatic baseline inventories useful for evaluating favorable conditions for activities dependent upon weather such as construction and recreation, local and regional climatic variation by weather type and season, climatic variability through time, and the responses of environmental and biological processes and activities at the earth-atmosphere interface.
145 citations
TL;DR: In this paper, the authors used observations of cloud to cloud ground lightning flashes in thunderstorms to obtain empirical relationships between this ratio (z), latitude (λ), and annual thunder-days (T).
Abstract: Observations of the ratio of cloud to cloud-ground lightning flashes in thunderstorms have been reviewed, and used to obtain empirical relationships between this ratio (z), latitude (λ) and annual thunder-days (T). The 29 observations, covering a latitude range 69°N to 37°S, gave a mean value of z of 3.35. The empirical relationship proposed between z and λ is z(λ) = 4.16 + 2.16 cos3λ, 0 ≤ λ ≤ 60°. From 26 pairs of values of z and T, covering the range 5 to 81 thunderdays per year, the proposed relationship is z(T) = 1.0 + 0.063T, 10 ≤ T ≤ 84 z = 6.3, T > 84. Information on z for high latitudes is sparse. It is probable that z lies between 1 and 2 for λ > 60° and T < 10. The existence of a relationship between z and T is attributed to the fact that both are related to latitude. The relationship between z and λ probably depends on the variation of freezing level height with latitude, and a possible relationship between z and freezing level height is examined. Where both λ and T are known, the prop...
138 citations
TL;DR: In this paper, a theoretical method is given which allows computing the acceleration to terminal velocity of cloud and raindrops at various levels in the atmosphere, and for drops of equivalent radius 800 μm ≤ a0 ≤ 3500 μm their theoretical predictions were found to agree well with the results of an experimental study carried out in the UCLA Rain-Shaft.
Abstract: A theoretical method is given which allows computing the acceleration to terminal velocity of cloud and raindrops at various levels in the atmosphere. For drops of equivalent radius 800 μm ≤ a0 ≤ 3500 μm our theoretical predictions were found to agree well with the results of an experimental study carried out in the UCLA Rain-Shaft. For drops of 20 μm ≤ a0 ≤ 80 μm our theoretical predictions were found to agree well with the experimental results of Sartor and Abbott (1975). Experiment and theory indicate that in air of 1000 mb and 20°C, drops of a0 > 1000 μm need distances of at least 12 m to accelerate to terminal velocity.
TL;DR: In this article, the Eppley pyrgeometer performance was compared to the desired theoretical performance due to battery voltage uncertainties, nonlinearity of circuitry at extreme temperature and differential heating of the instrument.
Abstract: The actual performance of an Eppley pyrgeometer is compared to the desired theoretical performance. Several systematic errors are identified and evaluated in detail. The three most significant errors identified are due to 1) battery voltage uncertainties, 2) nonlinearity of circuitry at extreme temperature and 3) differential heating of the instrument. The elimination of the error due to differential heating is found to be essential to the successful calibration of the instrument. A pyrgeometer laboratory calibration technique is described. Pyrgeometer measurements made from aircraft are shown to have potential errors as large as 60 W m−2. These errors, however, do not significantly affect the net radiation provided the upward and downward facing pyrgeometers are at the same equilibrium temperature, and may be largely eliminated by making accurate temperature measurements of the KRS-5 dome and the cold junctions of the thermopile. The corrections considered in this paper not only reduce the absol...
TL;DR: In this paper, a mathematical model was developed on the premise that mountain winds are the result of vector addition of wind components generated and modified by these influences, and the model was designed primarily for use in estimating wildland fire danger and computing fire spread in southern California.
Abstract: Many mechanisms and factors are responsible for winds in mountainous areas. A mathematical model was developed on the premise that mountain winds are the result of vector addition of wind components generated and modified by these influences. The functions and techniques used in the model were formulated to define and integrate such components of the resultant wind in mountainous areas as valley-mountain wind, slope wind, sea breeze and land breeze, larger scale wind systems, and sheltering and diverting effect of topography. The model is designed primarily for use in estimating wildland fire danger and computing fire spread in southern California. Data were obtained mainly from the San Bernardino Mountains of southern California. Model winds were computed and compared with available observed winds at four research sites in the San Bernardino Mountains. The model output compared well with observed wind velocities.
TL;DR: In this paper, the polarization of 37 GHz microwave radiances emerging from rain clouds above land, rough and calm water surfaces was computed from the equation of radiative transfer, and the brightness temperatures of radiances over water can be transformed into a single-valued function of the rainfall rate if polarization effects are considered.
