scholarly journals Roles of the Inner Eyewall Structure in the Secondary Eyewall Formation of Simulated Tropical Cyclones

2021 ◽  
Author(s):  
Nannan Qin ◽  
Liguang Wu ◽  
Qingyuan Liu
Keyword(s):  
Tropical Cyclones ◽  
Numerical Experiments ◽  
Large Scale ◽  
Forecasting Model ◽  
Diagnostic Analysis ◽  
Grid Spacing ◽  
Secondary Eyewall Formation ◽  
Spiral Rainband ◽  
Upper Level

Abstract. It has been suggested that the inner eyewall structure may play an important role in the secondary eyewall formation (SEF) of tropical cyclones (TCs). This study is to further examine the role of the inner eyewall structure by comparing two numerical experiments, which were conducted with the same large-scale environment and initial and boundary conditions but different grid sizes. The SEF was simulated in the experiment with the finer grid spacing, but not in the other.Comparing the eyewall structure in the simulated TCs with and without the SEF indicates that the eyewall structure can play an important role in the SEF. For the simulated TC with the SEF, the eyewall is more upright with stronger updrafts, accompanied by a wide eyewall anvil at a higher altitude. Compared to the simulated TC without the SEF, diagnostic analysis reveals that the cooling outside the inner eyewall is induced by the sublimation, melting and evaporation of hydrometeors falling from the eyewall anvil. The cooling also induces upper-level dry, cool inflow below the anvil, prompting the subsidence and moat formation between the inner eyewall and the spiral rainband. In the simulated TC without the SEF, the cooling induced by the falling hydrometeors is significantly reduced and offset by the diabatic warming. There is no upper-level dry inflow below the anvil and no moat formation between the inner eyewall and the spiral rainband. This study suggests that a realistic simulation of the intense eyewall convection is important to the prediction of the SEF in the numerical forecasting model.

scholarly journals The Outflow–Rainband Relationship Induced by Environmental Flow around Tropical Cyclones

2019 ◽  
Vol 76 (7) ◽  
pp. 1845-1863 ◽  
Author(s):  
Yi Dai ◽  
Sharanya J. Majumdar ◽  
David S. Nolan
Keyword(s):  
Numerical Simulation ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Inner Core ◽  
Vertical Wind Shear ◽  
Environmental Flow ◽  
Asymmetric Structure ◽  
Upper Level ◽  
The Relationship

Abstract This study investigates the role of the asymmetric interaction between the tropical cyclone (TC) and the environmental flow in governing the TC inner-core asymmetric structure. Motivated by the limitations of bulk measures of vertical wind shear in representing the complete environmental flow, the TC outflow is used as a focus for the asymmetric interaction. By analyzing an idealized numerical simulation, it is demonstrated that parcels can go directly from the asymmetric rainband to the upper-level outflow. The relatively large vertical mass flux in the rainband region also suggests that the asymmetric rainband is an important source of the outflow. In a simulation that suppresses convection by reducing the water vapor within the rainband region, the upper-level outflow is weakened, further supporting the hypothesis that the rainband and outflow are directly connected. Finally, it is demonstrated that the asymmetric outflow and the outer rainband are coupled through the descending inflow below the outflow. Some of the main characteristics of the outflow–rainband relationship are also supported by a real-case numerical simulation of Hurricane Bill (2009). The relationship is potentially useful for understanding and predicting the evolution of the TC inner-core structure during the interaction with the large-scale environmental flow.

