Downwelling Far-Infrared Emission Spectra Measured By First at Cerro Toco, Chile and Table Mountain, California

Abstract:

The Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument is a Fourier transform spectrometer developed to measure the important far-infrared spectrum between 100 and 650 cm^-1. Presented here are measurements made by FIRST during two successful deployments in a ground-based configuration to measure downwelling longwave radiation at Earth’s surface. The initial deployment was to Cerro Toco, Chile, where FIRST operated from August to October, 2009 as part of the Radiative Heating in Underexplored Bands Campaign (RHUBC-II) campaign. After recalibration, FIRST was deployed to the Table Mountain Facility from September through October, 2012. Spectra observed at each location are substantially different, due in large part to the order of magnitude difference in integrated precipitable water vapor (0.3 cm at Table Mountain, 0.03 cm at Cerro Toco). Dry days for both campaigns are chosen for analysis – 09/24/2009 and 10/19/2012. Also available during both deployments are coincident radiosonde temperature and water vapor vertical profiles which are used as inputs a line-by-line radiative transfer program. Comparisons between measured and modeled spectra are presented over the 200 to 800 cm^-1 range. An extensive error analysis of both the measured and modeled spectra is presented. In general, the differences between the measured and modeled spectra are within their combined uncertainties.