The Stratosphere-Troposphere Exchange Project (STEP) Data

This CD-ROM contains data collected from the Stratosphere-Troposphere
Exchange Project (STEP) conducted onboard the NASA ER-2 aircraft in
January and February, 1987 based in Darwin, Australia. This mission
was the last of 6 STEP missions which started with the Variability and
Global Tropospheric Experiment (GTE) Coop assignment in April 1984,
based in Moffett Field, California. Altogether, 4 science missions and
2 intercalibration missions comprised STEP, with the science missions
designed to investigate different aspects of stratosphere-troposphere
exchange (in mass, trace gases, and aerosols), including cloud-free
and cloud-dominated mechanisms in both the mid-latitudes and the
tropics. STEP also observed the extreme dryness of the
stratosphere. STEP was carried out under NASA and the National Oceanic
Atmospheric Administration (NOAA).

The Darwin, Australia phase of STEP utilized 15 instruments and
accessed the world's highest, coldest tropopause as well as the
largest penetrating cumulonimbus anvils. The flights were designed to
test a dehydration mechanism proposed by Danielsen (1982), as well as
to acquire sufficient data to test and develop other hypotheses.

STEP's first mission was flown in April-May 1984 using six instruments
on the NASA U-2 aircraft. The most striking result was the discovery
in the stratosphere of highly laminated structures of ozone, water
vapor, and condensation nuclei. The U-2 wind measurements indicated
that the laminae are caused by waves that fold mixing ratio and
potential vorticity surfaces. The folding process greatly increases
the vertical gradients of the mixing ratios and the potentials for
small-scale instabilities. The latter lead to irreversible mixing;
thus a reversible wave-generated transport is rendered irreversible by
small-scale instabilities.