Drop Spectra Research Articles

Influence of entrainment of CCN on microphysical properties of warm cumulus

Abstract. We use a 1-D cloud model with explicit microphysics and a binned representation of the aerosol size distribution to investigate the influence of entrainment of cloud condensation nuclei (CCN) on the microphysical development of warm cumulus clouds. For a more realistic representation of cloud drop spectral width, the model separates droplets that grow on aerosol that is initially present in the cloud from droplets growing on entrained aerosol. Model results are compared with observations of trade wind cumulus microphysics from the Rain in Cumulus over the Ocean experiment (RICO, 2004–2005). The results indicate that CCN are entrained throughout the entire cloud depth, and inside the cloud part of these may be activated. Compared to a simulation where entrainment of ambient CCN is neglected this leads to higher cloud droplet number concentrations (CDNC) and a continuous presence of droplets in the range smaller than ~5 μm that is consistent with the observations. Cloud dynamics are sensitive to the entrainment parameter as well as to the applied initial vertical velocity, as expressed by the liquid water content and cloud top height. However, simulated cloud drop spectra remain relatively unaffected for the specific conditions during RICO.

Fidelity of Analytic Drop Size Distributions in Drizzling Stratiform Clouds Based on Large-Eddy Simulations

Abstract Cloud microphysical parameterizations and retrievals rely heavily on knowledge of the shape of drop size distributions (DSDs). Many investigations assume that DSDs in the entire or partial drop size range may be approximated by known analytical functions. The most frequently employed approximations of function are of the type of gamma, lognormal, Khrgian–Mazin, and Marshall–Palmer. At present, little is known about the accuracy of these approximations. The authors employ a DSD dataset generated by the Cooperative Institute for Mesoscale Meteorological Studies Large-Eddy Simulation (CIMMS LES) explicit microphysics model for stratocumulus cases observed during the Atlantic Stratocumulus Transition Experiment (ASTEX) field project. The fidelity of analytic lognormal- and gamma-type DSD functions is evaluated according to how well they represent the higher-order moments of the drop spectra, such as precipitation flux and radar reflectivity. It is concluded that for boundary layer marine drizzling stratocumuli, a DSD based on the two-mode gamma distribution provides a more accurate estimate of precipitation flux and radar reflectivity than the DSD based on the lognormal distribution. The gamma distribution also provides a more accurate radar reflectivity field in two- and three-moment bulk microphysical models compared to the conventional Z–R relationship.

Spectral shift by half free-spectral-range for microring resonator employing the phase jump phenomenon in coupled-waveguide and application on all-microring wavelength interleaver

Using coupled-mode theory, we have shown that there is a pi phase jump between the input and the through/drop fields of a codirectional coupler when the gap width between the coupled-waveguides reaches certain values such that the length of the coupler equals to the odd integer (for through field) or even integer (for drop field) times of the Transfer Distance. We introduced an efficient numerical method based on combining the scattering matrix method and FDTD method for analyzing a microring that has material loss. By applying this method, we found that the phase jump phenomenon also occurs in a half-ring coupler when the gap width between the coupled half-ring waveguides reaches a critical value. We showed that, for a given operating bandwidth, it is important that the gap width between the rings has to be larger than a certain value in order to avoid the phase jump, or smaller in order to take advantage of the phase jump. Based on the phase jump phenomenon, we found that the through and the drop spectra of the single-arm and the double-arm microring can be manipulated to shift about one half free spectral range by selecting appropriate gap widths. A novel all-microring wavelength interleaver, based on the phase jump phenomenon, is proposed and numerically demonstrated.

