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  • Author or Editor: E. R. Reiter x
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Gene Wooldridge and E. R. Reiter

Abstract

From GHOST balloon data obtained over the Southern Hemisphere at the 200-mb level, phase velocities of cyclone waves were found to vary between 6.3 and 9.2 degrees of longitude per day. Spectrum analysis of the relative velocities of balloon pairs, measured with respect to their common center of gravity, yielded a spectrum peak in the v component near frequencies of 1/52 hr, and a “−3” spectrum slope at higher frequencies. (The latter may be contaminated by a spline function smoothing technique.) Spectral densities in v were found to be slightly larger in summer than in winter, while densities in u were half as large in summer than in winter. Significantly stronger anisotropy of flow prevails at cyclone wavelengths in the Southern than the the Northern Hemisphere, with the v perturbations exceeding the zonal flow perturbations. GHOST balloon cospectra yielded similar results of momentum transport as did data from the Northern Hemisphere.

Eulerian spectra of the v component over New Zealand agreed well with results from the Northern Hemisphere; spectral densities of the u component in the Southern Hemisphere,. however, were approximately half of those found in the Northern Hemisphere (Washington, D. C.); the v spectra showed a peak at 1/14 day. Spectrum slope5 of “−1” are indicated at higher frequencies. Eulerian cospectra permitted a preliminary estimate of meridional transports of zonal momentum.

A crude estimate of the relation between Eulerian and Lagrangian spectra yielded considerably different results for the Southern than for the Northern Hemisphere as did estimates of the coefficients of eddy diffusivity Kx and Ky.

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E. R. REITER and L. F. WHITNEY

Abstract

By means of satellite photographs originally analyzed by Oliver et al., it is shown that the polar-front jet stream and the subtropical jet stream do not behave as entities in regions where they approach each other closely. A crossover of flow is observed whereby the subtropical current overrides, and merges with, the polar-front jet.

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J. J. Stephens and E. R. Reiter

Abstract

Estimates of the spectrum of refractivity fluctuations to be expected in regions of clear turbulence are shown for scales in the inertial subrange. Based on the complete analysis by Atlas et al., it is concluded that radar detection of clear air turbulence with current technology is unlikely for all but inversion conditions. However, the present analysis can be used to provide consistent estimates for particular environmental conditions.

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A. I. Weinstein, E. R. Reiter, and J. R. Scoggins

Abstract

Several time series of vertical wind velocity profiles obtained by tracking spherical superpressure balloons using l1–20 radars at Point Mugu, California and Cape Kennedy, Florida are analyzed. In the altitude range 11–20 km the measured wind data are an order of magnitude better than standard GMD-1 data. Below 11 km the smooth 2-m diameter spherical balloon used is aerodynamically unstable, producing spurious high frequency oscillations. Each series contains from 8 to 18 wind velocity profiles spaced over a period of time from 8–12 hr.

Every profile in each series contained mesoscale perturbations of from 5–10 m sec−1 and 5–20 deg (referenced to an arbitrary smooth profile), through depths up to 2 km, which persisted in recognizable form at approximately constant altitude throughout the series. A model to account for such perturbations is presented, picturing the atmosphere from 11–20 km as having a distinctly layered structure. Each layer covers a large horizontal area and contains air whose motion is principally controlled by a quasi-inertial oscillation. Wind profile perturbations result from the relative horizontal motion between layers. It is suggested that, in the presence of geostrophic wind shear, overall thermal stability, and low turbulence energy normally found in the stratosphere, quasi-inertial oscillations, once started through a deep atmospheric layer, would soon disperse into a series of shallow individual ones of different wavelengths, capable of maintaining themselves for long periods of time.

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Adel F. Hanna, Duane E. Stevens, and Elmar R. Reiter

Abstract

A two-level, global, spectral model is used to study the response of the atmosphere to sea surface temperature anomalies. Two sea surface temperature anomaly patterns are investigated. The first, called the El Niño pattern (Experiment 1), represents a warm anomaly in the equatorial Pacific, whereas the second pattern (Experiment 2) represents coupled midlatitude (cold)/ equatorial (warm) sea surface temperature anomalies in the pacific Ocean.

