Table 1_Atmospheric and oceanic controls of coastal upwelling in the northern Gulf of Guinea: insights from Keta, Ghana.docx

GCUI shows no significant relationship with SST at lag 0 (r = -0.01), but exhibits a significant negative correlation at lags -5 and -6 (r = -0.23 and -0.20), indicating SST anomalies precede geostrophic anomalies by roughly half a year—distinct from the concurrent ECUI-SST response. The mEOF analysis identifies a dominant co-variability mode explaining 34.0% of shared interannual variance, well-separated by North's rule and stable under block-bootstrap resampling (congruence = 0.98).

Temporal evolution indicates no discrete regime shift; instead, change-point analysis reveals a long-term trend (predominantly in SSH) superimposed on shorter-timescale interannual variability.</p>Discussion<p>The Keta sector combines the domain's strongest diagnosed atmospheric forcing with a spatially consistent geostrophic signal (absent in the western Gulf), identifying it as a particularly favorable dynamical sector for coastal upwelling.

Sensitivity analyses confirm these findings are robust to coastline angle (10–30°), drag coefficient, and upwelling length scale variations. Ultimately, this study provides a transferable, robust diagnostic framework for examining joint atmospheric-oceanic upwelling dynamics in tropical coastal systems.</p>