Concentrations Of Small Ice Crystals Research Articles

Microphysical processes producing high ice water contents (HIWCs) in tropical convective clouds during the HAIC-HIWC field campaign: dominant role of secondary ice production

Abstract. High ice water content (HIWC) regions in tropical deep convective clouds, composed of high concentrations of small ice crystals, were not reproduced by Weather Research and Forecasting (WRF) model simulations at 1 km horizontal grid spacing using four different bulk microphysics schemes (i.e., the WRF single‐moment 6‐class microphysics scheme (WSM6), the Morrison scheme and the Predicted Particle Properties (P3) scheme with one- and two-ice options) for conditions encountered during the High Altitude Ice Crystals (HAIC) and HIWC experiment. Instead, overestimates of radar reflectivity and underestimates of ice number concentrations were realized. To explore formation mechanisms for large numbers of small ice crystals in tropical convection, a series of quasi-idealized WRF simulations varying the model resolution, aerosol profile, and representation of secondary ice production (SIP) processes are conducted based on an observed radiosonde released at Cayenne during the HAIC-HIWC field campaign. The P3 two-ice category configuration, which has two “free” ice categories to represent all ice-phase hydrometeors, is used. Regardless of the horizontal grid spacing or aerosol profile used, without including SIP processes the model produces total ice number concentrations about 2 orders of magnitude less than observed at −10 ∘C and about an order of magnitude less than observed at −30 ∘C but slightly overestimates the total ice number concentrations at −45 ∘C. Three simulations including one of three SIP mechanisms separately (i.e., the Hallett–Mossop mechanism, fragmentation during ice–ice collisions, and shattering of freezing droplets) also do not replicate observed HIWCs, with the results of the simulation including shattering of freezing droplets most closely resembling the observations. The simulation including all three SIP processes produces HIWC regions at all temperature levels, remarkably consistent with the observations in terms of ice number concentrations and radar reflectivity, which is not replicated using the original P3 two-ice category configuration. This simulation shows that primary ice production plays a key role in generating HIWC regions at temperatures <-40 ∘C, shattering of freezing droplets dominates ice particle production in HIWC regions at temperatures between −15 and 0 ∘C during the early stage of convection, and fragmentation during ice–ice collisions dominates at temperatures between −15 and 0 ∘C during the later stage of convection and at temperatures between −40 and −20 ∘C over the whole convection period. This study confirms the dominant role of SIP processes in the formation of numerous small crystals in HIWC regions.

Characterising optical array particle imaging probes: implications for small-ice-crystal observations

Abstract. The cloud particle concentration, size, and shape data from optical array probes (OAPs) are routinely used to parameterise cloud properties and constrain remote sensing retrievals. This paper characterises the optical response of OAPs using a combination of modelling, laboratory, and field experiments. Significant uncertainties are found to exist with such probes for ice crystal measurements. We describe and test two independent methods to constrain a probe's sample volume that remove the most severely mis-sized particles: (1) greyscale image analysis and (2) co-location using stereoscopic imaging. These methods are tested using field measurements from three research flights in cirrus. For these cases, the new methodologies significantly improve agreement with a holographic imaging probe compared to conventional data-processing protocols, either removing or significantly reducing the concentration of small ice crystals (< 200 µm) in certain conditions. This work suggests that the observational evidence for a ubiquitous mode of small ice particles in ice clouds is likely due to a systematic instrument bias. Size distribution parameterisations based on OAP measurements need to be revisited using these improved methodologies.

Effects of Sea Spray on Microphysics and Intensity of Deep Convective Clouds Under Strong Winds

AbstractDeep convective clouds similar to those arising in the tropical cyclone eyewall are simulated using a parcel model and 2‐D slab symmetric cloud model with spectral bin microphysics (the Hebrew University Cloud Model). The size distribution of sea spray particles (SSPs) at cloud base is calculated using the Lagrangian‐Eulerian bin microphysics model. The model describes the SSP production, advection, and formation of the size distribution of SSP in the hurricane atmospheric boundary layer at different strong wind speeds. The SSP distributions calculated by the Lagrangian‐Eulerian bin microphysics model are used in the parcel model and the Hebrew University Cloud Model to investigate the microphysical and dynamical effects of SSP on clouds. The SSPs ascending in cloud updrafts dramatically increase the number concentration of cloud drops within a wide range of drop sizes. As a result, sea spray creates clouds with unique property combinations of both maritime and continental types. These clouds have droplet size distributions characterized by a high drop concentration and a low effective radius, as in continental clouds. At the same time, the presence of SSP of a few hundred microns in radii triggers intense rain just above the cloud base, which is typical of extreme maritime clouds. In the presence of large sea spray drops, the smallest cloud condensational nuclei, including the smallest SSP, are activated, giving rise to the permanent in‐cloud nucleation of small droplets, which produce a high concentration of small ice crystals above the level of homogeneous freezing. We showed that the SSP substantially increased the maximum vertical velocity, cloud water content, and mass contents of ice particles. The results are compared with available observed data.

