Mechanism of the Double peaked El Nino

2020 ◽  
Author(s):  
Na-Yeon Shin ◽  
Jong-Seong Kug ◽  
Felicity S. McCormack ◽  
Neil J. Holbrook
Keyword(s):  
General Circulation ◽  
Heat Budget ◽  
Coupled Model ◽  
General Circulation Models ◽  
Warm Pool ◽  
Eastern Pacific ◽  
Dynamical Analysis ◽  
Cold Tongue ◽  
Central Pacific ◽  
Sst Anomalies

<p>   In the past decades, our understanding of the ENSO phenomenon increased steadily. Especially, one of the most interesting topics was the El Niño type because of the different global impacts. The classic classification is the two types of the El Niño and there are various terms to refer this. The conventional El Niño is called the Cold tongue El Niño or the Eastern pacific El Niño. And the other type of the El Niño is called the Warm pool El Niño, the Central pacific El Niño, the El Niño Modoki or the dateline El Niño. However, in Coupled Model Intercomparison Project version 5 (CMIP5) Coupled General Circulation Models (CGCMs) results, those have been shown the Double peaked El Niño events which are the new type of the El Niño due to the climatological cold tongue bias. Double peaked El Niño events are defined as a positive sea surface temperature anomalies are separated into two centers (in Western and Eastern Pacific) and grow individually and simultaneously, and the peak of SST anomalies exceeds the threshold.</p><p>   Double peaked El Niño events are found in not only the models, but also the observations. But there are no dynamical analysis of observations. In this study, the mechanism giving rise to Double peaked El Niño in observation is examined by analyzing the mixed layer heat budget equation and comparing with the Warm Pool El Niño and Cold tongue El Niño.</p><p>   The warm SST anomalies of the western peak and the eastern peak are caused by different dynamic mechanism. Western peaks of Double peaked El Niño are similar to the Warm Pool El Niño. Those can be developed by Zonal advection feedback terms and negative anomalous wind speed, whereas eastern peaks of Double peaked El Niño are different from Warm pool El Niño. Thermocline feedback term considerably contribute to the occurrence of eastern peak. Differences of intensity of the precipitation(4-8N, 195-225E) derive other significant differences of the zonal wind stress(5S-5N, 170-200E), sea level(5S-5N, 230-250E) and zonal current(5S-5N, 230-250E). Thus, the process above can induce the eastern peak of the Double peaked El Niño.</p>

scholarly journals Recharge Oscillator Mechanisms in Two Types of ENSO

2013 ◽  
Vol 26 (17) ◽  
pp. 6506-6523 ◽  
Author(s):  
Hong-Li Ren ◽  
Fei-Fei Jin
Keyword(s):  
Phase Transitions ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Warm Pool ◽  
Life Cycles ◽  
Eastern Pacific ◽  
Cold Tongue ◽  
Central Pacific ◽  
Easterly Wind ◽  
Budget Analysis

Abstract The El Niño–Southern Oscillation (ENSO) tends to behave arguably as two different “types” or “flavors” in recent decades. One is the canonical cold-tongue-type ENSO with major sea surface temperature anomalies (SSTA) positioned over the eastern Pacific. The other is a warm-pool-type ENSO with SSTA centered in the central Pacific near the edge of the warm pool. In this study, the basic features and main feedback processes of these two types of ENSO are examined. It is shown that the interannual variability of upper-ocean heat content exhibits recharge–discharge processes throughout the life cycles of both the cold tongue (CT) and warm pool (WP) ENSO types. Through a heat budget analysis with focus on the interannual frequency band, the authors further demonstrate that the thermocline feedback plays a dominant role in contributing to the growth and phase transitions of both ENSO types, whereas the zonal advective feedback contributes mainly to their phase transitions. The westward shift of the SSTA center of the WP ENSO and the presence of significant surface easterly wind anomalies over the far eastern equatorial Pacific during its mature warm phase are the two main factors that lead to a reduced positive feedback for the eastern Pacific SSTA. Nevertheless, both the WP and CT ENSO can be understood to a large extent by the recharge oscillator mechanism.

scholarly journals Cold Tongue and Warm Pool ENSO Events in CMIP5: Mean State and Future Projections

