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Assessing the dependence of bulk ice properties on environmental conditions using data obtained from probes with anti-shatter tips during ISDAC, IDEAS-2011, and SPARTICUS.

Event Type
Department of Atmospheric Sciences
Room 114 of the Transportation Building
May 5, 2014   3:30 pm  
Robert Jackson, Graduate Student, Department of Atmospheric Sciences, University of Illinois
Shirley Palmisano

Prior estimates of ice crystal size distributions (SDs) derived from 2D Cloud Probes (2DCs) have been artificially amplified by small ice crystals generated from the shattering of large ice crystals on probe tips. Although anti-shatter tips and algorithms exist, there is considerable uncertainty in their effectiveness. SDs from adjacent 2DCs with standard and anti-shatter tips, and processed with and without anti-shattering algorithms were obtained during the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) and 2011 Instrumentation Development and Education in Airborne Science 2011 (IDEAS-2011). Significant numbers of particles smaller than 500 m were generated by shattering. Anti-shatter tips were more effective than algorithms at removing artifacts, but neither alone removed all artifacts.  The number of artificially generated particles increased with median mass diameter and amount of riming. Agreement between SDs measured by a holographic detector and the 2DC with modified tips during IDEAS-2011 suggests that anti-shatter tips and algorithms combined are effective in removing most artifacts. Comparison of bulk microphysical quantities dominated by higher moments of the SDs (e.g., total mass content or extinction) from probes with and without tips and processed with and without shatter algorithms, show less than 20% differences, suggesting prior studies based on higher moments of SDs from conventional 2DCs are not significantly biased by shattering.

Using the understanding of probe performance gained from ISDAC and IDEAS-2011, an extensive 6-month set of airborne ice cloud data collected during the Small PARTicles in CirruS (SPARTICUS) experiment was analyzed to quantify the dependence of ice microphysical properties on meteorological conditions. Using probes equipped with anti-shattering tips and processed with shatter detection algorithms, routine in-situ observations of mid-latitude cirrus were made during SPARTICUS. Probability distribution functions of microphysical properties (e.g.,  total concentration, SDs, bulk extinction, ice water content, etc.) were derived for different meteorological conditions (i.e., for synoptically, convectively or orographically generated clouds), together with their dependence on environmental parameters (e.g.,  temperature, vertical velocity, and relative humidity). The results suggest that larger ice crystals are present at higher temperatures in synoptic clouds due to processes such as vapor diffusion and aggregation and that nucleation occurs throughout the cirrus. However, in anvil cirrus, results are consistent with the transport of larger ice crystals to higher altitudes in updrafts. These results have important implications on how ice clouds are represented in climate models.

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