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Orographic precipitation (meteorology)
AccessScience, Jul 10, 2015
Mountains may induce precipitation through orographic lifting, sensible heating, instability rele... more Mountains may induce precipitation through orographic lifting, sensible heating, instability release…
Bulletin of the American Physical Society, Nov 1, 2008
Submitted for the SES08 Meeting of The American Physical Society Effects of Southern Appalachian ... more Submitted for the SES08 Meeting of The American Physical Society Effects of Southern Appalachian Mountains on the Rainfall Associated with the Passage of Hurricane Iavn (2004) ALAN COVELL, YUH-LANG LIN, N. C. A&T State University -Effects of Appalachian Mountains on Hurricane Ivan ( ) are investigated using the Weather Research and Forecast (WRF) model. A single domain with 12 km resolution is used to simulate the storm from 0000UTC 16 to 1200UTC 18 September with a time interval of 3 h. The Appalachian Mountains have a much more profound effect at 1000mb than at 300mb, as revealed in vorticity fields. The simulated fields compare well with satellite imagery, however, the simulated track is slightly west of the actual track. The simulated rainfall indicates that most of the precipitation appears to be focused over the Appalachian mountains and far western N.C., as shown in the observed data, which is also known as rain-shadow phenomenon. The storm weakens as it passes over and around the mountains. The Appalachian mountains appear to have a focusing effect on getting the precipitation concentrated around the mountains. The mountains also seem to influence the path of the storm, causing it to move farther westward as it heads north.
Effects of thermal forcing in atmospheric shear flows with critical level
De Gruyter eBooks, Dec 31, 1996
... Figure 3. The vertical momentum flux for the flow field of Figure 2.(From Lin,[20 ... 109 (19... more ... Figure 3. The vertical momentum flux for the flow field of Figure 2.(From Lin,[20 ... 109 (1981), 194-199 [3] Anderson, CE, Dramatic development of thunderstorm circulation associated with the Wichita ... 47 (1990), 1755-1777 [24] Lin, Y.-L., Chun, H.-Y., Effects on diabatic cooling in a ...
31st Conference on Hurricanes and Tropical Meteorology, Apr 1, 2014
The tracks of all 42 tropical cyclones (TCs) passing over the Southern-Central Appalachians from ... more The tracks of all 42 tropical cyclones (TCs) passing over the Southern-Central Appalachians from the east or the west during 1850-2011 are found continuous. By estimating the basic-flow and vortex Froude numbers, and the basic-flow and vortex Rossby numbers (U/Nh, V max /Nh, U/fL x , and V max /fR, where U is the basic-flow speed, V max the maximum tangential wind speed, N the buoyancy frequency, f the Coriolis parameter, R the radius of cyclone center to V max , and L x the mountain width), from the hurricane reanalysis data, the lack of track discontinuity is explained by weaker blocking associated with lower mountains. The track discontinuity is found to be mainly controlled by V max /Nh and V max /fR (greater than 1.5 and 4.0, respectively), and less sensitive to U/Nh and U/fL x , consistent with a previous study. It is hypothesized that stronger blocking associated with weaker near-surface tangential winds of extratropical cyclones tends to make their tracks across the Appalachians discontinuous. This hypothesis is verified by investigating 13 heavy snowstorms with discontinuous tracks during 1950-2003. The present results show that all V max /Nh fall below 1.5 and all V max /fR fall below 4.0. To help understand the dynamics associated with orographic blocking, the 2-5 February 1995 Snowstorm is simulated by a numerical model. The simulated results indicate that the upstream V max /Nh and V max /fR are indeed less than 1.5 and 4.0, respectively. Therefore, it is concluded that track discontinuity of a cyclone passing over a mesoscale mountain is mainly controlled by strong orographic blocking as measured by lower vortex Froude number (V max /Nh) and/or lower vortex Rossby number (V max /fR).
