Abstract
The interannual variability of sea ice extent in the Okhotsk Sea and the sea surface temperature of the eastern equatorial Pacific Ocean suggested the negative correlation between the larger ice extent of the Okhotsk Sea and El Niho, and followed by the smaller ice extent of it after the El Nino events, that is, Anti-El Niho events(occasionally so called La Nina events).
El Nino events could influence the middle latitude anti-cyclone. Namely, the middle latitude westerlies in the region of the North Pacific Ocean become more zonal wind. The stress of intensified westerly winds drive the sea ice to the overall area of the Okhotsk Sea.
In this study, satellite passive microwave data, mainly DMSP-SMM/I data (1987-1994), were used to calculate the interannual variation of sea ice extent in this area. The derived interannual variation graph showed a small peak in each summer under the ice-free condition. In the former analysis, this phenomena was explained as land effect. However, we supported that this phenomena was mainly caused by the high water vapor in the atmosphere over the Okhotsk Sea in summer season. Considering this effect, we have re-evaluated the trend of the sea ice extent in this area and compared with El Nino/La Nina events.
We could result in almost the same interannual trend of sea ice extent, however, the smaller sea ice extent of the Okhotsk Sea, which was obtained by the former algorithm of sea ice concentration.
It also becomes very important for monitoring the interannual variability of sea ice extent in Okhotsk Sea because Noda (1996) pointed out that a notable CO2-induced warming has firstly appeared around the Okhotsk Sea, although the model resolutions are not enough to resolve the local climate changes and the sea ice model is simple. However, these transient response is plausible because the Okhotsk Sea locates at the southernmost boundary of sea ice formation in the Northern Hemisphere. Therefore, further studies on sea ice extent and El Niho events will be important and continued by satellite microwave data.
