WRF simulations of mesoscale convective systems at convection-allowing resolutions
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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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- College of Liberal Arts and Sciences (parent college)
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Abstract
Mesoscale convective systems (MCS) were studied using both idealized and real data
WRF simulations using grid spacings in the range from 0.5 km to 12 km with an emphasis on
3 km to determine the necessity of a convective parameterization scheme. The Kain-Fritsch
(KF) convective parameterization scheme was used as it is considered to give the best
forecasts of precipitation in mesoscale models.
The idealized simulations were used to conduct three sets of sensitivity tests. One set
tested the ability of the model to adequately resolve typical two-dimensional squall line
structure by varying the vertical grid resolution. It was determined that using 81 vertical grid
levels was sufficient to model squall lines. A second set tested the sensitivity of the partition
of precipitation into microphysics and convective scheme components to horizontal grid
spacing. A zone of grid spacing values from about 1 km to about 6 km was identified over
which the partition shifts from approximately 10% of precipitation from the KF scheme to
anywhere from 60% - 100%. This zone was found to be insensitive to microphysics scheme
and somewhat sensitive to initial conditions. The amount of precipitation produced per
activation of the deep convective part of the KF scheme was also found to shift significantly
across this range of horizontal grid spacing values. The third set tested the sensitivity of
precipitation forecasts to five treatments of the scheme. While two of the treatments
included the lack of a convective scheme and the unmodified KF scheme, the other three
treatments involved modifications to the scheme. These modifications included removing
the linear dependence of grid-resolvable vertical velocity on grid spacing, coarsening the
vertical motion, temperature, and water vapor mixing ratio fields before the KF scheme ran,
and coarsening the heat and moisture tendencies as well as convective scheme precipitation
after the KF scheme ran. When applied to a set of three-dimensional real data cases, it was
found that the use of no convective scheme and the unmodified KF scheme generally
performed the best. However, due to a small sample size, the spread of the data was large
and more tests are needed.
The conclusions from the sensitivity tests were that the KF scheme becomes less
active as grid spacing decreases below horizontal grid spacings of 6 - 8 km. Below 1 km
grid spacing, the KF scheme certainly should not be used. However, from 1 km to 3 km, it
likely is not necessary to use the KF scheme. Using it at 3 km does not hurt the forecast,
however. As other research has shown, there is some use for the KF scheme above 3 km.
Three-dimensional real data WRF simulations were conducted at 3 km horizontal
resolution for a set of 39 cases involving MCSs across the United States. The KF scheme
was not used. Convective initiation was found to err by approximately 150 km in the westsouthwesterly
direction with a nearly zero mean timing error. Large scatter was found
between the strength of large-scale forcing and the model skill at forecasting initiation, but
traditional skill measures (ETS and bias) showed that stronger-forced cases were better
forecast in the upscale evolution of the MCSs. Case studies were performed for a few cases
to illustrate the ways in which the WRF can succeed or fail to accurately predict convective
initiation.