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.

The atmospheric program on the Arctic Ocean Expedition of July through September 1996 (AOE‐96) was focused on aerosol climate feedback. The expedition took place close to the saddle point between a semipersistent anticyclonic ridge from near Scandinavia to the Arctic coast of eastern Siberia and a trough from the Canadian archipelago across the pole to north central Siberia. The weather varied from anticyclonic clear‐sky conditions to cyclonic cloudy conditions, and 13 identifiable migratory features (frontal bands, wave disturbances) clearly influenced local weather, clouds, atmospheric transport, and chemistry. This includes an explosive polar cyclone, born at the lateral heat gradient between Greenland and the pack ice rather than between open sea and the pack ice. The synoptic scale weather systems caused the strongest variability in trace gases (O3 in particular) and aerosols, and also strong variability in the cloud cover. The formation of air masses over the pack ice primarily depends on if there is cyclonic (convergent) or anticyclonic (divergent) flow. Cyclonic flow resulted in a modified marine air mass loaded with vapor, but with low aerosol number concentrations owing to frequent clouds and fogs and efficient cloud scavenging of the aerosol. Anticyclonic flow resulted in almost continental air masses with clear sky, long residence time over the pack ice and subsidence slowly replacing the boundary layer with free tropospheric air, low vapor concentrations, but large aerosol number in lack of efficient cloud scavenging. The synoptic variability and advection from south of the ice edge were weaker than during the predecessor International Arctic Ocean Expedition in 1991 (IAOE‐91), when on average the sampled air spent 55 hours over the pack ice compared to more than 120 hours during AOE‐96, owing to exceptionally high cyclone activity in 1991. This caused a large difference in atmospheric transport, chemistry, and aerosols between the two expeditions.

Thermally driven local circulation in valleys has been studied for many years with the result that the underlying physics are reasonably well understood. ASCOT experiments of the early 1980s were formulated to help quantify predictive models and to apply the resulting methods to transport and dispersion of airborne materials. During the performance and analysis of experiments in two quite different valleys, it became clear that important aspects of the structure of the valley circulation depend on subtle differences in the ambient atmospheric conditions. In this paper we interpret nocturnal drainage structure in terms of ambient characteristics. We are able to describe changes in the depth of drainage and volume flux in terms of the influence of external wind and radiative effects on the collection of cool air in a valley airshed, and on erosion of an established drainage by turbulent entrainment. We describe evidence for internal buoyancy waves and rotors that can have a major effect on transport and dispersion in the nocturnal cool-air drainage regime. Under ideal conditions of radiative cooling and light ambient winds the drainage depth fills the valley to the ridge level. The radiative driving factor is strongly suppressed by low cloud ceilings and this is reflected in drainage depths shallower than 25% of the valley depth. Further erosion of cold air drainage by turbulent entrainment of ambient air under conditions of moderate to strong ridge top winds results in a linear regression of the form:where v is the ridge top wind in m s−1. With these dependencies on clouds and wind it is not surprising that the "Climatology" of valley drainage winds favors the seasons of weak synoptic activity and low thunderstorm frequency. The transition layer that bounds the top of the drainage is variable in time and space and depends on the thermal stability and wind speed and direction at ridge level. Standing internal waves, predicted a Froude number criterion, may govern the encroachment of ambient air into the local valley regime. Brush Crek Canyon is a narrow, steep-waled valley that may frequently exhibit a shear-induced helix imposed upon the down-valley drainage. This circulation is supported by meteorological and tracer data and can significantly influence pollution distributions.

Hourly tethered-balloon wind soundings from the 650-m deep, narrow, Brush Creek Valley of Colorado are analyzed to determine the nocturnal atmospheric mass (or volume) budget of the valley. Under the assumption that the volume flux on an entire valley cross section can be approximated from balloon soundings over the valley center, volume fluxes are calculated from tethered balloon profiles taken on 30–31 July 1982 at several points along the valley's longitudinal axis in a 7-km long segment of the valley. Down-valley volume fluxes increased in the 3 h following sunset to levels that were basically maintained through the night. Down-valley volume fluxes increased with distance down the valley axis from 0.9 million m3 s−1 at the upper end of the segment to 2.8 million m3 s−1 at the lower end, producing an average volume flux divergence of 271 m2 s−1. If we assume that the volume flux divergence is supported entirely by subsidence of air into the valley, a peak sinking rate of 0.10 m s−1 is obtained at the level of the valley's rim. Mean vertical velocity profiles through the valley's depth are calculated, and an error analysis is performed.

A long-range application of a heavy methane atmospheric tracer system has been carried out using both 12CD4 and 13CD4. The experiment had several objectives including testing a newly developed cyrogenic air sampler, testing a new sample handling apparatus and demonstrating the use of heavy methanes over transport distances up to 2500 km and travel times of more than 100 h.

A local snowstorm in Los Alamos in April of 1975 is described. The meteorological conditions responsible for the storm are discussed.

Several aspects of canopy flow are investigated. The problem of steady flow in a horizontally infinite canopy under neutral thermal stratification is treated theoretically. The resulting analytical model is then used as a boundary condition for a nonlinear numerical model designed to study transition regions near the leading and trailing edges of a canopy. This model shows a wave effect downstream from a leading edge observed in the field and laboratory. A tendency for a splitting of the flow near a windward canopy edge is also brought out.

TIROS cloud photographs and fine-scale quasi-geostrophic calculations of vertical motion are used in an attempt to gain understanding of the evolution of vertices and other aspects of large-scale cloud masses and to explore the usefulness of the pictures in diagnosis of the vertical motions. Horizontal and vertical motions are found to be of roughly equal importance in the evolution of cloud patterns, except in the early phases of the storm, when the latter predominate. This circumstance complicates the diagnostic application of the pictures, but the evolution of cloud patterns is nicely accounted for. Cloud vortices occur in a variety of large-scale motion environments and seem to depend on fine-scale variations of motion and moisture structure which escape detection in conventional sounding networks. Quasi-geostrophic theory is found to yield at least qualitatively realistic vertical motions even in application to systems of smaller scale than can be justified a priori.