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- Author or Editor: J. BJERKNES x
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Abstract
Time series of surface winds and sea surface temperatures at Canton Island, covering the period 1962–67, are interpreted to show that the major changes in the temperature of the large central and eastern equatorial Pacific area are caused by the varying strength of the easterly winds and inherent variation in upwelling.
The feedback effects of the ocean temperature variations upon the atmosphere are illustrated by a comparison of the average November 1964 sounding with that of November 1965. In the cold ocean case (1964) the atmosphere has a pronounced stable layer between 900 and 800 mb, preventing convection and rainfall, and in the warm ocean case (1965) the heat supply from the ocean eliminates the atmospheric stability and activates heavy rainfall. The resulting vertical thermal expansion of the tropical troposphere from 1964 to 1965 is demonstrated by 200-mb topographic maps showing the emergence of two new anticyclonic centers symmetrically straddling the equator at the longitude of the maximum ocean warming. The same tropospheric heating can be seen to have been carried far eastward by the upper tropospheric winds, although with diminishing amplitude.
A side effect of the widespread warming of the tropical belt of the atmosphere shows up in the increase of exchange of angular momentum with the neighboring subtropical belt, whereby the subtropical westerly jet strengthens in 1965 compared to 1964 all the way from the central Pacific to the eastern Mediterranean.
The implications of the described ocean-atmosphere interaction for interannual climatic change, and the possible forecasting thereof, are mentioned. It is stressed that climatic forecasting will call for extensive additional coordinated research by oceanographers and meteorologists.
Abstract
Time series of surface winds and sea surface temperatures at Canton Island, covering the period 1962–67, are interpreted to show that the major changes in the temperature of the large central and eastern equatorial Pacific area are caused by the varying strength of the easterly winds and inherent variation in upwelling.
The feedback effects of the ocean temperature variations upon the atmosphere are illustrated by a comparison of the average November 1964 sounding with that of November 1965. In the cold ocean case (1964) the atmosphere has a pronounced stable layer between 900 and 800 mb, preventing convection and rainfall, and in the warm ocean case (1965) the heat supply from the ocean eliminates the atmospheric stability and activates heavy rainfall. The resulting vertical thermal expansion of the tropical troposphere from 1964 to 1965 is demonstrated by 200-mb topographic maps showing the emergence of two new anticyclonic centers symmetrically straddling the equator at the longitude of the maximum ocean warming. The same tropospheric heating can be seen to have been carried far eastward by the upper tropospheric winds, although with diminishing amplitude.
A side effect of the widespread warming of the tropical belt of the atmosphere shows up in the increase of exchange of angular momentum with the neighboring subtropical belt, whereby the subtropical westerly jet strengthens in 1965 compared to 1964 all the way from the central Pacific to the eastern Mediterranean.
The implications of the described ocean-atmosphere interaction for interannual climatic change, and the possible forecasting thereof, are mentioned. It is stressed that climatic forecasting will call for extensive additional coordinated research by oceanographers and meteorologists.
Abstract
No Abstract Available.
Abstract
No Abstract Available.
Abstract
The “high index” response of the northeast Pacific westerlies to big positive anomalies of equatorial sea temperature, observed in the winter of 1957–58, has been found to repeat during the major equatorial sea temperature maxima in the winters of 1963–64 and 1965–66. The 1963 positive temperature anomaly started early enough to exert the analogous effect on the atmosphere of the south Indian Ocean during its winter season.
The maxima of the sea temperature in the eastern and central equatorial Pacific occur as a result of anomalous weakening of the trade winds of the Southern Hemisphere with inherent weakening of the equatorial upwelling. These anomalies are shown to be closely tied to the “Southern Oscillation” of Sir Gilbert Walker.
Abstract
The “high index” response of the northeast Pacific westerlies to big positive anomalies of equatorial sea temperature, observed in the winter of 1957–58, has been found to repeat during the major equatorial sea temperature maxima in the winters of 1963–64 and 1965–66. The 1963 positive temperature anomaly started early enough to exert the analogous effect on the atmosphere of the south Indian Ocean during its winter season.
