Physical and optical properties of persistent contrails: Climatology and interpretation

Abstract

[1] The physical and optical properties of persistent contrails were studied with the measurements made by the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. MODIS data were used to determine the contrail locations on the basis of their artificial shapes easily distinguished from natural cirrus, and the so-identified contrails were analyzed with collocated CALIPSO lidar data. Statistics of the geography, geometry, meteorology, and optical properties are reported for approximately 3400 persistent contrails observed over North America, the North Atlantic Ocean, and Europe. The majority of the detected contrails appear in ice-supersaturated air with temperatures lower than À40C. On average, contrails have significantly larger backscattering coefficients and slightly higher linear depolarization ratios (LDRs) than neighboring cirrus clouds. Depolarization tends to be strong when ice crystals are small, and LDR is approximately 0.4-0.45 for young contrails and contrail cores. The mean LDR for the detected contrails increases with decreasing temperature and is not strongly dependent on the lidar pointing angle. The backscattering properties suggest that contrails are primarily composed of small, randomly oriented ice crystals but may also contain a few horizontally oriented plates. Most contrails are optically thin with a mean (median) optical thickness of approximately 0.19 (0.14); however, optically thicker contrails do exist and tend to occur in warmer and more humid ambient air. The mean value and range of the observed LDR data are consistent with theoretical predictions based on a mixture of nonspherical ice crystals randomly oriented in the atmosphere.

Contrail life cycle and properties from 1 year of MSG/SEVIRI rapid-scan images

“…The altitude is consistent with expected values: mean value 11.7 km, with 0.9 km standard deviation. Similar values are shown by Iwabuchi et al (2012): 10.9 km with a standard deviation of 1 km. The temporal evolution of the altitude does not show any conclusive results on the fall rates.…”

“…Only 2 % of the pixels have a τ > 1. The PDF behaviour is similar to the Iwabuchi et al (2012) findings, where τ was retrieved directly from CALIOP data even though they take into account only linear contrails. The average τ they retrieved is 0.19.…”

“…The average length, 130 km (standard deviation, 72 km), is consistent with the mean path length of ice supersaturated regions in the upper troposphere/lower stratosphere (UTLS) region of 150 km (Gierens and Spichtinger, 2000). Iwabuchi et al (2012) retrieved a considerably longer average contrail length of 264 km (standard deviation 294) for contrails over the Northern Hemisphere using MODIS. However, the PDF of their contrails has a mode at 50-100 km, as do the contrails in our data set.…”

“…In order to better understand the radiative forcing of contrails and aviation-induced cirrus clouds, it is necessary to thoroughly study their onset, development and the evolution of their physical properties. Despite the attention and numerous studies on radiative forcing (RF) and other properties of contrail and contrail cirrus in the past decades (Bakan et al, 1994;Mannstein et al, 1999;Minnis et al, 2004;Palikonda et al, 2005;Atlas et al, 2006;Meyer et al, 2007;Burkhardt and Kaercher, 2011;Iwabuchi et al, 2012;Duda et al, 2013, etc. ), the level of scientific understanding of this particular aspect of aviation is still classified as low, and that of induced contrail cirrus as very low (Lee et al, 2009).…”

Effects of optical depth variability on contrail radiative forcing

“…Spatial and temporal variability of contrail optical depth could be taken from detailed contrail simulations (e.g. those presented here) or from collocated space-borne lidar and infrared data (Iwabuchi et al, 2012). As our findings are based on a simple radiative transfer parametrization, we recommend study of the effects of optical depth inhomogeneity on CRF using sophisticated RTMs which include effects of multiple scattering and horizontal photon transport.…”