A diagnostic study of the global distribution of contrails part I: Presentday climate

The global distribution of contrail formation potential and contrail cloud coverage are estimated using meteorological analyses of temperature and hum idity (ECMWF re-analyses) and an aircraft fuel inventory. A large potential for contrail formation is found in the upper troposphere, in particular in the tropics, but also at mid-latitudes. The global potential contrail cove rage is calculated to be 16%. The actual contrail coverage is proportional to the product of the potentia l coverage and the fuel consumption of 1991/92 air traffic. The actual glob al contrail coverage is 0.09%, however, the pattern of main air routes show up in the geographical distribution of contrail coverage with maximum valu es of more than 5%. Regionally, contrail coverage shows a distinct annual c ycle, with larger values in winter than in summer, in the mid-latitudes. Th e result is only weakly sensitive to the propulsion efficiency of aircraft, but strongly sensitive to aircraft flight altitude.