Contrails and their impact on shortwave radiation and photovoltaic power production – a regional model study

Abstract. A high-resolution regional-scale numerical model was extended by a parameterization that allows for both the generation and the life cycle of contrails and contrail cirrus to be calculated. The life cycle of contrails and contrail cirrus is described by a two-moment cloud microphysical scheme that was extended by a separate contrail ice class for a better representation of the high concentration of small ice crystals that occur in contrails. The basic input data set contains the spatially and temporally highly resolved flight trajectories over Central Europe derived from real-time data. The parameterization provides aircraft-dependent source terms for contrail ice mass and number. A case study was performed to investigate the influence of contrails and contrail cirrus on the shortwave radiative fluxes at the earth's surface. Accounting for contrails produced by aircraft enabled the model to simulate high clouds that were otherwise missing on this day. The effect of these extra clouds was to reduce the incoming shortwave radiation at the surface as well as the production of photovoltaic power by up to 10 %.

Blowing Snow as a Natural Glaciogenic Cloud Seeding Mechanism

Abstract Winter storms are often accompanied by strong winds, especially over complex terrain. Under such conditions freshly fallen snow can be readily suspended. Most of that snow will be redistributed across the landscape (e.g., behind obstacles), but some may be lofted into the turbulent boundary layer, and even into the free atmosphere in areas of boundary layer separation near terrain crests, or in hydraulic jumps. Blowing snow ice crystals, mostly small fractured particles, thus may enhance snow growth in clouds. This may explain why shallow orographic clouds, with cloud-top temperatures too high for significant ice initiation, may produce (usually light) snowfall with remarkable persistence. While drifting snow has been studied extensively, the impact of blowing snow on precipitation on snowfall itself has not. Airborne radar and lidar data are presented to demonstrate the presence of blowing snow, boundary layer separation, and the glaciation of shallow supercooled orographic clouds. Further evidence for the presence of blowing snow comes from a comparison between snow size distributions measured at Storm Peak Laboratory (SPL) on Mount Werner (Colorado) versus those measured aboard an aircraft while passing overhead, and from an examination of snow size distributions at SPL under diverse weather conditions. Ice splintering following the collision of supercooled droplets on rimed surfaces such as trees does not appear to explain the large concentrations of small ice crystals sometimes observed at SPL.

Assessment of the performance of the inter-arrival time algorithm to identify ice shattering artifacts in cloud particle probe measurements

Abstract. Shattering presents a serious obstacle to current airborne in situ methods of characterizing the microphysical properties of ice clouds. Small shattered fragments result from the impact of natural ice crystals with the forward parts of aircraft-mounted measurement probes. The presence of these shattered fragments may result in a significant overestimation of the measured concentration of small ice crystals, contaminating the measurement of the ice particle size distribution (PSD). One method of identifying shattered particles is to use an inter-arrival time algorithm. This method is based on the assumption that shattered fragments form spatial clusters that have short inter-arrival times between particles, relative to natural particles, when they pass through the sample volume of the probe. The inter-arrival time algorithm is a successful technique for the classification of shattering artifacts and natural particles. This study assesses the limitations and efficiency of the inter-arrival time algorithm. The analysis has been performed using simultaneous measurements of two-dimensional (2-D) optical array probes with the standard and antishattering "K-tips" collected during the Airborne Icing Instrumentation Experiment (AIIE). It is shown that the efficiency of the algorithm depends on ice particle size, concentration and habit. Additional numerical simulations indicate that the effectiveness of the inter-arrival time algorithm to eliminate shattering artifacts can be significantly restricted in some cases. Improvements to the inter-arrival time algorithm are discussed. It is demonstrated that blind application of the inter-arrival time algorithm cannot filter out all shattered aggregates. To mitigate against the effects of shattering, the inter-arrival time algorithm should be used together with other means, such as antishattering tips and specially designed algorithms for segregation of shattered artifacts and natural particles.

