scholarly journals Internal tides in the Solomon Sea in contrasted ENSO conditions

2019 ◽  
Author(s):  
Michel Tchilibou ◽  
Lionel Gourdeau ◽  
Florent Lyard ◽  
Rosemary Morrow ◽  
Ariane Koch Larrouy ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Tidal Energy ◽  
Dominant Mode ◽  
La Niña ◽  
Internal Tides ◽  
Western Boundary ◽  
Boundary Current ◽  
Surface Cooling ◽  
La Nina

Abstract. The Solomon Sea is a place of intense Low Latitudes Western Boundary current transiting to the equator where mesoscale activity is superimposed on internal tides. In this marginal sea, the cumulated effects of these dynamical constraints result in water mass transformation as observed by in situ observations. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts based on two regional simulations with and without tides. Because the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are analyzed for two contrasted ENSO conditions: the 1997–1998 El Niño and the 1999 La Niña. The generation, propagation and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity between El Niño and La Niña. Mode 1 is the dominant mode to propagate baroclinic tidal energy within the Solomon Sea, but the El Niño conditions, with stratification closer to the surface, are favorable for the propagation of mode 2. The la Niña case with a high level of mesoscale activity favors the appearance of incoherent internal tides. These results illustrate the complexity in predicting internal tides in order to access meso and submesoscale signatures from altimetric missions, including the future SWOT mission. Diapycnal mixing induced by the internal tides is efficient in eroding the salinity maximum of the upper thermocline water, and in cooling the surface temperature interacting with the atmosphere. Such effects are particularly visible far from the strong currents, where particles may experience the tidal effects during a longer time. Nevertheless, the impacts are different when considering particular ENSO conditions. The interaction of internal tides with the surface mesoscale activity reduces surface cooling during El Niño 1998, but increases surface warming during La Niña 1999, with possible impacts on regional air sea interaction.

scholarly journals Internal tides in the Solomon Sea in contrasted ENSO conditions

Ocean Science ◽  
2020 ◽  
Vol 16 (3) ◽  
pp. 615-635 ◽  
Author(s):  
Michel Tchilibou ◽  
Lionel Gourdeau ◽  
Florent Lyard ◽  
Rosemary Morrow ◽  
Ariane Koch Larrouy ◽  
...  
Keyword(s):  
Case Studies ◽  
El Niño ◽  
Water Mass ◽  
El Nino ◽  
Tidal Energy ◽  
La Niña ◽  
Internal Tides ◽  
Diapycnal Mixing ◽  
La Nina ◽  
Water Mass Transformation

Abstract. Intense equatorward western boundary currents transit the Solomon Sea, where active mesoscale structures exist with energetic internal tides. In this marginal sea, the mixing induced by these features can play a role in the observed water mass transformation. The objective of this paper is to document the M2 internal tides in the Solomon Sea and their impacts on the circulation and water masses, based on two regional simulations with and without tides. Since the Solomon Sea is under the influence of ENSO, the characteristics of the internal tides are also analyzed for two contrasted conditions: the January–March 1998 El Niño and the April–June 1999 La Niña. The generation, propagation, and dissipation of the internal tides are sensitive to changes in stratification and mesoscale activity, and these differ between these contrasted El Niño and La Niña case studies. Mode 1 is the dominant vertical mode to propagate baroclinic tidal energy within the Solomon Sea, but mode 2 becomes more energetic during the El Niño period when the stratification is closer to the surface. The La Niña period with a higher level of mesoscale activity exhibits more incoherent internal tides. These results illustrate the complexity of predicting internal tides in marginal seas in order to clearly observe meso- and submesoscale signatures from altimetric missions, including the future Surface Water Ocean Topography (SWOT) mission. Diapycnal mixing induced by tides contributes to a stronger erosion of the salinity maximum of the upper thermocline water and to cooling of the surface temperature interacting with the atmosphere. Such effects are particularly visible in quieter regions, where particles may experience the tidal effects over a longer time. However, when averaged over the Solomon Sea, the tidal effect on water mass transformation is an order of magnitude less than that observed at the entrance and exits of the Solomon Sea. These localized sites appear crucial for diapycnal mixing, since most of the baroclinic tidal energy is generated and dissipated locally here, and the different currents entering/exiting the Solomon Sea merge and mix. Finally, the extreme ENSO condition case studies suggest the strong role of local circulation changes, as well as stratification changes, in modifying the internal tides.

scholarly journals Simulation of Asymmetric ENSO Transition in WCRP CMIP3 Multimodel Experiments

