scholarly journals Dual-Doppler Observations of Severe Tropical Storm Maggie 1999

2005 ◽  
Vol 20 (1) ◽  
pp. 112-123
Author(s):  
Sai-Choi Tai ◽  
Edwin Wing-Lui Ginn ◽  
Chiu-Ying Lam
Keyword(s):  
Hong Kong ◽  
Storm Track ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Ambient Flow ◽  
Steering Flow ◽  
Nonhydrostatic Model ◽  
Tropical Areas ◽  
Weather Stations ◽  
Experimental Runs

Abstract Severe Tropical Storm Maggie crossed Hong Kong, China, in June 1999. The dual-Doppler winds of Maggie captured by the Hong Kong Observatory's (HKO) S-band Doppler weather radar array were studied. The tracks of Maggie's vorticity centers at 1–3-km levels were analyzed and compared with that at the surface as determined from the wind observations of automatic weather stations. The results indicated that the storm had a vertical tilt toward the west to northwest during the transit over Hong Kong. The tracks also deviated significantly from the deep-layer environmental steering flow. The southward movement and vertical tilt could be partly attributed to the easterly vertical shear in the ambient flow. But the terrain of Hong Kong could have also played a significant role in the lowest 1 km of the atmosphere. The tendency of the storm track to avoid mountains was well illustrated and may serve as a useful forecasting guidance indicator for tropical areas with significant terrain. Experimental runs of a nonhydrostatic model at 5-km resolution were able to simulate the broad west-southwestward movement of Maggie and the vertical tilt of the circulation near the center of the tropical cyclone as revealed by the dual-Doppler observations.

Lagrangian Description of Air Masses Associated with Latent Heat Release in Tropical Storm Karl (2016) during Extratropical Transition

2019 ◽  
Vol 147 (7) ◽  
pp. 2657-2676 ◽  
Author(s):  
Christian Euler ◽  
Michael Riemer ◽  
Tobias Kremer ◽  
Elmar Schömer
Keyword(s):  
Inner Core ◽  
Vertical Wind Shear ◽  
Conveyor Belt ◽  
Tropical Storm ◽  
Vertical Shear ◽  
Lagrangian Description ◽  
Environment Impact ◽  
Extratropical Transition ◽  
Air Masses ◽  
Core Convection

Abstract Extratropical transition (ET) of tropical cyclones involves distinct changes of the cyclone’s structure that are not yet well understood. This study presents for the first time a comprehensive Lagrangian description of structure change near the inner core. A large sample of trajectories is computed from a convection-permitting numerical simulation of the ET of Tropical Storm Karl (2016). Three main airstreams are considered: those associated with the inner-core convection, inner-core descent, and the developing warm conveyor belt. Analysis of these airstreams is performed both in thermodynamic and physical space. Prior to ET, Karl is embedded in weak vertical wind shear and its intensity is impeded by excessive detrainment from the inner-core convection. At the start of ET, vertical shear increases and Karl intensifies, which is attributable to reduced detrainment and thus to the formation of a well-defined outflow layer. During ET, the thermodynamic changes of the environment impact Karl’s inner-core convection predominantly by a decrease of θe values in the inflow layer. Notably, notwithstanding Karl’s weak intensity, its inner core acts as a “containment vessel” that transports high-θe air into the increasingly hostile environment. Inner-core descent has two origins: (i) mostly from upshear-left above 4-km height in the environment and (ii) boundary layer air that ascends in the inner core first and then descends, performing rollercoaster-like trajectories. At the end of the tropical phase of ET, the developing warm conveyor belt comprises air masses from several different source regions, and only partly from the cyclone’s developing warm sector, as expected for extratropical cyclones.

scholarly journals Genesis of Tropical Storm Eugene (2005) from Merging Vortices Associated with ITCZ Breakdowns. Part II: Roles of Vortex Merger and Ambient Potential Vorticity

