Recent analysis of the spectroscopic properties of water vapor and its resultant cooling rate profile indicate that the tropics and subtropics lose the most heat to space in the upper troposphere but primarily at long wavelengths (20-22 microns or about 400-600 cm-1). Few observations of this portion of the spectrum, however, are available. During the height of the 1997-98 ENSO event, satellite observations of upper tropospheric humidity indicated extraordinarily dry air over the subtropical North Pacific with UTH less than 3% over a large area. The ETL Fourier Transform Interferometer (FTIR) was deployed at Mauna Loa Observatory in an attempt to obtain infrared spectra in these dry conditions. The FTIR observations show large variability in the 500-600 cm-1 region associated with the very dry upper troposphere. These data are being used to refine radiative transfer models and in studies of the vertical cooling rate