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Abstract
Differences of sea-level pressure between pairs of stations in the South Pacific Ocean are used to examine the trades and the trough in the westerlies during the development of the phase of the Southern Oscillation when pressures fall over the tropical Pacific, equatorial waters warm, and rainfall increases in many otherwise dry places. It is demonstrated that this phase is characterized by an appreciable enhancement of the annual cycle of the trades and the trough compared to the year before. The warm event of 1982 followed this pattern closely.
Abstract
Differences of sea-level pressure between pairs of stations in the South Pacific Ocean are used to examine the trades and the trough in the westerlies during the development of the phase of the Southern Oscillation when pressures fall over the tropical Pacific, equatorial waters warm, and rainfall increases in many otherwise dry places. It is demonstrated that this phase is characterized by an appreciable enhancement of the annual cycle of the trades and the trough compared to the year before. The warm event of 1982 followed this pattern closely.
Abstract
Although the numerical, daily operational analyses for the Southern Hemisphere, in particular those made in Australia since 1972, can be used to describe large-scale features in time and space, they are not suited to computations of quantities which rely for their accuracy on the correctness of the daily analysis at individual points. This conclusion is based on the analysis of transfer of sensible heat by the transient eddies during FGGE and the years 1972–77. In addition, the Australian daily operational analyses of the Southern Hemisphere were compared with those of the U.S. National Meteorological Center, and it was found that the former are generally the better ones.
Abstract
Although the numerical, daily operational analyses for the Southern Hemisphere, in particular those made in Australia since 1972, can be used to describe large-scale features in time and space, they are not suited to computations of quantities which rely for their accuracy on the correctness of the daily analysis at individual points. This conclusion is based on the analysis of transfer of sensible heat by the transient eddies during FGGE and the years 1972–77. In addition, the Australian daily operational analyses of the Southern Hemisphere were compared with those of the U.S. National Meteorological Center, and it was found that the former are generally the better ones.
Abstract
When the total eddy transport of sensible heat in middle latitudes of the Northern Hemisphere increases in winter, the zonally averaged temperature gradient in the subtropics tends to increase, while the temperature gradient decreases in the same latitude as, and north of, the given total eddy flux. This effect is associated mainly with the flux in the quasi-stationary or mean waves. In agreement with this relationship between temperature gradient and heat transport, the correlation between the total eddy flux divergence and zonally averaged temperature in middle latitudes is strongly negative; and the main contribution to this negative correlation also comes from the quasi-stationary eddies. When the mean-eddy flux increases at middle latitudes, the transient-eddy flux tends to decrease over the region of weaker gradients to the north of the stronger mean-eddy flux and to increase to the south of it; and conversely when the mean-eddy flux weakens. From the association between total eddy transport and temperature gradients it follows that the gradients at lower latitudes are negatively correlated with those at higher latitudes.
In the Southern Hemisphere, where the quasi-stationary eddies in temperate latitudes transport little sensible heat, the relationship between total eddy flux and zonally averaged temperature gradient is determined principally by the transient-eddy flux.
All the associations above refer to seasonal averages.
Abstract
When the total eddy transport of sensible heat in middle latitudes of the Northern Hemisphere increases in winter, the zonally averaged temperature gradient in the subtropics tends to increase, while the temperature gradient decreases in the same latitude as, and north of, the given total eddy flux. This effect is associated mainly with the flux in the quasi-stationary or mean waves. In agreement with this relationship between temperature gradient and heat transport, the correlation between the total eddy flux divergence and zonally averaged temperature in middle latitudes is strongly negative; and the main contribution to this negative correlation also comes from the quasi-stationary eddies. When the mean-eddy flux increases at middle latitudes, the transient-eddy flux tends to decrease over the region of weaker gradients to the north of the stronger mean-eddy flux and to increase to the south of it; and conversely when the mean-eddy flux weakens. From the association between total eddy transport and temperature gradients it follows that the gradients at lower latitudes are negatively correlated with those at higher latitudes.
In the Southern Hemisphere, where the quasi-stationary eddies in temperate latitudes transport little sensible heat, the relationship between total eddy flux and zonally averaged temperature gradient is determined principally by the transient-eddy flux.
All the associations above refer to seasonal averages.
