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FY 1998 ASR MMM Significant Accomplishments
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Major Research Programs
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Prediction of Precipitating Weather System
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 The Catalina eddy is a cyclonic circulation
that occasionally occurs in the southern California bight region and causes significant
alteration of the local weather conditions in the Los Angeles Basin. In an extension of
their recent research on coastally trapped disturbances (CTDs), William Skamarock, Richard
Rotunno, and Joseph Klemp successfully simulated idealized Catalina Eddy events and
demonstrated that the dynamics producing this circulation are essentially the same as
those generating CTDs that propagate northward along the coast. For flow over terrain
along a curving coastline, the distinguishing influence appears to be that CTD events are
favored when the synoptic scale offshore flow is more easterly (offshore), whereas the
Catalina Eddy forms when the flow is northerly onto the bight. (Click the image on
the left to view a caption and larger figure.) |
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Christopher Davis (joint appointment with RAP)
and Mark Stoelinga (University of Washington) submitted two papers examining the effect of
mountains on synoptic-scale baroclinic waves. The key aspect of the work was the
development of a mathematical framework (a perturbation expansion) which allows one to
interpret the wave-mountain interaction evinced in a simple quasi-geostrophic model in a
physically intuitive way that can easily be linked to observations. (Click the image
on the left to view a caption and larger figure.) |
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John Michalakes (visitor, Argonne National Laboratory), Jimy Dudhia, and
Daniel Hansen (joint appointment with RAP) added the MPP option to the MM5 Version-2
beginning with release-8. This adds scalable distributed memory computers, networks of
workstations and PCs, and distributed memory clusters of multi-processor machines to the
list of available platforms, which now covers all high-performance computers in use today.
Increased memory and performance from scalable parallel machines will support higher
resolution studies over larger domains and will be crucial to meeting the computational
requirements of variational data assimilation. (Click the image on the right to view
a caption and a larger figure.) |
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Joseph Klemp, William Skamarock, and Jimy Dudhia of the MMM Division
continued to work on the development of the Weather Research and Forecast (WRF) joint
research and operational model with colleagues from NCEP, NOAA/FSL, CAPS, and university
scientists. Development includes a thorough analysis of treatment of the lower boundary in
the vicinity of mountains (e.g., a stepped approach verses a terrain following
formulation), minimization of pressure gradient force errors near steep mountains,
exploration of various approaches to using only conservative quantities as prognostic
variables, and examination of the advantages of a hybrid vertical coordinate where the
information surfaces become isentropic surfaces away from the ground. In addition, a
prototype framework is being developed that will allow easy portability of model code to a
wide range of computing platforms including distributed shared memory machines as well as
workstations and vector machines. Early prototypes of the WRF model will be available in
calendar year 1999. (Click the image on the left to view a caption and a larger figure.) |
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Superposition of sources of VHF radiation from lightning channels with the
derived Doppler radar vertical air motion field for an active five-minute period of the 10
July 1997 STERAO/Deep Convection storm shows that most of the lightning occurred in
moderate updrafts. James Dye (joint appointment with ATD) and colleagues determined the
regions of downdraft were almost devoid of lightning sources with noticeably fewer sources
in the updraft cores of >10 m/sec than in less intense updrafts. |
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Mesoscale and Microscale Processes and Impacts
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Large-eddy simulations (LESs) by Chin-Hoh Moeng, Peter Sullivan, and Bjorn
Stevens (ASP) of the stratocumulus-topped planetary boundary layer (PBL) showed that the
infrared radiative cooling occurring above the average PBL top defined by the minimum in
turbulence heat flux is a major term in the heat budget of the entrainment zone, and hence
plays an important role in determining the PBL entrainment rate. (Click small image
below to view caption and larger figure.) |
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| Results from large-eddy simulations by Peter
Sullivan and colleagues showed that for a clear convective PBL, the finite thickness of
the inversion layer needs to be considered in entrainment rate parameterizations derived
from jump conditions. The usual assumption is that the entrainment rate can be estimated
solely on the basis of the jump in potential temperature. The deficiency of this
assumption is illustrated in the figure, where they compare the measured entrainment rate
with parameterizations based on the jump in potential temperature and one that includes
the finite thickness of the inversion. (Click image to the right to view caption and
larger figure.) |
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Wojciech Grabowski and Piotr Smolarkiewicz
developed a method (called cloud-resolving convection parameterization) to explicitly
represent the effects of convection at large scales. Rather than using a parameterization
scheme with its attendant uncertainty, convection is directly simulated. This approach
allows explicit interaction between convection and the environment and provides a new way
to quantify the role of convective cloud systems in the large-scale tropical circulation
(Click images to the left and below to view captions and larger figures). 
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Xiaoqing Wu and Mitchell Moncrieff showed the
surface energy budget of their cloud-resolving simulations of a month-long period in TOGA
COARE is within the observational measurement uncertainty of 10 W/m2 (Click on image on
the left to view a caption and a larger figure). The accompanying surface fields
provide realistic forcing for upper-ocean models at scales down to about a kilometer
(Click image below to view a caption and larger figure). This approach will help quantify
the physical role of clouds in coupled atmosphere-ocean general circulation models. 
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Smaller Research Programs
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Ice Microphysics Research
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| Work conducted by Andrew Heymsfield, Larry
Miloshevich, and Steven Aulenbach on vertical profiles of ice particle types and size
distributions in cirrus coupled with calculations showed that particles in the size range
50 to 300 microns contribute most to total cloud optical depth. (Click image to the
right to view a caption and larger figure.) |
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Wildfire Research
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Terry Clark, Larry Radke (ATD), and Janice
Coen successfully applied image flow analysis to estimate winds and heat flux profiles for
a NWT crown fire they observed using an IR camera. Their results indicate that IR imagery
can help quantify important aspects of the fluid dynamics associated with wildfires.
(Click image at left to view caption and larger figure.) |
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Geophysical Turbulence Research
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Terry Clark, William Hall, and Robert Kerr (joint appointment with CGD and
HAO), along with colleagues from NOAA, were able to identify a new source of clear air
turbulence (CAT) associated with the jet-stream perturbing the shear layer near the
tropopause. The jet-stream forcing and associated wave-dynamics resulted in the production
of Horizontal Vortex Tubes that may have contributed to the aircraft incident in December
of 1992 over Evergreen, Colorado. (Click image at left to view caption and larger
figure.) |
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Chemistry, Aerosols, and Dynamics Interactions Research
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Studies of chemistry occurring within clouds, and of convective transport,
have historically relied on simplified convective models in 1 or 2 spatial dimensions.
William Skamarock and Mary Barth (joint appointment with ACD) constructed a 3-D convection
model that simulates the chemical transport and reactions along with the dynamics.
Skamarock, James Dye (joint appointment with ATD), and Thomas Matejka (NSSL) are using the
model to determine NOx production by lightning within the STERAO program. They also
examined the general properties of convective transport and gaseous, aqueous and ice phase
chemistry within convective cloud systems, and identified important dependencies on the
dynamical cloud structure. (Click image at left to view caption and larger figure.) |
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