AN ENSEMBLE FORECAST EXPERIMENT OF A LANDING TYPHOON

Based on the Global Regional Assimilation and Prediction System-Tropical Cyclone Model(GRAPES-TCM),an ensemble forecast experiment was performed,in which Typhoon Wipha during the period immediately prior to landfall was selected for the study and the breeding of growing mode(BGM) method was used to perturb the initial conditions of the vortex field and the environment field.The results of the experiment indicate that each member had a different initial status in BGM processing and they show a reasonable spread among members along with the forecast phase.Changes in the large-scale field,thermodynamic structure,and spread among members took place when Wipha made landfall.The steering effect of the large-scale field and the interaction between the thermodynamics and the dynamics resulted in different tracks of the members.Meanwhile,the forecast uncertainty increased.In summary,the ensemble mean did not perform as well as the control forecast,but the cluster mean provided some useful information,and performed better than the control in some instances.The position error was 34 km for 24 h forecast,153 km for 48 h forecast,and 191 km for 66 h forecast.The strike probability chart qualitatively described the forecast uncertainty.

TERRAIN IMPACT ON THE PRECIPITATION OF LANDFALLING TYPHOON TALIM

The impact of terrains on the precipitation of landfalling typhoon Talim (2005) over China's Mainland is investigated using the fifth-generation Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model. The simulated precipitation of simulated typhoon (the control) matches the observations closely. To compare with the control simulation, four sensitivity simulations were carried out in which terrains of Wuyi Mountain, Lushan, Dabieshan, and both Lushan and Dabieshan are completely removed respectively, but other surface properties were retained. It is found that the complex terrains of Wuyi Mountain, Lushan and Dabieshan have a significant impact on the rainfall intensity and distribution of Talim. As the terrains are removed, the rainfall is decreased very greatly and the rainfall in inland area is decreased much more than that in the coastal area. Besides, the rainfall distribution near the Lushan and Dabieshan is spread much more westward compared with the control simulation. Further analysis shows that the Wuyi Mountain would increase both the lower level air convergence and the upper level air divergence for Talim that just made landfall and thus it would contribute to the convection and increase rainfall intensity. It can be concluded that the terrains of Wuyi Mountain, Lushan and Dabieshan have obvious impacts on the Talim rainfall, and their impacts are different in various landfalling periods. The present study is a useful attempt to explore the influence of orography on the TCs in China's Mainland.

Water Vapor,Cloud,and Surface Rainfall Budgets Associated with the Landfall of Typhoon Krosa(2007):A Two-Dimensional Cloud-Resolving Modeling Study

Water vapor, cloud, and surface rainfall budgets associated with the landfall of Typhoon Krosa on 6-8 October 2007 are analyzed based on a two-dimensional cloud-resolving model simulation. The model is integrated with imposed zonally-uniform vertical velocity, zonal wind, horizontal temperature, and vapor advection from NCEP/Global Data Assimilation System （GDAS） data. The simulation data that are validated with observations are examined to study physical causes associated with surface rainfall processes during the landfall. The time- and domain-mean analysis shows that when Krosa approached the eastern coast of China on 6 October, the water vapor convergence over land caused a local atmospheric moistening and a net condensation that further produced surface rainfall and an increase of cloud hydrometeor concentration. Meanwhile, latent heating was balanced by advective cooling and a local atmospheric warming. One day later, the enhancement of net condensation led to an increase of surface rainfall and a local atmospheric drying, while the water vapor convergence weakened as a result of the landfall-induced deprivation of water vapor flux. At the same time, the latent heating is mainly compensated the advective cooling. Further weakening of vapor convergence on 8 October enhanced the local atmospheric drying while the net condensation and associated surface rainfall was maintained. The latent heating is balanced by advective cooling and a local atmospheric cooling.

