Minimal impact of model biases on Northern Hemisphere El Niño–Southern Oscillation teleconnections

Correctly capturing the teleconnection between the El Niño–Southern Oscillation (ENSO) and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two-step bias correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias corrections are applied to the troposphere and stratosphere independently and jointly to produce a range of climates. ENSO-type sensitivity experiments are then performed to reveal the impact of differing climatologies on the ENSO–Europe teleconnections. The bias corrections do not affect the response of the tropical atmosphere or the Aleutian low to the strong ENSO anomalies imposed in our experiments. However, in El Niño experiments the anomalous upward wave flux and the response of the Northern Hemisphere polar vortex differ between the climatologies. We attribute this to a reduced sensitivity of the upward wave fluxes to the Aleutian low response in the bias correction experiments, where the reduced biases result in a deepened Aleutian low in the base state. Despite the differing responses of the polar vortex, the North Atlantic Oscillation (NAO) response is similar between the climatologies, implying that for strong ENSO events the stratospheric pathway may not be the dominant pathway for the ENSO–North Atlantic teleconnection.

Minimal impact of model biases on northern hemisphere ENSO teleconnections.

<p>Correctly capturing the teleconnection between the ENSO and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two–step bias–correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias–corrections are applied to the troposphere and stratosphere separately and together to produce a range of climates. ENSO type sensitivity experiments are then performed to reveal the impact of differing climatologies on ENSO–Europe teleconnections.</p><p>The bias–corrections do not affect the response of the tropical atmosphere, nor the Aleutian Low, to strong ENSO anomalies. However, the anomalous upward wave flux and the response of the northern hemisphere polar vortex differs between the climatologies. We attribute this to a reduced sensitivity of waves to the strength of the Aleutian Low. Despite the differing responses of the polar vortex, the NAO response is similar between the climatologies, implying that for strong ENSO events the stratospheric response may not be the primary driver for the ENSO–North Atlantic teleconnection.</p>

Minimal impact of model biases on northern hemisphere ENSO teleconnections

Correctly capturing the teleconnection between the El Niño–Southern Oscillation (ENSO) and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two–step bias–correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias–corrections are applied to the troposphere and stratosphere separately and together to produce a range of climates. ENSO type sensitivity experiments are then performed to reveal the impact of differing climatologies on ENSO–Europe teleconnections. The bias–corrections do not affect the response of the tropical atmosphere, nor the Aleutian Low, to strong ENSO anomalies. However, the anomalous upward wave flux and the response of the northern hemisphere polar vortex differs between the climatologies. We attribute this to a reduced sensitivity of waves to the strength of the Aleutian Low. Despite the differing responses of the polar vortex, the NAO response is similar between the climatologies, implying that for strong ENSO events a stratospheric response may not be necessary for the ENSO–North Atlantic teleconnection.

ENSO and TWC: a multi-model evaluation

<p><p>Previous research has extensively established that, during the last decades, the Trade Wind Charging (TWC) mechanism is a fundamental precursor of El Niño Southern Oscillation (ENSO). Moreover, recent results suggest that its relevance as an ENSO driver varies when a longer time interval is included the analysis. This article investigates whether TWC is isolated as a significant ENSO precursor; and how the internal variance of their coupling behaves, on a CMIP6 multi model ensemble. In particular, we consider the models participating to the CMIP6 HigResMIP, specifically designed to investigate the role that model resolution plays in simulating climate processes. For each model, we have included in the analysis 100-year long integrations of the present climate that are forced with constant radiative forcing representative of the 1950s at standard and enhanced resolutions.</p><br><p>The analysis follows two steps for each experiment. First, through a combination of Empirical Orthogonal Function (EOF) and Canonical Correlation Analysis (CCA) it isolates ENSO and TWC. Then, in order to study their mutual relation, the combination of EOF and CCA is repeated over shifting time intervals.</p><br><p>The analysis indicates TWC as a strong ENSO precursor for at least one model, and the coupling between the modes shows signs of internal variability. Also, the ways in which the models reconstruct the TWC, in its intensity and shape, and its coupling with ENSO appear to be affected by the changes in resolution. These results provide an insight over the different degrees at which HigResMIP model experiments are able to characterize the features of a fundamental process like ENSO. Moreover, they cast a light over the impacts that a change in oceanic or atmospheric resolution can have when simulating a coupled mode.</p></p>

