ERWIN: an E-region wind interferometer.

A field-widened Michelson interferometer designed to measure upper atmospheric winds at three altitudes near the mesopause by using airglow emissions from O(1)S, OH, and O(2) is described. A very large path difference (11 cm) is used to suppress the fringes from the hot F-region emission of O(1)S and to facilitate accurate measurements. Field widening and thermal compensation are achieved over the large spectral range (557.7-866.0 nm) by the use of three types of glass in the interferometer's arms. The instrument was installed at Resolute Bay, Canada (74.3 N, 94.5 W), in November 1992 and has been operated remotely from Toronto for four winter seasons. Some examples of data are shown to illustrate ERWIN's performance.