scholarly journals Evaluation of the Summertime Low-Level Winds Simulated by MM5 in the Central Valley of California

2010 ◽  
Vol 49 (11) ◽  
pp. 2230-2245 ◽  
Author(s):  
Sara A. Michelson ◽  
Irina V. Djalalova ◽  
Jian-Wen Bao
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Central Valley ◽  
State University ◽  
Low Level ◽  
Fifth Generation ◽  
Southern Central ◽  
The Difference ◽  
Upper Level ◽  
And Control

Abstract A season-long set of 5-day simulations between 1200 UTC 1 June and 1200 UTC 30 September 2000 are evaluated using the observations taken during the Central California Ozone Study (CCOS) 2000 experiment. The simulations are carried out using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), which is widely used for air-quality simulations and control planning. The evaluation results strongly indicate that the model-simulated low-level winds in California’s Central Valley are biased in speed and direction: the simulated winds tend to have a stronger northwesterly component than observed. This bias is related to the difference in the observed and simulated large-scale, upper-level flows. The model simulations also show a bias in the height of the daytime atmospheric boundary layer (ABL), particularly in the northern and southern Central Valley. There is evidence to suggest that this bias in the daytime ABL height is not only associated with the large-scale, upper-level bias but also linked to apparent differences in the surface forcing.

scholarly journals Sensitivity of Low-Level Winds Simulated by the WRF Model in California’s Central Valley to Uncertainties in the Large-Scale Forcing and Soil Initialization

2008 ◽  
Vol 47 (12) ◽  
pp. 3131-3149 ◽  
Author(s):  
Sara A. Michelson ◽  
Jian-Wen Bao
Keyword(s):  
Air Quality ◽  
Spatial Variation ◽  
Large Scale ◽  
Wrf Model ◽  
Central Valley ◽  
Weather Conditions ◽  
Atmospheric Forcing ◽  
Low Level ◽  
Lateral Boundary Conditions ◽  
Upper Level

Abstract The sensitivity of the Weather and Research Forecasting (WRF) model-simulated low-level winds in the Central Valley (CV) of California to uncertainties in the atmospheric forcing and soil initialization is investigated using scatter diagrams for a 5-day period in which meteorological conditions are typical of those associated with poor-air-quality events during the summer in the CV. It is assumed that these uncertainties can be approximated by two independent operational analyses. First, the sensitivity is illustrated using scatter diagrams and is measured in terms of the linear regression of the output from two simulations that differ in either the atmospheric forcing or the soil initialization. The spatial variation of the sensitivity is then investigated and is linked to the dominant low-level flows within the CV. The results from this case study suggest that the WRF-simulated low-level winds in the northern CV [i.e., the Sacramento Valley (SV)] are more sensitive to the uncertainties in the atmospheric forcing than to those in the soil initialization in the typical weather conditions during the summer that are prone to poor air quality in the CV. The simulated low-level winds in the southernmost part of the San Joaquin Valley (SJV) are more sensitive to the uncertainties in the soil initialization than they are in the SV. In the northern SJV, the simulated low-level winds are overall more sensitive to the uncertainties in the large-scale upper-level atmospheric forcing than to those in the soil initialization. This spatial variation in sensitivity reflects the important roles that the large-scale forcing, specified by the lateral boundary conditions and the local forcing associated with the soil state, play in controlling the low-level winds in the CV.

scholarly journals The Importance of the Boundary Layer Parameterization in the Prediction of Low-Level Convergence Lines

2008 ◽  
Vol 136 (6) ◽  
pp. 2173-2185 ◽  
Author(s):  
Gerald L. Thomsen ◽  
Roger K. Smith
Keyword(s):  
Boundary Layer ◽  
Mesoscale Model ◽  
State University ◽  
Pennsylvania State University ◽  
Low Level ◽  
Surface Pressure Distribution ◽  
Fifth Generation ◽  
Medium Range Forecast ◽  
The Arid Regions ◽  
Better Than

Abstract The importance of the boundary layer parameterization in the numerical prediction of low-level convergence lines over northeastern Australia is investigated. High-resolution simulations of convergence lines observed in one event during the 2002 Gulf Lines Experiment are carried out using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). Calculations using five different parameterizations are compared with observations to determine the optimum scheme for capturing these lines. The schemes that give the best agreement with the observations are the three that include a representation of countergradient fluxes and a surface layer scheme based on Monin–Obukhov theory. One of these, the Medium-Range Forecast scheme, is slightly better than the other two, based on its ability to predict the surface pressure distribution. The findings are important for the design of mesoscale forecasting systems for the arid regions of Australia and elsewhere.

