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Abstract
It is shown that long-term trends in the meridional components of the trade wind circulations in both hemisphere over the Pacific are highly correlated with the precipitation falling in the intertropical convergence zone (ITCZ) over that region. The trends in the trade wind regime, on the one hand, seem to be caused by extratropical sea surface temperature (SST) anomalies in the North Pacific which influence atmospheric meridional temperature and pressure gradients. On the other hand, the release of latent heat in the ITCZ provides a self-enforcing feedback for the trade winds.
A study of the recurrence frequency of precipitation surges over the Line Islands suggests the presence of three epoch (1911–28, 1929–62, 1963 to present) during which the Hadley cell circulation and attendant meteorological and oceanographic features showed different characteristics.
Abstract
It is shown that long-term trends in the meridional components of the trade wind circulations in both hemisphere over the Pacific are highly correlated with the precipitation falling in the intertropical convergence zone (ITCZ) over that region. The trends in the trade wind regime, on the one hand, seem to be caused by extratropical sea surface temperature (SST) anomalies in the North Pacific which influence atmospheric meridional temperature and pressure gradients. On the other hand, the release of latent heat in the ITCZ provides a self-enforcing feedback for the trade winds.
A study of the recurrence frequency of precipitation surges over the Line Islands suggests the presence of three epoch (1911–28, 1929–62, 1963 to present) during which the Hadley cell circulation and attendant meteorological and oceanographic features showed different characteristics.
Abstract
During September 1961 a series of balloon ascents made from Flin Flon, Canada, carrying scintillation counters sensitive to gamma radiation, revealed the existence of shallow stable atmospheric layers carrying radioactive debris, presumably from the Russian test series during the same month.
The debris layers encountered on 14 and 15 September have been studied in particular. The debris detected over Flin Flon on 14 September, 2221 GCT, at 650 mb had undergone strong sinking motion. One may conclude that it came from the region immediately underneath the tropopause shortly prior to 13 September, 12 GCT, entering the middle troposphere through the stable layer underneath the jet core, sometimes referred to as a “jet-stream front.”
Beginning with 17 September a distinct area of radioactive fallout begins to appear at the surface over the eastern United States. Some of this debris seems to be identical with the one detected over Flin Flon, and it apparently was transported by the same jet stream. Part of the fallout seems to be associated with a small collapsing cold dome travelling ahead of this jet stream.
Abstract
During September 1961 a series of balloon ascents made from Flin Flon, Canada, carrying scintillation counters sensitive to gamma radiation, revealed the existence of shallow stable atmospheric layers carrying radioactive debris, presumably from the Russian test series during the same month.
The debris layers encountered on 14 and 15 September have been studied in particular. The debris detected over Flin Flon on 14 September, 2221 GCT, at 650 mb had undergone strong sinking motion. One may conclude that it came from the region immediately underneath the tropopause shortly prior to 13 September, 12 GCT, entering the middle troposphere through the stable layer underneath the jet core, sometimes referred to as a “jet-stream front.”
Beginning with 17 September a distinct area of radioactive fallout begins to appear at the surface over the eastern United States. Some of this debris seems to be identical with the one detected over Flin Flon, and it apparently was transported by the same jet stream. Part of the fallout seems to be associated with a small collapsing cold dome travelling ahead of this jet stream.
Abstract
Precipitation surges in the equatorial Pacific “dry zone” (as delineated in a study by Doberitz) reveal statistically significant teleconnections with midlatitude tropospheric flow patterns during all seasons. These connections are strongest, however, during winter and agree with linear numerical model results. There is evidence that deep troughs in the central North Pacific antecede precipitation surges in the equatorial dry zone during that season, suggesting the possibility of triggering of such surges by middle latitude planetary-wave perturbations. Nonlinear numerical model results also indicate that the midlatitude planetary-wave response is strongest when North Pacific cold sea-surface temperature anomalies and equatorial East Pacific warm anomalies are present simultaneously.
The planetary-wave pattern associated with equatorial Pacific precipitation surges appears to be in phase with orographically generated wave patterns, whereas an anomalous low-latitude heat source over the extreme equatorial west Pacific, the Bay of Bengal and India, corresponding to rainfall during an active phase of the Indian monsoon, tends to be associated with wave perturbations out-of-phase with orographic forcing.
Abstract
Precipitation surges in the equatorial Pacific “dry zone” (as delineated in a study by Doberitz) reveal statistically significant teleconnections with midlatitude tropospheric flow patterns during all seasons. These connections are strongest, however, during winter and agree with linear numerical model results. There is evidence that deep troughs in the central North Pacific antecede precipitation surges in the equatorial dry zone during that season, suggesting the possibility of triggering of such surges by middle latitude planetary-wave perturbations. Nonlinear numerical model results also indicate that the midlatitude planetary-wave response is strongest when North Pacific cold sea-surface temperature anomalies and equatorial East Pacific warm anomalies are present simultaneously.
