A Numerical Study of Typhoon Megi (2010). Part II: Eyewall Evolution Crossing the Luzon Island

2020 ◽  
Author(s):  
Hui Wang ◽  
Yuqing Wang
Keyword(s):  
Control Experiment ◽  
Numerical Study ◽  
Wrf Model ◽  
Surface Friction ◽  
Weather Research And Forecasting ◽  
Sensitivity Experiment ◽  
Structure Changes ◽  
Surface Enthalpy ◽  
Spiral Rainbands ◽  
Reduced Surface

AbstractTyphoon Megi (2010) experienced drastic eyewall structure changes when it crossed the Luzon Island and entered the South China Sea (SCS), including the contraction and breakdown of the eyewall after landfall over the Luzon Island, the formation of a new large outer eyewall accompanied by re-intensification of the storm after it entered the SCS, and the appearance of a short-lived small inner eyewall. These features were reproduced reasonably well in a control simulation using the Advanced Weather Research and Forecasting (ARW–WRF) model. In this study, the eyewall processes of the simulated Megi during and after landfall have been analyzed.Results show that the presence of the landmass of Luzon Island increased surface friction and reduced surface enthalpy flux, leading to the original eyewall to contract and break down and the weakening of the storm. The formation of the new large eyewall results mainly from the axisymmetrization of outer spiral rainbands after the storm core moved across the Luzon Island and entered the SCS. The appearance of the small inner eyewall over the SCS was due to the increased surface enthalpy flux and the revival of convection in the central region of the storm core. In a sensitivity experiment with the mesoscale-mountain replaced by flat surface over the Luzon Island, a new large outer eyewall formed over the western Luzon Island with its size about one third smaller after the storm entered the SCS than that in the control experiment with the terrain over the Luzon Island unchanged.

Numerical Study of the 6 May 2012 Tsukuba Supercell Tornado: Vorticity Sources Responsible for Tornadogenesis

2020 ◽  
Vol 148 (3) ◽  
pp. 1205-1228 ◽  
Author(s):  
Tao Tao ◽  
Tetsuro Tamura
Keyword(s):  
Numerical Study ◽  
Wrf Model ◽  
Surface Friction ◽  
Weather Research And Forecasting ◽  
Streamwise Vorticity ◽  
Grid Spacing ◽  
Low Level ◽  
Vorticity Source ◽  
Horizontal Grid ◽  
Remarkable Progress

Abstract Remarkable progress has been achieved in understanding the vorticity source responsible for tornadogenesis. Nevertheless, the answer to this question remains elusive, particularly after introducing surface friction in realistic tornado simulations. In this study, a simulation using the Weather Research and Forecasting (WRF) Model is conducted based on the F3 supercell tornado that hit Tsukuba City, Japan, on 6 May 2012. The simulation uses triply nested domains, and the tornado is successfully reproduced in the innermost domain with 50-m horizontal grid spacing. The circulation analyses reveal that the frictional term is the dominant vorticity source responsible for the vortices at both the pretornadic and tornadogenesis times. The detailed vorticity source analyses of the air parcels show that the vorticity of the tornado at the genesis time mainly originates from the frictionally generated crosswise vorticity near the ground. The crosswise vorticity is directly tilted (or first exchanged into streamwise vorticity and then tilted) into vertical vorticity when the air parcels enter the tornado. A rear-flank downdraft (RFD) surge from the south and west sides of a primary low-level mesocyclone (LMC) may trigger tornadogenesis by increasing the convergence near the ground. The RFD surge is not necessarily associated with the baroclinically generated vorticity. In this study, the baroclinity is weak across the hook echo, which may cause a lack of baroclinically generated vorticity in the RFD surge.

