Binary Interaction between Typhoons Fengshen (2002) and Fungwong (2002) Based on the Potential Vorticity Diagnosis

Abstract A cyclonic loop was observed in the track of Typhoon Fungwong (2002) when it was about 765 n mi from Supertyphoon Fengshen (2002). It is shown that Fungwong’s special path is associated with the circulation of Fengshen, and such an association is regarded as an indication of binary interaction. In this paper, the binary interaction between Fengshen and Fungwong is studied based on the potential vorticity diagnosis. The impacts of large-scale flow fields on their motions are also investigated. Furthermore, the sensitivity of the storm characteristics to the binary interaction is demonstrated by the mesoscale numerical model simulations with different sizes and intensities for the initial bogused storms. Results of the study show that before Fungwong and Fengshen interacted with each other, their motions were governed by the large-scale environmental flow, that is, mainly associated with the subtropical high. During this binary interaction, Fungwong’s looping is partly attributed to Fengshen’s steering flow. This pattern shows up first as a case of one-way interaction in the early period, and then develops into a mutual interaction during the later stages. The numerical experiments show the sensitivity of the storm size and intensity to the binary interaction, implicating that a good representation of the initial storm vortex is important for the prediction of binary storms. Further analyses also indicate the influence of the monsoon trough and subtropical high systems on the binary interaction. These results provide some new insights into the motions of nearby typhoons embedded in the monsoon circulation.

Download Full-text

Interaction of Typhoon Shanshan (2006) with the Midlatitude Trough from both Adjoint-Derived Sensitivity Steering Vector and Potential Vorticity Perspectives

Monthly Weather Review ◽

10.1175/2008mwr2585.1 ◽

2009 ◽

Vol 137 (3) ◽

pp. 852-862 ◽

Cited By ~ 28

Author(s):

Chun-Chieh Wu ◽

Shin-Gan Chen ◽

Jan-Huey Chen ◽

Kun-Hsuan Chou ◽

Po-Hsiung Lin

Keyword(s):

Potential Vorticity ◽

Large Scale ◽

Mesoscale Model ◽

High Sensitivity ◽

Forecast Model ◽

Central China ◽

Subtropical High ◽

Steering Vector ◽

Steering Flow ◽

Targeted Observation

Abstract Targeted observation is one of the most important research and forecasting issues for improving tropical cyclone predictability. A new parameter [i.e., the adjoint-derived sensitivity steering vector (ADSSV)] has been proposed and adopted as one of the targeted observing strategies in the Dropwindsonde Observations for Typhoon Surveillance near the Taiwan Region (DOTSTAR). The ADSSV identifies the sensitive areas at the observing time to the steering flow at the verifying time through the adjoint calculation. In this study, the ADSSV is calculated from the nonlinear forecast model of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) and its adjoint to interpret the dynamical processes in the interaction between Typhoon Shanshan (2006) and the midlatitude trough. The ADSSV results imply that high-sensitivity regions affecting the motion of Typhoon Shanshan are located at the edge of the subtropical high and the 500-hPa midlatitude trough over northern central China. These ADSSV signals are in very good agreement with the quantitative evaluation based on the potential vorticity (PV) diagnosis. The vertical structure of the ADSSV is also shown for more physical insights into the typhoon–trough interaction. The maximum ADSSV occurs at 800–500 hPa to the southeast of Shanshan (associated with the subtropical high), while distinct ADSSV signals are located upstream of the storm center at about 500–300 hPa (associated with the mid- to upper-tropospheric midlatitude trough). Overall, it is demonstrated that the ADSSV features can well capture the signal of the large-scale trough feature affecting the motion of Shanshan, which can also be well validated from the PV analysis.

