Dependence of absorption properties of ice on morphology: a test of theory based on a case study using ARIES between 6 um and 15 um

摘要

In this paper we show the importance of infrared interferometer data to the understanding of cirrus crystal absorption and retrieval of cirrus microphysical and bulk properties. The sensitivity of interferometer data to cirrus size, shape, and absorption process is shown through simulation using two crystal shapes namely hexagonal columns and planar polycrystals. The ice water path (IWP) and mean crystal dimension is varied between 15 - 44 gm$+$MIN@2$/ and 20 - 80 micrometers respectively. The atmospheric radiative transfer modeling is done through line by line calculations in which an absorbing cirrus layer is placed and the optical depth predictions for the two habits and sizes are modelled according to anomalous diffraction theory (ADT) and Mie theory. To show potential retrievals we utilize actual cirrus interferometer data obtained from the Airborne Research Interferometer Evaluation (ARIES) instrument between the wavelengths of 6 micrometer to 15 micrometer. On the 10th June 1997 the Meteorological Office C-130 aircraft underflow a piece of semi-transparent cirrus which occurred off the east coast of England. Using the line by line model and assuming ADT as the absorption theory an IWP of 20 gm$+$MIN@2$/ and absorption optical depth of 0.5 are retrieved which gives an r$-e$/ of about 40 micrometers. The retrieved r$-e$/ is representative of mid-latitude cirrus.