The Role of Tropical Heating and Internal Variability in the California Response to the 2015/16 ENSO Event

2019 ◽  
Vol 76 (10) ◽  
pp. 3115-3128 ◽  
Author(s):  
Erik T. Swenson ◽  
David M. Straus ◽  
Chelsea E. Snide ◽  
Abdullah al Fahad
Keyword(s):  
El Niño ◽  
Diabatic Heating ◽  
El Nino ◽  
Internal Variability ◽  
Enso Event ◽  
Pacific Region ◽  
Height Field ◽  
Least Squares Regression ◽  
Mean Differences ◽  
Mean Trend

Abstract Ensemble reforecast experiments are performed for the boreal winters of 2015/16 (an El Niño year) and 2016/17 in order to understand the origin of the highly unexpected low precipitation over Southern California (SoCal) during 2015/16. The specific hypothesis tested is that the December–March anomalies in (i) SoCal precipitation (highly negative) and (ii) the 200-hPa height field in the Pacific–North American (PNA) region (unusual for an El Niño year) were forced by tropical diabatic heating, as estimated from reanalysis fields. Ten-member ensemble reforecasts for November–March for each year were carried out using the Community Earth System Model and the Climate Forecast System, version 2, models. They were repeated with diabatic heating fields added to the temperature tendencies produced by the models over the tropical Indo-Pacific region throughout the reforecasts. These added fields were obtained from an iterative process that greatly reduces the error in the seasonal mean, trend, and parabolic fit of the model heating (compared to reanalysis estimates). The SoCal precipitation and PNA height field ensemble-mean differences between 2015/16 and 2016/17 for the control and added-heating experiments showed a strong El Niño–like response in both models, including high SoCal precipitation anomalies. Using partial least squares regression to relate variations in SoCal precipitation to the PNA height field within the reforecasts, we further confirm that the observed anomalies are due to noise, and do not constitute a response forced by the seasonal-mean tropical diabatic heating in the Indo-Pacific region.

scholarly journals Indo-Western Pacific Climate Variability: ENSO Forcing and Internal Dynamics in a Tropical Pacific Pacemaker Simulation

2018 ◽  
Vol 31 (24) ◽  
pp. 10123-10139 ◽  
Author(s):  
Chuan-Yang Wang ◽  
Shang-Ping Xie ◽  
Yu Kosaka
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Tropical Pacific ◽  
Western Pacific ◽  
Ocean Atmosphere ◽  
Sst Anomalies

El Niño–Southern Oscillation (ENSO) peaks in boreal winter but its impact on Indo-western Pacific climate persists for another two seasons. Key ocean–atmosphere interaction processes for the ENSO effect are investigated using the Pacific Ocean–Global Atmosphere (POGA) experiment with a coupled general circulation model, where tropical Pacific sea surface temperature (SST) anomalies are restored to follow observations while the atmosphere and oceans are fully coupled elsewhere. The POGA shows skills in simulating the ENSO-forced warming of the tropical Indian Ocean and an anomalous anticyclonic circulation pattern over the northwestern tropical Pacific in the post–El Niño spring and summer. The 10-member POGA ensemble allows decomposing Indo-western Pacific variability into the ENSO forced and ENSO-unrelated (internal) components. Internal variability is comparable to the ENSO forcing in magnitude and independent of ENSO amplitude and phase. Random internal variability causes apparent decadal modulations of ENSO correlations over the Indo-western Pacific, which are high during epochs of high ENSO variance. This is broadly consistent with instrumental observations over the past 130 years as documented in recent studies. Internal variability features a sea level pressure pattern that extends into the north Indian Ocean and is associated with coherent SST anomalies from the Arabian Sea to the western Pacific, suggestive of ocean–atmosphere coupling.

Adjoint Sensitivity of the Niño-3 Surface Temperature to Wind Forcing

2011 ◽  
Vol 24 (16) ◽  
pp. 4480-4493 ◽  
Author(s):  
Xuebin Zhang ◽  
Bruce Cornuelle ◽  
Dean Roemmich
Keyword(s):  
Surface Temperature ◽  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Sensitivity Study ◽  
Enso Event ◽  
Equatorial Pacific ◽  
Wind Forcing ◽  
Adjoint Sensitivity ◽  
Eastern Equatorial Pacific

