Global SST and El Niño/La Niña Monitor

Global & Tropical Pacific SST Anomalies

Absolute Sea-Surface Temperature

The actual SST field (not anomaly), global and tropical Pacific. The warm pool, equatorial cold tongue, and western boundary currents are visible directly; watch them shift day to day.

SST Anomaly — Global-Mean Removed

The anomaly with the area-weighted global-mean SST anomaly subtracted at every point. This strips out the uniform background-warming signal and isolates the pattern of warming and cooling — the El Niño footprint stands out against a more balanced global ocean.

Equatorial Pacific Subsurface Temperature

Depth–longitude cross-section along the equator (0°N) from the TAO/TRITON moored-buoy array: temperature (top) and its anomaly versus the 1991–2020 average (bottom), 5-day smoothed.

What to look for: The thermocline (here the 26°C and 28°C isotherms) tilts upward toward the east. Subsurface warm or cool anomalies along the thermocline often lead the surface ENSO signal — watch them build and propagate eastward in the animation.

Relative Oceanic Niño Index (RONI)

RONI is an ENSO index that subtracts the tropical-mean SST anomaly (20°S–20°N) from the Niño-3.4 anomaly, then applies a 3-month running mean. By removing the slowly-rising tropical background, it isolates the ENSO signal more cleanly than the conventional ONI — increasingly useful as overall ocean temperatures trend upward.

How to read it: Red bars (positive) lean El Niño, blue bars (negative) lean La Niña; the dashed lines mark the ±0.5°C guides. This index is computed directly from OISST and shown in °C — it captures the shape and timing of CPC's RONI but is not their standardized published value.

Daily Equatorial Pacific SST Indices

All three daily metrics on one axis: the Niño-3.4 anomaly (the basis of ONI), the tropical-mean anomaly (20°S–20°N), and their difference — the daily relative index that underlies RONI. These are single-day values, so they are noisier than the 3-month running indices above, but they show the most recent evolution.

What to look for: When the red (Niño-3.4) and green (tropical-mean) lines move together, the blue relative line stays flat — that's background warming, not ENSO. The blue line separating from zero is the genuine ENSO signal.

CanSIPS Niño-3.4 Seasonal Forecast (GEM-NEMO)

Niño-3.4 SST-anomaly forecast plume from the GEM-NEMO component of Environment Canada's CanSIPS seasonal system (ensemble members 1–20), out ~11 months. Traditional (left) is the Niño-3.4 anomaly vs the model's own 1991–2020 hindcast climatology; relative (right) subtracts the 20°S–20°N tropical-mean anomaly (RONI-style). Using the model's hindcast climatology removes its drift/bias.

Bold red is the current issue's ensemble mean (thin red = members); dashed grey is last month's forecast (with its 10–90% spread) — where they overlap you can see how the outlook is trending month-to-month.

This Event vs. 1997, 2015 & 2023

Niño-3.4 evolution (7-day running mean) through each event's development year and the next. Bold lines are RONI — the relative index (Niño-3.4 minus the 20°S–20°N tropical-mean anomaly), which removes the rising warming background so events decades apart are comparable; faint dotted lines are the raw ONI for reference. The current event is red. Note how 2015's record ONI shrinks toward 1997 once the background is removed.

El Niño Flavor — Niño Regions vs. Analogs

Relative Niño-1+2 / 3 / 3.4 / 4 anomalies (7-day mean, each minus the 20°S–20°N tropical mean) at the same calendar day as the latest data, for the current event and the three analogs. Removing the tropical background makes the regions comparable across events; strong eastern (1+2, 3) relative to central (4) marks an East-Pacific-flavored event.

Matching-Phase SST Anomaly Maps

Relative SST anomaly — the area-weighted global-mean anomaly removed from each map — for the latest available week vs. the same calendar week in 1997, 2015 and 2023. Stripping the global mean removes the secular warming trend, so the ENSO spatial pattern is comparable across events that sat on very different baselines.

Subsurface Heat Content vs. Analogs

Equatorial Pacific upper-ocean (0–300 m) temperature anomaly — a heat-content proxy that leads the surface — through each event's development year and the next, current (bold red) overlaid on 1997, 2015 and 2023. The subsurface warm reservoir is the fuel for El Niño; watch whether the current build-up keeps pace with the analogs.

Subsurface Cross-Section vs. Analogs

Equatorial depth×longitude temperature anomaly at the same phase (~the latest data week) of each event. The eastward-deepening warm anomaly along the thermocline is the classic El Niño subsurface signature; comparing its depth and intensity against 1997/2015/2023 gauges how loaded the ocean is now.

Note: TAO mooring coverage varies by year (triangles mark moorings reporting), so 1997 and 2023 have missing longitudes.

Observed Equatorial Pacific Surface Wind

Latest daily 10°S–10°N surface wind — speed (shaded) with direction arrows — from the gap-filled gridded scatterometer (ASCAT) analysis. The observed companion to the wind forecast below: persistent easterly trades are the neutral/La Niña state, while westerly bursts along the equator push warm water east and favor El Niño.

Equatorial Pacific 10 m Wind Forecast

Forecast 10 m zonal-wind anomaly (5°S–5°N), longitude × forecast day, from the AIFS-ENS (AI) and ECMWF IFS-ENS (physics) ensemble means vs. the ERA5 1991–2020 climatology.