Download Full-text

The Climatological Analysis of Typhoon Tracks, Steering Flow, and the Pacific Subtropical High in the Vicinity of Taiwan and the Western North Pacific

Atmosphere ◽

10.3390/atmos11050543 ◽

2020 ◽

Vol 11 (5) ◽

pp. 543

Author(s):

Chih-wen Hung ◽

Ming-Fu Shih ◽

Te-Yuan Lin

Keyword(s):

Tropical Cyclones ◽

Large Scale ◽

Subtropical High ◽

Boreal Summer ◽

The South ◽

The West ◽

Steering Flow ◽

The Pacific ◽

Typhoon Season ◽

Typhoon Tracks

Taiwan frequently suffers from typhoon hits in the boreal summer and fall. The location of Taiwan makes it vulnerable to the pathways of typhoons mainly determined by the position of the Pacific subtropical high. In order to clarify the linkage between typhoon invasion and associated large-scale environments from a climatological perspective, this study counts the historical typhoon invasion days for each month in the typhoon season to establish analyzed cases and then categorizes them with statistical thresholds. Besides, the categorized cases with less typhoon invasion are further sorted to distinguish different movements of tropical cyclones. Therefore, corresponding composites are applied for each category. The results reveal that when the subtropical high retreats eastward, the accompanying steering flow guides typhoons to make an early recurvature toward Japan and South Korea. While the subtropical high further extends its property to the west covering Taiwan, the steering flow on the south transfers typhoons moving westward to the South China Sea. However, when the subtropical high lies in areas between the above two scenarios, the steering flow along the periphery of the subtropical high continuously sends typhoons toward Taiwan and the vicinity, which greatly increases the threat to the island.

Download Full-text

An Objective Identification and Climatology of Upper-Tropospheric Jets near Atlantic Tropical Cyclones

Monthly Weather Review ◽

10.1175/mwr-d-19-0262.1 ◽

2020 ◽

Vol 148 (7) ◽

pp. 3015-3036

Author(s):

Levi P. Cowan ◽

Robert E. Hart

Keyword(s):

Tropical Cyclones ◽

Potential Vorticity ◽

Clustering Analysis ◽

Large Scale ◽

Reanalysis Data ◽

Atlantic Basin ◽

Jet Behavior ◽

Consistent Feature ◽

Large Scale Flow ◽

Westerly Jets

Abstract An objective algorithm is developed for identifying jets in 200-hPa flow and applied to reanalysis data within 2000 km of Atlantic tropical cyclones (TCs) during 1979–2015. The resulting set of 16 512 jets is analyzed both qualitatively and quantitatively to describe the climatology of TC–jet configurations and jet behavior near TCs. Jets occur most commonly poleward of TCs within the 500–1000-km annulus, where TC outflow amplifies the background potential vorticity gradient. A rigorous clustering analysis is performed, resulting in statistically distinct clusters of jet traces that correspond to common configurations of large-scale flow near Atlantic TCs. The speed structure of westerly jets poleward of TCs is found to vary with location in the Atlantic basin, but acceleration of jets downstream of their closest approach to the TC due to interaction with the TC’s diabatic outflow is a consistent feature of these structures. In addition to the climatology developed here, this objectively constructed dataset of upper-tropospheric jets opens unique avenues for exploring TC–environment interactions and utilizing jets to quantitatively describe large-scale flow.

Download Full-text

Transient Mountain Waves and Their Interaction with Large Scales

Journal of the Atmospheric Sciences ◽

10.1175/jas3972.1 ◽

2007 ◽

Vol 64 (7) ◽

pp. 2378-2400 ◽

Cited By ~ 18

Author(s):

Chih-Chieh Chen ◽

Gregory J. Hakim ◽

Dale R. Durran

Keyword(s):