Evolution of the Moat Associated with the Secondary Eyewall Formation in a Simulated Tropical Cyclone

2021 ◽  
Author(s):  
Nannan Qin ◽  
Liguang Wu ◽  
Qingyuan Liu
Keyword(s):  
Tropical Cyclones ◽  
Vertical Wind Shear ◽  
Outer Edge ◽  
Vertical Shear ◽  
Subsequent Evolution ◽  
Secondary Eyewall Formation ◽  
Spiral Rainband ◽  
Spiral Rainbands ◽  
Upper Level ◽  
Negative Buoyancy

AbstractPrevious studies have focused on the formation and maintenance of spiral rainbands in the secondary eyewall formation (SEF) of tropical cyclones (TCs). However, the evolution of the moat, a region with weak precipitation separating spiral rainbands from the inner eyewall, is also essential for the SEF. In this study, a semi-idealized numerical experiment is conducted to understand the SEF by focusing on the evolution of the moat. In the simulated TC, a secondary eyewall forms around 32 h, and then intensifies and replaces the inner eyewall at 46 h.It is found that the occurrence and subsequent evolution of the moat in the simulated TC are closely associated with the inner-eyewall structure. As the eyewall updraft becomes strong and the eyewall anvil is well developed, the upper-level inflow develops below the eyewall anvil in response to the diabatic warming in the eyewall anvil. The warming-induced inflow causes a drying effect and promotes the sublimation cooling below the anvil, inducing strong subsidence between the inner eyewall and the spiral rainband through the resulting negative buoyancy. Moreover, the resulting subsidence is enhanced by the compensated downward motion in the outer edge of the inner eyewall. Further analysis indicates that the rapidly decreasing vertical shear of environmental wind and the rapid filamentation zone outside the inner eyewall also play important role in the axisymmetrization of the rainband and the moat subsidence. Our results demonstrate that an intense inner eyewall with a wide upper-level anvil is favorable for the SEF in an environment with decreasing vertical wind shear.

scholarly journals Sudden Track Changes of Tropical Cyclones in Monsoon Gyres: Full-Physics, Idealized Numerical Experiments*

2015 ◽  
Vol 72 (4) ◽  
pp. 1307-1322 ◽  
Author(s):  
Jia Liang ◽  
Liguang Wu
Keyword(s):  
Tropical Cyclones ◽  
Numerical Experiments ◽  
Large Scale ◽  
Wrf Model ◽  
Weather Research And Forecasting ◽  
Coalescence Process ◽  
The West ◽  
Steering Flow ◽  
Sharp Turn ◽  
Wind Profiles

Abstract Tropical cyclones (TCs) in the eastern semicircle of large-scale monsoon gyres (MGs) were observed to take either a northward (sudden northward and northward without a sharp turn) or a westward TC turn, but only the northward turn was previously simulated in a barotropic model. To understand what controls TC track types in MGs, idealized numerical experiments are performed using the full-physics Weather Research and Forecasting (WRF) Model. These experiments indicate that TCs initially located in the eastern semicircle of MGs can generally take three types of tracks: a sudden northward track, a westward track, and a northward track without a sharp turn. The track types depend upon the TC movement relative to the MG center. In agreement with barotropic simulations, the WRF simulation confirms that approaching and being collocated with the MG center is crucial to the occurrence of sudden northward TC track changes and that sudden northward track changes can be generally accounted for by changes in the steering flow. TCs that take westward tracks and northward tracks without a sharp turn do not experience such a coalescence process. Westward TCs move faster than MGs and are then located to the west of the MG center, while TCs move more slowly than MGs and then take a northward track without a sharp turn. This study reveals that the specific TC track in the eastern semicircle of an MG is sensitive to the initial wind profiles of both MGs and TCs, suggesting that improvement in the observation of TC and MG structures is very important for predicting TC track types in MGs.

