Parameterization of effective ice particle size for high‐latitude clouds

Abstract

A parameterization has been developed for mean effective size D ge in terms of ice water content (IWC) and temperature using in situ measurements of ice crystal spectra, cloud particle shapes and particle cross-sectional area A from four research projects conducted in latitudes north of 45°N. The cloud microphysical measurements were made using PMS 2D optical probes, a PMS forward scattering spectrometer probe (FSSP), and Nevzorov total water and liquid water content probes. The IWCs derived from particle spectra using three different methods were compared with IWC measured with the Nevzorov probe (IWC Nev ). The contribution of small particles to the total mass was estimated by integrating a gamma distribution function that was fitted to match the measured FSSP concentrations. The D ge was calculated from the derived IWC and total cross-sectional area per unit volume A c .This analysis indicates that there are significant differences among the schemes used to derive the IWC. It was found that the IWC derived based on the Cunningham scheme and IWC Nev have the highest correlation: r 2 = 0.78. After considering small particles, the derived IWC almost matched the IWC Nev . The average estimated contribution of small particles to the A c was 43%. The average estimated contribution of small particles to the total IWC, however, was 20%. Since D ge is directly proportional to the ratio IWC/A c , the addition of small particles reduced the derived D ge considerably. The largest changes in D ge associated with small particles, however, occur at the coldest temperature and at low IWC, reaching up to 45% for temperatures less than −25°C. Generally, D ge and IWC increase with increasing temperature. Good agreement between the parameterized D ge and derived D ge from measurements were found when small particles were included.

Bulk microphysical properties of semi-transparent cirrus from AIRS: a six year global climatology and statistical analysis in synergy with geometrical profiling data from CloudSat-CALIPSO

“…For ST-HICs with the same IWP, we recognize even a different behaviour of D e with T cld : it increases in the tropics whereas it decreases in the midlatitudes. Previous studies (Ivanova et al, 2001;Boudala et al, 2002;Edwards et al, 2007) used the temperature to parameterize D e . We found that these parameterizations, generally established for clouds warmer than 230 K, underestimate D e by about 10 to 20 µm compared to our data (not shown).…”

“…5), another sign that the dependence on IWP is better suited to parameterize D e (Baran et al, 2009). Compared to a parameterization developed for in situ measurements at a specific latitude band as for example by Boudala et al (2002), it seems to be difficult to determine a global multivariate parameterization for D e dependent on both IWP and temperature, because the latter is not independant as can be seen in Fig. 5.…”

“…Cloud optical properties are then calculated from the GCM diagnosed D e , assuming a single ice crystal habit. The former parameterizations are based on only a few field campaigns located about the Earth and for very limited time periods (Heymsfield and Platt, 1984;Korolev et al, 2001;Boudala et al, 2002;McFarquhar et al, 2003;Garrett et al, 2004). Moreover, recent studies by (Korolev and Isaac, 2004;Field et al, 2006;McFarquhar et al, 2007) have demonstrated that the particle size distribution (PSD) data on which the former parameterizations are based are probably biased to smaller D e values due to the shattering of ice crystals on the probe inlets.…”

A concept for a satellite mission to measure cloud ice water path, ice particle size, and cloud altitude

“…Different parametrizations of effective ice crystal radius as a function of ice water content. The parametrizations were taken from Lohmann and Roeckner (1996), McFarlane et al (1992), Boudala et al (2002), and Sun and Shine (1994). For those parametrizations that depend on temperature in addition to the ice water content, two different temperatures (−40°C and −70°C) were applied.…”

Turbulent heat fluxes over leads and polynyas, and their effects on arctic clouds during FIRE.ACE: Aircraft observations for April 1998

“…D eff values in Table 6 were estimated using a definition given in Fu (1996) which uses particle cross-section area. The uncertainty in D eff , due to many small ice crystals probably existing at sizes less than 100 µm, can be as high as 50% (Boudala et al, 2002).…”