Ground GNSS Atmospheric Sensing - GNSS Remote Sensing: Theory, Methods and Applications - page 47

mm

90

125

60

105

30 85

0 65

−30

45

−60

25

−90 5

0 60 120 180 240 300 360

Longitude (deg)

Fig. 3.11 Annual variation amplitude of ZTD at globally distributed 150 GPS sites

120

100

80

60

40

20

0

−90 −60 −30 0 30 60 90

Latitude (deg)

Fig. 3.12 Distribution of annual ZTD variation amplitude with the latitude

The distribution of the semiannual variation phase with the latitude has no clear
symmetry (Fig. 3.14 ). For example, at the latitudes of 40 ı N-50 ı N in the Northern
Hemisphere, the semiannual phase is about 30 ı (about January), while at the
latitudes of 40 ı S-50 ı S in the Southern Hemisphere, the semiannual phase is about
330 ı

(November).