Increased Occurrence of Stratospheric Sudden Warmings during El Niño as Simulated by WACCM

2006 ◽  
Vol 19 (3) ◽  
pp. 324-332 ◽  
Author(s):  
Masakazu Taguchi ◽  
Dennis L. Hartmann
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Distribution Functions ◽  
La Niña ◽  
Wave Forcing ◽  
Eddy Heat Flux ◽  
La Nina ◽  
Zonal Wavenumber ◽  
Stratospheric Sudden Warmings

Abstract Experiments with Whole Atmosphere Community Climate Model (WACCM) under perpetual January conditions indicate that stratospheric sudden warmings (SSWs) are twice as likely to occur in El Niño winters than in La Niña winters, in basic agreement with the limited observational dataset. Tropical SST anomalies that mimic El Niño and La Niña lead to changes in the shape of probability distribution functions (PDFs) of stratospheric day-to-day variability, resulting in a warmer pole and weaker vortex on average for El Niño conditions. The tropical SST forcing induces a response similar to the observed response in the enhancement of the planetary wave of zonal wavenumber 1 (wave 1) and the weakening of wave 2 in the upper troposphere and stratosphere of high latitudes. The enhanced wave 1 contributes to a shift of the PDFs of poleward eddy heat flux in the lower stratosphere, or wave forcing entering the stratosphere. The shift of the PDFs includes an increase of strong wave events that induce more frequent SSWs.

scholarly journals ENSO Modulation of the QBO: Results from MIROC Models with and without Nonorographic Gravity Wave Parameterization

2019 ◽  
Vol 76 (12) ◽  
pp. 3893-3917 ◽  
Author(s):  
Yoshio Kawatani ◽  
Kevin Hamilton ◽  
Kaoru Sato ◽  
Timothy J. Dunkerton ◽  
Shingo Watanabe ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
El Niño ◽  
El Nino ◽  
Horizontal Resolution ◽  
La Niña ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
La Nina ◽  
Zonal Wavenumber

Abstract Observational studies have shown that, on average, the quasi-biennial oscillation (QBO) exhibits a faster phase progression and shorter period during El Niño than during La Niña. Here, the possible mechanism of QBO modulation associated with ENSO is investigated using the MIROC-AGCM with T106 (~1.125°) horizontal resolution. The MIROC-AGCM simulates QBO-like oscillations without any nonorographic gravity wave parameterizations. A 100-yr integration was conducted during which annually repeating sea surface temperatures based on the composite observed El Niño conditions were imposed. A similar 100-yr La Niña integration was also conducted. The MIROC-AGCM simulates realistic differences between El Niño and La Niña, notably shorter QBO periods, a weaker Walker circulation, and more equatorial precipitation during El Niño than during La Niña. Near the equator, vertical wave fluxes of zonal momentum in the uppermost troposphere are larger and the stratospheric QBO forcing due to interaction of the mean flow with resolved gravity waves (particularly for zonal wavenumber ≥43) is much larger during El Niño. The tropical upwelling associated with the Brewer–Dobson circulation is also stronger in the El Niño simulation. The effects of the enhanced tropical upwelling during El Niño are evidently overcome by enhanced wave driving, resulting in the shorter QBO period. The integrations were repeated with another model version (MIROC-ECM with T42 horizontal resolution) that employs a parameterization of nonorographic gravity waves in order to simulate a QBO. In the MIROC-ECM the average QBO periods are nearly identical in the El Niño and La Niña simulations.

scholarly journals The Pause End and Major Temperature Impacts during Super El Niños are Due to Shortwave Radiation Anomalies

2020 ◽  
pp. 1-20
Author(s):  
Antero Ollila
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
La Niña ◽  
Global Temperature ◽  
Temperature Changes ◽  
Simple Climate Model ◽  
Enso Events ◽  
La Nina ◽  
Temperature Impacts

