| NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
| Recipient: |
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| Initial Amendment Date: | April 25, 2014 |
| Latest Amendment Date: | June 10, 2016 |
| Award Number: | 1359614 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
edward bensman
AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
| Start Date: | August 15, 2014 |
| End Date: | July 31, 2017 (Estimated) |
| Total Intended Award Amount: | $391,092.00 |
| Total Awarded Amount to Date: | $391,092.00 |
| Funds Obligated to Date: |
FY 2015 = $64,819.00 FY 2016 = $70,969.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
21 N PARK ST STE 6301 MADISON WI US 53715-1218 (608)262-3822 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1225 West Dayton Street Madison WI US 53706-1612 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Physical & Dynamic Meteorology |
| Primary Program Source: |
01001516DB NSF RESEARCH & RELATED ACTIVIT 01001617DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
Observations from mobile and fixed sites of the Plains Elevated Convection at Night (PECAN) project will be used in conjunction with analytical and numerical modeling approaches to investigate the principal physical mechanisms affecting the formation, evolution, and structure of Nocturnal Low Level Jets (NLLJs) in relation to night-time convection. Data from the PECAN Integrated Sounding Arrays (PISA), each measuring kinematic and thermodynamic profiles with a suite of instruments (including radiosondes, lidars, radiometers, and radars) will be complemented by turbulence measurements conducted using coordinated scanning strategies with two mobile platforms. These integrated datasets will provide a novel, holistic picture of the spatial and temporal evolution of the NLLJ as it interacts with the developing nocturnal stable boundary layer (SBL) and mesoscale disturbances. The effects of terrain slope, thermal SBL structure, environmental stratification, and synoptic-scale forcing on the evolution of NLLJs over gently sloping terrain characteristic of the Great Plains will be investigated in detail, as well as the role of interactions between NLLJs and mesoscale atmospheric disturbances (gust fronts, gravity waves, bores, solitons) in the initiation and development of night-time convection.
Intellectual Merit :
The nocturnal low-level jet (NLLJ) is an atmospheric boundary-layer phenomenon that is commonly observed over the Great Plains of the United States and in many other locations worldwide. The NLLJ typically begins to develop around sunset under dry cloud-free conditions conducive to strong radiative cooling at the surface. It reaches peak intensity late in the night, and then decays with the onset of daytime convective mixing. Despite many theoretical, numerical, and observational analyses conducted to date, which make a strong case for the NLLJ arising from a force imbalance induced by the sudden release of the frictional constraint near sunset, many aspects of NLLJs structure and evolution are still not well understood. A claim perpetuated in the literature regarding a close association between the height of the NLLJ and the top of the SBL does not hold up to scrutiny: the depth of the SBL generally increases throughout the night while many observations indicate that wind maxima often descend, remain steady, or rise during the night. It is also not clear how the terrain slope angle influences the relationship between the SBL and NLLJ structures. A number of recent studies suggest that the nature of turbulence within the developing SBL as it interacts with an NLLJ should be further investigated. Open questions also remain concerning the impacts of wind-profile curvature associated with NLLJs on bore propagation, interactions of NLLJs with mesoscale disturbances, and the mechanisms by which NLLJ/bore interactions may lead to convective initiation. Our study aims at providing new knowledge about the interactions between the NLLJ, developing nocturnal SBL, propagating mesoscale disturbances, and convective initiation.
Broader Impacts :
NLLJs exert significant and wide-ranging impacts on regional weather and climate by providing dynamic and thermodynamic support for the development of deep convective storms and heavy precipitation events over the Great Plains. They are efficient conveyors of moisture and lower-tropospheric air pollutants, such as ozone and fine particulates, as well as agricultural pests including fungi, spores, and insects. NLLJs also have major impact on the wind-energy industry since the enhanced winds provide a dependable source of energy, but the associated wind shear and turbulence can damage wind-turbine rotors. The downward transport of NLLJ momentum in the morning by convective turbulent mixing may produce strong and gusty surface winds that can intensify wildfires and generate dust storms. The integrated analysis of high-resolution observations and numerical model output in the proposed project will allow improving of SBL parameterizations currently employed in atmospheric models and lead to better predictions of the NLLJ and its role in the initiation of nocturnal convection. The use of state-of-the-art observational systems and advanced numerical simulations techniques will provide a superb opportunity for student training. Both graduate and undergraduate students will play important roles during field operations, in model studies, in data processing, and in scientific analyses.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The Plains Elevated Convection At Night (PECAN) field experiment was conducted in the early summer of 2015. Based out of Hays, Kansas, this experiment product together a diverse group of researchers from across the country to investigate nighttime storms. These storms are particularly vexing for weather forecasters, as scientists have a more thorough understanding of the processes that impact daytime storms than they do of nighttime ones. Because of that, our weather models lack the ability to forecast the timing, location, and intensity of nighttime storms as well as they do daytime ones.
PECAN was the scientific community’s plan to address these issues. By observing nighttime storms in unprecedented detail, from the ground and air, inside and outside the storm, a much more comprehensive understanding of nocturnal storm processes could be developed. This required the assembly of a mobile observation network to go to storm producing environments and observe atmospheric evolution from clear sky to significant weather.
The instrument system at the heart of this particular part of the PECAN campaign, the Space Science and Engineering Center (SSEC) Portable Atmospheric Research Center (SPARC) is a unique tool well-suited to such an effort. SPARC is a 35’ long towable trailer that houses a suite of instruments capable of measuring wind, temperature, moisture, and clouds at many different levels above the surface. This ability to create observation profiles throughout the depth of the atmosphere sets SPARC apart from many other instrument systems which can only sense weather conditions right at the surface.
During PECAN, SPARC travelled over 9,000 miles across parts of six states to capture storms forming in their natural environment. The data collected by SPARC have been made freely available, and numerous research groups are taking advantage of these observations to further their understanding of a variety of weather phenomena.
Our research group focused on a previously under-studied phenomenon called the atmospheric bore. A bore is a wavelike structure in the atmosphere that forms ahead of storms in the stable air that is found at night. On some occasions bores cause new storms to form, and other times they prevent them from forming, and the reasons behind this haven’t been clear. Bores have only ever been studied as individual cases, which tends to bias the investigations to the biggest, most interesting events. In our research, we created a composite of all the bores observed during PECAN (over twenty cases) and found that bores increase surface pressure, cause rising motion, and sustained lifting of low level air. In general, it appears that bores increase the chance that a new storm will be formed as they pass by, but those storms will be less intense than if there weren’t a bore at all. The research done here will lead to new forecasting techniques that will help better identify which locations will experience new storm development in the overnight hours, resulting in more accurate forecasts that will reduce harm to lives, livestock, and crops in the central United States.
Last Modified: 08/30/2017
Modified by: Wayne F Feltz
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