Prof. Hironobu Iwabuchi have made a new compilation of ice optical constant dependent on temperature, for a spectrum from the ultraviolet to the microwave and published in the Journal of Quantitative Spectroscopy and Radiative Transfer.

We compiled a new dataset of optical constants (refractive indices) of water ice for a spectrum from ultraviolet to microwave and a temperature range from 160 to 270 K. Conventional researches in the atmospheric sciences have been usually assumed ice optical constants not dependent on the temperature, and data for a high temperature of about ~7˚C have been used in many cases. We investigated and collected the best measurement data from the literature and derived optical constants for the entire spectrum based on a few theoretical laws of laws of physics and empirical formulas. The optical constants depend on temperature in the mid-infrared and microwave (Fig. 1). Even in the near infrared, the temperature dependence is not negligible. Optical properties of ice cloud calculated at the infrared split window wavelengths, 11 µm and 12 µm, showed non-negligible dependence on temperature.

Cirrus clouds form at low temperature from -40˚C to -80˚C in the upper troposphere and play important roles in the earth’s radiation budget. In he remote sensing of ice clouds using the infrared spectra, ice optical constants and optical properties of ice particles at appropriate temperature should be used.

The results of this research has been published in the Journal of Quantitative Spectroscopy and Radiative Transfer, this month. The new datasets of optical constants can be downloaded from the journal’s website or available from the authors on request.

Reference
Iwabuchi, H., and P. Yang, 2011: Temperature-dependence of ice optical constants: Implications for simulating the single-scattering properties of cold ice clouds. J. Quant. Spectrosc. Radiat. Transfer, 112, 2520-2525.

Fig. 1.  Ice refractive indices dependent on temperature (T), in the infrared.