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Paul H. Ruscher

For many years, readability indices have been utilized to estimate the reading grade level (RGL) of textual material. They have been used chiefly for primary and secondary grade level material, but are applicable to collegiate texts as well. In this study, seven readability indices for 52 atmospheric science textbooks were obtained to estimate their RGL. Half of the texts chosen were of a general or introductory nature, while the other half were specialized or advanced texts. Because only a small sample of the entire text was utilized in their computation, any index may not be exactly representative of RGL of the text as a whole; however, they sare likely to be useful in comparing one book to another.

While the readability level of a text should not be the sole reason for adopting or rejecting a textbook, it should be a consideration.

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Paul H. Ruscher and Thomas P. Condo

Abstract

The unusual case of a rapidly developing land cyclone that occurred on 15–17 November 1989 over the United States and Canada is investigated to determine the physical mechanisms responsible for its development. Hourly surface and 12-h upper-air data are analyzed for this storm for the 36-h period beginning on 0000 UTC 15 November.

Findings reveal that surface-based frontogenetic forcing and the diabatic effects of latent heating were primarily responsible for the initial development of the system. Proper positioning of the surface low with respect to a 500-mb short-wave trough and 250-mb jet streak yields the greatest deepening of 13 mb in 12 h at a later time. It is suggested that frontogenetic mechanisms contribute to development of this system prior to any favorable organization of the large-scale upper-tropospheric dynamic forcing.

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Paul H. Ruscher and Thomas P. Condo

Abstract

The relatively rare case of an explosive land cyclone that occurred on I5–17 November 1989 over the United States and Canada is investigated to determine the physical mechanisms responsible for its development. Hourly surface and 12-h upper-air data are analyzed for this storm for the 36-h period beginning on 0000 UTC 15 November. The system appears to develop through favorable positioning of the surface low with respect to a 5OO-hPa short-wave trough and 250-hPa jet streak and yields the greatest deepening of 13 hPa in 12 h.

Through an analysis of the terms in the quasigeostrophic height tendency equation, quasigeostrophic theory is deemed to be qualitatively inaccurate in diagnosing the development of this system. The performance of the National Meteorological Center's (currently known as the National Centers for Environmental Prediction) operational models is viewed, and errors in model forecasts of surface low position and intensity are attributed in large part to faulty initialization. A companion study examines the thermodynamic and frontogenetical aspects of this case.

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A. Birol Kara, James B. Elsner, and Paul H. Ruscher

Abstract

Nighttime minimum temperatures at the Tallahassee Regional Airport (TLH) are colder in comparison with surrounding locations and other parts of the city, especially during the cool season (TLH minimum temperature anomaly). These cold events are examined using the one-dimensional Oregon State University atmospheric boundary layer (ABL) model including a two-layer model of soil hydrology. The model is used for 12-h forecasts of the ABL parameters, such as surface fluxes, surface inversion height, and minimum temperature when clear, calm synoptic conditions existed over the region at night. The minimum temperature forecasts are performed at TLH and a nearby location. Cooling in the surface inversion layer is examined in terms of turbulence and clear-air radiative effects, and it is confirmed that the lower temperatures at TLH are related to the clear-air radiative cooling even in the lower part of the inversion layer but not to cold-air drainage. Stability, ABL height, and surface inversion height are examined with respect to a potential temperature curvature. Turbulent exchanges in the surface boundary layer are also taken into account. The model is able to simulate the nocturnal evolution of air temperatures well. Besides the soil moisture, the value of the roughness length momentum has a substantial effect on temperature forecasts in the model. The best overall agreement for the minimum temperature prediction over TLH is obtained using equal values for the roughness lengths of heat and momentum. Finally, use of the ABL model with its surface energy balance and crude radiative parameterization package under negligible synoptic-scale forcing can be valuable to a forecaster in predicting the daily maximum temperature drop.

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A. Birol Kara, James B. Elsner, and Paul H. Ruscher

Abstract

The return-flow of low-level air from the Gulf of Mexico over the southeast United States during the cool season is studied using numerical models. The key models are a newly developed airmass transformation (AMT) model and a one-dimensional planetary boundary layer (PBL) model. Both are employed to examine the thermodynamic structure over and to the north of the Gulf. Model errors for predicting minimum, maximum, and dewpoint temperatures at the surface during both offshore and onshore phases of the return-flow cycle are analyzed. PBL model forecasts indicate soil moisture values obtained from the Eta Model improve accuracy. It is shown that forecasts of maximum temperature for coastal locations are sensitive to the soil moisture used in the PBL model. The AMT model performs well in determining boundary layer parameters since it includes horizontal advective processes. The AMT model is also able to predict the regional differences caused by different surface forcing while passing over land or sea. Results lead to a strategy for making predictions during cool-season return-flow events over and around the Gulf of Mexico.

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