Abstract
Composite surface pressure, temperature, and precipitation anomalies are mapped over the Indian and Pacific sectors during the various stages of Warm and Cold Events in the Southern Oscillation. In the year before the development of positive sea surface temperature anomalies in the central and eastern equatorial Pacific (Year–1 of a Warm Event), a strong South Pacific High is associated with below normal surface pressure over Australia and the Indian Ocean. This occurs concurrently with a poleward displacement of the Pacific convergence zones, with above normal air temperature and precipitation over the subtropical Pacific, and opposite conditions along the equator. By the next year (Year 0) of the Warm Event, thew anomalies have the opposite sign. The sequence of anomalies during a Cold Event is inverse to that during a Warm Event but otherwise the anomaly patterns are remarkably similar.
It appears that enhanced convection and low surface pressure within the Pacific convergence zones contribute to the observed westerly wind anomalies in the western equatorial Pacific at the end of Year–1, which are in turn tied to the onset of above normal equatorial SST in the following year. The observed reversal in atmospheric anomalies over the Indian and Pacific oceans daring Warm Events is an extreme manifestation of a general biennial tendency in these anomalies, with Cold Events occupying the opposite extreme.
Abstract
Composite surface pressure, temperature, and precipitation anomalies are mapped over the Indian and Pacific sectors during the various stages of Warm and Cold Events in the Southern Oscillation. In the year before the development of positive sea surface temperature anomalies in the central and eastern equatorial Pacific (Year–1 of a Warm Event), a strong South Pacific High is associated with below normal surface pressure over Australia and the Indian Ocean. This occurs concurrently with a poleward displacement of the Pacific convergence zones, with above normal air temperature and precipitation over the subtropical Pacific, and opposite conditions along the equator. By the next year (Year 0) of the Warm Event, thew anomalies have the opposite sign. The sequence of anomalies during a Cold Event is inverse to that during a Warm Event but otherwise the anomaly patterns are remarkably similar.
It appears that enhanced convection and low surface pressure within the Pacific convergence zones contribute to the observed westerly wind anomalies in the western equatorial Pacific at the end of Year–1, which are in turn tied to the onset of above normal equatorial SST in the following year. The observed reversal in atmospheric anomalies over the Indian and Pacific oceans daring Warm Events is an extreme manifestation of a general biennial tendency in these anomalies, with Cold Events occupying the opposite extreme.
Abstract
The 200-mb tropical wind fields analyzed at Florida State University for 1965–74 and the 200 and 700 mb tropical wind fields from the National Meteorological Center for 1979–82 were used to explore the mechanism for the interannual variation of the tropical easterly jet. This jet is generally weaker during the summers of Warm Events (dry summers) in the Southern Oscillation when anomalously warm surface water appears over the eastern and central equatorial Pacific and drought occurs over the Indian subcontinent. It is observed that divergence (convergence) exists on the upstream (downstream) side of the jet. The tropical divergent circulations, i.e., the east-west Walker and the local Hadley circulations, during such summers are weakened and shifted eastward. Therefore, divergence anomalies appear in the upper troposphere over equatorial Africa or the cast coast of Africa, whole convergence anomalies exist over the Indian subcontinent or the Arabian Sea. These changes of the tropical divergent circulations may cause the change in the energetics maintenance of the tropical easterly jet. Our analysis shows that the divergence anomalies of the divergent kinetic energy flux appear over the east coast of Africa, and the convergence anomalies of divergent kinetic energy flux appear over the Indian subcontinent. It is inferred from these anomalies of kinetic energy flux that the kinetic energy generation and destruction associated with the tropical easterly jet are less in dry summers.
Based upon these changes in the upper-level tropical circulations during dry summers, a suggestion is altered that relates the anomalously warm surface water over the eastern and central equatorial Pacific to the weakening of the low-level monsoon circulation and the tropical easterly jet.
Abstract
The 200-mb tropical wind fields analyzed at Florida State University for 1965–74 and the 200 and 700 mb tropical wind fields from the National Meteorological Center for 1979–82 were used to explore the mechanism for the interannual variation of the tropical easterly jet. This jet is generally weaker during the summers of Warm Events (dry summers) in the Southern Oscillation when anomalously warm surface water appears over the eastern and central equatorial Pacific and drought occurs over the Indian subcontinent. It is observed that divergence (convergence) exists on the upstream (downstream) side of the jet. The tropical divergent circulations, i.e., the east-west Walker and the local Hadley circulations, during such summers are weakened and shifted eastward. Therefore, divergence anomalies appear in the upper troposphere over equatorial Africa or the cast coast of Africa, whole convergence anomalies exist over the Indian subcontinent or the Arabian Sea. These changes of the tropical divergent circulations may cause the change in the energetics maintenance of the tropical easterly jet. Our analysis shows that the divergence anomalies of the divergent kinetic energy flux appear over the east coast of Africa, and the convergence anomalies of divergent kinetic energy flux appear over the Indian subcontinent. It is inferred from these anomalies of kinetic energy flux that the kinetic energy generation and destruction associated with the tropical easterly jet are less in dry summers.
