A synoptic climatology of contrail outbreak events and associated surface temperature effects for the Continental United States

The artificial cloudiness, or “contrail cirrus” that results from multiple long-lasting (several hours or more) jet contrails (outbreaks) may alter the surface radiation budget and resultant temperatures. To determine the potential climatic impact of contrail outbreaks on surface temperatures, we utilized an extensive database of satellite-derived “clear-sky” contrail outbreaks over the continental U.S. (CONUS) for the mid-season months of 2008 and 2009, and selected those events spanning at least one half of the diurnal cycle of temperature and covering at least 10,000 km^2. The aggregated impact of outbreaks on maximum and minimum temperatures, and the diurnal temperature range (DTR), was determined by comparing anomalies at stations overlain by outbreaks with those at adjacent stations having similar synoptic conditions but not experiencing contrail cloudiness. In January 2008 and 2009, for example, the DTR is suppressed at the outbreak stations compared to the non-outbreak stations by approximately 6^oC, which is statistically significant at greater than the 95% confidence level.

A synoptic climatology of upper tropospheric (UT) variables for these longer-lasting jet contrail outbreaks was also developed for those regions of the CONUS characterized by high-frequencies of clear-sky outbreaks (the Midwest, Southeast, and Northeast). Composite mid-season month average and anomaly patterns of UT temperature, specific humidity, zonal wind, and vertical lapse rate for these outbreaks were computed, as well as their horizontal gradients over the area of each outbreak. Longer-lived contrail outbreaks had associated large anomaly gradients in UT variables of zonal wind and specific humidity. Also, the presence, on average, of a steep temperature lapse rate in the atmospheric layer bounding the outbreak likely results from radiational cooling at the cloud-top level, while typical inversion conditions in the mid-troposphere beneath the contrail cirrus may result from both subsiding air in the UT ridges with which outbreaks frequently occur, and re-radiated longwave due to the contrail layer. These results support not only an impact of contrail outbreaks on surface temperature conditions but the possibility of predicting their occurrence in near-real time based on their associated synoptic signatures.