Cyclogenesis Simulation of Typhoon Prapiroon (2000) Associated with Rossby Wave Energy Dispersion*

2010 ◽  
Vol 138 (1) ◽  
pp. 42-54 ◽  
Author(s):  
Xuyang Ge ◽  
Tim Li ◽  
Melinda S. Peng
Keyword(s):  
Rossby Wave ◽  
Wave Energy ◽  
Large Scale ◽  
Wave Train ◽  
Energy Dispersion ◽  
Sensitivity Experiment ◽  
Low Level ◽  
Filtering Technique ◽  
Upper Level

Abstract The genesis of Typhoon Prapiroon (2000), in the western North Pacific, is simulated to understand the role of Rossby wave energy dispersion of a preexisting tropical cyclone (TC) in the subsequent genesis event. Two experiments are conducted. In the control experiment (CTL), the authors retain both the previous typhoon, Typhoon Bilis, and its wave train in the initial condition. In the sensitivity experiment (EXP), the circulation of Typhoon Bilis was removed based on a spatial filtering technique of Kurihara et al., while the wave train in the wake is kept. The comparison between these two numerical simulations demonstrates that the preexisting TC impacts the subsequent TC genesis through both a direct and an indirect process. The direct process is through the conventional barotropic Rossby wave energy dispersion, which enhances the low-level wave train, the boundary layer convergence, and the convection–circulation feedback. The indirect process is through the upper-level outflow jet. The asymmetric outflow jet induces a secondary circulation with a strong divergence tendency to the left-exit side of the outflow jet. The upper-level divergence boosts large-scale ascending motion and promotes favorable environmental conditions for a TC-scale vortex development. In addition, the outflow jet induces a well-organized cyclonic eddy angular momentum flux, which acts as a momentum forcing that enhances the upper-level outflow and low-level inflow and favors the growth of the new TC.

Assessing the Influence of Upper-Tropospheric Troughs on Tropical Cyclone Intensification Rates after Genesis

2017 ◽  
Vol 145 (4) ◽  
pp. 1295-1313 ◽  
Author(s):  
Michael S. Fischer ◽  
Brian H. Tang ◽  
Kristen L. Corbosiero
Keyword(s):  
Tropical Cyclones ◽  
North Atlantic ◽  
Temporal Evolution ◽  
Tropical Cyclogenesis ◽  
Brightness Temperatures ◽  
The North ◽  
The North Atlantic ◽  
Upper Level ◽  
Infrared Brightness

Abstract The role of upper-tropospheric troughs on the intensification rate of newly formed tropical cyclones (TCs) is analyzed. This study focuses on TCs forming in the presence of upper-tropospheric troughs in the North Atlantic basin between 1980 and 2014. TCs were binned into three groups based upon the 24-h intensification rate starting at the time of genesis: rapid TC genesis (RTCG), slow TC genesis (STCG), and neutral TC genesis (NTCG). Composite analysis shows RTCG events are characterized by amplified upper-tropospheric flow with the largest upshear displacement between the TC and trough of the three groups. RTCG events are associated with greater quasigeostrophic (QG) ascent in upshear quadrants of the TC, forced by differential vorticity advection by the thermal wind, especially around the time of genesis. This pattern of QG ascent closely matches the RTCG composite of infrared brightness temperatures. Conversely, NTCG events are associated with an upper-tropospheric trough that is closest to the TC center. The distribution of QG ascent in NTCG events becomes increasingly asymmetric around the time of genesis, with a maximum that shifts downshear of the TC center, consistent with infrared brightness temperatures. It is hypothesized that the TC intensification rate after tropical cyclogenesis, in environments of upper-tropospheric troughs, is closely linked to the structure and temporal evolution of the upper-level trough. The TC–trough configurations that provide greater QG ascent to the left of, and upshear of, the TC center feature more symmetric convection and faster TC intensification rates.

The Amplification of the ENSO Forcing over Equatorial Amazon

2009 ◽  
Vol 10 (6) ◽  
pp. 1561-1568 ◽  
Author(s):  
Vasubandhu Misra
Keyword(s):  
South America ◽  
Diurnal Cycle ◽  
Land Surface ◽  
Large Scale ◽  
French Guiana ◽  
Southern Oscillation ◽  
Moisture Flux ◽  
Precipitation Anomalies ◽  
Upper Level