Abstract The evolution of sea surface temperature (SST) over the eastern equatorial Pacific plays a significant role in the intense tropical air–sea interaction there and is of central importance to the El Niño–Southern Oscillation (ENSO) phenomenon. Effects of atmospheric fields (especially wind stress) and ocean state on the eastern equatorial Pacific SST variations are investigated using the Massachusetts Institute of Technology general circulation model (MITgcm) and its adjoint model, which can calculate the sensitivities of a cost function (in this case the averaged 0–30-m temperature in the Niño-3 region during an ENSO event peak) to previous atmospheric forcing fields and ocean state going backward in time. The sensitivity of the Niño-3 surface temperature to monthly zonal wind stress in preceding months can be understood by invoking mixed layer heat balance, ocean dynamics, and especially linear equatorial wave dynamics. The maximum positive sensitivity of the Niño-3 surface temperature to local wind forcing usually happens ~1–2 months before the peak of the ENSO event and is hypothesized to be associated with the Ekman pumping mechanism. In model experiments, its magnitude is closely related to the subsurface vertical temperature gradient, exhibiting strong event-to-event differences with strong (weak) positive sensitivity during La Niña (strong El Niño) events. The adjoint sensitivity to remote wind forcing in the central and western equatorial Pacific is consistent with the standard hypothesis that the remote wind forcing affects the Niño-3 surface temperature indirectly by exciting equatorial Kelvin and Rossby waves and modulating thermocline depth in the Niño-3 region. The current adjoint sensitivity study is consistent with a previous regression-based sensitivity study derived from perturbation experiments. Finally, implication for ENSO monitoring and prediction is also discussed.

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.

scholarly journals Winter 2015/16 Atmospheric and Precipitation Anomalies over North America: El Niño Response and the Role of Noise

2018 ◽  
Vol 146 (3) ◽  
pp. 909-927 ◽  
Author(s):  
Mingyue Chen ◽  
Arun Kumar
Keyword(s):  
North America ◽  
El Niño ◽  
El Nino ◽  
Internal Variability ◽  
Precipitation Response ◽  
Sst Forcing ◽  
Precipitation Anomalies ◽  
The Mean ◽  
The U.S

Abstract The possible causes for the observed winter 2015/16 precipitation anomalies, which were opposite to the mean El Niño signal over the U.S. Southwest, are analyzed based on the ensemble of forecasts from the NCEP Climate Forecast System, version 2 (CFSv2). The analysis focuses on the role of anomalous sea surface temperature (SST) forcing and the contributions of atmospheric internal variability. The model-predicted ensemble mean forecast for December–January–February 2015/16 (DJF 2015/16) North American atmospheric anomalies compared favorably with the El Niño composite, although some difference existed. The predicted pattern was also like that in the previous strong El Niño events of 1982/83 and 1997/98. Therefore, the model largely predicted the teleconnection and precipitation response pattern in DJF 2015/16 like the mean El Niño signal. The observed negative precipitation anomalies over the U.S. Southwest in DJF 2015/16 were not consistent either with the observed or with the model-predicted El Niño composite. Analysis of the member-to-member variability in the ensemble of forecast anomalies allowed quantification of the contribution of atmospheric internal variability in shaping seasonal mean anomalies. There were considerable variations in the outcome of DJF 2015/16 precipitation over North America from one forecast to another even though the predicted SSTs were nearly identical. The observed DJF 2015/16 precipitation anomalies were well within the envelope of possible forecast outcomes. Therefore, the atmospheric internal variability could have played a considerable role in determining the observed DJF 2015/16 negative precipitation anomalies over the U.S. Southwest, and its role is discussed in the context of differences in response.

Highly Variable El Niño–Southern Oscillation Throughout the Holocene

Science ◽  
2013 ◽  
Vol 339 (6115) ◽  
pp. 67-70 ◽  
Author(s):  
Kim M. Cobb ◽  
Niko Westphal ◽  
Hussein R. Sayani ◽  
Jordan T. Watson ◽  
Emanuele Di Lorenzo ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Internal Variability ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Line Islands ◽  
Insolation Forcing ◽  
Fossil Coral

The El Niño–Southern Oscillation (ENSO) drives large changes in global climate patterns from year to year, yet its sensitivity to continued anthropogenic greenhouse forcing is uncertain. We analyzed fossil coral reconstructions of ENSO spanning the past 7000 years from the Northern Line Islands, located in the center of action for ENSO. The corals document highly variable ENSO activity, with no evidence for a systematic trend in ENSO variance, which is contrary to some models that exhibit a response to insolation forcing over this same period. Twentieth-century ENSO variance is significantly higher than average fossil coral ENSO variance but is not unprecedented. Our results suggest that forced changes in ENSO, whether natural or anthropogenic, may be difficult to detect against a background of large internal variability.

Cultural Responses to Environmental Catastrophes: Post-El Niño Subsistence on the Prehistoric North Coast of Peru

1991 ◽  
Vol 2 (1) ◽  
pp. 27-47 ◽  
Author(s):  
Jerry D. Moore
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Enso Event ◽  
North Coast ◽  
Archaeological Data ◽  
Enso Events ◽  
The North ◽  
Cultural Responses ◽  
North Coast Of Peru

Recent debate about the development of complex societies on the north coast of Peru has turned on the relative importance of marine vs. terrestrial resources and the extent to which different resource zones are upset by El Niño/Southern Oscillation (ENSO) events. While ENSO events are cited frequently as having important consequences for Prehispanic Andean societies, in fact there are few archaeological data about the nature of cultural responses to a specific ENSO event. Archaeological data from two Chimu settlements in the Casma Valley, Peru—Quebrada Sta. Cristina and Manchan—document the occurrence of a fourteenth-century A.D. ENSO event and some of the cultural responses to that prehistoric El Niño.

