Paul D. Green

Recent advances in measurement of the water vapour continuum in the far-infrared spectral region

We present a new derivation of the foreign-broadened water vapour continuum in the far-infrared (far-IR) pure rotation band between 24 μm and 120 μm (85–420 cm−1) from field data collected in flight campaigns of the Continuum Absorption by Visible and IR radiation and Atmospheric Relevance (CAVIAR) project with Imperial Colleges Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) far-IR spectro-radiometer instrument onboard the Facility for Airborne Atmospheric Measurement (FAAM) BAe-146 research aircraft; and compare this new derivation with those recently published in the literature in this spectral band. This new dataset validates the current Mlawer–Tobin-Clough–Kneizys–Davies (MT-CKD) 2.5 model parametrization above 300 cm−1, but indicates the need to strengthen the parametrization below 300 cm−1, by up to 50 per cent at 100 cm−1. Data recorded at a number of flight altitudes have allowed measurements within a wide range of column water vapour environments, greatly increasing the sensitivity of this analysis to the continuum strength.

Airborne and satellite remote sensing of the mid-infrared water vapour continuum.

Remote sensing of the atmosphere from space plays an increasingly important role in weather forecasting. Exploiting observations from the latest generation of weather satellites relies on an accurate knowledge of fundamental spectroscopy, including the water vapour continuum absorption. Field campaigns involving the Facility for Airborne Atmospheric Measurements research aircraft have collected a comprehensive dataset, comprising remotely sensed infrared radiance observations collocated with accurate measurements of the temperature and humidity structure of the atmosphere. These field measurements have been used to validate the strength of the infrared water vapour continuum in comparison with the latest laboratory measurements. The recent substantial changes to self-continuum coefficients in the widely used MT_CKD (Mlawer–Tobin–Clough–Kneizys–Davies) model between 2400 and 3200 cm−1 are shown to be appropriate and in agreement with field measurements. Results for the foreign continuum in the 1300–2000 cm−1 band suggest a weak temperature dependence that is not currently included in atmospheric models. A one-dimensional variational retrieval experiment is performed that shows a small positive benefit from using new laboratory-derived continuum coefficients for humidity retrievals.

Modelling of the Beamsplitter Properties within the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) and Associated Effect on Instrument Calibration

A polarising far infrared spectrometer has been simulated to investigate the effect of Mylar substrates on polarisers. Procedural errors were found to the calibration in certain spectral regions. Comparisons with laboratory measurements are discussed.

Water vapor continuum results in the far IR from the CAVIAR and RHUBC field measurement campaigns

We report results from the second CAVIAR and first RHUBC field campaigns, comparing a derived water vapor continuum parametrisation in the far IR spectral region with those in the mid IR and the literature.

The Recent Field Measurement Campaign of the Continuum Absorption by Visible and Infrared Radiation and Its Atmospheric Relevance (CAVIAR) Project

The objectives and component parts of the CAVIAR consortium are described. Preliminary data from the recent UK-based airborne field campaign are discussed, with a description of the analysis method and its expected scientific merit.

Investigations of Cirrus in the Far Infrared with the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS)

An overview of the results of recent field campaigns performed with the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) to study the radiative properties of cirrus in the far infrared spectral region is presented.

Far‐infrared Spectral Radiance Observations and Modeling of Arctic Cirrus: Preliminary Results From RHUBC

Recent studies have highlighted the important contribution of the far‐infrared (electromagnetic radiation with wavelengths greater than 12 μm) to the Earth’s radiative energy budget. In a cloud‐free atmosphere, a significant fraction of the Earth’s cooling to space from the mid‐ and upper troposphere takes place via the water vapor pure rotational band between 17 and 33 μm. Cirrus clouds also play an important role in the Earth’s outgoing longwave radiation. The effect of cirrus on far‐infrared radiation is of particular interest, since the refractive index of ice depends strongly on wavelength in this spectral region. The scattering properties of ice crystals are directly related to the refractive index, so consequently the spectral signature of cirrus measured in the FIR is sensitive to the cloud microphysical properties [1, 2]. By examining radiances measured at wavelengths between the strong water vapor absorption lines in the FIR, the understanding of the relationship between cirrus microphysics and ...

Far infrared radiation measurements from the TAFTS instrument during EMERALD 2001

The TAFTS instrument was flown at high altitude in clear and cloudy sky conditions during the EMERALD project. Here we discuss the results including clear sky net flux profiling in the far infrared.