2009 ◽  
Vol 66 (7) ◽  
pp. 1980-1996 ◽  
Author(s):  
Chanh Q. Kieu ◽  
Da-Lin Zhang
Keyword(s):  
Potential Vorticity ◽  
Tropical Storm ◽  
Heat Fluxes ◽  
Vertical Shear ◽  
Tropical Cyclogenesis ◽  
Small Scale ◽  
Absolute Vorticity ◽  
Surface Heat Fluxes ◽  
Vortex Merger ◽  
Bottom Upward

Abstract In this study, the roles of merging midlevel mesoscale convective vortices (MCVs) and convectively generated potential vorticity (PV) patches embedded in the intertropical convergence zone (ITCZ) in determining tropical cyclogenesis are examined by calculating PV and absolute vorticity budgets with a cloud-resolving simulation of Tropical Storm Eugene (2005). Results show that the vortex merger occurs as the gradual capture of small-scale PV patches within a slow-drifting MCV by another fast-moving MCV, thus concentrating high PV near the merger’s circulation center, with its peak amplitude located slightly above the melting level. The merging phase is characterized by sharp increases in surface heat fluxes, low-level convergence, latent heat release (and upward motion), lower tropospheric PV, surface pressure falls, and growth of cyclonic vorticity from the bottom upward. Melting and freezing appear to affect markedly the vertical structures of diabatic heating, convergence, absolute vorticity, and PV, as well the production of PV during the life cycle of Eugene. Results also show significant contributions of the horizontal vorticity to the magnitude of PV and its production within the storm. The storm-scale PV budgets show that the above-mentioned amplification of PV results partly from the net internal dynamical forcing between the PV condensing and diabatic production and partly from the continuous lateral PV fluxes from the ITCZ. Without the latter, Eugene would likely be shorter lived after the merger under the influence of intense vertical shear and colder sea surface temperatures. The vorticity budget reveals that the storm-scale rotational growth occurs in the deep troposphere as a result of the increased flux convergence of absolute vorticity during the merging phase. Unlike the previously hypothesized downward growth associated with merging MCVs, the most rapid growth rate is found in the bottom layers of the merger because of the frictional convergence. It is concluded that tropical cyclogenesis from merging MCVs occurs from the bottom upward.

scholarly journals A Synoptic-Scale Cold-Reservoir Hypothesis on the Origin of the Mature-Stage Super Cloud Cluster: A Case Study with a Global Nonhydrostatic Model

2016 ◽  
Vol 56 ◽  
pp. 14.1-14.24 ◽  
Author(s):  
Kazuyoshi Oouchi ◽  
Masaki Satoh
Keyword(s):  
Indian Ocean ◽  
Warm Pool ◽  
Vertical Shear ◽  
Fundamental Aspect ◽  
Boreal Summer ◽  
Squall Line ◽  
Synoptic Scale ◽  
Zonal Circulation ◽  
Nonhydrostatic Model ◽  
Cloud Cluster

