scholarly journals A Model Study of Gravity Waves over Hurricane Humberto (2001)

2008 ◽  
Vol 65 (10) ◽  
pp. 3231-3246 ◽  
Author(s):  
M. A. Kuester ◽  
M. J. Alexander ◽  
E. A. Ray
Keyword(s):  
Wavelet Analysis ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Weather Forecasting ◽  
Mesoscale Model ◽  
Deep Convection ◽  
State University ◽  
Fifth Generation ◽  
Model Study ◽  
Atmospheric Gravity

Atmospheric gravity waves are known to influence global circulations. Understanding these waves and their sources help to develop parameterizations that include their effects in climate and weather forecasting models. Deep convection is believed to be a major source for these waves and hurricanes may be particularly intense sources. Simulations of Hurricane Humberto (2001) are studied using the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5). Humberto is simulated at both tropical storm and hurricane stages. Fourier transform and wavelet analysis are employed to investigate wave characteristics and their behavior in the lower stratosphere. The Fourier analysis gives a regional view of storm affects, whereas wavelet analysis gives a local picture of isolated events. Analysis of the movement of convective sources and local winds gives further insight into the mechanisms that can cause gravity waves. Convectively generated gravity waves are observed in the lower stratosphere of this model with horizontal scales of 15–300 km, vertical scales of 4–8 km, and intrinsic periods of approximately 20–100 min.

scholarly journals Numerical Study of a Typhoon with a Large Eye: Model Simulation and Verification

2005 ◽  
Vol 133 (4) ◽  
pp. 725-742 ◽  
Author(s):  
Qing-Hong Zhang ◽  
Shou-Jun Chen ◽  
Ying-Hwa Kuo ◽  
Kai-Hon Lau ◽  
Richard A. Anthes
Keyword(s):  
Mesoscale Model ◽  
Model Simulation ◽  
Numerical Study ◽  
Deep Convection ◽  
Horizontal Wind ◽  
Mature Stage ◽  
State University ◽  
Convective Systems ◽  
Fifth Generation ◽  
Shallow Clouds

Typhoon Winnie (1997) was the fourth supertyphoon in the western North Pacific in 1997. In its mature stage, an outer eyewall, consisting of deep convection with a diameter of 370 km, was observed by satellite and radar. Within this unusually large outer eyewall existed an inner eyewall, which consisted of a ring of shallow clouds with a diameter of ∼50 km. In this study, Typhoon Winnie is simulated using a nested-grid version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with an inner grid length of 9 km. The model reproduces an outer cloud eyewall with a diameter of ∼350 km. The simulated radar reflectivity and hourly precipitation are verified with satellite microwave, infrared, and cloud brightness temperature images. Analysis of the model results indicates that the large outer eyewall in many ways possesses the structure of a typical hurricane eyewall. This includes strong tangential winds and radial inflow outside the eyewall as well as an extremely large horizontal wind shear right at the eyewall. The outer eyewall is characterized with a ring of high vorticity (RHV). This RHV is closely related to a ring of high convergence (RHC). This RHC is caused by organized convective systems along the eyewall. The eye simulated by Winnie is characterized by a broad region of warm, dry slowly sinking air. The factors determining the diameter of eyes in tropical cyclones are discussed by considering the scale of the environmental angular momentum and the maximum kinetic energy achieved by parcels of air originating in the environment and reaching the radius of maximum wind. It is hypothesized that the formation of a large eye is favored by large circulations in which parcels of air are drawn in toward the center of the storm from great distances, and trajectories of air in Winnie that support this hypothesis are shown.

