Some pointers to additional information about the STEP campaign.
The Stratosphere-Troposphere Exchange Project, An Overview and Handbook, 1986. STEP Office, NASA Ames Research Center MS 245-5, Moffett Field, CA 94035.
The STEP 1987 Tropical campaign is described in:
Russell, P.B., L. Pfister and H.B. Selkirk. The Tropical Experiment of the Stratosphere Troposphere Exchange Project (STEP): Science Objectives, Operations and Summary Findings. J. Geophys. Res. (Atmos), 98, D5, pp 8563-8589 (1993). This issue contains a special section with many papers devoted to the STEP tropical campaign.
The spring 1984 STEP Experiment is described in a paper by Russel et al. in J. Geophys. Res. (Atmos), 96, D9, pp 17401-17404 (1991).