On the Shortening of the Lead Time of Ocean Warm Water Volume to ENSO SST Since 2000

Abstract

The possible factors associated with the shortening of lead time between ocean warm water volume (WWV) variability along the equatorial Pacific and El Niño–Southern Oscillation (ENSO) variability after 2000 are documented. It is shown that the shortening of lead time is due to frequency increases of both WWV and ENSO. During 1979–99 the dominant frequencies were 1.5–3.5 years for both the Niño3.4 and WWV indices. In contrast, during 2000–16, both indices had a relatively flatter spectrum and were closer to a white noise process with a relative maximum at 1.5–2.0 years for the Niño3.4 index and 0.8–1.3 years for the WWV index. The frequency change of ENSO and WWV were linked to a westward shift of the Bjerknes feedback region. The results here are consistent with previous argument that the westward shift of the air-sea coupling region will cause an increase of ENSO frequency, as the corresponding zonal advection feedback reduces the period and growth of coupled instability, thus favoring more frequent and weak El Niño events.

Enhancing the ENSO Predictability beyond the Spring Barrier

“…The difference in the ENSO prediction skill before and after 2000 can be easily observed. The maximum lead time for the WWV index (green curves) before 2000 (6 months) was longer than that after 2000 (3 months), which is consistent with previous studies that the WWV lead time changed from 6-9 months in 1979-1999 to 3-4 months after 2000 21,56 . Moreover, the hindcast skill (correlation) between the observed Niño3.4 and WWV index was much higher before 2000, which is consistent with the decadal change since 2000 that was shown in previous studies 21,23 .…”

A Positive Feedback Onto ENSO Due to Tropical Instability Wave (TIW)‐Induced Chlorophyll Effects in the Pacific

“…The period has a sharp peak at 4.24 years in CTRL, but at 4.14 years in FILT, with a slight difference of approximately 1 month in the oscillation periods. The change in ENSO period may be related to the eastward shift of the zonal wind stresses in the western Pacific (Figure S2), as indicated by previous studies Hu et al, 2017). Thus, taking into account the Chl TIW effects leads to an increase in ENSO amplitude and frequency of strong ENSO events.…”

Understanding the Warm Water Volume Precursor of ENSO Events and its Interdecadal Variation

“…As noted by McPhaden () and Horii et al (), the Pacific Ocean has displayed some distinct changes since the year 2000, so it makes sense to assess these two periods separately. The most obvious of these pre‐2000 to post‐2000 changes is an ~30% reduction in the SD of the control simulation WWV signal, which can be seen in Figures a and c (black line) (e.g., Hu et al, ).…”