Abstract Temporal and longitudinal variations in mean meridional wind are estimated from GHOST and EOLE constant level balloon flights at 100 and 200 mb in south temperate latitudes during the period 1966/72. At these latitudes there is evidence of about a 0.3 m s −1 poleward flow in winter‐spring and equatorward flow in summer‐autumn, with the oscillation at 100 mb preceding that at 200 mb by 1 to 2 months. This annual oscillation may reflect a direct circulation between summer and winter hemispheres. At 200 mb in south temperate latitudes there is also evidence for about a 0.1 m s −1 poleward flow during the west wind phase, and equatorward flow during the east wind phase, of the quasi‐biennial zonal wind oscillation in the low tropical stratosphere. The significance of this relation has not yet been ascertained. The overall mean equatorward drift of 0.04 m s −1 points up the existence of the Ferrel Cell in the long‐term average. A breakdown of the data by longitude shows that the annual variation in zonal‐average meridional wind is due to large seasonal variations in meridional wind over the South Atlantic.
An analysis is presented of low-level trajectory data obtained by means of constant level balloon flights from Cape Hatteras, N.C., during September and October 1959. An approximately constant floating level was obtained by flying the nearly constant volume Mylar balloons (tetroons) with an internal superpressure of about 100 mb. The metalized tetroons were positioned a t 1-min. intervals by means of a manually operated SP–1M radar. From knowledge of these positions, overlapping 5-min. average velocities were determined for flight durations of up to 5 hr. On some of the flights the radar return was enhanced by the addition of a radar reflective mesh to the tetroon. With the addition of this mesh, flights at altitudes of less than 5,000 ft. were tracked as far as 92 n. mi. from the radar, or approximately to the radar horizon. Spectral analysis of the velocity data obtained from the four best flights shows some evidence for a (Lagrangian) wind speed periodicity of 26-min. period, a vertical motion periodicity of 13-min. period, and a cross-stream velocity periodicity of 17-min. period. Cross spectrum analysis shows that, with the exception of oscillations of 45-min. period, the wind speed is a t a maximum ahead of the trough in the trajectory. Thus, if the large-scale air flow is nearly geostrophic, there is evidence that kinetic energy and momentum are transported down the pressure gradient by these small-scale oscillations. The maximum upward motion of the tetroon tends to take place near the trajectory trough line for oscillations of a period exceeding 18 min. and near the trajectory crest for oscillations of smaller period. Therefore, looking downstream, the longer-period tetroon oscillations tend to be counterclockwise in a plane normal to the mean trajectory while the shorter-period oscillations tend to be clockwise. However, until more information is obtained on the small-scale temperature field and the extent to which the tetroons follow the vertical air motion, any statement regarding “direct” and “indirect” air circulations is tentative. The ratio of one minus the cross-stream and one minus the along-stream autocorrelation Coefficients for these flights is approximately 0.6, suggesting a certain similarity between Eulerian space and Lagrangian autocorrelation coefficients. The tetroon data also indicate that initially one minus the cross-stream autocorrelation coefficient is proportional to the time, as would be anticipated from Lagrangian turbulence theory. These data tend to confirm that, for the scale of motion under consideration, the Lagrangian-Eulerian scale factor β of Hay and Pasquill has a value near 4.
Previous studies of atmospheric pollution resulting from the 1963 eruption of Mt. Agung have shown that the volcanic dust caused temperature increases in the lower stratosphere over Australia. The present study provides time series of monthly-mean lower stratospheric temperatures for eight tropical stations on both sides of the equator. The data have been smoothed by taking 12-month running means. The results suggest that any effect of the eruption may be impossible to isolate. Some features of the quasi-biennial oscillation in zonal winds and temperatures are pointed out which must be considered in any attempt to explain the peculiarities in the curves of monthly mean temperatures.
Abstract Constant volume balloon (tetroon) flights made over New York City at heights of about 300 metres during June of 1965 are analysed. The transponder‐equipped tetroons were tracked to distances exceeding 100 km by means of the wsr‐57 weather radar located in Central Manhattan. On non‐sea breeze days the tetroons tend to move towards low pressure with an angle of 35 degrees, and to move with about two‐thirds of the geostrophic wind speed. There is a correlation of 0.73 between lapse rate and tetroon‐derived r.m.s. vertical velocity, and of 0.43 between lapse rate and Lagrangian period of vertical oscillation. Tetroon‐derived vertical velocities are also used to obtain estimates of the mean Reynolds stress (1.3 dynes cm −2 at flight level) and the downwind variation of vertical diffusion over an urban area.
