scholarly journals A study of the influence of forest gaps on fire–atmosphere interactions

2016 ◽  
Vol 16 (13) ◽  
pp. 8499-8509 ◽  
Author(s):  
Michael T. Kiefer ◽  
Warren E. Heilman ◽  
Shiyuan Zhong ◽  
Joseph J. Charney ◽  
Xindi Bian
Keyword(s):  
Sensible Heat Flux ◽  
Forest Canopies ◽  
Advanced Regional Prediction System ◽  
Forest Gaps ◽  
Low Intensity ◽  
Regional Prediction ◽  
Surface Sensible Heat Flux ◽  
Atmospheric Perturbations ◽  
The Impact ◽  
Enhanced Surface

Abstract. Much uncertainty exists regarding the possible role that gaps in forest canopies play in modulating fire–atmosphere interactions in otherwise horizontally homogeneous forests. This study examines the influence of gaps in forest canopies on atmospheric perturbations induced by a low-intensity fire using the ARPS-CANOPY model, a version of the Advanced Regional Prediction System (ARPS) model with a canopy parameterization. A series of numerical experiments are conducted with a stationary low-intensity fire, represented in the model as a line of enhanced surface sensible heat flux. Experiments are conducted with and without forest gaps, and with gaps in different positions relative to the fire line. For each of the four cases considered, an additional simulation is performed without the fire to facilitate comparison of the fire-perturbed atmosphere and the background state. Analyses of both mean and instantaneous wind velocity, turbulent kinetic energy, air temperature, and turbulent mixing of heat are presented in order to examine the fire-perturbed atmosphere on multiple timescales. Results of the analyses indicate that the impact of the fire on the atmosphere is greatest in the case with the gap centered on the fire and weakest in the case with the gap upstream of the fire. It is shown that gaps in forest canopies have the potential to play a role in the vertical as well as horizontal transport of heat away from the fire. Results also suggest that, in order to understand how the fire will alter wind and turbulence in a heterogeneous forest, one needs to first understand how the forest heterogeneity itself influences the wind and turbulence fields without the fire.

scholarly journals A study of the influence of forest gaps on fire-atmosphere interactions

2016 ◽  
Author(s):  
Michael T. Kiefer ◽  
Warren E. Heilman ◽  
Shiyuan Zhong ◽  
Joseph J. Charney ◽  
Xindi Bian
Keyword(s):  
Sensible Heat Flux ◽  
Multiple Time Scales ◽  
Multiple Time ◽  
Forest Canopies ◽  
Advanced Regional Prediction System ◽  
Forest Gaps ◽  
Regional Prediction ◽  
Surface Sensible Heat Flux ◽  
The Impact ◽  
Enhanced Surface

Abstract. Much uncertainty exists regarding the possible role that gaps in forest canopies play in modulating fire-atmosphere interactions in otherwise horizontally homogeneous forests. This study examines the impact of forest gaps on fire-atmosphere interactions using the ARPS-CANOPY model, a version of the Advanced Regional Prediction System (ARPS) model with a canopy parameterization. A series of numerical experiments are conducted with a stationary low-intensity fire, represented in the model as a line of enhanced surface sensible heat flux. Experiments are conducted with and without forest gaps, and with gaps in different positions relative to the fireline. For each of the four cases considered, an additional simulation is performed without the fire to facilitate comparison of the fire-perturbed atmosphere and the background state. Analyses of both mean and instantaneous wind velocity, turbulent kinetic energy, air temperature, and turbulent mixing of heat are presented in order to examine the fire-perturbed atmosphere on multiple time scales. Results of the analyses indicate that the impact of the fire on the atmosphere is greatest in the case with the gap centered on the fire, and weakest in the case with the gap upstream of the fire. It is shown that gaps in forest canopies have the potential to play a substantial role in the vertical as well as horizontal transport of heat away from the fire. Results also suggest that in order to understand how the fire will alter wind and turbulence in a heterogeneous forest, one needs to first understand how the forest heterogeneity itself influences the wind and turbulence fields without the fire.

