Showing papers in "Journal of the Atmospheric Sciences in 1971"
TL;DR: In this article, the free constants in several interpolation formulas can be adjusted to give excellent fits to the wind and temperature gradient data, and the behavior of the gradients under neutral conditions is unusual, however, and indicates that von Karman's constant is ∼0.35, rather than 0.40 as usually assumed, and that the ratio of eddy diffusivities for heat and momentum at neutrality is ∼1.0.
Abstract: Wind and temperature profiles for a wide range of stability conditions have been analyzed in the context of Monin-Obukhov similarity theory. Direct measurements of heat and momentum fluxes enabled determination of the Obukhov length L, a key independent variable in the steady-state, horizontally homogeneous, atmospheric surface layer. The free constants in several interpolation formulas can be adjusted to give excellent fits to the wind and temperature gradient data. The behavior of the gradients under neutral conditions is unusual, however, and indicates that von Karman's constant is ∼0.35, rather than 0.40 as usually assumed, and that the ratio of eddy diffusivities for heat and momentum at neutrality is ∼1.35, compared to the often-suggested value of 1.0. The gradient Richardson number, computed from the profiles, and the Obukhov stability parameter z/L, computed from the measured fluxes, are found to be related approximately linearly under unstable conditions. For stable conditions the Richar...
3,177 citations
TL;DR: In this paper, a very pronounced maximum was noted in the co-spectrum of the 850- and 150-mb zonal wind components in the frequency range 0.0245-0.0190 day−1 (41-53 days period).
Abstract: Nearly ten years of daily rawinsonde data for Canton Island (3S, 172W) have been subjected to spectrum and cross-spectrum analysis. In the course of this analysis a very pronounced maximum was noted in the co-spectrum of the 850- and 150-mb zonal wind components in the frequency range 0.0245–0.0190 day−1 (41–53 days period). Application of a posteriori sampling theory resulted in a significance level of ∼6% (0.1% prior confidence level). This type of significance test is appropriate because no prior evidence or reason existed for expecting such a spectral feature. Subsequent analysis revealed the following structure of the oscillation. Peaks in the variance spectra of the zonal wind are strong in the low troposphere, are weak or non-existent in the 700–400 mb layer, and are strong again in the upper troposphere. No evidence of this feature could be found above 80 mb, or in any of the spectra of the meridional component. The spectrum of station pressure possesses a peak in this frequency range and...
2,995 citations
TL;DR: In this article, the authors discussed the dynamics of the stratosphere sudden warming phenomenon in terms of the interaction of vertically propagating planetary waves with zonal winds, and verified the model by numerical integrations of the adiabatic-geostrophic potential vorticity equation.
Abstract: The dynamics of the stratosphere sudden warming phenomenon is discussed in terms of the interaction of vertically propagating planetary waves with zonal winds. If global-scale disturbances are generated in the troposphere, they propagate upward into the stratosphere, where the waves act to decelerate the polar night jet through the induction of a meridional circulation. Thus, the distortion and the break-down of the polar vortex occur. If the disturbance is intense and persists, the westerly jet may eventually disappear and an easterly wind may replace it. Then “critical layer interaction” takes place. Further intensification of the easterly wind and rapid warming of the polar air are expected to occur as well as weakening of the disturbance. The model is verified by numerical integrations of the adiabatic-geostrophic potential vorticity equation. Computed results possess features similar to those observed in sudden warming phenomena.
1,096 citations
TL;DR: In this paper, it was shown that from the observed freezing temperatures of the drops, one can derive both a differential and a cumulative nucleus spectrum, where the differential spectrum represents the concentrations of nuclei which are active at specific temperatures and the cumulative spectrum represented the concentrations for all temperatures warmer than the selected temperature.
Abstract: Freezing experiments using large numbers of small drops are frequently used for the study of both homogeneous and heterogeneous nucleation of water and of other substances. For heterogeneous nucleation, the spread in the observed freezing temperatures of drops has been shown to arise from the presence of nuclei of different activities in the sample. In the past no quantitative assessment of the nucleus content could be given independent of the drop sizes used. It is shown in this paper that from the observed freezing temperatures of the drops one can derive both a differential and a cumulative nucleus spectrum. The differential spectrum represents the concentrations of nuclei which are active at specific temperatures and the cumulative spectrum represents the concentrations of nuclei active at all temperatures warmer than the selected temperature. The accuracies of the derived spectra were examined by Monte Carlo simulation and are shown to be such that the concentrations are reliable to within f...