Finescale Spiral Rainbands Modeled in a High-Resolution Simulation of Typhoon Rananim (2004)

Finescale spiral rainbands associated with Typhoon Rananim （2004） with the band length ranging from 10 to nearly 100 km and band width varying from 5 to 15 km are simulated using the Fifth-Generation NCAR/Penn State Mesoscale Model （MM5）. The finescale rainbands have two types： one intersecting the eyewall and causing damaging wind streaks, and the other distributed azimuthally along the inner edge of the eyewall with a relatively short lifetime. The formation of the high-velocity wind streaks results from the interaction of the azimuthal flow with the banded vertical vorticity structure triggered by tilting of the horizontal vorticity. The vertical advection of azimuthal momentum also leads to acceleration of tangential flow at a relatively high Mtitude. The evolution and structures of the bands are also examined in this study. Further investigation suggests that the boundary inflection points are related tightly to the development of the finescale rainbands, consistent with previous findings using simple symmetric models. In particular; the presence of the level of inflow reversal in the boundary layer is a crucial factor controlling the formation of these bands. The near-surface wavy peaks of vertical vorticity always follow the inflection points in radial flow. The mesoscale vortices and associated convective updrafts in the eyewall are considered to strengthen the activity of finescale bands, and the updrafts can trigger the formation of the bands as they reside in the environment with inflow reversal in the boundary layer.

PRELIMINARY STUDY OF THE ASSESSMENT OF METHODS FOR DISASTER-INDUCING RISKS BY TCs USING SAMPLE EVENTS OF TCs THAT AFFECTED SHANGHAI

Hazard factors,hazard-bear1ing objects,disaster-developing environment,and disaster-preventing capability play key roles in the formation of Tropical Cyclone (TC) disasters.Of all of these,the most important is the intensity of hazard factors (risk sources).In this study,this intensity is uniformly defined by the probability of hazard factors;then a relationship is established between disaster risk intensity and hazard factors.The exceedance probability of various hazard factors,including frequency and timing,scope of wind and rain,and maximum wind and rain of impacting TC cases,are calculated using data from TCs that impacted Shanghai from 1959–2006.The relationship between disaster situation and risk probability of hazard factors is analyzed,and the indices and model of TC disaster assessment are established based on the results.The process maximum wind speed and maximum daily precipitation are very important in TC-related disaster formation in Shanghai.The results of disaster indices coordinate with the results of the assessment model,and both can show the extent of probability of a TC disaster.Tests using TC data in 2007 and 2008 show that disasters caused by TC Krosa (0716) would be more serious than those by TC Wipha (0713),and that TC Fung Wong (0808) would have a weak impact.Real-life situations validate these results.

A STUDY OF PARTITIONING Q VECTOR ON BACKGROUND CONDITIONS OF A TORRENTIAL RAINFALL OVER SHANGHAI,CHINA ON 25 AUGUST 2008

A rainfall that occurred during 0200–1400 Beijing Standard Time(BST)25 August 2008 shows the rapid development of a convective system,a short life span,and a record rate of 117.5 mm h-1for Xujiahui station since 1872.To study this torrential rainfall process,the partitioning method of Q vector is developed,in which a moist Q vector is first separated into a dry ageostrophic Q vector(DQ)and a diabatic-heating component.The dry ageostrophic Q vector is further partitioned along isothermal lines in the natural coordinate to identify different scale forcing in adiabatic atmosphere,and the large-scale and convective condensational heating in non-uniform saturated atmosphere,convective condensational heating, and Laplace of diabatic heating that includes radiative heating and other heating and cooling processes,are calculated to study the forcing from diabatic heating.The effects of the environmental conditions on the development of the rainfall processes are diagnosed by performing the partitioning of Q vector based on 6-hourly NCEP/NCAR Final Analysis(FNL)data with the horizontal resolution of 1°×1°.The results include the following:(1)a low-pressure inverted trough associated with the landfall of Typhoon Nuri (2008),a strong southwesterly jet along the western side of the subtropical high,and an eastward-propagating westerly low-pressure trough provide favorable synoptic conditions for the development of torrential rainfall;(2)the analysis of DQ vector showed that the upward motions forced by the convergence of DQ vector in the lower troposphere(1000–600 hPa)favor the development of torrential rainfall.When DQ vector converges in the upper troposphere(500–100 hPa),upward motions in the whole air column intensify significantly to accelerate the development of torrential rainfall;(3)the partitioning analysis of DQ vector reveals that large-scale forcing persistently favors the development of torrential rainfall whereas the mesoscale forcing speeds up the torrential rainfall;(4)the calculations of large-scale condensational heating in non-uniform saturated atmosphere,convective condensational heating, and Laplace of diabatic heating showed that the forcing related to diabatic heating has the positive feedback on the convective development,and such positive feedback decays and dissipates when the convective system propagates eastward and weakens.