An Intercomparison of Model Simulations and VPR Estimates of the Vertical Structure of Warm Stratiform Rainfall during TWP-ICE

Abstract A model of rain shaft microphysics that solves the stochastic advection–coalescence–breakup equation in an atmospheric column was used to simulate the evolution of a stratiform rainfall event during the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) in Darwin, Australia. For the first time, a dynamic simulation of the evolution of the drop spectra within a one-dimensional rain shaft is performed using realistic boundary conditions retrieved from real rain events. Droplet size distribution (DSD) retrieved from vertically pointing radar (VPR) measurements are sequentially imposed at the top of the rain shaft as boundary conditions to emulate a realistic rain event. Time series of model profiles of integral parameters such as reflectivity, rain rate, and liquid water content were subsequently compared with estimates retrieved from vertically pointing radars and Joss–Waldvogel disdrometer (JWD) observations. Results obtained are within the VPR retrieval uncertainty estimates. Besides evaluating the model’s ability to capture the dynamical evolution of the DSD within the rain shaft, a case study was conducted to assess the potential use of the model as a physically based interpolator to improve radar retrieval at low levels in the atmosphere. Numerical results showed that relative improvements on the order of 90% in the estimation of rain rate and liquid water content can be achieved close to the ground where the VPR estimates are less reliable. These findings raise important questions with regard to the importance of bin resolution and the lack of sensitivity for small raindrop size (<0.03 cm) in the interpretation of JWD data, and the implications of using disdrometer data to calibrate radar algorithms.

The role of boundary layer aerosol particles for the development of deep convective clouds: A high-resolution 3D model with detailed (bin) microphysics applied to CRYSTAL-FACE

This paper reproduces aircraft microphysical measurements using a three-dimensional model with bin resolved microphysics and is then used to analyze in particular the role of boundary layer aerosol particles in the anvil and the ice phase. The simulated case is a convective cloud which develops a large anvil of around 10 km height, which was sampled during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers — Florida Area Cirrus Experiment (CRYSTAL-FACE). The model couples the 3D dynamics of a cloud scale model with a detailed mixed phase microphysical code. The microphysical package considers the evolution of the wet aerosol particles, drop and ice crystal spectra on size grids with 39 bins. With this model hereafter called DESCAM 3D, we are able to simulate the cloud with features close to those observed and to provide explanations of the observed phenomena concerning cloud microphysics as well as cloud dynamics. The same CRYSTAL-FACE cloud has already been simulated by other groups using a similar model. They investigated the role of mid-tropospheric aerosol particles versus boundary layer aerosol on the microphysical properties of the anvil. Similar simulations with our DESCAM 3D lead to quite different results. Reducing the number of mid-tropospheric aerosol particles causes only minor changes in the cloud anvil. However, changing the aerosol particle spectrum in the boundary layer from clean to polluted conditions modifies strongly the dynamical evolution of the convective clouds and thus impacts significantly on the microphysical properties of the anvil. Possible reasons for the differences are discussed.

Comparison of Different Techniques for the Measurement of Precipitation in Tropical Montane Rain Forest Regions

Abstract Characteristics of different precipitation measurements in a tropical mountain valley in southern Ecuador are compared in this study to determine potential errors. The instruments are used for different ecological purposes like erosion studies, through fall measurements, investigation of atmospheric chemistry, and modeling of area rainfall distribution. Five recording devices (two precipitation radars, an electro-optical present weather sensor, and two tipping buckets) and three totaling gauges were operated in parallel at a designated site. Data were taken between 1998 and 2003 with different temporal resolution and different operational periods. The general agreement between the instruments is rather good; deviations are in the expected range of 10%–20% of the annual total of about 2200 mm. The remote sensing devices are superior in registering the frequent occurrence of light rain but are not capable of detecting the full range of rain intensities observed. The tipping buckets and the totaling gauges are reliable instruments, but a certain fraction of light drizzle and wind-driven rain is not detected. The present weather sensor has the widest range of sensitivity and supplies additional information on drop spectra. All datasets are affected by operational problems (interruptions, synchronization errors); hence, the redundancy given here seems reasonable for an ecosystem study.

