Search Results

You are looking at 1 - 6 of 6 items for :

  • Author or Editor: Joseph T. Schaefer x
  • Journal of Applied Meteorology and Climatology x
  • Refine by Access: All Content x
Clear All Modify Search
Joseph T. Schaefer

Abstract

The dryline, a narrow non-frontal zone of sharp moisture discontinuity, has long been known as a preferential location of thunderstorm development. Through an examination of several years of data, a conceptual model of the dryline life cycle is developed.

The dryline originates along the trailing edge of a continental air mass and is coincident with an old frontal surface. As it moves, it is located on the surface projection of the western edge of the low-level inversion. The dryline is destroyed either by a new cold air outbreak or by becoming too diffuse to be easily recognizable.

Full access
Joseph T. Schaefer

Abstract

Full access
Joseph T. Schaefer and Charles A. Doswell III

Abstract

A simple analysis of the position error inherent in double-theodolite pibal systems is presented. The quality of data collected by double theodolites is very sensitive to the geometric design of the system, and care must be taken in the interpretation of results.

Full access
Joseph T. Schaefer, Donald L. Kelly, and Robert F. Abbey

Abstract

One of the principle applications of climatological tornado data is in tornado-hazard assessment. To perform such a hazard-potential determination, historical tornado characteristics in either a regional or tom area are complied. A model is then used to determine a site-specific point probability of a tornado greater than a specified intensity occurring. Various models require different climatological input. However, a knowledge of the mean values of tornado track width, tornado track width, tornado affected area and tornado occurrence rate as both a function of tornado intensity and geographic area, along with a violence frequency distribution, enable Mod of the models to be applied.

The NSSFC-NRC tornado data base is used to supply input for the determination of these parameters over the United States. This climatic data base has undergone extensive updating and quality control since it was last reported. For track parameters, internally redundant data were used to cheek consistency. Further, reports which derivated significantly from the mean wore individually checked. Intensity data have been compared with the University of Chicago DAPPLE tornado base. All tornadoes whose recorded intensifies differed by more than one category were reclassified by an independent scientist so that the two data sets are consistent.

Full access
Jiang Chaowei, Donald L. Kelly, and Joseph T. Schaefer

Abstract

Beijing, People's Republic of China, and Topeka, Kansas, United States of America, are located at approximately the same latitude and are affected by similar synoptic weather patterns. However, their thunderstorm climatology differs significantly. Rowinsonde data from the two stations are compared. It is found that the typical distribution of the oceanic subtropical high pressure areas subtly modifies the synoptic scale environment accounting for the observed differences.

Full access
Ashton Robinson Cook, Lance M. Leslie, David B. Parsons, and Joseph T. Schaefer

Abstract

In recent years, the potential of seasonal outlooks for tornadoes has attracted the attention of researchers. Previous studies on this topic have focused mainly on the influence of global circulation patterns [e.g., El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation, or Pacific decadal oscillation] on spring tornadoes. However, these studies have yielded conflicting results of the roles of these climate drivers on tornado intensity and frequency. The present study seeks to establish linkages between ENSO and tornado outbreaks over the United States during winter and early spring. These linkages are established in two ways: 1) statistically, by relating raw counts of tornadoes in outbreaks (defined as six or more tornadoes in a 24-h period in the United States east of the Rocky Mountains), and their destructive potential, to sea surface temperature anomalies observed in the Niño-3.4 region, and 2) qualitatively, by relating ENSO to shifts in synoptic-scale atmospheric phenomena that contribute to tornado outbreaks. The latter approach is critical for interpreting the statistical relationships, thereby avoiding the deficiencies in a few of the previous studies that did not provide physical explanations relating ENSO to shifts in tornado activity. The results suggest that shifts in tornado occurrence are clearly related to ENSO. In particular, La Niña conditions consistently foster more frequent and intense tornado activity in comparison with El Niño, particularly at higher latitudes. Furthermore, it is found that tornado activity changes are tied not only to the location and intensity of the subtropical jet during individual outbreaks but also to the positions of surface cyclones, low-level jet streams, and instability axes.

Full access