INTENSITY CHANGE CHARACTERISTICS OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC AS REVEALED BY THREE DIFFERENT DATASETS

Analyzed in this paper are the 20-yr(1991-2010)tropical cyclone(TC)intensity from three forecast centers in the Western North Pacific,i.e.China Meteorological Administration(CMA),Japan Meteorological Agency(JMA),and Joint Typhoon Warning Center(JTWC)of the United States.Results show that there is more or less discrepancy in the intensity change of a TC among different datasets.The maximum discrepancy reaches 22 hPa/6h(42 hPa/6h,33 hPa/6h)between CMA and JMA(CMA and JTWC,JMA and JTWC).Special attention is paid to the records for abrupt intensity change,which is currently a difficult issue for forecasters globally.It is found that an abrupt intensity change process recorded by one dataset can have,in some extreme cases,intensity change in another dataset varying from 0 to≥10 hPa/6h with the same sign or the opposite sign.In a total of 2511 cases experiencing rapid intensity change,only 14%have consensus among all the three datasets and 25%have agreement between two of the three datasets.In spite of such a significant uncertainty,the three datasets agree on the general statistical characteristics of abrupt intensity change,including regional and seasonal distribution,the relationship with initial intensity and TC moving speed,and persistence features.Notable disagreement is on very strong systems(SuperTY)and TCs moving very fast.

Impacts of TRMM SRR assimilation on the numerical prediction of tropical cyclone

Impacts of the four-dimensional variation （4DVAR） assimilation of Tropical Rainfall Measuring Mission （TRMM）/TMI surface rainfall rate （SRR） on the initialization and simulation of TC Danas in 2001 are studied. A number of sensitivity experiments are designed to evaluate the performance of assimilation during the particular stage when Danas developed from a tropical depression towards a typhoon, as well as an abrupt turning. Under the dynamic and thermodynamic constraints of meso-scale model and the 4DVAR, the TRMM SRR data are directly assimilated in high horizontal resolution （ 18 kin）. On the basis of the adjustment of initial model field, 4DVAR of TRMM SRR considerably improved the depiction of TC＇ s structure and rainfall. The same explanation can also be given to the enhancement of simulation on TC＇ s intensity and track. In comparison with the popular idea of twice steps of SRR assimilation, namely, 4DVAR pins 1DVAR, the retrieval error is expected to be avoided in the procedure of direct 4DVAR. In addition, the TRMM SRR 4DVAR within a high-resolution model can take into account as much information as observed and is expected to be performed in operational use if the observed rainfall data are routinely available.

ANALYSIS OF THE CLIMATIC CHARACTERISTICS OF LANDING TROPICAL CYCLONES IN EAST CHINA

The intensity, landing time, track trend and intensity variation of tropical cyclones (TCs) afterlandfall are analyzed using the TCs data (of best track from the China Meteorological Administration)between 1949 and 2006 for the western North Pacific and South China Sea. The trend differences of trackand intensity between the TCs that directly land in East China and those making the second landfall in EastChina after landing in Taiwan Island are categorically discussed. The results show that the first kind oflanding TCs are more likely to go northward or turn while the second kind of TCs have a larger tendency tokeep going northwest. The intensity of the first kind of TCs is more persistent than the second one. There isa higher percentage for the intensity to be weakened significantly if the TCs keep going west to northwest orsouthwest after landing.

