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Mark D. Shulman and Reid A. Bryson

Abstract

Stepwise multiple regression analysis applied to annual radial growth increments of mid-latitude hardwood samples indicates that satisfactorily high levels of reduction of the growth variance can he achieved only by utilizing a number of climatic and temporal parameters, both simple and compound. A large part of the variance, as might be expected, is associated with the secular trend of the growth rate. Of the climatic parameters, July precipitation and July evaporative stress were found to be most significant. In particular, since these parameters occurred in the combination precipitation minus evaporative stress, a strong dependence of growth rate on water availability was found.

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Keith W. Dixon and Mark D. Shulman

Abstract

The predictive abilities of NOAA normals and running means of 2–30 years length are tested statistically. Heating degree-day (HDD) data from six northern United States sites are tested using root-mean-square error of prediction (RMSE) tests, mean absolute error (MAE) tests, and a “best versus worst” predictor methodology. Monte Carlo tests using biased and unbiased numbers are presented for the RMSE and “best versus worst” analyses. Results are consistent with past research in showing that running means 10–30 years in length perform better than shorter averaging periods for predictive purposes. The MAE values are generally found to be lowest for running mean lengths shorter than that for the RMSE statistic at the six sites. For the 30 years studied, NOAA HDD normals performed well along the east coast, indicating a possible regional difference that requires more detailed investigation. Limitations of the “best versus worst” predictor method are discussed, and it is suggested that such a procedure should not be solely relied on in determining the optimum length of prediction.

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Cynthia M. Scott and Mark D. Shulman

Abstract

Harmonic analysis, an objective method of analyzing precipitation seasonality, is applied to 1941–70 monthly precipitation normals for nearly 200 stations in the northeastern United States. Our analysis presents distribution of the annual precipitation as the sum of six different sine curves (harmonics). The first three harmonics account for most of the variance in the original precipitation distribution in this area. Maps are presented of percent variance reduction and phase angle, and possible meteorological factors responsible for the observed patterns are suggested. In addition, the results are compared to previous applications of harmonic analysis to monthly precipitation normals during 1921–50 and 1931–60. The greatest difference appears as a substantial increase in the third harmonic in the coastal region from Maryland to Massachusetts. Variance reductions as high as 73% occurred in the center of this area, compared to a maximum value of only 46% for the 1931–60 normal period. Several possible reasons for this phenomenon are discussed.

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