Comparison of Two-Moment Bulk Microphysics Schemes in Idealized Supercell Thunderstorm Simulations

2011 ◽  
Vol 139 (4) ◽  
pp. 1103-1130 ◽  
Author(s):  
Hugh Morrison ◽  
Jason Milbrandt
Keyword(s):  
Three Dimensional ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Cold Pool ◽  
Fall Velocity ◽  
Surface Precipitation ◽  
Single Category ◽  
Supercell Thunderstorm ◽  
Drop Size Distributions ◽  
Reduced Surface

Idealized three-dimensional supercell simulations were performed using the two-moment bulk microphysics schemes of Morrison and Milbrandt–Yau in the Weather Research and Forecasting (WRF) model. Despite general similarities in these schemes, the simulations were found to produce distinct differences in storm structure, precipitation, and cold pool strength. In particular, the Morrison scheme produced much higher surface precipitation rates and a stronger cold pool, especially in the early stages of storm development. A series of sensitivity experiments was conducted to identify the primary differences between the two schemes that resulted in the large discrepancies in the simulations. Different approaches in treating graupel and hail were found to be responsible for many of the key differences between the baseline simulations. The inclusion of hail in the baseline simulation using the Milbrant–Yau scheme with two rimed-ice categories (graupel and hail) had little impact, and therefore resulted in a much different storm than the baseline run with the single-category (hail) Morrison scheme. With graupel as the choice of the single rimed-ice category, the simulated storms had considerably more frozen condensate in the anvil region, a weaker cold pool, and reduced surface precipitation compared to the runs with only hail, whose higher terminal fall velocity inhibited lofting. The cold pool strength was also found to be sensitive to the parameterization of raindrop breakup, particularly for the Morrison scheme, because of the effects on the drop size distributions and the corresponding evaporative cooling rates. The use of a more aggressive implicit treatment of drop breakup in the baseline Morrison scheme, by limiting the mean–mass raindrop diameter to a maximum of 0.9 mm, opposed the tendency of this scheme to otherwise produce large mean drop sizes and a weaker cold pool compared to the hail-only run using the Milbrandt–Yau scheme.

scholarly journals A Numerical Study of the Track Deflection of Supertyphoon Haitang (2005) Prior to Its Landfall in Taiwan

2008 ◽  
Vol 136 (2) ◽  
pp. 598-615 ◽  
Author(s):  
Guo-Ji Jian ◽  
Chun-Chieh Wu
Keyword(s):  
Control Experiment ◽  
Inner Core ◽  
Numerical Study ◽  
Sensitivity Study ◽  
Weather Research And Forecasting ◽  
Translation Speed ◽  
Fine Mesh ◽  
Steering Flow ◽  
Moving Storm ◽  
Channeling Effect

Abstract A series of numerical simulations are conducted using the advanced research version of the Weather Research and Forecasting model with a 4-km fine mesh to examine the physical processes responsible for the significant track deflection and looping motion before the landfall of Supertyphoon Haitang (2005) in Taiwan, which poses a unique scientific and forecasting issue. In the control experiment, a low-level northerly jet induced by the channeling effect forms in the western quadrant of the approaching storm, where the inner-core circulation is constrained by the presence of Taiwan’s terrain. Because of the channeling effect, the strongest winds of the storm are shifted to the western portion of the eyewall. The northerly advection flow (averaged asymmetric winds within 100-km radius) results in a sharp southward turn of the westward-moving storm. The time series of the advection flow shows that the advection wind vectors rotate cyclonically in time and well match the motion of the simulated vortex during the looping process. A sensitivity study of lowering the Taiwan terrain elevations to 70% or 40% of those in the control experiment reduces the southward track deflection and loop amplitude. The experiment with the reduced elevation to 10% of the control experiment does not show a looping track and thus demonstrates the key role of the terrain-induced channeling effect. Experiments applying different values of the structure parameter α illustrate that increasing the strength, size, and translation speed of the initial storm results in a smaller interaction with Taiwan’s terrain and a smaller average steering flow caused by the asymmetric circulation, which leads to a proportionally smaller southward track deflection without making a loop.

scholarly journals Horizontal divergence of typhoon-generated gravity waves in the upper troposphere and lower stratosphere (UTLS) and its influence on typhoon evolution