Abstract: The polarization of 37 GHz microwave radiances emerging from rain clouds above land, rough and calm water surfaces was computed from the equation of radiative transfer. Scattering was assumed to be characterized by a Rayleigh phase matrix. The radiative transfer equation was solved by means of a Neumann solution. It was found that the brightness temperatures of the upward directed radiances emerging from rain clouds were relatively independent of polarization. The weak polarization of radiation emitted by rain clouds can be used to discriminate between cool brightness temperatures emerging from rain clouds and open water. The brightness temperatures of radiances emerging from rain clouds over water can be transformed into a single-valued function of the rainfall rate if polarization effects are considered. A sample of Nimbus 6 data is analyzed in accord with the results of the theoretical analysis.
TL;DR: In this paper, a monostatic lidar measurement of linear depolarization ratios and backscatter coefficients in an altostratus cloud revealed a horizontally layered structure and three different types of layers were observed.
Abstract: Measurements by monostatic lidar of linear depolarization ratios and backscatter coefficients in an altostratus cloud revealed a horizontally layered structure. Three different types of layers were observed. The bottom and central layers had depolarization ratios varying from 0.3 to 0.4, which identified them as layers containing mainly ice. The backscatter coefficients were similar to those found in cirrus ice clouds. A central, transient layer had depolarization ratios characteristic of a high-density water cloud, although the total integrated backscatter of 2.3 ± 1.2 was high for this type of cloud. The top layer had a depolarization ratio of 0.2 at the cloud base, decreasing to 0.04 at the cloud center. Backscatter coefficients ranged up to 30 km−1 and the total integrated backscatter was about 7.6 ± 3.8. This value is considerably higher than the range of values predicted for water or cirrus ice clouds and one possible explanation is that specular reflection was occurring from horizontally a...
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TL;DR: A review of available hail information presented in a series of time and space scales is presented in this article, where the authors focus on hailstones, point hailfalls, hailstreaks, hilstorm, hailswaths and hail days over various sized areas.
Abstract: The first climatic investigations of hail in North America were by Lemons and Flora during the 1940's. These were followed by more intensive, state-scale climatic investigations in the 1960's to meet insurance concerns. Subsequent concerns with hail by the aviation industry and the weather modification community led to the first collection of mesoscale hail data from dense networks and radar studies during the 1960's and 1970's. This paper is a review of available hail information presented in a series of time and space scales. Although the North American hail data and information are less than adequate, there is much more hail information than exists elsewhere in the world. Very extensive findings on hail are available for Alberta, Illinois and Colorado. Phenomenologically oriented studies have focused on hailstones, point hailfalls, hailstreaks, hailstorm, hailswaths and hail days over various sized areas. Results for each of these classifications are presented according to studies that focused...
TL;DR: In this paper, the regions between crop rows are modeled as infinitely long diffuse cavities and geometrical view factors are calculated, accounting for reflected radiation emanating internal to the cavity and from the background sky.
Abstract: The regions between crop rows are modeled as infinitely long diffuse cavities. Geometrical view factors are calculated, accounting for reflected radiation emanating internal to the cavity and from the background sky. A 'cavity' emissivity dependent on local geometry is defined to allow for correcting apparent temperatures to true temperatures. The total emissivity appropriate for correcting aircraft thermal data is then calculated by averaging all emissivity components to account for soil, crop, and background. It is shown that even for the lowest crop and vegetation emissivities, if the crop height-to-spacing ratio is greater than unity, the composite emissivity is greatly increased, giving rise to a decreased error in remotely sensed temperature data.
TL;DR: In this paper, the turbulent characteristics of 17 Canadian cumulus clouds have been documented using the measurements from a specially instrumented T-33 aircraft, and the modal root-mean-square gust velocity was 1.7 m s−1 and the calculated modal turbulent energy dissipation rate was 160 cm2 s−3.
Abstract: The turbulent characteristics of 17 Canadian cumulus clouds have been documented using the measurements from a specially instrumented T-33 aircraft. Most of the 33 cloud penetrations were made through the tops of cumuli 1–4.5 km in depth. Turbulent energy spectra over a range of wavelengths from 15 to 2500 m have been obtained for the two horizontal and the vertical gust velocities. Mean flow characteristics, especially any expected updrafts, tended to be obscured by turbulent fluctuations. The modal root-mean-square gust velocity was 1.7 m s−1 and the calculated modal turbulent energy dissipation rate was 160 cm2 s−3. Based on measured accelerations, estimates were made of expected vertical forces on several aircraft with a wide range of wing loadings. Cumulus clouds similar to those studied do not pose a safety hazard to these aircraft, and crew and passengers can easily tolerate the turbulence levels.