The impact of ground-based glaciogenic seeding on clouds and precipitation over mountains: A multi-sensor case study of shallow precipitating orographic cumuli

This paper examines reflectivity data from three different radar systems, as well as airborne and ground-based in situ particle imaging data, to study the impact of ground-based glaciogenic seeding on shallow, lightly precipitating orographic cumuli, observed on 13 February 2012, as part of the AgI Seeding Cloud Impact Investigation (ASCII) experiment in Wyoming. Three silver iodide (AgI) generators were used, located on the windward slopes of the target mountain. This case was chosen for several reasons: the AgI generators were near the lifting condensation level, where the temperature was about −6°C; cloud droplets were present in the cumulus clouds, which were rooted in the boundary layer; and the airflow, although weak, ascended over the mountain. The target mountain pass site was almost certainly impacted by seeding, according to a trace element analysis of the falling snow.Data from three radar systems were used in the analysis of the impact of seeding on precipitation: the airborne W-band (3mm wavelength) profiling Wyoming Cloud Radar (WCR), two Ka-band (1.2cm) profiling Micro-Rain Radars (MRR), and a X-band (3cm) scanning Doppler-on-Wheels (DOW) radar. The WCR was onboard a research aircraft flying geographically fixed tracks, the DOW and one MRR were located at the target mountain pass, and another MRR was upstream of the AgI generators. Composite data from the three radar systems, each with their own target and upwind control regions, indicate that the observed changes in reflectivity profiles can be explained largely by the natural emergence of shallow cumuli. A comparison with lateral control regions (i.e., over the mountain, but to the side of the AgI plumes) suggests that seeding may have further enhanced snowfall, but the signal is weak.Particle probes at flight level and at the mountain pass site show that the concentration of small ice crystals (<1mm) was significantly larger downwind of the AgI generators during seeding. This too is consistent with the emergence of shallow convection, but a comparison between flight sections downwind of the AgI point sources and those to the side suggests that glaciogenic seeding increased the concentration of ice crystals of all sizes in the shallow convection.

The Role of Small Soluble Aerosols in the Microphysics of Deep Maritime Clouds

AbstractSome observational evidence—such as bimodal drop size distributions, comparatively high concentrations of supercooled drops at upper levels, high concentrations of small ice crystals in cloud anvils leading to high optical depth, and lightning in the eyewalls of hurricanes—indicates that the traditional view of the microphysics of deep tropical maritime clouds requires, possibly, some revisions. In the present study it is shown that the observed phenomena listed above can be attributed to the presence of small cloud condensation nuclei (CCN) with diameters less than about 0.05 μm. An increase in vertical velocity above cloud base can lead to an increase in supersaturation and to activation of the smallest CCN, resulting in production of new droplets several kilometers above the cloud base. A significant increase in supersaturation can be also caused by a decrease in droplet concentration during intense warm rain formation accompanied by an intense vertical velocity. This increase in supersaturation also can trigger in-cloud nucleation and formation of small droplets. Another reason for an increase in supersaturation and in-cloud nucleation can be riming, resulting in a decrease in droplet concentration. It has been shown that successive growth of new nucleated droplets increases supercooled water content and leads to significant ice crystal concentrations aloft. The analysis of the synergetic effect of the smallest CCN and giant CCN on production of supercooled water and ice crystals in cloud anvils allows reconsideration of the role of giant CCN. Significant effects of small aerosols on precipitation and cloud updrafts have been found. The possible role of these small aerosols as well as small aerosols with combination of giant CCN in creating conditions favorable for lightning in deep maritime clouds is discussed.

The influence of observed cirrus microphysical properties on shortwave radiation: A case study over Oklahoma

[1] The shortwave radiative effect of an ice cloud observed over the Atmospheric Radiation Measurement program's Southern Great Plains site in Oklahoma is investigated. Airborne microphysical data from a cloud particle imager, optical array probes, and forward scattering probes are used to construct vertical profiles of the size and shape distributions of ice crystals. Due to uncertainties associated with measuring the sizes and shapes of small ice crystals with maximum dimensions less than 120 μm, five alternate size-shape distributions are derived and combined with existing databases of wavelength-dependent single-scattering properties of idealized ice crystals to obtain vertical profiles of optical properties. The dependence of the surface and the top-of-the-atmosphere fluxes on these uncertainties is simulated with a radiative transfer model. In addition, surface fluxes are compared against measurements at the surface. It is found that the differences between the modeled and measured fluxes are too large to be explained by uncertainties in the shape and concentrations of small ice crystals. Sensitivity tests suggest that the discrepancies occur because the real optical thickness is larger than that derived from the aircraft profiles most of the time. When the optical thickness was derived based on modeled and measured direct fluxes, the modeled total downward flux agreed well with the measurements. Slightly (less than 10%) reducing the asymmetry parameter, which is possibly associated with the presence of surface roughness, air bubble inclusions or other nonidealities in ice crystals, may further improve the agreement with observations.