Based upon these changes in the upper-level tropical circulations during dry summers, a suggestion is altered that relates the anomalously warm surface water over the eastern and central equatorial Pacific to the weakening of the low-level monsoon circulation and the tropical easterly jet.
Abstract
We describe the global correlations between a measure of the Southern Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the Northern Hemisphere for an 80-year period, and it turned out that most stable correlation coefficients were found over India, the North Pacific Ocean, the Rocky Mountains, and the central and western North Atlantic Ocean. On the Southern Hemisphere most records are too short for a similar test, but the following may tentatively be said about the Southern Oscillation in middle and high southern latitudes: when pressure is low in lower latitudes over the South Pacific Ocean it tends to be high at higher latitudes of that ocean, high over East Antarctica and low in the belt of westerlies in the Indian and South Atlantic oceans. In the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitudes than in the other extreme. The apparent large-scale sympathetic variations between the SO and temperature are shown to occur over the relatively wide range of periods dust have been attributed to the SO itself.
Abstract
We describe the global correlations between a measure of the Southern Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the Northern Hemisphere for an 80-year period, and it turned out that most stable correlation coefficients were found over India, the North Pacific Ocean, the Rocky Mountains, and the central and western North Atlantic Ocean. On the Southern Hemisphere most records are too short for a similar test, but the following may tentatively be said about the Southern Oscillation in middle and high southern latitudes: when pressure is low in lower latitudes over the South Pacific Ocean it tends to be high at higher latitudes of that ocean, high over East Antarctica and low in the belt of westerlies in the Indian and South Atlantic oceans. In the zonal average on both hemispheres the pressure gradients in this extreme of the oscillation tend to be steeper at lower latitudes and flatter at higher latitudes than in the other extreme. The apparent large-scale sympathetic variations between the SO and temperature are shown to occur over the relatively wide range of periods dust have been attributed to the SO itself.
Abstract
We have investigated the relationship between the extremes of the Southern Oscillation and the following quantities at 700 mb in winter, 1948/1949 to 1978/1979: eddy transfer of sensible heat, temperature, geopotential height and geostrophic wind. In the phase of the Southern Oscillation when pressures are high over the tropical South Indian Ocean and low over the tropical South Pacific Ocean, in contrast with the opposite pressure distribution, the zonal mean poleward flux of sensible heat in the quasistationary waves tends to be higher in middle latitudes; the temperatures and heights tend to be lower between 30 and 60°N with the maximum difference at 45°N; the geostrophic wind tends to be stronger south of 45°N and weaker to the north; and the transfer of sensible heat by the transient waves tends to be stronger south of 45°S, and weaker to the north.
In this extreme of the Southern Oscillation the zonal mean geostrophic wind on both hemispheres is stronger in the subtropics and weaker at higher latitudes than in the other extreme when pressures are high over the tropical South Pacific and low in the tropical South Indian Ocean.
Abstract
We have investigated the relationship between the extremes of the Southern Oscillation and the following quantities at 700 mb in winter, 1948/1949 to 1978/1979: eddy transfer of sensible heat, temperature, geopotential height and geostrophic wind. In the phase of the Southern Oscillation when pressures are high over the tropical South Indian Ocean and low over the tropical South Pacific Ocean, in contrast with the opposite pressure distribution, the zonal mean poleward flux of sensible heat in the quasistationary waves tends to be higher in middle latitudes; the temperatures and heights tend to be lower between 30 and 60°N with the maximum difference at 45°N; the geostrophic wind tends to be stronger south of 45°N and weaker to the north; and the transfer of sensible heat by the transient waves tends to be stronger south of 45°S, and weaker to the north.
In this extreme of the Southern Oscillation the zonal mean geostrophic wind on both hemispheres is stronger in the subtropics and weaker at higher latitudes than in the other extreme when pressures are high over the tropical South Pacific and low in the tropical South Indian Ocean.