The planetary-wave pattern associated with equatorial Pacific precipitation surges appears to be in phase with orographically generated wave patterns, whereas an anomalous low-latitude heat source over the extreme equatorial west Pacific, the Bay of Bengal and India, corresponding to rainfall during an active phase of the Indian monsoon, tends to be associated with wave perturbations out-of-phase with orographic forcing.
Abstract
Following the perturbation theory, the aircraft measurements of “Project Jet Stream” Flight No. 29 (4 April 1957) have been analyzed, applying a double-smoothing technique, thus treating the basic fields of flow and temperature separately from the superimposed mesoscale disturbances. Analyses of wind velocity and potential temperature lead to estimates of the distributions of vorticity, potential vorticity and divergence in a vertical cross-section. Several inferences are made as to the meso-structure of the atmosphere near the jet-stream core.
Abstract
Following the perturbation theory, the aircraft measurements of “Project Jet Stream” Flight No. 29 (4 April 1957) have been analyzed, applying a double-smoothing technique, thus treating the basic fields of flow and temperature separately from the superimposed mesoscale disturbances. Analyses of wind velocity and potential temperature lead to estimates of the distributions of vorticity, potential vorticity and divergence in a vertical cross-section. Several inferences are made as to the meso-structure of the atmosphere near the jet-stream core.
Abstract
The three-dimensional wind field in the vicinity of the jet stream is defined with the aid of four parameters: mean wind speed and direction, thickness, and mean altitude of the Layer of Maximum Wind (LMW). Routine methods of analysis of these quantities are discussed in view of the reliability of available wind data, and a statistical treatment of these quantities reveals the mean horizontal and vertical structure of the LMW. Forecasts of the LMW are attempted by means of a grid or “box” method, and a control-line method.
Abstract
The three-dimensional wind field in the vicinity of the jet stream is defined with the aid of four parameters: mean wind speed and direction, thickness, and mean altitude of the Layer of Maximum Wind (LMW). Routine methods of analysis of these quantities are discussed in view of the reliability of available wind data, and a statistical treatment of these quantities reveals the mean horizontal and vertical structure of the LMW. Forecasts of the LMW are attempted by means of a grid or “box” method, and a control-line method.
Abstract
Evidence is derived from observational data that the trade wind circulations in both hemispheres over the Pacific are related to the sea surface temperature (SST) anomalies in the North Pacific. The equatorward component of the surface trade winds leads the North Pacific SST anomalies by approximately 20 months, equivalent to the half-rotation time of the Pacific gyre.
Long-term trends in the Pacific trade wind regime appear to have an influence on hemispheric and global mean temperatures. The trade wind anomalies also seem to be tied to meridional atmospheric pressure- and temperature-gradient anomalies which, in turn, appear to respond to anomalies in the meridional SST gradients. Thus a closed feedback loop is demonstrated, in which SST anomalies in the North Pacific generate trade wind anomalies which promote the development of North Pacific SST anomalies of opposite sign. The trade wind surges also are related to El Niño through a feedback involving the hydrological cycle and upwelling of cold water forced by Ekman pumping.
Abstract
Evidence is derived from observational data that the trade wind circulations in both hemispheres over the Pacific are related to the sea surface temperature (SST) anomalies in the North Pacific. The equatorward component of the surface trade winds leads the North Pacific SST anomalies by approximately 20 months, equivalent to the half-rotation time of the Pacific gyre.
Long-term trends in the Pacific trade wind regime appear to have an influence on hemispheric and global mean temperatures. The trade wind anomalies also seem to be tied to meridional atmospheric pressure- and temperature-gradient anomalies which, in turn, appear to respond to anomalies in the meridional SST gradients. Thus a closed feedback loop is demonstrated, in which SST anomalies in the North Pacific generate trade wind anomalies which promote the development of North Pacific SST anomalies of opposite sign. The trade wind surges also are related to El Niño through a feedback involving the hydrological cycle and upwelling of cold water forced by Ekman pumping.
Abstract
A review is given of mathematical expressions for total and mean specific kinetic energies in the longitudinal, time, and mixed longitudinal-time domains. These coordinate domains differ from those defined earlier by Oort. Mathematical developments are extended into the vertical coordinate domain. A new symbolism is introduced for describing mean and eddy motions.
Abstract
A review is given of mathematical expressions for total and mean specific kinetic energies in the longitudinal, time, and mixed longitudinal-time domains. These coordinate domains differ from those defined earlier by Oort. Mathematical developments are extended into the vertical coordinate domain. A new symbolism is introduced for describing mean and eddy motions.
Abstract
Gridded NMC data for 500 mb geopotential height, and 300–500 mb and 500–700 mb thickness for the period 1951–78 wore subjected to linear trend analyses. These analyses were performed for each calendar month. Significant geographical and seasonal distributions of cooling and warming patterns emerged. An atmospheric cooling trend over the North Pacific during the winter months appears in a region where oceanic cooling has also been observed, but planetary-wave adjustments rather than ocean-atmosphere feedback mechanisms appear to dominate the atmospheric cooling on climatic time scales. Consistently large temperature trends also appear over the Asian continent. Comparisons between thickness trends in the layer 300–500 mb with those in the. layer 500–700 mb reveal well-pronounced patterns of stabilization and destabilization.
