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A Multiscale Numerical Study of Hurricane Andrew (1992). Part I: Explicit Simulation and Verification
, 1997
"... In this study, the inner-core structures of Hurricane Andrew (1992) are explicitly simulated using an improved version of the Penn. State/NCAR nonhydrostatic, two-way interactive, movable, triply-nested grid mesoscale model (MM5). A modified Betts-Miller cumulus parameterization scheme and an explic ..."
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Cited by 76 (8 self)
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In this study, the inner-core structures of Hurricane Andrew (1992) are explicitly simulated using an improved version of the Penn. State/NCAR nonhydrostatic, two-way interactive, movable, triply-nested grid mesoscale model (MM5). A modified Betts-Miller cumulus parameterization scheme and an explicit microphysics scheme were used simultaneously to simulate the evolution of the larger-scale flows over the coarser-mesh domains. The intense storm itself is explicitly resolved over the finest-mesh domain using a grid size of 6 km and an explicit microphysics package containing prognostic equations for cloud water, ice, rainwater, snow and graupel. The model is initialized with the National Centers for Environmental Prediction analysis enhanced by a modified moisture field. A model-generated tropical-storm-like vortex was also incorporated. A 72 h integration was made, which covers the stages for the storm's rapid deepening from tropical-storm intensity to a near-Category-5 hurricane intensity, and the stage for landfall over Florida. As verified
The structure and evolution of a continental winter cyclone. Part I: Frontal structure and the occlusion process
- Mon. Wea. Rev
, 1998
"... The production of a narrow, heavy, occasionally convective snowband that fell within a modest surface cyclone on 19 January 1995 is examined using gridded model output from a successful numerical simulation performed using the University of Wisconsin—Nonhydrostatic Modeling System. It is found that ..."
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Cited by 20 (5 self)
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The production of a narrow, heavy, occasionally convective snowband that fell within a modest surface cyclone on 19 January 1995 is examined using gridded model output from a successful numerical simulation performed using the University of Wisconsin—Nonhydrostatic Modeling System. It is found that the snowband was produced by a thermally direct vertical circulation forced by significant lower-tropospheric warm frontogenesis in the presence of across-front effective static stability differences as measured in terms of the equivalent potential vorticity (PVe). The sometimes convective nature of the snowband resulted from the development of freely convective motions forced by frontal lifting of the environmental stratification. Model trajectories demonstrate that a stream of warm, moist air ascended through the trowal portion of the warm-occluded structure that developed during the cyclone life cycle. The lifting of air in the trowal was, in this case, forced by lower-tropospheric frontogenesis occurring in the warm-frontal portion of the warm occlusion. This trowal airstream accounts for the production of the so-called wrap-around precipitation often associated with occluded cyclones and, in this case, accounted for the northern third of the heavy snowband. 1.
2000: Piecewise frontogenesis from a potential vorticity perspective: Methodology and a case study
"... Output from a numerical simulation by the University of Wisconsin Nonhydrostatic Modeling System is used to investigate the evolution of the surface frontal structure of an intense winter cyclone that occurred off the east coast of North America. Using the model data as input to the piecewise potent ..."
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Cited by 8 (4 self)
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Output from a numerical simulation by the University of Wisconsin Nonhydrostatic Modeling System is used to investigate the evolution of the surface frontal structure of an intense winter cyclone that occurred off the east coast of North America. Using the model data as input to the piecewise potential vorticity (PV) inversion method developed by Davis and Emanuel, the total surface frontogenesis is partitioned into contributions from discrete PV anomalies. These contributions are calculated using the nondivergent balanced winds associated with PV anomalies in the upper, interior, and surface layers as well as the balanced irrotational winds in what is termed piecewise frontogenesis. The cyclone of interest developed into a nearly stationary, well-occluded storm characterized by a cutoff PV anomaly at the tropopause and near-surface frontogenesis concentrated in the warm frontal zone. During the open wave stage of the cyclone life cycle, this frontogenesis was produced largely by the balanced flow, particularly that portion of it associated with the upper-level PV anomaly. Throughout the remainder of the cyclone life cycle, the upper-level contribution to the frontogenesis retained a distribution similar to that of the total frontogenesis. After the cyclone occluded, however, the frontogenesis forced by the unbalanced portion of the flow became increasingly significant despite the persistent smallness of the unbalanced winds. In fact, a substantial portion of the lower-tropospheric frontogenesis observed in the occluded quadrant, including that along a developing bent-back front, was eventually associated with the unbalanced flow. These results suggest a potentially significant role is played by unbalanced motions in the development and maintenance of lower-tropospheric frontal structure in midlatitude cyclones. 1.
2001: The effect of sea spray evaporation on tropical cyclone boundary layer structure and intensity
"... Strong winds in a tropical cyclone over the ocean can produce high seas with substantial amounts of spray in the lower part of the atmospheric boundary layer. The effects that the evaporation of this sea spray may have on the transfer of energy between the ocean and the atmosphere, and consequent ef ..."