LASER-DIFFRACTION CHARACTERIZATION OF FLAT-FAN NOZZLES USED TO DEVELOP AEROSOL CLOUDS OF AERIALLY APPLIED MOSQUITO ADULTICIDES

The importance of appropriate drop size and density for successful mosquito adulticide applications mandates the necessity for accurate determination of drop spectra of a particular nozzle. There is considerable disparity between mass median diameter (MMD) determinations for flat-fan nozzles relative to the horizontal or vertical orientation of the microscope slide used to collect the drops. To remove this ambiguity, the definitive MMDs of flat-fan nozzles used in aerially applied mosquito control adulticides were determined by laser-diffraction-based characterization and analysis. These data were compared with previous data, and the impact of these data on aerial adult mosquito control was discussed. At The Florida Wind Tunnel for Mosquito Control, the Malvern Spraytec Spray Particle Analysis System was used to characterize the entire aerosol plume of the nozzles. Nozzle characterizations were carried out at aircraft operational wind speeds and pressures with nozzles mounted at 135 degrees relative to the direction of air flow. The mean drop-diameter volumes (Dv) Dv(0.1), Dv(0.5), and Dv(0.9) with 95% confidence intervals for each scenario were determined. Characterizations of flat-fan nozzles of 80005 to 8005 for Orchex 796, Dibrom and a Permanone:Orchex 796 mix (1:1) resulted in no Dv(0.5) less than 50 microm and a maximum of 133 microm. The Dv(0.1) was greater than 25 min for 52% of the nozzles and ranged from 14 to 42 microm. The Dv(0.9) ranged from 130 to 296 microm. There was a decrease in drop-diameter values (Dv(0.1), Dv(0.5), Dv(0.9)) relative to increased wind speed and/or pressure for any particular nozzle. Relative to characterizations with Orchex 796, drop-diameter values for Dibrom varied from the same to slightly larger, whereas the Permanone:Orchex 796 mix values were larger except for 2. Relative to the goal of creating an aerosol cloud efficient in controlling adult mosquitoes, none of the nozzles were capable of producing a Dv(0.5) of less than 50 microm. Fifty percent of the spray was capable of causing visible damage to a car's finish. The concept that droplets larger than 25 microm are wasteful because they contain more malathion than required for kill suggests that for 52% of the nozzle configurations, those with Dv(0.1) greater than 25 microm, 90% of the spray is of little use in controlling mosquitoes. None of the flat-fan nozzle regimes tested will satisfy new label requirements of a Dv(0.5) and Dv(0.9) of around 50 and 100 microm, respectively, because of their high Dv(0.9).

Optimization of a 2D photonic crystal add/drop multiplexer based on contra-directional coupling

We present a highly integrated add/drop multiplexer, where the contra-directional coupling is realized by phase matching two photonic crystal waveguides. The device band structure, the corresponding transmission and drop spectra, and the coupling length are carefully analysed. Different device configurations are discussed and by tailoring the coupling factor, we optimize the frequency response of the filter, obtaining a μ -sized channel selector, characterized by a very high drop efficiency.

Correction of Radar Reflectivity and Differential Reflectivity for Rain Attenuation at X Band. Part I: Theoretical and Empirical Basis

Abstract In this two-part paper, a correction for rain attenuation of radar reflectivity (ZH) and differential reflectivity (ZDR) at the X-band wavelength is presented. The correction algorithm that is used is based on the self-consistent method with constraints proposed by Bringi et al., which was originally developed and evaluated for C-band polarimetric radar data. The self-consistent method is modified for the X-band frequency and is applied to radar measurements made with the multiparameter radar at the X-band wavelength (MP-X) operated by the National Research Institute for Earth Science and Disaster Prevention (NIED) in Japan. In this paper, characteristic properties of relations among polarimetric variables, such as AH–KDP, ADP–AH, AH–ZH, and ZDR–ZH, that are required in the correction methodology are presented for the frequency of the MP-X radar (9.375 GHz), based on scattering simulations using drop spectra measured by disdrometers at the surface. The scattering simulations were performed under conditions of three different temperatures and three different relations for drop shapes, in order to consider variability of polarimetric variables for these conditions. For the X-band wavelength, the AH–KDP and ADP–AH relations can be assumed to be nearly linear. The coefficient α of the AH–KDP relation varies over a wide range from 0.139 to 0.335 dB (°)−1 with a mean value of 0.254 dB (°)−1. The coefficient γ of the ADP–AH relation varies from 0.114 to 0.174, with a mean value of 0.139. The exponent b of the AH–ZH relation does not depend on drop shapes and is almost constant for a given temperature (about 0.78 at the temperature of 15°C). The ZDR–ZH relation depends primarily on drop shape, and does not vary with temperature.

