Premium
The impact of cirrus microphysical and macrophysical properties on upwelling far‐infrared spectra
Author(s) -
Baran Anthony J.
Publication year - 2007
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.132
Subject(s) - cirrus , ice crystals , middle latitudes , water vapor , crystal (programming language) , materials science , atmosphere (unit) , mixing ratio , atmospheric sciences , environmental science , geology , physics , optics , meteorology , computer science , programming language
The potential for exploiting upwelling high‐resolution far‐infrared measurements to obtain information on cirrus microphysical properties is evaluated assuming single‐layer and multiple‐layer cirrus embedded in standard midlatitude winter and tropical atmospheres. The microphysical sensitivity of two high‐resolution spectral regions (606 cm −1 –333 cm −1 and 250 cm −1 –80 cm −1 ) to changes in optically thin single‐layer cirrus height, and to perturbing the volume mixing ratio of water vapour of the standard midlatitude winter atmosphere by 30% is studied. It is found that there are spectral ‘windows’ in the far‐infrared which are strongly dependent on ice crystal effective size. In particular, ‘windows’ existing between the wave numbers of about 365 cm −1 to 500 cm −1 and 85 cm −1 to 140 cm −1 demonstrate potential sensitivity to ice crystal effective dimension of up to about 100.0 µm and 50.0 µm, respectively. However, these same spectral windows are also shown to be strongly sensitive to assumptions about the shape of the particle size distribution function and ice crystal geometry. Moreover, sensitivity to ice crystal effective dimension is further shown to be dependent on the location of the cirrus layer within the atmosphere, especially in the spectral region 606 cm −1 –333 cm −1 . Perturbing the volume mixing ratio of water vapour by 30% has its largest impact on the cirrus layer located higher in the atmosphere. In this case the sensitivity to the smallest ice crystal effective dimension of about 8.0 µm is essentially removed and the sensitivity to the largest ice crystal effective dimension of about 100 µm is significantly reduced in the spectral region of 606 cm −1 –333 cm −1 . Therefore, in order to retrieve cirrus microphysical properties in the far‐infrared, prior information on ice crystal geometry and shape of the distribution function is required. Moreover, the volume mixing ratio of water vapour should be measured to within an accuracy of better than 30%. It is further demonstrated that for selected wave numbers in the far‐infrared, assuming a three‐layer cloud, there is also some dependence on the vertical structure of the atmosphere as well as the vertical profile of ice crystal effective size. © Crown Copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.