scholarly journals Observed and WRF-Simulated Low-Level Winds in a High-Ozone Episode during the Central California Ozone Study

2008 ◽  
Vol 47 (9) ◽  
pp. 2372-2394 ◽  
Author(s):  
J-W. Bao ◽  
S. A. Michelson ◽  
P. O. G. Persson ◽  
I. V. Djalalova ◽  
J. M. Wilczak
Keyword(s):  
Large Scale ◽  
Central Valley ◽  
Transport Processes ◽  
Central California ◽  
Low Level ◽  
Lateral Boundary Conditions ◽  
Downslope Flows ◽  
Upper Level ◽  
Physical Reasons ◽  
The Impact

Abstract A case study is carried out for the 29 July–3 August 2000 episode of the Central California Ozone Study (CCOS), a typical summertime high-ozone event in the Central Valley of California. The focus of the study is on the low-level winds that control the transport and dispersion of pollutants in the Central Valley. An analysis of surface and wind profiler observations from the CCOS field experiment indicates a number of important low-level flows in the Central Valley: 1) the incoming low-level marine airflow through the Carquinez Strait into the Sacramento River delta, 2) the diurnal cycle of upslope–downslope flows, 3) the up- and down-valley flow in the Sacramento Valley, 4) the nocturnal low-level jet in the San Joaquin Valley, and 5) the orographically induced mesoscale eddies (the Fresno and Schultz eddies). A numerical simulation using the advanced research version of the Weather Research and Forecasting Model (WRF) reproduces the overall pattern of the observed low-level flows. The physical reasons behind the quantitative differences between the observed and simulated low-level winds are also analyzed and discussed, although not enough observations are available to diagnose thoroughly the model-error sources. In particular, hodograph analysis is applied to provide physical insight into the impact of the large-scale, upper-level winds on the locally forced low-level winds. It is found that the diurnal rotation of the observed and simulated hodographs of the local winds varies spatially in the Central Valley, resulting from the combining effect of topographically induced local forcing and the interaction between the upper-level winds and the aforementioned low-level flows. The trajectory analysis not only further confirms that WRF reproduces the observed low-level transport processes reasonably well but also shows that the simulated upper-level winds have noticeable errors. The results from this study strongly suggest that the errors in the WRF-simulated low-level winds are related not only to the errors in the model’s surface conditions and atmospheric boundary layer physics but also to the errors in the upper-level forcing mostly prescribed in the model’s lateral boundary conditions.

Interactions between Simulated Tropical Cyclones and an Environment with a Variable Coriolis Parameter

2007 ◽  
Vol 135 (5) ◽  
pp. 1889-1905 ◽  
Author(s):  
Elizabeth A. Ritchie ◽  
William M. Frank
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Inner Core ◽  
Mesoscale Model ◽  
Vertical Wind Shear ◽  
State University ◽  
Coriolis Parameter ◽  
Fine Mesh ◽  
Fifth Generation

Abstract Numerical simulations of tropical cyclones are performed to examine the effects of a variable Coriolis parameter on the structure and intensity of hurricanes. The simulations are performed using the nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model using a 5-km fine mesh and fully explicit representation of moist processes. When a variable Conolis parameter ( f ) environment is applied to a mature tropical cyclone, a persistent north-northwesterly shear develops over the storm center as a result of an interaction between the primary circulation of the storm and the gradient in absolute vorticity. As a result, the variable-f storm quickly develops a persistent wavenumber-1 asymmetry in its inner-core structure with upward motion and rainfall concentrated on the left side of the shear looking downshear, in agreement with earlier studies. In comparison, the constant-f storm develops weak transient asymmetries in structure that are only partially related to a weak vertical wind shear. As a result, it is found that the tropical cyclone with variable f intensifies slightly more slowly than that with constant f, and reaches a final intensity that is about 5 mb weaker. It is argued that this “beta shear” is not adequately represented in large-scale analyses and so does not figure into calculations of environmental shear. Although the effect of the beta shear on the tropical cyclone intensity seems small by itself, when combined with the environmental shear it can produce a large net shear or it can reduce an environmental shear below the apparent threshold to impact storm intensity. If this result proves to be generally true, then the presence of an additional overlooked beta shear may well explain differences in the response of tropical cyclone intensification to westerly versus easterly shear regimes.