Potential Vorticity ◽

Large Scale ◽

Wave Drag ◽

Mountain Waves ◽

Flow Acceleration ◽

Spatial Response ◽

Flow Deceleration ◽

Large Scale Flow ◽

The Impact ◽

Zonal Momentum

Abstract The impact of transient mountain waves on a large-scale flow is examined through idealized numerical simulations of the passage of a time-evolving synoptic-scale jet over an isolated 3D mountain. Both the global momentum budget and the spatial flow response are examined to illustrate the impact of transient mountain waves on the large-scale flow. Additionally, aspects of the spatial response are quantified by potential vorticity inversion. Nearly linear cases exhibit a weak loss of domain-averaged absolute momentum despite the absence of wave breaking. This transient effect occurs because, over the time period of the large-scale flow, the momentum flux through the top boundary does not balance the surface pressure drag. Moreover, an adiabatic spatial redistribution of momentum is observed in these cases, which results in an increase (decrease) of zonally averaged zonal momentum south (north) of the mountain. For highly nonlinear cases, the zonally averaged momentum field shows a region of flow deceleration downstream of the mountain, flanked by broader regions of weak flow acceleration. Cancellation between the accelerating and decelerating regions results in weak fluctuations in the volume-averaged zonal momentum, suggesting that the mountain-induced circulations are primarily redistributing momentum. Potential vorticity anomalies develop in a region of wave breaking near the mountain, and induce local regions of flow acceleration and deceleration that alter the large-scale flow. A “perfect” conventional gravity wave–drag parameterization is implemented on a coarser domain not having a mountain, forced by the momentum flux distribution from the fully nonlinear simulation. This parameterization scheme produces a much weaker spatial response in the momentum field and it fails to produce enough flow deceleration near the 20 m s−1 jet. These results suggest that the potential vorticity sources attributable to the gravity wave–drag parameterization have a controlling effect on the longtime downstream influence of the mountain.

Download Full-text

Stochastic resonance in a nonlinear model of a rotating, stratified shear flow, with a simple stochastic inertia-gravity wave parameterization

Nonlinear Processes in Geophysics ◽

10.5194/npg-11-127-2004 ◽

2004 ◽

Vol 11 (1) ◽

pp. 127-135 ◽

Cited By ~ 19

Author(s):

P. D. Williams ◽

T. W. N. Haine ◽

P. L. Read

Keyword(s):

Shear Flow ◽

Gravity Wave ◽

Stochastic Resonance ◽

Potential Vorticity ◽

Large Scale ◽

Zonal Wavenumber ◽

Stratified Shear Flow ◽

Balanced Flow ◽

Large Scale Flow ◽

The Impact

Abstract. We report on a numerical study of the impact of short, fast inertia-gravity waves on the large-scale, slowly-evolving flow with which they co-exist. A nonlinear quasi-geostrophic numerical model of a stratified shear flow is used to simulate, at reasonably high resolution, the evolution of a large-scale mode which grows due to baroclinic instability and equilibrates at finite amplitude. Ageostrophic inertia-gravity modes are filtered out of the model by construction, but their effects on the balanced flow are incorporated using a simple stochastic parameterization of the potential vorticity anomalies which they induce. The model simulates a rotating, two-layer annulus laboratory experiment, in which we recently observed systematic inertia-gravity wave generation by an evolving, large-scale flow. We find that the impact of the small-amplitude stochastic contribution to the potential vorticity tendency, on the model balanced flow, is generally small, as expected. In certain circumstances, however, the parameterized fast waves can exert a dominant influence. In a flow which is baroclinically-unstable to a range of zonal wavenumbers, and in which there is a close match between the growth rates of the multiple modes, the stochastic waves can strongly affect wavenumber selection. This is illustrated by a flow in which the parameterized fast modes dramatically re-partition the probability-density function for equilibrated large-scale zonal wavenumber. In a second case study, the stochastic perturbations are shown to force spontaneous wavenumber transitions in the large-scale flow, which do not occur in their absence. These phenomena are due to a stochastic resonance effect. They add to the evidence that deterministic parameterizations in general circulation models, of subgrid-scale processes such as gravity wave drag, cannot always adequately capture the full details of the nonlinear interaction.

Download Full-text

Potential vorticity structure of embedded convection in a warm conveyor belt and its relevance for the large-scale dynamics

10.5194/wcd-2019-3 ◽

2019 ◽

Author(s):

Annika Oertel ◽

Maxi Boettcher ◽

Hanna Joos ◽

Michael Sprenger ◽

Heini Wernli

Keyword(s):

