scholarly journals Model Forecast Improvements with Decreased Horizontal Grid Spacing over Finescale Intermountain Orography during the 2002 Olympic Winter Games

2005 ◽  
Vol 20 (4) ◽  
pp. 558-576 ◽  
Author(s):  
Kenneth A. Hart ◽  
W. James Steenburgh ◽  
Daryl J. Onton
Keyword(s):  
Mesoscale Model ◽  
Forecast Accuracy ◽  
Cooperative Networks ◽  
Intermountain West ◽  
Grid Spacing ◽  
Free Atmosphere ◽  
Wasatch Mountains ◽  
Cold Pools ◽  
Skill Scores ◽  
Horizontal Grid

Abstract Forecasts produced for the 2002 Olympic and Paralympic Winter Games (23 January–25 March 2002) by a multiply nested version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) are examined to determine if decreasing horizontal grid spacing to 4 km improves forecast accuracy over the finescale topography of the Intermountain West. The verification is based on high-density observations collected by the MesoWest cooperative networks, including approximately 200 wind and temperature sites and 100 precipitation sites across northern Utah. Wind and precipitation forecasts produced by the 4-km MM5 domain were more accurate (based on traditional measures) than those of its parent 12-km domain. The most significant improvements in wind speed forecasts occurred at night in valleys and lowland locations where the topography of the 4-km domain produced more accurate nocturnal flows. Wind direction forecast improvements were most substantial at mountain sites where the better topographic resolution of the 4-km domain more accurately reflected the exposure of these locations to the free atmosphere. The 4-km domain also produced quantitative precipitation forecasts that were either equally (small events) or more (large events) accurate than the 12-km domain. Precipitation bias errors varied substantially between the two domains since the representation of the region’s narrow, steeply sloped, basin-and-range topography improved dramatically at 4-km grid spacing. Curiously, the overall accuracy of temperature forecasts by the 4-km domain was not significantly better than that of the 12-km domain. This was due to an inability of the MM5 to properly simulate nocturnal and persistent cold pools within mountain valleys and the lowlands upstream of the Wasatch Mountains. Paradoxically, the added resolution of the 4-km domain, coupled with the failure of this version of the MM5 to fully capture the nocturnal and persistent cold pools, resulted in poorer skill scores. At upper elevations, which are typically above the cold pools, the 4-km domain was substantially more accurate. These results illustrate that decreasing horizontal grid spacing to less than 10 km does improve wind and precipitation forecasts over finescale Intermountain West topography. It is hypothesized that model improvements will ultimately enable the advantages of added model resolution to be fully realized for temperature forecasts over the Intermountain West.

Initial Conditions for Convection-Allowing Ensembles over the Conterminous United States

2020 ◽  
Vol 148 (7) ◽  
pp. 2645-2669
Author(s):  
Craig S. Schwartz ◽  
May Wong ◽  
Glen S. Romine ◽  
Ryan A. Sobash ◽  
Kathryn R. Fossell
Keyword(s):  
United States ◽  
Ensemble Kalman Filter ◽  
Initial Conditions ◽  
Limited Area ◽  
Grid Spacing ◽  
Forecast System ◽  
Skill Scores ◽  
Ensemble Mean ◽  
Horizontal Grid ◽  
Better Than

