|
A MAGIS-based Global Sea Level Analysis
 Fig. 6 Geographical distribution of primary frequency in global sea level variability After the major period of global sea level variability is obtained, a harmonic analysis is performed to extract the annual, semiannual and monthly components of the global sea level variability. We set the harmonic numbers to 4, and period to 52 (weeks). Figure 7 shows the annual and semiannual amplitudes of sea level variability.  (a) (b) Fig. 7 Harmonics of global SLA: (a) Annual component; (b) semiannual component Obviously, the sea level anomaly of the Northern Hemisphere is higher than that of the Southern Hemisphere, especially the northwest Pacific and the northwest Atlantic. Maxima are found at 10°N and 40°N, where it takes on a banded structure. And the area north of the Indian Ocean also has a relatively high sea level anomaly. In contrast, the Southern Hemisphere is lower. Higher frequency harmonics have less banded preference. As to the semiannual component, the maximum is found at the northern Indian Ocean, the second maximum at the equator Pacific. Figure 8 is the spatial distribution of the month in which maximum of annual sea level anomaly occur. The Northern Hemisphere reaches a maximum in JJA, while the Southern Hemisphere reaches maxima in DJF, which is obviously shown in the Atlantic and the Indian Ocean, but not very compellent in the Pacific. This is consistent with the fact: the Northern Hemisphere receives much more sun radiation in summer than in winter, and this leads to the expansion of sea water, and the sea level rise accordingly.  Fig. 8 Month in which annual sea level anomaly maxima occur |