As far back as the 1600s, Spanish fishermen off the west coast of South America noticed that ocean temperatures varied widely from year to year with noticeable effects on their catches. Since then, climatologists have come to understand that all of the Earth’s big water bodies experience temperature oscillations. As the biggest ocean, the Pacific gives us the most important cycle: the El Nino Southern Oscillation (ENSO). ENSO affects weather worldwide, and since it changes slowly, it can give forecasters the ability to make longer-range calls than they otherwise could.
Weather agencies make thousands of measurements of the complex ENSO phenomenon each day, such as temperature, air pressure, wind speed/direction, and outgoing longwave radiation from satellites and hundreds of buoys moored across the South Pacific. The sheer volume of data can lead to analysts disagreeing on ENSO’s status at any given time. As a result, Klaus Wolter, a scientist at the National Oceanographic and Atmospheric Administration (NOAA) formulated an index in 1987 that synthesized all of the data into one number: the Multivariate ENSO Index (MEI).
MEI is an index that synthesizes multiple data sets that keep track of ENSO and is a valuable tool for forecasting long-term weather trends.
As of August, Gro Intelligence’s data platform features the MEI as a data series that our users access through our web interface or our Python API client. With this information, they can achieve long-range weather and crop forecasting capability. When MEI is above zero, that indicates an El Nino condition. We currently see an MEI value of +0.30 for August 2019, which means we have a weak El Nino event in progress.
Most long-range weather forecasting relies on so-called ENSO teleconnections, which are associations between MEI values and weather conditions such as temperature and rainfall in specific locations. In Queensland, Australia, for example, a historical analysis shows that when August MEI is positive, the average October to December temperature in the northeastern state is higher than the average by 1.25 degrees Celsius, and rainfall is reduced by 25 millimeters. These differences have definite impact on Australian grains and livestock all along Australia’s eastern half, which is in its third year of drought. Such teleconnections exist for multiple regions and crops around the world.
Positive MEI readings for August are associated with higher October-December temperatures (left map) and lower rainfall (right map), historical analysis shows.
Gro intends to add a much larger body of relevant meteorological data to our platform over time, but since ENSO’s global impact correlates strongly with MEI, we added it first. Gro customers now use MEI in conjunction with our daily Global Forecast System (GFS), a shorter-term NOAA forecast data set, to build actionable custom outlooks for regions and crops of interest.