658 citations
TL;DR: In this paper, the authors measured the shear production, buoyant production, turbulent transport (flux divergence) and dissipation terms in the budget of turbulent kinetic energy, and production and turbulent transport terms in temperature variance budget.
Abstract: Measurements of the shear production, buoyant production, turbulent transport (flux divergence) and dissipation terms in the budget of turbulent kinetic energy, and production and turbulent transport terms in the temperature variance budget are presented. Direct observations of the surface stress and heat flux over a horizontally uniform site enable presentation of the data in terms of surface layer similarity theory. The dissipation term, obtained from differentiated hot-wire anemometer signals, agrees with estimates made from the inertial subrange levels of longitudinal velocity spectra with a value of 0.5 for the spectral constant. Under stable conditions dissipation essentially balances shear production, while turbulent transport and buoyant production are of secondary importance. Under unstable conditions, dissipation slightly exceeds the total production, and energy is also lost at a substantial rate due to upward export by the turbulence. The large imbalance among the measured terms in the...
521 citations
TL;DR: In this article, the conservation of Reynolds shear stress and the two components of heat flux (velocity-temperature covariance) in the homogeneous atmospheric surface layer are derived.
Abstract: Equations for the conservation of Reynolds shear stress and the two components of heat flux (velocity-temperature covariance) in the homogeneous atmospheric surface layer are derived. The behavior of the production and turbulent transport (flux divergence) terms in each budget is determined directly from measurements obtained over a wide range of stability conditions during the 1968 Kansas field program of AFCRL. The data are presented in the dimensionless form suggested by Monin-Obukhoy similarity theory, and follow universal functions quite well. The theory is extended to the “local free convection” regime which exists under very unstable conditions, and specific power law forms are predicted. Several of these are verified and values are given for the proportionality factors in the power laws. The flux divergence terms are small, implying that in each budget the local production and destruction rates are in balance. The third moments which represent the vertical fluxes of stress and heat flux a...
504 citations
TL;DR: In this article, the eddy-damped Markovian approximation to two-dimensional turbulence is applied to these motions to predict for an observed energy spectrum the nonlinear transfer rates, characteristic error spectra, and the rate of error growth.
Abstract: Recent observations indicate that the planetary-scale motions of the atmosphere obey some of the laws of two-dimensional turbulence. The eddy-damped Markovian approximation to two-dimensional turbulence is applied to these motions to predict for an observed energy spectrum the nonlinear transfer rates, characteristic error spectra, and the rate of error growth. In this way estimates are derived of the predictability of the atmosphere and of the errors inherent in numerical models. The use of stochastic models for turbulence approximations is described in an Appendix.
463 citations
TL;DR: In this paper, a physical model which predicts the shape of water drops falling at terminal velocity in air is presented, based on a balance of the forces which act on a drop falling under gravity in a viscous medium.
Abstract: A physical model which predicts the shape of water drops falling at terminal velocity in air is presented. The model is based on a balance of the forces which act on a drop falling under gravity in a viscous medium. The model was evaluated by numerical techniques and the shape of water drops of radii between 170 and 4000 μ (equivalent to Reynolds numbers between 30 and 4900) was determined. The results of our investigation show that the drop shapes predicted by the model agree well with those experimentally observed in our wind tunnel. Both theory and experiment demonstrate that: 1) drops with radii ≲170 μ are very slightly deformed and can be considered spherical, 2) the shape of drops between about 170 and 500 μ can be closely approximated by an oblate spheroid, 3) drops between about 500 and 2000 μ are deformed into an asymmetric oblate spheroid with an increasingly pronounced flat base, and 4) drops ≳2000 μ develop a concave depression in the base which is more pronounced for larger drop size...
435 citations
TL;DR: A compositing technique is used to obtain the average structure of 18 disturbances which traversed an area in the equatorial western Pacific during the wet season (July-September) of 1967 as mentioned in this paper.
Abstract: A compositing technique is used to obtain the average structure of 18 disturbances which traversed an area in the equatorial western Pacific during the wet season (July–September) of 1967. Principal emphasis is placed on the wave properties in the triangular area described by Ponape, Kwajalein and Eniwetok within which it was possible to measure divergence and vertical motion and to compute moisture and heat budgets. Meridional wind maxima of nearly opposite phase occurred in the lower and upper troposphere. Negative temperature deviations were found in the vicinity of the wave trough at low and high levels; positive deviations were observed at intermediate levels. Highest relative humidities occurred in the trough region. This was also the region of strongest upward motion and greatest rainfall and cloud amount. The maximum upward velocity of 2.5 cm sec−1 was found at 300 mb. Convergence was strongest in the sub-cloud layer; divergence was concentrated near 175 mb. The maximum anticyclonic vorti...