Abstract Five sets of 48-h, 10-member, convection-allowing ensemble (CAE) forecasts with 3-km horizontal grid spacing were systematically evaluated over the conterminous United States with a focus on precipitation across 31 cases. The various CAEs solely differed by their initial condition perturbations (ICPs) and central initial states. CAEs initially centered about deterministic Global Forecast System (GFS) analyses were unequivocally better than those initially centered about ensemble mean analyses produced by a limited-area single-physics, single-dynamics 15-km continuously cycling ensemble Kalman filter (EnKF), strongly suggesting relative superiority of the GFS analyses. Additionally, CAEs with flow-dependent ICPs derived from either the EnKF or multimodel 3-h forecasts from the Short-Range Ensemble Forecast (SREF) system had higher fractions skill scores than CAEs with randomly generated mesoscale ICPs. Conversely, due to insufficient spread, CAEs with EnKF ICPs had worse reliability, discrimination, and dispersion than those with random and SREF ICPs. However, members in the CAE with SREF ICPs undesirably clustered by dynamic core represented in the ICPs, and CAEs with random ICPs had poor spinup characteristics. Collectively, these results indicate that continuously cycled EnKF mean analyses were suboptimal for CAE initialization purposes and suggest that further work to improve limited-area continuously cycling EnKFs over large regional domains is warranted. Additionally, the deleterious aspects of using both multimodel and random ICPs suggest efforts toward improving spread in CAEs with single-physics, single-dynamics, flow-dependent ICPs should continue.

scholarly journals Sensitivity of a Bowing Mesoscale Convective System to Horizontal Grid Spacing in a Convection-Allowing Ensemble

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 384
Author(s):  
John R. Lawson ◽  
William A. Gallus ◽  
Corey K. Potvin
Keyword(s):  
Mesoscale Convective System ◽  
Real Data ◽  
The United States ◽  
Convective System ◽  
Grid Spacing ◽  
Structure Amplitude ◽  
Cold Pools ◽  
Bow Echo ◽  
Mesoscale Convective ◽  
Horizontal Grid

The bow echo, a mesoscale convective system (MCS) responsible for much hail and wind damage across the United States, is associated with poor skill in convection-allowing numerical model forecasts. Given the decrease in convection-allowing grid spacings within many operational forecasting systems, we investigate the effect of finer resolution on the character of bowing-MCS development in a real-data numerical simulation. Two ensembles were generated: one with a single domain of 3-km horizontal grid spacing, and another nesting a 1-km domain with two-way feedback. Ensemble members were generated from their control member with a stochastic kinetic-energy backscatter scheme, with identical initial and lateral-boundary conditions. Results suggest that resolution reduces hindcast skill of this MCS, as measured with an adaptation of the object-based Structure–Amplitude–Location method. The nested 1-km ensemble produces a faster system than in both the 3-km ensemble and observations. The nested 1-km simulation also produced stronger cold pools, which could be enhanced by the increased (fractal) cloud surface area with higher resolution, allowing more entrainment of dry air and hence increased evaporative cooling.

scholarly journals Sensitivity of Fine-Scale Structure in Tropical Cyclone Boundary Layer to Model Horizontal Resolution at Sub-Kilometer Grid Spacing

2021 ◽  
Vol 9 ◽  
Author(s):  
Hongxiong Xu ◽  
Yuqing Wang
Keyword(s):  
Boundary Layer ◽  
Tropical Cyclone ◽  
Inner Core ◽  
Mesoscale Model ◽  
Horizontal Resolution ◽  
Scale Structure ◽  
Fine Scale ◽  
Grid Spacing ◽  
Large Eddies ◽  
Horizontal Grid

In view of the increasing interest in the explicit simulation of fine-scale features in the tropical cyclone (TC) boundary layer (TCBL), the effects of horizontal grid spacing on a 7–10 h simulation of an idealized TC are examined using the Weather Research and Forecast (ARW-WRF) mesoscale model with one-way moving nests and the nonlinear backscatter with anisotropy (NBA) sub-grid-scale (SGS) scheme. In general, reducing the horizontal grid spacing from 2 km to 500 m tends to produce a stronger TC with lower minimum sea level pressure (MSLP), stronger surface winds, and smaller TC inner core size. However, large eddies cannot be resolved at these grid spacings. In contrast, reducing the horizontal grid spacing from 500 to 166 m and further to 55 m leads to a decrease in TC intensity and an increase in the inner-core TC size. Moreover, although the 166-m grid spacing starts to resolve large eddies in terms of TCBL horizontal rolls and tornado-scale vortex, the use of the finest grid spacing of 55 m tends to produce shorter wavelengths in the turbulent motion and stronger multi-scale turbulence interaction. It is concluded that a grid spacing of sub-100-meters is desirable to produce more detailed and fine-scale structure of TCBL horizontal rolls and tornado-scale vortices, while the relatively coarse sub-kilometer grid spacing (e.g., 500 m) is more cost-effective and feasible for research that is not interested in the turbulence processes and for real-time operational TC forecasting in the near future.

