A class of coupled system of the El Niño/La Niña-Southern Oscillation (ENSO) mechanism is studied. Using the perturbed theory, the asymptotic expansions of the solution for ENSO model are obtained and the asymptotic behavior of solution for corresponding problem is considered.
The central Pacific (CP) zonal wind divergence and convergence indices are defined, and the forming mechanism of CP El Niño (La Niña) events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly (ZWA) are the key process in the forming of CP El Niño (La Niña) events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Niño indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Niño (La Niña) events 5 months ahead.
The 1982-1983 El Niño event is examined in comparison with the other El Niño events in 1949-1983. The relationships of subtropical high to the sea surface temperature (SST) show the important influence of the atter, which vaired with the characters of El Niño events.
The 2002/03 El Niño event, a new type of El Niño with maximum warm anomaly occurring in the central equatorial Pacific, is known as central-Pacific (CP) El Niño. In this study, on the basis of an El Niño prediction system, roles of the initial ocean surface and subsurface states on predicting the 2002/03 CP 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 (Assim_SST), only the sea level (SL) data to update the initial subsurface state (Assim_SL), or both the SST and SL data (Assim_SST+SL). Results highlight that the hindcasts with three different initial states all can successfully predict the 2002/03 El Niño event one year in advance and that the Assim_SST+SL hindcast performs best. A comparison between the various sets of hindcast results further demonstrates that successful prediction is significantly affected by both of the initial surface and subsurface conditions, but in different developing phases of the 2002/03 El Niño event. The accurate initial surface state can easier trigger the prediction of the 2002/03 El Niño, whereas a more reasonable initial subsurface state can contribute to improving the prediction in the growth of the warm event.
Recently atmospheric and oceanic observations indicate the tropical Pacific is at the El Niño condition. However, it's not clear whether this El Niño event of this year is comparable to the very strong one of 1997/98 which brought huge influence on the whole world. In this study, based on the Ensemble Adjusted Kalman Filter (EAKF) assimilation scheme and First Institute of Oceanography-Earth System Model (FIO-ESM), the assimilation system is setup, which can provide reasonable initial conditions for prediction. And the hindcast results suggest the skill of El Niño-Southern Oscillation (ENSO) prediction is comparable to other dynamical coupled models. Then the prediction for 2015/16 El Niño by using FIO-ESM is started from 1 November 2015. The ensemble results indicate that the 2015/16 El Niño will continue to be strong. By the end of 2015, the strongest strength is very like more than 2.0℃ and the ensemble mean strength is 2.34℃, which indicates 2015/16 El Niño event will be very strong but slightly less than that of 1997/98 El Niño event (2.40℃) calculated relative a climatology based on the years 1992-2014. The prediction results also suggest 2015/16 El Niño event will be a transition to ENSO-neutral level in the early spring (FMA) 2016, and then may transfer to La Niña in summer 2016.
A class of El Niño atmospheric physics oscillation model is considered.The El Niño atmospheric physics oscillation is an abnormal phenomenon involved in the tropical Pacific ocean-atmosphere interactions.The conceptual oscillator model should consider the variations of both the eastern and westem Pacific anomaly patterns.An El Niño atmospheric physics model is proposed using a method for the variational iteration theory.Using the variational iteration method, the approximate expansions of the solution of corresponding problem are constructed.That is, firstly, introducing a set of functional and accounting their variationals, the Lagrange multiplicators are counted, and then the variational iteration is defined, finally, the approximate solution is obtained.From approximate expansions of the solution, the zonal sea surface temperature anomaly in the equatorial eastern Pacific and the thermocline depth anomaly of the seaair oscillation for El Niño atmospheric physics model can be analyzed.El Niño is a very complicated natural phenomenon.Hence basic models need to be reduced for the sea-air oscillator and are solved.The variational iteration is a simple and valid approximate method.
On the basis of the European Centre for Medium-range Weather Forecasts (ECMwF) 20 a wind field reanalysis data, the wave field of the north area of the South China Sea is calculated with the combination of the HIRHAM wind field model and the SWAN wave model. Then a significant wave height compared with the El Niño index to study the relationships between these variables. The following conclusions are drawn:(1) the wave height of the South China Sea has a strong seasonal variation, the wave height is much larger in winter than in summer; (2) in the South China Sea, the monthly average wave height of the north area has a negative correlation with the Niño3.4 index, most area of the South China Sea has a moderate correlation and the area between Taiwan Province of China and Philippines is highly correlated; and (3) in the strong El Niño years, the significant wave height in the north area of the South China Sea is significantly smaller than in other years; if the El Niño index variability is greater, the wave height decreases. In contrast, the significant wave height in the north area of the South China Sea is larger in the strong La Niña years.
The 2015/2016 El Niño event reached the threshold of super El Niño event, and was comparable to the super events in 1982/1983 and 1997/1998. Interestingly, the tropical cyclones (TCs) were found to have very late onsets in the decaying years of the super El Niño events. This study discusses the causes of late TC onsets related with atmospheric circulation, disturbance sources and trigger mechanisms. The analysis shows that the western North Pacific subtropical high (WNPSH) from January-June during the decaying years of the super El Niño events were stronger than the climatic mean, which resulted in a relatively stable atmospheric state by inhibiting deep convection. As a disturbance source, the April-June intertropical convergence zone (ITCZ) during the decaying years of the super El Niño events were significantly weaker than its climatic mean. The cross-equatorial flow and monsoon trough, as important TC generation triggers, were weaker from April-June during the decaying years of the super El Niño events, which further reduced the probability of TC generation. As for the late TC onsets, the role of atmospheric circulation anomalies (i.e., subtropical-high, the ITCZ, cross-equatorial flow, and monsoon trough) were more important. The cross-equatorial flow may take as predictor of TC onsets in the decaying years of the super El Niño events.
In order to investigate the relationships between the change of TCO2, △PCO2 and SST, current, upwelling and biological activities during El Niño event in the subtropical Pacific, the responses of TCO2 and △PCO2 in surface water in the subtropical Pacific during El Niño and La Nina have been simulated using a three-dimension carbon cycle model with biota pump.The results of numerical simulations show that TCO2 in sea water increases with reducing of SST during mature phase of El Niño in the subtropical West Pacific.At the same period, the Kuroshio in this region was weakened, the zonal currents were divergence, the upwelling carried the water with high concentrations of CO2 to the sea surface, so both of TCO2 and △PCO2 in surface water were increased.But TCO2 and △pCO2 were decreased during La Nina period.These simulated results confirmed the observations in 1982/1983, 1986/1987, 1991/1995 and 1997/1998 El Niño events.
Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea (NSCS) are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5-8 d and a weak peak at 3-4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Niño plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Niño condition. The first peak usually occurs during the mature phase of El Niño, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Niño has more active and stronger synoptic disturbances, especially for the 5-8 d period variations.