2014 ◽  
Vol 14 (7) ◽  
pp. 3175-3182 ◽  
Author(s):  
S. H. Kim ◽  
H.-Y. Chun ◽  
W. Jang
Keyword(s):  
Gravity Waves ◽  
Lower Stratosphere ◽  
Inner Core ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Sea Level Pressure ◽  
Upper Troposphere ◽  
Convective Clouds ◽  
Power Spectral ◽  
Spiral Rainbands

Abstract. The characteristics of horizontal divergence induced by typhoon-generated gravity waves (HDTGWs) and the influence of HDTGW on typhoon evolution are investigated based on the simulation results of Typhoon Saomai (2006) using the Weather Research and Forecasting (WRF) model. The power spectral density of HDTGW shows dominant powers at horizontal wavelengths of 20–30 km and at periods of less than 1 h. This is associated with gravity waves generated by vigorous convective clouds in an inner core region of the typhoon. However, the domain-averaged HDTGW in the upper troposphere and lower stratosphere had a spectral peak at 24 h, which is well correlated with the minimum sea-level pressure of the typhoon, especially during a rapidly developing period. The 24 h period of the averaged HDTGW stems from the inertia–gravity waves generated by the convective clouds in the spiral rainbands, and showed no clear association with the thermal tides or the diurnal variation of precipitation.

scholarly journals Horizontal divergence of typhoon-generated gravity waves in the upper troposphere and lower stratosphere (UTLS) and its influence on typhoon evolution

2013 ◽  
Vol 13 (11) ◽  
pp. 28953-28972
Author(s):  
S. H. Kim ◽  
H.-Y. Chun ◽  
W. Jang
Keyword(s):  
Gravity Waves ◽  
Lower Stratosphere ◽  
Inner Core ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Sea Level Pressure ◽  
Upper Troposphere ◽  
Convective Clouds ◽  
Power Spectral ◽  
Spiral Rainbands

Abstract. The characteristics of horizontal divergence induced by typhoon-generated gravity waves (HDTGW) and the influence of HDTGW on typhoon evolution are investigated based on the simulation results of Typhoon Saomai (2006) using the Weather Research and Forecasting (WRF) model. The power spectral density of HDTGW shows dominant powers at horizontal wavelengths of 20–30 km and at periods of less than one hour. This is associated with gravity waves generated by vigorous convective clouds in an inner core region of the typhoon. However, the domain-averaged HDTGW in the upper troposphere and lower stratosphere had a spectral peak at 24 h, which is well correlated with the minimum sea-level pressure of the typhoon, especially during a rapidly developing period. The 24 h period of the averaged HDTGW stems from the inertia-gravity waves generated by the convective clouds in the spiral rainbands, and showed no clear association with the thermal tides or the diurnal variation of precipitation.

scholarly journals Dynamics and Predictability of Hurricane Nadine (2012) Evaluated through Convection-Permitting Ensemble Analysis and Forecasts

2015 ◽  
Vol 143 (11) ◽  
pp. 4514-4532 ◽  
Author(s):  
Erin B. Munsell ◽  
Jason A. Sippel ◽  
Scott A. Braun ◽  
Yonghui Weng ◽  
Fuqing Zhang
Keyword(s):  
Ensemble Kalman Filter ◽  
Regional Scale ◽  
Wrf Model ◽  
Heat Fluxes ◽  
Sensitivity Analyses ◽  
Weather Research And Forecasting ◽  
Sensitivity Experiment ◽  
Steering Flow ◽  
General Success ◽  
Initial Intensity

