Vernon Meentemeyer

OBSERVATIONS OF NEEDLE ICE GROWTH AND POTENTIAL FOR ACCELERATED EROSION ON THE GEORGIA PIEDMONT

Needle ice is a frost form which grows as an accumulation of fine, bristle-like columns of ice protruding from the soil surface. (J) Field and laboratory investigations of this form of segregation ice have shown that needle ice forms only within narrow microclimatic and soil moisture and texture ranges. It forms often enough on the Southern Piedmont to be recognized as an agent capable ofenlarging gullies. (2) Field studies of the microclimatic and soil conditions under which needle ice will grow on the Georgia Piedmont were performed as part of a study ofthe soil texture and moisture limits of needle ice growth. Measurements included needle ice numbers per unit area, height, and mass and weight of soil displaced for two level sites and two sloping locations in Athens, Georgia. This paper reports the observations and measurements made and presents an estimate of the potential for accelerated erosion by a typical needle ice event. THE GROWTH OF NEEDLE ICE. For needle ice to grow, a freezing plane must develop at or just below the soil surface. Thin ice filaments grow molecule by molecule from a soil pore and lift whatever soil, stony debris, or organic matter is available above the freezing plane (Fig. 1). Soil water must be able to ascend rapidly to this freezing plane to provide water for growing ice and to keep the plane from descending deeper into the soil. The stable freezing plane from which the ice grows is maintained by a delicate balance between the rate of cooling and the rate of heat released as the latent heat of fusion. (3) Actual movement ofwater to the freezing plane is caused by the thermal gradients created

Temporal Trends of Mean and Extreme Wind Chill in Georgia, 1961-1990

Our primary goal in this paper is to examine temporal and spatial variability of mean and extreme wind chill in Georgia over the period 1961-1990. Because short-term moderations of extreme climatic conditions result in reduced demand for electricity, this type of climatological analysis is critical to the strategic planning and forecasting needs of electric power generation industries. Daily values of a wind chill index (WCI) were calculated for Georgias six primary weather stations for winter months of each year. From this time series mean daily WCI, the highest daily mean WCI, and the highest one-hour WCI in a given year are examined. The strongest temporal patterns are found to occur near the end of the study period, with mean and extreme recorded wind chills exhibiting robust downward trends into 1990. Although absolute values of recorded wind chill are found to vary across the state, there is substantial covariance among the six stations.