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Donald P. Delisi and Timothy J. Dunkerton


Observations of zonally averaged temperature from the Nimbus 7 Stratospheric and Mesospheric Sounder (SAMS) in 1979–82 demonstrate that a significant seasonal variation or asymmetry exists in the equatorial semiannual oscillation (SAO) in the sense that the “first” semiannual cycle beginning in the Northern Hemisphere winter (December–May) is much stronger than the “second” cycle beginning six months later (June–November). Calculation of balanced winds from the satellite data indicates a corresponding seasonality in SAO wind regimes; equatorial easterlies are stronger in December–February than in June–August and are followed by stronger westerly mean flow accelerations and, as a result, stronger westerlies in March–May than in September–November. This observation is in agreement with previous studies of the semiannual oscillation.

Strong coupling is observed during the first SAO cycle between equatorial and North Polar temperature. A model of this coupling via a mean meridional circulation suggests that planetary Rossby wave momentum deposition in the northern winter is the Underlying cause of the seasonal variation in the easterly phase of the SAO, This circulation can produce significant horizontal advection of angular momentum in the tropics even when the body force is confined to midlatitudes. At higher levels, the reverse component of the circulation or a reduced diabatic circulation combine with equatorial Kelvin and westerly gravity waves to produce the large westerly mean flow accelerations in the first SAO cycle.

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Timothy J. Dunkerton and Donald P. Delisi


Twenty years of radiosonde data have been analyzed in an attempt to develop a latitudinal structure climatology of winds, temperature and geopotential at 30 and 50 mb in the equatorial stratosphere. The fine latitudinal resolution provided by the WMO station network reveals several interesting features in the latitudinal structure of the annual and quasi-biennial cycles which dominate this region. For example, the westerly and easterly acceleration phases of the quasi-biennial oscillation are markedly different. Westerly accelerations appear first at the equator, spreading outward with time to higher latitude and an more intense, on average, than the easterly accelerations. The easterly accelerations are more uniform in latitude, but leer uniform in time, sometimes occurring in two stages.

The quasi-biennial wind and temperature oscillations are symmetric about the equator, while the annual harmonic in zonal wind is antisymmetric about the equator, but is not proportional to the Coriolis parameter. Monthly mean zonal wind and temperature appear to be in thermal wind balance at the equator.

Some brief remarks are also made concerning variability of the quasi-biennial oscillation and the effects of El Chichón.

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David Y. Lai, Vadim T. Paka, Donald P. Delisi, Anatoli V. Arjannikov, and Sergei A. Khanaev


An intercomparison study was performed with four Russian-made, electromagnetic probes capable of measuring three components of oceanic turbulent velocities and two single-axis velocity sensors familiar to western scientists, namely, a hot-film anemometer and an airfoil shear probe. The intercomparison measurements were conducted in a water flume tank in the Marine Scientific Production Corporation on Fishery Technology facility in Kaliningrad, Russia. Measurements were obtained in the turbulent region generated behind a grid at three different mean flow speeds (0.7, 1.1, and 1.7 m s−1). In all the intercomparison runs, data from the electromagnetic velocity probes behave in a manner expected from the sensor and filtering characteristics. On the average, turbulent velocity variances from the electromagnetic probes are about ±20% of those from both the hot-film and airfoil probes.

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