Inferring Cirrus Size Distributions through Satellite Remote Sensing and Microphysical Databases

Abstract Since cirrus clouds have a substantial influence on the global energy balance that depends on their microphysical properties, climate models should strive to realistically characterize the cirrus ice particle size distribution (PSD), at least in a climatological sense. To date, the airborne in situ measurements of the cirrus PSD have contained large uncertainties due to errors in measuring small ice crystals (D ≲ 60 μm). This paper presents a method to remotely estimate the concentration of the small ice crystals relative to the larger ones using the 11- and 12-μm channels aboard several satellites. By understanding the underlying physics producing the emissivity difference between these channels, this emissivity difference can be used to infer the relative concentration of small ice crystals. This is facilitated by enlisting temperature-dependent characterizations of the PSD (i.e., PSD schemes) based on in situ measurements. An average cirrus emissivity relationship between 12 and 11 μm is developed here using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite instrument and is used to “retrieve” the PSD based on six different PSD schemes. The PSDs from the measurement-based PSD schemes are compared with corresponding retrieved PSDs to evaluate differences in small ice crystal concentrations. The retrieved PSDs generally had lower concentrations of small ice particles, with total number concentration independent of temperature. In addition, the temperature dependence of the PSD effective diameter De and fall speed Vf for these retrieved PSD schemes exhibited less variability relative to the unmodified PSD schemes. The reduced variability in the retrieved De and Vf was attributed to the lower concentrations of small ice crystals in the retrieved PSD.

Investigation of Microphysical Parameterizations of Snow and Ice in Arctic Clouds during M-PACE through Model–Observation Comparisons

Abstract In this study the Weather Research Forecast model is used with 1-km horizontal grid spacing to investigate the microphysical properties of Arctic mixed-phase stratocumulus. Intensive measurements taken during the Department of Energy Atmospheric Radiation Measurement Program Mixed-Phase Arctic Cloud Experiment (M-PACE) on the North Slope of Alaska, during 9–12 October 2004, are used to verify the microphysical characteristics of the model’s simulation of mixed-phase clouds (MPCs). A series of one- and two-moment bulk microphysical cloud schemes are tested to identify how the treatment of snow and ice affects the maintenance of cloud liquid water at low temperatures. The baseline two-moment simulation results in realistic liquid water paths and in size distributions of snow reasonably similar to observations. With a one-moment simulation for which the size distribution intercept parameter for snow is fixed at values taken from the two-moment simulation, reasonable snow size distributions are again obtained but the cloud liquid water is reduced because the one-moment scheme couples the number concentration to the mixing ratio. The one-moment scheme with the constant snow intercept parameter set to a value typical of midlatitude frontal clouds results in a substantial underprediction of the liquid water path. In the simulations, the number concentration of small ice crystals is found to be underestimated by an order of magnitude. A sensitivity test with the concentration of ice particles larger than 53 μm increased to the observed value results in underprediction of the liquid water path. If ice (not snow) is the primary driver for the depletion of cloud liquid water, then the results of this study suggest that the feedbacks among ice–snow–cloud liquid water may be misrepresented in the model.

Impact of small ice crystal assumptions on ice sedimentation rates in cirrus clouds and GCM simulations

In the prediction of climate change, the greatest uncertainty lies in the representation of clouds. Ice clouds are particularly challenging, and to date there is no accepted method for measuring the smaller ice crystals (D &lt; 60 μm). This study examines the sensitivity of a global climate model to different assumptions regarding the number concentrations of small ice crystals when they are allowed to affect ice sedimentation rates. When their concentrations are relatively high, the GCM predicts a 12% increase in cloud ice amount and a 5.5% increase in cirrus cloud coverage globally. This produces a net cloud forcing of −5 W m−2 in the tropics and warms the upper tropical troposphere over 3°C. Ice crystal concentration differences assumed were modest in comparison to corresponding measurement uncertainties, revealing a potentially large source of uncertainty in the prediction of global climate.

