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mutual consistency of snow depth vs. snow extent over North America. Results from all three of
the datasets described above consistently indicate that at continental/regional scales, snow depth
and snow extent anomalies are not mutually consistent.
Figure 1a shows that the monthly evolution of both mean and variability of snow depth and
snow extent for North America follows different temporal patterns. Snow extent increases in the
early snow season and reaches its maximum value in January, but interannual variability of
monthly snow extent is small in January. On the contrary, both mean value and range of
variability of monthly snow depth increases steadily through February/March. Another indication
of different behavior between these two snow parameters is the monthly correlation between snow
depth and snow extent, presented in Figure 1b. The interannual snow depth and snow extent
timeseries are often poorly correlated, especially in winter. Figure 1c shows the coefficient of
variation (i.e., ration of standard deviation to mean) for both extent and depth, and indicates that
the interannual variability of snow depth comprises a larger percentage of its climatological mean
state than that for snow extent, consistently across all months. Hence the magnitude of snow depth
variability can be considered more substantial than the magnitude of snow extent variability.
Monthly scatterplots (Figure 1d) support the correlation results, i.e., wide scatter and a lack of an
apparent snow extent vs. snow depth relationship during winter, and a more noticeable but still
modest relationship during autumn and spring.
sne (10 6 km 2 )
snd(cm)
corr(snd,sne)
20
18
16
14
12
10
50
40
30
20
10
0
1
0.8
0.6
0.4
0.2
Nov Dec Jan Feb Mar Apr
month
Nov Dec Jan Feb Mar Apr
month
0
Nov Dec Jan Feb Mar Apr
month
a) b)
c) d)
Figure 1. Nov.–Apr. timeseries of North America snow extent “sne” (Brown, 2000) and grid domain average
snow-covered depth “snd” (Dyer and Mote, 2006) from 1956 to 1997. a) Monthly box plots of interannual
sne and snd; b) Monthly correlations between interannual sne and snd; c) Monthly cv (std/mean) of
interannual sne and snd time series; d) Monthly scatterplots of interannual sne and snd.
CV
snd (cm)
snd (cm)
46
0.2
0.15
0.1
0.05
0
Nov Dec Jan Feb Mar Apr
month
15
snd=0.81*sne-1.12
R2 Nov.
=0.2220
10
5
10 15 20
45
snd=1.61*sne+4.36
40 R2 Feb.
=0.1011
35
30
25
10 15 20
30
snd=0.78*sne+6.09
25 R2 Dec.
=0.1052
20
15
50
snd=1.86*sne+1.76
45 R
40
35
30
25
20
10 15 20
2 =0.1530
sne (10 6 km 2 10
10 15 20
sne (10
Mar.
)
6 km 2 )
40
snd=0.80*sne+13.05
35 R2 Jan.
=0.0269
30
25
20
10 15 20
35
snd=2.25*sne-9.23
30 R2 Apr.
=0.2508
25
20
15
snd
sne
10
10 15 20