TY - JOUR
T1 - A sudden warming in the middle atmosphere of the southern hemisphere
AU - Al‐Ajmi, D. N.
AU - Harwood, R. S.
AU - Miles, T.
PY - 1985/4
Y1 - 1985/4
N2 - This paper presents a case study of a wave‐mean flow interaction, or minor warming, near the southern hemisphere stratopause for 15‐30 July 1974. the analysis is based mainly on data from the selective chopper radiometer carried by Nimbus 5. A deceleration of the zonal mean wind of 70 m s‐1 from 20 to 25 July is observed in middle latitudes at 0.5 mb, with an acceleration further south. the polar vortex is, however, not disrupted. Eliassen‐Palm cross‐sections are presented for the event and a good correlation found between the E‐P flux convergence and the deceleration. the channelling of the E‐P fluxes from the tropopause to the convergent region is in broad agreement with the distribution of refractive index but there is a region of E‐P flux divergence at high levels in polar latitudes suggesting a source of wave activity there. The residual circulation is calculated both from the momentum budget and from an omega equation, both methods diagnosing a region of modest equatorward flow near the region of E‐P flux divergence embedded in the stronger poleward flow elsewhere. Maps of potential vorticity on the isentropic surface of 0 = 1640 K are presented and the evolving pattern related to zonal mean and isobaric descriptions. the event is shown to be associated with an incursion of low latitude air into middle latitudes with a corresponding irreversible mixing of potential vorticity reminiscent of the ‘wave breaking’ in northern hemisphere events reported by McIntyre and Palmer (J. At. Ter. Ph., 46, 825), but of much smaller amplitude.
AB - This paper presents a case study of a wave‐mean flow interaction, or minor warming, near the southern hemisphere stratopause for 15‐30 July 1974. the analysis is based mainly on data from the selective chopper radiometer carried by Nimbus 5. A deceleration of the zonal mean wind of 70 m s‐1 from 20 to 25 July is observed in middle latitudes at 0.5 mb, with an acceleration further south. the polar vortex is, however, not disrupted. Eliassen‐Palm cross‐sections are presented for the event and a good correlation found between the E‐P flux convergence and the deceleration. the channelling of the E‐P fluxes from the tropopause to the convergent region is in broad agreement with the distribution of refractive index but there is a region of E‐P flux divergence at high levels in polar latitudes suggesting a source of wave activity there. The residual circulation is calculated both from the momentum budget and from an omega equation, both methods diagnosing a region of modest equatorward flow near the region of E‐P flux divergence embedded in the stronger poleward flow elsewhere. Maps of potential vorticity on the isentropic surface of 0 = 1640 K are presented and the evolving pattern related to zonal mean and isobaric descriptions. the event is shown to be associated with an incursion of low latitude air into middle latitudes with a corresponding irreversible mixing of potential vorticity reminiscent of the ‘wave breaking’ in northern hemisphere events reported by McIntyre and Palmer (J. At. Ter. Ph., 46, 825), but of much smaller amplitude.
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U2 - 10.1002/qj.49711146406
DO - 10.1002/qj.49711146406
M3 - Article
AN - SCOPUS:0022190449
SN - 0035-9009
VL - 111
SP - 359
EP - 389
JO - Quarterly Journal of the Royal Meteorological Society
JF - Quarterly Journal of the Royal Meteorological Society
IS - 464
ER -