scholarly journals The Impact of a Stochastically Perturbing Microphysics Scheme on an Idealized Supercell Storm

2017 ◽  
Vol 146 (1) ◽  
pp. 95-118 ◽  
Author(s):  
Xiaoshi Qiao ◽  
Shizhang Wang ◽  
Jinzhong Min
Keyword(s):  
Stochastic Methods ◽  
Microphysics Scheme ◽  
Advanced Regional Prediction System ◽  
Recursive Filters ◽  
Supercell Storm ◽  
Regional Prediction ◽  
Double Moment ◽  
The Impact ◽  
Temperature Tendency ◽  
Stochastically Perturbed

Abstract The concept of stochastic parameterization provides an opportunity to represent spatiotemporal errors caused by microphysics schemes that play important roles in supercell simulations. In this study, two stochastic methods, the stochastically perturbed temperature tendency from microphysics (SPTTM) method and the stochastically perturbed intercept parameters of microphysics (SPIPM) method, are implemented within the Lin scheme, which is based on the Advanced Regional Prediction System (ARPS) model, and are tested using an idealized supercell case. The SPTTM and SPIPM methods perturb the temperature tendency and the intercept parameters (IPs), respectively. Both methods use recursive filters to generate horizontally smooth perturbations and adopt the barotropic structure for the perturbation r, which is multiplied by tendencies or parameters from this parameterization. A double-moment microphysics scheme is used for the truth run. Compared to the multiparameter method, which uses randomly perturbed prescribed parameters, stochastic methods often produce larger ensemble spreads and better forecast the intensity of updraft helicity (UH). The SPTTM method better predicts the intensity by intensifying the midlevel heating with its positive perturbation r, whereas it performs worse in the presence of negative perturbation. In contrast, the SPIPM method can increase the intensity of UH by either positive or negative perturbation, which increases the likelihood for members to predict strong UH.

scholarly journals Analysis and Forecast of a Tornadic Thunderstorm Using Multiple Doppler Radar Data, 3DVAR, and ARPS Model

2013 ◽  
Vol 2013 ◽  
pp. 1-18
Author(s):  
Edward Natenberg ◽  
Jidong Gao ◽  
Ming Xue ◽  
Frederick H. Carr
Keyword(s):  
Doppler Radar ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Radar Data ◽  
Advanced Regional Prediction System ◽  
Regional Prediction ◽  
Upper Level ◽  
Using Data ◽  
Nwp Model ◽  
The Impact

A three-dimensional variational (3DVAR) assimilation technique developed for a convective-scale NWP model—advanced regional prediction system (ARPS)—is used to analyze the 8 May 2003, Moore/Midwest City, Oklahoma tornadic supercell thunderstorm. Previous studies on this case used only one or two radars that are very close to this storm. However, three other radars observed the upper-level part of the storm. Because these three radars are located far away from the targeted storm, they were overlooked by previous studies. High-frequency intermittent 3DVAR analyses are performed using the data from five radars that together provide a more complete picture of this storm. The analyses capture a well-defined mesocyclone in the midlevels and the wind circulation associated with a hook-shaped echo. The analyses produced through this technique are used as initial conditions for a 40-minute storm-scale forecast. The impact of multiple radars on a short-term NWP forecast is most evident when compared to forecasts using data from only one and two radars. The use of all radars provides the best forecast in which a strong low-level mesocyclone develops and tracks in close proximity to the actual tornado damage path.

scholarly journals Mean and Turbulent Flow Downstream of a Low-Intensity Fire: Influence of Canopy and Background Atmospheric Conditions

2015 ◽  
Vol 54 (1) ◽  
pp. 42-57 ◽  
Author(s):  
Michael T. Kiefer ◽  
Warren E. Heilman ◽  
Shiyuan Zhong ◽  
Joseph J. Charney ◽  
Xindi Bian
Keyword(s):  
Wind Speed ◽  
Turbulent Flow ◽  
Atmospheric Conditions ◽  
Advanced Regional Prediction System ◽  
Low Intensity ◽  
Regional Prediction ◽  
Vertical Heat Flux ◽  
Weak Wind ◽  
Canopy Model ◽  
Neutral Stratification

