Digital Signal Processing Reference
In-Depth Information
90
6
.2
6
.2
7
.5
4
.8
60
4
.8
7
.5
8
.9
1
1.
6
6
.2
1
1.6
15.7
6.2
6.
2
3
.5
13.0
30
2.
1
1
1.6
4
.8
8.
9
6
.2
4
.8
3
.5
7
.5
7
.5
2
.1
15.7
0
2.1
7.
5
1
1.6
8
.9
−30
3. 5
4
.8
3
.5
3.5
2
. 1
−60
−90
0
60
120
180
240
300
360
Longitude (deg)
Fig. 3.23
Amplitude (in mm) of annual PWV variations from global IGS observations
latitude, the water vapor in western China is lower than in eastern China, which
may be caused by a colder atmosphere over the high, snow-covered surface over the
western areas, i.e. Tibet (Jin et al.
2008
). Therefore, the distribution of atmospheric
water vapor in the globe is mainly dominated by the latitude, topographical features,
and climatic conditions.
3.4.4
Seasonal PWV Variations
The annual cycle of water vapor reflects the atmospheric process and circulation
patterns. Figure
3.23
shows the amplitude (in units of mm) of annual PWV
variations from global IGS observations. The higher amplitudes are found in mid-
latitudes with about 10-20
˙
0.5 mm and the lower amplitudes with about 5
˙
0.5 mm are located in high latitudes and equatorial areas (Fig.
3.24
). The peak of
maximum water vapor concentration is in summer, i.e. July-August for the Northern
Hemisphere and January-February for the Southern Hemisphere (Fig.
3.25
). In
contrast, the minimum water vapor content is in winter. The strong seasonal cycles
in summer with a maximum water vapor are due to the influence of a moist summer
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