Pre-Monsoon Cyclogenesis Over Bay of Bengal

Cyclonic disturbances in the Bay of Bengal are natural, recurrent, and a regular devastator to the east coasts of Ceylon and India (especially to Odisha coast), Bangladesh and Myanmar. The destruction depends upon the frequency, intensity, place of formation, life span in Bay, SST, ENSO, El Nino Modoki, Indian Ocean Dipole, boreal summer atmospheric phenomena, Madden–Julian oscillation and the climatology of India’s mainland. The effective management of these vulnerable storms can reduce fatalities, degradation to environment and socio-economic consequences. The investigation to decadal trend of pre-monsoon bay disturbances for last 129 years reveals that the decadal distributions of cyclonic disturbances in BOB were irregular. From last 30 years pre-monsoon landfall data (1990 to 2019) divulges that frequencies of CS in BOB are increasing during La-Nina Modoki years than normal La-Nina years. The frequencies of SCS increase during warm, strong La-Nina years than La-Nina Modoki years and particularly during negative ONI events, La Nada, Strong ENSO, high PIOD events. Individually the events may not be conclusive regarding conceive strong pre-monsoon cyclonic storms but they become severe when taken in combination.

Calcification and growth rate recovery of the reef-buildingPocilloporaspecies in the northeast tropical Pacific following an ENSO disturbance

Pocilloporids are one of the major reef-building corals in the eastern tropical Pacific (ETP) and also the most affected by thermal stress events, mainly those associated with El Niño/Southern Oscillation (ENSO) periods. To date, coral growth parameters have been poorly reported inPocilloporaspecies in the northeastern region of the tropical Pacific. Monthly and annual growth rates of the three most abundant morphospecies (P. cf. verrucosa,P. cf. capitata, andP. cf. damicornis) were evaluated during two annual periods at a site on the Pacific coast of Mexico. The first annual period, 2010–2011 was considered a strong ENSO/La Niña period with cool sea surface temperatures, then followed by a non-ENSO period in 2012–2013. The linear extension rate, skeletal density, and calcification rate averaged (±SD) were 2.31 ± 0.11 cm yr−1, 1.65 ± 0.18 g cm−3, 5.03 ± 0.84 g cm−2yr-1respectively, during the strong ENSO event. In contrast, the respective non-ENSO values were 3.50 ± 0.64 cm yr−1, 1.70 ± 0.18 g cm−3, and 6.02 ± 1.36 g cm−2yr−1. This corresponds to 52% and 20% faster linear extension and calcification rates, respectively, during non-ENSO period. The evidence suggests thatPocilloporabranching species responded positively with faster growth rates following thermal anomalies, which allow them to maintain coral communities in the region.

Impact of Strong ENSO on Regional Tropical Cyclone Activity in a High-Resolution Climate Model in the North Pacific and North Atlantic Oceans

Tropical cyclone (TC) activity in the North Pacific and North Atlantic Oceans is known to be affected by the El Niño–Southern Oscillation (ENSO). This study uses the GFDL Forecast Oriented Low Ocean Resolution Model (FLOR), which has relatively high resolution in the atmosphere, as a tool to investigate the sensitivity of TC activity to the strength of ENSO events. This study shows that TCs exhibit a nonlinear response to the strength of ENSO in the tropical eastern North Pacific (ENP) but a quasi-linear response in the tropical western North Pacific (WNP) and tropical North Atlantic. Specifically, a stronger El Niño results in disproportionate inhibition of TCs in the ENP and North Atlantic, and leads to an eastward shift in the location of TCs in the southeast of the WNP. However, the character of the response of TCs in the Pacific is insensitive to the amplitude of La Niña events. The eastward shift of TCs in the southeast of the WNP in response to a strong El Niño is due to an eastward shift of the convection and of the associated environmental conditions favorable for TCs. The inhibition of TC activity in the ENP and Atlantic during El Niño is attributed to the increase in the number of days with strong vertical wind shear during stronger El Niño events. These results are further substantiated with coupled model experiments. Understanding of the impact of strong ENSO on TC activity is important for present and future climate as the frequency of occurrence of extreme ENSO events is projected to increase in the future.