The hiatus or temperature pause during the 21st century has been the subject of numerous research studies with very different results and proposals. In this study, two simple climate models have been applied to test the causes of global temperature changes. The climate change factors have been shortwave (SW) radiation changes, changes in cloudiness and ENSO (El Niño Southern Oscillation) events assessed as the ONI (Oceanic Niño Index) values and anthropogenic climate drivers. The results show that a simple climate model assuming no positive water feedback follows the satellite temperature changes very well, the mean absolute error (MAE) during the period from 2001 to July 2019 being 0.073°C and 0.082°C in respect to GISTEMP. The IPCC’s simple climate model shows for the same period errors of 0.191°C and 0.128°C respectively. The temperature in 2017-2018 was about 0.2°C above the average value in 2002–2014. The conclusion is that the pause was over after 2014 and the SW anomaly forcing was the major reason for this temperature increase. SW anomalies have had their greatest impacts on the global temperature during very strong (super) El Niño events in 1997-98 and 2015-16, providing a new perspective for ENSO events. A positive SW anomaly continued after 2015-16 which may explain the weak La Niña 2016 temperature impacts, and a negative SW anomaly after 1997-98 may have contributed two strong La Niña peaks 1998-2001. No cause and effect connection could be found between the SW radiation and temperature anomalies in Nino areas.

The Pacific’s Response to Surface Heating in 130 Yr of SST: La Niña–like or El Niño–like?

2010 ◽  
Vol 67 (8) ◽  
pp. 2649-2657 ◽  
Author(s):  
Ka-Kit Tung ◽  
Jiansong Zhou
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Walker Circulation ◽  
Dominant Mode ◽  
Equatorial Region ◽  
La Niña ◽  
Radiative Heating ◽  
Modified Method ◽  
La Nina

Abstract Using a modified method of multiple linear regression on instrumented sea surface temperature (SST) in the two longest historical datasets [the Extended Reconstructed SST dataset (ERSST) and the Met Office Hadley Centre Sea Ice and SST dataset (HadISST)], it is found that the response to increased greenhouse forcing is a warm SST in the mid- to eastern Pacific Ocean in the equatorial region in the annual or seasonal mean. The warming is robustly statistically significant at the 95% confidence level. Consistent with this, the smaller radiative heating from solar forcing produces a weak warming also in this region, and the spatial pattern of the response is neither La Niña–like nor El Niño–like. It is noted that previous reports of a cold-tongue (La Niña–like) response to increased greenhouse or to solar-cycle heating were likely caused by contaminations due to the dominant mode of natural response in the equatorial Pacific. The present result has implications on whether the Walker circulation is weakened or strengthened in a warmer climate and on coupled atmosphere–ocean climate model validation.

scholarly journals Sensitivity of RegCM3 Simulated Precipitation over Southern Brazil with Different Boundary Conditions: ENSO Case

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Simone Erotildes Teleginski Ferraz ◽  
Diego Pedroso
Keyword(s):  
Boundary Conditions ◽  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Regional Climate ◽  
La Niña ◽  
Southern Brazil ◽  
Different Boundary Conditions ◽  
La Nina ◽  
Simulated Precipitation

This paper investigates the capability of a regional climate model (RegCM3) to simulate the Southern Brazil rainfall during three periods: the El Niño (1982), the neutral intermediary phase (1985), and the La Niña (1988). Each integration has used three of different boundary conditions available: NCEP-NCAR Reanalysis (I and II) and ECMWF Reanalysis—ERA-40. The simulations were performed covering a South America domain and some descriptive statistics analyses have been applied, like arithmetic mean, median, standard deviation and Pearson’s correlation; and frequencies histogram over Southern Brazil. The main results show that the model satisfactorily reproduces the rainfall in this region during the El Niño, neutral, and La Niña events, indicating that the boundary conditions which were tested adequately describe this simulations type.

scholarly journals Parameterization of Tropical Instability Waves and Examination of Their Impact on ENSO Characteristics

2012 ◽  
Vol 25 (13) ◽  
pp. 4568-4581 ◽  
Author(s):  
Yukiko Imada ◽  
Masahide Kimoto
Keyword(s):  
Heat Transport ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
La Niña ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Eddy Heat Flux ◽  
La Nina ◽  
The Impact