Large Eddy Simulation of Aircraft Wake Vortices: Atmospheric Turbulence Effects
ABSTRACT Ambient atmospheric turbulence effects on aircraft wake vortices are studied using a val... more ABSTRACT Ambient atmospheric turbulence effects on aircraft wake vortices are studied using a validated large eddy simulation model. Our results confirm that the most amplified wavelength of the Crow instability and the lifetime of wake vortices are significantly influenced by ambient turbulence (Crow, S. C., "Stability Theory for a Pair of Trailing Vortices,'' AlAA Journal, Vol. 8, No. 12, 1970, pp. 2172-2179). The Crow instability becomes well developed in most atmospheric turbulence levels, but in strong turbulence the vortex pair deforms more irregularly due to turbulence advection. The most amplified wavelength of the instability decreases with increasing dimensionless turbulence intensity eta, although it increases with increasing turbulence integral length scale. The vortex lifespan is controlled primarily by eta and decreases with increasing eta, whereas the effect of integral scale of turbulence on vortex lifespan is of minor importance. The lifespan is estimated to be about 40% larger than Crow and Bate's predicted value (Crow, S. C., and Bate, E. R,, "Lifespan of Trailing Vortices on a Turbulent Atmosphere," Journal of Aircraft, Vol. 13, No. 7, 1976, pp. 476-482) but in agreement with Sarpkaya's recent modification (Sarpkaya, T., "Decay of Wake Vortices of Large Aircraft,'' AlAA Journal, Vol. 36, No. 9, 1998, pp. 1671-1679) to Crow and Bate's theory. This larger lifespan is also supported by data from water tank experiments and direct numerical simulations. There appears to be a possibility that the scatter in vortex lifespans due to ambient turbulence alone decreases with increasing Reynolds number, whereas larger scatter of lifespans in Right tests may result from other factors such as stratification, wind shear, and inhomogeneous ambient turbulence.
Kelvin waves in a simple air-sea coupled model in the tropics
In the local thermal equilibrium case, (here are no unstable coupled disturbances in the tropical... more In the local thermal equilibrium case, (here are no unstable coupled disturbances in the tropical ccu-pled system which only contains the atmospheric Kelvin wave and oceanic Kelvin wave
The interactions between an Appalachian coldair damming event and the near passage of Tropical St... more The interactions between an Appalachian coldair damming event and the near passage of Tropical Storm along the coastal Carolinas are assessed by using a numerical weather prediction model. As the storm moved along the coastline, it began extra-tropical transition, bringing heavy rains to both the coastal region and inland towards the Piedmont of North Carolina. Our goal is to quantify the effects of both interacting weather systems on heavy precipitation to improve the dynamical understanding of such effects, as well as precipitation forecasts in the study region. A series of sensitivity tests were performed to isolate and quantify the effects of both systems on the total accumulated precipitation. It was found that (a) for this type of along-coast track, the pre-existing coldair damming played only a minor role on the total accumulated precipitation, (b) the outer circulation of Kyle weakened the cold-air damming due to a redirection of the mean flow away from the east side of the Appalachian Mountains, and (c) the combination of Kyle with a shortwave mid-to upper-level trough and a surface coastal front were responsible for the heavy precipitation experienced in the study area through the advection of moisture, vorticity, and the forcing of upward motion. ADR Appalachian Damming Region B03 Bailey et al. (2003) CAD Cold-air damming CF Coastal front CPC Climate Prediction Center CTL Control case dBZ Reflectivity DC District of Columbia
The nonlinear response of a dynamically unstable shear flow with critical level to an initial tem... more The nonlinear response of a dynamically unstable shear flow with critical level to an initial temperature anomaly is investigated using a nonlinear numerical model. Both nonconstant and constant shear profiles of the basic flow are considered. Effects of the solid lower boundary on the dynamically unstable, nonlinear flow are also studied. It is found that in a dynamically unstable, linear flow with a hyperbolic tangent wind profile, the updraft is tilted upshear. The result in consistent with that of a linear stability model (LC). The upshear tilt can be explained by the Orr mechanism (1907) and the energy argument proposed by LC. In a dynamically unstable, nonlinear flow, the updrafts produced by a sinusoidal initial temperature perturbation are stronger in the lower layer and are more compact and located further apart compared to the corresponding linear flow. In addition, the perturbed wave energy is slightly smaller than the linear case. It is found that the growth rate is smaller during the early stage and much larger during the later stage. For a localized initial temperature perturbation in a dynamically unstable flow, a stronger updraft with two compensated downdrafts are produced. Gravity waves are produced in a dynamically stable flow with both a hyperbolic tangent wind profile and a linear wind profile. For a linear shear flow with Richardson number less than 1/4, the disturbance grows in the early stage and then decays algebraically at later times, similar to that found in other linear theoretical studies. The influence of the solid lower boundary is to suppress the shear instability in a nonlinear flow with a hyperbolic tangent wind profile of Ri < 1/4.
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Papers by Yuh-Lang Lin