Ice nucleating particles in and around West Coast U.S. storm systems

Description

Wintertime precipitation represents the majority of the annual water supply for large portions of the western U.S. Clouds and precipitation are largely controlled by the frequency and strengths of storms approaching from the Pacific Ocean, including those advecting tropical moisture in “atmospheric rivers”. Orographic clouds and rain over the Sierra Nevada are often supercooled down to -21°C which is hypothesized to be due to an absence of ice nucleating particles (INPs) in lofted marine layers. Major objectives of the interagency CalWater-2/ACAPEX (ARM Cloud Aerosol Precipitation Experiment) campaign (January to March 2015) included comprehensive characterization of atmospheric rivers and of cloud-active particles that can influence precipitation in the California. Herein we focus solely on the aerosol objectives for assessing the roles of pollution and of transported dust and biogenic particles, whether regional or transported across the Pacific, in affecting West Coast precipitation. Instrumentation was deployed on the DOE G-1 aircraft, based from Sacramento, CA, along with the DOE AMF-2 on the NOAA Ron Brown vessel offshore from CA, and at the Bodega Bay Marine Laboratory on the CA coast. The Bodega Bay site characterized cloud particle precursors (i.e., aerosol size distribution, size-resolved cloud condensation nuclei (CCN), ice nucleating particles (INPs), fluorescent particles (WIBS-4A) and particulate matter chemical composition). Continuous flow diffusion chambers (CFDCs) on the G-1 and at Bodega Bay measured INP number concentrations in real-time. We also performed particle-into-liquid sampling, collection of precipitation samples, and collection of filter samples for offline analyses to fully characterize bioaerosol contents and their contributions to the abundance of INPs. Offline INP measurements and use of an aerosol concentrator with the CFDC at the Bodega Bay site improved the dynamic range of INP measurements possible in comparison to previous studies. Filter collections were also made on the Ron Brown (for upstream marine boundary layer aerosols) and on the G-1. G-1 flights were made over the marine and coastal sites and over the Sierra Nevada to characterize orographic cloud properties and the impact of ingested aerosols. This poster describes the methods and presents first results toward combining ground-based, ship-, and aircraft-based data to develop a four-dimensional view of INP concentrations for CalWater-2/ACAPEX case studies