scholarly journals Alongfront Variability of Precipitation Associated with a Midlatitude Frontal Zone: TRMM Observations and MM5 Simulation

2009 ◽  
Vol 137 (3) ◽  
pp. 1008-1028 ◽  
Author(s):  
Mei Han ◽  
Scott A. Braun ◽  
P. Ola G. Persson ◽  
Jian-Wen Bao
Keyword(s):  
Mesoscale Model ◽  
Model Simulation ◽  
Tropical Rainfall Measuring Mission ◽  
State University ◽  
Low Level ◽  
Brightness Temperatures ◽  
Northern Portion ◽  
Upper Level ◽  
Microwave Imager ◽  
Ice Production

Abstract On 19 February 2001, the Tropical Rainfall Measuring Mission (TRMM) satellite observed complex alongfront variability in the precipitation structure of an intense cold-frontal rainband. The TRMM Microwave Imager brightness temperatures suggested that, compared to the northern and southern ends of the rainband, a greater amount of precipitation ice was concentrated in the middle portion of the rainband where the front bowed out. A model simulation conducted using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is examined to explain the distribution of precipitation associated with the cold-frontal rainband. The simulation reveals that the enhanced precipitation ice production and the implied mean ascent along the central part of the front were associated with a synergistic interaction between a low-level front and an upper-level front associated with an intrusion of high-PV stratospheric air. The low-level front contributed to an intense bow-shaped narrow cold-frontal rainband (NCFR). The upper-level front was dynamically active only along the central to northern portion of the NCFR, where the upper-level PV advection and Q-vector convergence were most prominent. The enhanced mean ascent associated with the upper-level front contributed to a wide cold-frontal rainband (WCFR) that trailed or overlapped with the NCFR along its central to northern segments. Because of the combination of the forcing from both lower- and upper-level fronts, the ascent was deepest and most intense along the central portion of the front. Thus, a large concentration of precipitation ice, attributed to both the NCFR and WCFR, was produced.

scholarly journals Wavelet Support Vector Machines for Forecasting Precipitation in Tropical Cyclones: Comparisons with GSVM, Regression, and MM5

2012 ◽  
Vol 27 (2) ◽  
pp. 438-450 ◽  
Author(s):  
Chih-Chiang Wei
Keyword(s):  
Statistical Models ◽  
Mesoscale Model ◽  
Gaussian Kernel ◽  
Support Vector ◽  
State University ◽  
Rainfall Prediction ◽  
Fifth Generation ◽  
Shihmen Reservoir ◽  
Reservoir Watershed ◽  
Lag Times

Abstract This study presents two support vector machine (SVM) based models for forecasting hourly precipitation during tropical cyclone (typhoon) events. The two SVM-based models are the traditional Gaussian kernel SVMs (GSVMs) and the advanced wavelet kernel SVMs (WSVMs). A comparison between the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) and statistical models, including SVM-based models and linear regressions (regression), was made in terms of performance of rainfall prediction at the Shihmen Reservoir watershed in Taiwan. Data from 73 typhoons affecting the Shihmen Reservoir watershed were included in the analysis. This study designed six attribute combinations with different lag times for the forecast target. The modified RMSE, bias, and estimated threat score (ETS) results were employed to assess the predicted outcomes. Results show that better attribute combinations for typhoon climatologic characteristics and typhoon precipitation predictions occurred at 0-h lag time with modified RMSE values of 0.288, 0.257, and 0.296 in GSVM, WSVM, and the regression, respectively. Moreover, WSVM having average bias and ETS values close to 1.0 gave better predictions than did the GSVM and regression models. In addition, Typhoons Zeb (1998) and Nari (2001) were selected for comparison between the MM5 model output and the developed statistical models. Results showed that the MM5 tended to overestimate the peak and cumulative rainfall amounts while the statistical models were inclined to yield underestimations.

scholarly journals Barotropic Regeneration of Upper-Level Synoptic Disturbances in Different Configurations of the Zonal Weather Regime

2008 ◽  
Vol 65 (10) ◽  
pp. 3159-3178 ◽  
Author(s):  
Gwendal Rivière
Keyword(s):  
Large Scale ◽  
Deformation Field ◽  
Regeneration Process ◽  
Barotropic Model ◽  
Weather Regime ◽  
The North ◽  
The Difference ◽  
Upper Level ◽  
Composite Maps ◽  
Large Scale Flow

