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 troposphere and stratosphere in the subtropical Pacific, which appears to be associated with the extreme El Niño‐Southern Oscillation (ENSO) event of 1997–1998. During the driest periods, transmission windows opened in the wavenumber range of 500–600 cm−1, a water vapor rotational band that normally has high opacity. These data demonstrate the potential value of long‐term mountain‐top measurements for monitoring upper tropospheric water vapor and for validating satellite measurements of upper‐tropospheric water vapor.