Measurements and Analysis of Ice Nucleating Particles during ACAPEX/CalWater-2015

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Description

Ice nucleating particles (INPs) impact the phase (ice/liquid), lifetime, and precipitation development in all mixed-phase cloud regions. A comprehensive suite of INP measurements was deployed during the CalWater-2/ACAPEX (ARM Cloud Aerosol Precipitation Experiment) campaign (January to March 2015). This interagency campaign was focused on characterizing the role of atmospheric rivers (ARs) and the modulating influences of cloud-active particles on wintertime clouds and precipitation in the California. Instrumentation was deployed on the DOE AAF G-1 aircraft, along with the DOE AMF-2 on the NOAA Ron Brown vessel offshore from CA, and at the Bodega Bay Marine Laboratory (UC Davis) on the CA coast. Cloud particle precursors (i.e., aerosol size distribution, size-resolved cloud condensation nuclei (CCN), ice nucleating particles (INPs), fluorescent particles (WIBS-4A) and aerosol chemical composition) were characterized throughout the study at Bodega Bay. Continuous flow diffusion chambers (CFDCs) on the G-1 and at Bodega Bay measured INP number concentrations in real-time. Particle-into-liquid sampling, collection of precipitation samples, and collection of filter samples for offline immersion freezing INP analyses were performed at Bodega Bay. INP filter collections were also made on 29 G-1 research flights over the marine and coastal sites, and over the Sierra Nevada, to characterize aerosols feeding orographic clouds at different levels. INP filter samples were made on the Ron Brown for one month of the period, where repeated sampling within atmospheric rivers was possible. Here we describe some preliminary analyses of temporal and spatial INP number concentrations and inferences on compositions within the marine boundary layer, especially in and around atmospheric rivers, as well as the vertical structure of INP distributions on the basis of G-1 flights at different times. INP number concentrations (via immersion freezing) within ARs were consistent with a clean marine INP temperature spectrum (DeMott et al., PNAS, 2015), and INPs present in AR precipitation over the coastal range were consistent with the INP content of this marine air. Vertical profiles over land show a typical decrease of INP number concentrations with altitude, despite altitudinal differences in sources. Transport or production of apparent biological INPs occurred throughout the boundary layer near shore and over land following a land-falling AR event.