scholarly journals Evolution and forcing mechanisms of ENSO over the last 300,000 years in CCSM3

2017 ◽  
Author(s):  
Zhengyao Lu ◽  
Zhengyu Liu ◽  
Guangshan Chen ◽  
Jian Guan
Keyword(s):  
Annual Cycle ◽  
Southern Oscillation ◽  
Linear Part ◽  
Ice Sheets ◽  
Nonlinear Frequency ◽  
Enso Variability ◽  
Thermocline Feedback ◽  
Acceleration Technique ◽  
Cycle Amplitude ◽  
Continental Ice Sheets

Abstract. The responses of El Niño-Southern Oscillation (ENSO) and the equatorial Pacific annual cycle to external forcing changes are studied in three 3,000-year-long NCAR-CCSM3 model simulations. The simulations represent the period from 300 thousand years before present (ka BP) to present day. The first idealized simulation is forced only with accelerated orbital variations, and the rest are conducted more realistically by further adding on the time-varying boundary conditions of greenhouse gases (GHGs) and continental ice sheets. It is found that orbital forcing dominates slow ENSO evolution, while the effects of GHGs and ice-sheet forcing tend to compensate each other. On the orbital time scales, ENSO variability and annual cycle amplitude change in-phase and both have pronounced precessional cycles (~ 21,000 years) modulated by variations of eccentricity. Orbital forced ENSO intensity is dominated linearly by the change of the coupled ocean-atmosphere instability, notably the Ekman upwelling feedback and the thermocline feedback; and is also possibly affected during ENSO intrinsic developing season by the remote (or extratropical) influences of the short-scale stochastic weather noises. The acceleration technique is found to dampen the precessional signal in ENSO intensity. In glacial-interglacial cycles, additionally, the weakening/strengthening of ENSO owning to a more concentrated/depleted GHGs level leaves little net signal as compensated by the effect coherent change of decaying/expanding ice sheets. They influence the ENSO variability through changes in annual cycle amplitude via a common nonlinear frequency entrainment mechanism while the GHGs effect might has an additional linear part.

Prominent precession-band variance in El Niño–Southern Oscillation Intensity over the last 300,000 years

2020 ◽  
Author(s):  
Zhengyao Lu
Keyword(s):  
Greenhouse Gases ◽  
Climate Model ◽  
Southern Oscillation ◽  
Nonlinear Frequency ◽  
Tropical Eastern Pacific ◽  
Glacial Cycles ◽  
Thermocline Feedback ◽  
Climate Model Simulations ◽  
Forcing Mechanisms ◽  
Continental Ice Sheets

<p>It remains unclear how El Niño–Southern Oscillation (ENSO)—the prominent interannual anomalous climate mode—varied during the full glacial cycles. We study the evolution of ENSO of the last 300,000 years using continuous fully-coupled climate model simulations. How the slow time‐varying changes in insolation, greenhouse gases concentration, and continental ice sheets could influence the behaviours of El Niño are taken into account. The simulated ENSO variance and the tropical eastern Pacific annual cycle (AC) amplitude change in phase, and both have pronounced precession-band variance (~21,000 years) rather than the obliquity-band (~40,000 years). The precession‐modulated slow (orbital time scales) ENSO evolution is determined linearly by the change of the coupled ocean‐atmosphere instability, notably the Ekman upwelling feedback and thermocline feedback. In contrast, the greenhouse gases and ice sheet forcings (~100,000‐year cycles with sawtooth shapes) are opposed to each other as they influence ENSO variability through changes in AC amplitude via a common nonlinear frequency entrainment mechanism. The relatively long simulations which involve pronounced glacial‐interglacial forcing effects gives us more confidence in understanding ENSO forcing mechanisms, so they may shed light on ENSO dynamics and how ENSO will change in the future.</p>

scholarly journals ENSO Seasonal Synchronization Theory

2014 ◽  
Vol 27 (14) ◽  
pp. 5285-5310 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Niklas Schneider ◽  
Fei-Fei Jin ◽  
Malte F. Stuecker
Keyword(s):  
Annual Cycle ◽  
General Circulation ◽  
Phase Synchronization ◽  
Southern Oscillation ◽  
General Circulation Models ◽  
Boreal Winter ◽  
Nonlinear Frequency ◽  
Coupled Models ◽  
Frequency Locking ◽  
Enso Events

Abstract One of the key characteristics of El Niño–Southern Oscillation (ENSO) is its synchronization to the annual cycle, which manifests in the tendency of ENSO events to peak during boreal winter. Current theory offers two possible mechanisms to account the for ENSO synchronization: frequency locking of ENSO to periodic forcing by the annual cycle, or the effect of the seasonally varying background state of the equatorial Pacific on ENSO’s coupled stability. Using a parametric recharge oscillator (PRO) model of ENSO, the authors test which of these scenarios provides a better explanation of the observed ENSO synchronization. Analytical solutions of the PRO model show that the annual modulation of the growth rate parameter results directly in ENSO’s seasonal variance, amplitude modulation, and 2:1 phase synchronization to the annual cycle. The solutions are shown to be applicable to the long-term behavior of the damped model excited by stochastic noise, which produces synchronization characteristics that agree with the observations and can account for the variety of ENSO synchronization behavior in state-of-the-art coupled general circulation models. The model also predicts spectral peaks at “combination tones” between ENSO and the annual cycle that exist in the observations and many coupled models. In contrast, the nonlinear frequency entrainment scenario predicts the existence of a spectral peak at the biennial frequency corresponding to the observed 2:1 phase synchronization. Such a peak does not exist in the observed ENSO spectrum. Hence, it can be concluded that the seasonal modulation of the coupled stability is responsible for the synchronization of ENSO events to the annual cycle.

