An Analysis of Cloud Drop Growth by Collection: Part IV. A New Parameterization

A method of analyzing radar data is developed and applied to determine whether the X-band radar reflectivity evolution of clouds observed during summertime on the northeast Florida coast during the Small Cumulus Microphysics Study (SCMS) shows distinct differences in precipitation development that can be associated with the clouds' maritime or continental characteristics. For this study, the entire National Center for Atmospheric Research CP2 radar dataset from SCMS was examined, and 38 clouds were used. For these clouds the evolution in X-band radar reflectivity, from the clouds' earliest detection through precipitation, was clearly documented and met specific requirements concerning the clouds' location relative to the coastline and direction of movement. Since cloud condensation nuclei (CCN) and giant and ultragiant nuclei (GN) measurements were not available for the specific clouds used in this study, proxies were used to partition the clouds into four groups based on the cloud location and direction of movement. Specifically, it was assumed that clouds forming over the ocean during onshore flow had maritime characteristics (group 1: low CCN, high GN), clouds forming over land during onshore flow would have modified maritime characteristics (group 2: high CCN, high GN), clouds forming over land during offshore flow would have continental characteristics (group 3: high CCN, low GN), and clouds forming over the ocean during offshore flow would have modified continental characteristics (group 4: high CCN, high GN). These assumptions are based on past measurements presented by Sax and Hudson. Then, these populations were statistically compared using the nonparametric multiresponse permutation procedure developed by Mielke et al. A comparison of groups 1 and 2 provided a test of the role of CCN concentrations in precipitation development in these cloud populations. A comparison of groups 3 and 4 provided a test of the role of GN concentrations in precipitation development in these cloud populations. The two cloud populations that were disjoint at a statistically significant level were groups 1 and 2. For these groups, the analysis showed that the median characteristic total water content of the truly maritime clouds (group 1) was about half that of the modified maritime clouds (group 2) at the time of precipitation formation. The characteristic time to precipitation formation was about 60% smaller for the truly maritime clouds. Thus, the characteristic reflectivity threshold for precipitation development was reached at a much lower altitude above cloud base in a much faster time in the truly maritime clouds. This result supports the conclusions of Hudson and Yum that precipitation development in the SCMS clouds was primarily controlled by CCN concentrations rather than GN concentrations.

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“…The basis for this method is the parameterization of the production of rainwater in warm clouds found in Berry and Reinhardt (1974). Their Eq.…”

Section: Methodsmentioning

confidence: 99%

Radar Analysis of Precipitation Initiation in Maritime versus Continental Clouds near the Florida Coast: Inferences Concerning the Role of CCN and Giant Nuclei

Göke

Ochs

Rauber

2007

Journal of the Atmospheric Sciences

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“…6 and 10, must replenish the drops in the FSSP spectrum lost by detrainment and by coalescence to the drizzle part of the spectrum. Given this scenario, where a constant supply of FSSP-sized droplets feed through coalescence the larger drops formed on UGN, means that if these conditions had persisted and these Cu had grown taller and more mature, the growth of the drizzle spectrum would have accelerated and likely resulted in precipitation (see for comparison stochastic coalescence calculations by Berry andReinhardt 1974, andOchs 1978).…”

