11/12/2022 0 Comments Cirrus cloud![]() This is because while cirrus and cirrostratus clouds usually contain small, hexagonal ‘prism’ crystals such as thick plates, short solid columns – simple crystals that refract the sun’s light as it passes through them, deeper altostratus clouds generally have larger more complicated crystals and snowflakes that do not permit simple refraction even when the sun’s position is plainly evident. In contrast, thicker ice clouds, such as altostratus ( Figures 11 and 12), cannot produce haloes when seen from the ground. Cirrus cloud full#Cirrus clouds do not usually produce full haloes due to their patchy nature. Haloes are usually seen with cirrostratus clouds, and occasionally, partial haloes are seen with cirrus clouds. Due to the slow settling of ice crystals, and depth of moist air below the formation level, mature cirrus and cirrostratus clouds are often 1 km or more thick though the sun may not be appreciably dimmed. The long, usually curved filaments that often comprise cirriform clouds are caused by the growth of larger ice crystals that fall out into regions of changing wind speeds and directions below the parent cloud. An exception to this is at the moment of formation when a spec or small, hard looking tuft of cirrus can have many thousands per liter of tiny quasispherical ice crystals which then gradually disperse after the moment of formation. The coldest cirriform cloud tops (i.e., cirrus and cirrostratus) can be −80 ☌ or lower in deep storms with high cloud tops such as in anvils associated with exceptional thunderstorms.Ĭirrus and cirrostratus clouds are fibrous, wispy, and diffuse because the concentrations of ice crystals that comprise them are relatively low (from less than 1 per liter to tens per liter) compared with particle concentrations in other clouds. The ‘bases’ or visual bottoms of cirrus and cirrostratus clouds are composed of generally low concentrations of ice crystals that are about to evaporate. In these cases, droplets may be briefly present at the instant of formation. However, many such clouds so described would actually be classified as ‘altostratus’ clouds by ground observers due to the gray shading they produced.) Cirrus ( Figures 1 and 2) and cirrostratus ( Figure 3) clouds are composed of ice crystals with, perhaps, a few momentary exceptions at formation when the temperature is higher than −40 ☌. (Many users of satellite data refer to ‘cirrus’ or ‘cirriform’ those clouds with cold tops in the upper troposphere without regard to whether they produce shading as seen from below. By WMO definition, they are not dense enough to produce shading except when the sun is near the horizon, with the single exception of a thick patchy cirrus species called cirrus spissatus ( Figure 2) in which gray shading is allowable. Rangno (Retiree), in Encyclopedia of Atmospheric Sciences (Second Edition), 2015 High CloudsĬirrus, cirrostratus, and cirrocumulus clouds ( Figures 1–5, respectively) comprise ‘high’ clouds. This will be realised with the launch of the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, ESA’s 9th Earth Explorer.A.L. These results suggest that the CIC algorithm will be a useful addition to existing cloud classification tools but that further analyses of nadir radiance observations spanning the infrared and sampling a wider range of atmospheric and cloud conditions are required to fully probe its capabilities. However, in this case, the limited temporal and spatial variability in the measured spectra results in a less obvious advantage being apparent when using both mid- and far-infrared radiances compared to using mid-infrared information only. When the CIC is applied to the airborne radiance measurements, the classification performance of the algorithm is very high. These tests also suggest that, for conditions encompassing those sampled by the flight campaigns, the additional information contained within the far-infrared improves the algorithm’s performance compared to using mid-infrared data only. Theoretical sensitivity studies show that the performance of the CIC algorithm improves with cloud altitude. Co-located measurements of the two sensors allow observations of the upwelling radiance for clear and cloudy conditions across the far- and mid-infrared part of the spectrum. Data comprise a set of spectral radiances measured by the Tropospheric Airborne Fourier Transform Spectrometer (TAFTS) and the Airborne Research Interferometer Evaluation System (ARIES). Airborne interferometric data, obtained from the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) and from the PiknMix-F field campaign, are used to test the ability of a machine learning cloud identification and classification algorithm (CIC). ![]()
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