387 citations
354 citations
TL;DR: In this paper, the intensity and polarization of sunlight reflected by terrestrial water clouds are computed with the doubling method, which can be used to derive information about planetary clouds, including those of the earth, from polarimetric observations.
Abstract: The intensity and polarization of sunlight reflected by terrestrial water clouds are computed with the doubling method. The calculations illustrate that this method can be effectively used in problem involving strongly anisotropic phase matrices. The method can therefore be used to derive information about planetary clouds, including those of the earth, from polarimetric observations. The results of the computations indicate that the polarization is more sensitive than the intensity to cloud microstructure, such as the particle size and shape. Multiple scattering does not wash out features in the polarization as effectively as it does in the intensity, because the polarization arises primarily from photons scattered once or a small number of times. Hence polarization measurements, particularly in the near infrared, are potentially a valuable tool for cloud identification and for studies of the microphysics of clouds. The computations are made primarily at four wavelengths in the near infrared, fr...
TL;DR: In this article, the size distribution of raindrops at heights below the 0C level was computed using the updraft UR deduced by Rogers' method and two other updrafts, namely UR − 1 and UR + 1 m sec−1.
Abstract: Data obtained in a thunderstorm with a vertically pointing Doppler radar are analyzed to find the size distribution of raindrops at heights below the 0C level. Drop-size distributions were computed using the updraft UR deduced by Rogers' method and two other updrafts, namely, UR − 1 and UR + 1 m sec−1. It is found that the drop-size data at all the heights may be well represented by the exponential equation, N (D) = N0 exp(− ΛD), in which N (D)ΔD is the concentration of drops in the diameter range D to D + ΔD, N0 = 0.07 R0.37 [cm−4], and Λ = 38R−0.14 [cm−1], R being the rainfall rate (mm hr−1). For R ≳ 3 mm hr−1, the distribution is steeper and N0 is greater as compared to the Marshall-Palmer distribution. For radar reflectivity factors Z in the range 1–105 mm6 m−3, the relationship between the mean Doppler velocity and Z for the distribution agrees with that given by Rogers to within 1 m sec−1. The following equations have been found between the water content M, median volume diameter D0, radar ...
TL;DR: In this article, the effect of ventilation on the rate of evaporation of millimeter sized water drops failing at terminal velocity in air has been carried out in a wind tunnel where drops were suspended freely in the tunnel air stream.
Abstract: An experimental study of the effect of ventilation on the rate of evaporation of millimeter sized water drops failing at terminal velocity in air has been carried out in a wind tunnel where drops were suspended freely in the tunnel air stream. It was found that for drops in the size range 1150 µm≤a0≤2500 µm, the mean ventilation coefficient fvfh could be expressed as f=(0.78±0.02)+(0.308±0.010)X, where X=N&frac13Sc,v N½Re. Previously, we showed that this relation holds for drops in the size range 60 µm≤a0≤400 µm. Taken together, our present and previous data suggest that with reasonable accuracy f=0.78+0.308X, for 1.4≤X≤51.4 (60 µm≤a0≤2500 µm). For 0≤X≤1.4 (0≤a≤60 µm), one may use our previous result f=1.00+0.108 X2. To illustrate how the present data may be applied, we computed the distance which is required for a water drop to travel from cloud base through a NACA Standard Atmosphere of various relative humidities, in order to reach the earth's surface with a given size.
TL;DR: In this paper, the authors present the geometry and intensity of the mean east-west circulation during the northern winter and show that near the equatorial latitudes two pronounced regions of divergent mass outflow in the upper troposphere are found near the convective regions over the northwestern part of South America and Indonesia.
Abstract: In this Paper we present the geometry and intensity of the mean east–west circulation during the northern winter. We show that near the equatorial latitudes two pronounced regions of divergent mass outflow in the upper troposphere are found near the convective regions over the northwestern part of South America and Indonesia. The intensity of the east–west circulation is shown to be of the order of 1 m sec−1 which is comparable to the intensity of the Hadley circulation. The divergent streamlines are shown to be important for the maintenance of the three waves of the subtropical westerly jet in the Northern Hemisphere, and are shown to exhibit asymptotes of convergence in the regions of mid-oceanic upper tropospheric troughs over the tropical southern oceans. Kinetic energy exchanges for a tropical belt 15S to 15N at 200 mb are expressed as a function of zonal wavenumber. Results for northern summer and winter seasons are compared. We find that wave interactions with the mean zonal flow differ in...
