A General Approach for Deriving the Properties of Cirrus and Stratiform Ice Cloud Particles

Abstract

A new approach is described for calculating the mass (m) and terminal velocity (V t) of ice particles from airborne and balloon-borne imaging probe data as well as its applications for remote sensing and modeling studies. Unlike past studies that derived these parameters from the maximum (projected) dimension (D) and habit alone, the ''two-parameter approach'' uses D and the particle's projected cross-sectional area (A). Expressions were developed that relate the area ratio (A r ; the projected area of an ice particle normalized by the area of a circle with diameter D) to its effective density (e) and to V t. Habit-dependent, power-law relationships between e and A r were developed using analytic representations of the geometry of various types of planar and spatial ice crystals. Relationships were also derived from new or reanalyzed data for single ice particles and aggregates observed in clouds and at the ground. The mass relationships were evaluated by comparing calculations to direct measurements of ice water content (IWC). The calculations were from Particle Measuring Systems (PMS) 2D-C and 2D-P probes of particle size distributions in ice cloud layers on 3 days during an Atmospheric Radiation Measurement (ARM) field campaign in Oklahoma; the direct measurements were from counterflow virtual impactor (CVI) observations in ice cloud layers during the field campaign. Agreement was generally to within 20%, whereas using previous massdimension relationship approaches usually produced larger differences. Comparison of ground-based measurements of radar reflectivity with calculations from collocated balloon-borne ice crystal measurements also showed that the new method accurately captured the vertical reflectivity structure. Improvements in the accuracy of the estimates from the earlier mass-dimension relationships were achieved by converting them to the new form. A new, more accurate mass-dimension relationship for spatial, cirrus-type crystals was deduced from the comparison. The relationship between V t and A r was derived from a combination of theory and observations. A new expression accounting for the drag coefficients of large aggregates was developed from observational data. Explicit relationships for calculating V t as a function of D for aggregates with a variety of component crystals were developed.

A microphysics guide to cirrus clouds – Part 1: Cirrus types

“…Sassen, 2002;Heymsfield et al, 2002b;Muhlbauer et al, 2014;Jackson et al, 2015). Here we intend to compare our findings of the two in situ origin types and the liquid origin cirrus with the present classifications.…”

Constraining mass–diameter relations from hydrometeor images and cloud radar reflectivities in tropical continental and oceanic convective anvils

“…A detailed description of the particle habits which is needed for the previous approach was provided by the high resolution 2-D images from the cloud particle imager (CPI) (Lawson et al, 1998). (Heymsfield et al, 2002 then used the retrieved m(D) relationships to compute Ka-band radar equivalent reflectivities, which are in good agreement with measured reflectivities. Baker and Lawson (2006; hereafter B&L) introduced a new scheme which is a combination of fundamentals geometric parameters (perimeter, width, D max and projected area) of the 2-D images to deduce the mass of individual particles.…”

“…BF95 used a Lyman-α absorption hygrometer (Nicholls et al, 1990) and a 2-D optical array probe (OAP) simultaneously to determine coefficients α and β for cirrus clouds. Heymsfield et al (2002) developed an expression of the crystal mass as a function of D max and the area ratio A r (the projected area of an ice particle normalized by the area of a disc having the same D max ) for bullet-rosettes present in cirrus clouds. This approach was confronted with real measurements of CWC measured with a counterflow virtual impactor (Ogren et al 1985) and corresponding 2-D images (OAP 2DC and 2DP) in cirrus clouds from airborne measurements.…”

Interpreting an evaluation of the ECMWF global model with CloudSat observations: ambiguities due to radar reflectivity forward operator uncertainties

“…For cloud ice, the values of single particle backscattering and extinction given by Liu (2008) for fivebullet rosettes (Type 07) are used. This choice is justified by the fact that in situ observations reveal that bullet rosettes are the most commonly observed shapes in the upper layers of ice clouds (Heymsfield et al, 2002). The single particle properties of both stratiform and convective snow have been modelled using the results for aggregates of columns evaluated in Hong (2007).…”