scholarly journals ANALISIS DAMPAK ENSO (EL-NINO SOUTHERN OSCILLATION) TERHADAP TINGKAT KEKERINGAN UNTUK TANAMAN PANGAN DAN PALAWIJA (STUDI KASUS : SULAWESI SELATAN)

Agromet ◽  
2009 ◽  
Vol 23 (2) ◽  
pp. 182
Author(s):  
Yon Sugiarto ◽  
Dori Kurniawan
Keyword(s):  
El Niño ◽  
Crop Production ◽  
Drought Index ◽  
El Nino ◽  
Southern Oscillation ◽  
Enso Event ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation ◽  
Food Crops ◽  
Weather Changes

<p>Weather and climate variability is a long-term weather changes that are characterized by fluctuations and deviations from normal conditions. One possible cause is the ENSO (El-Nino Southern Oscillation) which affected in drought events. This research was conducted to determine and analyze the level of drought in South Sulawesi due to the influence of ENSO and compare the production of food crops and secondary food crops in normal years and ENSO.<br />Drought index is calculated based on the Palmer method by using data of rainfall, air temperature and soil moisture as input. Based on the calculations using the method of Palmer drought index, the regions with monsoon rain patterns have a range of values between -22.71 drought until 18:23, Equatorial patterns ranging from -4.03 to 5:07, and on local patterns ranged<br />from -8.57 until 10:07. Verification test results on the drought index of crop production data showed that each ENSO event is always followed by a decline in rice production, especially of rice fields. Food crop production generally tends to increase at each ENSO event because most crops are plants that are resistant to drought, particularly local varieties that have adapted well to their environment. Thus, the drought caused by the influence of ENSO can affect the production of food crops and secondary food crops.</p>

scholarly journals How unusual was late 20th century El Niño-Southern Oscillation (ENSO)? Assessing evidence from tree-ring, coral, ice-core and documentary palaeoarchives, A.D. 1525-2002

2006 ◽  
Vol 6 ◽  
pp. 173-179 ◽  
Author(s):  
J. L. Gergis ◽  
A. M. Fowler
Keyword(s):  
20Th Century ◽  
Tree Ring ◽  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Southern Oscillation ◽  
Enso Event ◽  
Late 20Th Century ◽  
Enso Events ◽  
Proxy Records

Abstract. Multiple proxy records (tree-ring, coral, ice and documentary) were examined to isolate ENSO signals associated with both phases of the phenomenon for the period A.D. 1525-2002. To avoid making large-scale inferences from single proxy analysis, regional signals were aggregated into a network of high-resolution records, revealing large-scale trends in the frequency, magnitude and duration of pre-instrumental ENSO using novel applications of percentile analysis. Here we use the newly introduced coupled ocean-atmosphere ENSO index (CEI) as a baseline for the calibration of proxy records. The reconstruction revealed 83 extreme or very strong ENSO episodes since A.D. 1525, expanding considerably on existing ENSO event chronologies. Significantly, excerpts of the most comprehensive list of La Niña events complied to date are presented, indicating peak activity during the 16th to mid 17th and 20th centuries. Although extreme events are seen throughout the 478-year reconstruction, 43% of the extreme ENSO events noted since A.D. 1525 occur during the 20th century, with an obvious bias towards enhanced El Niño conditions in recent decades. Of the total number of extreme event years reconstructed, 30% of all reconstructed ENSO event years occur post-1940 alone suggesting that recent ENSO variability appears anomalous in the context of the past five centuries.

scholarly journals Uncertainty in El Niño-like warming and California precipitation changes linked by the Interdecadal Pacific Oscillation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Lu Dong ◽  
L. Ruby Leung ◽  
Fengfei Song ◽  
Jian Lu
Keyword(s):  
El Niño ◽  
El Nino ◽  
Internal Variability ◽  
Winter Precipitation ◽  
Adaptation Planning ◽  
Interdecadal Pacific Oscillation ◽  
The North ◽  
Westerly Jet ◽  
Precipitation Changes

AbstractMarked uncertainty in California (CA) precipitation projections challenges their use in adaptation planning in the region already experiencing severe water stress. Under global warming, a westerly jet extension in the North Pacific analogous to the El Niño-like teleconnection has been suggested as a key mechanism for CA winter precipitation changes. However, this teleconnection has not been reconciled with the well-known El Niño-like warming response or the controversial role of internal variability in the precipitation uncertainty. Here we find that internal variability contributes > 70% and > 50% of uncertainty in the CA precipitation changes and the El Niño-like warming, respectively, based on analysis of 318 climate simulations from several multi-model and large ensembles. The Interdecadal Pacific Oscillation plays a key role in each contribution and in connecting the two via the westerly jet extension. This unifying understanding of the role of internal variability in CA precipitation provides critical guidance for reducing and communicating uncertainty to inform adaptation planning.

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