Nocturnal Low-Level Jet in a Mountain Basin Complex. Part I: Evolution and Effects on Local Flows

2004 ◽  
Vol 43 (10) ◽  
pp. 1348-1365 ◽  
Author(s):  
Robert M. Banta ◽  
Lisa S. Darby ◽  
Jerome D. Fast ◽  
James O. Pinto ◽  
C. David Whiteman ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Vertical Motion ◽  
Cold Pool ◽  
Lake Basin ◽  
The South ◽  
Low Level ◽  
Low Level Jet ◽  
Convergence Zones

Abstract A Doppler lidar deployed to the center of the Great Salt Lake (GSL) basin during the Vertical Transport and Mixing (VTMX) field campaign in October 2000 found a diurnal cycle of the along-basin winds with northerly up-basin flow during the day and a southerly down-basin low-level jet at night. The emphasis of VTMX was on stable atmospheric processes in the cold-air pool that formed in the basin at night. During the night the jet was fully formed as it entered the GSL basin from the south. Thus, it was a feature of the complex string of basins draining toward the Great Salt Lake, which included at least the Utah Lake basin to the south. The timing of the evening reversal to down-basin flow was sensitive to the larger-scale north–south pressure gradient imposed on the basin complex. On nights when the pressure gradient was not too strong, local drainage flow (slope flows and canyon outflow) was well developed along the Wasatch Range to the east and coexisted with the basin jet. The coexistence of these two types of flow generated localized regions of convergence and divergence, in which regions of vertical motion and transport were focused. Mesoscale numerical simulations captured these features and indicated that updrafts on the order of 5 cm s−1 could persist in these localized convergence zones, contributing to vertical displacement of air masses within the basin cold pool.

Estimation of selenium loads entering the south arm of Great Salt Lake, Utah, from May 2006 through March 2008

2009 ◽  
Author(s):  
David L. Naftz ◽  
William P. Johnson ◽  
Michael L. Freeman ◽  
Kimberly Beisner ◽  
Ximena Diaz ◽  
...  
Keyword(s):  
Salt Lake ◽  
Great Salt Lake ◽  
The South

scholarly journals Nocturnal Low-Level Jet in a Mountain Basin Complex. Part II: Transport and Diffusion of Tracer under Stable Conditions

2006 ◽  
Vol 45 (5) ◽  
pp. 740-753 ◽  
Author(s):  
Lisa S. Darby ◽  
K. Jerry Allwine ◽  
Robert M. Banta
Keyword(s):  
Surface Pressure ◽  
Salt Lake ◽  
Low Level ◽  
Stable Conditions ◽  
Basin Scale ◽  
Flow Features ◽  
Transport And Diffusion ◽  
Low Level Jet ◽  
The City ◽  
And Diffusion

Abstract Differences in nighttime transport and diffusion of sulfur hexafluoride (SF6) tracer in an urban complex-terrain setting (Salt Lake City, Utah) are investigated using surface and Doppler lidar wind data and large-scale surface pressure differences. Interacting scales of motion, as studied through the URBAN 2000 field program combined with the Vertical Transport and Mixing (VTMX) experiment, explained the differences in the tracer behavior during three separate intensive operating periods. With an emphasis on nighttime stable boundary layer conditions, these field programs were designed to study flow features responsible for the nighttime transport of airborne substances. This transport has implications for air quality, homeland security, and emergency response if the airborne substances are hazardous. The important flow features investigated included thermally forced canyon and slope flows and a low-level jet (LLJ) that dominated the basin-scale winds when the surface pressure gradient was weak. The presence of thermally forced flows contributed to the complexity and hindered the predictability of the tracer motion within and beyond the city. When organized thermally forced flows were present, the tracer tended to stay closer to the city for longer periods of time, even though a strong basin-scale LLJ did develop. When thermally forced flows were short lived or absent, the basin-scale low-level jet dominated the wind field and enhanced the transport of tracer material out of the city.

scholarly journals Impact of enriched analyses on regional numerical forecasts over southeastern South America during SALLJEX

2014 ◽  
Vol 29 (3) ◽  
pp. 315-330
Author(s):  
Yanina García Skabar ◽  
Matilde Nicolini
Keyword(s):  
Data Assimilation ◽  
South America ◽  
Atmospheric Modeling ◽  
South American ◽  
The South ◽  
Low Level ◽  
Positive Effects ◽  
Accumulated Rainfall ◽  
Low Level Jet ◽  
The Impact

During the warm season 2002-2003, the South American Low-Level Jet Experiment (SALLJEX) was carried out in southeastern South America. Taking advantage of the unique database collected in the region, a set of analyses is generated for the SALLJEX period assimilating all available data. The spatial and temporal resolution of this new set of analyses is higher than that of analyses available up to present for southeastern South America. The aim of this paper is to determine the impact of assimilating data into initial fields on mesoscale forecasts in the region, using the Brazilian Regional Atmospheric Modeling System (BRAMS) with particular emphasis on the South American Low-Level Jet (SALLJ) structure and on rainfall forecasts. For most variables, using analyses with data assimilated as initial fields has positive effects on short term forecast. Such effect is greater in wind variables, but not significant in forecasts longer than 24 hours. In particular, data assimilation does not improve forecasts of 24-hour accumulated rainfall, but it has slight positive effects on accumulated rainfall between 6 and 12 forecast hours. As the main focus is on the representation of the SALLJ, the effect of data assimilation in its forecast was explored. Results show that SALLJ is fairly predictable however assimilating additional observation data has small impact on the forecast of SALLJ timing and intensity. The strength of the SALLJ is underestimated independently of data assimilation. However, Root mean square error (RMSE) and BIAS values reveal the positive effect of data assimilation up to 18-hours forecasts with a greater impact near higher topography.