The Influence of the Acoustic-electric Coalescence on Phase and Mass Transfer of Supercooled Drops

The objective of this work is to study the influence of electrical discharge on the evolution of the cloud droplet spectra using a 1-D cloud model. It is shown that droplet motion and the electrical effects produced by lightning may cause a rapid and effective droplet coalescence process, with noticeably more phase transfer from liquid toward frozen water. As a measure of the drop spectra changes, we investigated variations of the radar reflectivity factor and the mass-weighted mean diameters at five temperature levels (0, −5, −10, −15, and −20C) with 15 combinations of the initial conditions. The model simulations suggest that about where the lightning occurred, after a few seconds, the initial unimodal spectra of supercooled water drops can be transferred to the bimodal spectra of unfrozen and frozen water drops. The number of newly created frozen drops is a few orders less than unfrozen water drops, but can still be very important for further transformations due to gravitational coagulation and other microphysical processes, e.g. glaciation. The results indicate that the procedure established to describe processes related to the electrical discharge and droplet spectra transformations can be used within a 3-D mesoscale model. It is concluded that the outcome can be also used to explain some of the physical characteristics inferred from polarimetric radar observations.

The effect of wind velocity fluctuations on drop spectrum broadening in stratocumulus clouds

In this study, a Lagrangian adiabatic parcel model and a trajectory ensemble model (TEM) are used in a sequence of experiments to investigate effects of velocity fluctuations on drop spectrum broadening in stratocumulus clouds. Using the adiabatic parcel model, it is found that even with a weakly buoyant temperature profile, if the initial updraft velocity is low enough, new drop nucleation above the cloud base region can occur via updraft acceleration accompanied by an increase in supersaturation. New nucleation can also occur via parcel recirculation as drops that have not fully evaporated during downdraft reduce the cloud base supersaturation peak in subsequent updrafts. The new nucleation produces new modes in the drop spectrum, broadening the spectrum towards smaller drops. Spectral broadening is also reproduced in the TEM, where an ensemble of 680 parcel trajectories is derived from a large eddy simulation (LES) velocity field. In the TEM, the mechanisms of in-cloud nucleation and growth/evaporation asymmetry caused by updraft acceleration and parcel recirculation promote spectral broadening predominantly in the lower and intermediate levels of the cloud, where parcels with initially low updraft velocities reside. To explicitly evaluate the effect of subgrid scale turbulent velocity fluctuations on drop spectrum evolution, such fluctuations are added to the mean LES velocity field. The velocity fluctuations are simulated using the Langevin equation, where turbulent diffusion is represented as an autoregression random process of the 1st order. The velocity fluctuations alter parcel trajectories, allowing parcels with initially low vertical velocities to be swept into higher vertical velocity eddies and to penetrate deeper into the cloud. The resulting updraft acceleration and parcel circulation lead to new drop nucleation and to broadening of the upper level drop spectra. The added subgrid turbulent velocity fluctuations also increase the overall number of parcels that exhibit new drop nucleation, bringing the fraction to half of the total ensemble under the assumption of strong turbulence. The above mechanisms help explain the existence of quite broad and bimodal stratiform cloud drop spectra, as well as the variation in stratiform drop spectra over short spatial scales. The sensitivity of the above mechanisms to the shape of the CCN spectrum and to variation in the turbulence parameters is investigated.

Coupled mode theory for photonic crystal cavity-waveguide interaction

We derive a coupled mode theory for the interaction of an optical cavity with a waveguide that includes waveguide dispersion. The theory can be applied to photonic crystal cavity waveguide structures. We derive an analytical solution to the add and drop spectra arising from such interactions in the limit of linear dispersion. In this limit, the spectra can accurately predict the cold cavity quality factor (Q) when the interaction is weak. We numerically solve the coupled mode equations for the case of a cavity interacting with the band edge of a periodic waveguide, where linear dispersion is no longer a good approximation. In this regime, the density of states can distort the add and drop spectra. This distortion can lead to more than an order of magnitude overestimation of the cavity Q.

