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

Saito, Masanori; Yang, Ping; Huang, Xianglei; Brindley, Helen E.; Mlynczak, Martin G.; Kahn, Brian H.

doi:10.1029/2020gl087491

Cited by 8 publications

(5 citation statements)

References 46 publications

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“…The wavelength-dependent LBLRTM-derived layer optical depths were then passed to LBLDIS, which takes scattering by particles in the cloud layer into account via the Discrete Ordinate Radiative Transfer (DISORT) code (Stamnes et al, 2000). In this study, the bulk optical properties used to simulate cloudy radiances were those provided by Baum et al (2014) using 16 streams.…”

Section: Simulation Methodologymentioning

confidence: 99%

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

et al. 2020

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Abstract. 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 property models. Through use of a minimization approach, we find that the simulations can reproduce the observed spectra in the mid-infrared to within measurement uncertainty, but they are unable to simultaneously match the observations over the far-infrared frequency range. When both mid- and far-infrared observations are used to minimize residuals, first-order estimates of the spectral flux differences between the best-performing simulations and observations indicate a compensation effect between the mid- and far-infrared such that the absolute broadband difference is < 0.7 W m−2. However, simply matching the spectra using the mid-infrared (far-infrared) observations in isolation leads to substantially larger discrepancies, with absolute differences reaching ∼ 1.8 (3.1) W m−2. These results show that simulations using these microphysical models may give a broadly correct integrated longwave radiative impact but that this masks spectral errors, with implicit consequences for the vertical distribution of atmospheric heating. They also imply that retrievals using these models applied to mid-infrared radiances in isolation will select cirrus optical properties that are inconsistent with far-infrared radiances. As such, the results highlight the potential benefit of more extensive far-infrared observations for the assessment and, where necessary, the improvement of current ice bulk optical models.

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Section: Simulation Methodologymentioning

confidence: 99%

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

et al. 2020

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“…It has been proven that the application of the Chou scheme results in a systematic overestimation of simulated nadir radiances at the TOA [33]. These discrepancies can be primarily attributed to the average quantities employed to approximate Equations ( 6) and (7), which are larger than their true values. To establish a more accurate computational scheme for upward radiances, it is essential to incorporate a more realistic representation of these two terms.…”

Section: The Radiative Transfer Equation and The Mama Approximationmentioning

confidence: 99%

“…Radiation fields at FIR wavelengths are also strongly influenced by the presence of clouds. In particular, recent studies have demonstrated the larger sensitivity of FIR radiance to scattering by ice particles with respect to the mid-infrared part of the spectrum [5][6][7]. Despite its significance, mostly due to technical difficulties, the FIR remains currently unobserved from space.…”

Section: Introductionmentioning

confidence: 99%

The MAMA Algorithm for Fast Computations of Upwelling Far- and Mid-Infrared Radiances in the Presence of Clouds

Martinazzo,

Maestri

2023

Remote Sensing

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A methodology for the computation of spectrally resolved upwelling radiances in the presence of atmospheric diffusive layers is presented. The algorithm, called MAMA (Martinazzo–Maestri), provides fast simulations over the whole longwave spectrum, with high accuracy, particularly for optically thin scattering layers like cirrus clouds. The solution is obtained through a simplification of the multiple-scattering term in the general equation of the radiative transfer in a plane-parallel assumption. The scattering contribution is interpreted as a linear combination of the mean ambient radiances involved in the forward and back-scatter processes, which are multiplied by factors derived from the diffusive features of the layer. For this purpose, a fundamental property of the layer is introduced, named the angular back-scattering coefficient, which describes the fraction of radiation coming from a hemisphere and back-scattered into a specific direction (the observer in our case). This property, easily derived from the phase function of the particle size distribution, can be calculated from any generic single-scattering properties database, which allows for simple upgrades of the reference optical properties within the code. The paper discusses the solutions for mean upward and downward ambient radiances and their use in the simplification of the general radiative transfer equation for thermal infrared. To assess the algorithm performance, the results obtained with the MAMA code are compared with those derived with a discrete ordinate-based radiative transfer model for a large range of physical and optical properties of ice and liquid water clouds and for multiple atmospheric conditions. It is demonstrated that, for liquid water clouds, the MAMA code accuracy is mostly within 0.4 mW/(m2cm−1sr) with respect to the reference code both at far- and mid-infrared wavelengths. Ice cloud spectra are also accurately simulated at mid-infrared for all realistic cloud cases, which makes the MAMA code suitable for the analysis of any spectral measurements of current satellite infrared sounders. At far infrared, the MAMA accuracy is excellent when ice clouds with an optical depth of less than 2 are considered, which is particularly valuable since cirrus clouds are one of the main targets of the future mission FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) of the European Space Agency. In summary, the MAMA method allows computations of cloudy sky high-resolution radiances over the full longwave spectrum (4–100 μm) in less than a second (for pre-computed gas optical depths and on a standard personal computer). The algorithm exploits the fundamental properties of the scattering layers, and the code can be easily updated in relation to new scattering properties.

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“…Early theoretical studies implied that measurements of the outgoing far‐IR spectrum should give unique information of crystal habit and size distribution (Yang et al., 2003). More recent work has demonstrated that measurements of ice cloud optical properties across the full IR range can improve the quantification of cloud optical thicknesses and effective sizes of ice clouds under nighttime conditions robustly when visible and near‐IR solar‐band measurements are unavailable (Saito et al., 2020). Nonetheless, work exploiting airborne observations of far‐IR radiances in the presence of cirrus clouds demonstrate an inability to simulate measurements consistently across the far‐IR and Mid‐IR spectrum using available ice‐cloud bulk optical property data sets (Bantges et al., 2020; Cox et al., 2010).…”

Section: Introductionmentioning

confidence: 99%

Improved Temperature‐Dependent Ice Refractive Index Compilation in the Far‐Infrared Spectrum

Wang,

Ren,

Yang

et al. 2024

Geophysical Research Letters

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A new ice refractive index compilation is reported for a broad spectrum ranging from 0.0443 to 106 μm, focusing on the pronounced temperature‐dependence of ice optical properties in the far‐infrared (far‐IR) segment (15–100 μm). A sensitivity study assuming spherical particles shows that selecting ice refractive indices at 12 temperatures and 215 wavelengths in the far‐IR region gives sufficient accuracy in interpolated refractive indices for developing a new ice crystal optical property database. Furthermore, we demonstrate the differences between the bulk single‐scattering properties computed for hexagonal ice particles with this new compilation compared to a previous iteration at three far‐IR wavelengths where substantial differences are noticed between the two ice refractive index compilations. We suggest that our new ice refractive index data set will improve downstream light‐scattering applications for upcoming far‐IR satellite missions and allow robust modeling of outgoing longwave radiation under ice cloud conditions.

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

Cited by 8 publications

References 46 publications

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

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

The MAMA Algorithm for Fast Computations of Upwelling Far- and Mid-Infrared Radiances in the Presence of Clouds

Improved Temperature‐Dependent Ice Refractive Index Compilation in the Far‐Infrared Spectrum

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