La Nina conditions continue across the Equatorial Pacific – Is it increasing because of that?
Paul Dorian
Sea surface temperatures continue to stay cooler than normal (indicated in blue) in the equatorial portion of the Pacific and La Nina is likely to persist at least into the coming early summer. Map provided by NOAA, Tropicaltidbits.com
La Nina conditions continue over the equatorial Pacific… likely to last into at least early summer with potential impact on tropical activity… see impact on temperature Global
Overview
La Nina conditions dominated the scene in the equatorial part of the Pacific during this winter as well as during the winter before 2020-2021. Multiple computer models suggest that colder-than-normal sea surface temperatures in the tropical Pacific will last into at least the beginning of next summer. If so, La Nina could actually have the same impact on global tropical activity this summer as it did during the final tropical season in 2021. In addition to its impact on tropical activity in the Atlantic. The Atlantic and Pacific, these La Nina-backed episodes appear to have been affected by global temperatures over the past several months that have dropped to near-normal levels in the most recent monthly reading.
This graph shows the projections made using dynamical and statistical models of sea surface temperature (SST) anomalies in the “Nino 3.4” (central Pacific) region. in nine overlapping 3-month periods. Many of the models assume the current La Nina episode will continue at least into the upcoming summer. Data sources: IRI / CPC
Background
The Pacific Ocean is the largest Pacific Ocean on the planet, covering more than 30% of the Earth’s surface and larger than the land area of all the continents combined. The warm waters of the equatorial Pacific store a very large amount of latent heat when compared to cooler waters and create a lot of convection that impacts downstream gullies and creates trenches in the atmosphere. Thus, its sea surface temperature (SST) has a tremendous influence on all weather and climate worldwide, and the more unusual the sea surface temperature, the more impact it has on the atmosphere worldwide. world. El Nino-Southern Oscillation (ENSO) is a repeatable climate pattern associated with temperature variations of water bodies in the central and eastern tropical Pacific Ocean. El Nino and La Nina are the extreme phases of the ENSO cycle; Between these two phases is a third phase called ENSO-neutral.
Weak to moderate La Nina continues in the equatorial Pacific
During the winter of 2020-2021, La Nina conditions (i.e. colder-than-usual water) persisted in the equatorial part of the Pacific Ocean and then they weakened to a quasi-neutral state throughout the season. last spring and summer. New cooling then formed in the same part of the Pacific Ocean last fall, and La Nina’s conditions solidified in time for the winter that is still underway for 2021-2022. It’s actually not unusual to have two La Nina events in succession with eight of the twelve “first year” La Nina events since 1950, followed by a second-year episode throughout the season. next winter.
Cyclone Cumulative Energy (ACE) is the best measure of overall tropical activity and it is below normal for the 2021 season across the entire Northern Hemisphere (boxed at the bottom value). right, where 430.5 is actual and 543.7 is normal). While the Atlantic basin experiences ACE above normal, the Pacific Ocean more than offsets this with much less activity than normal; especially, when considering the number of “major” hurricanes. Data provided by Colorado State University, NOAA
La Nina’s Impact on Global Tropical Activity
What happens in the tropical Pacific in relation to ENSO does indeed have an effect on tropical activity in the Atlantic basin. El Nino, which refers to warmer-than-normal waters in the equatorial Pacific Ocean, tends to inhibition Formation/strengthening factors of tropical cyclones in the Atlantic basin. First, El Niños tend to produce faster-than-normal high-altitude winds over the tropical Atlantic, and this increase in wind shear (change in wind speed with altitude) is associated with increased or sustained by tropical cyclones. Second, El Niño tends to lead to subduction motion in parts of the Atlantic basin, which is also responsible for tropical cyclone formation/strengthening.
The El-Nino Southern Oscillation Areas (ENSO) in the equatorial Pacific are typically subdivided into smaller sections as labeled on this map (NOAA permitting).
On the other hand, La Nina, which refers to colder-than-normal waters in the equatorial part of the Pacific Ocean, is generally correlated with weaker wind shear over the breeding grounds of tropical Atlantic waters. This often leads to a more advantageous tropical environments in the Atlantic for the development/intensification of tropical activities. Indeed, with La Nina being active last summer, the tropical season in the Atlantic basin was the third most active on record for the number of named storms with 21.
While La Nina conditions are a favorable factor for tropical activity in the Atlantic basin in 2021, it tends to suppress activity in the equatorial portion of the Pacific Ocean. In both areas of the Pacific (that is, east and west of the “international date line”), tropical activity is generally below normal for 2021 in terms of cumulative cyclone energy (ACE). ). The ACE Index – originally created by Dr. William Gray and colleagues at Colorado State University and later adjusted by NOAA – not only factors in intensity of a tropical cyclone, it also takes into account longevity. For example, a “major” storm that lasts for a long time will have a much larger impact on the accumulated cyclone energy than a shorter-lived and weaker tropical system. The number of “major” storms over the Pacific during the tropical season of 2021 is much lower than normal.
In general, an El Niño in the tropical Pacific Ocean tends to increase global temperatures, and often there is a significant drop during and after La Nina events, as has happened in the past few months. The latest monthly reading for January 2022 for UAH global temperature anomalies is +0.03 degrees (C) using the 1991-2020 base period for comparison. Data sources: Dr. Roy SpencerUniversity of Alabama at Huntsville (UAH)
Impact of La Nina on global temperature
In addition to the impact on tropical activity, La Nina may actually have a global temperature divide driven primarily by solar and ocean cycles. In recent decades, the number of El Niño events has surpassed the number of La Nina events, and global temperatures have often responded with notable spikes. For example, temperatures spiked in 2016/2017 after a strong El Niño event, and they had a second peak in 2019 related to a second El Niño in the tropical Pacific. Prior to this, strong El Niño events centered on the years 1997/1998 and 2009/2010 were associated with a sharp increase in global temperatures in the lower atmosphere.
Warm (red) and cold (blue) periods are listed in this table from 2010 and are based on a threshold of +/- 0.5°C for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v5 SST anomalies in the Niño 3.4 region (5°N-5°S, 120°-170°W)], based on a central 30-year baseline that is updated every 5 years. La Nina conditions develop in late spring 2020 and continue into winter 2021-2022 although it does weaken at times. Data sources: NOAA / CPC
During La Nina periods such as 2007/2008 and 2010/2011/2012, the global temperature of the lower atmosphere has experienced significant declines. Since the most recent El Nino incident in 2018/2019, La Nina has been under control and global temperatures have reacted accordingly. In fact, global temperatures have dropped dramatically over the past few months to near-normal levels worldwide since the latest UAH data reading in January 2022. If La Nina really continues, several months Furthermore, as described by some computer models, global temperatures may respond by staying at this near-normal level or may even drop below normal.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com
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