Scale Dependence of Radar-Rainfall Rates—An Assessment Based on Raindrop Spectra

Abstract Scale differences may introduce a bias when comparing, merging, or assimilating rainfall measurements because the dynamic range of values representing the underlying physical process strongly depends on the resolution of the data. The present study addresses this issue from the perspective of how well coarser-resolution radar-rainfall observations may be used for evaluation of hydrologic point processes occurring at the land surface, such as rainfall erosion, infiltration, ponding, and runoff. Conceptual and quantitative analyses reveal that scale differences may yield substantial biases. Even for perfect measurements, the overall bias is composed of two contributing factors: one related to a reduction of dynamic range of rain rates and the other related to a dependence of the relationship between observed radar reflectivity factor and retrieved rainfall rate on the scale of observation. The effects of scale differences are evaluated empirically from a perspective of averaging in time based on raindrop spectra observations. Averaging drop spectra over 5 min, on average over a large dataset, resulted in an underestimation of median and maximum rainfall rates of approximately 50% compared to the corresponding 1-min values. Overall, standard deviations of rain rates retrieved from 5-min-averaged radar reflectivity factors may easily be off a corresponding high-resolution (1 min) rainfall rate by a factor 2 or more. This magnitude is larger than the uncertainty resulting from limitations of the radar measurement precision. Scale-difference effects are thus important and should be considered when comparing, merging, or assimilating data from very different spatial and temporal scales. A similar challenge arises for downscaling schemes attempting to recover subgrid-scale features from coarse-resolution information.

Düsen für die Gemüsewäsche

The drop spectra formed in the spray jet of various nozzles were tested on their energy and evaluated for their efficiency. Forming an efficient spray structure for vegetable cleaning is significantly defined by volume flow in combination with the nozzle d

Multisensor analysis of a squall line in the Amazon Region

Mesoscale features of the 26 January 1999 squall line are described with measurements made during the field experiment in Rondônia, Brazil, in the wet season (WET) of the Amazon region (AMC) as part of the Large‐Scale Biosphere‐Atmosphere Experiment in the Amazon (LBA) and the Tropical Rainfall Measurement Mission (TRMM); henceforth referred to as the WET AMC and TRMM‐LBA field experiment. The squall line moved through the experiment area from northeast to southwest with high rainfall rates in its leading edge and a poorly defined trailing stratiform precipitating area. Polarimetric and Doppler measurements from the Portable Polarimetric S‐band Radar (S‐POL) were analyzed in conjunction with surface and upper level data, satellite visible (VIS) and infrared (IR) measurements. These remote and local measurements of variables such as cloud spatial and temporal distribution, pressure, temperature, moisture, precipitation, and wind fields are consistent with each other as well as with similar mesoscale dynamics and thermodynamics features measured, analyzed, and modeled elsewhere [e.g., Rotunno et al., 1988; Garstang et al., 1994; Houze et al., 1990]. This tropical squall line is similar to its cousins in the midlatitudes with finer‐scale structural and dynamic features such as rotation and divergence. Results suggest that the cold pool has its origins in midlevels between 400 and 600 hPa from where evaporative cooling and drop‐dragging bring down colder air to the surface. The convective region is dominated by warm microphysics, while the stratiform region is dominated by cold microphysics. Moreover, both regions are characterized by monomodal drop spectra centered around 2.0 and 1.0 mm, respectively. Horizontal circulation associated with strong updrafts tends to increase cloud growth efficiency in the leading edge of the squall line.

Studies of HTO Washout and Deposition in the Vicinity of Emission Source II: Model - Experiment Intercomparison

ABSTRACTThere are presented in the research results of HTO washout and the model of HTO atmosphere concentration in the vicinity of a long-term HT and HTO emission source. The site of the scavenging experiments was around a 30 m emission source. The sampling arcs were chosen at 150–300 m from the base of the source to minimize dry deposition on the precipitation collectors. To study dependence of scavenging of tritium on raindrops characteristics, an optical device was constructed and used to measure the distribution of the drop radii and velocities during the period of experiment.The washout model, used for assessments, takes into account dispersion, deposition and re-emission. The model of HTO wet deposition is taken into account kinetics of HTO exchange between vapor and liquid phase with parameters such as rain drop spectra, rain intensity, condensation-evaporation on drop’s interface. Gauss type formulae for permanent emission source is used to calculate HTO atmospheric concentration. Meteorological data are used as input parameters for modeling.

