The dynamics of a polar low assessed using potential vorticity inversion

2009 ◽  
Vol 135 (641) ◽  
pp. 880-893 ◽  
Author(s):  
Thomas J. Bracegirdle ◽  
Suzanne L. Gray
Keyword(s):  
Potential Vorticity ◽  
Potential Vorticity Inversion ◽  
Polar Low

Geostrophy via potential vorticity inversion in the Yucatan Channel

2001 ◽  
Vol 59 (5) ◽  
pp. 725-747 ◽  
Author(s):  
J. Ochoa ◽  
J. Sheinbaum ◽  
A. Badan ◽  
J. Candela ◽  
D. Wilson
Keyword(s):  
Potential Vorticity ◽  
Potential Vorticity Inversion ◽  
Yucatan Channel

Local Mass Conservation and Velocity Splitting in PV-Based Balanced Models. Part II: Numerical Results

2007 ◽  
Vol 64 (6) ◽  
pp. 1794-1810 ◽  
Author(s):  
Ali R. Mohebalhojeh ◽  
Michael E. McIntyre
Keyword(s):  
Potential Vorticity ◽  
Wave Speed ◽  
Invariant Manifolds ◽  
Mass Conservation ◽  
Flow Speed ◽  
Local Mass ◽  
Potential Vorticity Inversion ◽  
Divergence Equation ◽  
Local Mass Conservation ◽  
Derivatives Of

The effects of enforcing local mass conservation on the accuracy of non-Hamiltonian potential-vorticity- based balanced models (PBMs) are examined numerically for a set of chaotic shallow-water f-plane vortical flows in a doubly periodic square domain. The flows are spawned by an unstable jet and all have domain-maximum Froude and Rossby numbers Fr ∼0.5 and Ro ∼1, far from the usual asymptotic limits Ro → 0, Fr → 0, with Fr defined in the standard way as flow speed over gravity wave speed. The PBMs considered are the plain and hyperbalance PBMs defined in Part I. More precisely, they are the plain-δδ, plain-γγ, and plain-δγ PBMs and the corresponding hyperbalance PBMs, of various orders, where “order” is related to the number of time derivatives of the divergence equation used in defining balance and potential-vorticity inversion. For brevity the corresponding hyperbalance PBMs are called the hyper-δδ, hyper-γγ, and hyper-δγ PBMs, respectively. As proved in Part I, except for the leading-order plain-γγ each plain PBM violates local mass conservation. Each hyperbalance PBM results from enforcing local mass conservation on the corresponding plain PBM. The process of thus deriving a hyperbalance PBM from a plain PBM is referred to for brevity as plain-to-hyper conversion. The question is whether such conversion degrades the accuracy, as conjectured by McIntyre and Norton. Cumulative accuracy is tested by running each PBM alongside a suitably initialized primitive equation (PE) model for up to 30 days, corresponding to many vortex rotations. The accuracy is sensitively measured by the smallness of the ratio ϵ = ||QPBM − QPE||2/||QPE||2, where QPBM and QPE denote the potential vorticity fields of the PBM and the PEs, respectively, and || ||2 is the L2 norm. At 30 days the most accurate PBMs have ϵ ≈ 10−2 with PV fields hardly distinguishable visually from those of the PEs, even down to tiny details. Most accurate is defined by minimizing ϵ over all orders and truncation types δδ, γγ, and δγ. Contrary to McIntyre and Norton’s conjecture, the minimal ϵ values did not differ systematically or significantly between plain and hyperbalance PBMs. The smallness of ϵ suggests that the slow manifolds defined by the balance relations of the most accurate PBMs, both plain and hyperbalance, are astonishingly close to being invariant manifolds of the PEs, at least throughout those parts of phase space for which Ro ≲ 1 and Fr ≲ 0.5. As another way of quantifying the departures from such invariance, that is, of quantifying the fuzziness of the PEs’ slow quasimanifold, initialization experiments starting at days 1, 2, . . . 10 were carried out in which attention was focused on the amplitudes of inertia–gravity waves representing the imbalance arising in 1-day PE runs. With balance defined by the most accurate PBMs, and imbalance by departures therefrom, the results of the initialization experiments suggest a negative correlation between early imbalance and late cumulative error ϵ. In such near-optimal conditions the imbalance seems to be acting like weak background noise producing an effect analogous to so-called stochastic resonance, in that a slight increase in noise level brings PE behavior closer to the balanced behavior defined by the most accurate PBMs when measured cumulatively over 30 days.

scholarly journals About the Reliability of Manual Model PV Corrections to Improve Forecasts

2012 ◽  
Vol 27 (6) ◽  
pp. 1554-1567 ◽  
Author(s):  
Philippe Arbogast ◽  
Karine Maynard ◽  
Catherine Piriou
Keyword(s):  
Potential Vorticity ◽  
Initial Conditions ◽  
Primary Source ◽  
Weather Forecast ◽  
Initial State ◽  
Sea Level Pressure ◽  
Potential Vorticity Inversion ◽  
Human Modification ◽  
Balanced Distribution ◽  
Source Of Information

Abstract The National Weather Forecast Centre of Météo-France has developed a tool that corrects the state of the atmosphere within the Action de Recherche Petite Echelle Grande Echelle (ARPEGE) operational global model by adjusting the potential vorticity when the initial conditions and available observations disagree. Among observational datasets, geostationary satellite data are the primary source of information. Here, the representation of the coherent structures of the tropopause in the model is assessed with Meteosat ozone and water vapor images. Modifications to the initial conditions of the potential vorticity (PV) in areas where the model fails can be applied using a potential vorticity inversion, thus providing a new balanced distribution of the wind and temperature that will then be used as a new initial state. The purpose of the paper is to investigate the degrees of weakness of the present qualitative approach. To this end, PV modifications to the initial conditions are applied by different experts on the eve of the windstorm Klaus (24 January 2009) that hit southwestern France. The different initial PV fields and the subsequent forecasts show significant differences in terms of wind and mean sea level pressure, while sharing some common features. The human modification process is therefore partially reproducible and skillful since the forecast is improved most of the time.

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.

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