The Inverse Effect of Annual-Mean State and Annual-Cycle Changes on ENSO

2010 ◽  
Vol 23 (5) ◽  
pp. 1095-1110 ◽  
Author(s):  
Soon-Il An ◽  
Yoo-Geun Ham ◽  
Jong-Seong Kug ◽  
Axel Timmermann ◽  
Jung Choi ◽  
...  
Keyword(s):  
Annual Cycle ◽  
Western Pacific ◽  
Max Planck ◽  
Central Pacific ◽  
Enso Variability ◽  
Cycle Amplitude ◽  
State Changes ◽  
The Western Pacific ◽  
Background State ◽  
Mean State

Abstract The influence of the tropical Pacific annual-mean state on the annual-cycle amplitude and El Niño–Southern Oscillation (ENSO) variability is studied using the Max Planck Institute for Meteorology coupled general circulation model (CGCM) ECHAM5/Max Planck Institute Ocean Model (MPI-OM1). In a greenhouse warming experiment, an intensified annual cycle of sea surface temperature (SST) in the eastern tropical Pacific is associated with reduced ENSO variability, and vice versa. Analysis showed that the annual-mean states, especially the surface warming in the western Pacific and the thermocline deepening in the central Pacific, which is concurrent with the strong annual cycle, act to suppress ENSO amplitude and to intensify the annual-cycle amplitude, and vice versa. The western Pacific warming acts to reduce air–sea coupling strength and to shorten the ocean adjustment time scale, and the deepening of central Pacific thermocline acts to diminish vertical advection of the anomalous ocean temperature by the annual-mean upwelling. Consequently, ENSO activity is suppressed by the annual-mean states during the strong annual-cycle decades, and the opposite case associated with the weak annual-cycle decades is also true. Furthermore, the time integration of an intermediate ENSO model forced with different background state configurations, and a stability analysis of its linearized version, show that annual-mean background states during the weak (strong) annual-cycle decades are characterized by an enhanced (reduced) linear growth rate of ENSO or similarly large (small) variability of ENSO. However, the annual-cycle component of the background state changes cannot significantly modify ENSO variability. Using a hybrid coupled model, it is demonstrated that diagnosed annual-mean background states corresponding to a reduced (enhanced) annual cycle suppress (enhance) the development of the annual cycle of SST in the eastern equatorial Pacific, mainly through the weakening (intensifying) of zonal temperature advection of annual-mean SST by the annual-cycle zonal current. The above results support the idea that climate background state changes control both ENSO and the annual-cycle amplitude in opposing ways.

scholarly journals Last Glacial Maximum and Holocene Climate in CCSM3

2006 ◽  
Vol 19 (11) ◽  
pp. 2526-2544 ◽  
Author(s):  
Bette L. Otto-Bliesner ◽  
Esther C. Brady ◽  
Gabriel Clauzet ◽  
Robert Tomas ◽  
Samuel Levis ◽  
...  
Keyword(s):  
Last Glacial Maximum ◽  
Ice Sheets ◽  
Ocean Model ◽  
Arctic Sea Ice ◽  
Glacial Maximum ◽  
Climate System Model ◽  
Last Glacial ◽  
Global Cooling ◽  
Climate Forcings ◽  
Continental Ice Sheets

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current and Antarctic Bottom Water formation, and with increased ocean stratification, somewhat weaker and much shallower North Atlantic Deep Water. The mid-Holocene CCSM3 simulation has a global, annual cooling of less than 0.1°C compared to the PI simulation. Much larger and significant changes occur regionally and seasonally, including a more intense northern African summer monsoon, reduced Arctic sea ice in all months, and weaker ENSO variability.

