Terrestrial atmosphere

The terrestrial atmosphere has regions with opposite signs of the atmospheric lapse rate: the troposphere usually cools upward, the stratosphere warms upward through ultraviolet heating, the mesosphere cools, and the thermosphere warms. A monotone atmospheric pressure-temperature profile can approximate one such interval, but cannot describe all their transitions with one fixed branch.

A tropical zonal overturning circulation in the terrestrial atmosphere, coupled to east–west ocean temperature contrasts. Its mean Pacific branch has rising air over the warmer western Pacific and sinking air farther east. The circulation is named after Gilbert Walker.

Persistent low-latitude surface winds with a westward component, associated with the lower branch of the Hadley cell. Their weakening or reversal in the equatorial Pacific can excite equatorial Kelvin waves that contribute to the development of El Niño.

Surface heating, upward sensible and latent energy transport, expansion cooling and atmospheric radiative cooling shape the tropospheric temperature decrease. Ozone ultraviolet absorption gives the mean stratospheric inversion. Reduced ozone heating and radiative losses allow mesospheric cooling with height; energetic solar absorption heats the tenuous thermosphere. Boundaries depend on latitude, season and dynamical state, and a schematic profile is not a measured global sounding. ^[ref]

The thermosphere is a high atmospheric region where absorption of energetic stellar radiation can produce an upward-rising kinetic temperature. Its very low density distinguishes kinetic temperature from a large thermal energy content.

The mesosphere lies above the stratosphere and below the thermosphere. Its typical terrestrial temperature decreases upward.

The terrestrial stratosphere lies above the troposphere and has an upward-warming region associated with ultraviolet heating by the ozone layer.

Transport of air and trace species across the tropopause. Downward ozone transport can supply the troposphere even when local tropospheric photochemical production is unchanged. Regional pathways, mixing and residence times determine the resulting burden.

The wave-driven mean stratospheric circulation with tropical ascent and extratropical descent. Changes in wave propagation and momentum deposition can alter its strength and transport times. Its response redistributes ozone and trace gases; local chemistry and transport must be considered together.

A wintertime region of strong circumpolar flow that can isolate polar stratospheric air and sustain cold conditions. Isolation, cloud formation, sunlight return and subsequent breakup jointly influence seasonal ozone chemistry. Cooling alone does not determine the full ozone evolution.

An increase of atmospheric carbon dioxide can cool the stratosphere through enhanced infrared cooling relative to non-infrared heating and through changes in the spectrum of upwelling radiation. A local emissivity-only explanation is incomplete because absorption and emission both change. The response depends on ozone solar heating, spectral opacity, altitude and adjustments of the layers below.^[ref]

Cold-region stratospheric particles that can support heterogeneous reactions activating reactive halogen chemistry. Their occurrence and effect depend on temperature, available condensable species, halogen reservoirs and sunlight history.

Removal of reactive nitrogen from an air mass through formation and sedimentation of nitric-acid-containing particles. This can delay reformation of chlorine nitrate and prolong active chlorine chemistry. It is a physical/chemical atmospheric removal process, distinct from biological denitrification.

Conversion of relatively unreactive chlorine reservoirs into forms that produce active radicals in sunlight. Heterogeneous reactions on appropriate particle surfaces can turn hydrogen chloride and chlorine nitrate into photolabile species. Available surface composition, temperature, reservoir supply and subsequent illumination all matter; adding arbitrary particles does not guarantee activation.

The troposphere is the lowest main layer of the terrestrial atmosphere, with weather and generally decreasing temperature with altitude. Local inversions and moist convection complicate a single lapse-rate description.

The troposphere above the directly surface-coupled atmospheric boundary layer. Entrainment between these regions can change pollutant abundances even when local chemical production is unchanged.

The lowest part of the terrestrial atmosphere that responds directly to surface fluxes on relatively short timescales through turbulence. Its depth changes with heating, stability and weather; a sharp composition or temperature change can mark its top. A uniform-layer chemical budget converts a surface flux into a volume tendency by dividing by layer depth.

The atmospheric boundary layer over an ocean surface. A box-model ozone budget can include in-layer production, chemical loss, dry deposition, entrainment from the free troposphere and horizontal Advection. Fixed-depth local steady-state assumptions must be checked against transport and day–night variation.