scholarly journals Southern Africa Summer Drought and Heat Waves: Observations and Coupled Model Behavior

2009 ◽  
Vol 22 (22) ◽  
pp. 6033-6046 ◽  
Author(s):  
Bradfield Lyon
Keyword(s):  
Conditional Probability ◽  
Heat Wave ◽  
Southern Africa ◽  
El Niño ◽  
Heat Waves ◽  
El Nino ◽  
Coupled Model ◽  
Climate Projections ◽  
Seasonal Precipitation ◽  
Drought Conditions

Abstract Observations of daily maximum temperature (Tx) and monthly precipitation and their counterpart fields from three coupled models from the Coupled Model Intercomparison Project Phase 3 (CMIP3) archive have been used for exploratory research into the behavior of heat waves, drought, and their joint occurrence across the southern Africa subcontinent. The focus is on seasonal drought and heat waves during austral summer [December–February (DJF)] for land areas south of 15°S. Observational results (Tx available only for South Africa) are compared with those based on CMIP3 twentieth-century climate runs for a common analysis period of 1961–2000 while climate projections for the twenty-first century are also considered using the Special Report on Emissions Scenarios (SRES) A1B forcing scenario. Heat waves were defined when daily Tx values exceeded the 90th percentile for at least 3 consecutive days, while drought was identified via a standardized index of seasonal precipitation. When assessed over the entire study domain the unconditional probability of a heat wave, and its conditional probability given drought conditions, were similar in the models and (for a smaller domain) observations. The models exhibited less ability in reproducing the observed conditional probability of a heat wave given El Niño conditions. This appears to be related to a comparatively weak seasonal precipitation teleconnection pattern into southern Africa in the models during El Niño when drought conditions often develop. The heat wave–drought relationship did not substantially change in climate projections when computing anomalies from future climate means. However, relative to a 1981–2000 base period, the probability of a heat wave increases by over 3.5 times relative to the current climate. Projections across the three models suggest a future drying trend during DJF although this was found to be a model-dependent result, consistent with other studies. However, a decreasing trend in the evaporative fraction was identified across models, indicating that evaluation of future drought conditions needs to take into account both the supply (precipitation) and demand (evaporation) side of the surface water balance.

Anthropogenic Enhancement of Moderate-to-Strong El Niño Events Likely Contributed to Drought and Poor Harvests in Southern Africa During 2016

2018 ◽  
Vol 99 (1) ◽  
pp. S91-S96 ◽  
Author(s):  
Chris Funk ◽  
Frank Davenport ◽  
Laura Harrison ◽  
Tamuka Magadzire ◽  
Gideon Galu ◽  
...  
Keyword(s):  
Southern Africa ◽  
El Niño ◽  
El Nino ◽  
El Niño Events ◽  
El Nino Events

scholarly journals Local Coupled Equatorial Variability versus Remote ENSO Forcing in an Intermediate Coupled Model of the Tropical Atlantic

2006 ◽  
Vol 19 (20) ◽  
pp. 5227-5252 ◽  
Author(s):  
Serena Illig ◽  
Boris Dewitte
Keyword(s):  
Mixed Layer ◽  
El Niño ◽  
Time Scale ◽  
El Nino ◽  
Coupled Model ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Layer Model ◽  
Intermediate Coupled Model ◽  
Mixed Layer Model

Abstract The relative roles played by the remote El Niño–Southern Oscillation (ENSO) forcing and the local air–sea interactions in the tropical Atlantic are investigated using an intermediate coupled model (ICM) of the tropical Atlantic. The oceanic component of the ICM consists of a six-baroclinic mode ocean model and a simple mixed layer model that has been validated from observations. The atmospheric component is a global atmospheric general circulation model developed at the University of California, Los Angeles (UCLA). In a forced context, the ICM realistically simulates both the sea surface temperature anomaly (SSTA) variability in the equatorial band, and the relaxation of the Atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an El Niño event. The results of coupled experiments with or without Pacific ENSO forcing and with or without explicit air–sea interactions in the equatorial Atlantic indicate that the background energy in the equatorial Atlantic is provided by ENSO. However, the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by ENSO remote forcing. It is demonstrated that the peak of SSTA variability in the 1–3-yr band as observed in the equatorial Atlantic is due to the local air–sea interactions and is not a linear response to ENSO. Seasonal phase locking in boreal summer is also the result of the local coupling. The analysis of the intrinsic sustainable modes indicates that the Atlantic El Niño is qualitatively a noise-driven stable system. Such a system can produce coherent interdecadal variability that is not forced by the Pacific or extraequatorial variability. It is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical Atlantic (NTA) SST variability, the warming over NTA following El Niño events have characteristics (location and peak phase) that depend on air–sea interaction in the equatorial Atlantic. In the model, the interaction between the equatorial mode and NTA can produce a dipolelike structure of the SSTA variability that evolves at a decadal time scale. The results herein illustrate the complexity of the tropical Atlantic ocean–atmosphere system, whose predictability jointly depends on ENSO and the connections between the Atlantic modes of variability.