The South American Low-Level Jet: A New Climatology, Variability, and Changes

2019 ◽  
Vol 124 (3) ◽  
pp. 1200-1218 ◽  
Author(s):  
Tessa L. Montini ◽  
Charles Jones ◽  
Leila M. V. Carvalho
Keyword(s):  
South American ◽  
The South ◽  
Low Level ◽  
Low Level Jet

Climate and Diet in Fremont Prehistory: Economic Variability and Abandonment of Maize Agriculture in the Great Salt Lake Basin

2002 ◽  
Vol 67 (3) ◽  
pp. 453-485 ◽  
Author(s):  
Joan Brenner Coltrain ◽  
Steven W. Leavitt
Keyword(s):  
Stable Isotope ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Temporal Correlation ◽  
Bone Collagen ◽  
Initial Increase ◽  
Lake Basin ◽  
Maize Agriculture ◽  
Economic Diversity ◽  
Economic Strategies

Research reported here is based on the stable isotope (δ 13C,δ 15N) and radiocarbon chemistry of Fremont burials from wetlands lining the eastern shores of the Great Salt Lake (GSL). Bone collagen stable isotope signatures covary with reliance on maize and intake of animal protein, facilitating useful reconstructions of past diet. Among the GSL Fremont, economic strategies vary over time with an initial increase in reliance on maize (A.D. 400–850) followed by a period of marked economic diversity (A.D 850–1150) then a return to reliance on wild foods (after A.D. 1150). During the period of greatest economic diversity, male and female diets vary significantly and male diets are correlated with status differences evidenced by grave goods. There is also a clear temporal correlation between the rapid abandonment of maize agriculture and significant moisture anomalies in regional tree-ring chronologies and pollen profiles. These results are discussed in the context of recent arguments regarding economic diversity, social complexity, and the demise of the Fremont.

scholarly journals Climatology of Warm Rain and Associated Latent Heating Derived from TRMM PR Observations

2009 ◽  
Vol 22 (18) ◽  
pp. 4908-4929 ◽  
Author(s):  
Yasu-Masa Kodama ◽  
Masaki Katsumata ◽  
Shuichi Mori ◽  
Sinsuke Satoh ◽  
Yuki Hirose ◽  
...  
Keyword(s):  
Lower Latitude ◽  
Convergence Zone ◽  
Small Contribution ◽  
Latent Heating ◽  
The South ◽  
Low Level ◽  
Warm Rain ◽  
Convergence Zones ◽  
Subtropical Oceans ◽  
The Tropics

Abstract The large-scale distribution of precipitation and latent heating (LH) profiles in the tropics, subtropics, and part of the midlatitudes was studied using a 9-yr dataset derived from Tropical Rainfall Measuring Mission precipitation radar observations, with emphasis on the contribution of warm rain. The distribution of warm rain showed features unique from those of rain in other categories and those of outgoing longwave radiation. Warm rain was weak over land but widely distributed over oceans, especially along the intertropical convergence zone (ITCZ) and the western part of the subtropical oceans. The observed amount of warm rain depended on the rainfall intensity rather than on the frequency of warm rain events. The amount of warm rain over ocean was positively correlated with sea surface temperature (SST); this dependency was found in the tropics, subtropics, and part of the midlatitudes, whereas dependency of SST on total rain was confined to the tropics. Both total rain and warm rain were concentrated in the ITCZ, which elongated along the local SST maximum. Small amounts of warm rain were found along subtropical convergence zones (the baiu frontal zone and subtropical portions of the South Pacific convergence zone and the South Atlantic convergence zone) with ample total rainfall. However, larger amounts of warm rain were observed at the lower-latitude sides of these zones in the upstream portions of low-level moisture flow toward the zones. Warm rain may cultivate the subtropical convergence zones by deepening the moist boundary layer and increasing moisture flux toward the zones. The statistical relationship between warm rain and low-level cloudiness showed that the warm rain amount was large when low-level cloudiness was 20%–30% and small when low-level cloudiness was greater than 40%. This indicates that intense warm rain is provided by convective clouds, not by stratiform clouds, in conditions of substantial cloudiness. Despite the small contribution to total rain, warm rain maintained positive LH values over most of the tropical and subtropical oceans. The LH by warm rain masked low-level cooling observed in stratiform rain and maintained positive LH in the lower atmosphere below the melting layer. Because warm rain was confined to oceans, a strong LH contrast was maintained along the coast; this contrast reached values of 1–2 K day−1 in certain places and may affect local and monsoonal circulation across continental coasts.

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