2010 ◽  
Vol 23 (22) ◽  
pp. 6051-6067 ◽  
Author(s):  
Masamichi Ohba ◽  
Daisuke Nohara ◽  
Hiroaki Ueda
Keyword(s):  
El Niño ◽  
El Nino ◽  
Transition Process ◽  
La Niña ◽  
Western Boundary ◽  
Central Pacific ◽  
Cold Event ◽  
Transition Processes ◽  
La Nina ◽  
Rapid Transition

Abstract Based on the Coupled Model Intercomparison Project phase 3 (CMIP3) multimodel dataset, the relationships between the climatological states and transition processes of simulated ENSO are investigated. The air–sea coupled system of the observed ENSO can remain in the weak cold event for up to 2 yr, whereas those of the warm events tend to turn rapidly into a cold phase. Therefore, the authors separately investigate the simulated transition process of a warm-phase and a cold-phase ENSO in the CMIP3 models. Some of the models reproduce the features of the observed transition process of El Niño/La Niña, whereas most models fail to concurrently reproduce the process during both phases. In the CMIP3 models, four climate models simulate well the rapid transition from El Niño to La Niña. The intensity of a rapid transition of El Niño is mainly related to the intensity of the simulated climatological precipitation over the western–central Pacific (WCP). The models that have strong WCP precipitation can simulate the rapid termination of the equatorial zonal wind in the WCP, which tends to result in the termination of El Niño phase. This relationship is not applicable for the La Niña transition phase. The simulation of La Niña persistency is related to the reflection of off-equatorial Rossby waves at the western boundary of the Pacific and the seasonal evolution of the climatological precipitation in the WCP. Differences in the transition processes between El Niño and La Niña events are fundamentally due to the nonlinear atmospheric (convective) response to SST, which originates from the distribution of climatological SST and its seasonal changes. The results of the present study indicate that a realistic simulation of the climatological state and its seasonality in the WCP are important to be able to simulate the observed transition process of the ENSO.

scholarly journals Simulated enhancement of ENSO-related rainfall variability due to Australian dust

2011 ◽  
Vol 11 (1) ◽  
pp. 1595-1639 ◽  
Author(s):  
L. D. Rotstayn ◽  
M. A. Collier ◽  
R. M. Mitchell ◽  
Y. Qin ◽  
S. K. Campbell
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Rainfall Variability ◽  
La Niña ◽  
Climate Feedback ◽  
Surface Cooling ◽  
Atmospheric Heating ◽  
La Nina ◽  
Eastern Australia

Abstract. Average dust emissions from Australia are small compared to those from the major sources in the Northern Hemisphere. However, they are highly episodic, and this may increase the importance of Australian dust as a climate feedback agent. We compare two 160-year coupled atmosphere-ocean simulations of modern-day climate using the CSIRO Mark 3.6 global climate model (GCM). The first run (DUST) includes an interactive treatment of mineral dust and its direct radiative effects. The second run (NODUST) is otherwise identical, but has the Australian dust source set to zero. We focus on the austral spring season, when the correlation between rainfall and the El Niño Southern Oscillation (ENSO) is strongest over Australia. We find that the ENSO-rainfall relationship over eastern Australia is stronger in the DUST run: dry (El Niño) years tend to be drier, and wet (La Niña) years wetter. The ENSO-rainfall relationship is also weaker over north-western Australia in the DUST run. The amplification of ENSO-related rainfall variability over eastern Australia and the weaker ENSO-rainfall relationship over the north-west both represent an improvement relative to observations. The suggested mechanism over eastern Australia involves stabilisation of the surface layer due to enhanced atmospheric heating and surface cooling in El Niño years, and enhanced ascent and moisture convergence driven by atmospheric heating in La Niña years. The results suggest that (1) a realistic treatment of Australian dust may be necessary for accurate simulation of the ENSO-rainfall relationship over Australia, and (2) radiative feedbacks involving dust may be important for understanding natural rainfall variability over Australia.

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 INFLUENCE OF ENSO ON WET AND DRY SPELL FREQUENCY FOR RAINFED CROPPING PERIOD OVER TAMIL NADU

2019 ◽  
Vol XLII-3/W6 ◽  
pp. 63-65
Author(s):  
M. Vengateswari ◽  
V. Geethalakshmi ◽  
K. Bhuvaneswari ◽  
S. Panneerselvam
Keyword(s):  
El Niño ◽  
Tamil Nadu ◽  
El Nino ◽  
Southern Oscillation ◽  
India Meteorological Department ◽  
Dominant Mode ◽  
La Niña ◽  
Annual Rainfall ◽  
La Nina ◽  
Dry Spell