AbstractThis study examines the sensitivity of mean and turbulent flow in the planetary boundary layer and roughness sublayer to a low-intensity fire and evaluates whether the sensitivity is dependent on canopy and background atmospheric properties. The ARPS-CANOPY model, a modified version of the Advanced Regional Prediction System (ARPS) model with a canopy parameterization, is utilized for this purpose. A series of numerical experiments are conducted to evaluate whether the ability of the fire to alter downstream wind, temperature, turbulent kinetic energy (TKE), and vertical heat flux differs between forested and open areas, sparse and dense forests, weak and strong background flow, and neutral and convective background stability. Analysis of all experiments shows that, in general, mean and turbulent flow both prior to and during a low-intensity fire is damped in the presence of a canopy. Greater sensitivity to the fire is found in cases with strong ambient wind speed than in cases with quiescent or weak wind speed. Furthermore, sensitivity of downstream atmospheric conditions to the fire is shown to be strongest with a neutrally stratified background. An analysis of the TKE budget reveals that both buoyancy and wind shear contribute to TKE production during the period of time in which the fire conditions are applied to the model. On the basis of the results of the ARPS simulations, caution is advised when applying ARPS-simulation results to predictions of smoke transport and dispersion: smoke-model users should consider whether canopy impacts on the atmosphere are accounted for and whether neutral stratification is assumed.

scholarly journals Sensitivity of Surface Analyses over the Western United States to RAWS Observations

2008 ◽  
Vol 23 (1) ◽  
pp. 145-158 ◽  
Author(s):  
David T. Myrick ◽  
John D. Horel
Keyword(s):  
United States ◽  
Wind Speed ◽  
Winter Season ◽  
Western United States ◽  
Cold Pool ◽  
Federal State ◽  
Advanced Regional Prediction System ◽  
Average Analysis ◽  
Regional Prediction ◽  
The Impact

Abstract Federal, state, and other wildland resource management agencies contribute to the collection of weather observations from over 1000 Remote Automated Weather Stations (RAWS) in the western United States. The impact of RAWS observations on surface objective analyses during the 2003/04 winter season was assessed using the Advanced Regional Prediction System (ARPS) Data Assimilation System (ADAS). A set of control analyses was created each day at 0000 and 1200 UTC using the Rapid Update Cycle (RUC) analyses as the background fields and assimilating approximately 3000 surface observations from MesoWest. Another set of analyses was generated by withholding all of the RAWS observations available at each time while 10 additional sets of analyses were created by randomly withholding comparable numbers of observations obtained from all sources. Random withholding of observations from the analyses provides a baseline estimate of the analysis quality. Relative to this baseline, removing the RAWS observations degrades temperature (wind speed) analyses by an additional 0.5°C (0.9 m s−1) when evaluated in terms of rmse over the entire season. RAWS temperature observations adjust the RUC background the most during the early morning hours and during winter season cold pool events in the western United States while wind speed observations have a greater impact during active weather periods. The average analysis area influenced by at least 1.0°C (2.5°C) by withholding each RAWS observation is on the order of 600 km2 (100 km2). The spatial influence of randomly withheld observations is much less.

scholarly journals A Doppler Radar Emulator with an Application to the Detectability of Tornadic Signatures

2007 ◽  
Vol 24 (12) ◽  
pp. 1973-1996 ◽  
Author(s):  
Ryan M. May ◽  
Michael I. Biggerstaff ◽  
Ming Xue
Keyword(s):  
Pulse Propagation ◽  
Doppler Radar ◽  
Doppler Spectrum ◽  
Doppler Velocity ◽  
Advanced Regional Prediction System ◽  
Adaptive Sensing ◽  
Regional Prediction ◽  
Sampling Intervals ◽  
Half Power ◽  
The Impact