Barotropic dynamics of upper-tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime (i.e., in different zonal-like large-scale flows) were studied using observational analyses and barotropic model experiments. The contraction stage of upper-level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text. This barotropic mechanism is studied through notions of barotropic critical regions (BtCRs) and effective deformation that have been introduced in a previous paper. The effective deformation field is equal to the difference between the square of the large-scale deformation magnitude and the square of the large-scale vorticity. Regions where the effective deformation is positive correspond to regions where the large-scale flow tends to strongly stretch synoptic disturbances. A BtCR is an area separating two large-scale regions of positive effective deformation, one located upstream and on the south side of the jet and the other downstream and on the north side. Such a region presents a discontinuity in the orientation of the dilatation axes and is a potential area where the barotropic regeneration process may occur. Winter days presenting a zonal weather regime in the 40-yr ECMWF Re-Analysis dataset are decomposed, via a partitioning algorithm, into different configurations of the effective deformation field at 300 hPa. A six-cluster partition is obtained. Composite maps of the barotropic generation rate for each cluster exhibit a succession of negative and positive values on both sides of the BtCRs. It confirms statistically that the barotropic regeneration mechanism occurs preferentially about BtCRs. Numerical experiments using a forced barotropic model on the sphere are performed. Each experiment consists of adding a synoptic-scale perturbation to one of the zonal-like jet configurations found in observations, which is kept fixed with time. The combined effects of the effective deformation and nonlinearities are shown to be crucial to reproduce the barotropic regeneration process about BtCRs.

scholarly journals Numerical Simulations of Seasonal Variations of Rainfall over the Island of Hawaii

2019 ◽  
Vol 58 (6) ◽  
pp. 1219-1232
Author(s):  
Yu-Fen Huang ◽  
Yi-Leng Chen
Keyword(s):  
Seasonal Variations ◽  
Mesoscale Model ◽  
Early Morning ◽  
State University ◽  
Pennsylvania State University ◽  
Reversed Flow ◽  
Trade Winds ◽  
Fifth Generation ◽  
Offshore Flow ◽  
Wake Zone

AbstractThe seasonal variations of rainfall over the island of Hawaii are studied using the archives of the daily model run from the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) from June 2004 to February 2010. Local effects mainly drive the rainfall on the Kona coast in the early morning and the lower slopes in the afternoon. During the summer, the incoming trade winds are more persistent and moister than in winter. The moisture content in the wake zone is higher than open-ocean values because of the convergent airflow associated with dual counterrotating vortices. As the westerly reversed flow moves toward the Kona coast, it decelerates with increasing moisture and a moisture maximum over the coastal area, especially in the afternoon hours in summer months. The higher afternoon rainfall on the Kona lower slopes in summer than in winter is caused by a moister (>6 mm) westerly reversed flow bringing moisture inland and merging with a stronger upslope flow resulting from solar heating. Higher nocturnal rainfall off the Kona coast in summer than in winter is caused by the low-level convergence between a moister westerly reversed flow and offshore flow. On the windward slopes, the simulated rainfall accumulation in winter is higher because of frequently occurring synoptic disturbances during the winter storm season. Nevertheless, early morning rainfall along the windward coast and afternoon rainfall over the windward slopes of the Kohala Mountains is lower in winter because the incoming trades are drier.

scholarly journals A High-Resolution Simulation of Typhoon Rananim (2004) with MM5. Part I: Model Verification, Inner-Core Shear, and Asymmetric Convection

2008 ◽  
Vol 136 (7) ◽  
pp. 2488-2506 ◽  
Author(s):  
Qingqing Li ◽  
Yihong Duan ◽  
Hui Yu ◽  
Gang Fu
Keyword(s):  
High Resolution ◽  
Inner Core ◽  
Mesoscale Model ◽  
Lower Troposphere ◽  
Model Verification ◽  
Vertical Shear ◽  
State University ◽  
Surface Winds ◽  
Fifth Generation ◽  
Divergence Pattern

