Determination of a Consistent Time for the Extratropical Transition of Tropical Cyclones. Part II: Potential Vorticity Metrics

2010 ◽  
Vol 138 (12) ◽  
pp. 4344-4361 ◽  
Author(s):  
David E. Kofron ◽  
Elizabeth A. Ritchie ◽  
J. Scott Tyo
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Potential Vorticity ◽  
Potential Temperature ◽  
Threshold Value ◽  
Complex Problem ◽  
Extratropical Transition ◽  
Subtropical Anticyclone ◽  
Isentropic Potential Vorticity ◽  
Absolute Potential

Abstract As a tropical cyclone moves poleward and interacts with the midlatitude circulation, the question of whether it will undergo extratropical transition (ET) and, if it does, whether it will reintensify or dissipate, is a complex problem. Uncertainties include the tropical cyclone, the midlatitude circulation, the subtropical anticyclone, and the nonlinear interactions among these systems. A large part of the uncertainty is due to a lack of an understanding of when extratropical transition begins and how it progresses. In this study, absolute potential vorticity and isentropic, or Ertel’s, potential vorticity is examined for its ability to more consistently determine significant times (i.e., beginning or end) of the ET life cycle using the Navy Operational Global Assimilation and Prediction System gridded analyses. It is found that isentropic potential vorticity on the 330-K potential temperature isentropic level is a good discriminator for examining the extratropical transition of tropical cyclones. At this level, a consistent “ET time” is defined as when the TC-centered circular average of isentropic potential vorticity reaches a minimum value. All 82 tropical cyclones moving into the midlatitudes meet this criterion. The completion of extratropical transition for the reintensifying cases is defined as when the storm exceeds an isentropic potential vorticity threshold value of 1.6 PVU at the 330-K potential temperature isentropic level. The success rate of this threshold value for the completion of extratropical transition for the reintensification cases is found to be 94.3% with a 27.6% false-alarm rate.

Simulations of the Extratropical Transition of Tropical Cyclones: Phasing between the Upper-Level Trough and Tropical Cyclones

2007 ◽  
Vol 135 (3) ◽  
pp. 862-876 ◽  
Author(s):  
Elizabeth A. Ritchie ◽  
Russell L. Elsberry
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Critical Factor ◽  
Complex Problem ◽  
Initial Position ◽  
Extratropical Cyclone ◽  
Extratropical Transition ◽  
Subtropical Anticyclone ◽  
Temperature And Precipitation ◽  
The Impact

Abstract Whether the tropical cyclone remnants will become a significant extratropical cyclone during the reintensification stage of extratropical transition is a complex problem because of the uncertainty in the tropical cyclone, the midlatitude circulation, the subtropical anticyclone, and the nonlinear interactions among these systems. In a previous study, the authors simulated the impact of the strength of the midlatitude circulation trough without changing its phasing with the tropical cyclone. In this study, the impact of phasing is simulated by fixing the initial position and amplitude of the midlatitude trough and varying the initial position of the tropical cyclone. The peak intensity of the extratropical cyclone following the extratropical transition is strongly dependent on the phasing, which leads to different degrees of interaction with the midlatitude baroclinic zone. Many aspects of the simulated circulation, temperature, and precipitation fields appear quite realistic for the reintensifying and dissipating cases. Threshold values of various parameters in quadrants near and far from the tropical cyclone are extracted that discriminate well between reintensifiers and dissipators. The selection and distribution of threshold parameters are consistent with the Petterssen type-B conceptual model for extratropical cyclone development. Thus, these simulations suggest that phasing between the tropical cyclone and the midlatitude trough is a critical factor in predicting the reintensification stage of extratropical transition.

Evolution of African Easterly Waves in Potential Vorticity Fields

2012 ◽  
Vol 140 (11) ◽  
pp. 3634-3652 ◽  
Author(s):  
Bryce Tyner ◽  
Anantha Aiyyer
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Potential Vorticity ◽  
African Easterly Waves ◽  
Synoptic Scale ◽  
Easterly Waves ◽  
Tropical Cyclone Formation ◽  
Closed Circulation ◽  
Isentropic Potential Vorticity

Abstract The evolution of African easterly waves (AEWs) leading to tropical cyclones (TCs) in the Atlantic during 2000–08 is examined from isentropic potential vorticity (PV) and Lagrangian streamline perspectives. Tropical cyclone formation is commonly preceded by axisymmetrization of PV, scale contraction of the wave, and formation of a closed circulation within the wave. In these cases, PV associated with the synoptic-scale wave is irreversibly deformed and subsumed within the developing vortex. Less commonly, filamentation of the PV leads to separation and independent propagation of the wave and the TC vortex. In an example presented here, the remnant wave with a closed circulation persisted for several days after separation from the TC. A second TC did not result, consistent with several past studies that show that a midtropospheric closed gyre is not sufficient for TC genesis. Sometimes, an AEW and a weak TC remain coupled for a few days, followed by the dissipation of the TC and the continued propagation of the wave. Merger of tropical and extratropical PV anomalies is also often observed and likely helps maintain some waves. The results of this study are broadly consistent with recent Lagrangian analyses of AEW evolution during TC genesis.

