Convective Initiation in an Idealized Cloud Model Using an Updraft Nudging Technique

Naylor, Jason; Gilmore, Matthew S.

doi:10.1175/mwr-d-12-00163.1

Cited by 41 publications

(18 citation statements)

References 27 publications

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“…As noted by Weisman and Klemp (1982), the goal of introducing perturbations in simulations of convection is to use the smallest magnitude necessary, so that the perturbations do not affect the characteristics of the convection. It is for that reason that the perturbations introduced are one to two orders of magnitude smaller than what is traditionally used for thunderstorm modeling (Weisman and Klemp 1982;Naylor and Gilmore 2012).…”

Section: B Idealized Generating Cell Simulationsmentioning

confidence: 97%

Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

Keeler

Jewett

Rauber

et al. 2016

Journal of the Atmospheric Sciences

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This paper assesses the influence of radiative forcing and latent heating on the development and maintenance of cloud-top generating cells (GCs) in high-resolution idealized Weather Research and Forecasting Model simulations with initial conditions representative of the vertical structure of a cyclone observed during the Profiling of Winter Storms campaign. Simulated GC kinematics, structure, and ice mass are shown to compare well quantitatively with Wyoming Cloud Radar, cloud probe, and other observations. Sensitivity to radiative forcing was assessed in simulations with longwave-only (nighttime), longwave-and-shortwave (daytime), and no-radiation parameterizations. The domain-averaged longwave cooling rate exceeded 0.50 K h 21 near cloud top, with maxima greater than 2.00 K h 21 atop GCs. Shortwave warming was weaker by comparison, with domain-averaged values of 0.10-0.20 K h 21 and maxima of 0.50 K h 21 atop GCs. The stabilizing influence of cloud-top shortwave warming was evident in the daytime simulation's vertical velocity spectrum, with 1% of the updrafts in the 6.0-8.0-km layer exceeding 1.20 m s 21 , compared to 1.80 m s 21 for the nighttime simulation. GCs regenerate in simulations with radiative forcing after the initial instability is released but do not persist when radiation is not parameterized, demonstrating that radiative forcing is critical to GC maintenance under the thermodynamic and vertical wind shear conditions in this cyclone. GCs are characterized by high ice supersaturation (RH ice . 150%) and latent heating rates frequently in excess of 2.00 K h 21 collocated with vertical velocity maxima. Ice precipitation mixing ratio maxima of greater than 0.15 g kg 21 were common within GCs in the daytime and nighttime simulations.

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Section: B Idealized Generating Cell Simulationsmentioning

confidence: 97%

Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

Keeler

Jewett

Rauber

et al. 2016

Journal of the Atmospheric Sciences

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“…The specifications of the model design are shown in Table 1. To initiate a strong, isolated, and sustained supercell thunderstorm in the environment discussed above, the updraft nudging technique is adapted from Naylor and Gilmore (2012) with slightly modified parameters. The ellipsoidal vertical velocity perturbation is located 1500 m above the surface with a 7500-m horizontal radius and a 1500-m vertical radius.…”

Section: A Cm1 Configurationmentioning

confidence: 99%

Comparing Observations and Simulations of the Streamwise Vorticity Current and the Forward Flank Convergence Boundary in a Supercell Storm

Schueth

Weiss

Dahl

2021

Monthly Weather Review

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The forward-flank convergence boundary (FFCB) in supercells has been well documented in many observational and modeling studies. It is theorized that the FFCB is a focal point fore baroclinic generation of vorticity. This vorticity is generally horizontal and streamwise in nature, which can then be tilted and converted to mid-level (3-6 km AGL) vertical vorticity. Previous modeling studies of supercells often show horizontal streamwise vorticity present behind the FFCB, with higher resolution simulations resolving larger magnitudes of horizontal vorticity. Recently, studies have shown a particularly strong realization of this vorticity called the streamwise vorticity current (SVC). In this study, a tornadic supercell is simulated with the Bryan Cloud Model at 125-m horizontal grid spacing, and a coherent SVC is shown to be present. Simulated range-height indicator (RHI) data show the strongest horizontal vorticity is located on the periphery of a steady-state Kelvin-Helmholtz billow in the FFCB head. Additionally, similar structure is found in two separate observed cases with the Texas Tech University Ka-band (TTUKa) mobile radar RHIs. Analyzing vorticity budgets for parcels in the vicinity of the FFCB head in the simulation, stretching of vorticity is the primary contributor to the strong streamwise vorticity, while baroclinic generation of vorticity plays a smaller role.

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“…Precipitation microphysics were parameterized using the NSSL two-moment scheme including both graupel and hail (Mansell et al 2010). In each simulation, deep convection was initialized at the center of the domain using an updraft nudging technique following Naylor and Gilmore (2012). The only changes in the updraft nudging from Naylor and Gilmore (2012) were a modified vertical position (z 5 1000 m) and vertical radius (1000 m) of the spheroid over which the updraft forcing is applied as well as reduction of the period of forcing to the first 1200 s of the model integration.…”

Section: B Numerical Model Configurationmentioning

confidence: 99%

Evaluating the Effective Inflow Layer of Simulated Supercell Updrafts

Nowotarski

Peters

Mulholland

2020

Monthly Weather Review

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Proper prediction of the inflow layer of deep convective storms is critical for understanding their potential updraft properties and likelihood of producing severe weather. In this study, an existing forecast metric known as the effective inflow layer (EIL) is evaluated with an emphasis on its performance for supercell thunderstorms, where both buoyancy and dynamic pressure accelerations are common. A total of 15 idealized simulations with a range of realistic base states are performed. Using an array of passive fluid tracers initialized at various vertical levels, the proportion of simulated updraft core air originating from the EIL is determined. Results suggest that the EIL metric performs well in forecasting peak updraft origin height, particularly for supercell updrafts. Moreover, the EIL metric displays consistent skill across a range of updraft core definitions. The EIL has a tendency to perform better as convective available potential energy, deep-layer shear, and EIL depth are increased in the near-storm environment. Modifications to further constrain the EIL based on the most-unstable parcel height or storm-relative flow may lead to marginal improvements for the most stringent updraft core definitions. Finally, effects of the near-storm environment on low-level and peak updraft forcing and intensity are discussed.

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Convective Initiation in an Idealized Cloud Model Using an Updraft Nudging Technique

Cited by 41 publications

References 27 publications

Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

Dynamics of Cloud-Top Generating Cells in Winter Cyclones. Part I: Idealized Simulations in the Context of Field Observations

Comparing Observations and Simulations of the Streamwise Vorticity Current and the Forward Flank Convergence Boundary in a Supercell Storm

Evaluating the Effective Inflow Layer of Simulated Supercell Updrafts

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