Studying the Potential of Terahertz Radiationfor Deriving Ice Cloud Microphysical Information

摘要

With wavelengths in the order of the size of typical ice cloud particles and therefore being sensitive to ice clouds, the Terahertz (THz) region is expected to bear a high potential concerning measuring ice cloud properties, in particular microphysical parameters. In this paper we give an introduction to the characteristics of atmospheric THz radiation between 0 -5 THz (wavelengths > 60 μm and wavenumber < 170 cm~(-1)respectively) as well as ice cloud optical properties and cloud effects in the THz region. Using radiative transfer model simulations we analyze the sensitivity of THz spectra to ice content and particle size. For tropical cases cloud effects in the order of 0.1 K/(g/m2) are found. Assuming instrumental sensitivities of typically around 1 K these effects allow for detection of clouds with columnar ice content of 10 g/m~2. It is demonstrated that submillimeter (SMM) instruments are sensitive to particles with sizes larger than 100 μm, while THz observations potentially can measure particles as small as 10 pm.