Transition to El Nino
Phase obs. by OCTS and NSCAT

Chlorophyll-a Concentration and Wind Stress Change
during the Transition to El Nino Phase observed
by ADEOS-OCTS and NSCAT

Monthly WS, SST and CHL in November 1996 (upper) and June 1997 (lower).

As westward wind stress weakened in the equatorial Pacific, SST rose from the eastern part to the eastern coast (140-E to 80-W), and CHL became low in the central part (160-E to 160-W) and near the eastern coast (100-W to 80-W).
GIF Data File revtau.gif	GIF Data File revsst.gif	GIF Data File revchl.gif
TIFF Data File revtau.tif [ 642 Kbyte ]	TIFF Data File revsst.tif [ 703 Kbyte ]	TIFF Data File revchl.tif [ 709 Kbyte ]
PostScript Data File revtau.ps [ 271 Kbyte ]	PostScript Data File revsst.ps [ 1.1 Mbyte ]	PostScript Data File revchl.ps [ 4.3 Mbyte ]







Weekly Wind stress (from NSCAT) and Chlorophyll-a Concentration (from OCTS) from November 1996 to June 1997 for every month.

As westward wind stress weakened in the central part of the equatorial Pacific (160E to 160W), Chlorophyll-a decresed in the area.
GIF Data File windstress.gif	GIF Data File chlconc.gif
TIFF Data File windstress.tif [ 1.0 Mbyte ]	TIFF Data File chlconc.tif [ 1.1 Mbyte ]
PostScript Data File windstress.ps [ 4.3 Mbyte ]	PostScript Data File chlconc.ps [ 12.4 Mbyte ]







Time-longitude sections for WSz, SST and CHL from 100-E to 70-W at the equator in Figures 2.1 (WSz), 2.2 (SST) and 2.3 (CHL). These figures are made from weekly global data. The horizontal axis indicates longitude, and the vertical axis indicates time in weeks (passing from upper to lower). The labels indicate the first days of the weeks. The plus values of WSz indicate an eastward direction. The data were processed by an older version algorithms, so SST values are lower than real.

Westward WSz became weaker in the central and eastern parts, and the boundary between westward and eastward moved from 170-E to 160-W from March to June in 1997. As a result, the zonal gradient of the SST became weaker,and the SST rose near the eastern coast. This is assumed to be caused by the depth of the thermocline, which is deeper in the east and shallower in the west in normal periods, but the gradient is weakened in El Nino periods because the westward WSz decreases. A deep thermocline suppresses cold water upwelling at the eastern coast. In contrast, CHL seemed to change according to the area of westward WSz movement. It is notable that SST and CHL changes differ, even though both are in the same upper ocean process. The data used in this study is Sea Surface Temperature (SST) and Chlorophyll-a concentration (CHL), which were observed by OCTS, and sea surface wind stress (WS) from NSCAT. WS is estimated by wind vectors using formulas developed by Kondo [1975] (the atmosphere is assumed to be stable). CHL, SST and WS were interpolated and averaged for time and space from daily (or weekly) mapped data. The weekly data were processed by an older version (Version 2) algorithm. Their values are not calibrated, but the tendencies are not so bad.

GIF Data File tlonsec.gif

TIFF Data File tlonsec.tif [ 757 Kbyte ]

PostScript Data File tlonsec.ps [ 2.9 Mbyte ]