Abstract The impact of tropical instability waves (TIWs) on El Niño–Southern Oscillation (ENSO) characteristics is investigated by introducing a new parameterization of TIWs into an atmosphere–ocean general circulation model (AOGCM), the Model for Interdisciplinary Research on Climate (MIROC), with a medium-resolution (~1.4°) ocean model (known as MIROCmedres). Because this resolution is not sufficient to reproduce eddies at the spatial scale of TIWs, this approach isolates TIW effects from other factors that can affect ENSO characteristics. The parameterization scheme represents the effect of baroclinic eddy heat transport by TIWs. A 100-yr integration reveals a significant role of TIWs in observed ENSO asymmetry. Asymmetric heat transport associated with TIWs that are active (inactive) during La Niña (El Niño) generates a significant asymmetric negative feedback to ENSO and explains the observed asymmetric feature of a stronger-amplitude El Niño and weaker-amplitude La Niña. Furthermore, the parameterized eddy heat flux also affects the mean subsurface heat balance via the shallowing and steepening thermocline. This change in subsurface stratification induces a stronger thermocline feedback and a longer ENSO period.

scholarly journals Why might stratospheric sudden warmings occur with similar frequency in El Niño and La Niña winters?

2012 ◽  
Vol 117 (D19) ◽  
pp. n/a-n/a ◽  
Author(s):  
C. I. Garfinkel ◽  
A. H. Butler ◽  
D. W. Waugh ◽  
M. M. Hurwitz ◽  
L. M. Polvani
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Similar Frequency ◽  
La Nina ◽  
Stratospheric Sudden Warmings

scholarly journals Pausing of the ENSO Cycle: A Case Study from 1998 to 2002

2008 ◽  
Vol 21 (2) ◽  
pp. 342-363 ◽  
Author(s):  
Motoki Nagura ◽  
Kentaro Ando ◽  
Keisuke Mizuno
Keyword(s):  
Heat Flux ◽  
Mixed Layer ◽  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Heat Advection ◽  
Instability Waves ◽  
Tropical Instability Waves ◽  
Eddy Heat Flux ◽  
La Nina

Abstract The heat balance of the surface mixed layer is analyzed at the eastern equatorial Pacific Ocean (0°, 140°W) in order to examine the transition from the 1998 La Niña to the 2002 El Niño. The data used are observations from the Tropical Atmosphere Ocean/Triangle Trans-Ocean Buoy Network (TAO/TRITON). Results show that interannual variation of eddy heat flux due to tropical instability waves slows the transition from La Niña to El Niño. Previous studies have described this slow transition as a pausing period of the ENSO cycle; that is, La Niña lingers and El Niño does not immediately appear despite a deepened thermocline. Heat balance analysis shows that the vertical heat advection anomaly and surface heat flux anomaly warm the mixed layer from 1999 to 2002. These warming anomalies cause the rise of the mixed layer temperature anomaly in the transition from La Niña to El Niño. In contrast, a cooling anomaly of the horizontal heat advection reduces the warming anomaly and slows down the transition from La Niña to El Niño. In horizontal heat advection terms, the eddy heat flux anomaly significantly contributes to the cooling anomaly associated with weakened variability in the 14–50-day-period band, that is, weakened tropical instability waves. During the transition from La Niña to El Niño, the meridional shear between the South Equatorial Current (SEC) and North Equatorial Counter Current is weakened because of the eastward current anomaly at the equator (i.e., weakened SEC) associated with relaxing trade winds. Weakened shear would suppress tropical instability waves. The results presented here suggest that the synoptic-scale processes work effectively at the basin scale to slow down the transition from La Niña to El Niño.