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 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.

scholarly journals The Ability of MM5 to Simulate Ice Clouds: Systematic Comparison between Simulated and Measured Fluxes and Lidar/Radar Profiles at the SIRTA Atmospheric Observatory

2006 ◽  
Vol 134 (3) ◽  
pp. 897-918 ◽  
Author(s):  
M. Chiriaco ◽  
R. Vautard ◽  
H. Chepfer ◽  
M. Haeffelin ◽  
J. Dudhia ◽  
...  
Keyword(s):  
Mesoscale Model ◽  
Sedimentation Velocity ◽  
State University ◽  
Pennsylvania State University ◽  
Ice Clouds ◽  
Water Ice ◽  
Fifth Generation ◽  
Profile Inversion ◽  
Selection Of

Abstract The ability of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) to simulate midlatitude ice clouds is evaluated. Model outputs are compared to long-term meteorological measurements by active (radar and lidar) and passive (infrared and visible fluxes) remote sensing collected at an atmospheric observatory near Paris, France. The goal is to understand which of four microphysical schemes is best suited to simulate midlatitude ice clouds. The methodology consists of simulating instrument observables from the model outputs without any profile inversion, which allows the authors to use fewer assumptions on microphysical and optical properties of ice particles. Among the four schemes compared in the current study, the best observation-to-simulations scores are obtained with Reisner et al. provided that the particles’ sedimentation velocity from Heymsfield and Donner is used instead of that originally proposed. For this last scheme, the model gives results close to the measurements for clouds with medium optical depth of typically 1 to 3, whatever the season. In this configuration, MM5 simulates the presence of midlatitude ice clouds in more than 65% of the authors’ selection of observed cloud cases. In 35% of the cases, the simulated clouds are too persistent whatever the microphysical scheme and tend to produce too much solid water (ice and snow) and not enough liquid water.

scholarly journals High-Resolution Simulation of Hurricane Bonnie (1998). Part I: The Organization of Eyewall Vertical Motion

2006 ◽  
Vol 63 (1) ◽  
pp. 19-42 ◽  
Author(s):  
Scott A. Braun ◽  
Michael T. Montgomery ◽  
Zhaoxia Pu
Keyword(s):  
High Resolution ◽  
Mesoscale Model ◽  
Dynamic Balance ◽  
Vertical Wind Shear ◽  
Vertical Motion ◽  
State University ◽  
Upward Motion ◽  
Pennsylvania State University ◽  
Fifth Generation ◽  
Hurricane Bonnie

Abstract The fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) is used to simulate Hurricane Bonnie at high resolution (2-km spacing) in order to examine how vertical wind shear impacts the distribution of vertical motion in the eyewall on both the storm and cloud scale. As in many previous studies, it is found here that the shear produces a wavenumber-1 asymmetry in the time-averaged vertical motion and rainfall. Several mechanisms for this asymmetry are evaluated. The vertical motion asymmetry is qualitatively consistent with an assumed balance between horizontal vorticity advection by the relative flow and stretching of vorticity, with relative asymmetric inflow (convergence) at low levels and outflow (divergence) at upper levels on the downshear side of the eyewall. The simulation results also show that the upward motion portion of the eyewall asymmetry is located in the direction of vortex tilt, consistent with the vertical motion that required to maintain dynamic balance. Variations in the direction and magnitude of the tilt are consistent with the presence of a vortex Rossby wave quasi mode, which is characterized by a damped precession of the upper vortex relative to the lower vortex. While the time-averaged vertical motion is characterized by ascent in a shear-induced wavenumber-1 asymmetry, the instantaneous vertical motion is typically associated with deep updraft towers that generally form on the downtilt-right side of the eyewall and dissipate on the downtilt-left side. The updrafts towers are typically associated with eyewall mesovortices rotating cyclonically around the eyewall and result from an interaction between the shear-induced relative asymmetric flow and the cyclonic circulations of the mesovortices. The eyewall mesovortices may persist for more than one orbit around the eyewall and, in these cases, can initiate multiple episodes of upward motion.

scholarly journals Observations of atmospheric gravity waves using airglow all-sky CCD imager at Cachoeira Paulista, Brazil (23° S, 45° W)

2004 ◽  
Vol 43 (1) ◽  
pp. 29-39
Author(s):  
A. F. Medeiros ◽  
H. Takahashi ◽  
P. P. Batista ◽  
D. Gobbi ◽  
M. J. Taylor
Keyword(s):  
Gravity Waves ◽  
State University ◽  
Utah State University ◽  
Atmospheric Gravity Waves ◽  
Atmospheric Gravity