APPLICATION OF GENERALIZED CONVECTIVE VORTICITY VECTOR IN A RAINFALL PROCESS CAUSED BY A LANDFALLING TROPICAL DEPRESSION

A heavy rainfall process, which occurred in Shanghai during 5-6 August, 2001 from a landfalling tropical depression (TD),is examined with a control numerical experiment based on MM5 model. It is found that the contours of generalized equivalent potential temperature (θ*) are almost vertical with respect to horizontal surfaces near the TD center and more densely distributed than those of equivalent potential temperature (θe).Because the atmosphere is non-uniformly saturated in reality, θ* takes the place of θe in the definition of convective vorticity vector (CVV) so that a new vector, namely the generalized convective vorticity vector (CVV*), is applied in this study. Since CVV* can reflect both the secondary circulation and the variation of horizontal moist baroclinicity, the vertical integration of vertical component of CVV* is found, in this study, to represent the rainfall areas in the TD case better than potential vorticity (PV), moist potential vorticity (MPV), generalized moist potential vorticity (Pm), and CVV, with high-value area of CVV* corresponding to heavy-rainfall area. Moreover, the analysis from CVV* implies that the Hangzhou Bay might play an important role in the heavy rain process. A sensitivity experiment without the Hangzhou Bay is then designed and compared with the control run. It is found that the CVV* becomes weaker than that in the control run, implying that the elimination of Hangzhou Bay results in reduced rainfall. Further analyses show that the Hangzhou Bay provides sufficient water vapor and surface heat flux to the TD system, which is very important to the genesis and development of mesoscale cloud clusters around the TD and the associated heavy rainfall.

IMPROVED ANALYSES AND FORECASTS WITH AIRS TEMPERATURE RETRIEVALS USING THE LOCAL ENSEMBLE TRANSFORM KALMAN FILTER

In this paper we investigate the impact of the Atmospheric Infra-Red Sounder (AIRS) temperature retrievals on data assimilation and the resulting forecasts using the four-dimensional Local Ensemble Transform Kalman Filter (LETKF) data assimilation scheme and a reduced resolution version of the NCEP Global Forecast System (GFS).Our results indicate that the AIRS temperature retrievals have a significant and consistent positive impact in the Southern Hemispheric extratropics on both analyses and forecasts,which is found not only in the temperature field but also in other variables.In tropics and the Northern Hemispheric extratropics these impacts are smaller,but are still generally positive or neutral.

ASYMMETRICAL STRUCTURES OF THE TEMPERATURE AND HUMIDITY OF TROPICAL CYCLONES

Based on NCEP/CFSR 0.5° reanalysis data and the best track data from the Japan Tokyo Typhoon Center,composite and comparative analyses demonstrate the asymmetrical structures of the temperature and humidity in tropical cyclones over the Western North Pacific and the South China Sea from 1979 to 2010.The results are shown as follows.(1) With intensifying tropical cyclones,the flow field tends to become gradually more axisymmetric;however,the asymmetry of the specific humidity in the outer regions is more obvious.(2) In general,tropical cyclones have a non-uniform,vertical, "double warm-core" structure.The "warm-cores" in the lower level of weak tropical cyclones and in the higher level of strong tropical cyclones are the stronger of the two.(3) The distribution area of a "warm-core" is enhanced with cyclone intensification and tends to become more axisymmetric.At 200 hPa,the "warm-core" of a weak cyclone has a weak anticyclone in the center,whereas that of a strong cyclone has a weak cyclone in the center.(4)The "wet-core" of a tropical cyclone is primarily located in the lower level(700-850 hPa).With the cyclone's intensification,the intensity of the "wet-core" increases and the scope of the 0.8 g kg^(-1) specific humidity anomaly tends to expand to higher levels.(5) With the cyclone's deepening,the pseudo-equivalent potential temperature at different levels in different regions increases.In addition,the largest warming rates at each intensity level in the different regions occur in the core area,followed in turn by the envelope and outer areas.

