El Niño – Latest Images

The latest images of the current El Niño have been released from NASA, which I find both surprising and intriguing. Surprising because in the middle of the Pacific the extremes of the scale are in such close proximity to each other; intriguing because... well it just is!

Source: Jet Propulsion Lab, NASA

These images have been created by taking the average of 10 days worth of data, from the 12^th – 21^st October 2015. The data used to construct them are sea surface height residuals. A residual (also referred to as the irregular component) is the remaining component after seasonality and trends have been removed from a time series. The seasonality aspect is a systematic, calendar related effect, whilst a trend is a long term movement in a particular direction. The residual that remains shows short term fluctuations which are unsystematic and usually unpredictable. This is how the uncharacteristic sea surface height data is captured and displayed as above. Hence, the areas coloured green-light blue in the images have anomalies of 0 mm, meaning their levels are normal and can be explained by the seasonal and trend components. This method of modelling is powerful because it breaks down the data into manageable parts for discovering underlying characteristics, and, forecasting relies on previous observations. However, it can have its limitations if the data available only covers a short period of time relative to the process.

But, we’re looking at sea level heights here, isn’t El Niño to do with temperatures? Well, there is a strong correlation between sea surface height anomalies and the thermal structure of the ocean. The steric changes in the ocean (temperature and density) cause the sea levels to fluctuate accordingly. Warmer water has a lower density therefore a greater volume than colder water, conversely, the higher the sea level, the warmer the water. This animation shows sea surface height and temperature anomalies in the Pacific Ocean from October 1992 to August 2002.

All of the data used to construct these images and animations has been recorded by the Jason-2 satellite, for the Ocean Surface Topography Mission (OSTM). Launched in 2008, the OSTM/Jason-2 satellite altimeter mission aims to provide scientists with a multi-decadal climate record for analysis of global sea level rise and a better understanding of the relationship between ocean circulation and climate change (Lambin et al, 2010).

So, bear with me, and let’s see how this progresses over the coming weeks.