HR: 08:15h
AN: GC21A-02    [Abstracts]
TI: U.S. Jet Contrail Frequency Changes: Influences of Jet Aircraft Flight Activity, Atmospheric Conditions, and Resultant Policy Implications
AU: * Travis, D J
EM: travisd@uww.edu
AF: University of Wisconsin-Whitewater, Department of Geography and Geology, Whitewater, WI 53190 United States
AU: Carleton, A M
EM: carleton@essc.psu.edu
AF: The Pennsylvannia State University, Department of Geography and Earth and Environmental Systems Institute, University Park, PA 16802 United States
AB: In regions where jet air traffic is most abundant, condensation trails (contrails) may substantially increase the high cloud coverage, potentially affecting climate. This is particularly so when atmospheric conditions support prolonged persistence of contrails, which results in their occurrence in clusters, or ``outbreaks'', thus, allowing them to represent a substantial percentage of the overall high cloud amount. In the U.S., jet kilometers flown have increased dramatically during the past three decades leading to speculation that contrail coverage also has increased. However, contrail occurrence depends heavily upon the meteorological conditions near aircraft cruising altitudes (i.e., near the tropopause, 10-12 km altitude). Moreover, the tropopause figures prominently in projecting future climate changes. This study reports a contrail mid-season climatology for the coterminous U.S. (2000-02), and compares the frequencies with those previously reported for an earlier (1977-79) period, to determine the contrail frequency increase (CFI). For the 2000-02 period, we also report the seasonal frequency and areal coverage of contrail outbreaks as a means to assess the typical size of contrail susceptible regions on a seasonal and daily basis. Contrail frequency for both periods, and occurrence of outbreaks for 2000-02, is derived from analysis of high-resolution satellite imagery. Data on jet aircraft flight activity (JFA) over the U.S. were obtained to assess their relationship to CFI, as were NCEP-NCAR reanalysis data to determine changes in tropopause-level conditions. For 2000-02, contrails comprise distinct high (low) frequencies in the East (West) U.S. Seasonally, there is a contrail association with the latitudinal migration of the jet stream. The inter-monthly variations in contrail frequency are statistically significant but show no association with JFA, indicating a greater role for meteorological conditions. Contrail outbreaks occur most frequently during the transition seasons with greatest overall coverage during the spring (April). The mean daily coverage of contrail outbreaks for the coterminous U.S. is 229,238.9 km2, which is roughly the size of the U.S. state of Montana. The mean areal size of contrail outbreaks is 316,811.8 km2, which is similar in size to that of typical Mesoscale Convective Complexes, areas regularly avoided by aircraft. To reduce potential climate impacts of contrails, aviation policy decision-makers should consider implementing similar guidance whereby pilots avoid contrail susceptible regions. Between 1977-79 and 2000-02, a U.S.-wide average CFI of just over 100% occurred, similar to the percentage increase in JFA, but there are strong spatial and seasonal asymmetries to the CFI not reflected in the JFA. The most (least) positive CFI are associated with a cooling (warming) of the tropopause. The spatial pattern of tropopause temperature change generally matches that which occurs when the Arctic Oscillation index switches from negative to positive, suggesting a hemispheric-scale teleconnection to CFI. The role of upper-tropospheric conditions, their potential future changes, and links to hemispheric-scale teleconnections, should be considered when projecting CFI and its possible climate impacts.
UR: http://facstaff.uww.edu/travisd/webapp/contrail_app_1.php
DE: 0319 Cloud optics
DE: 0321 Cloud/radiation interaction
DE: 1605 Abrupt/rapid climate change (4901, 8408)
DE: 1630 Impacts of global change (1225)
DE: 1637 Regional climate change
SC: Global Climate Change [GC]
MN: Fall Meeting 2005