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 Evaluation of Interregional Transport Using the MM5–SCIPUFF System

2004 ◽  
Vol 43 (12) ◽  
pp. 1864-1886 ◽  
Author(s):  
Aijun Deng ◽  
Nelson L. Seaman ◽  
Glenn K. Hunter ◽  
David R. Stauffer
Keyword(s):  
Mesoscale Model ◽  
Numerical Models ◽  
Dispersion Model ◽  
Three Dimensional ◽  
Tracer Experiment ◽  
Plume Dispersion ◽  
State University ◽  
Wind Fields ◽  
The Impact ◽  
Horizontal Grid

Abstract Improved understanding of transport issues and source–receptor relationships on the interregional scale is dependent on reducing the uncertainties in the ability to define complex three-dimensional wind fields evolving in time. The numerical models used for this purpose have been upgraded substantially in recent years by introducing finer grid resolution, better representation of subgrid-scale physics, and practical four-dimensional data assimilation (FDDA) techniques that reduce the accumulation of errors over time. The impact of these improvements for interregional transport is investigated in this paper using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) and the Second-Order Closure Integrated Puff (SCIPUFF) dispersion model to simulate the 1983 Cross-Appalachian Tracer Experiment (CAPTEX-83) episode 1 of 18–19 September 1983. Combining MM5 and SCIPUFF makes it possible to verify predicted tracer concentrations against observed surface concentrations collected during the CAPTEX-83 study. Conclusions from this study are as follows. 1) Not surprisingly, a baseline model configuration reflecting typical capabilities of the late 1980s (70-km horizontal grid, 15 vertical layers, older subgrid physics, and no FDDA) produced large meteorological errors that severely degraded the accuracy of the surface tracer concentrations predicted by SCIPUFF. 2) Improving the horizontal and vertical resolution of the MM5 to 12 km (typical for current operational model) and 32 layers led to some improvements in the statistical skill, but the further addition of more advanced physics produced much greater reductions of simulation errors. 3) The use of FDDA, along with 12-km resolution and improved physics, produced the overall best performance. 4) Further reduction of the horizontal grid size to 4 km had a detrimental effect on meteorological and plume-dispersion solutions in this case because of misrepresentation of convection associated with a cold front by the MM5's explicit moist physics.

Warm Cores, Eyewall Slopes, and Intensities of Tropical Cyclones Simulated by a 7-km-Mesh Global Nonhydrostatic Model

2016 ◽  
Vol 73 (11) ◽  
pp. 4289-4309 ◽  
Author(s):  
Tomoki Ohno ◽  
Masaki Satoh ◽  
Yohei Yamada
Keyword(s):  
Tropical Cyclones ◽  
Inner Core ◽  
Grid Spacing ◽  
Satellite Measurements ◽  
Warm Core ◽  
Nonhydrostatic Model ◽  
Proposed Model ◽  
Tangential Wind ◽  
Balanced Model ◽  
Horizontal Grid

Abstract Based on the data of a 1-yr simulation by a global nonhydrostatic model with 7-km horizontal grid spacing, the relationships among warm-core structures, eyewall slopes, and the intensities of tropical cyclones (TCs) were investigated. The results showed that stronger TCs generally have warm-core maxima at higher levels as their intensities increase. It was also found that the height of a warm-core maximum ascends (descends) as the TC intensifies (decays). To clarify how the height and amplitude of warm-core maxima are related to TC intensity, the vortex structures of TCs were investigated. By gradually introducing simplifications of the thermal wind balance, it was established that warm-core structures can be reconstructed using only the tangential wind field within the inner-core region and the ambient temperature profile. A relationship between TC intensity and eyewall slope was investigated by introducing a parameter that characterizes the shape of eyewalls and can be evaluated from satellite measurements. The authors found that the eyewall slope becomes steeper (shallower) as the TC intensity increases (decreases). Based on a balanced model, the authors proposed a relationship between TC intensity and eyewall slope. The result of the proposed model is consistent with that of the analysis using the simulation data. Furthermore, for sufficiently strong TCs, the authors found that the height of the warm-core maximum increases as the slope becomes steeper, which is consistent with previous observational studies. These results suggest that eyewall slopes can be used to diagnose the intensities and structures of TCs.

scholarly journals Parameterizing the impact of vegetated urban canopies on wind and temperature fields by using a simple nudging method