Section: Droplet Spectramentioning

confidence: 99%

Entrainment, Mixing, and Microphysics in Trade-Wind Cumulus

Gerber

Frick

Jensen

et al. 2008

Journal of the Meteorological Society of Japan

180

236

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The vertical evolution of microphysics in trade-wind cumuli (Cu) observed from the NCAR C-130 research aircraft during one flight of the RICO (Rain in Cumulus Over the Ocean) study is analyzed. Conditional sampling of > 200 Cu traversed on this flight is used to chose Cu for which the aircraft penetrated single and growing Cu turrets about 250-m below cloud top where maximum LWC is often found and where radar has often observed initial stages of precipitation. The vertical evolution of the sampled set of Cu was assumed to follow Lagrangian behavior. The entrainment rate, entrained parcel scales, mixing mechanisms, and effects on the droplet size distribution are measured and evaluated. A parcel model is applied over the 1100-m maximum Cu height of the traverses to determine the relationship between the observed large number of small droplets and the fewer ultra-giant sea-salt nuclei (UGN) in order to assess the role of these nuclei in evolving the size spectrum and in causing a growing "drizzle tail". New insight on these topics is obtained by using the PVM (Particle Volume Monitor) probe to measure incloud microphysics with 10-cm resolution.The results include the following: Entrainment causes primarily dilution of the drops without significant size changes, thus either extreme inhomogeneous mixing or more likely homogeneous mixing resulting from mixing with cool and humid entrained air take place. The entrained parcels are surprisingly small following lognormal behavior and decaying rapidly upon entering the Cu, as a result super-adiabatic drops are not evident. The entrained parcels are consistent with the Bragg-scattering "mantle echo" often observed by radar in small Cu. The FSSP (Forward Scattering Spectrometer Probe) droplet spectra are nearly constant with height. These "self-preserving" spectra are a result of an approximate balance between dilution by entrainment of droplets originating at cloud base, droplet activation on entrained CCN (cloud condensation nuclei), and detrainment and coalescence losses. Sea-salt nuclei follow Woodcock's wind dependence, and are shown with the parcel model to play an important role in forming the observed drizzle that increases with cloud height. Accretion is the dominant coalescence mechanism near cloud top in these Cu.

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“…The model is the result of a coupling between a multiphase chemical box model as described by Leriche et al [2000] and a quasi‐spectral microphysical model based upon a parameterization of a cloud evolution following Berry and Reinhardt [1974a, 1974b, 1974c, 1974d] and Huret et al [1994]. The detailed description of the coupling between the chemical and the microphysical modules are given by Leriche et al [2001].…”

Section: Description Of the Modelmentioning

confidence: 99%

“…We use the model from Leriche et al [2001], which presents a coupling between a fully explicit multiphase chemistry model [ Leriche et al , 2000] and a quasi‐spectral microphysics model based upon Berry and Reinhardt 's [1974a, 1974b, 1974c, 1974d] parameterization. The microphysical scheme considers two categories of particles (cloud drops and raindrops) and aerosol particles are not taken into account.…”

Section: Introductionmentioning

confidence: 99%

Modeling study of strong acids formation and partitioning in a polluted cloud during wintertime

Leriche¹

2003

J. Geophys. Res.

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[1] A multiphase chemistry model coupled with a quasi-spectral microphysical model has been applied to measurements from the European Cloud Ice Mountain Experiment campaign to quantify the formation of the strong acids nitrate and sulfate and to evaluate the role of microphysical processes in redistributing reactive species among the different phases (gas versus cloud and/or rain). Significant formation of nitrate and sulfate are found to be due to the reaction of pernitric acid with the sulfite ion. Moreover, pernitric acid, because of its equilibrium in the gas phase and its high solubility, is always available both in cloud water and in rainwater via mass transfer from the gas phase. The sulfite ion comes from the mass transfer from the gas phase of sulfur dioxide in cloud water. When rain formation begins, it is efficiently transferred to the rainwater by collision/ coalescence processes. This leads to an enhancement in strong acid production when microphysics is activated in the model. Modeled results have been compared with experimental data in an effort to retrieve a behavior law related to the partitioning between the gas and aqueous phases of the cloud. In particular, when collision/coalescence processes are considered, an improvement in retrieving the partitioning of soluble species and especially nitrate is observed. A higher production in sulfate could help interpret the discrepancy of global model calculations with observed sulfate concentrations in Europe in wintertime.

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An Analysis of Cloud Drop Growth by Collection: Part IV. A New Parameterization

Cited by 46 publications

References 0 publications

Radar Analysis of Precipitation Initiation in Maritime versus Continental Clouds near the Florida Coast: Inferences Concerning the Role of CCN and Giant Nuclei

Radar Analysis of Precipitation Initiation in Maritime versus Continental Clouds near the Florida Coast: Inferences Concerning the Role of CCN and Giant Nuclei

Entrainment, Mixing, and Microphysics in Trade-Wind Cumulus

Modeling study of strong acids formation and partitioning in a polluted cloud during wintertime

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