What to look for: Westerly (red) anomalies along the equator push warm water eastward and favor El Niño development; easterly (blue) anomalies favor La Niña. Agreement between the AI and physics ensembles raises confidence.

Southern Oscillation Index — Forecast

The Troup SOI (the standardized Tahiti−Darwin sea-level-pressure difference) tracks the atmospheric side of ENSO. Observed values are from LongPaddock (Queensland Govt / BoM); the forecast is the Tahiti−Darwin MSL from the combined AIFS-ENS + IFS-ENS ensemble (~100 members), bias-corrected to the recent observed level. Bold lines are the 30-day running SOI; the faint daily series and shaded 10–90% band show the noisier day-to-day spread.

How to read it: Sustained negative SOI (below −7) is El Niño-favorable; sustained positive (above +7) is La Niña-favorable. A forecast that holds the 30-day SOI deep negative reinforces an El Niño signal.

Atmospheric Angular Momentum

Relative AAM is the angular momentum carried by the winds — the atmosphere's total westerly momentum, ∫ u·cos²φ over the whole globe. It's dominated by the upper-tropospheric subtropical jets and the deep tropics (largest moment arm), shown here for the globe and each hemisphere from the AIFS-ENS 13-level winds.

How to read it: top — this year's observed AAM (black) and the 15-day forecast (red) on the climatological annual cycle. The hemispheres are strongly out of phase (each peaks in its own winter), so much of the absolute rise/fall is just the season. Bottom — the anomaly (departure from the 1991–2020 normal), which removes the seasonal cycle, with a “% of climatology” axis.

Why it matters for ENSO: El Niño shifts tropical convection east, strengthens the subtropical jets and weakens the trade winds — so the atmosphere holds more westerly momentum. AAM also ties to the MJO / Global Wind Oscillation and to length of day (more atmospheric momentum → the solid Earth spins fractionally slower).

AAM Forecast Trend (run-to-run)

Each line is one AIFS-ENS run's ensemble-mean AAM anomaly forecast — for the globe and each hemisphere — with successive runs coloured oldest→newest (newest bold). Watching the lines shift run-to-run shows whether the outlook is trending more or less anomalous, and how consistent (or jumpy) the forecast is. The archive grows with each daily run.

What Drives AAM — the Torque Budget

Atmospheric angular momentum only changes through torques the Earth exerts on the atmosphere. With $M$ the relative (wind) AAM, the budget has two resolved terms — friction (surface wind stress) and mountain (pressure on topography):

$$M=\frac{a^3}{g}\iiint u\cos^2\!\phi\;d\lambda\,d\phi\,dp,\qquad \frac{dM}{dt}=T_{\text{fric}}+T_{\text{mtn}}\;(+\,T_{\text{gw}})$$

$$T_{\text{mtn}}=-a^2\!\iint p_s\,\frac{\partial h_s}{\partial\lambda}\,\cos\phi\;d\lambda\,d\phi,\qquad T_{\text{fric}}=-a^3\!\iint \tau_\lambda\,\cos^2\!\phi\;d\lambda\,d\phi$$

The two panels show the torque anomalies (vs the ERA5 1991–2020 climatology, evaluated by day-of-year), so the standing departure from normal — the El Niño signal — shows alongside the day-to-day synoptic systems. The mountain term is the form drag h ∂p_s/∂λ (terrain height × east–west pressure gradient); the grey contours are the surface-pressure anomaly — the very field the torque uses (solid +, dashed −) — so colours and contours read together (no surface-vs-sea-level mismatch). Top — friction ($\tau_\lambda\!\approx\!\rho\,C_d\,|V_{10}|\,u_{10}$): trade-wind and jet stress anomalies (e.g. western-Pacific westerly bursts). Bottom — mountain (form drag $h_s\,\partial p_s/\partial\lambda$, the same net torque as $-p_s\,\partial h_s/\partial\lambda$ but without the cross-ridge dipole): synoptic pressure systems crossing the Andes, Rockies, Himalaya/Tibet and Greenland. Insets are the ±60° cosφ-weighted zonal-mean anomaly; AIFS-ENS ensemble mean of all 51 members (friction averaged per-member; mountain, MSLP & the d(AAM)/dt overlay are linear), ~5°. (The sub-grid gravity-wave-drag term $T_{\text{gw}}$ appears only as the residual.)

Meridional Overturning — the Hadley Cell Response

The zonal-mean meridional mass streamfunction $\Psi(\phi,p)$ traces the overturning cells — Hadley, Ferrel, polar — from the AIFS-ENS 0-h analysis:

$$\Psi(\phi,p)=\frac{2\pi a\cos\phi}{g}\int_0^p [v]\,dp',\qquad [v]=\text{zonal-mean }v$$

Shown as the anomaly $\Psi'$ from the ERA5 1991–2020 harmonic climatology (mean + annual + semiannual, by day-of-year) — how the overturning departs from its normal seasonal state. The black contours are the absolute $\Psi$ (the actual cells) and the arrows show the vertical motion (up = ascent, scaled by strength); the strong equatorial signal tracks the El Niño Walker/Hadley response. Each new 0-h analysis is stashed into a rolling animation with a fixed colour scale, so the cells can be watched as the event evolves.