Sensitivity of the shortwave radiative budget to the parameterization of ice crystal effective radius

Abstract

[1] A new effective particle size (R eff ) parameterization for ice clouds has been formulated based on depth into cloud relative to cloud top. This parameterization has been developed based on an extensive data set of lidar and radar ice cloud retrievals. Using this parameterization within the stand-alone radiation code from the European Centre for Medium Range Weather Forecasting (cy23r4), the performance of the new parameterization is compared with the more commonly used parameterizations based on temperature and/or ice water content. An evaluation is performed on the basis of observed shortwave fluxes for 13 days with persistent ice cloud decks, with no liquid clouds beneath, over the Cabauw Experimental Site for Atmospheric Research in the Netherlands. For each of these clouds the shortwave flux is calculated after which the distribution of the differences between the observed and modeled shortwave fluxes from the combined 13 days are compared with each other. The new parameterization shows a median absolute difference of 0.7 W m À2 relative to the observations. The control parameterization based on temperature shows a median absolute difference of 15 W m À2. Within the framework of the KNMI regional climate model (RACMO2), the new parameterization yields an effective particle size versus temperature distribution very similar to the observed distributions from lidar and radar retrievals. Results from a 1-year integration indicate that the domain averaged monthly mean planetary albedo and transmissivity change by a maximum of 2.6 and 2.4%, respectively, using the new parameterization compared to the temperature-based parameterization.

Ice water content of Arctic, midlatitude, and tropical cirrus – Part 2: Extension of the database and new statistical analysis

“…2.1.3. The CLH was used in the 2002 CRYSTAL-FACE (Jensen et al, 2004), the 2004 Midlatitude Cirrus Experiment (Mid-CiX), the 2006 Tropical Composition, Cloud, and Climate Coupling mission (TC4, Toon et al, 2010), and the 2008 Stratosphere-Troposphere Analyses of Regional Transport (START08) campaign (Pan et al, 2010). The IWC measurements from these campaigns were taken primarily in the midlatitudes and the northern tropics.…”

“…Therefore, they are able to produce either a warming or a cooling effect on the Earth, depending on the balance between these two processes. The microphysical properties of an individual cirrus cloud, such as the cloud particle sizes (Liou et al, 2008) and the crystal habits (van Zadelhoff et al, 2007), contribute to whether absorption or reflection will dominate for a particular cloud. Determining the exact role of cirrus in the radiation budget of the atmosphere is difficult, however, owing to the assortment and variability of the microphysical, and thus radiative, properties involved, as well as the current lack of understanding of how and why some of those variations occur.…”

Diagnosing Land–Atmosphere Interaction from a Regional Climate Model Simulation over West Africa

“…RACMO2.1 is used extensively for regional climate downscaling (e.g., Lenderink et al 2007) and evaluating of various components of the physical parameterization (e.g., Van Zadelhoff et al 2007). The simulation used in the present study is a regional downscaling experiment focusing on the West African monsoon area applied in the context of the European Commission-sponsored project ENSEMBLES (Hewitt and Griggs 2004).…”

General Macro- and Microphysical Properties of Deep Convective Clouds as Observed by MODIS

“…The difference can be as large as 32 W m 22 on the daily time scale and 4 W m 22 on the seasonal scale according to Iacoellis et al (2003). Van Zadelhoff et al (2007) showed that observation-model difference in terms of radiation flux is reduced from as large as 15 W m 22 with an old scheme to 0.7 W m 22 using a new parameterization of ice particle sizes (Donovan 2003). They also reported significant changes of yearly average albedo in the model due to parameterization alone.…”