Search Results

You are looking at 1 - 10 of 18,848 items for :

  • Refine by Access: All Content x
Clear All
Thomas Spengler and Joseph Egger

1. Introduction In this study we test the concept of a causal linkage between a potential vorticity (PV) anomaly and the balanced flow that is attributed to it via PV inversion. Attribution seeks to associate to a “feature on a weather chart, such as a vorticity anomaly, a unique influence on the rest of the atmosphere” ( Bishop and Thorpe 1994 , henceforth BT ). The concept of this attribution is encapsulated in the so-called electrostatics analogy ( BT ; Hoskins et al. 1985 , hereafter HMR

Full access
N. Robb McDonald and E. R. Johnson

current along the Alaskan coast through Unimak Pass. Johnson and McDonald (2004a , 2005) have studied the motion of barotropic vortices in the presence of an infinite barrier perforated by either a single gap or two gaps. They obtained exact analytical expressions for the trajectories of point vortices and compared these to numerical computations of finite area patches of constant vorticity. In the case of point vortices, Crowdy and Marshall (2006) subsequently extended the results of Johnson and

Full access
Eric A. Hendricks, Wayne H. Schubert, Richard K. Taft, Huiqun Wang, and James P. Kossin

1. Introduction Diabatic heating in the core of a tropical storm tends to produce a tower of potential vorticity (PV) that extends into the upper troposphere ( Schubert and Alworth 1987 ). As the storm strengthens into a hurricane and an eye forms, diabatic heating becomes confined to the eyewall region and this PV tower becomes hollow. This hollow tower structure ( Möller and Smith 1994 ) has been recently simulated in a high-resolution full-physics model by Yau et al. (2004) . The sign

Full access
Daniel Gombos and James A. Hansen

piecewise potential vorticity (PV) inversion. The current paper reinterprets Hakim and Torn’s (HT) statistical piecewise PV “inversion” technique as being a PV regression and compares HT08 ’s PV regression results to those from the established dynamical inversion technique of Davis and Emanuel (1991 , hereafter DE91 ) in an effort to explore the applicability of the approach. Section 2 introduces PV, presents the theory of piecewise PV inversion, and describes Davis and Emmanuel’s (DE) piecewise PV

Full access
Timothy J. Dunkerton

1. Introduction Prograde jets are ubiquitous in planetary fluid dynamics ( Baldwin et al. 2007 ). These rotating stratified systems support Rossby waves, quasi-2D turbulent eddies, and their associated lateral transports of angular momentum and potential vorticity (PV), with overturning meridional circulations required to maintain large-scale balance. Various kinds of positive feedbacks exist between the waves, eddies, and mean flow, such that the prograde jets become self-reinforcing. The

Full access
Joseph Egger, Klaus-Peter Hoinka, and Thomas Spengler

1. Introduction Potential vorticity (PV) is an important variable in dynamic meteorology and oceanography and is widely used for the simulation and interpretation of a broad range of flow phenomena (e.g., Vallis 2006 ), where potential vorticity is and is absolute vorticity, η is a function of space and time, and ρ is density ( Ertel 1942 ). Use of is not widespread except for ( θ is potential temperature) where is conserved in adiabatic and inviscid flow. The explicit expression

Full access
Cristiana Stan and David A. Randall

coordinate surfaces whether heating occurs or not. A detailed analysis of the advantages and disadvantages of using potential temperature as vertical coordinate is given by Hsu and Arakawa (1990) . In this paper, we propose a system of coordinates (PVPT coordinates) that consists of longitude, potential vorticity (PV), and potential temperature (PT). The general definition of potential vorticity, as introduced by Ertel (1942) for the adiabatic atmosphere is where ρ is the fluid density, ζ a is the

Full access
Michelle M. Gierach, Mark A. Bourassa, Philip Cunningham, James J. O’Brien, and Paul D. Reasor

systems of apparently organized convection that maintain their identity for 24 h or more but are too weak to be classified as tropical cyclones (i.e., tropical depressions, tropical storms, and/or hurricanes) by the National Hurricane Center (NHC). Each technique utilized surface wind data obtained by the SeaWinds scatterometer; however, the criteria that defined their identification method differed. Sharp et al. (2002) employed surface relative vorticity in their detection condition, whereas Liu

Full access
Robert Davies-Jones

1. Introduction Three-dimensional high-resolution numerical simulations of supercell storms are now capable of reproducing violent tornadoes (e.g., Orf et al. 2017 ; Orf 2019 ). Despite excellent visualizations and extensive diagnostic studies of these complex simulations, there is still no universally accepted explanation of how the tornadoes form. This paper develops formulas for the partial vorticities of parcels that can be used to detect the origins of tornado vorticity in

Restricted access
Joseph Egger and Klaus-Peter Hoinka

of the wave amplitudes upstream and downstream. This pattern is normally moving eastward, intensifies with increasing negative lag, and becomes weaker for positive increasing lag. An example is presented in Fig. 1 where potential vorticity (PV) is selected as a variable with density ρ , vorticity ζ , potential temperature θ , and Coriolis parameter f . The data evaluation is based on the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data (see section

Full access