The Pacific Northwest, the Tennessee/Ohio Valleys, and parts of the Midwest tend to see more rain and snow than average. In summary, La Niña winters tend to be drier and warmer across the southern third of the U.S., and cooler in the northern U.S. But the most substantial La Niña effect on North American rain, snow, and temperature happens during winter. We’ve already seen one likely effect of La Niña this year-a more active Atlantic hurricane season, with nearly twice as many storms as average so far this year.
For more on how this works, check out Nat’s excellent post on double-dip La Niña. The less-clean end to La Niña means that it’s not hard for the system to tip back into La Niña the next year. NOAA figure with ERSSTv5 data obtained from the NOAA Physical Sciences Laboratory.Įl Niño events end when the equatorial temperature anomalies are dispersed away from the equator, and this process tends to be less robust in La Niña. Anomalies are calculated with respect to 30-year base periods updated every 5 years (see here for a description). The difference in strength and location means the trade winds response is not exactly opposite in La Niña and El Niño-unsurprisingly, the response tends to be weaker and centered farther west during La Niña than El Niño.Īverage November – January sea surface temperature anomalies (☌) for the top 10 strongest (top) El Niño and (bottom) La Niña events since 1950 based on the November – January Niño3.4 index. The reason for this is difficult to explain in brief, but researchers think it’s partly due to differences in atmosphere-ocean coupling between La Niña and El Niño.Īs you can see int he map below, the center of the ocean surface temperature anomaly tends to be a bit weaker and a bit farther west during La Niña than El Niño. However, La Niña often occurs in consecutive winters, while El Niño rarely does. Overall, La Niña is not more common that El Niño-in the historical record dating back to 1950, there have been 25 El Niños and 24 La Niñas (counting this year). La Niña has probably earned silver-elite, frequent-flier status here, as this is the fourth time we’ve written a “La Niña is here” post on the ENSO Blog! (Earlier posts are September 2020, November 2017, and November 2016.) That’s four of the seven-and-a-half years we’ve been standing on this digital street corner yelling about ENSO.
TROPICO 1 (MAYBE 3 FREE
The Walker circulation is driven by the difference between the very warm ocean surface in the far western Pacific and the relatively cool eastern Pacific during La Niña, this difference is enhanced, leading to a stronger Walker circulation.įollow the blue brick road, and we get to La Niña! Buy one, get one free
A stronger Walker circulation is the expected atmospheric response to La Niña. These signs, along with more rain than average over Indonesia and less in the central Pacific, tell us that the Walker circulation is juiced up. Over the past month, the low-level winds near the equator, which usually blow from east to west (the trade winds), were stronger than average, as were the west-to-east winds high up in the atmosphere. The final requirement to get to La Niña conditions is that the atmosphere is showing signs of responding to that cooler-than-average surface water. NOAA animation, based on data from NOAA's Climate Prediction Center. Water temperatures in the top 700 meters (2,300 feet) of the tropical Pacific Ocean compared to the 1991-2020 average in late summer 2021.
0 kommentar(er)