2021 ◽  
Author(s):  
Ge Cheng ◽  
David Grawe ◽  
K. Heinke Schlünzen
Keyword(s):  
Mesoscale Model ◽  
Three Dimensional ◽  
Urban Canopy ◽  
Temperature Fields ◽  
Simple Method ◽  
Local Climate ◽  
Local Climate Zones ◽  
Urban Canopy Parameterizations ◽  
The Impact ◽  
Nudging Method

<p>Nudging is a simple method that aims to dynamically adjust the model toward the observations by including an additional feedback term in the model governing equation. This method is widely applied in data assimilation due to its simple implementation and reasonable model results. The basic concept of nudging is similar to that of urban canopy parameterization, in which additional terms are usually added in the conservation equations of momentum and energy aiming to simulate the canopy effects. However, few studies have investigated the implementation of nudging methods in urban canopy parameterizations. In this study we developed a multi-layer urban canopy parameterization (UCP) by using a nudging approach to represent the impacts of vegetated urban canopies on temperatures and winds in mesoscale models.</p><p>The difficulty of developing UCP by using a nudging method lies in defining appropriate values for the nudging coefficients and the forcing fields (e.g. indoor temperature fields for temperature nudging). To determine nudging coefficients, we use three major urban canopy morphological parameters: building height, frontal area density and building density. The ranges of these parameters are taken from the values for the Local Climate Zones datasets, in our case for the city of Hamburg. The UCP is employed in the three -dimensional atmospheric mesoscale model METRAS. Results show that this UCP can well simulate wind-blocking effects induced from obstacles as buildings and trees and urban heat island phenomenon for cities. Thus, nudging is an efficient and effective method that can be used for urban canopy parameterizations. However, as well known for nudging, it is not conserving energy. Therefore, we investigated the energy loss by tracking the reduced kinetic energy and internal energy. The UCP and model results will be presented.</p>

The Impact of Horizontal Grid Spacing on the Microphysical and Kinematic Structures of Strong Tropical Cyclones Simulated with the WRF-ARW Model

2009 ◽  
Vol 137 (11) ◽  
pp. 3717-3743 ◽  
Author(s):  
Alexandre O. Fierro ◽  
Robert F. Rogers ◽  
Frank D. Marks ◽  
David S. Nolan
Keyword(s):  
Mass Flux ◽  
High Surface ◽  
Surface Fluxes ◽  
Small Range ◽  
Grid Spacing ◽  
Arw Model ◽  
Parent Domain ◽  
Model Features ◽  
The Impact ◽  
Horizontal Grid

Abstract Using the Advanced Weather Research and Forecasting numerical model, the impact of horizontal grid spacing on the microphysical and kinematic structure of a numerically simulated tropical cyclone (TC), and their relationship to storm intensity was investigated with a set of five numerical simulations using input data for the case of Hurricane Rita (2005). The horizontal grid spacing of the parent domain was systematically changed such that the horizontal grid spacing of the inner nest varied from 1 to 5 km by an increment of 1 km, this while keeping geographical dimensions of the domains identical. Within this small range of horizontal grid spacing, the morphology of the simulated storms and the evolution of the kinematic and microphysics field showed noteworthy differences. As grid spacing increased, the model produced a wider, more tilted eyewall, a larger radius of maximum winds, and higher-amplitude, low wavenumber eyewall asymmetries. The coarser-resolution simulations also produced larger volume, areal coverage, and mass flux of updraft speeds ≥5 m s−1; larger volumes of condensate and ice-phase particles aloft; larger boundary layer kinetic energy; and a stronger secondary circulation. While the contribution of updrafts ≥5 m s−1 to the total updraft mass flux varied little between the five cases, the contribution of downdrafts ≤−2 m s−1 to the total downdraft mass flux was by far the largest in the finest-resolution simulation. Despite these structural differences, all of the simulations produced storms of similar intensity, as measured by peak 10-m wind speed and minimum surface pressure, suggesting that features in the higher-resolution simulations that tend to weaken TCs (i.e., smaller area of high surface fluxes and weaker total updraft mass flux) compensate for features that favor TC intensity (i.e., smaller-amplitude eyewall asymmetries and larger radial gradients). This raises the possibility that resolution increases in this range may not be as important as other model features (e.g., physical parameterization and initial condition improvements) for improving TC intensity forecasts.