2014 ◽  
Vol 27 (8) ◽  
pp. 2861-2885 ◽  
Author(s):  
Andréa S. Taschetto ◽  
Alexander Sen Gupta ◽  
Nicolas C. Jourdain ◽  
Agus Santoso ◽  
Caroline C. Ummenhofer ◽  
...  
Keyword(s):  
Southern Oscillation ◽  
Heat Content ◽  
Coupled Model ◽  
Warm Pool ◽  
Cmip5 Models ◽  
Cold Tongue ◽  
Future Projections ◽  
Enso Events ◽  
Almost All ◽  
Sst Anomalies

Abstract The representation of the El Niño–Southern Oscillation (ENSO) under historical forcing and future projections is analyzed in 34 models from the Coupled Model Intercomparison Project phase 5 (CMIP5). Most models realistically simulate the observed intensity and location of maximum sea surface temperature (SST) anomalies during ENSO events. However, there exist systematic biases in the westward extent of ENSO-related SST anomalies, driven by unrealistic westward displacement and enhancement of the equatorial wind stress in the western Pacific. Almost all CMIP5 models capture the observed asymmetry in magnitude between the warm and cold events (i.e., El Niños are stronger than La Niñas) and between the two types of El Niños: that is, cold tongue (CT) El Niños are stronger than warm pool (WP) El Niños. However, most models fail to reproduce the asymmetry between the two types of La Niñas, with CT stronger than WP events, which is opposite to observations. Most models capture the observed peak in ENSO amplitude around December; however, the seasonal evolution of ENSO has a large range of behavior across the models. The CMIP5 models generally reproduce the duration of CT El Niños but have biases in the evolution of the other types of events. The evolution of WP El Niños suggests that the decay of this event occurs through heat content discharge in the models rather than the advection of SST via anomalous zonal currents, as seems to occur in observations. No consistent changes are seen across the models in the location and magnitude of maximum SST anomalies, frequency, or temporal evolution of these events in a warmer world.

scholarly journals Natural variability contributes to model–satellite differences in tropical tropospheric warming

2021 ◽  
Vol 118 (13) ◽  
pp. e2020962118
Author(s):  
Stephen Po-Chedley ◽  
Benjamin D. Santer ◽  
Stephan Fueglistaler ◽  
Mark D. Zelinka ◽  
Philip J. Cameron-Smith ◽  
...  
Keyword(s):  
Climate Sensitivity ◽  
General Circulation ◽  
Climate Model ◽  
Coupled Model ◽  
General Circulation Models ◽  
Satellite Observations ◽  
Sea Surface ◽  
Eastern Pacific ◽  
Surface Warming ◽  
The Tropics

A long-standing discrepancy exists between general circulation models (GCMs) and satellite observations: The multimodel mean temperature of the midtroposphere (TMT) in the tropics warms at approximately twice the rate of observations. Using a large ensemble of simulations from a single climate model, we find that tropical TMT trends (1979–2018) vary widely and that a subset of realizations are within the range of satellite observations. Realizations with relatively small tropical TMT trends are accompanied by subdued sea-surface warming in the tropical central and eastern Pacific. Observed changes in sea-surface temperature have a similar pattern, implying that the observed tropical TMT trend has been reduced by multidecadal variability. We also assess the latest generation of GCMs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). CMIP6 simulations with muted warming over the central and eastern Pacific also show reduced tropical tropospheric warming. We find that 13% of the model realizations have tropical TMT trends within the observed trend range. These simulations are from models with both small and large climate sensitivity values, illustrating that the magnitude of tropical tropospheric warming is not solely a function of climate sensitivity. For global averages, one-quarter of model simulations exhibit TMT trends in accord with observations. Our results indicate that even on 40-y timescales, natural climate variability is important to consider when comparing observed and simulated tropospheric warming and is sufficiently large to explain TMT trend differences between models and satellite data.

scholarly journals Two Leading ENSO Modes and El Niño Types in the Zebiak–Cane Model

2018 ◽  
Vol 31 (5) ◽  
pp. 1943-1962 ◽  
Author(s):  
Ruihuang Xie ◽  
Fei-Fei Jin
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Budget ◽  
Coupled Model ◽  
Warm Pool ◽  
Central Pacific ◽  
El Niño Events ◽  
Instrumental Records ◽  
El Nino Events