TL;DR: In this article, an extended time series of measurements of the earth's radiation budget from the first and second generation United States meteorological satellites is presented. But the role of these radiation budget measurements in the total global energy balance is noted.
Abstract: This paper summarizes an extended time series of measurements of the earth's radiation budget from the first and second generation United States meteorological satellites. Values of planetary albedo, infrared radiant emittance, and the resulting net radiation budget are now available for 39 months during the period 1962–66. These measurements show a mean global albedo of 30%, and net radiation balance within measurement accuracy. The discussion treats global and zonally averaged values for the “mean annual” case, for “mean seasons,” and includes a comparison of measurements during the same seasons in different years. The role of these radiation budget measurements in the total global energy balance is noted.
TL;DR: In this paper, the authors describe results of measurements of the fluxes of momentum, moisture and sensible heat by both the eddy correlation and dissipation techniques on R/V Flip during BOMEX (Barbados Oceanographic and Meteorological Experiment) and during a pre-BOMEX trial cruise near San Diego in February 1969.
Abstract: This paper describes results of measurements of the fluxes of momentum, moisture and sensible heat by both the eddy correlation and “dissipation” techniques. The data were collected on the R/V Flip during BOMEX (Barbados Oceanographic and Meteorological Experiment) and during a pre-BOMEX trial cruise near San Diego in February 1969. The results are mainly based on data collected by personnel from Oregon State University and the University of British Columbia. We are grateful to the University of Washington personnel who have made their data and results available to us to check some of our results and allowed us to use their temperature fluctuation data from the San Diego cruise when our equipment failed to provide such data. The methods of determining the fluxes are discussed. The instrumentation and methods of data analysis are described. The effects of Flip's interference on the flow are described and the method of removing the interference from the results is given. The spectra of the three co...
TL;DR: In this paper, the authors investigated an important natural source of NO, the reaction O(1D + N2O → 2NO, and compared the natural source with estimates for the source due to a fleet of 500 planes cruising for an average of 7 hr a day.
Abstract: Supersonic transport planes currently under development will cruise in the stratosphere and there is concern about possible environmental effects. In particular, NO emitted by these aircraft may catalytically affect atmospheric ozone. Here we investigate an important natural source of NO, the reaction O(1D) + N2O → 2NO, and compare the natural source with estimates for the source due to a fleet of 500 planes cruising for an average of 7 hr a day. The natural and artificial inputs above 15 km are of comparable magnitude. The natural source corresponds to a net production of NO, averaged over the globe, of about 2 × 107 molecules cm−2 sec−1, and offers a yardstick for judging the possible significance of any artificial input. Additional sources of stratosphere NO, due to downward diffusion from the ionosphere and upward transport from the earth's surface, are discussed but have not been quantitatively estimated at this time.
TL;DR: In this article, the evolution of raindrop-size distributions under the operation of the processes of drop breakup and coalescence are presented, and it is found that the size distribution approaches a stationary state.
Abstract: Some computations of the evolution of raindrop-size distributions under the operation of the processes of drop breakup and coalescence are presented. It is found that the size distribution approaches a stationary state. The stationary size distributions for different rainfall rates are roughly parallel to each other when logf(r) is plotted against r, f(r) being the concentration density of drops of radius r. A comparison with observations shows that the computed distributions are flatter than the observed ones. It is suggested that other processes besides the breakup and coalescence of raindrops shape their distribution with size.
TL;DR: In this article, measurements were made from aircraft of the 1.55-cm microwave emission from the North Sea and North Atlantic at surface wind speeds ranging from less than 5 to 25 m sec−1.
Abstract: Measurements were made from aircraft of the 1.55-cm microwave emission from the North Sea and North Atlantic at surface wind speeds ranging from less than 5 to 25 m sec−1. Brightness temperatures in the nadir direction increased almost linearly with wind speed from 7 to 25 m sec−1 at a rate of about 1.2C (m sec−1)−1. At 70° from nadir the rate was 1.8C (m sec−1)−1. This increase was directly proportional to the occurrence of white water on the sea surface. At wind speeds <7 m sec−1, essentially no white water was observed and brightness temperatures in the nadir direction were ∼120K; at wind speeds of 25 m sec−1 white water cover was on the order of 30% and average brightness temperatures at nadir were −142K. Maximum brightness temperatures for foam patches large enough to fill the entire radiometer beam were 220K.
