The paper introduces two indices to characterize the El Niño–Southern Oscillation (ENSO) phenomenon: the Niño-3.4 (N3.4) index, which represents the average sea surface temperature (SST) anomalies in the equatorial Pacific, and the Trans-Niño Index (TNI), which reflects the gradient in SST across the same region. These indices are approximately orthogonal and provide a more comprehensive understanding of ENSO's evolution. The TNI is defined as the difference in normalized SST anomalies between the Niño-1+2 and Niño-4 regions. The TNI leads N3.4 by 3 to 12 months prior to the 1976/77 climate shift and follows N3.4 with opposite sign 3 to 12 months later. After 1976/77, the sign of the TNI leads and lags are reversed. The study uses data from two datasets: the NCEP Climate Prediction Center's SST analysis and the HADISST dataset. The time series of N3.4 and TNI show that ENSO events are identified by SST anomalies exceeding 0.4°C in magnitude. The TNI reveals differences in SST patterns across the Pacific, particularly in the central and eastern tropical Pacific. The cross-correlation analysis shows that TNI leads N3.4 by 3 to 12 months before the 1976/77 climate shift and follows it with opposite sign afterward. After 1977, TNI lags N3.4 by about 12 months, with strong correlations. The SST patterns associated with N3.4 and TNI show distinct features, with N3.4 showing a "boomerang" shape of opposite-signed anomalies in the central and eastern tropical Pacific. TNI, on the other hand, shows different patterns before and after the 1976/77 climate shift. The study concludes that two indices are necessary to capture the different flavors of ENSO. The TNI is important for understanding the evolution of ENSO and its predictive potential. The 1976/77 climate shift is associated with changes in the thermocline, which may be linked to climate change and global warming. The study highlights the importance of using multiple indices to accurately characterize ENSO and its impacts.The paper introduces two indices to characterize the El Niño–Southern Oscillation (ENSO) phenomenon: the Niño-3.4 (N3.4) index, which represents the average sea surface temperature (SST) anomalies in the equatorial Pacific, and the Trans-Niño Index (TNI), which reflects the gradient in SST across the same region. These indices are approximately orthogonal and provide a more comprehensive understanding of ENSO's evolution. The TNI is defined as the difference in normalized SST anomalies between the Niño-1+2 and Niño-4 regions. The TNI leads N3.4 by 3 to 12 months prior to the 1976/77 climate shift and follows N3.4 with opposite sign 3 to 12 months later. After 1976/77, the sign of the TNI leads and lags are reversed. The study uses data from two datasets: the NCEP Climate Prediction Center's SST analysis and the HADISST dataset. The time series of N3.4 and TNI show that ENSO events are identified by SST anomalies exceeding 0.4°C in magnitude. The TNI reveals differences in SST patterns across the Pacific, particularly in the central and eastern tropical Pacific. The cross-correlation analysis shows that TNI leads N3.4 by 3 to 12 months before the 1976/77 climate shift and follows it with opposite sign afterward. After 1977, TNI lags N3.4 by about 12 months, with strong correlations. The SST patterns associated with N3.4 and TNI show distinct features, with N3.4 showing a "boomerang" shape of opposite-signed anomalies in the central and eastern tropical Pacific. TNI, on the other hand, shows different patterns before and after the 1976/77 climate shift. The study concludes that two indices are necessary to capture the different flavors of ENSO. The TNI is important for understanding the evolution of ENSO and its predictive potential. The 1976/77 climate shift is associated with changes in the thermocline, which may be linked to climate change and global warming. The study highlights the importance of using multiple indices to accurately characterize ENSO and its impacts.