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Cited by 8 (1 self)
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Strong winds in a tropical cyclone over the ocean can produce high seas with substantial amounts of spray in the lower part of the atmospheric boundary layer. The effects that the evaporation of this sea spray may have on the transfer of energy between the ocean and the atmosphere, and consequent effects on the boundary layer structure, cumulus convection, and the evolution of the tropical cyclone, are largely unknown. In this study, a high-resolution tropical cyclone model with explicit cloud microphysics, developed by Y. Wang, has been used to study these potential effects. The sea spray evaporation is incorporated into the model by two bulk parameterization schemes with quite different properties. The numerical results show that inclusion of the Fairall et al. sea spray parameterization increases the direct sensible heat flux from the ocean by about 70%, but has little effect on the direct latent heat flux. Sea spray itself causes a sensible heat flux of only about 6 % of the direct sensible heat flux, while it contributes a latent heat flux by evaporation of sea spray droplets by 60%–70 % of the direct latent heat flux. As a result, the total enthalpy flux with sea spray evaporation increases by about 20%, while the net contribution by sea spray is only about 1.5 % of the total enthalpy flux. Consistent with this, the intensity of the model tropical cyclone is moderately increased by 8 % in the maximum wind speed by the introduction of sea spray. The lower atmosphere
Quasigeostrophic Forcing of Ascent in the Occluded Sector of Cyclones and the Trowal
, 1997
"... A numerical model-based analysis of the quasigeostrophic forcing for ascent in the occluded quadrant of three cyclones is presented based upon a natural coordinate partitioning of the Q vector into its along- and across-isentrope components, Qs and Qn, respectively. The Qn component describes the ge ..."
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Cited by 7 (0 self)
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A numerical model-based analysis of the quasigeostrophic forcing for ascent in the occluded quadrant of three cyclones is presented based upon a natural coordinate partitioning of the Q vector into its along- and across-isentrope components, Qs and Qn, respectively. The Qn component describes the geostrophic contribution to the rate of change of the magnitude of =pu (traditional frontogenesis), whereas the Qs component describes the geostrophic contribution to the rate of change of direction of =pu (rotational frontogenesis). It is shown that convergence of Qs simultaneously creates the isobaric thermal ridge characteristic of the thermal structure of occluded cyclones and provides the predominant dynamical support for ascent within the occluded quadrant. The absence of significant Qn convergence there suggests that quasigeostrophic (Q-G) frontogenesis plays a subordinate role both in forcing vertical motions and in affecting three-dimensional structural changes in the occluded sector of post-mature phase midlatitude cyclones. A cyclonically ascending, cloud- and precipitation-producing airstream that originates in the warm-sector boundary layer and flows through the trowal portion of the occluded structure is supported by the upward vertical motions implied by the identified Q-G forcing. This airstream is referred to as the ‘‘trowal airstream’ ’ and it is shown to be responsible for the production of the ‘‘wrap around’ ’ cloud and precipitation commonly associated with occluded systems. The relationship of the trowal airstream to previously identified cloud and precipitation producing airflows in cyclones is discussed. 1.
A modeling study of an East Asian convective complex during March 2001
- J. Geophy. Res
, 2004
"... [1] During March-April 2001 the University of Wisconsin Nonhydrostatic Modeling System (UWNMS) was used to provide flight planning and estimation of ozone flux into the troposphere over East Asia in support of the Transport and Chemical Evolution over the Pacific (TRACE-P) mission. On 24 March a co ..."
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Cited by 5 (2 self)
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[1] During March-April 2001 the University of Wisconsin Nonhydrostatic Modeling System (UWNMS) was used to provide flight planning and estimation of ozone flux into the troposphere over East Asia in support of the Transport and Chemical Evolution over the Pacific (TRACE-P) mission. On 24 March a convective complex developed in eastern China and propagated eastward over the Pacific south of Japan. Aircraft and satellite observations, together with the UWNMS simulations, captured this convective event, which first entrained urban boundary layer air over Asia and then marine boundary layer air over the Pacific. The convective updraft split the subtropical westerly jet, deformed the tropopause upward, radiated gravity waves into the stratosphere, and induced a ring of stratospheric ozone to descend around its periphery into the middle troposphere. The DC-8 observations and UWNMS show a vault of moderate ozone ($65 ppbv) in the 8-12 km layer within the convection, with high stratospheric values ($100 ppbv) subsiding around the periphery into the troposphere near 6.5 km. A new two-scale method for diagnosing cross-tropopause ozone flux is compared with an annular volume estimate. During this 24 hour convective event, $0.8 Tg ozone entered the troposphere from the stratosphere, comparable in magnitude to ozone fluxes in midlatitude cyclones.
Nonorographic generation of Arctic polar stratospheric clouds during
- J. Geophys. Res.,
, 2003
"... [1] During December 1999, polar stratospheric clouds (PSCs) were observed in the absence of conditions conducive to generation by topographic gravity waves. The possibility is explored that PSCs can be generated by inertia gravity waves (IGW) radiating from breaking synoptic-scale Rossby waves on t ..."
