It’s Q&A Time — NOAA – Coyote Gulch

Click the link to read the article on the NOAA website (Emily Becker):

Ocean and atmospheric conditions tell us that La Niña, the cold phase of the El Niño-Southern Oscillation (ENSO) climate model, is currently prevailing in the tropical Pacific. It seems very likely that the long-expected third consecutive La Niña winter will occur, with a 91% chance of La Niña until September-November and an 80% chance until early winter (November-January). ).

91%! It is very high. Why so confident?

The first reason is that La Niña is already clearly in effect in the tropical Pacific. August sea surface temperature in the Niño-3.4 region, our primary location for ENSO monitoring, was about 1.0°C (1.8°F) cooler than the long-term average, according to ERSSTv5, our favorite dataset for sea surface temperature. (“Long term” is currently 1991-2020.) That’s significantly cooler than the La Niña threshold of 0.5°C (0.9 °F) below average.

Sea surface temperatures in the tropical Pacific Ocean from mid-June to early September 2022 relative to the long-term average. East of the International Date Line (180˚), waters remained cooler than average, a sign of La Niña. Graph from Climate.gov, based on data from NOAA’s Environmental Visualization Lab. Description of the historical reference period here.

The characteristic La Niña tropical atmospheric response—more rain and cloud over Indonesia, less over the central Pacific, and stronger-than-average winds both aloft and near the surface—was also clearly visible. active in August. Together, the ocean and atmospheric conditions tell us that La Niña is firmly in place. Once active, La Niña conditions are enhanced by feedback processes between the ocean and the atmosphere. Read more about these returns here.

La Niña feedbacks between the ocean and the atmosphere. Diagram from Climate.gov by Emily Eng and inspired by NOAA PMEL.

What else gives confidence in forecasts?

There is a significant amount of cooler than average water beneath the surface of the eastern central tropical Pacific. This groundwater will provide a cooler source of surface water for the next two months. Also, the consensus of the computer climate model predicts that La Niña will continue through the winter.

How long will La Niña last?

While there is broad agreement throughout the winter, there is a lot of uncertainty as to how long this La Niña will last and when we will see a transition to neutral conditions. The current consensus of forecasters gives La Niña the advantage from January to March (54%), with a 56% probability of neutrality for the period from February to April.

NOAA Climate Prediction Center forecasts for each of the three possible ENSO categories for the next 8 overlapping 3-month seasons. The blue bars indicate the chances of La Niña, the gray bars the chances of neutrality and the red bars the chances of El Niño. Graphic by Michelle L’Heureux.

When did previous La Niñas go neutral?

There are 24 La Niña winters in our historical record, dating back to 1950. Of these, only one (2016-17) turned neutral in December-February. Four went into neutral in January-March, one (2000-01) in February-April, two in March-May and 16 in April-June or later. Especially when you’re slicing and dicing a relatively short record, it’s hard to find truly analogous events. For example, this will be only the third La Niña triple on record, and the first not to follow a strong El Niño event.

Three-year history of sea surface temperatures in the Niño-3.4 region of the tropical Pacific for the 8 existing double dip La Niña events (gray lines) and the current event (purple line). Of the previous 7 events, 2 went into La Niña in their third year (below the blue dotted line), 2 continued at or near El Niño levels (above the blue dotted line) dotted red) and three were neutral. The chart is based on monthly CPC Niño-3.4 index data using ERSSTv5. Created by Michelle L’Heureux.

All this to say that past La Niña doesn’t provide much guidance on how long this event will last. The forecasters’ current estimate, which favors an earlier than usual transition to neutral, is based on indications from a computer model.

Remind me why I should care about La Niña…?

I admit that as scientists, we are sometimes captivated by the interest of the internal mechanisms of El Niño and La Niña! But ENSO has serious practical applications. In a nutshell, La Niña and El Niño affect global atmospheric circulation patterns in (somewhat) predictable patterns, altering jet streams and storm tracks around the world and influencing temperature, rain/snow and weather conditions. tropical cyclone seasons. Since we can predict ENSO months in advance, we can get an early picture of potential future climate patterns. Of course, nothing is guaranteed with weather and climate – ENSO only “tips the balance” towards certain models. To learn more about how ENSO affects climate models, as well as why it’s so difficult to make specific predictions, check out Michelle’s post here.

Can I have examples of how La Niña can affect the North American climate?

Yes! Here is a map, followed by a list of some details.

During La Niña, the Pacific Jet Stream often meanders high in the North Pacific. Southern and interior Alaska and the Pacific Northwest tend to be cooler and wetter than average, and the southern parts of the US states from California to the Carolinas tend to be warmer and drier than average. Further north, the Ohio and upper Mississippi valleys can be wetter than usual. ImageClimate.gov.

What about global impacts?

Typical La Niña temperature and precipitation patterns during Northern Hemisphere winters (top) and summers (bottom). Map from NOAA Climate.gov, based on originals from the Climate Prediction Center. Larger images and maps for El Niño are available in this article.

That’s enough for now! Thanks!

Whenever! See you next month.

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