TL;DR: In this paper, the authors studied the photochemical air pollution in the lower Great Lakes region of southern Ontario, Canada, using O3 data for 1973-76 inclusive, and found that high O3 concentrations in the boundary layer are correlated primarily with the several meteorological variables in warm seasons: pressure, temperature, radiation, wind speed and direction.
Abstract: Photochemical air pollution was studied in the lower Great Lakes region of southern Ontario, Canada, using O3 data for 1973–76 inclusive. High O3 concentrations in the boundary layer are correlated primarily with the several meteorological variables in warm seasons: pressure, temperature, radiation, wind speed and direction. Fluctuations of O3 are highly dependent on the synoptic-, regional- and small-scale air flows at low levels. In general, O3 concentrations were observed to increase when the ridge of a surface anticyclone was passing over the region. Relatively high values (>80 ppb) were observed on the rear sides of high pressure centers and in the warm sectors of cyclones (well ahead of cold fronts). In turn, high concentrations of surface O3 usually occurred during periods of high temperature with southerly and/or southwesterly airflows. After the passage of a cold front, when strong north-northwest flows developed in the low levels (e.g., at the forward side of a “new” anticyclone with ge...
TL;DR: In this article, a temporal study of variance sources that leads to the evaluation of equivalent independent hours was performed to determine duration of survey requirements for stated confidence levels and desired accuracy, and the results showed significant correlation in the wind at a single site for a period of 8-12 h and between sites for similar time lags and separations up to 100 km or more.
Abstract: Variance analysis of hourly wind data is utilized to assist in wind characteristic assessment for direct energy conversion systems. Feasibility of large-scale wind energy utilization, as well as sitting, sizing and operating policy, depend on the variability of the wind. Several Midwestern sites are used to illustrate a temporal study of variance sources that leads to the evaluation of equivalent independent hours. For the sites considered these vary from two to three per day. This information is utilized to determine duration of survey requirements for stated confidence levels and desired accuracy. Reasonably reliable and accurate estimates of the mean seasonal wind can be obtained in one or two years for the sites analyzed. Autocorrelation and cross-correlation analysis confirms the existence of significant correlation in the wind at a single site for a period of 8–12 h and between sites for similar time lags and separations up to 100 km or more. Meaningful prediction of variation from the mean...
TL;DR: By fitting a trigonometrical regression model to a regionally averaged time series for the period 1910-72, and by extrapolation to the year 2000, an estimate of future extended wet and dry spells has been made for the summer rainfall region of South Africa as mentioned in this paper.
Abstract: By fitting a trigonometrical regression model to a regionally averaged time series for the period 1910–72, and by extrapolation to the year 2000, an estimate of future extended wet and dry spells has been made for the summer rainfall region of South Africa. It is suggested that the periods 1972–81 and 1991–2000 will experience above normal rainfall and the period 1981–90 will be drier than normal. Results to date show that mean regional rainfall for the hydrological years 1972–73 to 1975–76 has conformed to the suggested pattern.
TL;DR: In this paper, a near-linear relationship is described between aerosol optical depth for Saharan dust over the eastern tropical Atlantic Ocean and radiance measured aboard the NOAA 3 satellite by the VHRR.
Abstract: A near-linear relationship is described between aerosol optical depth for Saharan dust over the eastern tropical Atlantic Ocean and radiance measured aboard the NOAA 3 satellite by the VHRR.
TL;DR: The phase and amplitude of the annual, semiannual, and quasi-biennial oscillations to total ozone data for the Northern Hemisphere in the period 1957-1972 and for Northern Hemisphere ozonesonde data for variable periods from 1962-1974 have been plotted as functions of latitude, longitude, and altitude.
Abstract: The phase and amplitude of the annual, semiannual, and quasi-biennial oscillations to total ozone data for the Northern Hemisphere in the period 1957-1972 and for Northern Hemisphere ozonesonde data for variable periods from 1962-1974 have been plotted as functions of latitude, longitude, and altitude. The largest annual wave amplitude in total ozone occurs over eastern Siberia. In total ozone, the region of maximum quasi-biennial oscillation (QBO) coincides with that of the annual wave. The major feature of the QBO in the vertical distribution is the maximum amplitude in the arctic just above the tropopause. As for the semiannual wave, the maximum in total ozone lies in the arctic, displaced slightly to the Siberian side. In the vertical, its maximum amplitude is near 18 km. The phase appears to progress poleward, with maxima at high latitudes occurring in March-April.
TL;DR: In this paper, a scanning lidar system has been used to observe convection in the atmospheric boundary layer and circulation patterns in and around the cells have been measured, showing that the preferred form of convective cells are plumes with roots near the surface.