TL;DR: In this paper, the doubling method for multiple scattering of light in plane-parallel atmospheres is described for realistic simulations of clear, hazy and cloudy planetary atmospheres, where the polarization of the radiation and the azimuth dependence are correctly accounted for.
Abstract: The doubling method is described for multiple scattering of light in plane-parallel atmospheres. The polarization of the radiation and the azimuth dependence are correctly accounted for. The method is practical for application to realistic simulations of clear, hazy and cloudy planetary atmospheres.
TL;DR: In this paper, the drag coefficients of planar snow crystals, two conical graupel and three conical small-hail particles were determined experimentally in glycerin-water mixtures and salt solutions.
Abstract: Drag coefficients and Best numbers of models of six planar snow crystals, two conical graupel and two conical small-hail particles were determined experimentally in glycerin-water mixtures and salt solutions. The Reynolds number (Re) range covered for the crystals was 0.1 to 200 and for the conical models 10 to 2000. It was found that the drag coefficients of dendritic shapes differed by factors of up to 4 from that of a disc of equal thickness and at an equal Reynolds number. The drag ratio is roughly constant with Re and linearly related to the ratio of the respective surface areas. The drag coefficients of the conical models assumed values between 0.5 and 2.0. During steady fall they decreased with increasing Re; however, as soon as oscillations started this trend reversed. Since tumbling does occur for larger graupel and small hail at Re > 300–1000 their main characteristic motions and frequencies are also discussed. Values for oscillation frequencies are given and the motions are described i...
Journal Article•
TL;DR: In this paper, the authors calculate the limb radiance as a function of tangent height and the vertical distribution of temperature and the pressure at one level, using an iterative technique.
Abstract: The calculation of limb radiance as a function of tangent height is shown to require information about the vertical distribution of temperature and the pressure at one level. Conversely, given the limb radiance curve and the pressure corresponding to one tangent point, it is possible to determine the temperature profile as a function of height relative to the given level, using an iterative technique. Results of inverting synthesized realistic data are presented. The data include the effects of water vapor and ozone contamination of the carbon dioxide signal, instrument field of view, and random and systematic noise for real atmospheres having small-scale vertical structure.
TL;DR: In this article, the vertical distribution of temperature and the pressure at one level is used to determine the temperature profile as a function of height relative to the given level, using an iterative technique.
Abstract: The calculation of limb radiance as a function of tangent height is shown to require the vertical distribution of temperature and the pressure at one level. Conversely, given the limb radiance curve and the pressure corresponding to one tangent point, it is possible to determine the temperature profile as a function of height relative to the given level, using an iterative technique. If the given pressure is incorrect, there will be systematic errors in the inferred temperatures. This feature may he used to determine the correct pressure by requiring that temperatures inferred from measurements in two spectral regions of differing opacities agree. Results of inverting synthesized realistic data are presented. The data include the effects of water vapor and ozone contamination of the carbon dioxide signal, instrument field of view, and random and systematic noise for real atmospheres having small-scale vertical structure. Results indicate that the temperature may be obtained from the tropopause to...
TL;DR: In this paper, the authors examined the presence and dimensions of lake-effect clouds over the Great Lakes and Gulf of St Lawrence and found that nearly all lake effect clouds occurred when the 850-mb temperature was more than 13C colder than the lake surface temperature.
Abstract: Satellite photographs of the TIROS and ESSA series were examined for the presence and dimensions of lake-effect clouds over the Great Lakes and Gulf of St. Lawrence. It was found that nearly all lake-effect clouds occurred when the 850-mb temperature was more than 13C colder than the lake surface temperature. The clouds were organized into parallel bands resembling but having larger dimensions than cloud streets. Enlarged cloud bands were found which were 2.5 times larger than normal lake-effect bands. These enlarged lake storms had preferred origins and appear to be generated by frictional differences between land and water, by the geometry of the body of warm water with respect to the prevailing wind, and by certain urban influences.
TL;DR: In this article, a simple linear filter of order n is adapted for use in numerical models of the large-scale circulation to act in place of an explicit horizontal diffusion term in the equations.