Abstract
Tropical teleconnections to the seesaw in winter mean temperatures between Greenland and northern Europe are described in terms of the trade winds, African precipitation, sea surface temperatures and Gulf Stream intensity as indicated by changes in relative sea levels. There is a statistically significant correlation between the strength of the northeast and southeast trades in the Atlantic during seesaw winters, but not in other winters. Latitudinal differences in the position of the ITCZ over Africa, as defined by the belt of heaviest precipitation, are seen between the two modes of the seesaw but not in other circulation types.
Relative sea levels on either side of the Gulf Stream show that geostrophic velocity of the surface current is out of phase with the strength of the trades in the North Atlantic Ocean during seesaw winters, which presumably indicates that in this region steric effects on the current prevail over the influence of the wind. Small-magnitude pressure anomaly patterns of the type seen during seesaw winters are present in autumns preceding those winters, and sea surface temperature anomalies associated with the seesaw occur at all latitudes in summers and autumns preceding, and springs following seesaw winters.
Abstract
Tropical teleconnections to the seesaw in winter mean temperatures between Greenland and northern Europe are described in terms of the trade winds, African precipitation, sea surface temperatures and Gulf Stream intensity as indicated by changes in relative sea levels. There is a statistically significant correlation between the strength of the northeast and southeast trades in the Atlantic during seesaw winters, but not in other winters. Latitudinal differences in the position of the ITCZ over Africa, as defined by the belt of heaviest precipitation, are seen between the two modes of the seesaw but not in other circulation types.
Relative sea levels on either side of the Gulf Stream show that geostrophic velocity of the surface current is out of phase with the strength of the trades in the North Atlantic Ocean during seesaw winters, which presumably indicates that in this region steric effects on the current prevail over the influence of the wind. Small-magnitude pressure anomaly patterns of the type seen during seesaw winters are present in autumns preceding those winters, and sea surface temperature anomalies associated with the seesaw occur at all latitudes in summers and autumns preceding, and springs following seesaw winters.
Abstract
We have investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely. Well-defined pressure anomalies over most of the Northern Hemisphere are associated with this regional seesaw in temperature, and these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East, but positively correlated with the pressure over the Rocky Mountains. The composite patterns of pressure anomalies in the seesaw are almost identical to the fist eigenvector in the monthly mean pressure, but the standard deviations of pressure anomalies in seesaw mouths are as large as the standard deviations of monthly means in general. Since 1840 the seesaw, as defined by temperatures in Scandinavia and Greenland, occurred in more than 40% of the winter months and the occurrences are seemingly not randomly distributed in time as one anomaly pattern would be more frequent than the other for several decades. For this reason the circulation anomalies in the seesaw come to play an important part in deciding the level of regional mean temperatures in winter and thus in deciding the long-term temperature trends. These regional temperature trends are then closely associated with change in frequency of atmospheric circulation types, and it is therefore unlikely that the trends are caused directly by changes in insolation or in atmospheric constituents and aerosols.
Abstract
We have investigated the well-known tendency for winter temperatures to be low over northern Europe when they are high over Greenland and the Canadian Arctic, and conversely. Well-defined pressure anomalies over most of the Northern Hemisphere are associated with this regional seesaw in temperature, and these pressure anomalies are so distributed that the pressure in the region of the Icelandic low is negatively correlated with the pressure over the North Pacific Ocean and over the area south of 50°N in the North Atlantic Ocean, Mediterranean and Middle East, but positively correlated with the pressure over the Rocky Mountains. The composite patterns of pressure anomalies in the seesaw are almost identical to the fist eigenvector in the monthly mean pressure, but the standard deviations of pressure anomalies in seesaw mouths are as large as the standard deviations of monthly means in general. Since 1840 the seesaw, as defined by temperatures in Scandinavia and Greenland, occurred in more than 40% of the winter months and the occurrences are seemingly not randomly distributed in time as one anomaly pattern would be more frequent than the other for several decades. For this reason the circulation anomalies in the seesaw come to play an important part in deciding the level of regional mean temperatures in winter and thus in deciding the long-term temperature trends. These regional temperature trends are then closely associated with change in frequency of atmospheric circulation types, and it is therefore unlikely that the trends are caused directly by changes in insolation or in atmospheric constituents and aerosols.
