Abstract. Ice particle activation and evolution have important atmospheric implications
for cloud formation, initiation of precipitation and radiative
interactions. The initial formation of atmospheric ice by heterogeneous ice
nucleation requires the presence of a nucleating seed, an ice-nucleating
particle (INP), to facilitate its first emergence. Unfortunately, only a few
long-term measurements of INPs exist, and as a result, knowledge about
geographic and seasonal variations of INP concentrations is sparse. Here we
present data from nearly 2 years of INP measurements from four stations in
different regions of the world: the Amazon (Brazil), the Caribbean
(Martinique), central Europe (Germany) and the Arctic (Svalbard). The sites
feature diverse geographical climates and ecosystems that are associated with
dissimilar transport patterns, aerosol characteristics and levels of
anthropogenic impact (ranging from near pristine to mostly
rural). Interestingly, observed INP concentrations, which represent
measurements in the deposition and condensation freezing modes, do not differ
greatly from site to site but usually fall well within the same order of
magnitude. Moreover, short-term variability overwhelms all long-term trends
and/or seasonality in the INP concentration at all locations. An analysis of
the frequency distributions of INP concentrations suggests that INPs tend to
be well mixed and reflective of large-scale air mass movements. No universal
physical or chemical parameter could be identified to be a causal link driving
INP climatology, highlighting the complex nature of the ice nucleation
process. Amazonian INP concentrations were mostly unaffected by the biomass
burning season, even though aerosol concentrations increase by a factor of 10
from the wet to dry season. Caribbean INPs were positively correlated to
parameters related to transported mineral dust, which is known to increase
during the Northern Hemisphere summer. A wind sector analysis revealed the
absence of an anthropogenic impact on average INP concentrations at the site in
central Europe. Likewise, no Arctic haze influence was observed on INPs
at the Arctic site, where low concentrations were generally measured. We
consider the collected data to be a unique resource for the community that
illustrates some of the challenges and knowledge gaps of the field in general,
while specifically highlighting the need for more long-term observations of
INPs worldwide.
A Search for Rotationally Modulated Hα Variability in OB Supergiants