Modern instrumental records reveal that El Niño events differ in their spatial patterns and temporal evolutions. Attempts have been made to categorize them roughly into two main types: eastern Pacific (EP; or cold tongue) and central Pacific (CP; or warm pool) El Niño events. In this study, a modified version of the Zebiak–Cane (MZC) coupled model is used to examine the dynamics of these two types of El Niño events. Linear eigenanalysis of the model is conducted to show that there are two leading El Niño–Southern Oscillation (ENSO) modes with their SST patterns resembling those of two types of El Niño. Thus, they are referred to as the EP and CP ENSO modes. These two modes are sensitive to changes in the mean states. The heat budget analyses demonstrate that the EP (CP) mode is dominated by thermocline (zonal advective) feedback. Therefore, the weak (strong) mean wind stress and deep (shallow) mean thermocline prefer the EP (CP) ENSO mode because of the relative dominance of thermocline (zonal advective) feedback under such a mean state. Consistent with the linear stability analysis, the occurrence ratio of CP/EP El Niño events in the nonlinear simulations generally increases toward the regime where the linear CP ENSO mode has relatively higher growth rate. These analyses suggest that the coexistence of two leading ENSO modes is responsible for two types of El Niño simulated in the MZC model. This model result may provide a plausible scenario for the observed ENSO diversity.

scholarly journals The Role of Atmosphere Feedbacks during ENSO in the CMIP3 Models. Part III: The Shortwave Flux Feedback

2012 ◽  
Vol 25 (12) ◽  
pp. 4275-4293 ◽  
Author(s):  
James Lloyd ◽  
Eric Guilyardi ◽  
Hilary Weller
Keyword(s):  
General Circulation ◽  
Southern Oscillation ◽  
Dominant Role ◽  
Coupled Model ◽  
General Circulation Models ◽  
Dynamical Response ◽  
Eastern Equatorial Pacific ◽  
Intercomparison Project ◽  
High Level ◽  
Sst Anomalies

Abstract Previous studies using coupled general circulation models (GCMs) suggest that the atmosphere model plays a dominant role in the modeled El Niño–Southern Oscillation (ENSO), and that intermodel differences in the thermodynamical damping of sea surface temperatures (SSTs) are a dominant contributor to the ENSO amplitude diversity. This study presents a detailed analysis of the shortwave flux feedback (αSW) in 12 Coupled Model Intercomparison Project phase 3 (CMIP3) simulations, motivated by findings that αSW is the primary contributor to model thermodynamical damping errors. A “feedback decomposition method,” developed to elucidate the αSW biases, shows that all models underestimate the dynamical atmospheric response to SSTs in the eastern equatorial Pacific, leading to underestimated αSW values. Biases in the cloud response to dynamics and the shortwave interception by clouds also contribute to errors in αSW. Changes in the αSW feedback between the coupled and corresponding atmosphere-only simulations are related to changes in the mean dynamics. A large nonlinearity is found in the observed and modeled SW flux feedback, hidden when linearly calculating αSW. In the observations, two physical mechanisms are proposed to explain this nonlinearity: 1) a weaker subsidence response to cold SST anomalies than the ascent response to warm SST anomalies and 2) a nonlinear high-level cloud cover response to SST. The shortwave flux feedback nonlinearity tends to be underestimated by the models, linked to an underestimated nonlinearity in the dynamical response to SST. The process-based methodology presented in this study may help to correct model ENSO atmospheric biases, ultimately leading to an improved simulation of ENSO in GCMs.

The Impact of Horizontal Resolution on the Tropical Heat Budget in an Atlantic Ocean Model

2005 ◽  
Vol 18 (6) ◽  
pp. 841-851 ◽  
Author(s):  
Markus Jochum ◽  
Raghu Murtugudde ◽  
Raffaele Ferrari ◽  
Paola Malanotte-Rizzoli
Keyword(s):  
Heat Flux ◽  
General Circulation ◽  
Heat Budget ◽  
Circulation Model ◽  
Warm Pool ◽  
Shear Instability ◽  
Entrainment Rate ◽  
Cold Tongue ◽  
Coarse Resolution ◽  
The Impact

Abstract An ocean general circulation model (OGCM) of the tropical Atlantic is coupled to an advective atmospheric boundary layer model. This configuration is used to investigate the hypothesis that resolving tropical instability waves (TIWs) in OGCMs will remove the equatorial cold bias that is a feature common to coarse-resolution OGCMs. It is shown that current eddy parameterizations cannot capture the TIW heat flux because diffusion in coarse-resolution OGCMs removes heat from the warm pool to heat the equatorial cold tongue, whereas TIWs draw their heat mostly from the atmosphere. Thus, they can bring more heat to the equatorial cold tongue without cooling the warm pool, and the SST in the warm pool is higher and more realistic. Contrary to expectations, the SST in the equatorial cold tongue is not significantly improved. The equatorial warming due to TIWs is slightly greater than the warming due to diffusion, but this increased equatorial heat flux in the high-resolution experiment is compensated by increased equatorial entrainment there. This is attributed to the Equatorial Undercurrent being stronger, thereby increasing the entrainment rate through shear instability. Thus, higher resolution does not significantly increase the total oceanic heat flux convergence in the equatorial mixed layer.

