Journal article

Formation of large (≃100 μm) ice crystals near the tropical tropopause

Jensen E, Pfister L, Bui T, Lawson P, Baker B, Mo Q, Baumgardner D, Weinstock E, Smith J, Moyer E, Hanisco T, Sayres D, Clair J, Alexander M, Toon O, Smith J ...see all

Atmospheric Chemistry and Physics, vol. 8, issue 6 (2008) pp. 1621-1633

  • 13


    Mendeley users who have this article in their library.
  • 40


    Citations of this article.
Sign in to save reference


Recent high-altitude aircraft measurements with in situ imaging instruments indicated the presence of relatively large (≃100 μm length), thin (aspect ratios of ≃6:1 or larger) hexagonal plate ice crystals near the tropical tropopause in very low concentrations (3 ppmv). On the other hand, if the crystal aspect ratios are quite a bit larger (≃10:1), then H2O concentrations toward the low end of the measurement range (≃2–2.5 ppmv) would suffice to grow the large crystals. Gravity-wave driven temperature and vertical wind perturbations only slightly modify the H2O concentrations needed to grow the crystals. We find that it would not be possible to grow the large crystals with water concentrations less than 2 ppmv, even with assumptions of a very high aspect ratio of 15 and steady upward motion of 2 cm s−1 to loft the crystals in the tropopause region. These calculations would seem to imply that the measurements indicating water vapor concentrations less than 2 ppmv are implausible, but we cannot rule out the possibility that higher humidity prevailed upstream of the aircraft measurements and the air was dehydrated by the cloud formation. Simulations of the cloud formation with a detailed model indicate that homogeneous freezing should generate ice concentrations larger than the observed concencentrations (20 L−1), and even concentrations as low as 20 L−1 should have depleted the vapor in excess of saturation and prevented growth of large crystals. It seems likely that the large crystals resulted from ice nucleation on effective heterogeneous nuclei at low ice supersaturations. Improvements in our understanding of detailed cloud microphysical processes require resolution of the water vapor measurement discrepancies in these very cold, dry regions of the atmosphere.

Get free article suggestions today

Mendeley saves you time finding and organizing research

Sign up here
Already have an account ?Sign in

Find this document

Get full text


  • E. J. Jensen

  • L. Pfister

  • T. V. Bui

  • P. Lawson

  • B. Baker

  • Q. Mo

Cite this document

Choose a citation style from the tabs below

Save time finding and organizing research with Mendeley

Sign up for free