Changes in Northern Hemisphere Contrail Properties between 2006 and 2012 Determined from MODIS Imagery

One year (2012) of linear contrail coverage, optical property, and radiative forcing (CRF) data over the Northern Hemisphere (NH) are derived from MODIS imagery, and are compared with 2006 results using a consistent retrieval methodology. A comparison between the observed Terra-minus-Aqua screened contrail coverage differences and the differences in the 2012 annual-mean air traffic estimated with respect to satellite overpass time shows that most contrails detected by the contrail detection algorithm (CDA) form approximately 2 h before overpass time. The 2012 screened Northern Hemisphere contrail coverage (Mask B) increased by 3% compared to 2006 data for Terra and increased by almost 7% for Aqua.

A new post-processing algorithm added to the contrail mask processing estimated that the total contrail cirrus coverage visible in the MODIS imagery may be 3 – 4 times larger than the linear contrail coverage detected by the CDA. This estimate is similar in magnitude to the spreading factor estimated by Minnis et al. (2013). Contrail property retrievals of the 2012 data indicate that both contrail optical depth and contrail effective particle diameter decreased approximately 10% between 2006 and 2012. The decreases may be attributed to better background cloudiness characterization and/or differences resulting from the changes in the waypoint screening, including changes in contrail temperature. The total mean contrail radiative forcing (TCRF) for all 2012 Terra observations were -6.3, 14.3, and 8.0 mW m^-2 for the shortwave, longwave, and net forcings, respectively, which are approximately 20% less than the corresponding 2006 Terra estimates. The drop in TCRF results from both the decrease in normalized CRF and the 3% rise in overall contrail coverage in 2012. The total CRFs for 2012 Aqua are similar, -6.4, 15.5, and 9.0 mW m^-2 for shortwave, longwave, and net radiative forcing. The strong correlation between the relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the corresponding relative changes in screened contrail coverage over nine air traffic regions suggests that regional changes in total contrail radiative forcing from year to year are dominated by inter-annual changes in contrail coverage over each area.