Observations of downwelling infrared spectral radiance at Mauna Loa, Hawaii during the 1997-1998 ENSO event

Measurements of downwelling infrared spectral radiance at Mauna Loa, Hawaii during April and May of 1998 indicate unusually high infrared atmospheric transmittance. This is linked to large-scale drying of the upper tropospher e and stratosphere in the subtropical Pacific, which appears to be associat ed with the extreme El Nino-Southern Oscillation (ENSO) event of 1997-1998. During the driest periods, transmission windows opened in the wavenumber r ange of 500-600 cm(-1), a water vapor rotational band that normally has hig h opacity. These data demonstrate the potential value of long-term mountain -top measurements for monitoring upper tropospheric water vapor and for val idating satellite measurements of upper-tropospheric water vapor.