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.

Evaluation of the Impact of Horizontal Grid Spacing in Terra Incognita on Coupled Mesoscale–Microscale Simulations Using the WRF Framework

2019 ◽  
Vol 147 (3) ◽  
pp. 1007-1027 ◽  
Author(s):  
Raj K. Rai ◽  
Larry K. Berg ◽  
Branko Kosović ◽  
Sue Ellen Haupt ◽  
Jeffrey D. Mirocha ◽  
...  
Keyword(s):  
Spatial Scales ◽  
Wrf Model ◽  
Spectral Energy ◽  
Grid Spacing ◽  
Terra Incognita ◽  
Wide Range ◽  
Large Eddy ◽  
Microscale Simulations ◽  
The Impact ◽  
Horizontal Grid

Abstract Coupled mesoscale–microscale simulations are required to provide time-varying weather-dependent inflow and forcing for large-eddy simulations under general flow conditions. Such coupling necessarily spans a wide range of spatial scales (i.e., ~10 m to ~10 km). Herein, we use simulations that involve multiple nested domains with horizontal grid spacings in the terra incognita (i.e., km) that may affect simulated conditions in both the outer and inner domains. We examine the impact on simulated wind speed and turbulence associated with forcing provided by a terrain with grid spacing in the terra incognita. We perform a suite of simulations that use combinations of varying horizontal grid spacings and turbulence parameterization/modeling using the Weather Research and Forecasting (WRF) Model using a combination of planetary boundary layer (PBL) and large-eddy simulation subgrid-scale (LES-SGS) models. The results are analyzed in terms of spectral energy, turbulence kinetic energy, and proper orthogonal decomposition (POD) energy. The results show that the output from the microscale domain depends on the type of turbulence model (e.g., PBL or LES-SGS model) used for a given horizontal grid spacing but is independent of the horizontal grid spacing and turbulence modeling of the parent domain. Simulation using a single domain produced less POD energy in the first few modes compared to a coupled simulation (one-way nesting) for similar horizontal grid spacing, which highlights that coupled simulations are required to accurately pass the mesoscale features into the microscale domain.

scholarly journals On the Relative Contribution of Inertia–Gravity Wave Radiation to Asymmetric Instabilities in Tropical Cyclone–like Vortices

2016 ◽  
Vol 73 (9) ◽  
pp. 3345-3370 ◽  
Author(s):  
Konstantinos Menelaou ◽  
David A. Schecter ◽  
M. K. Yau
Keyword(s):  
Tropical Cyclone ◽  
Gravity Wave ◽  
Tropical Cyclones ◽  
Potential Vorticity ◽  
Three Dimensional ◽  
Life Cycles ◽  
Wave Radiation ◽  
Ambient Conditions ◽  
Layer Potential ◽  
The Impact

Abstract Intense atmospheric vortices such as tropical cyclones experience various asymmetric instabilities during their life cycles. This study investigates how vortex properties and ambient conditions determine the relative importance of different mechanisms that can simultaneously influence the growth of an asymmetric perturbation. The focus is on three-dimensional disturbances of barotropic vortices with nonmonotonic radial distributions of potential vorticity. The primary modes of instability are examined for Rossby numbers between 10 and 100 and Froude numbers in the broad neighborhood of unity. This parameter regime is deemed appropriate for tropical cyclone perturbations with vertical length scales ranging from the depth of the vortex to moderately smaller scales. At relatively small Froude numbers, the main cause of instability inferred from analysis typically involves the interaction of vortex Rossby waves with each other and/or critical-layer potential vorticity perturbations. As the Froude number increases from its lower bound, the main cause of instability transitions to inertia–gravity wave radiation. In some cases, the transition occurs abruptly at a critical point where a mode whose growth is driven almost entirely by radiation suddenly becomes dominant. In other cases, the transition is gradual and less direct as the fastest-growing mode continuously changes its structure. Examination of the angular pseudomomentum budget helps quantify the impact of radiation. The radiation-driven instabilities examined herein are shown to be quite fast and potentially relevant to real-world tropical cyclones. Their sensitivities to parameterized moisture and outer vorticity skirts are briefly addressed.

