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- Author or Editor: Harry Van Loon x
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Abstract
Meridional profiles of sea-level and 500-mb average zonal winds at mid-season in both hemispheres are presented and described. Over much of the southern hemisphere the mean zonal westerly flow changes little during the year, and in each season it is always stronger for the hemisphere as a whole in the southern than in the northern hemisphere. The southern hemisphere circulation and its seasonal changes are shown to be closely related to the surface temperature distribution.
It is pointed out that despite the seemingly symmetrical distribution of heat and cold sources over the southern hemisphere, regional differences in the strength and distribution of the mean zonal wind do exist, particularly during the colder part of the year. Thus, although on the whole there is a strong control arising from the ocenic dominance of the hemisphere, there are, especially in the Australian sector, large disturbances connected with continental influences on heating and cooling.
The strongest zonal westerly mean circulation in the southern hemisphere at the levels dealt with here is found over the Indian Ocean.
Abstract
Meridional profiles of sea-level and 500-mb average zonal winds at mid-season in both hemispheres are presented and described. Over much of the southern hemisphere the mean zonal westerly flow changes little during the year, and in each season it is always stronger for the hemisphere as a whole in the southern than in the northern hemisphere. The southern hemisphere circulation and its seasonal changes are shown to be closely related to the surface temperature distribution.
It is pointed out that despite the seemingly symmetrical distribution of heat and cold sources over the southern hemisphere, regional differences in the strength and distribution of the mean zonal wind do exist, particularly during the colder part of the year. Thus, although on the whole there is a strong control arising from the ocenic dominance of the hemisphere, there are, especially in the Australian sector, large disturbances connected with continental influences on heating and cooling.
The strongest zonal westerly mean circulation in the southern hemisphere at the levels dealt with here is found over the Indian Ocean.
Abstract
Time sections of monthly average zonal geostrophic wind at sea level and 500 mb in the Southern Hemisphere confirm that the strongest zonal westerlies usually are found in summer, but since the westerlies expand over a bigger area in the colder part of the year their average relative angular momentum is greater in winter than in summer. For the earth as a whole the westerly relative angular momentum at sea level and 500 mb is greater in January than in July.
The highest frequency of surface fronts in the Southern Hemisphere forms a belt round the hemisphere in middle latitude in summer and coincides with the strongest zonal wind at sea level and 500 mb, and with the steepest temperature gradient in the lower half of the troposphere. In winter there are two separate zones of highest frequency of fronts.
The frequencies of sea level highs, lows and cyclogenesis plotted as a function of latitude have their peaks in three different latitudes zones so arranged that the peak frequency of highs is farthest equatorward and that of the lows farthest poleward.
The meridional geostrophic flow at 500 mb between the 30th and 60th parallels, weighted according to area, was used as a relative measure of the mass flux across the given latitude belt. It was found that the flux is considerably greater during the southern than during the northern summer, but little greater during the northern than during the southern winter. The shape of the meridional profiles of mass exchange is the same in the. northern and southern summers and in the northern and southern winters.
An analysis of the 500-mb data on Hovmöller diagrams shows that horizontal dispersion of energy, seen as the downstream intensification of alternating troughs and ridges, took place on several occasions during the period investigated.
Abstract
Time sections of monthly average zonal geostrophic wind at sea level and 500 mb in the Southern Hemisphere confirm that the strongest zonal westerlies usually are found in summer, but since the westerlies expand over a bigger area in the colder part of the year their average relative angular momentum is greater in winter than in summer. For the earth as a whole the westerly relative angular momentum at sea level and 500 mb is greater in January than in July.
The highest frequency of surface fronts in the Southern Hemisphere forms a belt round the hemisphere in middle latitude in summer and coincides with the strongest zonal wind at sea level and 500 mb, and with the steepest temperature gradient in the lower half of the troposphere. In winter there are two separate zones of highest frequency of fronts.
The frequencies of sea level highs, lows and cyclogenesis plotted as a function of latitude have their peaks in three different latitudes zones so arranged that the peak frequency of highs is farthest equatorward and that of the lows farthest poleward.