Abstract The remote influence of the El Niño–Southern Oscillation (ENSO) strongly manifests over the equatorial Amazon (EA)—including parts of southern Venezuela, Guyana, French Guiana, and Suriname—when there is a large-scale anomalous upper-level divergence over continental tropical South America. Modeling studies conducted in this paper suggest that it is because of the modulation of the local diurnal cycle of the moisture flux convergence, which results in the local amplification of the ENSO signal over the EA. Further, it is shown that the local land surface feedback plays a relatively passive but important role of maintaining these interannual precipitation anomalies over the EA region.

scholarly journals Role of Large-Scale Circulation and Terrain in Causing Extreme Heat in Western North China

2016 ◽  
Vol 29 (7) ◽  
pp. 2511-2527 ◽  
Author(s):  
Ruidan Chen ◽  
Riyu Lu
Keyword(s):  
Large Scale ◽  
North China ◽  
Surface Air Temperature ◽  
Extreme Heat ◽  
Large Scale Circulation ◽  
Air Temperatures ◽  
Higher Temperature ◽  
Upper Level ◽  
Topographic Relief

Abstract Previous studies have suggested that, because of its particular location on the southeastern lee side of mountains, extreme heat (EH) over western north China (WNC) is affected by the foehn phenomenon. In this study, the EH days during summer over this region are categorized into foehn-favorable EH and no-foehn EH, according to whether there are anomalous northwesterlies over mountains, and composite analyses are performed on them. The analyzed results indicate that the no-foehn EH is characterized by an anticyclonic anomaly and a large-scale higher surface air temperature, while the foehn-favorable EH is featured by a cyclonic anomaly to the northeast and a localized higher temperature. Associated with the cyclonic anomaly, northwesterlies prevail over the mountain surface and provide a favorable environment for the occurrence of the foehn effect over WNC, which is located on the southeastern lee side of mountains. That is, both cyclonic and anticyclonic anomalies can induce EH over WNC (i.e., foehn-favorable EH and no-foehn EH, respectively). Further investigation indicates that large-scale cyclonic and anticyclonic anomalies tend to favor local descent and ascent anomalies over the lee side, respectively, through interaction with the particular terrain. Therefore, large-scale circulations and local terrain-induced winds play an offsetting role in affecting the surface air temperatures over WNC, and EH occurs when anomalous large-scale anticyclone or terrain-induced descent dominate. This study implies that attention should be paid to not only the upper-level/large-scale circulations but also to their impact on lower-level/local winds for temperature variability over the places with great topographic relief worldwide.

scholarly journals Secondary Eyewall Formation in Tropical Cyclones by Outflow–Jet Interaction

2017 ◽  
Vol 74 (6) ◽  
pp. 1941-1958 ◽  
Author(s):  
Yi Dai ◽  
Sharanya J. Majumdar ◽  
David S. Nolan
Keyword(s):  
Wind Speed ◽  
Numerical Simulations ◽  
Tropical Cyclones ◽  
Deep Convection ◽  
Stratiform Cloud ◽  
Jet Interaction ◽  
Secondary Eyewall Formation ◽  
Stratiform Region ◽  
Upper Level ◽  
Convective Cells

Abstract This study uses idealized numerical simulations to show that the interaction between tropical cyclones and a midlatitude jet can result in secondary eyewall formation. It is argued that the eddy activity by the outflow–jet interaction can enhance the upper-level outflow, thereby creating an asymmetric stratiform region outside of the primary eyewall. Numerous long-lasting deep convective cells are able to form in the stratiform cloud, creating forcing necessary for the secondary eyewall. The low-level inflow and the TC’s primary circulation advect the deep convective cells inward and cyclonically. The secondary eyewall forms after the deep convection has surrounded the TC. In contrast, numerical simulations without the jet do not show secondary eyewall formation. For moderately strong jets of wind speed 15–30 m s−1, there is little sensitivity to the jet strength. There is sensitivity to the distance between the jet and the TC, with secondary eyewall formation evident when their separation is 15° latitude but not when the separation exceeds 20°.

