Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part I: Observations

2008 ◽  
Vol 47 (7) ◽  
pp. 2023-2038 ◽  
Author(s):  
C. David Whiteman ◽  
Shiyuan Zhong
Keyword(s):  
Salt Lake ◽  
Temperature Inversion ◽  
Maximum Speed ◽  
Salt Lake Valley ◽  
Typical Situation ◽  
Thermally Driven ◽  
Downslope Flows ◽  
Downslope Flow ◽  
Deep Temperature ◽  
Using Data

Abstract Thermally driven downslope flows were investigated on a low-angle (1.6°) slope on the west side of the floor of Utah’s Salt Lake Valley below the Oquirrh Mountains using data from a line of four tethered balloons running down the topographic gradient and separated by about 1 km. The study focused on the evolution of the temperature and wind structure within and above the slope flow layer and its variation with downslope distance. In a typical situation, on clear, undisturbed October nights a 25-m-deep temperature deficit of 7°C and a 100–150-m-deep downslope flow with a jet maximum speed of 5–6 m s−1 at 10–15 m AGL developed over the slope during the first 2 h following sunset. The jet maximum speed and the downslope volume flux increased with downslope distance. The downslope flows weakened in the late evening as the stronger down-valley flows expanded to take up more of the valley atmosphere and as ambient stability increased in the lower valley with the buildup of a nocturnal temperature inversion. Downslope flows over this low-angle slope were deeper and stronger than has been reported previously by other investigators, who generally investigated steeper slopes and, in many cases, slopes on the sidewalls of isolated mountains where the downslope flows are not subject to the influence of nighttime buildup of ambient stability within valleys.

scholarly journals Temperature Inversion and Ultrafine Particulate/Near Ultrafine Particulate Matter Concentrations in the Salt Lake Valley

2021 ◽  
Vol 2 (7) ◽  
pp. 422-435
Author(s):  
Danielle Mecate ◽  
Rod Handy ◽  
Leon Pahler ◽  
Darrah Sleeth ◽  
Joemy Ramsay ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Health Outcomes ◽  
Salt Lake ◽  
Temperature Inversion ◽  
Linear Regression Models ◽  
Salt Lake Valley ◽  
Adverse Health Outcomes ◽  
The Mean ◽  
Ultrafine Particulate Matter ◽  
Negative Health Outcomes

Ultrafine particulate (UFP) matter exposures are associated with negative health outcomes. UFPs (<100nm) and near UFP (NUFP) matter (4.5nm - 250nm) are trapped by the bowl-like geography of the Salt Lake Valley causing winter inversions (i.e., trapped particulate matter (PM)). Enmont PUFP C100 and Grimm 1.109 particle counters were used to define NUFP concentrations during inversion (n=5) and non-inversion (n=5) days at 7 sites. NUFP concentrations served as a proxy for the UFP fraction. NUFP concentrations were log-transformed and multivariable mixed effects linear regression models determined if NUFP concentration differed between inversion and non-inversion or by length of inversion. Difference in fraction NUFP was also analyzed. The mean NUFP concentration was 1.49-fold higher during inversions (95% CI 1.11–2.02), whereas the fraction declined by 0.22 (95% CI -0.31– -0.13). Increased NUFP concentrations during inversions may lead to increased adverse health outcomes. These findings have serious implications for inversion-prone regions.

The influence of thermally driven circulation on PM10 concentration in the Salt Lake Valley

2003 ◽  
Vol 37 (3) ◽  
pp. 421-437 ◽  
Author(s):  
Olga A. Alexandrova ◽  
Don L. Boyer ◽  
James R. Anderson ◽  
Harindra J.S. Fernando
Keyword(s):  
Salt Lake ◽  
Pm10 Concentration ◽  
Salt Lake Valley ◽  
Thermally Driven

scholarly journals Pseudovertical Temperature Profiles in a Broad Valley from Lines of Temperature Sensors on Sidewalls

2014 ◽  
Vol 53 (11) ◽  
pp. 2430-2437 ◽  
Author(s):  
C. David Whiteman ◽  
Sebastian W. Hoch
Keyword(s):  
Salt Lake ◽  
Low Cost ◽  
Temperature Inversion ◽  
Temperature Sensors ◽  
Lapse Rate ◽  
Future Research ◽  
Temperature Structure ◽  
Salt Lake Valley ◽  
The North ◽  
Free Air

AbstractPseudovertical temperature “soundings” from lines of inexpensive temperature sensors on the sidewalls of Utah’s Salt Lake valley are compared with contemporaneous radiosonde soundings from the north, open end of the valley. Morning [0415 mountain standard time (MST)] soundings are colder, and afternoon (1615 MST) soundings are warmer than radiosonde soundings because of warm and cold boundary layers that form over the slopes. Cross-valley temperature differences occur between east- and west-facing sidewalls because of differing insolation. Differences in vertically averaged pseudovertical and radiosonde temperatures are generally within 1°C, with a standard deviation of 2°–3°C. The pseudovertical soundings are especially good proxies for radiosondes in winter. The sounding comparisons identified along-valley differences in temperature, inversion depth, and lapse rate that have led to hypotheses concerning their causes, to be evaluated with future research. The low cost and much better time resolution of the pseudovertical soundings suggest that such lines will be a useful supplement to valley radiosondes and will have significant operational advantages if available in real time. Lines of surface-based sensors will prove useful in identifying intravalley meteorological differences and may be used to estimate free-air temperature structure in other valleys where radiosondes are unavailable.

