Structure of an Atmospheric River Over Australia and the Southern Ocean: II. Microphysical Evolution

Joseph A. Finlon, Robert M. Rauber, Wei Wu, Troy J. Zaremba, Greg M. McFarquhar, Stephen W. Nesbitt, Martin Schnaiter, Emma Järvinen, Fritz Waitz, Thomas C.J. Hill, Paul J. DeMott

Research output: Contribution to journalArticlepeer-review

Abstract

An atmospheric river affecting Australia and the Southern Ocean on 28–29 January 2018 during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) is analyzed using nadir-pointing W-band cloud radar measurements and in situ microphysical measurements from a Gulfstream-V aircraft. The AR had a two-band structure, with the westernmost band associated with a cold frontal boundary. The bands were primarily stratiform with distinct radar bright banding. The microphysical evolution of precipitation is described in the context of the tropical- and midlatitude-sourced moisture zones above and below the 0°C isotherm, respectively, identified in Part I. In the tropical-sourced moisture zone, ice particles at temperatures less than −8°C had concentrations on the order of 10 L−1, with habits characteristic of lower temperatures, while between −8°C and −4°C, an order of magnitude increase in ice particle concentrations was observed, with columnar habits consistent with Hallett-Mossop secondary ice formation. Ice particles falling though the 0°C level into the midlatitude-sourced moisture region and melting provided “seed” droplets from which subsequent growth by collision-coalescence occurred. In this region, raindrops grew to sizes of 3 mm and precipitation rates averaged 16 mm hr−1.

Original languageEnglish (US)
Article numbere2020JD032514
JournalJournal of Geophysical Research: Atmospheres
Volume125
Issue number18
DOIs
StatePublished - Sep 27 2020

Keywords

  • atmospheric river
  • cloud processes
  • ice microphysics
  • seeder feeder

ASJC Scopus subject areas

  • Geophysics
  • Atmospheric Science
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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