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Cited by 4 (2 self)
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[1] During December 1999, polar stratospheric clouds (PSCs) were observed in the absence of conditions conducive to generation by topographic gravity waves. The possibility is explored that PSCs can be generated by inertia gravity waves (IGW) radiating from breaking synoptic-scale Rossby waves on the polar front jet. The aerosol features on 7 and 12 December are selected for comparison with theory and with simulations using the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). Consistent with Rossby adjustment theory, a common feature in the UWNMS simulations is radiation of IGW from the tropopause polar front jet, especially from sectors which are evolving rapidly in the Rossby wave breaking process. Packets of gravity wave energy radiate upward and poleward into the cold pool, while individual wave crests propagate poleward and downward, causing mesoscale variations in vertical motion and temperature. On 12 December the eastbound DC-8 lidar observations exhibited a fairly uniform field of six waves in aerosol enhancement in the 14-20 km layer, consistent with vertical displacement by a field of IGW propagating antiparallel to the flow, with characteristic horizontal and vertical wavelengths of $300 and $10 km. UWNMS simulations show emanation of a field of IGW upward and southwestward from a northward incursion of the polar front jet. The orientation and evolution of the aerosol features on 7 December are consistent with a single PSC induced by an IGW packet propagating from a breaking Rossby wave over western Russia toward the northeast into the coldest part of the base of the polar vortex, with characteristic period $9 hours, vertical wavelength $12 km, and horizontal wavelength $1000 km. Linear theory shows that for both of these cases, IGW energy propagates upward at $1 km/hour and horizontally at $100 km/hour, with characteristic trace speed $30 m/s. The spatial orientation of the PSC along IGW phase lines is contrasted with the nearly horizontal filamentary structures in the PSC, which are indicative of flow streamlines. It is suggested that vertical displacement is a crucial factor in determining whether a PSC will form and that most PSCs are relatable to specific synoptic and mesoscale motions.
2005: Dynamics of orographic rain associated with the passage of a tropical cyclone over a mesoscale mountain
- Terr. Atmos. Ocean
"... was used to simulate Supertyphoon Bilis (2000) in order to improve the prediction and the understanding of dynamics of orographic rainfall asso-ciated with the passage of typhoons over the Central Mountain Range (CMR) of Taiwan. The rainfall prediction is significantly improved by bogussing a vortex ..."
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Cited by 2 (1 self)
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was used to simulate Supertyphoon Bilis (2000) in order to improve the prediction and the understanding of dynamics of orographic rainfall asso-ciated with the passage of typhoons over the Central Mountain Range (CMR) of Taiwan. The rainfall prediction is significantly improved by bogussing a vortex, compared to a previous study (Lin et al. 2002). We identified sev-eral common ingredients present in this case which are responsible for pro-ducing heavy rainfall. The most important ingredients appear to be the presence of convective available potential energy (CAPE), a potentially unstable layer, a very moist airstream impinging on the CMR, and the pres-ence of a low level wind maximum associated with the outer circulation of the typhoon. A simple moisture flux model was also used to estimate rainfall, which compares well with observations. In addition, we also found that the orographic rainfall is dominated by moisture convergence and the contri-bution of moisture advection in the vicinity of the mountain is negligible.
Numerical Investigations of a Tornado Vortex Using Vorticity Confinement
, 2007
"... The numerical simulation of a realistically strong tornado vortex and its associated condensation funnel has proven to be very difficult to resolve in atmospheric modeling. Many have attributed this failure to insufficient resolution of the models being used. Others have conjectured that the problem ..."
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Cited by 1 (0 self)
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The numerical simulation of a realistically strong tornado vortex and its associated condensation funnel has proven to be very difficult to resolve in atmospheric modeling. Many have attributed this failure to insufficient resolution of the models being used. Others have conjectured that the problem lies in the fact that strong gradients are eroded by numerical diffusion, thus prohibiting the formation of strong vortices. This latter hypothesis led engineers Steinhoff and Underhill (1994) to conceive the Vorticity Confinement (VC) technique, in an effort to restore the vorticity gradients lost to diffusion. In this study, the University of Wisconsin Non-Hydrostatic Modeling System (UW-NMS) is used to investigate the aforementioned hypotheses on a three-dimensional extension of the Wicker and Wilhelmson (1995) tornado vortex. These idealized simulations are carried out with two-way interactive nested grids at horizontal resolutions of 24 m and 12 m. Simulations without the VC technique do produce tornado vortices at both resolutions, however they are too weak to form condensation funnels extending to the surface. Comparisons with simulations employing the VC technique show that a realistically strong tornado vortex is
CORRECTING FOR PRECIPITATION EFFECTS IN SATELLITE-BASED PASSIVE MICROWAVE TROPICAL CYCLONE INTENSITY ESTIMATES
, 2005
"... Public reporting burden for this collection of Information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments ..."
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Public reporting burden for this collection of Information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this