Un fotómetro imageador CCD all-sky fue operado en Cachoeira Paulista (CP), Brasil (23° S, 45° O), con la colaboración de la Utah State University - EUA, durante 12 meses para la observación de las emisiones de aeroluminiscencia en OH, O2 y OI (557.7 nm). De estas observaciones fueron retiradas las componentes dominantes de las ondas de gravedad e investigadas sus variaciones con las estaciones del año. Estas ondas tienen típicamente longitud de onda horizontal corta (5 - 60 km), período corto (5 - 35 minutes) y velocidad de fase horizontal entre 1 y 80 m/s. Las ondas del tipo banda (longitud de onda horizontal entre 10 y 60 km), muestran una clara dependencia en su dirección de propagación horizontal, moviéndose para el sudeste en el verano y para el noroeste en el invierno. La dirección de propagación cambia a mediados del mes de marzo y al final de septiembre. Nuestros resultados sugieren que las ondas de gravedad en CP son generadas por una fuerte convección troposférica. En el verano esta región se extiende en una linea entre los 10° S, 45° O y 40° S, 78° O cubriendo desde la parte septentrional de la Argentina al nordeste del Brasil, teniendo una acentuada distribuición en la parte central brasileña y siendo que CP está abajo de esta región. En el invierno y en contraste con el verano, la región convectiva se localiza abajo de CP, principalmente sobre el mar, sin esta convección en la región central del Brasil, arriba de CP. La conclusión más importante es que la anisotropía en la dirección de propagación de las ondas se debe principalmente a la localización de la fuente y su filtraje por los vientos estratosféricos.

scholarly journals Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki

2005 ◽  
Vol 23 (10) ◽  
pp. 3237-3260 ◽  
Author(s):  
I. V. Subba Reddy ◽  
D. Narayana Rao ◽  
A. Narendra Babu ◽  
M. Venkat Ratnam ◽  
P. Kishore ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Wave Length ◽  
Wave Activity ◽  
Lower Atmosphere ◽  
Wind Fields ◽  
Atmospheric Gravity Wave ◽  
Short Period ◽  
Atmospheric Gravity

Abstract. MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.

scholarly journals Objective Bias Correction for Improved Skill in Forecasting Diurnal Cycles of Temperature over Multiple Locations: The Summer Case

2011 ◽  
Vol 26 (1) ◽  
pp. 26-43 ◽  
Author(s):  
P. Goswami ◽  
S. Mallick
Keyword(s):  
Bias Correction ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Numerical Models ◽  
State University ◽  
Pennsylvania State University ◽  
Diurnal Cycles ◽  
Fifth Generation ◽  
Comprehensive Development ◽  
Environmental Prediction

Abstract One factor that limits skill of the numerical models is the bias in the model forecasts with respect to observations. Similarly, while the mesoscale models today can support horizontal grid spacing down to a few kilometers or fewer, downscaling of model forecasts to arrive at station-scale values will remain a necessary step for many applications. While generic improvement in model skill requires parallel and comprehensive development in model and other forecast methodology, one way of achieving skill in station-scale forecasts without (intensive effort) calibration of the model is to implement an objective bias correction (referred to as debiasing). This study shows that a nonlinear objective debiasing can transform zero-skill forecasts from a mesoscale model [fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5)] to forecasts with significant skill. Twelve locations over India, representing urban sites in different geographical conditions, during May–August 2009 were considered. The model MM5 was integrated for 24 h with initial conditions from the National Centers for Environmental Prediction Global Forecast System (final) global gridded analysis (FNL) for each of the days of May–August 2009 in a completely operational setting (without assuming any observed information on dynamics beyond the time of the initial condition). It is shown that for all the locations and the four months, the skill of the debiased forecast is significant against essentially zero skill of raw forecasts. The procedure provides an applicable forecast strategy to attain realizable significant skill in station-scale forecasts. Potential skill, derived using in-sample data for calibrating the debiasing parameters, shows promise of further improvement with large samples.

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