scholarly journals High-Resolution Simulations and Microphysical Validation of an Orographic Precipitation Event over the Wasatch Mountains during IPEX IOP3

2005 ◽  
Vol 133 (10) ◽  
pp. 2947-2971 ◽  
Author(s):  
Brian A. Colle ◽  
Justin B. Wolfe ◽  
W. James Steenburgh ◽  
David E. Kingsmill ◽  
Justin A. W. Cox ◽  
...  
Keyword(s):  
Mesoscale Model ◽  
Salt Lake ◽  
Great Salt Lake ◽  
Cloud Water ◽  
Precipitation Event ◽  
Convergence Zone ◽  
Grid Spacing ◽  
Surface Precipitation ◽  
Wasatch Mountains ◽  
Precipitation Enhancement

Abstract This paper investigates the kinematic flow and precipitation evolution of a winter storm over and upstream of the Wasatch Mountains [Intermountain Precipitation Experiment third intensive observing period (IPEX IOP3)] using a multiply nested version of the fifth-generation Pennsylvania State University (PSU)––National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). Validation using in situ aircraft data, radiosondes, ground-based radar, and surface observations showed that the MM5, which featured four domains with 36-, 12-, 4-, and 1.33-km grid spacing, realistically simulated the observed partial blocking of the 8–12 m s−1 ambient southwesterly flow and development of a convergence zone and enhanced lowland precipitation region upwind of the initial Wasatch slope. The MM5 also properly simulated the advance of this convergence zone toward the base of the Wasatch during the passage of a midlevel trough, despite not fully capturing the westerly wind shift accompanying the trough. Accurate simulation of the observed precipitation over the central Wasatch Mountains (within 25% of observed at all stations) required a horizontal grid spacing of 1.33 km. Despite close agreement with the observed surface precipitation, the Reisner2 bulk microphysical scheme produced too much supercooled cloud water and too little snow aloft. A model microphysical budget revealed that the Reisner2 generated over half of the surface precipitation through riming and accretion, rather than snow deposition and aggregation as implied by the observations. Using an intercept for the snow size distribution that allows for greater snow concentrations aloft improved the snow predictions and reduced the cloud water overprediction. Sensitivity studies illustrate that the reduced surface drag of the Great Salt Lake (GSL) enhanced the convergence zone and associated lowland precipitation enhancement upstream of the Wasatch Mountains. The presence of mountain ranges south of the Great Salt Lake appears to have weakened the along-barrier flow and windward convergence, resulting in a slight decrease in windward precipitation enhancement. Diabatic cooling from falling precipitation was also important for maintaining the blocked flow.

Objectively Determined Fair-Weather CBL Depths in the ARW-WRF Model and Their Comparison to CASES-97 Observations

2013 ◽  
Vol 141 (1) ◽  
pp. 30-54 ◽  
Author(s):  
Margaret A. LeMone ◽  
Mukul Tewari ◽  
Fei Chen ◽  
Jimy Dudhia
Keyword(s):  
Boundary Layer ◽  
Potential Temperature ◽  
Wrf Model ◽  
Grid Spacing ◽  
Fair Weather ◽  
Free Atmosphere ◽  
Convective Boundary ◽  
Surface Exchange ◽  
Weather Observations ◽  
Horizontal Grid