The maxima of the sea temperature in the eastern and central equatorial Pacific occur as a result of anomalous weakening of the trade winds of the Southern Hemisphere with inherent weakening of the equatorial upwelling. These anomalies are shown to be closely tied to the “Southern Oscillation” of Sir Gilbert Walker.
Abstract
The “tendency equation” is applied to analyze the pressure changes produced in wave-shaped westerly flow. With sufficiently strong westerlies horizontal divergence and convergence occur in such distribution as to cause eastward displacement of troughs and crests. When the westerlies drop under a “critical speed” the distribution of divergence and convergence is reversed.
In the normal case of supercritical speed and increasing west wind with height, incipient waves will develop thermal asymmetry and will intensify. The same kind of irreversible growth of incipient waves would occur in easterlies which increase with height. Therefore, the temperate westerlies in all seasons, and the subtropical easterlies in summer and fall, are the regions of dynamic instability, where, respectively, the extratropical and the tropical cyclones are generated.
The tendency equation applied to closed circulations shows such distribution of pressure rise and fall as to make the patterns drift westwards unless they are strongly “eccentric.” The main reason for the usual eastward drift of closed isobar patterns in the temperate latitudes lies, however, in the fact that the superimposed wave pattern in the upper layers produces overcompensating accumulation of air where the low levels show depletion, and depletion of air where the low levels show accumulation. The behavior of the composite low and high-level depression is discussed from this viewpoint.
Abstract
The “tendency equation” is applied to analyze the pressure changes produced in wave-shaped westerly flow. With sufficiently strong westerlies horizontal divergence and convergence occur in such distribution as to cause eastward displacement of troughs and crests. When the westerlies drop under a “critical speed” the distribution of divergence and convergence is reversed.
In the normal case of supercritical speed and increasing west wind with height, incipient waves will develop thermal asymmetry and will intensify. The same kind of irreversible growth of incipient waves would occur in easterlies which increase with height. Therefore, the temperate westerlies in all seasons, and the subtropical easterlies in summer and fall, are the regions of dynamic instability, where, respectively, the extratropical and the tropical cyclones are generated.
The tendency equation applied to closed circulations shows such distribution of pressure rise and fall as to make the patterns drift westwards unless they are strongly “eccentric.” The main reason for the usual eastward drift of closed isobar patterns in the temperate latitudes lies, however, in the fact that the superimposed wave pattern in the upper layers produces overcompensating accumulation of air where the low levels show depletion, and depletion of air where the low levels show accumulation. The behavior of the composite low and high-level depression is discussed from this viewpoint.
Abstract
No Abstract Available.
Abstract
No Abstract Available.
The generally held assumption, that the bulk of tropical rain over the oceans is generated where the sea is warmer than the air, is being largely verified in this article with the new tool of satellite cloudiness mapping. The discussion focuses on the satellite-observed variable position of the boundary between the west Pacific equatorial rain clouds over warm ocean water and the east Pacific aridity along the equator over cool upwelling water. The often quite abrupt changes between these two regimes in the mid-Pacific are known from an eighteen-year sequence of ocean and atmosphere data at Canton Island. This article describes the same phenomena delineated by satellite television data recorded during 1962–67, and adds features of the geographic cloudiness distribution not obtainable from the widely spaced fixed points of observation.
The generally held assumption, that the bulk of tropical rain over the oceans is generated where the sea is warmer than the air, is being largely verified in this article with the new tool of satellite cloudiness mapping. The discussion focuses on the satellite-observed variable position of the boundary between the west Pacific equatorial rain clouds over warm ocean water and the east Pacific aridity along the equator over cool upwelling water. The often quite abrupt changes between these two regimes in the mid-Pacific are known from an eighteen-year sequence of ocean and atmosphere data at Canton Island. This article describes the same phenomena delineated by satellite television data recorded during 1962–67, and adds features of the geographic cloudiness distribution not obtainable from the widely spaced fixed points of observation.