Abstract: A simple linear filter is adapted for use in numerical models of the large-scale circulation to act in place of an explicit horizontal diffusion term in the equations. The filter can be shown to be ideally suited for this purpose in the sense that it can be made increasingly scale-dependent as the order of the filter is increased. The one-dimensional filter of order n is constructed from n three-point symmetrical operators and involves 2n/1 grid points. It is capable of eliminating two-grid-interval waves completely, yet allowing little or no damping of longer waves. In one space dimension, the use of the n = 1 order filter can be shown to be equivalent to the incorporation of a one-dimensional Fickian diffusion term in the differential equation. For any order n, the use of the one-dimensional filter is equivalent to the incorporation of a one-dimensional linear diffusion of order 2n. It is therefore apparent that as n increases, the ability of the filter to discriminate in its response to short-...
TL;DR: In this paper, the authors describe the method of incorporating into the NCAR global circulation model the dynamic effect of mountains, the prediction of cloudiness for radiation calculations, and the calculation of ground surface temperature using a heat balance equation.
Abstract: This paper describes the method of incorporating into the NCAR global circulation model the dynamic effect of mountains, the prediction of cloudiness for radiation calculations, and the calculation of ground surface temperature using a heat balance equation. Other aspects of the physics of the model and the finite-difference schemes are very similar to those discussed by the authors in 1967 and 1970. For the simulation of seasonal climate we specify two parameters: the sun's declination and the distribution of ocean surface temperatures. Since the prediction of cloudiness is parameterized in terms of the relative humidity and the vertical motion fields, solar and atmospheric radiation processes interact closely with the dynamics of the atmosphere through variations in the fields of cloudiness, temperature and water vapor. Coupling between radiation and dynamics helps to maintain stronger baroclinic activity in middle latitudes. Although a hydrologic cycle is included in the model atmosphere and t...
TL;DR: In this paper, the similarities and differences between temperature and humidity and on their cospectra and correlations with the velocity fluctuations were investigated on the R/V Flip during BOMEK in May 1969 and during a pre-BOMEX trial cruise near San Diego in February 1969.
Abstract: Temperature and humidity fluctuation data were collected on the R/V Flip during BOMEK (Barbados Oceanographic and Meteorological Experiment) in May 1969 and during a pre-BOMEX trial cruise near San Diego in February 1969. The program was a cooperative one with a number of groups on board. In a companion paper with the personnel from the University of British Columbia, the equipment and data analysis are described in more detail and the results of measurements of the fluxes of momentum, moisture and sensible heat are given. The emphasis of this paper is on the similarities and differences between temperature and humidity and on their cospectra and correlations with the velocity fluctuations. During the San Diego experiment it was found that humidity and temperature fluctuations were very similar with only minor differences. During BOMEX the humidity fluctuations were similar to those obtained during the San Diego experiment and to measurements over land, but the low-frequency ends of the temperatu...
TL;DR: In this paper, a method of computing the rate of growth of nonspherical ice crystals by deposition is described, and predictions of growth characteristics over the temperature range of −1 through −35C are shown and compared with meager experimental data available within this temperature range.
Abstract: A method of computing the rate of growth of ice crystals by deposition is described. Predictions of growth characteristics over the temperature range of −1 through −35C are shown and compared with meager experimental data available within this temperature range. The growth rate equations are based on Fick's law of diffusion. In applying this law to nonspherical ice crystals, the analogy between an electrostatic potential field surrounding a charged body and the vapor-density field surrounding a similarly shaped ice crystal is utilized. Allowances are made for effects of forced convection caused by the movement of the crystal through the air and the change in shape and bulk density of the ice crystal; these effects are predicted to be of significant importance. A simple, empirical equation using two temperature-dependent parameters was found to describe the crystal growth rate as a, function of mass. For many cases where only the rate of mass conversion from vapor to solid is required, the simple ...
TL;DR: In this article, a comparison of the roles played by thermophoresis, Brownian diffusion and diffusi-phoresis in the precipitation scavenging of aerosol particles is made.
Abstract: A comparison is made of the roles played by thermophoresis, Brownian diffusion and diffusiophoresis in the precipitation scavenging of aerosol particles. It is shown, for a certain range of particles sizes, that thermophoresis dominates provided that the latent heat associated with the phase transition of water is transferred through the air, to or from the precipitation element by conduction. A plot of the resulting washout coefficient shows that thermophoresis enhances the below-cloud rain scavenging of aerosol particles whose radii are between 0.01 and 1.0μ. The solution is presented for the appropriate convective diffusion equation which describes thermophoretic effects on the in-cloud scavenging problem.