Abstract This chapter proposes a working assumption as a way of conceptual simplification of the origin of Madden–Julian oscillation (MJO)-associated convection, or super cloud cluster (SCC). To develop the simplification, the importance of the synoptic-scale cold reservoir underlying the convection and its interaction with the accompanying zonal–vertical circulation is highlighted. The position of the convection with respect to that of climatological warm pool is postulated to determine the effectiveness of this framework. The authors introduce a prototype hypothesis to illustrate the usefulness of the above assumption based on a numerical simulation experiment with a global nonhydrostatic model for the boreal summer season. Premises for the hypothesis include 1) that the cloud cluster (CC) is a basic building block of tropical convection accompanying the precipitation-generated cold reservoir in its subcloud layer and 2) that a warm-pool-induced quasi-persistent zonal circulation is key for the upscale organization of CCs. The theory of squall-line structure by Rotunno, Klemp, and Weisman (hereafter RKW) is employed for the interpretation. No account is taken regarding the influences of equatorial waves as a first-order approximation. Given the premises, an SCC of O(1000) km scale is interpretable as a gigantic analog of a multicellular squall line embedded in the quasi-stationary westerly shear branch of the zonal circulation east of the warm water pool. A CC corresponds to the “cell,” and its successive formation to the east and westward movement represents an upshear-tilting core of intense updraft. The upshear-tilted SCC is favorably maintained with the precipitating area being separated from the gust front boundary between the cold reservoir and a low-level easterly, which is supported in the realm of the RKW theory where two horizontal vortices associated with the cold reservoir and vertical shear are opposite in sign but cold reservoir’s vorticity can be inferred to be larger, leading to upshear-tilted and multicellular behavior. As a counterexample, CCs to the west of the warm pool (Indian Ocean and Arabian Sea) are embedded in the easterly shear and organized into a less coherent cloud cluster complex (CCC) given the situation of RKW where two horizontal vortices associated with the cold reservoir and vertical shear are still opposite in sign, but the smaller vertical shear west of the warm pool causes even more suboptimal vorticity imbalance in the western flank of cold reservoir, leading to larger tilt with height and intermittent, less viable storm situations. A cold pool or cold reservoir, having been prevalent in mesoscale convection research, is argued to be important for the MJO as pointed out by the emerging evidence in the international field campaign for the MJO called Cooperative Indian Ocean Experiment on Intraseasonal Variability (CINDY)/DYNAMO. The simplified and idealistic hypothesis proposed here does not cover all aspects of MJO and its validation awaits further modeling and observational studies, but it can offer a framework for characterizing a fundamental aspect of the origin of MJO-associated convection.

An Operational Statistical Scheme for Tropical Cyclone Induced Wind Gust Forecasts

2016 ◽  
Vol 31 (6) ◽  
pp. 1817-1832 ◽  
Author(s):  
Qinglan Li ◽  
Pengcheng Xu ◽  
Xingbao Wang ◽  
Hongping Lan ◽  
Chunyan Cao ◽  
...  
Keyword(s):  
Hong Kong ◽  
South China ◽  
Wind Direction ◽  
Container Terminal ◽  
Wind Gust ◽  
Forecast Method ◽  
Wind Influence ◽  
Weather Stations ◽  
The Relationship ◽  
Potential Maximum

Abstract This study provides a quantitative forecast method for predicting the potential maximum wind gust at certain automatic weather stations (AWSs) in South China through the investigation of the relationship between the wind gusts observed at the stations and tropical cyclones’ (TCs) main characteristics: TC intensity, TC distance to the station, TC azimuth relative to the station, and TC size. Historical TC data from 1968 to June 2014 within a distance of 700 km to several AWSs in South China are analyzed. The wind gust data available for the same period taken from six coastal AWSs: Yantian International Container Terminal (YICT), Mawan Port (MWP), and Shekou Ferry Terminal (SFT) in Shenzhen, and Hong Kong Observatory (HKO), Cheung Chau Island (CCH), and Waglan Island (WGL) in Hong Kong, are used to build the statistical relationship. The probability of gust gale occurrence (wind gust ≥ 17 m s−1) at these six stations is also computed. Results show that the wind induced by offshore TCs is strongly affected by the surrounding terrain conditions of the stations. Coastal stations open to the wind direction suffer a greater wind influence than do stations with obstructions located in the wind direction. When TCs are approaching the coast in South China, the most dangerous area is the northeast quadrant of TCs. In this quadrant, typhoons might incur gust gales at coastal stations in South China even at a distance of more than 400 km from the stations.

scholarly journals Sub-seasonal variations of the tropical storm track in the western north Pacific

MAUSAM ◽  
2021 ◽  
Vol 48 (2) ◽  
pp. 189-194
Author(s):  
BIN WANG ◽  
LIGUANG WU
Keyword(s):  
Summer Monsoon ◽  
Seasonal Variations ◽  
North Pacific ◽  
Time Scale ◽  
Western North Pacific ◽  
Storm Track ◽  
Tropical Storm ◽  
Climatological Data ◽  
Seasonal Oscillation ◽  
The Western Pacific

