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Kenneth H. Jehn

Abstract

An analysis is presented of continentality in the Texas coastal zone, based on standard climatological data from the existing National Weather Service network. In spite of prevailing onshore winds throughout the year, Texas coastal zone stations (Gulf of Mexico to 150 mi inland) exhibit a substantial degree of continentality by any of the usual definitions. Continentality by the Conrad definition ranged from approximately 25% in the Brownsville area to about 38% inland, with a mean value of approximately 33% for the 1941–70 period in the entire coastal zone.

Additionally, some measurements are presented of horizontal gradients of air temperature in summer and winter along a line perpendicular to the Gulf coast from near Port Aransas to near Sinton, Tex., approximately 30 mi inland. Mean daily temperature range and other statistical parameters for these stations underscored the continentality findings, and demonstrated substantial horizontal gradients of continentality in the immediate coastal zone, with a value of continentality of about 20% at the Port Aransas beach. Overwater values of continentality from summarized ship reports off the Texas coast were of the order of 18–20%.

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Kenneth H. Jehn
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Kenneth H. Jehn and Keith Zimmermann
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HSING-WU WU and KENNETH H. JEHN

Abstract

Wind data at and above the 500-mb level taken from the El Paso, Tex., rawinsonde Station (rawin) and pressure-height data at the same levels from Albuquerque, N. Mex., Midland, Tex., Tueson, Ariz., and Chihuahua, Mexico, during the 1965–66 winter and the 1966 summer periods were used to study geostrophic wind deviation. Geostrophic winds were computed directly from the pressure-height data by a finite-difference method and compared to the actual wind as measured at El Paso. The variations of the “apparent” geostrophic wind deviation with wind speed and pressure-height were examined. Errors involved were analyzed and the “true” geostrophic wind deviation and the total wind accelerations were estimated. Results of the study reveal: (1) that despite the improvement in the accuracies of the radiosonde pressure-height and rawin data, the errors in the data still account for a large portion of the apparent geostrophic wind deviation at higher levels (at and above the 150-mb level); (2) that to use the geostrophic wind approximation in cases with wind speed less than 20 m/s would probably result in vector wind errors of the order of 40 percent or more; and (3) that the mean true geostrophic wind deviation increases when the mean actual wind speed increases, and the estimated mean total wind accelerations range from 1 × 10−4 to 5 × 10−4 m·s−2 at and above the 500-mb level.

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Herschel T. Knowles and Kenneth H. Jehn

Abstract

A synoptic precipitation climatology was derived for central Texas centering on Austin. Characteristics of the 500 mb wind field were combined with a surface wind parameter to “type” the 1200 GMT circulation pattern for 2327 days of study. The relative frequency of precipitation was computed for three consecutive 12 h periods following 1200 GMT for each circulation type. Use of the derived precipitation frequencies as a first estimate of the probability of precipitation, given a predicted circulation pattern, was evaluated for its effectiveness as a forecast tool. Results indicated that for the first 12 h period, use of the synoptic climatology provided guidance inferior to that currently available to forecasters in the field. However, for the second and the third 12 h periods, the synoptic climatology provided guidance better than that available to meteorologists over teletype and the weather facsimile network.

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