The Need to Represent Raindrop Size Spectra as Normalized Gamma Distributions for the Interpretation of Polarization Radar Observations

Polarization radar techniques essentially rely on detecting the oblateness of raindrops to provide a measure of mean raindrop size and then using this information to give a better estimate of rainfall rate R than is available from radar reflectivity Z alone. To derive rainfall rates from these new parameters such as differential reflectivity ZDR and specific differential phase shift KDP and to gauge their performance, it is necessary to know the range of naturally occurring raindrop size spectra. A three parameter gamma function is in widespread use, with the three variables No, Do, and μ providing a measure of drop concentration, mean size, and spectral shape, respectively. It has become standard practice to derive the range of these three variables in rain by comparing the 69 published values of the constants a and b in the empirical relationships Z = aRb with the values of a and b obtained when R and Z are derived by integrating the appropriately weighted gamma function. The relationships in common use both for inferring R from Z, ZDR, and KDP, and for developing attenuation correction routines have been derived from a best fit through the values obtained by cycling over these predicted ranges of No, Do, and μ. It is pointed out that this derivation of the predicted range of No, Do, and μ arises using a flawed logic for a particular nonnormalized form of the gamma function, and it is shown that the predicted ranges give rise to some very unrealistic drop spectra, including many with high rainfall and very small drop sizes. It is suggested that attenuation correction routines relying on differential phase may be suspect and the commonly used relationships between rainfall rate and Z, ZDR, and KDP need to be reexamined. When more realistic drop shapes are also used, it may be that published relationships for deriving R from Z and ZDR are in error by over a factor of 2; a new equation is proposed that, in the absence of hail and attenuation, should yield values of R accurate to 25%, provided that ZDR can be estimated to 0.2 dB and Z is calibrated to 1 dB. Relationships of the form R = aKbDP, with b = 1.15, are in widespread use, but more realistic drop spectra and drop shapes yield a value of b closer to 1.4, similar to the exponent in Z–R relationships. In accord, although KDP has the advantage of insensitivity to hail, it may have the same sensitivity to variations in drop spectra as Z does. In addition, the higher value of the exponent b implies that the proposed use of the total phase shift to give the path-integrated total rainfall is also questionable. However, the consistency of Z, ZDR, and KDP in rain can be used to provide absolute calibration of Z to 0.5 dB (12%), and when it fails it indicates that hail is present, in which case a relationship of the form KDP = aR1.4 should be used. The technique should work at S, C, and X band, but, in all cases, paths should be chosen so that the total phase shift is not large enough to introduce significant attenuation of Z and ZDR.

Studies of HTO washout and deposition in the vicinity of emission source

There are presented in the report research results of HTO wash-out and the model of HTO atmosphere concentration in the vicinity of a long-term HT and HTO emission source. The site of the scavenging experiments was around a 30 m emission source. The sampling arcs were chosen at 150-300 m from the base of the source to minimize dry deposition on the precipitation collectors. To study dependence of scavenging of tritium on raindrops characteristics, an optical device was constructed and used to measure the distribuuon of the drop radii and velocities during the period of experiment. The wash-out model, used for assessments, takes into account dispersion, deposition and re-emission. Soil surface is considered as secondary area source. Primary source is characterized as a source of infinite duration and permanent strength. Ingress of HTO to soil from primary source is occurred due to both dry and wet deposition. The model of HTO wet deposition is taken into account kinetics of HTO exchange between vapor and liquid phase with parameters such as rain drop spectra, rain intensity, condensation-evaporation on drop's interface Ingress of HT in soil is only due to HT dry deposition. Gauss type formulae for permanent emission source is used to calculate HTO atmosphere concentration. Averaged real meteorological data are used as input parameters for modeling. One of the key processes underlying environmental HTO propagation is HTO washout with precipitation from atmosphere. HTO interaction with water drops was studied both in laboratory and field (real-life) conditions. The paper (1) describes the laboratory experiments studying kinetics of exchange between the airflow containing deuterium oxide and water drops with no evaporation-condensation processes involved. The experiments performed were used to predict kinetics of HTO exchange with water drops. The paper (2) describes the experiments studying the rate of exchange with water drops flying through the atmosphere containing HTO. The paper (3) presents the kinetics model and identifies various phases of the said process. The experiments described in the paper (4) were conducted with the layout close to those in the papers (2,3). The experiments involving researches into HTO exchange between atmosphere and water drops under field conditions are described in the paper (5). No other publications concerning experiments in field conditions were presented. The current paper presents the results of field experiments and demonstrates that the model of irreversible HTO washout with raindrops yields overestimated results.