 With 20-year (1975-94) climatological data, we demonstrate that the tropical storm track over the western North Pacific (0° - 40°N, 100 - 180°E) exhibits prominent sub-seasonal variations on a time scale of about 40 days from May to November. The storm track variability is regulated by the conspicuous Climatological Intra Seasonal Oscillation (CISO) in the strength of the western North Pacific summer monsoon and the associated position of the western Pacific Sub-tropical High. The CISO cycle regulates the number of tropical storm formation during the Pre-Onset and Withdraw Cycles but not during the Onset and Peak Monsoon Cycles (from mid-June to mid-September).    

scholarly journals Eddy Energy along the Tropical Storm Track in Association with ENSO

2009 ◽  
Vol 87 (4) ◽  
pp. 687-704 ◽  
Author(s):  
Pang-Chi HSU ◽  
Chih-Hua TSOU ◽  
Huang-Hsiung HSU ◽  
Jui-Hsin CHEN
Keyword(s):  
Storm Track ◽  
Tropical Storm

Understanding the Impacts of Upper-Tropospheric Cold Low on Typhoon Jongdari (2018) Using Piecewise Potential Vorticity Inversion

2021 ◽  
Vol 149 (5) ◽  
pp. 1499-1515
Author(s):  
Ziyu Yan ◽  
Xuyang Ge ◽  
Zhuo Wang ◽  
Chun-Chieh Wu ◽  
Melinda Peng
Keyword(s):  
Potential Vorticity ◽  
Control Experiment ◽  
Early Stage ◽  
Numerical Models ◽  
Storm Track ◽  
Vertical Wind Shear ◽  
Sensitivity Experiment ◽  
Steering Flow ◽  
Potential Vorticity Inversion ◽  
Indirect Impacts

AbstractTyphoon Jongdari (2018) had an unusual looping path before making landfall in Japan, which posed a forecasting challenge for operational numerical models. The impacts of an upper-tropospheric cold low (UTCL) on the track and intensity of Jongdari are investigated using numerical simulations. The storm track and intensity are well simulated in the control experiment using the GFS analysis as the initial and boundary conditions. In the sensitivity experiment (RCL), the UTCL is removed from the initial-condition fields using the piecewise potential vorticity inversion (PPVI), and both the track and intensity of Jongdari change substantially. The diagnosis of potential vorticity tendency suggests that horizontal advection is the primary contributor for storm motion. Flow decomposition using the PPVI further demonstrates that the steering flow is strongly affected by the UTCL, and the looping path of Jongdari results from the Fujiwhara interaction between the typhoon and UTCL. Jongdari first intensifies and then weakens in the control experiment, consistent with the observation. In contrast, it undergoes a gradual intensification in the RCL experiment. The UTCL contributes to the intensification of Jongdari at the early stage by enhancing the eddy flux convergence of angular momentum and reducing inertial stability, and it contributes to the storm weakening via enhanced vertical wind shear at the later stage when moving closer to Jongdari. Different sea surface temperatures and other environmental conditions along the different storm tracks also contribute to the intensity differences between the control and the RCL experiments, indicating the indirect impacts of the UTCL on the typhoon intensity.

scholarly journals Effects of extreme rainfall, typhoons and declaration of marine reserve status on corals beached at Cape d'Aguilar (1998 and 1999)

2002 ◽  
Vol 82 (5) ◽  
pp. 729-743 ◽  
Author(s):  
Brian Morton
Keyword(s):  
Hong Kong ◽  
Species Richness ◽  
Marine Reserve ◽  
Extreme Rainfall ◽  
Tropical Storm ◽  
Tropical Storms ◽  
Relative Dominance ◽  
Ecological Parameters ◽  
Tropical Depressions ◽  
Goniastrea Aspera