Annual, Interannual, and Intraseasonal Variability of Tropical Tropopause Transition Layer Cirrus

2010 ◽  
Vol 67 (10) ◽  
pp. 3097-3112 ◽  
Author(s):  
Katrina S. Virts ◽  
John M. Wallace
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
Transition Layer ◽  
El Nino ◽  
Southern Oscillation ◽  
Cirrus Clouds ◽  
Boreal Winter ◽  
Central Pacific ◽  
Tropical Tropopause ◽  
The Pacific

Abstract Cloud fields based on the first three years of data from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission are used to investigate the relationship between cirrus within the tropical tropopause transition layer (TTL) and the Madden–Julian oscillation (MJO), the annual cycle, and El Niño–Southern Oscillation (ENSO). The TTL cirrus signature observed in association with the MJO resembles convectively induced, mixed Kelvin–Rossby wave solutions above the Pacific warm pool region. This signature is centered to the east of the peak convection and propagates eastward more rapidly than the convection; it exhibits a pronounced eastward tilt with height, suggestive of downward phase propagation and upward energy dispersion. A cirrus maximum is observed over equatorial Africa and South America when the enhanced MJO-related convection enters the western Pacific. Tropical-mean TTL cirrus is modulated by the MJO, with more than twice as much TTL cirrus fractional coverage equatorward of 10° latitude when the enhanced convection enters the Pacific than a few weeks earlier, when the convection is over the Indian Ocean. The annual cycle in cirrus clouds around the base of the TTL is equatorially asymmetric, with more cirrus observed in the summer hemisphere. Higher in the TTL, the annual cycle in cirrus clouds is more equatorially symmetric, with a maximum in the boreal winter throughout most of the tropics. The ENSO signature in TTL cirrus is marked by a zonal shift of the peak cloudiness toward the central Pacific during El Niño and toward the Maritime Continent during La Niña.

scholarly journals Competing Influences of Anthropogenic Warming, ENSO, and Plant Physiology on Future Terrestrial Aridity

2017 ◽  
Vol 30 (17) ◽  
pp. 6883-6904 ◽  
Author(s):  
Céline Bonfils ◽  
Gemma Anderson ◽  
Benjamin D. Santer ◽  
Thomas J. Phillips ◽  
Karl E. Taylor ◽  
...  
Keyword(s):  
Global Warming ◽  
Radiative Forcing ◽  
Potential Evapotranspiration ◽  
Southern Oscillation ◽  
Stomatal Resistance ◽  
Ocean Warming ◽  
Evaporative Demand ◽  
Enso Variability ◽  
Soil Desiccation ◽  
Plant Water Use

The 2011–16 California drought illustrates that drought-prone areas do not always experience relief once a favorable phase of El Niño–Southern Oscillation (ENSO) returns. In the twenty-first century, such an expectation is unrealistic in regions where global warming induces an increase in terrestrial aridity larger than the changes in aridity driven by ENSO variability. This premise is also flawed in areas where precipitation supply cannot offset the global warming–induced increase in evaporative demand. Here, atmosphere-only experiments are analyzed to identify land regions where aridity is currently sensitive to ENSO and where projected future changes in mean aridity exceed the range caused by ENSO variability. Insights into the drivers of these changes in aridity are obtained using simulations with the incremental addition of three different factors to the current climate: ocean warming, vegetation response to elevated CO2levels, and intensified CO2radiative forcing. The effect of ocean warming overwhelms the range of ENSO-driven temperature variability worldwide, increasing potential evapotranspiration (PET) in most ENSO-sensitive regions. Additionally, about 39% of the regions currently sensitive to ENSO will likely receive less precipitation in the future, independent of the ENSO phase. Consequently aridity increases in 67%–72% of the ENSO-sensitive area. When both radiative and physiological effects are considered, the area affected by arid conditions rises to 75%–79% when using PET-derived measures of aridity, but declines to 41% when an aridity indicator for total soil moisture is employed. This reduction mainly occurs because plant stomatal resistance increases under enhanced CO2concentrations, resulting in improved plant water-use efficiency, and hence reduced evapotranspiration and soil desiccation. Imposing CO2-invariant stomatal resistance may overestimate future drying in PET-derived indices.

scholarly journals Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.

1975 ◽  
Vol 14 (72) ◽  
pp. 407-420 ◽  
Author(s):  
Marith Jean Reheis
Keyword(s):  
Ice Sheets ◽  
Front Range ◽  
Denudation Rate ◽  
The Past ◽  
Glacier Front ◽  
Till Fabric ◽  
Continental Ice Sheets

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.

scholarly journals Erosion by Continental Ice Sheets

1979 ◽  
Vol 23 (89) ◽  
pp. 401-402
Author(s):  
I. M. Whillans
Keyword(s):  
Mass Balance ◽  
Short Distance ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Present Theory ◽  
Frictional Heat ◽  
Break Up ◽  
Basal Melting ◽  
Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

Suppression of earthquakes by large continental ice sheets

Nature ◽  
1987 ◽  
Vol 330 (6147) ◽  
pp. 467-469 ◽  
Author(s):  
Arch C. Johnston
Keyword(s):  
Ice Sheets ◽  
Continental Ice Sheets

scholarly journals Modulation of Annual Cycle of Tornadoes by El Niño–Southern Oscillation

2018 ◽  
Vol 45 (11) ◽  
pp. 5708-5717 ◽  
Author(s):  
John T. Allen ◽  
Maria J. Molina ◽  
Vittorio A. Gensini
Keyword(s):  
Annual Cycle ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
El Niño Southern Oscillation ◽  
El Nino Southern Oscillation
Sign in / Sign up

Export Citation Format

Share Document