The essential role of early-spring westerly wind burst in generating the centennial extreme 1997/98 El Niño

2021 ◽  
pp. 1-38
Author(s):  
Tao Lian ◽  
Dake Chen
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Low Frequency ◽  
Coupled Model ◽  
Early Spring ◽  
Strong Nonlinearity ◽  
Westerly Wind ◽  
Enso Dynamics

AbstractWhile both intrinsic low-frequency atmosphere–ocean interaction and multiplicative burst-like event affect the development of the El Niño–Southern Oscillation (ENSO), the strong nonlinearity in ENSO dynamics has prevented us from separating their relative contributions. Here we propose an online filtering scheme to estimate the role of the westerly wind bursts (WWBs), a type of aperiodic burst-like atmospheric perturbation over the western-central tropical Pacific, in the genesis of the centennial extreme 1997/98 El Niño using the CESM coupled model. This scheme highlights the deterministic part of ENSO dynamics during model integration, and clearly demonstrates that the strong and long-lasting WWB in March 1997 was essential for generating the 1997/98 El Niño. Without this WWB, the intrinsic low-frequency coupling would have only produced a weak warm event in late 1997 similar to the 2014/15 El Niño.

scholarly journals Roles of initial ocean surface and subsurface states on successfully predicting 2006–2007 El Niño with an intermediate coupled model

Ocean Science ◽  
2015 ◽  
Vol 11 (1) ◽  
pp. 187-194 ◽  
Author(s):  
F. Zheng ◽  
J. Zhu
Keyword(s):  
El Niño ◽  
El Nino ◽  
Surface Condition ◽  
Coupled Model ◽  
Ocean Surface ◽  
Sea Surface ◽  
Initial Surface ◽  
El Niño Event ◽  
Successful Prediction ◽  
Intermediate Coupled Model

Abstract. The 2006–2007 El Niño event, an unusually weak event, was predicted by most models only after the warming in the eastern Pacific had commenced. In this study, on the basis of an El Niño prediction system, roles of the initial ocean surface and subsurface states on predicting the 2006–2007 El Niño event are investigated to determine conditions favorable for predicting El Niño growth and are isolated in three sets of hindcast experiments. The hindcast is initialized through assimilation of only the sea surface temperature (SST) observations to optimize the initial surface condition, only the sea level (SL) data to update the initial subsurface state, or both the SST and SL data. Results highlight that the hindcasts with three different initial states can all successfully predict the 2006–2007 El Niño event 1 year in advance and that the hindcast initialized by both the SST and SL data performs best. A comparison between the various sets of hindcast results further demonstrates that successful prediction is more significantly affected by the initial subsurface state than by the initial surface condition. The accurate initial surface state can trigger the easier prediction of the 2006–2007 El Niño, whereas a more reasonable initial subsurface state can contribute to improving the prediction in the growth of the warm event.

scholarly journals Correction to: The impact of stochastic physics on the El Niño Southern Oscillation in the EC-Earth coupled model

2019 ◽  
Vol 53 (3-4) ◽  
pp. 2479-2479 ◽  
Author(s):  
Chunxue Yang ◽  
Hannah M. Christensen ◽  
Susanna Corti ◽  
Jost von Hardenberg ◽  
Paolo Davini
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Coupled Model ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
The Impact ◽  
Stochastic Physics

scholarly journals Effect of precipitation seasonality on annual oxygen isotopic composition in the area of spring persistent rain in southeastern China and its paleoclimatic implication