Abstract A Doppler radar emulator was developed to simulate the expected mean returns from scanning radar, including pulse-to-pulse variability associated with changes in viewing angle and atmospheric structure. Based on the user’s configuration, the emulator samples the numerical simulation output to produce simulated returned power, equivalent radar reflectivity, Doppler velocity, and Doppler spectrum width. The emulator is used to evaluate the impact of azimuthal over- and undersampling, gate spacing, velocity and range aliasing, antenna beamwidth and sidelobes, nonstandard (anomalous) pulse propagation, and wavelength-dependent Rayleigh attenuation on features of interest. As an example, the emulator is used to evaluate the detection of the circulation associated with a tornado simulated within a supercell thunderstorm by the Advanced Regional Prediction System (ARPS). Several metrics for tornado intensity are examined, including peak Doppler velocity and axisymmetric vorticity, to determine the degradation of the tornadic signature as a function of range and azimuthal sampling intervals. For the case of a 2° half-power beamwidth radar, like those deployed in the first integrated project of the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA), the detection of the cyclonic shear associated with this simulated tornado will be difficult beyond the 10-km range, if standard metrics such as azimuthal gate-to-gate shear from a single radar are used for detection.

scholarly journals The Impact of the Temperature Inversion Breakup on the Exchange of Heat and Mass in an Idealized Valley: Sensitivity to the Radiative Forcing

2015 ◽  
Vol 54 (11) ◽  
pp. 2199-2216 ◽  
Author(s):  
Daniel Leukauf ◽  
Alexander Gohm ◽  
Mathias W. Rotach ◽  
Johannes S. Wagner
Keyword(s):  
Radiative Forcing ◽  
Sensible Heat Flux ◽  
Temperature Inversion ◽  
Shortwave Radiation ◽  
Weather Research And Forecasting ◽  
Sensible Heat ◽  
Vertical Fluxes ◽  
Nocturnal Inversion ◽  
Surface Sensible Heat Flux ◽  
The Impact

Abstract The breakup of a nocturnal temperature inversion during daytime is studied in an idealized valley by means of high-resolution numerical simulations. Vertical fluxes of heat and mass are strongly reduced as long as an inversion is present; hence it is important to understand the mechanisms leading to its removal. In this study breakup times are determined as a function of the radiative forcing. Further, the effect of the nocturnal inversion on the vertical exchange of heat and mass is quantified. The Weather Research and Forecasting Model is applied to an idealized quasi-two-dimensional valley. The net shortwave radiation is specified by a sine function with amplitudes between 150 and 850 W m−2 during daytime and at zero during the night. The valley inversion is eroded within 5 h for the strongest forcing. A minimal amplitude of 450 W m−2 is required to reach the breakup, in which case the inversion is removed after 11 h. Depending on the forcing amplitude, between 10% and 57% of the energy provided by the surface sensible heat flux is exported out of the valley during the whole day. The ratio of exported energy to provided energy is approximately 1.6 times as large after the inversion is removed as before. More than 5 times the valley air mass is turned over in 12 h for the strongest forcing, whereas the mass is turned over only 1.3 times for 400 W m−2.

scholarly journals Toward Generalizing the Impact of Surface Heating, Stratification, and Terrain Geometry on the Daytime Heat Export from an Idealized Valley

2017 ◽  
Vol 56 (10) ◽  
pp. 2711-2727 ◽  
Author(s):  
Daniel Leukauf ◽  
Alexander Gohm ◽  
Mathias W. Rotach
Keyword(s):  
Sensible Heat Flux ◽  
Wrf Model ◽  
Total Export ◽  
Surface Heating ◽  
Sensible Heat ◽  
Initial Stability ◽  
Surface Sensible Heat Flux ◽  
The Impact ◽  
Breakup Parameter ◽  
Crest Height