Abstract
Gridded NMC data for 500 mb geopotential height, and 300–500 mb and 500–700 mb thickness for the period 1951–78 wore subjected to linear trend analyses. These analyses were performed for each calendar month. Significant geographical and seasonal distributions of cooling and warming patterns emerged. An atmospheric cooling trend over the North Pacific during the winter months appears in a region where oceanic cooling has also been observed, but planetary-wave adjustments rather than ocean-atmosphere feedback mechanisms appear to dominate the atmospheric cooling on climatic time scales. Consistently large temperature trends also appear over the Asian continent. Comparisons between thickness trends in the layer 300–500 mb with those in the. layer 500–700 mb reveal well-pronounced patterns of stabilization and destabilization.
Abstract
Cases of explosive cyclogenesis (“bombs”) were identified over the central and eastern United States and were compared with nonexplosive cyclone development in the same region. The tendency equations for vorticity and geopotential thickness, and a modified divergence equation were used to find signatures of distinction between these two types of cyclogenesis, whose recognition might improve forecasting skills.
Bombs tend to show a marked decrease of vorticity with height during their incipient and explosive stages, whereas regular cyclones reveal only weak vertical vorticity gradients in the troposphere. The low-tropospheric spin-up in bombs precedes significantly that in the upper troposphere. Preexisting low-tropospheric vorticity maxima are associated with low-level jet streaks.
Whereas regular cyclones possess an ill-defined level of nondivergence (i.e., a broad region between 800 and 400 mb, of divergence values close to zero), incipient bombs have a well-marked zero-divergence level near 500 mb, associated with a sharp maximum of rising motions.
We observed a marked increase in large-scale latent beat release between the incipient and the explosive phases of bomb development. The convective component of latent beating shows a distinct maximum in the incipient phase of bombs and a decrease which continues through the explosive and mature phases. Regular cyclones show much less heating and much less change between the phases of development than is observed with the bombs. Static stability reveals little change as the bomb grows and mature. There also is little difference between the stability associated with bombs and regular cyclones.
Abstract
Cases of explosive cyclogenesis (“bombs”) were identified over the central and eastern United States and were compared with nonexplosive cyclone development in the same region. The tendency equations for vorticity and geopotential thickness, and a modified divergence equation were used to find signatures of distinction between these two types of cyclogenesis, whose recognition might improve forecasting skills.
Bombs tend to show a marked decrease of vorticity with height during their incipient and explosive stages, whereas regular cyclones reveal only weak vertical vorticity gradients in the troposphere. The low-tropospheric spin-up in bombs precedes significantly that in the upper troposphere. Preexisting low-tropospheric vorticity maxima are associated with low-level jet streaks.
Whereas regular cyclones possess an ill-defined level of nondivergence (i.e., a broad region between 800 and 400 mb, of divergence values close to zero), incipient bombs have a well-marked zero-divergence level near 500 mb, associated with a sharp maximum of rising motions.
We observed a marked increase in large-scale latent beat release between the incipient and the explosive phases of bomb development. The convective component of latent beating shows a distinct maximum in the incipient phase of bombs and a decrease which continues through the explosive and mature phases. Regular cyclones show much less heating and much less change between the phases of development than is observed with the bombs. Static stability reveals little change as the bomb grows and mature. There also is little difference between the stability associated with bombs and regular cyclones.
Abstract
Detailed analyses are presented of the temperature and pressure fields of the planetary boundary layer (PBL) and their seasonal variability over the western United States and over the Plateau of Tibet (Qinghai-Xizang Plateau). Over the United States these analyses rely on 850 mb data, augmented by surface data. Over Tibet the 600 mb surface adequately describes the PBL.
The effects of a “plateau monsoon” appear prominently during winter and summer over both plateaus. Together with continental monsoon effects they help to shape prominent circulation features, such as the low-level jet stream (LLJ) over Texas and Oklahoma. The complex, seasonal characteristics of precipitation regimes over the North American continent can be explained, to a large extent, by considering these monsoonal changes in the PBL, especially over the mountains.
Abstract
Detailed analyses are presented of the temperature and pressure fields of the planetary boundary layer (PBL) and their seasonal variability over the western United States and over the Plateau of Tibet (Qinghai-Xizang Plateau). Over the United States these analyses rely on 850 mb data, augmented by surface data. Over Tibet the 600 mb surface adequately describes the PBL.
The effects of a “plateau monsoon” appear prominently during winter and summer over both plateaus. Together with continental monsoon effects they help to shape prominent circulation features, such as the low-level jet stream (LLJ) over Texas and Oklahoma. The complex, seasonal characteristics of precipitation regimes over the North American continent can be explained, to a large extent, by considering these monsoonal changes in the PBL, especially over the mountains.