Comment on “Partitioning tropical oceanic convective and stratiform rains by draft strength” by David Atlas et al.

[1] The crux of this comment is to clarify attribution. If someone looks at a published graph and has a different interpretation from that of the original authors, that new interpretation should not be attributed to the original authors. [2] The references given by Atlas et al. [2000] regarding distinct convective and stratiform reflectivity Z to rain rate R relations attributed to Yuter and Houze [1997] are incorrect. The convective and stratiform Z-R relations labeled as those of Yuter and Houze in Table 3 (incorrectly referred to there as 1996) and mentioned in the text on pp. 2262, 2264, and 2265 of Atlas et al. [2000] do not appear anywhere in the Yuter and Houze [1997] paper. The Yuter and Houze [1997] study used two-dimensional (2-D) particle probe drop spectra collected by the National Center for Atmospheric Research Electra aircraft during the Tropical Ocean-Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) to compute Z and R values over 6 s intervals of flight track ( 1400 L sample volumes). These data were classified into convective and stratiform subsets using radar data obtained by the National Oceanic and Atmospheric Administration WP-3D airborne radar. Segments of the Electra flight track were categorized by noting when the Electra flew within regions of convective and stratiform precipitation classified according to a radar reflectivity texture algorithm based on the paper by Steiner et al. [1995]. The main conclusion of the Yuter and Houze [1997] study was that the populations of radarclassified convective and stratiform Z-R points overlapped in dbZ-log R space and did not form two statistically distinct populations. [3] The previous statements do not rule out the possibility that different physical processes can yield different drop size distributions (DSD) [e.g., Braun and Houze, 1994, pp. 2749–2750]. However, in the large areas of radar-classified convective and stratiform precipitation examined in this study, the physical processes mixed, exhibited natural variation, and were subject to sampling error to such a degree that the Z and Rvalues associated with the DSD samples in the convective and stratiform populations did not form distinct populations. A classification method that can truly distinguish between dominant precipitation growth by vapor deposition versus accretion (riming and collection/coalescence) would have the property of yielding distinct populations in lowrain-rate regions of dbZ-log R space where both processes are known to occur. 2. Follow-up

A numerical model of the cloud‐topped marine boundary layer with explicit treatment of supersaturation–number concentration correlations

AbstractA numerical model of the cloud‐topped marine boundary layer is presented. The model, based on ensemble‐averaged conservation equations and containing detailed aerosol microphysics, differs from previous models in one major respect: the mean supersaturation–cloud drop number concentration correlation term, generally neglected in previous numerical mean cloud models, is parametrized using a traditional boundary‐layer flux‐gradient relationship. The present work highlights the importance of this correlation term and shows how a simple representation of this correlation can lead to dramatically different, and improved, simulations of cloud behaviour. Simulations are presented for a well‐studied marine boundary‐layer stratocumulus case. Inclusion of the supersaturation–cloud drop number concentration correlation leads to more physically realistic cloud drop spectra and cloud drop concentrations throughout the height of the cloud. Although the parametrization presented must be viewed as a first approximation, the crudeness of the approach should be seen as a justification and starting point for future work. Copyright © 2002 Royal Meteorological Society