The results demonstrate that both of these sea surface temperature anomaly patterns produce statistically significant midtropospheric geopotential responses in middle latitudes. However, the geopotential response forced by the coupled sea surface temperature anomaly is qualitatively more similar to the geopotential height pattern which is observed in association with the negative phase of the Southern Oscillation (Horel and Wallace). Analysis of the differences (anomaly minus control) of the meridional transports of momentum. sensible heat and latent heat indicates that the coupled pattern tends to largely enhance the northward transports of momentum and sensible heat, especially for the transient and stationary eddy components. The maximum difference in the total (transient, stationary eddies and mean meridional circulation) transport of momentum is nearly double that revealed by the El Niño experiment.

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James E. Bossert, John D. Sheaffer, and Elmar R. Reiter

Abstract

Mountaintop data from remote stations in the central Rocky Mountains have been used to analyze terrain-induced regional (meso-β to meso-α) scale circulation patterns. The circulation consists of a diurnally oscillating wind regime, varying between daytime inflow toward, and nocturnal outflow from, the highest terrain. Both individual case days and longer term averages reveal these circulation characteristics. The persistence and broadscale organization of nocturnal outflow at mountaintop, well removed from valley drainage processes, demonstrates that this flow is part of a distinct regime within the hierarchy of terrain-induced wind systems.

The diurnal cycle of summertime convective storm development imparts a strong influence upon regional-scale circulation patterns. Subcloud cooling processes, associated with deep moist convection, alter the circulation by producing early and abrupt shifts in the regional winds from an inflow to outflow direction. These wind events occur frequently when moist conditions prevail over the central Rocky Mountains. Atmospheric soundings suggest that significant differences occur in the vertical profile of the topographically influenced layer, depending upon the dominant role of either latent or radiative forcing.

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Elmar R. Reiter, J. D. Sheaffer, J. E. Bossert, Eric A. Smith, Greg Stone, Robert McBeth, and Qinglin Zheng

A long-planned field-measurement program to determine surface-energy budgets at two sites in Tibet was carried out during June 1986 in collaboration with scientists from the State Meteorological Administration, Academy of Meteorological Sciences, People's Republic of China. The data set obtained in Tibet is unique for this remote region of the world. The present report describes some of the experiences of the United States scientific team and its medical officer, M. Otteman of Ft. Collins, Colorado. The data are presently being archived on computer tapes. Preliminary analysis results are presented as typical examples of the conditions encountered at the two experimental sites near Lhasa (3635 m) and Nagqu (4500 m).

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Elmar R. Reiter, John D. Sheaffer, James E. Bossert, Richard C. Fleming, William E. Clements, J. T. Lee, Sumner Barr, John A. Archuleta, and Donald E. Hoard

During the late summer of 1985 a field experiment was conducted to investigate mountaintop winds over a broad area of the Rocky Mountains extending from south central Wyoming through northern New Mexico. The principal motivation for this experiment was to further investigate an unexpectedly strong and potentially important wind cycle observed at mountaintop in north central Colorado during August 1984. These winds frequently exhibited nocturnal maxima of 20 to 30 m · s−1 from southeasterly directions and often persisted for eight to ten hours. It appears that these winds originate as outflow from intense mesoscale convective systems that form daily over highland areas along the Continental Divide. However, details of the spatial extent and variability of these winds could not be determined from “routine” regional weather data that are mostly collected in valleys. Although synoptic conditions during much of the 1985 experiment period did not favor diurnally recurring convection over the study area, sufficient data were obtained to verify the regional-scale organization of strong convective outflow at mountaintop elevations. In addition, the usefulness and feasibility of a mountain-peak weather-data network for routine synoptic analysis is demonstrated.

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