Mid-tropospheric circulation features under essentially clear sky conditions have been noted in the data of the 6.7 μm channel of the Nimbus 4 Temperature-Humidity Infrared Radiometer (THIR) while at the same time these features were undetected by the 11.5 μm channel of the same instrument. The characteristic response of the 6.7 μm channel to atmospheric water vapor emission is primarily from the 250-mb (10.5 km) to 500-mb (5.5 km) levels with a peak contribution at 350 mb (8 km). Dry and moist patterns seen in the 6.7 μm data on 21 February 1971 have been integrated into a 400-mb moisture analysis over the United States. This analysis provided more detailed and timely information than was conventionally available about the advection of dry air aloft prior to development of the Mississippi Tornado of February 1971. The derivation of middle to upper atmosphere flow patterns from the Nimbus 4 THIR, 6.7 μm data under cloud-free conditions has a direct application on a global scale for the GARP and World Weather Watch Programs.

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