Topographically Generated Cloud Plumes

Abstract Two topographically generated cirrus plume events have been examined through satellite observations and real-data simulations. On 30 October 2002, an approximately 70-km-wide cirrus plume, revealed by a high-resolution Moderate Resolution Imaging Spectroradiometer (MODIS) image and a series of Geostationary Operational Environmental Satellite (GOES) images, originated from the Sierra Nevada ridge and extended northeastward for more than 400 km. On 5 December 2000, an approximately 400-km-wide cloud plume originated from the Southern Rocky Mountain massif and extended eastward for more than 500 km, the development of which was captured by a series of GOES images. The real-data simulations of the two cirrus plume events successfully capture the presence of these plumes and show reasonable agreement with the MODIS and GOES images in terms of the timing, location, orientation, length, and altitude of these cloud plumes. The synoptic and mesoscale aspects of the plume events, and the dynamics and microphysics relevant to the plume formation, have been discussed. Two common ingredients relevant to the cirrus plume formation have been identified, namely, a relatively deep moist layer aloft with high relative humidity and low temperature (≤−40°C near the cloud top), and strong updrafts over high terrain and slow descent downstream in the upper troposphere associated with terrain-induced inertia–gravity waves. The rapid increase of the relative humidity associated with strong updrafts creates a high number concentration of small ice crystals through homogeneous nucleation. The overpopulated ice crystals decrease the relative humidity, which, in return, inhibits small crystals from growing into large crystals. The small crystals with slow terminal velocities (&amp;lt;0.2 m s−1) can be advected hundreds of kilometers before falling out of the moist layer.

An overview of the microphysical structure of cirrus clouds observed during EMERALD-1

High-resolution ice microphysical, turbulence, heat and water vapour flux data in cirrus clouds were collected by the Airborne Research Australia's (ARA) Egret Grob 520T research aircraft during the first Egret Microphysics with Extended Radiation and Lidar experiment (EMERALD-1). The in situ cirrus measurements were guided by simultaneous airborne lidar measurements collected by the ARA Super King Air research aircraft which flew below the cirrus and whose horizontal position was synchronized with the Egret. This allowed the microphysics and turbulence measurements to be interpreted and evaluated within the context of large-scale cirrus structure and its evolution. A significant feature of the clouds observed was the presence on occasion of active convective columns. Large variations in the cirrus dynamics were observed, with significant variations in the ice crystal habit from cloud top to cloud base and within the evaporating fall-streaks of precipitation. However, on average the picture presented is consistent with that shown by Heymsfield and Miloshevich, and by Kajikawa and Heymsfield, with the upper supersaturated region of the cloud acting as an active particle-generation zone where homogeneous nucleation proceeds apace; ice crystals there are initially dominated by small irregular or spheroidally shaped particles, some of which can be identified as proto or ‘germ’ rosettes. These are then observed to grow into more open bullet rosette and columnar types as they fall into the less supersaturated middle and lower layers of the cloud. The mean recognisable ice particle size fell within a very narrow size band, 70–90 µm, but the actual size distribution is thought to increase in a continuous manner to smaller sizes. However, there are currently instrument limitations that make it difficult to confirm this unambiguously. Unlike most previous studies, however, the cirrus clouds observed here were mostly devoid of pristine plate-like crystals, as nucleation and growth within the planar growth regime was rarely encountered. During some cases bullet rosettes, once formed, did undergo transition to the plate growth regime with complex crystal shapes resulting. The mean size of pristine bullet rosettes was again confined to a relatively narrow range. The likely nucleation processes dominating in cirrus clouds are discussed in the light of the observations. Very high concentrations of small ice crystals were sometimes detected, concentrations reaching a maximum of 10 000 L−1. There is strong evidence supporting these high concentrations which are probably produced by the homogeneous freezing of aerosol. Copyright © 2005 Royal Meteorological Society

Properties of embedded convection in warm‐frontal mixed‐phase cloud from aircraft and polarimetric radar

