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Sources and sinks of zonal momentum in the middle atmosphere diagnosed using the diabatic circulation
Author(s) -
Shine Keith
Publication year - 1989
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49711548604
Subject(s) - diabatic , stratosphere , climatology , atmospheric sciences , atmosphere (unit) , northern hemisphere , stratopause , environmental science , mesosphere , atmospheric circulation , momentum (technical analysis) , gravity wave , radiative transfer , geology , gravitational wave , meteorology , physics , astrophysics , adiabatic process , finance , quantum mechanics , economics , thermodynamics
Radiative heating rates calculated using monthly mean climatological fields of temperature and ozone are used to diagnose the diabatic circulation in the middle atmosphere. This circulation is then used to infer the zonal force per unit mass. Previous diagnostic studies of the zonal force per unit mass have considered only the northern hemisphere outside the summer period and for heights up to about 60 km. The present study allows calculations for both hemispheres in all seasons at heights up to about 75 km. Strong inter‐hemispheric differences in the diagnosed fields are found in the winter and spring hemispheres, whilst the summer and autumn hemispheres are quite similar. The drag on the mean wind in the southern winter mesosphere is found to be up to double that found in the northern winter mesosphere. It is argued that this feature may be due to an enhanced transmission of gravity waves through the southern winter stratosphere; this may, in turn, explain observed inter‐hemispheric differences in temperature for the winter months. Differences between the diagnosed fields and those inferred in modelling studies are also discussed. Some attention is also paid to a problem that pervades this and similar studies. The calculated radiative heating rates do not allow a unique diabatic circulation to be diagnosed because of unexplained departures from the global mean mass balance. The diagnosed circulation is thus subject to some uncertainty which puts definite limits on the confidence that can be placed on diagnosed quantities, especially in the stratosphere. It must be recognized that derived quantities are admixtures of the true quantity and imperfections in the data and radiative transfer scheme.