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Last modified
7/28/2009 2:29:18 PM
Creation date
7/18/2007 11:59:32 AM
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Weather Modification
Title
A Comparison of Snow Telemetry and Snow Course Measurements in the Colorado River Basin
Prepared For
Journal of Hydrometeorology
Prepared By
Dressler, Fassnacht, Bales
Date
8/1/2006
Weather Modification - Doc Type
Report
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<br />710 <br /> <br />ogram origin, a measure of sampling error or short- <br />scale variability in the dataset. <br />Snow course variance was best modeled by the Gauss- <br />ian model (Fig. 8), while SNOTEL variance was best <br />modeled by the spherical model, as determined by <br />maximizing the "indicativeness of fit" parameter, which <br />is a statistical measure of the model fit to data vari- <br />nce across spatial lag distances, in the UNIX-based <br />Geostatistical Environmental Assessment Software (in- <br />formation available online at http://www.ai-geostats. <br />org/software/Geostats_software/ geoeas.htm). Vari- <br />ogram model fits for 1993 show that snow course data <br />had an approximate range (correlation length scale, de- <br />fined as the range or the practical lag distance at which <br />variance does not change significantly with increasing <br />lag distance) of 500 km for collocated sites and 550 for <br />all snow course locations, while SNOTEL data had a <br />correlation length scale of approximately 300 km. Snow <br />course correlation length scales in the average snow <br />year of 1998 (400 km) were smaller than in 1993, but <br />within the dry snow year of 1999 (500 km) they are <br />comparable (Table 2). In all cases, the nugget, defined <br />as the discontinuity at the origin of the variogram and <br />explained by factors such as sampling error and short- <br />scale variability (Isaaks and Srivastava 1989), was <br />larger for SNOTEL than for snow course data and was <br />as much as twice that of collocated snow course data for <br />1993 and 1999. Nugget values are largest in 1993 and <br />smallest in 1999 for both datasets, and are larger for <br />SNOTEL than snow course data for all years. <br /> <br />5. Discussion <br /> <br />~. .J <br /> <br />VOLUME 7 <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br /> <br />- Gaussian Model <br />. Variance <br /> <br />. <br /> <br /> <br />- Gaussian Model <br />· Variance <br /> <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />- Spherical Model <br />. Variance <br /> <br />200 <br /> <br />400 <br />lag distance, km <br /> <br />600 <br /> <br />800 <br /> <br />FIG. 8. The 30 Mar 1993 variograms and model fits for the <br />Colorado River basin. <br /> <br />occurred during years of lower snow accumulation. <br />The 1990-99 average correlation (0.90) for the 93 Horever, relative differences in season-averaged SWE <br />collocated sites is the same as that of Serreze et al. were somewhat smaller in higher-accumulation years, <br />(1999), in which they calculated correlation for the fori example, 1 % in 1993 versus 13% in 1999. The 4 yr <br />1980-87 period using 92 collocated sites over the entire with the greatest relative differences (9%-13%) had a <br />western United States. Higher correlations generally me~n peak SWE of 191 versus 232 mm for the 6 yr with <br /> <br /> <br />TMill' Th, 30 MM'" =;0"=' '0< ,1. 000= ~d SNOTEL d,". <br />I <br /> <br />Data Model Nugget Sill Range Correlation length (km) <br />1993 <br />Snow course (collocated) Gaussian 22 000 45 000 42 750 500 <br />Snow course (all) Gaussian 34 000 38 000 36100 550 <br />SNOTEL Spherical 49 000 26 000 26 000 300 <br />1998 <br />Snow course (collocated) Spherical 28 000 3000 3000 400 <br />Snow course (all) Spherical 29 000 2000 3000 400 <br />SNOTEL Spherical 34 000 9500 3000 300 <br />1999 <br />Snow course (collocated) Gaussian 11 000 15 000 14250 500 <br />Snow course (all) Spherical 16000 11 000 11000 500 <br />SNOTEL Spherical 22 000 19000 19000 300 <br />
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