Tetroon flights across the northern California coast indicate the influence of a laterally extensive and fairly abrupt 100-m change in terrain height near the shoreline on the three-dimensional low-level air flow. Beneath the wind speed maximum at a height of 300 m, the wind speed is stronger over the land than over the sea, resulting in nearly equal horizontal mass transport between this height and the earth's surface. Across the 4-km interval bracketing the shoreline, the wind backs by 11° and 4° at heights of 200 and 400 m, respectively. The maximum upward velocity, of magnitude 6 cm sec−l, occurs 250 m above the sudden change in terrain height near the shoreline, with the compensating downward motion commencing 3 km inland. Over the hills inland from the coast, the magnitude of the tetroon height variation is closely related to the magnitude of the height variations of the underlying terrain, with tetroon oscillations in the vertical generally preceding the variations in terrain height by a distance exceeding the height of the tetroon above the ground.
Carefully screened transosonde flights are analyzed for evidences of inertial oscillations. The most frequent period of wind speed oscillation along these flights is found to be 12 hr., considerably shorter than the theoretical mode for inertial oscillations. However, when the data are subdivided according to latitude, there is a tendency for wind speed oscillations appropriate to the theoretical inertial period to occur with above average frequency. This tendency is less pronounced when the period of wind speed oscillation is compared with the curvature of the geostrophic flow and is scarcely noticeable when the period of oscillation is compared with the horizontal wind shear. Combining these effects, it is shown that, to a good approximation, wind speed oscillations of above average frequency vary with the absolute (geostrophic) vorticity along the trajectories in the manner theoretically prescribed for inertial oscillations. There is also a tendency for an above average frequency of very short period wind oscillations when the anticyclonic angular velocity of the flow is large. It is tentatively suggested that this phenomenon is associated with the occurrence of “abnormal” flow.
Sea surface temperature (SST) variations in the equatorial eastern Pacific (0–10°S, 180–90°W) are compared with variations in atmospheric temperature, circulation, rainfall and trace-constituent amount. Significant at the 99.9% level (taking into account the serial correlation in the seasonal data) is the zero-lag correlation of −0.62 between this SST and the Southern Oscillation Index (normalized pressure difference between Tahiti and Darwin) during 1932–79, the correlation of 0.72 between this SST and the zonally averaged temperature in the tropical troposphere two seasons later during 1958–79, and the correlation of −0.62 between this SST and Indian summer monsoon rainfall 1–2 seasons earlier during 1868–1977. Significant at the 99% level is the correlation of 0.67 between this SST and rate of increase of CO2 at the South Pole 2–3 seasons later during 1965–76, and significant at the 95% level the correlation or 0.37 between this SST and rate of increase of CO2 at Mauna Loa one season later during 1958–78. Also significant at nearly the 99% level is the negative zero-lag correlation between this SST and rainfall in eastern Australia. Correlations of marginal significance (95% level) have been obtained between this SST and the Northern Hemisphere, temperate-latitude and United States temperatures, north circumpolar vortex area at 10 km and vortex displacement, latitude of the subpolar low and subtropical high, and total ozone, stratospheric water vapor and sunshine duration in the North American region. Implied relationships include enhanced Hadley circulation near time of warmest SST, minimum Indian summer monsoon rainfall and United States sunshine duration at time of expanded polar vortex and equatorward displacement of subpolar low and subtropical high, and cold winter temperature in the United States at time of warm SST, or at the time both of expanded polar vortex and displacement of the vortex toward 90°W.
Examined are annual, quasi-biennial and long-term variations in percentage of possible sunshine (S) within six regions of the contiguous United States, based on observations at 103 stations for the years 1950–1972. S averages 20% greater in summer than in winter, and 20–25% greater in the Southwest than in the Northeast. There is a tendency for S to be maximum near the time of quasi-biennial east wind maximum at 50 mb in the tropics, with the average difference in S at times of east and west wind maxima varying from 1.5% to 0.7% within the regions, and equal to 1.0% for the United States as a whole. The authors believe this difference is related to a quasi-biennial variation in eccentricity of the polar vortex. Within the United States during the 23-year period there has been a highly significant 8% decrease in S during autumn, and a somewhat compensatory 3% increase during spring. The pronounced long-term downward trend in S during autumn, with its implication of an upward trend in albedo, represents an interesting climatological phenomenon with impact on a local and perhaps hemispheric scale. In all six regions there has been a year-average decrease in S since 1964, with values varying from 2.9% in the Northeast to 0.2% in the Southwest, and amounting to a significant 1.3% for the United States as a whole. The possibility is considered that this decrease is related either to an overall increase in cloudiness, an increase in aircraft-induced cirrus cloudiness, or an increase in turbidity due to pollution.
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