An Equivalent Isobaric Geopotential Height and Its Application to Synoptic Analysis and a Generalized v Equation in s Coordinates

• Main Authors: Qiu-shi Chen, David, H. Bromwich
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1997
• Subjects: Greenland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.670.7667; http://polarmet.osu.edu/PMG_publications/chen_bromwich_mwr_1999.pdf

In s coordinates, a variable f e(x, y, s, t) whose horizontal gradient 2=f e is equal to the irrotational part of the horizontal pressure gradient force is referred to as an equivalent isobaric geopotential height. Its inner part can be derived from the solution of a Poisson equation with zero Dirichlet boundary value. Because 2=f (x, y, p, t) is also the irrotational part of the horizontal pressure gradient force in p coordinates, the equivalent geopotential f e in s coordinates can be used in the same way as the geopotential f (x, y, p, t) used in p coordinates. In the sea level pressure (SLP) analysis over Greenland, small but strong high pressure systems often occur due to extrapolation. These artificial systems can be removed if the equivalent geopotential f e is used in synoptic analysis on a constant s surface, for example, at s 5 0.995 level. The geostrophic relation between the equivalent geopotential and streamfunction at s 5 0.995 is approximately satisfied. Because weather systems over the Tibetan Plateau are very difficult to track using routine SLP, 850-hPa, and 700-hPa analyses, equivalent isobaric geopotential analysis in s coordinates is especially useful over this area. An example of equivalent isobaric geopotential analysis at s 5 0.995 shows that a secondary high separated from a major anticyclone over the Tibetan Plateau when cold air affected the northeastern part of the plateau, but this secondary high is hardly resolved by the SLP analysis. The early stage of a low (or vortex), called a