The Impact of Assimilating SSM/I and QuikSCAT Satellite Winds on Hurricane Isidore Simulations

2007 ◽  
Vol 135 (2) ◽  
pp. 549-566 ◽  
Author(s):  
Shu-Hua Chen
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Mesoscale Model ◽  
Three Dimensional ◽  
Storm Track ◽  
Initial Position ◽  
Wind Speeds ◽  
The Impact ◽  
Quikscat Winds

Abstract Three observational datasets of Hurricane Isidore (in 2002) were analyzed and compared: the Special Sensor Microwave Imager (SSM/I), the Quick Scatterometer (QuikSCAT) winds, and dropsonde winds. SSM/I and QuikSCAT winds were on average about 1.9 and 0.3 m s−1 stronger, respectively, than dropsonde winds. With more than 20 000 points of data, SSM/I wind speed was about 2.2 m s−1 stronger than QuikSCAT. Comparison of the wind direction observed by QuikSCAT with those from the dropsondes showed that the quality of QuikSCAT data is good. The effect of assimilating SSM/I wind speeds and/or QuikSCAT wind vectors for the analysis of Hurricane Isidore was assessed using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) and its three-dimensional variational data assimilation system. For the Hurricane Isidore case study, it was found that the assimilation of either satellite winds strengthened the cyclonic circulation in the analysis. However, the increment of the QuikSCAT wind analysis is more complicated than that from the SSM/I analysis due to the correction of the storm location, a positive result from the assimilation of wind vectors. The increase in low-level wind speeds enhanced the air–sea interaction processes and improved the simulated intensity for Isidore. In addition, the storm structure was better simulated. Assimilation of QuikSCAT wind vectors clearly improved simulation of the storm track, in particular during the later period of the simulation, but lack of information about the wind direction from SSM/I data prevented it from having much of an effect. Assessing the assimilation of QuikSCAT wind speed versus wind vector data confirmed this hypothesis. The track improvement partially resulted from the relocation of the storm’s initial position after assimilation of the wind vectors. For this case study, it was found that the assimilation of SSM/I or QuikSCAT data had the greatest impact on the Hurricane Isidore simulation during the first 2 days.

scholarly journals Improving Large-Domain Convection-Allowing Forecasts with High-Resolution Analyses and Ensemble Data Assimilation

2016 ◽  
Vol 144 (5) ◽  
pp. 1777-1803 ◽  
Author(s):  
Craig S. Schwartz
Keyword(s):  
Data Assimilation ◽  
Three Dimensional ◽  
Weather Research And Forecasting ◽  
Analysis Method ◽  
Grid Spacing ◽  
Background Error ◽  
Ensemble Data Assimilation ◽  
Ensemble Data ◽  
Horizontal Length ◽  
Horizontal Grid

Analyses with 20-km horizontal grid spacing were produced from continuously cycling three-dimensional variational (3DVAR), ensemble square root Kalman filter (EnSRF), and “hybrid” variational–ensemble data assimilation (DA) systems over a domain spanning the conterminous United States. These analyses initialized 36-h Weather Research and Forecasting Model forecasts containing a large convection-allowing 4-km nested domain, where downscaled 20-km 3DVAR, EnSRF, and hybrid analyses initialized the 4-km forecasts. Overall, hybrid analyses initialized the best 4-km precipitation forecasts. Furthermore, whether 4-km precipitation forecasts could be improved by initializing them with true 4-km analyses was assessed. As it was computationally infeasible to produce 4-km continuously cycling ensembles over the large 4-km domain, several “dual-resolution” hybrid DA configurations were adopted where 4-km backgrounds were combined with 20-km ensembles to produce 4-km hybrid analyses. Additionally, 4-km 3DVAR analyses were produced. In both hybrid and 3DVAR frameworks, initializing 4-km forecasts with true 4-km analyses, rather than downscaled 20-km analyses, yielded superior precipitation forecasts over the first 12 h. Differences between forecasts initialized from 4-km and downscaled 20-km hybrid analyses were smaller for 18–36-h forecasts, but there were occasionally meaningful differences. Continuously cycling the 4-km backgrounds and using static background error covariances with larger horizontal length scales in the hybrid led to better forecasts. All hybrid-initialized forecasts, including those initialized from downscaled 20-km analyses, were more skillful than forecasts initialized from 4-km 3DVAR analyses, suggesting the analysis method was more important than analysis resolution.

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