Determination of a Consistent Time for the Extratropical Transition of Tropical Cyclones. Part I: Examination of Existing Methods for Finding “ET Time”

2010 ◽  
Vol 138 (12) ◽  
pp. 4328-4343 ◽  
Author(s):  
David E. Kofron ◽  
Elizabeth A. Ritchie ◽  
J. Scott Tyo
Keyword(s):  
Phase Space ◽  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Geopotential Height ◽  
Asymmetry Parameter ◽  
Complex Problem ◽  
Prediction System ◽  
Threshold Values ◽  
Extratropical Transition

Abstract As a tropical cyclone moves poleward and interacts with the midlatitude circulation, the question of whether it will undergo extratropical transition (ET) and, if it does, whether it will reintensify or dissipate, is a complex problem. Several quantities have been proposed in previous studies to describe extratropical transition including frontogenesis, 500-hPa geopotential heights, and cyclone phase-space parameters. In this study, these parameters are explored for their utility in defining an ET time using the Navy’s Operational Global Assimilation and Prediction System gridded analyses. The 500-hPa geopotential heights and frontogenesis currently do not have objective numerical definitions. Therefore, this study attempts to establish and examine threshold values that may be used to objectively define the ET time. Cyclone phase space already has numerical threshold values that can be examined. Results show that the 500-hPa geopotential height open wave distinguishes 81 of 82 cases, but it fails to discriminate between transitioning ET and recurving non-ET cases and cannot be determined automatically. The 2D scalar frontogenesis distinguishes 77 of 82 cases but does not discriminate between transitioning ET and recurving non-ET cases. Finally, phase space successfully distinguishes 81 of 82 cases for the “ET time” defined by the asymmetry parameter but is only successful at capturing transitioning ET and recurving non-ET cases properly for 60 of 82 cases. All of the definitions are found to have disadvantages that preclude them from providing consistent guidance for when extratropical transition of a poleward-recurving tropical cyclone is occurring.

scholarly journals Tropical Cyclone–Relative Environmental Helicity and the Pathways to Intensification in Shear

2016 ◽  
Vol 73 (2) ◽  
pp. 869-890 ◽  
Author(s):  
Matthew J. Onderlinde ◽  
David S. Nolan
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Latent Heat ◽  
Wind Shear ◽  
Potential Temperature ◽  
Reanalysis Data ◽  
Heat Fluxes ◽  
Equivalent Potential ◽  
Vertical Variations ◽  
The Difference

Abstract Tropical cyclone–relative environmental helicity (TCREH) is a measure of how the wind vector changes direction with height, and it has been shown to modulate the rate at which tropical cyclones (TCs) develop both in idealized simulations and in reanalysis data. The channels through which this modulation occurs remain less clear. This study aims to identify the mechanisms that lead to the observed variations in intensification rate. Results suggest that the difference in intensification rate between TCs embedded in positive versus negative TCREH primarily results from the position of convection and associated latent heat fluxes relative to the wind shear vector. When TCREH is positive, convection is more readily advected upshear and air parcels that experience larger fluxes are more frequently ingested into the TC core. Trajectories computed from high-resolution simulations demonstrate the recovery of equivalent potential temperature downwind of convection, latent heat flux near the TC core, and parcel routes through updrafts in convection. Differences in trajectory characteristics between TCs embedded in positive versus negative TCREH are presented. Contoured frequency-by-altitude diagrams (CFADs) show that convection is distributed differently around TCs embedded in environments characterized by positive versus negative TCREH. They also show that the nature of the most intense convection differs only slightly between cases of positive and negative TCREH. The results of this study emphasize the fact that significant variability in TC-intensification rate results from vertical variations in the environmental wind direction, even when the 850–200-hPa wind shear vector remains unchanged.

scholarly journals Attributing Tropical Cyclogenesis to Equatorial Waves in the Western North Pacific