AbstractThe convective export of heat from different types of idealized valleys for fair-weather daytime conditions is studied with the Weather Research and Forecasting (WRF) Model. The goal is to test the hypothesis that the total export of heat over the course of the day depends on a so-called breakup parameter B. The breakup parameter is the ratio between the energy required to neutralize the initially stably stratified valley atmosphere and the total energy provided by the surface sensible heat flux. To achieve this goal, simulations with different surface heating, initial stability, and terrain geometry are performed. The fraction of the sensible heat provided at the surface that is exported at crest height over the course of the day depends exponentially on B. The effects of variations of the valley width, crest height, forcing amplitude, and initial stratification on the total export of heat can be described by this function. The complete neutralization of the stratification in the valley is never reached if B exceeds a critical value of about 0.65 for an initially constant stratification. For a valley geometry with linear slopes and sharp crests, up to 60% of the provided heat is exported for the strongest forcing and the weakest stability (i.e., B ≈ 0.1), whereas less than 5% is exported for B > 0.65. The minimum heat export for larger B is higher for rounded crests (10%) and for a deep residual layer that extends to above crest height (17%).

Impact of a Vertical Vorticity Constraint in Variational Dual-Doppler Wind Analysis: Tests with Real and Simulated Supercell Data

2012 ◽  
Vol 29 (1) ◽  
pp. 32-49 ◽  
Author(s):  
Corey K. Potvin ◽  
Alan Shapiro ◽  
Ming Xue
Keyword(s):  
Vertical Velocity ◽  
Three Dimensional ◽  
Mass Conservation ◽  
Vorticity Equation ◽  
Vertical Vorticity ◽  
Advanced Regional Prediction System ◽  
Supercell Storm ◽  
Radar Networks ◽  
Regional Prediction ◽  
The Impact

Abstract One of the greatest challenges to dual-Doppler retrieval of the vertical wind is the lack of low-level divergence information available to the mass conservation constraint. This study examines the impact of a vertical vorticity equation constraint on vertical velocity retrievals when radar observations are lacking near the ground. The analysis proceeds in a three-dimensional variational data assimilation (3DVAR) framework with the anelastic form of the vertical vorticity equation imposed along with traditional data, mass conservation, and smoothness constraints. The technique is tested using emulated radial wind observations of a supercell storm simulated by the Advanced Regional Prediction System (ARPS), as well as real dual-Doppler observations of a supercell storm that occurred in Oklahoma on 8 May 2003. Special attention is given to procedures to evaluate the vorticity tendency term, including spatially variable advection correction and estimation of the intrinsic evolution. Volume scan times ranging from 5 min, typical of operational radar networks, down to 30 s, achievable by rapid-scan mobile radars, are considered. The vorticity constraint substantially improves the vertical velocity retrievals in our experiments, particularly for volume scan times smaller than 2 min.

scholarly journals Basic Diagnosis and Prediction of Persistent Contrail Occurrence Using High-Resolution Numerical Weather Analyses/Forecasts and Logistic Regression. Part II: Evaluation of Sample Models

2009 ◽  
Vol 48 (9) ◽  
pp. 1790-1802 ◽  
Author(s):  
David P. Duda ◽  
Patrick Minnis
Keyword(s):  
Relative Humidity ◽  
Wind Direction ◽  
Meteorological Data ◽  
Logistic Models ◽  
Satellite Observations ◽  
Lapse Rate ◽  
Prediction System ◽  
Advanced Regional Prediction System ◽  
Regional Prediction ◽  
Surface Models

Abstract A probabilistic forecast to accurately predict contrail formation over the conterminous United States (CONUS) is created by using meteorological data based on hourly meteorological analyses from the Advanced Regional Prediction System (ARPS) and the Rapid Update Cycle (RUC) combined with surface and satellite observations of contrails. Two groups of logistic models were created. The first group of models (SURFACE models) is based on surface-based contrail observations supplemented with satellite observations of contrail occurrence. The most common predictors selected for the SURFACE models tend to be related to temperature, relative humidity, and wind direction when the models are generated using RUC or ARPS analyses. The second group of models (OUTBREAK models) is derived from a selected subgroup of satellite-based observations of widespread persistent contrails. The most common predictors for the OUTBREAK models tend to be wind direction, atmospheric lapse rate, temperature, relative humidity, and the product of temperature and humidity.

Sign in / Sign up

Export Citation Format

Share Document