Open AccessInfrared radiative forcing and atmospheric lifetimes of trace species based on observations from UARS
Author(s) -
Minschwaner K.,
Carver R. W.,
Briegleb B. P.,
Roche A. E.
Publication year - 1998
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/98jd02116
Subject(s) - radiative forcing , stratosphere , atmospheric sciences , tropopause , forcing (mathematics) , trace gas , radiative transfer , cloud forcing , atmosphere (unit) , environmental science , climatology , physics , meteorology , geology , aerosol , quantum mechanics
Observations from instruments on the Upper Atmosphere Research Satellite (UARS) have been used to constrain calculations of infrared radiative forcing by CH 4 , CCl 2 F 2 , and N 2 O and to determine lifetimes of CCl 2 F 2 and N 2 O. Radiative forcing is calculated as a change in net infrared flux at the tropopause that results from an increase in trace gas amount from preindustrial (1750) to contemporary (1992) times. Latitudinal and seasonal variations are considered explicitly, using distributions of trace gases and temperature in the stratosphere from UARS measurements and seasonally averaged cloud statistics from the International Satellite Cloud Climatology Project. Top‐of‐atmosphere fluxes calculated for the contemporary period are in good agreement with satellite measurements from the Earth Radiation Budget Experiment. Globally averaged values of the radiative forcing are 0.550, 0.132, and 0.111 W m −2 for CH 4 , CCl 2 F 2 , and N 2 O, respectively. The largest forcing occurs near subtropical latitudes during summer, predominantly as a result of the combination of cloud‐free skies and a high, cold tropopause. Clouds are found to play a significant role in regulating infrared forcing, reducing the magnitude of the forcing by 30–40% compared with the case of clear skies. The vertical profile of CCl 2 F 2 is important in determining its radiative forcing; use of a height‐independent mixing ratio in the stratosphere leads to an overprediction of the forcing by 10%. The impact of stratospheric profiles on radiative forcing by CH 4 and N 2 O is 2% or less. UARS‐based distributions of CCl 2 F 2 and N 2 O are used also to determine global destruction rates and instantaneous lifetimes of these gases. Rates of photolytic destruction in the stratosphere are calculated using solar ultraviolet irradiances measured on UARS and a line‐by‐line model of absorption in the oxygen Schumann‐Runge bands. Lifetimes are 114±22 and 118±25 years for CCl 2 F 2 and N 2 O, respectively.