Abstract High-resolution 24-h runs of the Advanced Research version of the Weather Research and Forecasting Model are used to test eight objective methods for estimating convective boundary layer (CBL) depth h, using four planetary boundary layer schemes: Yonsei University (YSU), Mellor–Yamada–Janjic (MYJ), Bougeault–LaCarrere (BouLac), and quasi-normal scale elimination (QNSE). The methods use thresholds of virtual potential temperature Θυ, turbulence kinetic energy (TKE), Θυ,z, or Richardson number. Those that identify h consistent with values found subjectively from modeled Θυ profiles are used for comparisons to fair-weather observations from the 1997 Cooperative Atmosphere–Surface Exchange Study (CASES-97). The best method defines h as the lowest level at which Θυ,z = 2 K km−1, working for all four schemes, with little sensitivity to horizontal grid spacing. For BouLac, MYJ, and QNSE, TKE thresholds did poorly for runs with 1- and 3-km grid spacing, producing irregular h growth not consistent with Θυ-profile evolution. This resulted from the vertical velocity W associated with resolved CBL eddies: for W > 0, TKE profiles were deeper and Θυ profiles more unstable than for W < 0. For the 1-km runs, 25-point spatial averaging was needed for reliable TKE-based h estimates, but thresholds greater than free-atmosphere values were sensitive to horizontal grid spacing. Matching Θυ(h) to Θυ(0.05h) or Θυ at the first model level were often successful, but the absence of eddies for 9-km grids led to more unstable Θυ profiles and often deeper h. Values of h for BouLac, MYJ, and QNSE, are mostly smaller than observed, with YSU values close to slightly high, consistent with earlier results.

scholarly journals Influences of Horizontal Grid Spacing and Microphysics on WRF Forecasts of Convective Morphology Evolution for Nocturnal MCSs in Weakly Forced Environments

2019 ◽  
Vol 34 (5) ◽  
pp. 1495-1517 ◽  
Author(s):  
Jonathan E. Thielen ◽  
William A. Gallus
Keyword(s):  
Wrf Model ◽  
Forecast Accuracy ◽  
Warm Season ◽  
Grid Spacing ◽  
Convective Systems ◽  
Model Configuration ◽  
Mesoscale Convective ◽  
Microphysical Parameterization ◽  
The Impact ◽  
Horizontal Grid

Abstract Nocturnal mesoscale convective systems (MCSs) are important phenomena because of their contributions to warm-season precipitation and association with severe hazards. Past studies have shown that their morphology remains poorly forecast in current convection-allowing models operating at 3–4-km horizontal grid spacing. A total of 10 MCS cases occurring in weakly forced environments were simulated using the Weather Research and Forecasting (WRF) Model at 3- and 1-km horizontal grid spacings to investigate the impact of increased resolution on forecasts of convective morphology and its evolution. These simulations were conducted using four microphysics schemes to account for additional sensitivities to the microphysical parameterization. The observed and corresponding simulated systems were manually classified into detailed cellular and linear modes, and the overall morphology depiction and the forecast accuracy of each model configuration were evaluated. In agreement with past studies, WRF was found to underpredict the occurrence of linear modes and overpredict cellular modes at 3-km horizontal grid spacing with all microphysics schemes tested. When grid spacing was reduced to 1 km, the proportion of linear systems increased. However, the increase was insufficient to match observations throughout the evolution of the systems, and the accuracy scores showed no statistically significant improvement. This suggests that the additional linear modes may have occurred in the wrong subtypes, wrong systems, and/or at the wrong times. Accuracy scores were also shown to decrease with forecast length, with the primary decrease in score generally occurring during upscale growth in the early nocturnal period.

scholarly journals Impact of the Tropopause Temperature on the Intensity of Tropical Cyclones: An Idealized Study Using a Mesoscale Model

