In Situ Measurements Of Stratospheric Aerosol Size Distributions During The Post Pinatubo Period And In Preparation For The Next Major Volcanic Eruption.

Abstract:

The low background concentrations of stratospheric aerosol in the post Pinatubo era have presented challenges to both remote sensing and in situ measurements. Total aerosol number density has fallen by nearly two orders of magnitude since the eruption of Pinatubo, and the size distributions have shifted to smaller sizes. This has lead to challenges in measuring stratospheric aerosols using optical remote sensing techniques that have limited sensitivity to smaller particles. Regular in situ profile measurements of stratospheric aerosol have helped refine and validate the retrievals of stratospheric aerosol properties under these challenging conditions. We have developed a new set of balloon borne in situ instrumentation for measuring stratospheric aerosol size distributions and number density at low background concentrations. The balloon payload consists of a the LASP Optical Particle Counter (LOPC) which measures particle size distributions of particles from radius 0.125 – 10 microns at concentrations ranging from 10^-3 - 10³ cm^-3, and a Condensation Nuclei Counter (CNC) that measures the total aerosol concentrations for particles larger than 0.01 micron. This instrumentation is a replacement for the University of Wyoming instrumentation that has provided the in situ aerosol record for the past 45 years. The new instrumentation will be used for routine soundings from Boulder, Colorado, but has also been designed to be quickly deployable any where in the world. This capability makes the instrumentation well suited for a rapid response to the next major volcanic eruption, which will also pose measurement challenges to optical remote sensors due to increased stratospheric aerosol optical depths. The new instruments can also be deployed to monitor the ongoing low-level volcanism that is driving the current variability in stratospheric aerosol.