Potential Vorticity ◽

Large Scale ◽

Potential Temperature ◽

Conveyor Belt ◽

Cloud Band ◽

Surface Precipitation ◽

Upper Level ◽

Large Scale Flow ◽

Eastern North Atlantic ◽

Warm Conveyor Belts

Abstract. Warm conveyor belts (WCBs) are important airstreams in extratropical cyclones. They can influence the large-scale flow evolution due to the modification of the potential vorticity (PV) distribution during their cross-isentropic ascent. Although WCBs are typically described as slantwise ascending and stratiform cloud producing airstreams, recent studies identified convective activity embedded within the large-scale WCB cloud band. Yet, the impacts of this WCB-embedded convection have not been investigated in detail. In this study, we systematically analyse the influence of embedded convection in an eastern North Atlantic WCB on the cloud and precipitation structure, on the PV distribution, and on the larger-scale flow. For this, we apply online trajectories in a high-resolution convection-permitting simulation and perform a composite analysis to compare quasi-vertically ascending convective WCB trajectories with typical slantwise ascending WCB trajectories. We find that the convective WCB ascent leads to stronger surface precipitation including the formation of graupel, which is absent for the slantwise WCB category, indicating the key role of WCB-embedded convection for precipitation extremes. Compared to the slantwise WCB trajectories, the initial equivalent potential temperature of the convective WCB trajectories is higher and they originate from a region of larger potential instability, which gives rise to more intense cloud diabatic processes and stronger cross-isentropic ascent. Moreover, the signature of embedded convection is distinctly imprinted in the PV structure. The diabatically generated low-level positive PV anomalies, associated with a cyclonic circulation anomaly, are substantially stronger for the convective WCB trajectories. While the slantwise WCB trajectories form a wide-spread negative PV anomaly (but still with weakly positive PV values) in the upper troposphere, in agreement with previous studies, the convective WCB trajectories, in contrast, form mesoscale horizontal PV dipoles at upper levels, with one pole reaching negative PV. On the larger-scale, these individual mesoscale PV anomalies can aggregate to elongated PV dipole bands extending from the convective updraft region, which are associated with coherent larger-scale circulation anomalies. An illustrative example of such a convectively generated PV dipole band shows that within around 10 hours the negative PV pole is advected closer to the upper-level waveguide, where it strengthens the isentropic PV gradient and contributes to the formation of a jet streak. This suggests that the mesoscale PV anomalies produced by embedded convection upstream organise and persist for several hours, and therefore can influence the synoptic-scale circulation. They thus can be dynamically relevant. Finally, our results imply that a distinction between slantwise and convective WCB trajectories is meaningful because the convective WCB trajectories are characterized by distinct properties, such as the formation of graupel and of an upper-level PV dipole, which are absent for slantwise WCB trajectories.

Download Full-text

Revisiting the steering principal of tropical cyclone motion in a numerical experiment

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-14925-2016 ◽

2016 ◽

Vol 16 (23) ◽

pp. 14925-14936 ◽

Cited By ~ 12

Author(s):

Liguang Wu ◽

Xiaoyu Chen

Keyword(s):

Tropical Cyclone ◽

Numerical Experiment ◽

Potential Vorticity ◽

Large Scale ◽

Inner Core ◽

Dominant Role ◽

Wave Number ◽

Steering Flow ◽

Vorticity Component ◽

Tropical Cyclone Center

Abstract. The steering principle of tropical cyclone motion has been applied to tropical cyclone forecasting and research for nearly 100 years. Two fundamental questions remain unanswered. One is why the steering flow plays a dominant role in tropical cyclone motion, and the other is when tropical cyclone motion deviates considerably from the steering. A high-resolution numerical experiment was conducted with the tropical cyclone in a typical large-scale monsoon trough over the western North Pacific. The simulated tropical cyclone experiences two eyewall replacement processes. Based on the potential vorticity tendency (PVT) diagnostics, this study demonstrates that the conventional steering, which is calculated over a certain radius from the tropical cyclone center in the horizontal and a deep pressure layer in the vertical, plays a dominant role in tropical cyclone motion since the contributions from other processes are largely cancelled out due to the coherent structure of tropical cyclone circulation. Resulting from the asymmetric dynamics of the tropical cyclone inner core, the trochoidal motion around the mean tropical cyclone track cannot be accounted for by the conventional steering. The instantaneous tropical cyclone motion can considerably deviate from the conventional steering that approximately accounts for the combined effect of the contribution of the advection of the symmetric potential vorticity component by the asymmetric flow and the contribution from the advection of the wave-number-one potential vorticity component by the symmetric flow.

Download Full-text