Radiative properties of cirrus clouds in the infrared (8–) spectral region

Abstract

A ground-based observation system has been developed at the Meteorological Research Institute (MRI) for simultaneous measurements of cloud structure and radiative properties of high-level ice clouds. In this observation system, the cloud microphysical quantities and spectral radiances in the region of the 10um window could be simultaneously observed by a Hydrometeor Video Sonde (HYVIS) and a Fourier Transform Infrared (FTIR) spectro-radiometer. On the basis of the results measured by HYVIS, the size distribution of ice particles was approximated by the power law distribution, and the simulation calculations of observed radiances were made for the some combination of the lower limit of power law distribution (r1) and the optical thickness at 10.5um (Tlo.5). Using these data, the minimum error point is searched in the error map. By this method, we retrieve optical thickness and particle size information. The optically thin, medium and thick cases were analyzed in order to investigate the characteristic of our retrieval method. It is found that the optical thickness determined the magnitude of observed radiance, and size distributions determined the slope of the spectrum in the 860 to 980cm-1 region. The simulated and observed radiances agree within +2mW/(m2 sr cm-1), except the 9.6um ozone band and the root mean squares error 1.2mW/(m2 sr cm-1). The error analysis showed that though 5% systematic error is permitted to optical thickness retrieval in some cases, 1% systematic error causes large errors in the size information retrieval, and that a +500m height error corresponds to 1 to 3% radiance error. Furthermore, the values estimated from the radiance in the region of wavenumber 860 to 980cm-1 were almost the same as those from radiance in the whole region, and the optical thickness may be determined from data in the region 1080 to 1200cm-1 without being affected by the size distribution. We also retrieved 1O.5 and effective radius (reff) using the log-normal size distribution within the same degree of error as obtained by the power law model. Furthermore, we investigated the relationship between the parameters retrieved. The ratio of the visible optical thickness at 0.5,um (T0.5) to the infrared one at 10.5um (T1o.5) on June 22 is 0.4 to 1.0, and that on June 30 is 1.0 to 1.8. There is a tendency that the ratio of T1o.5 to T0.5 becomes large as the effective radius increases. We also investigated the relation between n o.5 and the effective radius (reff) of log-normal size distribution. The relation between them changes case by case. There is a negative correlation between them in the case of June 22. In the case of June 30, the effective radius is scattered between 20 and 85um. Concurrent NOAA-11 satellite data over the Tsukuba area were also analyzed. The results show that observation from the satellite is consistent with the ground based observation, and that the large difference of the brightness temperature observed by the different window channels is closely related to the existence of small ice particles ...

Impacts of cloud heterogeneities on cirrus optical properties retrieved from space-based thermal infrared radiometry

“…Several parametrizations were developed for visible and infrared wavelengths (Magono, 1966;Labonnote et al, 2000;Yang et al, 2001Yang et al, , 2005Baum et al, 2005bBaum et al, , 2011Baran and Labonnote, 2007;Baran et al, 2009;Baran, 2012;Baran et al, 2013). For cirrus cases 1 to 8 we employ the aggregate ice crystal model (Yang et al, 2001(Yang et al, , 2005 with a monodisperse distribution used in the IIR retrieval algorithm (Garnier et al, 2013) that provides an extinction coefficient, a single-scattering albedo and an asymmetry factor (Yang et al, 2001(Yang et al, , 2005.…”

Retrieval of effective ice crystal size in the infrared: Sensitivity study and global measurements from TIROS‐N Operational Vertical Sounder

“…[9] At present, ice crystal single scattering properties in the IR have been reliably calculated for hexagonal columns [Sun and Fu, 1999;Yang et al, 2001;Baran et al, 2001a] and planar polycrystals [Mitchell, 2002] using different theoretical approaches.…”

“…[24] More recently, Yang et al [2001] have developed the stretched scattering potential method (SSPM) to overcome the discontinuity at size parameters around 20 between FDTD and IGOM results for the absorption coefficient in the IR, where strong absorption is involved. One possible reason for this discontinuity is the tunneling or above-edge effect, which indirectly has been taken into account in parameterizations involving Mie-Lorenz theory and in the approach of Sun and Fu [1999].…”

Error consistency analysis scheme for infrared ultraspectral sounding retrieval error budget estimation

“…The RTM −1 (Zhou et al 2007(Zhou et al , 2009) used here only uses observed radiance and instrument random noise; no other 'truth' data from satellite or surface-based instruments or from numerical weather analysis/prediction models are utilized in assisting or constraining the retrieval products. The fast transmittance model used herein is a combination of the Stand-alone AIRS Radiative Transfer Algorithm (SARTA) Version 1.07 and the physically based cloud RTM based on the discrete ordinate radiative transfer (DISORT) calculations performed for a wide variety of cloud microphysical properties (Stamnes et al 1988, Yang et al 2001, Strow et al 2003. The studies presented here only deal with clear-sky conditions; therefore, DISORT (or the cloud radiative transfer) model error is not estimated.…”