A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid-and far-infrared

Abstract

<p><strong>Abstract.</strong> Measurements of mid- to far-infrared nadir radiances obtained from the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft during the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) are used to assess the performance of various ice cloud bulk optical (single-scattering) property models. Through use of a minimisation approach, we find that the simulations can reproduce the observed spectra in the mid-infrared to within measurement uncertainty but are unable to simultaneously match the observations over the far-infrared frequency range. When both mid and far-infrared observations are used to minimise residuals, first order estimates of the flux differences between the best performing simulations and observations indicate a strong compensation effect between the mid and far infrared such that the absolute broadband difference is < 0.7 W m<sup>−2</sup>. However, simply matching the spectra using the mid-infrared observations in isolation leads to substantially larger discrepancies, with absolute differences reaching ~ 1.8 W m<sup>−2</sup>. These results highlight the benefit of far infrared observations for better constraining retrievals of cirrus cloud properties and their radiative impact, and provide guidance for the development of more realistic ice cloud optical models.</p>

Retrievals of High‐Latitude Surface Emissivity Across the Infrared From High‐Altitude Aircraft Flights

“…TAFTS is a Martin‐Puplett polarizing interferometer (Martin & Puplett, 1969) covering the spectral range of 80–600 cm −1 and has been deployed in numerous airborne field campaigns (e.g., Bantges et al, 2020; Cox et al, 2010; Green et al, 2012). TAFTS uses two sets of liquid helium‐cooled detectors.…”

Spaceborne Middle‐ and Far‐Infrared Observations Improving Nighttime Ice Cloud Property Retrievals

“…Between 400 and 600 cm −1 , several semitransparent FIR “dirty window” bands where water vapor absorption is moderate (Rathke et al, 2002) are useful for ice cloud property retrievals as they have sufficient sensitivity to ice cloud properties (Yang et al, 2003). Most previous studies focus on the sensitivity of ground‐based FIR measurements to ice cloud properties (Di Natale et al, 2017; Maestri et al, 2014; Mlynczak et al, 2016), and only a few studies investigate the corresponding sensitivity of upwelling FIR signals (Bantges et al, 2020; Cox et al, 2010). Libois and Blanchet (2017) demonstrate that synergistic measurements of upwelling MIR‐FIR radiation significantly reduce the uncertainty in ice cloud property retrievals.…”