2014 ◽  
Vol 71 (11) ◽  
pp. 4333-4348 ◽  
Author(s):  
Shuguang Wang ◽  
Suzana J. Camargo ◽  
Adam H. Sobel ◽  
Lorenzo M. Polvani
Keyword(s):  
Tropical Cyclones ◽  
Mesoscale Model ◽  
Three Dimensional ◽  
Grid Spacing ◽  
Stratospheric Temperature ◽  
Similar Dependence ◽  
Temperature Equilibrium ◽  
The Impact ◽  
Horizontal Grid ◽  
Tropopause Temperature

Abstract This study investigates the impact of the tropopause temperature on the intensity of idealized tropical cyclones (TCs) superimposed on background states of radiative–convective equilibrium (RCE) in a three-dimensional (3D) mesoscale model. Simulations are performed with constant sea surface temperature and an isothermal stratosphere with constant tropopause temperature. The potential intensity (PI) computed from the thermodynamic profiles of the RCE state (before the TCs are superimposed on it) increases by 0.4–1 m s−1 for each 1 K of tropopause temperature reduction. The 3D TC experiments yield intense tropical cyclones whose intensities exceed the PI value substantially. It is further shown that the discrepancy may be largely explained by the supergradient wind in the 3D simulations. The intensities of these 3D TCs increase by ~0.4 m s−1 per 1 K of cooling in the tropopause temperature in RCE, on the low end of the PI dependence on the tropopause temperature. Sensitivity experiments with a larger horizontal grid spacing of 8 km produce less intense TCs, as expected, but similar dependence (~−0.5 m s−1 K−1) on tropopause temperature. Equilibrium TC solutions are further obtained in 200-day experiments with different values of constant stratospheric temperature. Similar relationships between TC intensity and tropopause temperature are also found in these equilibrium TC solutions.

scholarly journals Dynamical Downscaling of Wind Speed in Complex Terrain Prone To Bora-Type Flows

2011 ◽  
Vol 50 (8) ◽  
pp. 1676-1691 ◽  
Author(s):  
Kristian Horvath ◽  
Alica Bajić ◽  
Stjepan Ivatek-Šahdan
Keyword(s):  
Wind Speed ◽  
Complex Terrain ◽  
Dynamical Downscaling ◽  
Mesoscale Model ◽  
Spectral Power ◽  
Grid Spacing ◽  
Model Data ◽  
Mean Wind Speed ◽  
The Mean ◽  
Horizontal Grid

AbstractThe results of numerically modeled wind speed climate, a primary component of wind energy resource assessment in the complex terrain of Croatia, are given. For that purpose, dynamical downscaling of 10 yr (1992–2001) of the 40-yr ECMWF Re-Analysis (ERA-40) was performed to 8-km horizontal grid spacing with the use of a spectral, prognostic full-physics model Aire Limitée Adaptation Dynamique Développement International (ALADIN; the “ALHR” version). Then modeled data with a 60-min frequency were refined to 2-km horizontal grid spacing with a simplified and cost-effective model version, the so-called dynamical adaptation (DADA). The statistical verification of ERA-40-, ALHR-, and DADA-modeled wind speed on the basis of data from measurement stations representing different regions of Croatia suggests that downscaling was successful and that model accuracy generally improves as horizontal resolution is increased. The areas of the highest mean wind speeds correspond well to locations of frequent and strong bora flow as well as to the prominent mountain peaks. The best results are achieved with DADA and contain bias of 1% of the mean wind speed for eastern Croatia while reaching 10% for complex coastal terrain, mainly because of underestimation of the strongest winds. Root-mean-square errors for DADA are significantly smaller for flat terrain than for complex terrain, with relative values close to 12% of the mean wind speed regardless of the station location. Spectral analyses suggest that the shape of the kinetic energy spectra generally relaxes from k−3 at the upper troposphere to the shape of orographic spectra near the surface and shows no seasonal variability. Apart from the buildup of energy on smaller scales of motions, it is shown that mesoscale simulations contain a considerable amount of energy related to near-surface and mostly divergent meso-β-scale (20–200 km) motions. Spectral decomposition of measured and modeled data in temporal space indicates a reasonable performance of all model datasets in simulating the primary maximum of spectral power related to synoptic and larger-than-diurnal mesoscale motions, with somewhat increased accuracy of mesoscale model data. The primary improvement of dynamical adaptation was achieved for cross-mountain winds, whereas mixed results were found for along-mountain wind directions. Secondary diurnal and tertiary semidiurnal maxima are significantly better simulated with the mesoscale model for coastal stations but are somewhat more erroneous for the continental station. The mesoscale model data underestimate the spectral power of motions with less-than-semidiurnal periods.