scholarly journals Change in Destructiveness of Landfalling Tropical Cyclones over China in Recent Decades

2017 ◽  
Vol 30 (9) ◽  
pp. 3367-3379 ◽  
Author(s):  
Richard C. Y. Li ◽  
Wen Zhou ◽  
C. M. Shun ◽  
Tsz Cheung Lee
Keyword(s):  
Tropical Cyclones ◽  
South China ◽  
Large Scale ◽  
Vertical Wind Shear ◽  
Cyclonic Circulation ◽  
East China ◽  
Diagnostic Analysis ◽  
Translation Speed ◽  
Positive Effects ◽  
Landfalling Tropical Cyclones

This study investigates changes in the destructiveness of landfalling tropical cyclones (TCs) over China during 1975–2014. Using four different TC datasets, it is found that TCs making landfall over east China (TCEC) have tended to be more destructive in recent decades, with a significant increase in the power dissipation index (PDI) after landfall. Both time series analysis and diagnostic analysis reveal that such an increase in the PDI of TCEC is associated with concomitant enhancement in landfall frequency as well as landfall intensity over east China. In contrast, changes in the PDI of TCs making landfall over south China (TCSC) are less apparent. Examination of different TC-related parameters shows no obvious changes in terms of landfall frequency, duration, and maximum intensity of TCSC. Diagnostic analysis further suggests that the reduction in TC occurrence over south China offsets considerably the positive effects of the intensity and the nonlinear term. Further examination of the environmental parameters reveals significant changes in the large-scale steering flow in recent decades, which is characterized by a prominent cyclonic circulation centered over southeast China. The southeasterly flows on the eastern flank of the cyclonic circulation tend to favor subsequent landfall of TCs over east China, resulting in an increase in landfall frequency, which contributes in part to the enhanced PDI of TCs over this region. Meanwhile, the slowing down of the mean translation speed of TCEC and the weakening of vertical wind shear coupled with warmer SSTs in the WNP tend to favor the intensification of TCEC, leading to an increase in intensity and hence the PDI of TCs over east China.

Probabilistic Evaluation of the Dynamics and Predictability of the Mesoscale Convective Vortex of 10–13 June 2003

2007 ◽  
Vol 135 (4) ◽  
pp. 1544-1563 ◽  
Author(s):  
Daniel P. Hawblitzel ◽  
Fuqing Zhang ◽  
Zhiyong Meng ◽  
Christopher A. Davis
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Critical Role ◽  
Probabilistic Evaluation ◽  
Mesoscale Convective ◽  
Upper Level ◽  
Mesoscale Convective Vortex ◽  
Horizontal Grid ◽  
Development And Evolution

Abstract This study examines the dynamics and predictability of the mesoscale convective vortex (MCV) of 10–13 June 2003 through ensemble forecasting. The MCV of interest developed from a preexisting upper-level disturbance over the southwest United States on 10 June and matured as it traveled northeastward. This event is of particular interest given the anomalously strong and long-lived nature of the circulation. An ensemble of 20 forecasts using a 2-way nested mesoscale model with horizontal grid increments of 30 and 10 km are employed to probabilistically evaluate the dynamics and predictability of the MCV. Ensemble mean and spread as well as correlations between different forecast variables at different forecast times are examined. It is shown that small-amplitude large-scale balanced initial perturbations may result in very large ensemble spread, with individual solutions ranging from a very strong MCV to no MCV at all. Despite similar synoptic-scale conditions, the ensemble MCV forecasts vary greatly depending on intensity and coverage of simulated convection, illustrating the critical role of convection in the development and evolution of this MCV. Correlation analyses reveal the importance of a preexisting disturbance to the eventual development of the MCV. It is also found that convection near the center of the MCV the day after its formation may be an important factor in determining the eventual growth of a surface vortex and that a stronger midlevel vortex is more conducive to convection, especially on the downshear side, consistent with the findings of previous MCV studies.

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