On Corrections for Monthly Mean Sea Level

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  • 月平均潮位の補正について
  • ツキ ヘイキン チョウイ ノ ホセイ ニ ツイテ

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Among effects of various factors on monthly mean sea level, barometric pressure, water temperature and oceanographic conditions are predominant. For the correction of barometric pressure, the theoretical value of -10 mm/mb instead of the actual ones can be adopted. The water temperature during the same month is conventionally used for the temperature correction of monthly mean sea level in a month. Considering the irregular seasonal variation of the thermocline, the modified tem perature at lm below sea surface is proposed. As its application, a method of temperature correction in which the water temperature is shifted in phase, is derived in this paper. This method can be considered as an approximation to the dynamic depth anomaly, of which determination is very difficult because of scantiness of oceanographic data. The following are clarified. 1) The change of monthly mean sea level has the time lag of 1-2 months for the change of water temperature at lm below sea surface, showing the maximum time lag at Abratsubo, as shown in Table III. 2) The temperature coefficients rather vary year by year at each tide gauge station, as shown in Table IV. 3) The standard deviation of noises left after the present correction reduces by 20-35% comparing with that of the conventional correction. The noises remained after the correction seem to be caused by the oceanographic conditions. So long as the effect of oceanographic conditions on monthly mean sea level is not clarified, it seems likely that the vertical displacement of the earth's crust within a few months can not be discussed with confidence.

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