Exploring Clear‐Sky Longwave Radiative Closure in the Arctic: A Downwelling Case Study

ABSTRACT The far infrared region plays a critical role in the Earth's greenhouse effect. Measurements across this range are limited and previous studies have found it challenging to achieve radiative closure between different instruments across the mid‐far infrared. This study compares high‐resolution downwelling spectra measured from the surface in the Arctic to radiative transfer simulations run with atmospheric profiles from a radiosonde, microwave radiometer, and the 5th ECMWF atmospheric reanalysis. The radiosonde‐driven simulation generates the closest agreement to the radiance observations. The HATPRO‐driven simulation matches within its uncertainty across the entire range. However, it has a larger uncertainty envelope than the other sources. There is a bias in all three simulations associated with underestimated humidity. Our results reiterate the sensitivity of the far infrared to the humidity profile. This suggests that the wider deployment of spectrometers capable of measuring across this region, in parallel with efforts to improve knowledge of far infrared water vapour spectroscopy, could markedly improve our ability to routinely characterise polar environments.