AbstractResults are presented from a case‐study in which the macrophysical and microphysical characteristics of a warm‐frontal mixed‐phase cloud were investigated using simultaneous aircraft and polarimetric‐radar measurements. A region of embedded convection was located and sampled at various stages of its ascent through the cloud from −5° to −11°, and evidence is presented that it was triggered by Kelvin–Helmholtz instability near the melting layer. High concentrations of small crystals were observed in and above narrow convective turrets, around 1 km across, that contained supercooled liquid‐water droplets with an effective diameter of 24 µm and riming ice particles. The area surrounding the turrets was found to contain pristine columns, and was strikingly visible to the radar as a broad plume of high differential reflectivity ZDR (around 3 dB), contrasting with the 0–0.5 dB range usually found in ice clouds. The columns observed in situ had axial ratios of around 5:1, in close agreement with the values predicted theoretically from ZDR assuming horizontal alignment of the crystals. We argue that the high concentrations of small ice crystals (up to 103 l−1) observed in this case were splinters produced via the Hallett–Mossop mechanism in the riming process, and these then grew rapidly by deposition in the water‐saturated environment into pristine columns. Later in the ascent the picture was complicated by the presence of a fallstreak containing large, low‐ZDR aggregates which appeared to rapidly accrete the columns. A number of plumes of high ZDR were observed by the radar on the same day, each of which persisted for at least half an hour. In the vicinity of cloud top −15°, the regions of high ZDR tended to spread out horizontally, and attain values as high as 7 dB. At these temperatures plates and dendrites are known to grow, so these ZDR observations are in good agreement with our theoretical finding that columns alone cannot produce values of ZDR greater than 4 dB, no matter how extreme their axial ratios, whereas planar crystals can attain values up to 10 dB. Embedded convection could clearly be important in determining the distribution of ice and liquid water in frontal clouds, which affects both cloud glaciation and the radiation budget, and is important for aircraft icing. Copyright © 2002 Royal Meteorological Society

Cloud properties leading to highly reflective tropical cirrus: Interpretations from CEPEX, TOGA COARE, and Kwajalein, Marshall Islands

This study addresses whether high concentrations of small ice crystals in the upper 1 km or so of high, thick tropical cirrus clouds are principally responsible for the highly reflective clouds observed over the equatorial Pacific “warm pool.” This region of the tropics has recently been shown to contain extensive shields of cirrus clouds which significantly influence the global climate through their effect on the radiation budget of the tropics. In‐situ and remote sensing measurements of cloud microphysical and radiative properties from field programs in the central and western tropical Pacific and radiative transfer calculations are used to derive distributions of cloud microphysical properties with height and their relationship to cloud radiative properties. Clouds associated directly with convection are shown to have sufficiently high optical depths near cloud top to produce localized areas of bright or optically “thick” cirrus, reflecting more than 40% of the incoming solar radiation. However, in general the upper parts of cirrus cannot alone account for the high albedos (fraction of incoming solar energy reflected) but do contribute substantially when high albedos are observed. The lower parts of the cirrus, in some cases extending down to the melting layer or below when they are called stratiform cloud regions, are usually necessary to produce high albedos.

A Double-Moment Multiple-Phase Four-Class Bulk Ice Scheme. Part I: Description

A detailed ice-phase bulk microphysical scheme has been developed for simulating the hydrometeor distributions of convective and stratiform precipitation in different large-scale environmental conditions. The proposed scheme involves 90 distinct microphysical processes, which predict the mixing ratios and the number concentrations of small ice crystals, snow, graupel, and frozen drops/hail, as well as the mixing ratios of liquid water on wet precipitation ice (snow, graupel, frozen drops). The number of adjustable coefficients has been significantly reduced in comparison with other bulk schemes. Additional improvements have been made to the parameterization in the following areas: (1) representing small ice crystals with nonzero terminal fall velocities and dispersive size distributions, (2) accurate and computationally efficient calculations of precipitation collection processes, (3) reformulating the collection equation to prevent unrealistically large accretion rates, (4) more realistic conversion by riming between different classes of precipitation ice, (5) preventing unrealistically large rates of raindrop freezing and freezing of liquid water on ice, (6) detailed treatment of various rime-splintering ice multiplication mechanisms, (7) a simple representation of the Hobbs-Rangno ice enhancement process, (8) aggregation of small ice crystals and snow, and (9) allowing explicit competition between cloud water condensation and ice deposition rates rather than using saturation adjustment techniques. For the purposes of conserving the higher moments of the particle distributions, preserving the spectral widths (or slopes) of the particle spectra is shown to be more important than strict conservation of particle number concentration when parameterizing changes in ice-particle number concentrations due to melting, vapor transfer processes (sublimation of dry ice, evaporation from wet ice), and conversion between different hydrometeor species. The microphysical scheme is incorporated into a nonhydrostatic cloud model in Part 2 of this study. The model performed well in simulating the radar and microphysical structures of a midlatitude-continental squall lines and a tropical-maritime squall system with minimal tuning of the parameterization, even though the vertical profiles of radar reflectivity differed substantially between these storms.