Estimated Desert-Dust Ice Nuclei Profiles from CALIPSO

We present retrieval of Ice Nuclei particle concentration profiles for pure Saharan dust over the Mediterranean detected by CALIPSO. The approach we use is based on the work of Mamouri and Ansmann (2016), as follows. The pure desert dust layers is first identified, distinguished and separated from the total CALIPSO backscatter profiles using the particle depolarization ratio at 532nm (Tesche et al., 2009). Pure dust aerosol extinction profiles are then calculated utilizing typical lidar ratio using climatological values from EARLINET (Amiridis et al., 2013). Vertical profiles of dust particle concentrations with radius greater than 250nm (known to contribute to the IN population) are then estimated from pure-dust extinction distributions from extinction conversion factors obtained from analysis of a large AERONET dataset (where the aerosol optical thickness is direct related to the column-integrated particle size distribution for dust; Mamouri and Ansmann 2016). From the retrieved size distribution, IN concentrations are retrieved using published IN parameterization schemes (DeMott et al. 2015, Steinke et al. 2015, Niemand et al. 2012). IN concentrations are evaluated using a number of in-situ observations of size distribution and IN concentrations.

The data presented here offer the first comprehensive view of IN distributions over the Mediterranean, during periods that are strongly influenced by dust IN. Apart from the dataset being used for evaluation of global models, we use a state of the art cirrus parameterization (Barahona and Nenes, 2009) to quantify the potential concentration of cirrus ice crystal number in dust-influenced clouds, and the importance of vertical velocity and IN variations as drivers of cirrus properties following the approach of Sullivan et al., (2016).

References

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