2020 ◽  
Vol 16 (1) ◽  
pp. 211-225 ◽  
Author(s):  
Haiwei Zhang ◽  
Hai Cheng ◽  
Yanjun Cai ◽  
Christoph Spötl ◽  
Ashish Sinha ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Precipitation Amount ◽  
Annual Precipitation ◽  
Lower Amount ◽  
Seasonal Precipitation ◽  
Precipitation Seasonality ◽  
Precipitation Δ18o

Abstract. This study examines the seasonality of precipitation amount and δ18O over the monsoon region of China (MRC). We found that the precipitation amount associated with the East Asian summer monsoon (EASM) in the spring persistent rain (SPR) region is equivalent to that of the nonsummer monsoon (NSM). The latter contributes ∼50 % to amount-weighted annual δ18O values, in contrast with other areas in the MRC, where the δ18O of annual precipitation is dominated by EASM precipitation. Interannual relationships between the El Niño–Southern Oscillation (ENSO) index, simulated δ18O data from IsoGSM, and seasonal precipitation amount in the SPR region were also examined. We found that on interannual timescales, the seasonality of precipitation amount (EASM ∕ NSM ratio) was modulated by ENSO and primarily influences the variability of amount-weighted annual precipitation δ18O values in the SPR region, although integrated regional convection and moisture source and transport distance may also play subordinate roles. During El Niño (La Niña) phases, less (more) EASM and more (less) NSM precipitation leading to lower (higher) EASM ∕ NSM precipitation amount ratios results in higher (lower) amount-weighted annual precipitation δ18O values and, consequently, in higher (lower) speleothem δ18O values. Characterizing spatial differences in seasonal precipitation is, therefore, key to correctly interpreting speleothem δ18O records from the MRC.

scholarly journals No significant difference between Australian heat wave impacts of Modoki and eastern Pacific El Niño

2017 ◽  
Vol 44 (10) ◽  
pp. 5150-5157 ◽  
Author(s):  
Tammas F. Loughran ◽  
Sarah E. Perkins-Kirkpatrick ◽  
Lisa V. Alexander ◽  
Andrew J. Pitman
Keyword(s):  
Heat Wave ◽  
El Niño ◽  
El Nino ◽  
Eastern Pacific ◽  
Eastern Pacific El Niño ◽  
Significant Difference

scholarly journals Effects of Tropical Cyclones on ENSO

2019 ◽  
Vol 32 (19) ◽  
pp. 6423-6443 ◽  
Author(s):  
Tao Lian ◽  
Jun Ying ◽  
Hong-Li Ren ◽  
Chan Zhang ◽  
Ting Liu ◽  
...  
Keyword(s):  
Tropical Cyclones ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Heat Content ◽  
Coupled Model ◽  
Enso Event ◽  
Central Pacific ◽  
Final State ◽  
Enso Dynamics

AbstractNumerous studies have investigated the role of El Niño–Southern Oscillation (ENSO) in modulating the activity of tropical cyclones (TCs) in the western Pacific on interannual time scales, but the effects of TCs on ENSO are less discussed. Some studies have found that TCs sharply increase surface westerly anomalies over the equatorial western–central Pacific and maintain them there for a few days. Given the strong influence of equatorial surface westerly wind bursts on ENSO, as confirmed by much recent literature, the effects of TCs on ENSO may be much greater than previously expected. Using recently released observations and reanalysis datasets, it is found that the majority of near-equatorial TCs (simply TCs hereafter) are associated with strong westerly anomalies at the equator, and the number and longitude of TCs are significantly correlated with ENSO strength. When TC-related wind stresses are added into an intermediate coupled model, the simulated ENSO becomes more irregular, and both ENSO magnitude and skewness approach those of observations, as compared with simulations without TCs. Adding TCs into the model system does not break the linkage between the heat content anomaly and subsequent ENSO event in the model, which manifest the classic recharge–discharge ENSO dynamics. However, the influence of TCs on ENSO is so strong that ENSO magnitude and sometimes its final state—that is, either El Niño or La Niña—largely depend on the number and timing of TCs during the event year. Our findings suggest that TCs play a prominent role in ENSO dynamics, and their effects must be considered in ENSO forecast models.

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