Atmospheric Rotors and Severe Turbulence in a Long Deep Valley

2016 ◽  
Vol 73 (4) ◽  
pp. 1481-1506 ◽  
Author(s):  
Lukas Strauss ◽  
Stefano Serafin ◽  
Vanda Grubišić
Keyword(s):  
Sierra Nevada ◽  
Flow Separation ◽  
Owens Valley ◽  
Mountain Waves ◽  
Side Pressure ◽  
Thermally Driven ◽  
Rotor Experiment ◽  
Downslope Flow ◽  
Using Data ◽  
Turbulence Generation

Abstract The conceptual model of an atmospheric rotor is reexamined in the context of a valley, using data from the Terrain-Induced Rotor Experiment (T-REX) conducted in 2006 in the southern Sierra Nevada and Owens Valley, California. All T-REX cases with strong mountain-wave activity have been investigated, and four of them (IOPs 1, 4, 6, and 13) are presented in detail. Their analysis reveals a rich variety of rotorlike turbulent flow structures that may form in the valley during periods of strong cross-mountain winds. Typical flow scenarios in the valley include elevated turbulence zones, downslope flow separation at a valley inversion, turbulent interaction of in-valley westerlies and along-valley flows, and highly transient mountain waves and rotors. The scenarios can be related to different stages of the passage of midlatitude frontal systems across the region. The observations from Owens Valley show that the elements of the classic rotor concept are modulated and, at times, almost completely offset by dynamically and thermally driven processes in the valley. Strong lee-side pressure perturbations induced by large-amplitude waves, commonly regarded as the prerequisite for flow separation, are found to be only one of the factors controlling rotor formation and severe turbulence generation in the valley. Buoyancy perturbations in the thermally layered valley atmosphere appear to play a role in many of the observed cases. Based on observational evidence from T-REX, extensions to the classic rotor concept, appropriate for a long deep valley, are proposed.

scholarly journals Orographic Influences on a Great Salt Lake–Effect Snowstorm

2013 ◽  
Vol 141 (7) ◽  
pp. 2432-2450 ◽  
Author(s):  
Trevor I. Alcott ◽  
W. James Steenburgh
Keyword(s):  
Snow Water Equivalent ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Salt Lake Valley ◽  
Wasatch Mountains ◽  
Lake Effect ◽  
Thermally Driven ◽  
Precipitation Band ◽  
Northern Utah ◽  
Snow Water

Abstract Although several mountain ranges surround the Great Salt Lake (GSL) of northern Utah, the extent to which orography modifies GSL-effect precipitation remains largely unknown. Here the authors use observational and numerical modeling approaches to examine the influence of orography on the GSL-effect snowstorm of 27 October 2010, which generated 6–10 mm of precipitation (snow-water equivalent) in the Salt Lake Valley and up to 30 cm of snow in the Wasatch Mountains. The authors find that the primary orographic influences on the event are 1) foehnlike flow over the upstream orography that warms and dries the incipient low-level air mass and reduces precipitation coverage and intensity; 2) orographically forced convergence that extends downstream from the upstream orography, is enhanced by blocking windward of the Promontory Mountains, and affects the structure and evolution of the lake-effect precipitation band; and 3) blocking by the Wasatch and Oquirrh Mountains, which funnels the flow into the Salt Lake Valley, reinforces the thermally driven convergence generated by the GSL, and strongly enhances precipitation. The latter represents a synergistic interaction between lake and downstream orographic processes that is crucial for precipitation development, with a dramatic decrease in precipitation intensity and coverage evident in simulations in which either the lake or the orography are removed. These results help elucidate the spectrum of lake–orographic processes that contribute to lake-effect events and may be broadly applicable to other regions where lake effect precipitation occurs in proximity to complex terrain.

scholarly journals Pannonian Basin Nocturnal Boundary Layer and Fog Formation: Role of Topography

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 712
Author(s):  
Joan Cuxart ◽  
Maja Telisman Prtenjak ◽  
Blazenka Matjacic
Keyword(s):  
Boundary Layer ◽  
Pannonian Basin ◽  
Temperature Inversion ◽  
Early Morning ◽  
Mountain Range ◽  
Mountain Ranges ◽  
Mesoscale Structures ◽  
Downslope Flows ◽  
Using Data ◽  
Ecmwf Model

Under high-pressure systems, the nocturnal atmospheric boundary layer in the Pannonian Basin is influenced by gravity flows generated at the mountain ranges and along the valleys, determining the variability of wind and temperature at a local scale and the presence of fog. The mechanisms at the mountain foothills are explored at Zagreb Airport using data from a sodar and high-resolution WRF-ARW numerical simulations, allowing identification of how the downslope flows from the nearby Medvednica mountain range condition the temperature inversion and the visibility at night and early morning. These flows may progress tens of kilometres away from the mountain ranges, merging with valley flows and converging in the central areas of the basin. The ECMWF model outputs allow us to explore the mesoscale structures generated in form of low-level jets, how they interact when they meet, and what is the effect of the synoptic pressure field over eastern Europe, to illustrate the formation of a basin-wide cold air pool and the generation of fog in winter.

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