Abstract The governing dynamics and uncertainties of an ensemble simulation of Hurricane Nadine (2012) are assessed through the use of a regional-scale convection-permitting analysis and forecast system based on the Weather Research and Forecasting (WRF) Model and an ensemble Kalman filter (EnKF). For this case, the data that are utilized were collected during the 2012 phase of the National Aeronautics and Space Administration’s (NASA) Hurricane and Severe Storm Sentinel (HS3) experiment. The majority of the tracks of this ensemble were successful, correctly predicting Nadine’s turn toward the southwest ahead of an approaching midlatitude trough, though 10 members forecasted Nadine to be carried eastward by the trough. Ensemble composite and sensitivity analyses reveal the track divergence to be caused by differences in the environmental steering flow that resulted from uncertainties associated with the position and subsequent strength of a midlatitude trough. Despite the general success of the ensemble track forecasts, the intensity forecasts indicated that Nadine would strengthen, which did not happen. A sensitivity experiment performed with the inclusion of sea surface temperature (SST) updates significantly reduced the intensity errors associated with the simulation. This weakening occurred as a result of cooling of the SST field in the vicinity of Nadine, which led to weaker surface sensible and latent heat fluxes at the air–sea interface. A comparison of environmental variables, including relative humidity, temperature, and shear yielded no obvious differences between the WRF-EnKF simulations and the HS3 observations. However, an initial intensity bias in which the WRF-EnKF vortices are stronger than the observed vortex appears to be the most likely cause of the final intensity errors.

scholarly journals Numerical Study of the Impact of Complex Terrain and Soil Moisture on Convective Initiation

Atmosphere ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 871
Author(s):  
Beilei Zan ◽  
Ye Yu ◽  
Longxiang Dong ◽  
Jianglin Li ◽  
Guo Zhao ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Complex Terrain ◽  
Numerical Study ◽  
Dominant Role ◽  
Deep Convection ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Local Circulation ◽  
Convective Initiation ◽  
The Impact

The relative importance of topography and soil moisture on the initiation of an afternoon deep convection under weak synoptic-scale forcing was investigated using the weather research and forecasting (WRF) model with high resolution (1.33 km). The convection occurred on 29 June 2017, over the Liupan Mountains, west of the Loess Plateau. The timing and location of the convective initiation (CI) simulated by the WRF model compared well with the radar observations. It showed that the warm and humid southerly airflow under 700 hPa was divided into east and west flows due to the blockage of the Liupan Mountains. The warm and humid air on the west side was forced to climb along the slope and enhanced the humidity near the ridge. The accumulation of unstable energy in the middle and north of the ridge led to a strong vertical convergence and triggered the convection. Sensitivity experiments showed that terrain played a dominant role in triggering the convection, while the spatial heterogeneity of soil moisture played an indirect role by affecting the local circulation and the partition of surface energy.

scholarly journals Assimilating X- and S-Band Radar Data for a Heavy Precipitation Event in Italy

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1727
Author(s):  
Valerio Capecchi ◽  
Andrea Antonini ◽  
Riccardo Benedetti ◽  
Luca Fibbi ◽  
Samantha Melani ◽  
...  
Keyword(s):  
Extreme Event ◽  
Wrf Model ◽  
Heavy Precipitation ◽  
Radar Data ◽  
Flash Floods ◽  
Precipitation Event ◽  
Weather Research And Forecasting ◽  
Limited Area ◽  
Heavy Precipitation Event ◽  
The Town

During the night between 9 and 10 September 2017, multiple flash floods associated with a heavy-precipitation event affected the town of Livorno, located in Tuscany, Italy. Accumulated precipitation exceeding 200 mm in two hours was recorded. This rainfall intensity is associated with a return period of higher than 200 years. As a consequence, all the largest streams of the Livorno municipality flooded several areas of the town. We used the limited-area weather research and forecasting (WRF) model, in a convection-permitting setup, to reconstruct the extreme event leading to the flash floods. We evaluated possible forecasting improvements emerging from the assimilation of local ground stations and X- and S-band radar data into the WRF, using the configuration operational at the meteorological center of Tuscany region (LaMMA) at the time of the event. Simulations were verified against weather station observations, through an innovative method aimed at disentangling the positioning and intensity errors of precipitation forecasts. A more accurate description of the low-level flows and a better assessment of the atmospheric water vapor field showed how the assimilation of radar data can improve quantitative precipitation forecasts.

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