Composite Atmospheric Environments of Jet Contrail Outbreaks for the United States

Abstract

The cirrus-level "condensation trails" (contrails) produced by jet aircraft are considered to influence surface climate and its recent changes. To reveal the synoptic atmospheric environments typically associated with multiple co-occurrences of contrails occurring in otherwise clear or partly cloudy skies (outbreaks) for the United States, and ultimately to assist in forecasting these events, a composite (i.e., multicase average) "synoptic climatology" at regional scales is developed for the midseason months (January, April, July, October) of 2000-02. The NCEP-NCAR reanalysis data that emphasize upper-troposphere (UT) variables are allied with manually identified outbreaks appearing on satellite Advanced Very High Resolution Radiometer digital data, using a geographic information system. The highest frequencies of outbreaks by far occur in the Midwest (32.6% of all-U.S. total), followed by the Northeast (17.6%) and Southeast (17.2%). In these regions, all of which have a high density of jet air traffic, an additional 2% cirrus cloud coverage from outbreak-related contrails is inferred. Large interannual and interseasonal variations in contrail outbreak frequencies support the role of meteorological variations. For most regions, the outbreakassociated synoptic circulation composite conditions involve UT ridging and a higher and colder tropopause than the climatological average; meridionally enhanced gradients of the UT vertical motion, located between sinking air to the east (in the ridge) and rising air to the west, in advance of a trough; similarly strong gradients of mid-upper-troposphere humidity, comprising dry air located to the east and moist air to the west; and horizontal speed shear ahead of an advancing jet stream. Notwithstanding, there is a geography (i.e., areal differentiation) to contrail outbreak environments: composites for the Northeast suggest an influence of land-sea contrasts on synoptic systems and, therefore, on contrail outbreaks. For the Northwest, there is evident a greater impact of horizontal wind shear contrasted with other regions. The synoptic climatology results are supported by the all-U.S. averages of contrail outbreak UT conditions [climate diagnostics (CDNs)] previously determined for early-mid-September periods of 1995-2001. Moreover, a comparison of these CDNs with those derived for nearby thick natural clouds, including cirrus, helps to clarify their different synoptic associations: the UT conditions typical of thick clouds represent an intensification of those associated with contrail outbreaks and include the greater upward vertical motion, moister air, and stronger westerly winds characteristic of a trough. Given the location of most contrail outbreaks downstream of multilayered cloud systems, contrails may help to extend the "natural" cirrus and cirrostratus spatial coverage.

Basic Diagnosis and Prediction of Persistent Contrail Occurrence Using High-Resolution Numerical Weather Analyses/Forecasts and Logistic Regression. Part II: Evaluation of Sample Models

“…Previous studies of contrail occurrence suggest that high contrail incidence is associated with areas of baroclinity, and thus with areas where wind speed, vertical velocity and lapse rate may have significant departures from mean conditions (DeGrand et al, 2000). The results from Carleton et al (2008) suggest that atmospheric variables lower in the atmosphere that were not included in this study may also be valuable predictors. The list of meteorological variables in Table 4 is not exhaustive, and other combinations of variables not presented here may be better predictors of contrail occurrence.…”

Estimating Contrail Climate Effects from Satellite Data

“…As noted earlier, the overlapping and spread of contrails can diminish the detection efficiency. Carleton et al 20 report that contrail outbreaks occur twice as often over the Midwest than over any other CONUS region. Thus, the bulk of contrail coverage over this heavy air traffic region may be missed because too many contrails of various ages occur together and are difficult to separate in an automated fashion.…”

“…Close inspection of the imagery suggests that the clouds in that vicinity are very likely older contrails that have lost some of their distinct contrail "signatures", having diffused, overlapped, and grown in particle size. This evolution 19 is common, especially in contrail outbreaks 20 . Such outbreaks may be responsible for much of the excess cloudiness due to contrails, but are difficult to quantify with automated methods and, hence, are analyzed manually 20 .…”

“…This evolution 19 is common, especially in contrail outbreaks 20 . Such outbreaks may be responsible for much of the excess cloudiness due to contrails, but are difficult to quantify with automated methods and, hence, are analyzed manually 20 . The ambiguity resulting from the older and overlapping contrails in such outbreaks should be considered when defining the extent of linear contrails.…”

Aviation-Contrail Impacts on Climate and Climate Change: A Ready-to-Wear Research Mantle for Geographers

“…These radiative attributes are most characteristic of relatively young line-shaped contrails (Meyer et al 2002) that are horizontally narrow and vertically thick. An individual line contrail might be of interest meteorologically (e.g., for briefly reducing the surface incident solar radiation; Wendland and Semonin 1982), but contrails that persist on time scales exceeding about one hour (persisting contrails) likely are important for climate, especially when occurring as clusters or "outbreaks" of multiple contrails on spatial scales exceeding 1 × 10 3 km 2 Nguyen 2001, 2004;Carleton et al 2008). Persisting contrails undergo vertical thinning and horizontal widening, which tends to increase the contrail greenhouse effect relative to its albedo effect (e.g., Strauss et al 1997;Haywood et al 2009).…”