The meridional geostrophic flow at 500 mb between the 30th and 60th parallels, weighted according to area, was used as a relative measure of the mass flux across the given latitude belt. It was found that the flux is considerably greater during the southern than during the northern summer, but little greater during the northern than during the southern winter. The shape of the meridional profiles of mass exchange is the same in the. northern and southern summers and in the northern and southern winters.
An analysis of the 500-mb data on Hovmöller diagrams shows that horizontal dispersion of energy, seen as the downstream intensification of alternating troughs and ridges, took place on several occasions during the period investigated.
Abstract
The seasonal variations during the IGY of sea-level pressures, 500-mb heights, and 1000-500 mb thickness in the Southern Hemisphere are examined to see if they conform to patterns which are deemed intrinsic to the hemisphere. These are: 1) the arrangement of the annual temperature range in four concentric zones of alternating low and high range; 2) the coldness of the lower and middle troposphere over Australasia in winter compared with South America and Africa; 3) the positive temperature isanomals in middle and high latitudes over the South Pacific Ocean in both summer and winter; and 4) the sea-level pressure and 500-mb height variations of opposite sign in middle and high latitudes which give rise to a second harmonic of large amplitude in temperature and height gradients, and in winds and sea-level pressure.
The speed of movement of lows between 30 and 70S was, on the average, only slightly lower in the IGY summer than in the winter.
A comparison between the standard deviations of daily sea-level pressures and 500-mb heights in the two hemispheres shows that the variability is nearly the same in the northern and southern winters, but that the standard deviations in the latitudes near 50N in summer are only two-thirds of those in the same latitudes in the southern summer.
Abstract
The seasonal variations during the IGY of sea-level pressures, 500-mb heights, and 1000-500 mb thickness in the Southern Hemisphere are examined to see if they conform to patterns which are deemed intrinsic to the hemisphere. These are: 1) the arrangement of the annual temperature range in four concentric zones of alternating low and high range; 2) the coldness of the lower and middle troposphere over Australasia in winter compared with South America and Africa; 3) the positive temperature isanomals in middle and high latitudes over the South Pacific Ocean in both summer and winter; and 4) the sea-level pressure and 500-mb height variations of opposite sign in middle and high latitudes which give rise to a second harmonic of large amplitude in temperature and height gradients, and in winds and sea-level pressure.
The speed of movement of lows between 30 and 70S was, on the average, only slightly lower in the IGY summer than in the winter.
A comparison between the standard deviations of daily sea-level pressures and 500-mb heights in the two hemispheres shows that the variability is nearly the same in the northern and southern winters, but that the standard deviations in the latitudes near 50N in summer are only two-thirds of those in the same latitudes in the southern summer.
Abstract
Abstract
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
The standard deviations of mean sea-level pressure in January are compared for five discrete 16-year periods between 1901 and 1980. The changes from one period to another are large and larger in the North Atlantic than in the North Pacific Ocean. The differences between the periods are associated with variations in the position and central pressure of the Aleutian and Icelandic lows. There is no consistent link between the two lows as their central pressure varied in parallel till the late 1930s and oppositely thereafter.
Abstract
Observations of monthly mean sea level pressure, surface air temperature, and 500 mb and 300 mb geopotential heights and temperatures are used to study trends in the Southern Hemisphere from 1951–81.
The winter mean sea level pressure fell over the Indian/Atlantic half of the hemisphere from the 1950s to the 1960s, and rose over the other half. Generally, these trends reversed from the 1960s to the 1970s. The trends are equivalent barotropic.
The trends of temperatures are often regionally dependent. There was a significant warming over Antarctica from the 1960s to 1970s at all upper levels except for a small area on the Indian Ocean side.
Abstract
Observations of monthly mean sea level pressure, surface air temperature, and 500 mb and 300 mb geopotential heights and temperatures are used to study trends in the Southern Hemisphere from 1951–81.
The winter mean sea level pressure fell over the Indian/Atlantic half of the hemisphere from the 1950s to the 1960s, and rose over the other half. Generally, these trends reversed from the 1960s to the 1970s. The trends are equivalent barotropic.
The trends of temperatures are often regionally dependent. There was a significant warming over Antarctica from the 1960s to 1970s at all upper levels except for a small area on the Indian Ocean side.