scholarly journals Evaluation of Surface Upward Longwave Radiation in the CMIP6 Models with Ground and Satellite Observations

2021 ◽  
Vol 13 (21) ◽  
pp. 4464
Author(s):  
Jiawen Xu ◽  
Xiaotong Zhang ◽  
Chunjie Feng ◽  
Shuyue Yang ◽  
Shikang Guan ◽  
...  
Keyword(s):  
General Circulation ◽  
Bayesian Model Averaging ◽  
Mean Squared Error ◽  
Radiant Energy ◽  
Coupled Model ◽  
Model Averaging ◽  
Longwave Radiation ◽  
Energy System ◽  
General Circulation Models ◽  
The Individual

Surface upward longwave radiation (SULR) is an indicator of thermal conditions over the Earth’s surface. In this study, we validated the simulated SULR from 51 Coupled Model Intercomparison Project (CMIP6) general circulation models (GCMs) through a comparison with ground measurements and satellite-retrieved SULR from the Clouds and the Earth’s Radiant Energy System, Energy Balanced and Filled (CERES EBAF). Moreover, we improved the SULR estimations by a fusion of multiple CMIP6 GCMs using multimodel ensemble (MME) methods. Large variations were found in the monthly mean SULR among the 51 CMIP6 GCMs; the bias and root mean squared error (RMSE) of the individual CMIP6 GCMs at 133 sites ranged from −3 to 24 W m−2 and 22 to 38 W m−2, respectively, which were higher than those found between the CERES EBAF and GCMs. The CMIP6 GCMs did not improve the overestimation of SULR compared to the CMIP5 GCMs. The Bayesian model averaging (BMA) method showed better performance in simulating SULR than the individual GCMs and simple model averaging (SMA) method, with a bias of 0 W m−2 and an RMSE of 19.29 W m−2 for the 133 sites. In terms of the global annual mean SULR, our best estimation for the CMIP6 GCMs using the BMA method was 392 W m−2 during 2000–2014. We found that the SULR varied between 386 and 393 W m−2 from 1850 to 2014, exhibiting an increasing tendency of 0.2 W m−2 per decade (p < 0.05).

scholarly journals Precipitation in the Amazon and its relationship with moisture transport and tropical Pacific and Atlantic SST from the CMIP5 simulation

2015 ◽  
Vol 12 (1) ◽  
pp. 671-704 ◽  
Author(s):  
G. Martins ◽  
C. von Randow ◽  
G. Sampaio ◽  
A. J. Dolman
Keyword(s):  
Moisture Transport ◽  
General Circulation ◽  
Regional Analysis ◽  
Coupled Model ◽  
General Circulation Models ◽  
Moisture Convergence ◽  
Cmip5 Models ◽  
Wet Season ◽  
The Pacific ◽  
Eastern Edge

Abstract. Studies on numerical modeling in Amazonia show that the models fail to capture important aspects of climate variability in this region and it is important to understand the reasons that cause this drawback. Here, we study how the general circulation models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) simulate the inter-relations between regional precipitation, moisture convergence and Sea Surface Temperature (SST) in the adjacent oceans, to assess how flaws in the representation of these processes can translate into biases in simulated rainfall in Amazonia. Using observational data (GPCP, CMAP, ERSST.v3, ERAI and evapotranspiration) and 21 numerical simulations from CMIP5 during the present climate (1979–2005) in June, July and August (JJA) and December, January and February (DJF), respectively, to represent dry and wet season characteristics, we evaluate how the models simulate precipitation, moisture transport and convergence, and pressure velocity (omega) in different regions of Amazonia. Thus, it is possible to identify areas of Amazonia that are more or less influenced by adjacent ocean SSTs. Our results showed that most of the CMIP5 models have poor skill in adequately representing the observed data. The regional analysis of the variables used showed that the underestimation in the dry season (JJA) was twice in relation to rainy season as quantified by the Standard Error of the Mean (SEM). It was found that Atlantic and Pacific SSTs modulate the northern sector of Amazonia during JJA, while in DJF Pacific SST only influences the eastern sector of the region. The analysis of moisture transport in JJA showed that moisture preferentially enters Amazonia via its eastern edge. In DJF this occurs both via its northern and eastern edge. The moisture balance is always positive, which indicates that Amazonia is a source of moisture to the atmosphere. Additionally, our results showed that during DJF the simulations in northeast sector of Amazonia have a strong bias in precipitation and an underestimation of moisture convergence due to the higher influence of biases in the Pacific SST. During JJA, a strong precipitation bias was observed in the southwest sector associated, also with a negative bias of moisture convergence, but with weaker influence of SSTs of adjacent oceans. The poor representation of precipitation-producing systems in Amazonia by the models and the difficulty of adequately representing the variability of SSTs in the Pacific and Atlantic oceans may be responsible for these underestimates in Amazonia.

