CR 56:209-230 (2013)  -  DOI: https://doi.org/10.3354/cr01148

ABSTRACT: The cirrus-level ‘condensation trails’ (contrails) produced by jet aircraft often occur as sub-regional-scale ‘outbreaks’ of multiple contrails, suggested as contributing to post ~1965 climate trends in parts of the US and Europe. Several previously-developed, satellite-image based contrail spatial inventories for the conterminous US (CONUS) revealed regional-scale differences in frequency. However, the use of such geographically-fixed regions was not ideal for climate studies. As a first step towards determining the potential climate impacts of contrail outbreaks for the CONUS, we develop maps of overlapping (in time, space) outbreak occurrences—‘overlaps’— by applying GIS to a recent period (2000–2002) satellite-image derived inventory for mid-season months. The higher-frequency outbreak overlap regions undergo substantial between-season vari- ations in magnitude and extent that reflect an association with upper-tropospheric temperature gradients and winds. Overlap maps generated for additional mid-season months in 2008–2009 indicate the inter-annual variability of the outbreak regionalization. To clarify the role of upper- troposphere synoptic meteorological conditions in contrail outbreak occurrence, we form compo- sites—multi-case averages—for the sub-region of maximum overlap frequency in each mid- season month. Regional and seasonal variations in the relative roles of ‘thermo-dynamic’ (here, temperature, humidity) and ‘dynamic’ (vertical motion of air, horizontal wind) controls in outbreaks are identified. Last, we demonstrate potential utility of the spatial overlap method by deriving fall- season surface station trends (1951–1993) of sky cover variables for contrasting high versus low contrail and overlap frequency grid cells in the eastern CONUS. These suggest a contrail contribu- tion to recent high-cloud increases, notably for the Midwest.

KEY WORDS: Contrails · Climate diagnostics · Regionalization · Composite analysis · Sky cover · Trends