Dr. David M. Schultz

National Severe Storms Laboratory


Frontal/Cyclone Conceptual Models

While at SUNY, my Ph.D. thesis was aimed at reconciling a controversy over the structure and evolution of midlatitude cyclones (these are the phenomena that are commonly called "low pressure systems"). For about seventy years, meteorologists have been using a conceptual model of cyclone evolution proposed by the Norwegians. About eight years ago, it became apparent that cyclones off the East Coast of the United States (and in other areas) evolved somewhat differently (the Shapiro-Keyser model). My research was entitled "The Effect of Large-Scale Flow on Low-Level Frontal Structure and Evolution in Midlatitude Oceanic Cyclones", where I show that the structure of the cyclone and its attendant fronts is highly dependent on the shape of the jet stream in which the cyclone is embedded. When the cyclone is embedded in diffluent, high-amplitude flow, the structure resembles the Norwegian cyclone model, whereas when the cyclone is embedded in confluent, low-amplitude flow, the structure resembles the Shapiro-Keyser model.

Two conceptual models of cyclone evolution showing lower-tropospheric (i.e., 850 hPa) geopotential height and conventional frontal symbols (top) and potential temperature (bottom). (a) Norwegian cyclone model: (I) incipient frontal cyclone, (II) and (III) narrowing warm sector, (IV) occlusion; (b) Shapiro--Keyser cyclone model: (I) incipient frontal cyclone, (II) frontal fracture, (III) frontal T-bone and bent-back warm front, (IV) frontal T-bone and warm-core seclusion. The stages in the respective cyclone evolutions are separated by approximately 12 h. Panel (b) is adapted from Shapiro and Keyser (1990, their Fig.~10.27) to enhance the zonal elongation of the cyclone and fronts and to reflect the continued existence of the frontal T-bone in stage IV.

This research is published in July 1998 Monthly Weather Review.
Download an Adobe Acrobat version of this manuscript.

Idealized primitive-equation simulations of cyclones embedded in confluence and diffluence have been performed by Heini Wernli of ETH in Zurich, Switzerland. His simulations support the Schultz et al. (1998) results. Here are his results.
If you have any further questions about the research discussed here, or desire a manuscript, please feel free to write to me: david.schultz@noaa.gov.

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