scholarly journals On the Forecast Sensitivity of MCS Cold Pools and Related Features to Horizontal Grid Spacing in Convection-Allowing WRF Simulations

2020 ◽  
Vol 35 (2) ◽  
pp. 325-346 ◽  
Author(s):  
Brian J. Squitieri ◽  
William A. Gallus
Keyword(s):  
Forecast Skill ◽  
Cold Pool ◽  
Grid Spacing ◽  
Convective Structures ◽  
Cold Pools ◽  
Areal Coverage ◽  
Horizontal Grid

Abstract While the implementation of convection-allowing models has improved the representation of convective features, a consensus is lacking regarding what horizontal grid spacing most appropriately resolves convective structures, is computationally feasible, and provides the most useful output to forecasters. The present study evaluates 14 simulated MCSs with 3-, 1- and 0.333-km horizontal grid spacing in order to understand sensitivity in simulated MCS forward propagation speeds and cold pool behavior with decreased grid spacing. MCS cold pools were found to be significantly larger in runs using finer grid spacing. In addition, a greater similarity in solutions occurred when grid spacing was refined to 1 km and less, with 1- and 0.333-km MCS cold pools more similar in magnitude, depth, length, and areal coverage, than 3-km cold pools. The 1-km simulations demonstrated a small increase in forecast skill for 3-h QPF throughout MCS evolution compared to 3-km runs. The 1-km MCS 9-h precipitation swaths were also better aligned with observations compared to 3-km simulations. When evaluating MCS forward propagation speeds, however, 3-km simulated MCS speeds were more similar to observations compared to 1 km.

scholarly journals Tests of an Adjoint Mesoscale Model with Explicit Moist Physics on the Cloud Scale

2008 ◽  
Vol 136 (6) ◽  
pp. 2120-2132 ◽  
Author(s):  
Clark Amerault ◽  
Xiaolei Zou ◽  
James Doyle
Keyword(s):  
Data Assimilation ◽  
Mesoscale Model ◽  
Naval Research ◽  
Model Resolution ◽  
Grid Spacing ◽  
Adjoint Model ◽  
Forecast Period ◽  
Atmospheric Component ◽  
Ocean Atmosphere ◽  
Horizontal Grid

Abstract An adjoint modeling system based upon the Naval Research Laboratory’s Coupled Ocean–Atmosphere Mesoscale Prediction System’s atmospheric component has been developed. The system includes the adjoint model of the explicit moist physics parameterization, which allows for gradients with respect to the initial hydrometeor concentrations to be calculated. This work focuses on the ability of the system to calculate evolved perturbations and gradients for the hydrometeor variables. Tests of the tangent linear and adjoint models for an idealized convective case at high model resolution (4-km horizontal grid spacing) are presented in this study. The tangent linear approximation is shown to be acceptable for all model variables (including the hydrometeors) with sizable perturbations for forecasts of 1 h. The adjoint model was utilized with the same convective case to demonstrate its applicability in four-dimensional variational data assimilation experiments. Identical twin experiments were conducted where the adjoint model produced gradients for all model variables, leading to improved analyses and forecasts. The best agreement between model forecasts and simulated observations occurred when information on all model variables was assimilated. In the case where only conventional data were assimilated, the agreement was not as good in the early forecast period. However, the hydrometeor values spun up quickly, and at later times, the forecast performed almost as well as when all data were assimilated.

Sign in / Sign up

Export Citation Format

Share Document