A “La Niña-like” state occurring in the second year after large tropical volcanic eruptions during the past 1500 years

Abstract

Using an ensemble of nine El Niño/Southern Oscillation (ENSO) reconstructed proxies and volcano eruption proxies for the past 1500 years, this study shows that a significant La Niña state emerges in the second year (year (2) hereafter) after large tropical volcanic eruptions. The reasons for the development of La Niña are investigated using the Community Earth System Model (CESM). In the volcanic eruption experiment (Vol), a robust La Niña signal occurs in year (2), resembling the proxy records. The eastward positioning of the western North Pacific anomalous anticyclone (WNPAC) in Vol plays a critical role in the advanced decay of year (2) warming and the strong intensification of cooling in the equatorial eastern Pacific. The enhanced easterlies located on the southern edge of the WNPAC can stimulate consecutive oceanic upwelling Kelvin waves, shallowing the thermocline in the eastern Pacific, thereby resulting in a greater cooling rate by the enhanced thermocline feedback and cold zonal advection. Over the equatorial eastern Pacific, the reduced shortwave radiation contributes to the advanced decay of warming, while the upward latent heat flux augments the strong intensification of the cooling. Essentially, the eastward positioning of the WNPAC is a result of the volcanic forcing. The volcanic effect cools the maritime continent more than its adjacent oceans, thus pushing convective anomalies eastward during year (1). This induces vertical thermal advection and upward surface latent heat flux, thereby suppressing the development of warm Sea Surface Temperature over the central-western Pacific and causing the eastward positioning of the WNPAC in Vol.

El Niño–Southern Oscillation variability, teleconnection changes and responses to large volcanic eruptions since AD 1000

“…This shift towards negative SSTs was also found by Wilson et al (2010) at years 4 and 7. Using the CESM (Community Earth System Model), Sun et al (2018) also found a transition from El Niño-like to a significant La Niña-like state after large tropical eruptions; however, the significant La Niñalike state already occurred 2 years after the eruptions. The apparent discrepancies in the literature on the response of ENSO to volcanic forcing illustrate that there is no consensus yet.…”

The Influences of Tropical Volcanic Eruptions with Different Magnitudes on Persistent Droughts over Eastern China

“…The mechanisms behind the volcano-related droughts can be explained directly by the retreat of the Eastern Asian summer monsoon (EASM) [23][24][25] through the reduced ocean-land thermal contrast after volcanic eruptions [8,24]. Moreover, many studies also highlighted that strong volcanic eruptions can influence the evolution of drought in Eastern China [26], through triggering increased occurrences of El Nino-like states during the years of eruptions, and La Nina-like states in the second years after eruptions [27][28][29]. On a decadal time scale, strong volcanic eruptions can induce negative PDO-like (Pacific Decadal Oscillation) phases [30], as well as the negative AMO-like (Atlantic Multidecadal Oscillation) states [25,31], and then influence the precipitation changes over Eastern China [32,33].Moreover, previous studies demonstrated that the linear combination of volcanic forcing and drought events triggered by internal variability over Eastern China may intensify and extend the drought conditions for about 3-4 years, and the duration and intensity of droughts depend on the volcanic eruptions occurring at different drought phases [34].…”

Strong link between large tropical volcanic eruptions and severe droughts prior to monsoon in the central Himalayas revealed by tree-ring records

“…However, it still remains inconclusive as to whether or not there is a causal link between volcanic activity and the ENSO events [1,45,46]. A recent study based on proxy data and model simulation, however, clearly showed that a La Niña-like state occurred in the second year after large tropical volcanic eruptions during the past 1500 years [47]. The cold SSTs in the East Pacific may have caused the Asian drought from 1998 to 2001 [48].…”