<p><strong>Abstract.</strong> Several factors are responsible for recent climatic anomalies includes seasonal and inter-annual variability of rainfall in the region in which regional and global sea surface temperature (SST) changes is the most significant factor. It is well recognized that El Niño Southern Oscillation (ENSO) is the dominant mode of climate variability on seasonal to inter-annual scales and its impacts are felt worldwide. Seasonal to inter-annual rainfall fluctuations strongly affect the success of agriculture and the abundance of water resources. Daily rainfall data at district scale was obtained from India Meteorological Department (IMD) for a period of 43 years (1971&amp;ndash;2013) was categorized based on the ENSO episodes and the analysis was performed for the rainfed cropping period (RCP, September&amp;ndash;December). A week (7 days) with the cumulative rainfall amount of 50&amp;thinsp;mm was considered as one wet spell. Non rainy days observed continuously for a decade (10 days) that period was considered to be one dry spell. Results revealed that El Niño conditions positively influenced the rainfall. Compared to neutral years, La Niña years received less rainfall as it showed the negative deviation in most of districts of Tamil Nadu. More wet spell and lesser dry spell weeks was observed under El Niño condition while the lesser wet spell and more dry spell was observed under La Niña conditions. Higher amount of rainfall during El Niño led to more number of wet spells under El Niño event.</p>

scholarly journals Impact of Strong Tropical Volcanic Eruptions on ENSO Simulated in a Coupled GCM

2013 ◽  
Vol 26 (14) ◽  
pp. 5169-5182 ◽  
Author(s):  
Masamichi Ohba ◽  
Hideo Shiogama ◽  
Tokuta Yokohata ◽  
Masahiro Watanabe
Keyword(s):  
El Niño ◽  
General Circulation ◽  
El Nino ◽  
Southern Oscillation ◽  
Volcanic Eruptions ◽  
La Niña ◽  
Subsurface Water ◽  
Surface Cooling ◽  
La Nina ◽  
The Impact

Abstract The impact of strong tropical volcanic eruptions (SVEs) on the El Niño–Southern Oscillation (ENSO) and its phase dependency is investigated using a coupled general circulation model (CGCM). This paper investigates the response of ENSO to an idealized SVE forcing, producing a peak perturbation of global-mean surface shortwave radiation larger than −6.5 W m−2. Radiative forcing due to volcanic aerosols injected into the stratosphere induces tropical surface cooling around the volcanic forcing peak. Identical-twin forecast experiments of an ENSO-neutral year in response to an SVE forcing show an El Niño–like warming lagging one year behind the peak forcing. In addition to a reduced role of the mean subsurface water upwelling (known as the dynamical thermostat mechanism), the rapid land surface cooling around the Maritime Continent weakens the equatorial Walker circulation, contributing to the positive zonal gradient of sea surface temperature (SST) and precipitation anomalies over the equatorial Pacific. Since the warm and cold phases of ENSO exhibit significant asymmetry in their transition and duration, the impact of a SVE forcing on El Niño and La Niña is also investigated. In the warm phase of ENSO, the prediction skill of the SVE-forced experiments rapidly drops approximately six months after the volcanic peak. Since the SVE significantly facilitates the duration of El Niño, the following transition from warm to cold ENSO is disrupted. The impact of SVE forcing on La Niña is, however, relatively weak. These results imply that the intensity of a dynamical thermostat-like response to a SVE could be dependent on the phase of ENSO.

Equatorial Pacific Easterly Wind Surges and the Onset of La Niña Events*

2015 ◽  
Vol 28 (2) ◽  
pp. 776-792 ◽  
Author(s):  
Andrew M. Chiodi ◽  
D. E. Harrison
Keyword(s):  
Wind Stress ◽  
El Niño ◽  
El Nino ◽  
Equatorial Pacific ◽  
La Niña ◽  
Surface Cooling ◽  
Easterly Wind ◽  
La Nina ◽  
El Niño Events ◽  
El Nino Events

Abstract The processes responsible for the onset of La Niña events have not received the same attention as those responsible for the onset of El Niño events, for which westerly wind events (WWEs) in the tropical Pacific have been identified as important contributors. Results here show that synoptic-scale surface easterly wind surges (EWSs) play an important role in the onset of La Niña events, akin to the role of WWEs in the onset of El Niño events. It is found that EWSs are a substantial component of zonal wind stress variance along the equatorial Pacific. Using reanalysis wind stress fields, validated against buoy measurements, 340 EWS events are identified between 1986 and 2012. Their distributions in space, time, and El Niño–Southern Oscillation (ENSO) state are described. About 150 EWSs occur during ENSO-neutral conditions, during the months associated with La Niña initiation and growth (April–December). Composites of changes in sea surface temperature anomaly (SSTA) following these ~150 events show statistically significant cooling (0.1°–0.4°C) along the oceanic waveguide that persists for 2–3 months following the EWSs. Experiments with EWS forcing of an ocean general circulation model show SSTA patterns like those in the observations. It is suggested that EWSs play an important role in the onset of La Niña waveguide surface cooling and deserve additional study.

