The impact of upper-level flow regime change from spring to summer on QPF accuracy over the Midwest

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2008-01-01
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Loeffelbein, Mark
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Tsing-Chang Chen
William A. Gallus
Raymond Arritt
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Geological and Atmospheric Sciences

The Department of Geological and Atmospheric Sciences offers majors in three areas: Geology (traditional, environmental, or hydrogeology, for work as a surveyor or in mineral exploration), Meteorology (studies in global atmosphere, weather technology, and modeling for work as a meteorologist), and Earth Sciences (interdisciplinary mixture of geology, meteorology, and other natural sciences, with option of teacher-licensure).

History
The Department of Geology and Mining was founded in 1898. In 1902 its name changed to the Department of Geology. In 1965 its name changed to the Department of Earth Science. In 1977 its name changed to the Department of Earth Sciences. In 1989 its name changed to the Department of Geological and Atmospheric Sciences.

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1898-present

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  • Department of Geology and Mining (1898-1902)
  • Department of Geology (1902-1965)
  • Department of Earth Science (1965-1977)
  • Department of Earth Sciences (1977-1989)

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Geological and Atmospheric Sciences
Abstract

Quantitative precipitation forecasts (QPF) are potentially the most significant challenge of weather forecasting, and have been historically difficult for numerical weather prediction (NWP) models to produce. Given the importance of QPF to weather forecasts, there is a need to improve its accuracy. Understanding and recognizing patterns prone to produce errors in model QPF can help predictions made by weather forecasters.;The low level jet (LLJ) observed over the Great Plains is responsible for supporting warm-season convection by transporting heat and moisture into the Midwest. This study examines the two types of dominant mid and upper-level flow patterns during the warm-season months of May-September over the United States, and how the LLJ interacts with this flow. Near the onset of the North American Monsoon there is a flow regime change that causes the mid and upper-levels of the troposphere to transition from a more frequent trough pattern to an anticyclone over the Midwest. Each of the two different flow regimes exists with one of two different types of LLJs. The LLJ is divided into two types, A-type and C-type. C-type LLJs are characterized by the coupling of the jet with an upper-level trough and are more likely to occur before the onset of the monsoon. A-type LLJs show no coupling with the upper atmosphere and are more likely to occur after the onset of the monsoon. With an anticyclone present, it is not possible for a C-type low-level jet to form over the Midwest, only an A-type is possible. Distinguishing the two types of events and examining them independently led to evidence that NWP models more accurately produce QPF in C-type cases than in A-type cases. Improper simulation of the LLJ, and precipitation dissipation are examined for potential reasons for the inferior accuracy of the A-type cases.

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Tue Jan 01 00:00:00 UTC 2008