There’s been a lot of talk this winter about La Niña and El Niño. La Niña’s making it cold someplace and El Niño’s making it wet someplace else. For example, Australia’s current flooding is being blamed on a strong La Niña. La Niña? El Niño? Which is which? And, which causes what, to where, and to whom. They’re very different, yet similar; they’re opposite, yet confusingly alike. How do you keep them separate? And what do they mean?
At the risk of being sexist, I’ll let you in on my clarification secret. “El Niño” is the little boy or little baby (masculine) in Spanish, while “La Niña” is Spanish for the little girl or little baby (feminine). With that in mind, I always picture a screaming little boy when I hear El Niño (fitting?) and a calm, sleeping little girl when I hear La Niña (not always so fitting!). Of course, screaming baby boys would likely be jumping up and down, wouldn’t they? Just like the up and down drafts within thunderstorms. And there’s my association! El Niño, a cyclical warming of the eastern and central Pacific waters near the equator, is responsible for active weather (enhanced and more numerous thunderstorms) in the eastern Pacific. In the winter this translates to more cloudcover over North America (with many areas cooler and wetter), while in the summer it tends to suppress Atlantic hurricane activity. Conversely, cooler waters in the eastern Pacific, aka La Niña, lead to less active weather in this region (drier and cooler) and drier and warmer weather across the southern U.S.A.
Where do we stand today? It’s cloudy and unusually cold in Houston at this writing. Not exactly the stuff of La Niña, yet eastern Pacific waters are cooler than normal allowing western Pacific waters to be warmer than normal which, in turn, allows abundant precipitation across equatorial waters of the western Pacific. Translation? Classic La Niña. Look no further than recent headlines and postings from YourWeatherBlog to confirm the widespread flooding across eastern Australia.
For more detail on the current La Niña which, depending on which data set you study, can be considered one of the strongest of recorded history, I talked to ImpactWeather’s StormWatch manager and our lead long-range meteorologist Fred Schmude. “If you base [La Niña’s strength] on the SOI (Southern Oscillation Index), it is one of the strongest. However, if you base it on the magnitude of the temperature anomaly, now in the Niño 3.4 region, then it’s not nearly the strongest. The winter seasons of 1955-56, 1973-74, and 1988-89 were all clearly colder. Also the seasons of 1970-71, 1975-76, 1998-99 and 1999-2000 were just as cold if not colder than this season, as well.”
[The Niño regions are divided up into four main parts, named Niño 3.0, Niño 4.0, Niño 3.4 (most critical) and Niño 1.2.]
Another La Niña trait is rising sea water levels in the western Pacific (colder ocean waters are more dense and sink; less dense warmer waters will rise). Warmer waters coupled with a persistent trough of low pressure over eastern Australia keep atmospheric moisture levels high. According to Fred, “With that in mind, I think there is something else going on in the worldwide weather pattern not directly related to La Niña which is causing the flooding in Australia. Overall the worldwide weather pattern is locked in place not only over Australia, but over other parts of the globe which is causing some extreme weather, including the western European winter storms and the eastern U.S. blizzards and severe cold. The reason for the locked pattern is a mystery that can’t be solved so easily. Over Australia, well above normal water levels are surrounding the continent — which is not unusual when you consider we are dealing with a La Niña and a negative phase of the IOD (Indian Ocean Dipole) which shifts warm water over the western Pacific and cool water over the eastern Pacific. In addition to this, the MJO (Madden-Julian Oscillation) has been stuck over the western Pacific for months — further aggravating the problem when you consider the MJO is responsible for creating an environment suitable for widespread thunderstorm development. As a result, the combination of a locked weather pattern, a strong La Niña, a nearly stagnant MJO over the western Pacific and very warm water surrounding the continent have resulted in a deadly quartet over Australia. I partly blame the strong La Niña for the problems there, but more importantly the MJO and the locked weather pattern are the main culprits.”
So it’s not an easily answered question. World climate patterns with regionalized and local effects are still being studied and pondered. Decades ago, it was El Niño and La Niña that seemed so complicated. Today the baby seems to be one of the more understood aspects of global climate, but nobody who knows what they’re talking about ever said it was easy.