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Xubin Zeng, Mike Barlage, Chris Castro, and Kelly Fling

Abstract

Numerous studies have attempted to address the land–precipitation coupling, but scientists’ understanding remains limited and discrepancies still exist from different studies. A new parameter Γ is proposed here to estimate the land–precipitation coupling strength based on the ratio of the covariance between monthly or seasonal precipitation and evaporation anomalies (from their climatological means) over the variance of precipitation anomalies. The Γ value is easy to compute and insensitive to the horizontal scales used; however, it does not provide causality. A relatively high Γ is a necessary—but not sufficient—condition for a relatively strong land–precipitation coupling. A computation of Γ values using two global reanalyses (ECMWF and NCEP), one regional reanalysis [North American Regional Reanalysis (NARR)], and observed precipitation along with Variable Infiltration Capacity (VIC)-derived evaporation data indicates that the land–precipitation coupling is stronger in summer and weaker in winter. The strongest coupling (i.e., hot spots) occurs over the western and central parts of North America, part of the Eurasia midlatitude, and Sahel in boreal summer and over most of Australia, Argentina, and South Africa in austral summer. The Community Climate System Model, version 3 (CCSM3) shows much higher Γ values, consistent with the strong coupling shown by its atmosphere–land coupled components in previous studies. Its overall spatial pattern of Γ values is not affected much over most regions by the doubling of CO2 in CCSM3. The Γ values from the Regional Atmospheric Modeling System (RAMS) are more realistic than those from CCSM3; however, they are still higher than those from observations over North America.

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Rod Frehlich, Robert Sharman, Charles Clough, Michael Padovani, Kelly Fling, Ward Boughers, and W. Scott Walton

Abstract

The effects of atmospheric turbulence on munition target scatter are determined from numerical simulations of ballistic trajectories through many realizations of realistic simulated turbulent wind fields. A technique is evaluated for correcting for the effects of turbulence on ballistic testing procedures by using a line of sonic anemometer measurements taken along the trajectory path. The metric used to evaluate the correction is the difference between the target impact scatter produced with and without the use of the anemometers in the trajectory calculations. The improvement in the testing procedure as measured by this metric is determined as a function of the number of sonic anemometers in the line and the sonic averaging time interval. The performance of the simulations is also compared with data from a field test for a standard small-caliber munition, and the predicted and observed target scatter are in good qualitative agreement, supporting the feasibility of the approach.

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