The Mean and the Time Variability of the Shallow Meridional Overturning Circulation in the Tropical South Pacific Ocean

2013 ◽  
Vol 26 (12) ◽  
pp. 4069-4087 ◽  
Author(s):  
N. V. Zilberman ◽  
D. H. Roemmich ◽  
S. T. Gille
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
Western Boundary ◽  
Meridional Transport ◽  
La Nina ◽  
The Pacific ◽  
Meridional Overturning ◽  
The Mean ◽  
Subtropical Cell

Abstract The meridional transport in the Pacific Ocean subtropical cell is studied for the period from 2004 to 2011 using gridded Argo temperature and salinity profiles and atmospheric reanalysis surface winds. The poleward Ekman and equatorward geostrophic branches of the subtropical cell exhibit an El Niño–Southern Oscillation signature with strong meridional transport occurring during La Niña and weak meridional transport during El Niño. At 7.5°S, mean basinwide geostrophic transport above 1000 dbar is 48.5 ± 2.5 Sv (Sv ≡ 106 m3 s−1) of which 30.3–38.4 Sv return to the subtropics in the surface Ekman layer, whereas 10.2–18.3 Sv flow northward, feeding the Indonesian Throughflow. Geostrophic transport within the subtropical cell is stronger in the ocean interior and weaker in the western boundary during La Niña, with changes in the interior dominating basinwide transport. Using atmospheric reanalyses, only half of the mean heat gain by the Pacific north of 7.5°S is compensated by oceanic heat transport out of the region. The National Oceanography Centre at Southampton air–sea flux climatology is more consistent for closing the oceanic heat budget. In summary, the use of Argo data for studying the Pacific subtropical cell provides an improved estimate of basinwide mean geostrophic transport, includes both interior and western boundary contributions, quantifies El Niño/La Niña transport variability, and illustrates how the meridional overturning cell dominates ocean heat transport at 7.5°S.

ANALISIS DAERAH RAWAN KEKERINGAN LAHAN JAGUNG BERDASARKAN IKLIM OLDEMAN DAN KETERSEDIAN AIR TANAH DI NUSA TENGGARA TIMUR SAAT PERIODE EL NINO DAN LA NINA

2019 ◽  
Vol 3 ◽  
pp. 1219
Author(s):  
Oki Adrianto ◽  
Sudirman Sudirman ◽  
Suwandi Suwandi
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
La Nina

Perekonomian Provinsi Nusa Tenggara Timur secara sektoral masih didominasi sektor pertanian.Tanaman jagung menjadi salah satu produksi tanaman pangan terbesar berdasarkan data dari Dinas Pertanian dan Perkebunan Provinsi Nusa Tenggara Timur tahun 2015. Peningkatan produksi pertanian dapat dilakukan melalui berbagai strategi adaptasi dan upaya penanganan bencana, salah satu upaya tersebut adalah dengan penyediaan informasi iklim terkait penentuan daerah-daerah rawan kekeringan. Tujuan dari penelitian ini adalah untuk mengetahui sebaran wilayah rawan kekeringan lahan jagung bulanan di Provinsi Nusa Tenggara Timur saat kondisi El Nino dan La Nina dengan periodeisasi bulanan januari hingga desember. Data yang digunakan dalam penelitian ini adalah data curah hujan rata rata bulanan di 19 pos hujan di Provinsi Nusa Tenggara Timur dan suhu udara rata-rata bulanan dihitung menggunakan pendekatan teori Brack dengan titik referensi Stasiun Klimatologi Lasiana Kupang. Periode dari masing-masing data yang digunakan adalah dari tahun 1991 dan 1997 digunakan sebagai tahun El Nino dan tahun 1999 dan 2010 digunakan sebagai tahun La Nina. Metode yang digunakan untuk menentukan tingkat rawan kekeringan dengan menggunakan pembobotan berdasarkan penjumlahan bobot tipe iklim Oldeman dan bobot ketersediaan air tanah. Hasil penelitian menunjukkan sebaran daerah kekeringan di Provinsi Nusa Tenggara Timurpada tahun el nino lebih luas dibandingkan tahun la nina.

A Influência dos fenômenos El Niño e La Niña sobre a dinâmica climática da região Amazônica

2018 ◽  
Vol 1 ◽  
pp. e2018014
Author(s):  
Samya de Freitas MOREIRA ◽  
Cleiciane Silva da CONCEIÇÃO ◽  
Milla Cristina Santos da CRUZ ◽  
Antônio PEREIRA JÚNIOR
Keyword(s):  
El Niño ◽  
El Nino ◽  
La Niña ◽  
La Nina
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