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- Author or Editor: Harry Van Loon x
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Abstract
In mid-tropospheric levels of the Southern Hemisphere, the temperature contrast between middle and high latitudes reaches two maxima near the times of the equinoxes, the strongest contrast being at the autumnal equinox. This variation is dominated by the seasonal changes over the Antarctic Ocean where the second (semiannual) harmonic of the mid-tropospheric meridional temperature gradient has a magnitude exceeding that of the first (annual) harmonic. The existence of the marked semiannual component in this region is shown to be a consequence of the difference between the heating and cooling rates in different latitudes where the mid-tropospheric annual temperature ranges are similar. In latitude 50S cooling in autumn is rapid compared with the warming in spring, the reverse being true at latitude 65S. This behavior is related to the heat budget of the oceanic upper layers.
The semiannual maximum temperature gradients in the middle troposphere over the Antarctic Ocean, through increased cyclonic activity, cause the mean position of the circumpolar trough to be closer to the pole during the transition seasons. In turn, this produces a semiannual oscillation in the pressures and winds over the area affected by the trough.
While the hemispheric mean pressure in middle latitudes falls with the equatorward shift in the mean position of the circumpolar trough from autumn to winter, the pressure rises over Australia, South America, and Africa. The resulting increased longitudinal pressure contrast between the continents and the neighboring sea is expressed as an amplification of the mean wave pattern at the surface, greatest in the half hemisphere centered on Australia. The enhanced poleward transfer of warm air accompanying this amplification apparently accounts for the cessation of rapid temperature falls over Antarctica in early winter, and for actual temperature rises at some stations such as Little America.
Abstract
In mid-tropospheric levels of the Southern Hemisphere, the temperature contrast between middle and high latitudes reaches two maxima near the times of the equinoxes, the strongest contrast being at the autumnal equinox. This variation is dominated by the seasonal changes over the Antarctic Ocean where the second (semiannual) harmonic of the mid-tropospheric meridional temperature gradient has a magnitude exceeding that of the first (annual) harmonic. The existence of the marked semiannual component in this region is shown to be a consequence of the difference between the heating and cooling rates in different latitudes where the mid-tropospheric annual temperature ranges are similar. In latitude 50S cooling in autumn is rapid compared with the warming in spring, the reverse being true at latitude 65S. This behavior is related to the heat budget of the oceanic upper layers.
The semiannual maximum temperature gradients in the middle troposphere over the Antarctic Ocean, through increased cyclonic activity, cause the mean position of the circumpolar trough to be closer to the pole during the transition seasons. In turn, this produces a semiannual oscillation in the pressures and winds over the area affected by the trough.
While the hemispheric mean pressure in middle latitudes falls with the equatorward shift in the mean position of the circumpolar trough from autumn to winter, the pressure rises over Australia, South America, and Africa. The resulting increased longitudinal pressure contrast between the continents and the neighboring sea is expressed as an amplification of the mean wave pattern at the surface, greatest in the half hemisphere centered on Australia. The enhanced poleward transfer of warm air accompanying this amplification apparently accounts for the cessation of rapid temperature falls over Antarctica in early winter, and for actual temperature rises at some stations such as Little America.
Abstract
In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice.
A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.
Abstract
In the tropics of the Southern Hemisphere the zonal wind in the troposphere above the 500-mb level has a well defined half-yearly oscillation with westerly maxima (easterly minima) in May and November. It is demonstrated that the oscillation is associated with second harmonics of opposite phase in the temperature above the equator and in the subtropics. The temperature oscillations are tentatively explained as being the result of an intensification of vertical motions from autumn to winter. The half-yearly temperature oscillations reverse phase near the tropopause, and again near the 50-mb level. Above this level they are thus in the same phase as in the upper troposphere. The phase reversals imply that the second harmonic of the zonal component of the thermal wind likewise changes phase twice.
A marked longitudinal asymmetry is observed with the oscillations being considerably stronger in the Eastern than in the Western Hemisphere.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
An evaluation is made of the synoptic features and characteristic pressure patterns of the Southern Hemisphere as they relate to the seasonal circulations. Examples of both strong and weak polar outbreaks are presented, and their effect on the zonal circulation is discussed. The implication of the strong zonal circulation and its short-term as well as seasonal variations are examined.
Abstract
An evaluation is made of the synoptic features and characteristic pressure patterns of the Southern Hemisphere as they relate to the seasonal circulations. Examples of both strong and weak polar outbreaks are presented, and their effect on the zonal circulation is discussed. The implication of the strong zonal circulation and its short-term as well as seasonal variations are examined.
