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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.
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.
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.
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.
Abstract
The influence of sensible heating from the earth's surface on the development of summertime vortices over the Tibetan Plateau was investigated using a numerical model. It was found that sensible heating could cause local intensification of vortices over high elevations and sometimes act in combination with topography to block intrusions of cold air. Sensible heating can play an important role, not indicated by its magnitude, when it is combined with topography and the proper synoptic situation. Sensible heating had a greater impact over higher elevations, areas with strong cold advection, and areas under the upper-tropospheric jet stream. Sensible heating tends to destabilize an air column, permitting downward transfer of westerly momentum in the vicinity of the jet stream and causing an increase in cyclonic vorticity in the lower troposphere north of the upper-level jet. During the premonsoon period, when the upper-level jet was located over the southern plateau, sensible heating acted to intensify plateau vortices. After the transition into the summer monsoon period, the jet was north of the plateau and sensible heating had only localized and gradual effects on plateau vortices.
Abstract
The influence of sensible heating from the earth's surface on the development of summertime vortices over the Tibetan Plateau was investigated using a numerical model. It was found that sensible heating could cause local intensification of vortices over high elevations and sometimes act in combination with topography to block intrusions of cold air. Sensible heating can play an important role, not indicated by its magnitude, when it is combined with topography and the proper synoptic situation. Sensible heating had a greater impact over higher elevations, areas with strong cold advection, and areas under the upper-tropospheric jet stream. Sensible heating tends to destabilize an air column, permitting downward transfer of westerly momentum in the vicinity of the jet stream and causing an increase in cyclonic vorticity in the lower troposphere north of the upper-level jet. During the premonsoon period, when the upper-level jet was located over the southern plateau, sensible heating acted to intensify plateau vortices. After the transition into the summer monsoon period, the jet was north of the plateau and sensible heating had only localized and gradual effects on plateau vortices.
