Amazonian Contribution to Sargassum Enhancement in the Tropical Atlantic

AbstractThere is a well-known mode of rainfall variability associating opposite hydrological conditions over the Sahel region and the Gulf of Guinea, forming a dipole pattern. Previous meteorological observations show that the dipole pattern varies at interannual timescales. Using an EC-Earth climate model simulation for last millennium (850–1850 CE), we investigate the rainfall variability in West Africa over longer timescales. The 1000-year-long simulation data show that this rainfall dipole presents at decadal to multidecadal and centennial variability and long-term trend. Using the singular value decomposition (SVD) analysis, we identified that the rainfall dipole present in the first SVD mode with 60% explained variance and associated with the variabilities in tropical Atlantic sea surface temperature (SST). The second SVD mode shows a monopole rainfall variability pattern centred over the Sahel, associated with the extra-tropical Atlantic SST variability. We conclude that the rainfall dipole-like pattern is a natural variability mode originated from the local ocean–atmosphere-land coupling in the tropical Atlantic basin. The warm SST anomalies in the equatorial Atlantic Ocean favour an anomalous low pressure at the tropics. This low pressure weakens the meridional pressure gradient between the Saharan Heat Low and the tropical Atlantic. It leads to anomalous northeasterly, reduces the southwesterly moisture flux into the Sahel and confines the Gulf of Guinea's moisture convergence. The influence from extra-tropical climate variability, such as Atlantic multidecadal oscillation, tends to modify the rainfall dipole pattern to a monopole pattern from the Gulf of Guinea to Sahara through influencing the Sahara heat low. External forcing—such as orbital forcing, solar radiation, volcanic and land-use—can amplify/dampen the dipole mode through thermal forcing and atmosphere dynamical feedback.

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Correction to: Weakened SST variability in the tropical Atlantic Ocean since 2000

Climate Dynamics ◽

10.1007/s00382-021-05905-7 ◽

2021 ◽

Author(s):

Arthur Prigent ◽

Joke F. Lübbecke ◽

Tobias Bayr ◽

Mojib Latif ◽

Christian Wengel

Keyword(s):

Atlantic Ocean ◽

Tropical Atlantic ◽

Tropical Atlantic Ocean ◽

Sst Variability

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Spurious North Tropical Atlantic precursors to El Niño

Nature Communications ◽

10.1038/s41467-021-23411-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Wenjun Zhang ◽

Feng Jiang ◽

Malte F. Stuecker ◽

Fei-Fei Jin ◽

Axel Timmermann

Keyword(s):

El Niño ◽

Cross Correlation ◽

El Nino ◽

Southern Oscillation ◽

Global Climate ◽

Tropical Atlantic ◽

The North ◽

Sst Variability ◽

Primary Driver ◽

North Tropical Atlantic

AbstractThe El Niño-Southern Oscillation (ENSO), the primary driver of year-to-year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead-lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies did not properly account for ENSO’s autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time-varying ENSO frequency, and greenhouse warming, we demonstrate that the cross-correlation characteristics between NTA SST and ENSO, are consistent with a one-way Pacific to Atlantic forcing, even though the interpretation of lead-lag relationships may suggest otherwise.

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