scholarly journals PLASIM-ENTSem: a spatio-temporal emulator of future climate change for impacts assessment

2013 ◽  
Vol 6 (2) ◽  
pp. 3349-3380 ◽  
Author(s):  
P. B. Holden ◽  
N. R. Edwards ◽  
P. H. Garthwaite ◽  
K. Fraedrich ◽  
F. Lunkeit ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
General Circulation ◽  
Coupled Model ◽  
Co2 Concentration ◽  
General Circulation Models ◽  
Climate Impacts ◽  
Future Climate ◽  
Future Climate Change ◽  
Climate Data ◽  
Spatio Temporal

Abstract. Many applications in the evaluation of climate impacts and environmental policy require detailed spatio-temporal projections of future climate. To capture feedbacks from impacted natural or socio-economic systems requires interactive two-way coupling but this is generally computationally infeasible with even moderately complex general circulation models (GCMs). Dimension reduction using emulation is one solution to this problem, demonstrated here with the GCM PLASIM-ENTS. Our approach generates temporally evolving spatial patterns of climate variables, considering multiple modes of variability in order to capture non-linear feedbacks. The emulator provides a 188-member ensemble of decadally and spatially resolved (~ 5° resolution) seasonal climate data in response to an arbitrary future CO2 concentration and radiative forcing scenario. We present the PLASIM-ENTS coupled model, the construction of its emulator from an ensemble of transient future simulations, an application of the emulator methodology to produce heating and cooling degree-day projections, and the validation of the results against empirical data and higher-complexity models. We also demonstrate the application to estimates of sea-level rise and associated uncertainty.

Evaluation of the tail of the probability distribution of daily and sub-daily precipitation in CMIP6 models

2021 ◽  
pp. 1-61
Author(s):  
Jesse Norris ◽  
Alex Hall ◽  
J. David Neelin ◽  
Chad W. Thackeray ◽  
Di Chen
Keyword(s):  
General Circulation ◽  
Daily Precipitation ◽  
Precipitation Amount ◽  
Coupled Model ◽  
Lower Troposphere ◽  
General Circulation Models ◽  
Intercomparison Project ◽  
Cloud Tops ◽  
The Tropics ◽  
Fraction Models

AbstractDaily and sub-daily precipitation extremes in historical Coupled-Model-Intercomparison-Project-Phase-6 (CMIP6) simulations are evaluated against satellite-based observational estimates. Extremes are defined as the precipitation amount exceeded every x years, ranging from 0.01–10, encompassing the rarest events that are detectable in the observational record without noisy results. With increasing temporal resolution there is an increased discrepancy between models and observations: for daily extremes the multi-model median underestimates the highest percentiles by about a third, and for 3-hourly extremes by about 75% in the tropics. The novelty of the current study is that, to understand the model spread, we evaluate the 3-D structure of the atmosphere when extremes occur. In midlatitudes, where extremes are simulated predominantly explicitly, the intuitive relationship exists whereby higher-resolution models produce larger extremes (r=–0.49), via greater vertical velocity. In the tropics, the convective fraction (the fraction of precipitation simulated directly from the convective scheme) is more relevant. For models below 60% convective fraction, precipitation amount decreases with convective fraction (r=–0.63), but above 75% convective fraction, this relationship breaks down. In the lower-convective-fraction models, there is more moisture in the lower troposphere, closer to saturation. In the higher-convective-fraction models, there is deeper convection and higher cloud tops, which appears to be more physical. Thus, the low-convective models are mostly closer to the observations of extreme precipitation in the tropics, but likely for the wrong reasons. These inter-model differences in the environment in which extremes are simulated hold clues into how parameterizations could be modified in general circulation models to produce more credible 21st-Century projections.

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