2011 ◽  
Vol 68 (2) ◽  
pp. 195-209 ◽  
Author(s):  
Carl J. Schreck ◽  
John Molinari ◽  
Karen I. Mohr
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Wave Spectrum ◽  
Vertical Wind Shear ◽  
Warm Season ◽  
Threshold Value ◽  
Rainfall Anomaly ◽  
Tropical Cyclogenesis ◽  
Positive Anomaly ◽  
Equatorial Wave

Abstract Tropical cyclogenesis is attributed to an equatorial wave when the filtered rainfall anomaly exceeds a threshold value at the genesis location. It is argued that 0 mm day−1 (simply requiring a positive anomaly) is too small a threshold because unrelated noise can produce a positive anomaly. A threshold of 6 mm day−1 is too large because two-thirds of storms would have no precursor disturbance. Between these extremes, consistent results are found for a range of thresholds from 2 to 4 mm day−1. Roughly twice as many tropical cyclones are attributed to tropical depression (TD)-type disturbances as to equatorial Rossby waves, mixed Rossby–gravity waves, or Kelvin waves. The influence of the Madden–Julian oscillation (MJO) is even smaller. The use of variables such as vorticity and vertical wind shear in other studies gives a larger contribution for the MJO. It is suggested that its direct influence on the rainfall in forming tropical cyclones is less than for other variables. The impacts of tropical cyclone–related precipitation anomalies are also presented. Tropical cyclones can contribute more than 20% of the warm-season rainfall and 50% of its total variance. The influence of tropical cyclones on the equatorial wave spectrum is generally small. The exception occurs in shorter-wavelength westward-propagating waves, for which tropical cyclones represent up to 27% of the variance. Tropical cyclones also significantly contaminate wave-filtered rainfall anomalies in their immediate vicinity. To mitigate this effect, the tropical cyclone–related anomalies were removed before filtering in this study.

A Geospatial Analysis of Convective Rainfall Regions Within Tropical Cyclones After Landfall

2010 ◽  
Vol 1 (2) ◽  
pp. 71-91 ◽  
Author(s):  
Corene J. Matyas
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Accurate Assessment ◽  
Areal Extent ◽  
Convective Rainfall ◽  
Extratropical Transition ◽  
Storm Intensity ◽  
The Right

In this article, the author utilizes a GIS to spatially analyze radar reflectivity returns during the 24 hours following 43 tropical cyclone (TC) landfalls. The positions of convective rainfall regions and their areal extent are then examined according to storm intensity, motion, vertical wind shear, time until extratropical transition, time after landfall, and distance from the coastline. As forward velocity increases in conjunction with an extratropical transition, these regions move outward, shift from the right side to the front of the TC, and grow in size. A similar radial shift, but with a decrease in areal extent, occurs as TCs weaken. Further quantification of the shapes of these regions could yield a more spatially accurate assessment of where TCs may produce high rainfall totals.

A Comparison between Moist and Dry Tropical Cyclones: The Low Effectiveness of Surface Sensible Heat Flux in Storm Intensification

2021 ◽  
Author(s):  
Zhanhong Ma ◽  
Jianfang Fei
Keyword(s):  
Heat Flux ◽  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Potential Temperature ◽  
Sensible Heat Flux ◽  
Equivalent Potential Temperature ◽  
Sensible Heat ◽  
Budget Analysis ◽  
Equivalent Potential ◽  
Surface Sensible Heat Flux

AbstractRecent numerical modeling studies demonstrate that dry tropical cyclones can be stably sustained via supply of surface sensible heat flux. This raises questions of whether surface sensible heat flux (SHX) and latent heat flux (LHX) have the same effect on the intensity evolution of tropical cyclones. An estimation of equivalent potential temperature budget in the boundary layer shows that LHX leads to larger increase in equivalent potential temperature than SHX even when they possess the same magnitude. By formulating these two kinds of surface heat fluxes with the same mathematical framework, the simulated intensifications of moist and dry tropical cyclones are compared, with the former driven exclusively by LHX and the latter by SHX. Results show significantly larger intensification rates for the tropical cyclone driven by LHX than that by SHX, revealing low effectiveness of SHX in the intensification of tropical cyclones. The diabatic heating in the moist tropical cyclone occurs accompanying the convection, while it is merely pronounced near the surface in the dry tropical cyclone and is decoupled from the dry convection. A new surface pressure tendency equation is proposed, without incorporating implicit pressure tendency term on the right-hand side. The budget analysis indicates that the SHX is less effective than LHX in lowering surface central pressure and therefore in tropical cyclone intensification. A series of sensitivity experiments suggest that the threshold of energy input required for spinning up a tropical cyclone is lower in the form of LHX than that of SHX.