Energy Spectrum Characteristics of Boreal Summer Intraseasonal Oscillations: Climatology and Variations during the ENSO Developing and Decaying Phases*

2008 ◽  
Vol 21 (23) ◽  
pp. 6304-6320 ◽  
Author(s):  
Ailan Lin ◽  
Tim Li
Keyword(s):  
Energy Spectrum ◽  
El Niño ◽  
El Nino ◽  
Intraseasonal Oscillation ◽  
La Niña ◽  
Western Pacific ◽  
Boreal Summer ◽  
La Nina ◽  
Zonal Wavenumber ◽  
Northward Propagation

Abstract The geographic-dependence characteristics of the energy spectrum of the boreal summer intraseasonal oscillation (BSISO; May–October) over the Indo–western Pacific region were analyzed using 25-yr (1979–2003) observational data. The BSISO energy spectrum distribution exhibits a distinctive regional characteristic. The stationary and eastward-propagating modes are most pronounced at the equator (5°S–5°N), while the westward-propagating modes are dominant in the off-equatorial region (10°–20°N). While the eastward intraseasonal oscillation (ISO) spectrum agglomerates on the 30–60-day period and zonal wavenumber 1, the westward mode covers wider spatial (wavenumber) and temporal (period) range. Along the Arabian Sea, Bay of Bengal, and South China Sea (SCS) latitudes, the dominant wavenumber 1 mode is the eastward (westward) propagation at the 30–60-day (10–20 day) period; for zonal wavenumber 2, the dominant mode is the westward propagation at both the 30–60-day and 10–20-day periods. Compared to the absolute amplitude of both zonal and meridional mode energy spectrum, northward propagation is the most predominant mode in boreal summer over the Indo–western Pacific regions. The strongest northward-propagating BSISO signal appears in the eastern tropical Indian Ocean. The variation of BSISO differs significantly in the El Niño and La Niña developing and decaying phases. During the El Niño (La Niña) developing summer, the eastward propagation is enhanced (weakened) at the equator, while the northward propagation is also strengthened (weakened) over the western Pacific (east of 140°E). During the El Niño (La Niña) decaying summer, the eastward propagation weakens (strengthens) at the equator, opposite to that in the developing summer; the westward propagation off the equator and the northward propagation over SCS and the western Pacific are suppressed (enhanced). The amplitude of the BSISO variation is stronger in the decaying summer than that in the developing summer. This asymmetry in BSISO variations is primarily attributed to the asymmetry of the background mean flow change associated with the developing and decaying phases of ENSO.

Influences of ENSO on Stratospheric Variability, and the Descent of Stratospheric Perturbations into the Lower Troposphere

2013 ◽  
Vol 26 (13) ◽  
pp. 4725-4748 ◽  
Author(s):  
Ying Li ◽  
Ngar-Cheung Lau
Keyword(s):  
El Niño ◽  
Climate Model ◽  
El Nino ◽  
Polar Vortex ◽  
La Niña ◽  
Stratospheric Polar Vortex ◽  
Near Surface ◽  
Annular Mode ◽  
Model Version ◽  
La Nina

Abstract The linkage between El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) through the stratospheric pathway is examined using a global coupled climate model [GFDL Climate Model version 3 (CM3)], with increased vertical resolution and extent in the stratosphere as compared to an earlier model [GFDL Climate Model version 2 (CM2)]. It is demonstrated that the relationship between ENSO and NAO is stronger in CM3 than in CM2. It is found that ENSO plays an important role in modulating the frequency of occurrence of the stratospheric polar vortex anomalies through enhancement/attenuation of the amplitudes of zonal wavenumbers 1 and 2, especially in late winter. A higher frequency of weak (strong) stratospheric vortex events is simulated in CM3 during El Niño (La Niña) episodes. The weak vortex events during El Niño winters are preceded by enhancement of the zonal wave-1 pattern and weakening of zonal wave-2 pattern. These modified tropospheric planetary waves propagate upward and then weaken the stratospheric polar vortex through eddy–mean flow interaction. The zonal-mean geopotential response in the stratosphere propagates downward and weakens the polar vortex throughout the troposphere. The effects of planetary wave refraction in the upper troposphere on the zonally averaged circulation cells in the tropospheric meridional plane, and the linkage between the lower branches of these cells and the near-surface wind patterns, play an important role in the flow pattern over the region corresponding to the southern lobe of the NAO. Specifically, a negative annular mode and NAO response is discernible in weak stratospheric vortex events during El Niño. Conversely, the positive annular mode and NAO is evident in strong vortex events during La Niña.

Sign in / Sign up

Export Citation Format

Share Document