Tuesday, 14 May 2002: 2:30 PM
Contrail climatology over the USA from MODIS and AVHRR data
Persistent contrails have become a common feature in the skies over the United States. In addition to their reduction of clear skies, these man-made clouds may have a significant impact on climate through radiative processes. Like natural clouds, contrail cirrus reflect incoming solar and absorb outgoing infrared radiation. Current estimates of their overall effect suggest an overall maximum warming effect equivalent to almost 0.4°C. A more modest increase of slightly less than 0.1 °C is more realistic. The uncertainties in such estimates are quite large, however, covering almost two orders of magnitude. The contrail effects depend on many factors including areal coverage, altitude, underlying background, optical depth, particle size, lifetime, and the time of day. To gain a better quantification of some of these parameters, this paper analyzes data taken during 2000 and 2001 over the USA from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra (EOS-AM-1) satellite and the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA polar orbiting satellites. Linear contrails are automatically derived from temperature difference images created from 11 and 12 µm channels on each satellite. The temperature, optical depth, effective particle size, and areal coverage are derived from the multispectral data available for each imager. The reflected and emitted radiances are used to compute the radiative forcing for each contrail to obtain an estimate of the overall impact of these contrails on the radiation budget. The results are compared to theoretical estimates of contrail coverage derived from meteorological and flight track data.