ENSO Structure

The upper tropospheric geopotential height (pressure) signature of ENSO differs to its surface signature. At these heights, an equatorially symmetric wave pattern over the central Pacific dominates, which forms a pair of anticyclonic gyres during El Niño. This signature is accompanied by a rise in pressure due to a tropics-wide warming during El Niño.

Schematic describing the upper and lower tropospheric structure of ENSO.

Schematic describing the upper and lower tropospheric structure of ENSO.

Robust changes in the surface temperature of the ocean across the equatorial Pacific has been observed by Peruvian fishermen for more than a century. They coined the term El Niño to the part of the cycle when the temperatures are unusually warm, since the warming was most noticeable around Christmas (the name comes after el niño Jesús, baby Jesus). More recently, the term La Niña began to be used to describe the part of the cycle when the sea surface is unusually cold

The sea level pressure signature of ENSO (shown in contours in the middle panel in the figure) is known as the Southern Oscillation. It consists of an east-west, planetary-scale see-saw with its western pole in the Indo-Pacific sector and its eastern pole in the southeast Pacific trade winds near the coast of South America.

The upper tropospheric geopotential height (pressure) signature of ENSO differs to its surface signature. At these heights, an equatorially symmetric wave pattern over the central Pacific dominates, which forms a pair of anticyclonic gyres during El Niño. This signature is accompanied by a rise in pressure due to a tropics-wide warming during El Niño.

Building blocks of ENSO

My research seeks to understand why ENSO has such a rich, multifaceted structure. Using data from satellites and from the Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim), we decompose the structure of ENSO into different components. By doing this, we can attribute how much of the signature is due to ocean warming, warming of the tropical troposphere, and to the tropical and extratropical waves that are generated due to the ENSO-related convection.