Large (1-10 Micron) Particles Observed In Situ in the Tropical Western Pacific Lower Stratosphere During the ATTREX Campaign

Abstract:

The NASA Airborne Tropical TRopopause EXperiment (ATTREX) was designed to provide in situ measurements in the tropical upper troposphere/lower stratosphere for understanding of cirrus properties, dehydration, and transport of water vapor and trace gases into the stratosphere. During early-March 2014 Global Hawk flights in the western Pacific near the equator, 1-10 micron diameter particles were detected in the lower stratosphere with concentrations of about 10-30 per liter by the Fast Cloud Droplet Probe (FCDP). The relative humidity with respect to ice in these particle layers was far too low (<40%) for existence of ice crystals. We hypothesize that the particles detected by the FCDP were ash particles injected into the stratosphere by the Kelud eruption in Indonesia a month earlier. Vernier et al. [2016] documented the injection of ash particles well into the stratosphere by the Kelud eruption. It might seem surprising that such large particles would persist in the stratosphere for up to a month; however, fall speed calculations suggest that particles with diameters of a few micron would fall no more than a kilometer or two in a few weeks. We will present the ATTREX observations in the context of airborne and satellite lidar measurements, balloon-borne in situ measurements, and global-model simulations of the Kelud plume.