Atmospheric Physics Branch
An anomalous particle event observed during the 970513 POLARIS flight
On May 13, 1997, during one of the flights during the POLARIS campaign, an anomalous particle cloud was observed between 16-18 km during a vertical profile at the north end of the flight track (approximately 84° N latitude) by two different instruments. An Ames Wire Impactor (AWI) sample was taken within this cloud event. The AWI functions by collecting particles on thin metal wires, and saves the sample for later analysis. Subsequent electron microscopy of the wire showed columns of 1 to 5 micron in length with an aspect ratio of approximately 10:1 in addition to a distribution of sulfuric acid droplets typical of the stratospheric background. The aspect ratio of sulfuric acid droplets is approximately 1:1. Also, X-ray energy analysis of the particles show that they did not contain heavy metal elements. These analyses were done in 1998.
The National Center for Atmospheric Research (NCAR) multi-angle aerosol spectrometer probe (MASP), also part of the NASA sponsored POLARIS payload, observed a large increase in particle concentration during this time. The MASP measurements of the ratio of forward to back light scattering also suggest a high degree of asphericity with these particles, unlike the small aspect ratio typical of particles normally found in the stratospheric background. The MASP measures particle size in the range of range 0.4 to 40 micrometers.
The temperature in this area was 40 degrees warmer than the frost point which effectively rules out a cirrus cloud. Back trajectories of this air parcel for 10 days show little variation in latitude, altitude or temperature. The AWI wires were heated to 220° C for 6 hrs. but the columns did not sublimate. The source and potential composition of these particles remains a mystery, however, the evidence suggest that the particles are organic.
Electron micrograph and x-ray spectrum of the anomalous particle observed on May 13, 1997. The particle relative to typical sulfuric acid aerosol typically colleted in the stratosphere (top left); The particle at 90,000 times magnification (top right); The particle length is about 1 micrometer. An x-ray spectrum of the particle showing only peaks due ot Carbon and Palladium, substances used in the impactor wire (bottom).
Four electron micrographs of anomalous particles collectd by the AWI on 13 May 1997 during POLARIS. The two top figures and the bottom right figure show particles at 5,000 time magnification. The bottom left figure shows an oblique view of the particles at 10,000 times magnification.
Research Staff
Anthony W. Strawa
Point of Contact
Point of Contact: Anthony W. Strawa, 650/604-3437
astrawa@mail.arc.nasa.gov
Collaborators
K. Drdla, NRC, NASA Ames Research Center
B. W. Gandrud, NCAR
D. Baumgardner, NCAR
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Atmospheric Physics Branch / Earth Science Division
ESD Information Exchange Group (esd@gaia.arc.nasa.gov)
Last Modified: 9/3/99