scholarly journals On the Relative Contribution of Inertia–Gravity Wave Radiation to Asymmetric Instabilities in Tropical Cyclone–like Vortices

2016 ◽  
Vol 73 (9) ◽  
pp. 3345-3370 ◽  
Author(s):  
Konstantinos Menelaou ◽  
David A. Schecter ◽  
M. K. Yau
Keyword(s):  
Tropical Cyclone ◽  
Gravity Wave ◽  
Tropical Cyclones ◽  
Potential Vorticity ◽  
Three Dimensional ◽  
Life Cycles ◽  
Wave Radiation ◽  
Ambient Conditions ◽  
Layer Potential ◽  
The Impact

Abstract Intense atmospheric vortices such as tropical cyclones experience various asymmetric instabilities during their life cycles. This study investigates how vortex properties and ambient conditions determine the relative importance of different mechanisms that can simultaneously influence the growth of an asymmetric perturbation. The focus is on three-dimensional disturbances of barotropic vortices with nonmonotonic radial distributions of potential vorticity. The primary modes of instability are examined for Rossby numbers between 10 and 100 and Froude numbers in the broad neighborhood of unity. This parameter regime is deemed appropriate for tropical cyclone perturbations with vertical length scales ranging from the depth of the vortex to moderately smaller scales. At relatively small Froude numbers, the main cause of instability inferred from analysis typically involves the interaction of vortex Rossby waves with each other and/or critical-layer potential vorticity perturbations. As the Froude number increases from its lower bound, the main cause of instability transitions to inertia–gravity wave radiation. In some cases, the transition occurs abruptly at a critical point where a mode whose growth is driven almost entirely by radiation suddenly becomes dominant. In other cases, the transition is gradual and less direct as the fastest-growing mode continuously changes its structure. Examination of the angular pseudomomentum budget helps quantify the impact of radiation. The radiation-driven instabilities examined herein are shown to be quite fast and potentially relevant to real-world tropical cyclones. Their sensitivities to parameterized moisture and outer vorticity skirts are briefly addressed.

scholarly journals Determining the Extratropical Transition Onset and Completion Times of Typhoons Mindulle (2004) and Yagi (2006) Using Four Methods

2012 ◽  
Vol 27 (6) ◽  
pp. 1394-1412 ◽  
Author(s):  
Qian Wang ◽  
Qingqing Li ◽  
Gang Fu
Keyword(s):  
Phase Space ◽  
Potential Vorticity ◽  
Onset Time ◽  
Data Sources ◽  
Extratropical Transition ◽  
Forecast Uncertainty ◽  
Factors Associated ◽  
Space Technique ◽  
Isentropic Potential Vorticity ◽  
Completion Times

Abstract Four methods for determining the extratropical transition (ET) onset and completion times of Typhoons Mindulle (2004) and Yagi (2006) were compared using four numerically analyzed datasets. The open-wave and scalar frontogenesis parameter methods failed to smoothly and consistently determine the ET completion from the four data sources, because some dependent factors associated with these two methods significantly impacted the results. Although the cyclone phase space technique succeeded in determining the ET onset and completion times, the ET onset and completion times of Yagi identified by this method exhibited a large distinction across the datasets, agreeing with prior studies. The isentropic potential vorticity method was also able to identify the ET onset times of both Mindulle and Yagi using all the datasets, whereas the ET onset time of Yagi determined by such a method differed markedly from that by the cyclone phase space technique, which may create forecast uncertainty.

A Geospatial Analysis of Convective Rainfall Regions within Tropical Cyclones after Landfall

2013 ◽  
pp. 1069-1088
Author(s):  
Corene J. Matyas
Keyword(s):  
Tropical Cyclone ◽  
Tropical Cyclones ◽  
Wind Shear ◽  
Vertical Wind Shear ◽  
Transition Time ◽  
Accurate Assessment ◽  
Areal Extent ◽  
Convective Rainfall ◽  
Extratropical Transition ◽  
The Right

In this article, the author utilizes a GIS to spatially analyze radar reflectivity returns during the 24 hours following 43 tropical cyclone (TC) landfalls. The positions of convective rainfall regions and their areal extent are then examined according to storm intensity, motion, vertical wind shear, time until extratropical transition, time after landfall, and distance from the coastline. As forward velocity increases in conjunction with an extratropical transition, these regions move outward, shift from the right side to the front of the TC, and grow in size. A similar radial shift, but with a decrease in areal extent, occurs as TCs weaken. Further quantification of the shapes of these regions could yield a more spatially accurate assessment of where TCs may produce high rainfall totals.

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