Abstract In this study, the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Rananim (2004) at high resolution (2-km grid size). The simulation agrees well with a variety of observations, especially for intensification, maintenance, landfall, and inner-core structures, including the echo-free eye, the asymmetry in eyewall convection, and the slope of the eyewall during landfall. The asymmetric feature of surface winds is also captured reasonably well by the model, as well as changes in surface winds and pressure near the storm center. The shear-induced vortex tilt and storm-relative asymmetric winds are examined to investigate how vertical shear affects the asymmetric convection in the inner-core region. The inner-core vertical shear is found to be nonunidirectional, and to induce a nonunidirectional vortex tilt. The distribution of asymmetric convection is, however, inconsistent with the typical downshear-left pattern for a deep-layer shear. Qualitative agreement is found between the divergence pattern and the storm-relative flow, with convergence (divergence) generally associated with asymmetric inflow (outflow) in the eyewall. The collocation of the inflow-induced lower-level convergence in the boundary layer and the lower troposphere and the midlevel divergence causes shallow updrafts in the western and southern parts of the eyewall, while the deep and strong upward motion in the southeastern portion of the eyewall is due to the collocation of the net convergence associated with the strong asymmetric flow in the midtroposphere and the inflow near 400 hPa and its associated divergence in the outflow layer above 400 hPa.

The impacts of ENSO and PNA teleconnections on upper-level coupling to the Great Plains low-level jet

2020 ◽  
Author(s):  
D. Alex Burrows ◽  
Craig Ferguson ◽  
Shubhi Agrawal ◽  
Lance Bosart
Keyword(s):  
Great Plains ◽  
Large Scale ◽  
The United States ◽  
Jet Stream ◽  
Central Pacific ◽  
Frequency Distributions ◽  
Low Level ◽  
Enso Events ◽  
Low Level Jet ◽  
Upper Level

<p>The United States (U.S.) Great Plains southerly low-level jet (GPLLJ) is a ubiquitous feature of the summertime climatological flow in the central U.S. contributing to a large percentage of mean and extreme summertime rainfall, the generation of vast quantities of U.S. renewable wind energy, and severe weather outbreaks.  Like other LLJs across the globe, the GPLLJ can be 1) vertically coupled to the large-scale cyclone-anticyclone flow pattern associated with an upper-level jet stream or 2) uncoupled to the large-scale flow but sustained in response to various local land-atmosphere coupling mechanisms.  Many studies have focused on the interactions between teleconnection patterns and associated GPLLJ variability, treating the GPLLJ as a singular phenomenon.  Here, we treat the GPLLJ as two phenomena, coupled and uncoupled to the upper-level flow, and explore the multiscale impacts of SST forced and internally generated modes of variability on the GPLLJ.  With mounting evidence for the low-frequency control on higher frequency GPLLJ variability, the current study analyzes the contribution of the Pacific/North America (PNA) pattern on sub-seasonal timescales and ENSO on interannual timescales to changes in the frequency distributions of both coupled and uncoupled GPLLJs.</p><p> </p><p>This analysis utilizes 1) the Coupled ERA 20th Century (CERA-20C; 1901-2010) reanalysis from ECMWF which provides a large sample of teleconnection conditions and their impacts on GPLLJ variability and 2) a recently developed automated technique to differentiate those GPLLJs that are coupled or uncoupled to the upper-level flow.  Many studies have already shown that two distinct synoptic regimes dominate GPLLJ variability, a western U.S. trough and a central U.S. ridge.  This leads to changes in the frequency ratio of coupled and uncoupled GPLLJ events and ultimately in the location and intensity of precipitation across the GP.  Recently, Burrows et al. (2019) showed that during the Dust Bowl period of 1932-1938, the central and northern GP experienced anomalously high (low) uncoupled (coupled) GPLLJ event frequencies that coincided with a multi-year dry period across the entire region.  Understanding the upscale and lower frequency forcing patterns that lead to these distinct synoptic regimes would lead to greater predictability and forecasting skill.  On sub-seasonal timescales, it is shown that the negative phase of the PNA, which is associated with a southerly displaced Pacific jet stream and a western U.S. trough, leads to increases in the frequency of GPLLJs that are coupled to the upper-level flow, increases in Gulf of Mexico moisture flux and a redistribution of GP precipitation.  On interannual timescales, the location of ENSO events, i.e., eastern or central Pacific, is explored to determine the relationship between tropical forced variability and upper-level coupling to the GPLLJ.  In line with recent studies, it is hypothesized that central Pacific ENSO events may lead to increases in coupled GPLLJ events and precipitation, particularly in the southern GP.</p>

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