Dynamical tropopause based on isentropic potential vorticity gradients

2011 ◽  
Vol 116 (D1) ◽  
Author(s):  
A. Kunz ◽  
P. Konopka ◽  
R. Müller ◽  
L. L. Pan
Keyword(s):  
Potential Vorticity ◽  
Isentropic Potential Vorticity

scholarly journals On the use and significance of isentropic potential vorticity maps

2007 ◽  
Vol 111 (470) ◽  
pp. 877-946 ◽  
Author(s):  
B. J. Hoskins ◽  
M. E. McIntyre ◽  
A. W. Robertson
Keyword(s):  
Potential Vorticity ◽  
Isentropic Potential Vorticity

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.

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.

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.

Static Stability Associated with Southern Hemisphere Blocking Onsets

2020 ◽  
Author(s):  
Li Dong ◽  
Stephen Colucci
Keyword(s):  
Southern Hemisphere ◽  
Potential Vorticity ◽  
Local Minimum ◽  
Static Stability ◽  
Upper Troposphere ◽  
Horizontal Advection ◽  
Budget Analysis ◽  
Isentropic Potential Vorticity ◽  
Extratropical Tropopause ◽  
Vorticity Anomaly

<p>The horizontal and temporal variation of static stability prior to blocking onset is characterized through composite analysis of blocking events in the Southern Hemisphere. It is found that a local minimum of static stability in the upper troposphere and on the tropopause is achieved over the block-onset region when blocking onset takes place. From the perspective of isentropic potential vorticity, blocking onset is accompanied by extratropical tropopause elevation and a local low isentropic potential vorticity anomaly that is formed right under the elevated tropopause. This low isentropic potential vorticity anomaly is coincident with a local minimum of static stability over the block-onset region. In addition, based on static stability budget analysis, it revealed that the decrease of static stability in the upper troposphere and on the tropopuase prior to blocking onset is attributable to horizontal advection of low static stability from subtropics to midlatitude as well as the stretching effect associated with upper-level convergence, with the horizontal advection forcing being the primary contributor. On the other hand, the vertical advection of static stability tends to oppose the decreasing static stability through advecting more stable air downward such that it stabilizes the local air over the block-onset region. Furthermore, the indirect and direct effect of latent heat to the local change of static stability over the block-onset region are also discussed, respectively.</p>

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