In the years 1996 and 1997, the pattern of deposition of beached coral heads and pieces onto the shore of Telecom Bay within the Cape d'Aguilar Marine Reserve, Hong Kong suggested that typhoons were a significant natural perturbation. In August 1997, 808 pieces weighing 60,930 g were washed up following passage of Typhoon Victor. 1997 was also Hong Kong's wettest year on record and a survey of the living corals in the reserve in 1998 showed changes in a number of ecological parameters of species richness, composition and diversity but, most noticeably, that the formerly dominant Goniastrea aspera had been superseded by Platygyra sinensis. In 1998 and 1999, this was reflected in the changed proportions of these two beached corals. Dramatically lowered salinities in the bay during July and August 1997 may have effected this change in relative dominance. Following Typhoon Dan in October 1998, 342 pieces of corals weighing 75,600 g were collected. The 1996 and 1997 pattern seemed to be repeating itself. 1999 was a bad year for severe tropical storms and typhoons in Hong Kong, seven being reported upon. Yet, after each one only 12,490 g (Typhoon Leo), 3390 g (Typhoon Maggie), 3550 g (Severe Tropical Storm: no-name), 55 g (Typhoon Sam), 4500 g (Typhoon York and Typhoon Cam) and 3160 g (Typhoon Dan) were washed up. That is, the seven tropical depressions deposited about 27,640 g coral, approximately the same amount as only Typhoon Sally in 1996 (25,000 g) and Tropical Storm Penny and Typhoon Babs in 1998 (24,574 g) and less than half that of Typhoon Victor in 1997 (60,000 g). In July 1996, Cape d'Aguilar was declared a marine reserve, fishing banned in its 18 hectares of sea and ghost nets removed. The fishing ban seems to be halting the dislodgement of corals and they are thus not now being beached by typhoons.

scholarly journals On the Similarity of Lower-Stratospheric Potential Vorticity Dipoles above Tropical and Midlatitude Deep Convection

2017 ◽  
Vol 74 (8) ◽  
pp. 2593-2613 ◽  
Author(s):  
Matthew H. Hitchman ◽  
Shellie M. Rowe
Keyword(s):  
Potential Vorticity ◽  
Deep Convection ◽  
Potential Temperature ◽  
Vertical Shear ◽  
Ambient Flow ◽  
Westerly Jet ◽  
University Of Wisconsin ◽  
Upward Deflection ◽  
The University ◽  
The Relationship

Abstract Simulations of the effects of deep convection on the structure of potential vorticity (PV) in the upper troposphere and lower stratosphere (UTLS) have shown that a common signature in the presence of ambient horizontal vorticity is a horizontal PV dipole. Here, the relationship between convection and PV structures in the UTLS in Tropical Cyclone Talas and the extratropical “Super Tuesday” cyclone is investigated with the University of Wisconsin Nonhydrostatic Modeling System (UWNMS). Dipoles of potential temperature in the UTLS are interpreted as an upward deflection of the ambient flow over the updraft (cold), followed by subsidence in its lee (warm), aligned with the wind direction. PV dipoles larger than ±20 PV units (1 PVU = 10−6 K kg−1 m2 s−1) are identified, with typical vertical and horizontal extents of ~3 and ~200 km, respectively, and lifetimes up to 12 h. Confirming the findings of Chagnon and Gray, it is found that horizontal PV dipoles are related to vortex tilting, where horizontally oriented vorticity associated with vertical shear of the ambient wind is bent into a horseshoe shape by the updraft, yielding a PV dipole. This suggests that theta dipoles are perpendicular to PV dipoles and that “low PV lies to the left of the wind shear,” or, in the case of tropical cyclones, “low PV lies radially outward.” Mesoscale jets occur between the dipoles, which oppose the ambient anticyclonic flow. During the extratropical transition of Talas, convective PV anomalies evolved under synoptic-scale deformation into a pair of PV streamers, which modified the midlatitude westerly jet.

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