[Grad-postdoc-assn] TLS: Dr. Lohmann lecture this morning (11 AM @ Foothills)

Colin Zarzycki zarzycki at ucar.edu
Thu Dec 11 10:20:57 MST 2014

Hi all,

Just a reminder that Dr. Lohmann will be also giving a science lecture as
part of the Thompson Lecture Series at 11 AM this morning (40 minutes from
now!) in FL2 1022.

Hope to see you there!

*"Observations and model simulations of orographic mixed-phase clouds at
mountain range site”*

Abstract: Aerosol-cloud interactions constitute the highest uncertainties
in radiation forcing estimates. Uncertainties due to the phase and
longevity of mixed-phase clouds (MPCs) influence the radiative balance and
the hydrological cycle. Due to Wegener-Bergeron-Findeisen-process (WBF)
which describes the glaciation of MPC due to the lower saturation vapor
pressure over ice than over water, the MPCs are mostly expected to be
short-lived. In contrast, in-situ measurements have shown that MPCs can
persist over longer time.

We present measurements obtained at the high-altitude research station
Jungfraujoch (JFJ, 3580 m asl) in the Swiss Alps partly taken during the
CLoud-Aerosol Interaction Experiments (CLACE). During the winter season,
the JFJ has a high frequency of super-cooled clouds and is considered
representative for being in the free troposphere. In-situ measurements of
the microstructure of MPCs have been obtained with the digital imager
HOLIMO II, that delivers phase-resolved size distributions, concentrations,
and water contents. The data set of MPCs at JFJ shows that for northerly
wind cases partially-glaciated MPCs are more frequently observed than for
southerly wind cases. The higher frequency of these intermediate states of
MPCs at the JFJ suggests either higher updraft velocities, and therefore
higher supersaturations with respect to water, or the absence of
sufficiently high IN concentrations to quickly glaciate the MPC.

Because of the limitation of the in-situ information, i.e. point
measurements and missing measurements of vertical velocities at JFJ, the
mechanism of the long persistence of MPCs at JFJ cannot be fully
understood. Therefore, in addition to measurements we investigate the JFJ
region with a regional model study with a new version of the
non-hydrostatic model COSMO that includes the online coupled Aerosol
reactive trace gases model (ART) and the aerosol module M7. The combination
of kilometer-scale simulations with measurements allows to systematically
study the effect of vertical velocity and temperatures on MPCs at JFJ, the
synoptic conditions, origins of air masses and aerosol concentration.

Colin M. Zarzycki, ASP postdoctoral fellow
Atmospheric Modeling and Predictability
National Center for Atmospheric Research
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