A Wind Tunnel Investigation of the Growth of Graupel Initiated from Frozen Drops

Pflaum, John C.; Pruppacher, H. R.

doi:10.1175/1520-0469(1979)036<0680:awtiot>2.0.co;2

Cited by 52 publications

(36 citation statements)

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“…The wind tunnel experiment of Pflaum and Pruppacher (1979) showed that a cone-like graupel forms, when riming occurs on the bottom side of a falling planar crystal. However, if the particle flips over during fallout, a lump graupel forms ultimately.…”

Section: Characteristics Of Rimingmentioning

confidence: 81%

Growth of ice particle mass and projected area during riming

Erfani

Mitchell

2017

Atmos. Chem. Phys.

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Abstract. There is a long-standing challenge in cloud and climate models to simulate the process of ice particle riming realistically, partly due to the unrealistic parameterization of the growth of ice particle mass (m) and projected area (A) during riming. This study addresses this problem, utilizing ground-based measurements of m and ice particle maximum dimension (D) as well as theory to formulate simple expressions describing the dependence of m and A on riming. It was observed that β in the m − D power law m = α D β appears independent of riming during the phase 1 (before the formation of graupel), with α accounting for the ice particle mass increase due to riming. This semi-empirical approach accounts for the degree of riming and renders a gradual and smooth ice particle growth process from unrimed ice particles to graupel, and thus avoids discontinuities in m and A during accretional growth. Once the graupel with quasispherical shape forms, D increases with an increase in m and A (phase 2 of riming). The treatment for riming is explicit, and includes the parameterization of the ice crystal-cloud droplet collision efficiency (E c ) for hexagonal columns and plates using hydrodynamic theory. In particular, E c for cloud droplet diameters less than 10 µm are estimated, and under some conditions observed in mixed-phase clouds, these droplets can account for roughly half of the mass growth rate from riming. These physically meaningful yet simple methods can be used in models to improve the riming process.

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Section: Characteristics Of Rimingmentioning

confidence: 81%

Growth of ice particle mass and projected area during riming

Erfani

Mitchell

2017

Atmos. Chem. Phys.

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“…Mainly, the minor dimension is expected to increase; but when the particle effective density is large enough, associated with a quasi-spherical shape, the filling process has to be replaced by an increase of both dimensions with the aspect ratio maintained (e.g., Morrison and Grabowski, 2010). Different options of change of particle aspect ratio accompanying the growth by riming in the model use the rime density calculated from empirical formulas (Macklin, 1962;Pflaum and Pruppacher, 1979;Heymsfield and Pflaum, 1985). The following options for the evolution of the area ratio for a given increase of the rimed fraction can be selected in the model: (i) using one of the empirical relations of mass-density-area ratio (by choosing an appropriate relation from the table in Szyrmer et al, 2012 or others), or (ii) obtained by interpolation based on rimed fraction between the values associated with the unrimed particle and graupel (as in Lin and Colle, 2011), or (iii) calculated from the assumed relation of particle geometry between area ratio and aspect ratio (e.g., Avramov et al, 2011;Jensen and Harrington, 2015).…”

Section: Appendix A: Parameterizations Of Riming Efficiency and Physicsmentioning

confidence: 99%

Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

Kalesse¹,

Szyrmer²,

Kneifel³

et al. 2016

Atmos. Chem. Phys.

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Abstract. Radar Doppler spectra measurements are exploited to study a riming event when precipitating ice from a seeder cloud sediment through a supercooled liquid water (SLW) layer. The focus is on the "golden sample" case study for this type of analysis based on observations collected during the deployment of the Atmospheric Radiation Measurement Program's (ARM) mobile facility AMF2 at Hyytiälä, Finland, during the Biogenic Aerosols -Effects on Clouds and Climate (BAECC) field campaign. The presented analysis of the height evolution of the radar Doppler spectra is a state-of-the-art retrieval with profiling cloud radars in SLW layers beyond the traditional use of spectral moments. Dynamical effects are considered by following the particle population evolution along slanted tracks that are caused by horizontal advection of the cloud under wind shear conditions. In the SLW layer, the identified liquid peak is used as an air motion tracer to correct the Doppler spectra for vertical air motion and the ice peak is used to study the radar profiles of rimed particles. A 1-D steady-state bin microphysical model is constrained using the SLW and air motion profiles and cloud top radar observations. The observed radar moment profiles of the rimed snow can be simulated reasonably well by the model, but not without making several assumptions about the ice particle concentration and the relative role of deposition and aggregation. This suggests that in situ observations of key ice properties are needed to complement the profiling radar observations before process-oriented studies can effectively evaluate ice microphysical parameterizations.

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“…Size distributions are taken to be exponentials, N 5 N 0 e 2lD , where N 0 is taken as 0.1 or 0.01 cm 23 to bound values used in earlier studies (Braun and Tao 2000), D is particle diameter, and l is the slope of the size distribution; N 0 is taken to be 0.01 cm 24 as a lower bound. Ice density (r) at temperatures below 2108C have been assumed to be 0.15 g cm 23 , which was found as the ensemble mean for heavily rimed particles for a typical C-F updraft ; 0.4 g cm 23 from wind tunnel observations of Pflaum and Pruppacher (1979) and Knight and Heymsfield (1983); and 0.25 g cm 23 as an intermediate value. For an exponential distribution, IWC 5 N 0 rG(4)/l 4 .…”

Section: Fall Speed Calculationsmentioning

confidence: 99%

Characteristics of Deep Tropical and Subtropical Convection from Nadir-Viewing High-Altitude Airborne Doppler Radar

Heymsfield

Tian

Heymsfield

et al. 2010

Journal of the Atmospheric Sciences

170

154

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This paper presents observations of deep convection characteristics in the tropics and subtropics that have been classified into four categories: tropical cyclone, oceanic, land, and sea breeze. Vertical velocities in the convection were derived from Doppler radar measurements collected during several NASA field experiments from the nadir-viewing high-altitude ER-2 Doppler radar (EDOP). Emphasis is placed on the vertical structure of the convection from the surface to cloud top (sometimes reaching 18-km altitude). This unique look at convection is not possible from other approaches such as ground-based or lower-altitude airborne scanning radars. The vertical motions from the radar measurements are derived using new relationships between radar reflectivity and hydrometeor fall speed. Various convective properties, such as the peak updraft and downdraft velocities and their corresponding altitude, heights of reflectivity levels, and widths of reflectivity cores, are estimated. The most significant findings are the following: 1) strong updrafts that mostly exceed 15 m s 21 , with a few exceeding 30 m s 21 , are found in all the deep convection cases, whether over land or ocean; 2) peak updrafts were almost always above the 10-km level and, in the case of tropical cyclones, were closer to the 12-km level; and 3) land-based and sea-breeze convection had higher reflectivities and wider convective cores than oceanic and tropical cyclone convection. In addition, the high-resolution EDOP data were used to examine the connection between reflectivity and vertical velocity, for which only weak linear relationships were found. The results are discussed in terms of dynamical and microphysical implications for numerical models and future remote sensors.

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A Wind Tunnel Investigation of the Growth of Graupel Initiated from Frozen Drops

Cited by 52 publications

References 0 publications

Growth of ice particle mass and projected area during riming

Growth of ice particle mass and projected area during riming

Fingerprints of a riming event on cloud radar Doppler spectra: observations and modeling

Characteristics of Deep Tropical and Subtropical Convection from Nadir-Viewing High-Altitude Airborne Doppler Radar

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