Abstract: A scanning lidar system has been used to observe convection in the atmospheric boundary layer. In particular, cell sizes and geometry have been determined and circulation patterns in and around the cells have been measured. The lidar data show that the preferred form of convective cells are plumes with roots near the surface. The majority of these plumes have aspects ratios between 0.5 and 1.5. The measurements of circulation patterns show the strongest rising motion on the upwind side of the cell with sinking motion on the downwind side. These observations show that lidar is a powerful tool for observing convection.
TL;DR: Doppler radar observations are utilized to describe the evolution of the severe thunderstorm updraft mesocyclone and its associated gust front as mentioned in this paper, and tornadoes form within the elliptical mesocyclonic circulation, apparently along the major axis.
Abstract: Doppler radar observations are utilized to describe the evolution of the severe thunderstorm updraft mesocyclone and its associated gust front. Tornadoes form within the elliptical mesocyclonic circulation, apparently along the major axis, and may denote a critical development stage.
TL;DR: A condensation nuclei (CN) counter was developed for balloonborne use at ambient pressures in the troposphere and stratosphere as discussed by the authors, which employs a thermal gradient diffusion cloud chamber to produce particle growth and a photoelectric particle counter for detection.
Abstract: A condensation nuclei (CN) counter has been developed for balloonborne use at ambient pressures in the troposphere and stratosphere. The instrument employs a thermal gradient diffusion cloud chamber to produce particle growth and a photoelectric particle counter for detection. After extensive laboratory tests, the instrument was successfully flown on several balloon soundings over Laramie. The results show a roughly constant mixing ratio in the stratosphere with a CN concentration of about 20 cm−3 at 15 km. The vertical profile of CN in the troposphere displayed concentration fluctuations ranging between 200 and 2000 cm−3 with a definite maximum in the mixing ratio just below the tropopause.
TL;DR: In this paper, a technique for computing power spectra based on the concept of utilizing non-integer values in the sine and cosine waveforms (NI technique) is developed and applied to climatological rainfall data.
Abstract: A technique for computing climatological power spectra based on the concept of utilizing non-integer values in the sine and cosine waveforms (NI technique) is developed and applied to climatological rainfall data. This technique provides a powerful alternative to the more common techniques used in the computation of climatological power spectra. The major advantage of this technique is the greatly improved resolution of wavelengths in the 5–25 year region, often a critical region of interest for climatologists. The technique produces spectral density values which are not necessarily independent; however, methods of specifying and then testing the departure from independence (orthogonality) are given. Furthermore, it is shown that the usual equations for the Fourier coefficients are special cases of the more general condition in which the spectral estimates include some degree of non-independence (i.e., lack of orthogonality). It is anticipated that this technique will have wide applicability in c...
TL;DR: In this paper, Rayleigh optical depths were calculated for six standard atmospheres using the latest value of the depolarization factor (ρn = 0.0139), and the new values are 3.5-3.7% lower than previously reported values.
Abstract: Rayleigh optical depths are calculated for six standard atmospheres using the latest value of the depolarization factor (ρn = 0.0139). Present uncertainties in the Rayleigh optical depth of ±0.16% exist for the values calculated in this paper but the new values are 3.5–3.7% lower than previously reported values. As a consequence it is shown that previous aerosol optical depth or turbidity values from Volz sunphotometer measurements, for example, are reported with systematic errors 2–100% too low. The new Rayleigh optical depths are shown to largely explain the systematic differences between the various wavelength pair determinations of total ozone by the Dobson spectrophotometer. Other possible applications of the results of this paper are also indicated.
TL;DR: In this article, acoustic echo sounder (echosonde) and meteorological tower measurements of the turbulent velocity structure parameters D(r) and Cv2 and the rate of dissipation of turbulent energy ϵ are compared.
Abstract: Acoustic echo sounder (echosonde) and meteorological tower measurements of the turbulent velocity structure parameters D(r) and Cv2 and the rate of dissipation of turbulent energy ϵ are compared. The two acoustic Doppler methods attempted, utilizing pulse differencing and Taylor hypothesis approaches, show good agreement. The small discrepancy in these parameters between the tower and echosonde is explained by the wind noise and ambient noise characteristics of the echosonde and by the effects of pulse volume averaging. Time-averaged, acoustically derived Cv2 values are compared with acoustic facsimile records in both stable and unstable atmospheric conditions. The temporal and (implicitly) the spatial variations of Cv2 were observed to be large, and correlated well with echosonde-detected waves, turbulent layers and thermal plumes. The hour-average vertical ϵ profiles for the two stability cases show reasonable comparison with those calculated by other investigators.