Abstract. The radiative forcings and global warming potentials for 39 greenhouse gases are evaluated using narrowband and broadband radiative transfer models. Unlike many previous studies, latitudinal and seasonal variations are considered explicitly, using distributions of major greenhouse gases from a combination of chemical-transport model results and Upper Atmosphere Research Satellite (UARS) measurements and cloud statistics from the International Satellite Cloud Climatology Project. The gases examined include CO2, CH4, N20, plus a number of chlorofiuorocarbons, hydrochlorofiuorocarbons, hydrofiuorocarbons, hydrochlorocarbons, bromocarbons, iodocarbons, and perfiuorocarbons (PFCs). The model calculations are performed on a 5 ø latitude grid from 82.5øS to 82.5øN. The radiative forcings determined by the model are then used to derive global warming potential for each of the compounds, which are compared with prior analyses. In addition, the latitudinal and seasonal dependence of radiative forcing since preindustrial time is calculated. The vertical profiles of the gases are found to be important in determining the radiative forcings; the use of height-independent vertical distributions of greenhouse gases, as used in many previous studies, produce errors of several percent in estimated radiative forcings for gases studied here; the errors for the short-lived compounds are relatively higher. Errors in evaluated radiative forcings caused by neglecting both the seasonal and the latitudinal distributions of greenhouse gases and atmospheres are generally smaller than those due to height-independent vertical distributions. Our total radiative forcing due to increase in major greenhouse gas concentrations for the period 1765-1992 is 2.32 Wm -2, only 2% higher than other recent estimates; however, the differences for individual gases are as large as 23%.

An accurate line‐by‐line model is used to evaluate effects of absorption in the Schumann‐Runge bands of O2 on transmission of ultraviolet radiation. Allowing also for absorption in the Herzberg continuum, the model is shown to provide a reliable simulation of observed transmission in the spectral interval 192 to 200 nm. The model is used to evaluate rates for photolysis of N2O, CFCl3, and CF2Cl2, and to infer global loss rates (1.22×l010 kg N yr−1, 7.21×107 and 3.04×l07 kg Cl yr−1, respectively) and instantaneous lifetimes (123, 44, and 116 years, respectively) appropriate for 1980. A parameterized version of the line‐by‐line model enabling rapid evaluation of transmission in the Schumann‐Runge region is described. Photochemical calculations employing the parameterization and constrained by data from the Atmospheric Trace Molecule Spectroscopy experiment are used to examine the budget of odd oxygen. Consistent with previous studies, it is shown that photochemical loss of odd oxygen exceeds production by photolysis of O2 for altitudes above 40 km. The imbalance between production and loss is shown to be consistent with a source of odd oxygen proportional to the product of the mixing ratio and photolysis rate of ozone, which suggests that processes involving vibrationally excited O2 may play an important role in production of odd oxygen.

Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere.

Daily ozonesondes were launched from 14 North American sites during August 2006, providing the best set of free tropospheric ozone measurements ever gathered across the continent in a single season. The data reveal a distinct upper tropospheric ozone maximum above eastern North America and centered over the southeastern USA. Recurring each year, the location and strength of the ozone maximum is influenced by the summertime upper tropospheric anticyclone that traps convectively lofted ozone, ozone precursors and lightning NOx above the southeastern USA. The North American summer monsoon that flows northward along the Rocky Mountains is embedded within the western side of the anticyclone and also marks the westernmost extent of the ozone maximum. Removing the influence from stratospheric intrusions, median ozone mixing ratios (78 ppbv) in the upper troposphere (>6 km) above Alabama, near the center of the anticyclone, were nearly twice the level above the U.S. west coast. Simulations by an atmospheric chemistry general circulation model indicate lightning NOx emissions led to the production of 25–30 ppbv of ozone at 250 hPa above the southern United States during the study period. On the regional scale the ozone enhancement above the southeastern United States produced a positive all‐sky adjusted radiative forcing up to 0.50 W m−2.

Global water vapor (H2O) measurements from Microwave Limb Sounder (MLS) are used to evaluate upper tropospheric (UT) and lower stratospheric (LS) H2O products produced by NASA Modern‐Era Retrospective Analysis for Research and Applications (MERRA), its newest release MERRA2, and European Centre for Medium‐Range Weather Forecasts (ECMWF) Interim Reanalyses. Focusing on the H2O amount and transport from UT to LS, we show that all reanalyses overestimate annual global mean UT H2O by up to ~150% compared to MLS observations. Substantial differences in H2O transport are also found between the observations and reanalyses. Vertically, H2O transport across the tropical tropopause (16–20 km) in the reanalyses is faster by up to ~86% compared to MLS observations. In the tropical LS (21–25 km), the mean vertical transport from ECMWF is 168% faster than the MLS estimate, while MERRA and MERRA2 have vertical transport velocities within 10% of MLS values. Horizontally at 100 hPa, both observation and reanalyses show faster poleward transport in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Compared to MLS observations, the H2O horizontal transport for both MERRA and MERRA2 is 106% faster in the NH but about 42–45% slower in the SH. ECMWF horizontal transport is 16% faster than MLS observations in both hemispheres. The ratio of northward to southward transport velocities for ECMWF is 1.4, which agrees with MLS observation, while the corresponding ratios for MERRA and MERRA2 are about 3.5 times larger.