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  • Author or Editor: ELMAR R. REITER x
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Elmar R. Reiter

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Elmar R. Reiter

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.

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Elmar R. Reiter and Abele Nania

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Cloud-photogrammetric studies conducted from the ground reveal the existence of wave perturbations near tropopause level, of a wavelength the same order of magnitude as is experienced in clear-air turbulence. A case study of the CAT occurrence on 13 April 1962 reveals the importance of the confluence mechanism of two jet streams, and the turning of wind with height in CAT generation.

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Elmar R. Reiter and Harry P. Foltz

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Recent aircraft measurements of clear air turbulence over Australia have shown that the phenomenon of CAT in a thermally stable environment is associated with a breakdown of waves, presumably gravity waves or Helmholtz waves on a stable interface, into random turbulent eddies. The energy distribution in the wavelength range in which clear air turbulence is experienced seems to follow the “−5/3 law” postulated by Kolmogorov's similarity hypothesis. The “−5/3 law” seems to extend to much longer wavelengths than previously anticipated.

Combining these results of aircraft measurements with the theory on lee waves which has been derived by the use of perturbation equations, one finds that the energy involved in standing lee waves over mountains may “cascade” down from a wavelength range of approximately 10 km to a range near 100 m which then would be experienced as clear air turbulence, provided that the energy levels are high enough to cause any responses in an aircraft.

This physical model of turbulence being “fed” by mountain waves has been used in developing a forecasting scheme of CAT over mountains. Results of a preliminary, but very encouraging, study are reported in this paper.

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James F. Bresch and Elmar R. Reiter

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Observations of extremely high fine particulate sulfur concentrations during early April 1983 in the western United States are linked to a strong cyclone over the midwestern United States. The strong winds around this cyclone circulated polluted midwestern air as far west as the Pacific Coast. A retrograding upper wave pattern was conducive for this polluted air to move southwestward. Both a long-range trajectory analysis and a subjective evaluation of synoptic conditions confirm this hypothesis.

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

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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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Eric A. Smith, Elmar R. Reiter, and Youxi Gao

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An investigation of the transition between spring and summer seasons of the surface energy budget in the Gobi desert is presented. The motivation behind this study is to determine eventually the degree to which changes in a desert system can be monitored over a short-term climate time scale (decadel) by remote means. A seasonal transition is used to evaluate the control factors involved in a variational process. The measurements incorporated in the analysis were obtained in 1984 from a specialized surface energy budget monitoring system deployed at a site in the western Gobi desert, just north of the northeastern edge of the Tibet Plateau in western Gansu province, P.R.C. The data were collected during the spring and summer periods in 1984 by a joint team of United States and Chinese scientists.

Results of the analysis reveal an interesting feature of the seasonal transition which had not been expected of a midlatitude desert. That is, although radiative forcing at the surface is altered between spring and summer through the diurnal net radiation heating function, the total radiative energy integral available for heating is largely unchanged. In some sense, the partitioning of the radiative heat supply at the surface can be viewed as a principal ingredient in defining the seasonal cycle. In terms of the Gobi desert, it may well be the only important ingredient.

Both similarities and differences in the spring and summer surface energy budgets arise from differences imparted to the system by an increase in the summertime atmospheric moisture content. Changes in the near-surface mixing ratio are shown to alter the effectiveness of the desert surface in absorbing radiative energy and redistributing it to the lower atmosphere through sensible and latent heat exchange.

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