DYNAMIC FACTORS RELATED TO DECAY PROCESS OF OFFSHORE TROPICAL CYCLONES IN NORTHWEST PACIFIC

Intensity variation of tropical cyclones(TCs),especially that of coastal or landfalling TCs,is of great concern in current research.Most of the research papers,however,focus on intensification processes of TCs;only a few discuss decay processes in the lifetime of a TC.In the daily weather operation related to TCs,it is challenging when a TC weakens and/or disappears suddenly,because it brings more difficulties than the forecast of intensifying TCs does.Overestimation of a decaying landfalling TC would lead to over-preparation of defensive measures and result in"crying wolf"mentality with adverse effects.This study summarized physical mechanisms that dominate the decaying process of TCs and listed several possible dynamical factors:reduced level of air temperature,too large or too small speed,contraction of TC size amplification of TC's core,and lightning number in a TC.

AN OBSERVATIONAL STUDY ON DISTRIBUTION OF PRECIPITATION ASSOCIATED WITH LANDFALLING TROPICAL CYCLONES AFFECTING CHINA

In order to provide an operational reference for tropical cyclone precipitation forecast,this study investigates the spatial distributions of precipitation associated with landfalling tropical cyclones(TCs) affecting China using Geostationary Meteorological Satellite 5(GMS5)-TBB dataset.All named TCs formed over the western North Pacific that made direct landfall over China during the period 2001-2009 are included in this study.Based on the GMS5-TBB data,this paper reveals that in general there are four types of distribution of precipitation related to landfalling TCs affecting China.(a) the South-West Type in which there is a precipitation maximum to the southwestern quadrant of TC;(b) the Symmetrical South Type in which the rainfall is more pronounced to the south side of TC in the inner core while there is a symmetrical rainfall distribution in the outer band region;(c) the South Type,in which the rainfall maxima is more pronounced to the south of TC;and(d) the North Type,in which the rainfall maxima is more pronounced to the north of TC.Analyses of the relationship between precipitation distributions and intensity of landfalling TCs show that for intensifying TCs,both the maximum and the coverage area of the precipitation in TCs increase with the increase of TC intensity over northern Jiangsu province and southern Taiwan Strait,while decreasing over Beibu Gulf and the sea area of Changjiang River estuary.For all TCs,the center of the torrential rain in TC shifts toward the TC center as the intensity of TC increases.This finding is consistent with many previous studies.The possible influences of storm motion and vertical wind shear on the observed precipitation asymmetries are also examined.Results show that the environmental vertical wind shear is an important factor contributing to the large downshear rainfall asymmetry,especially when a TC makes landfall on the south and east China coasts.These results are also consistent with previous observational and numerical studies.

NUMERICAL ANALYSIS ON THE ROLE OF TROPICAL STORM NAMTHEUN IN THE UNUSUAL TRACKS OF THREE TROPICAL CYCLONES IN 2010

Tropical cyclones(TCs) Lionrock,Kompasu,and Namtheun were formed successively within 40 hours in 2010.Over the next several days afterwards,these TCs exhibited unusual movements which made operational prediction difficult.Verifications are performed on the forecasts of the tracks of these TCs with six operational models,including three global and three regional models.Results showed that the trends of TC tracks could be reproduced by these models,whereas trajectory turning points and landfall locations were not simulated effectively.The special track of Lionrock should be associated with its direct interaction with Namtheun,according to a conceptual model of binary TC interaction.By contrast,the relation between Kompasu and Namtheun satisfied the criteria for a semi-direct interaction.Numerical experiments based on the Global and Regional Assimilation and Prediction System-Tropical Cyclone forecast Model(GRAPES-TCM) further confirmed the effect of Namtheun on the unusual tracks of Lionrock and Kompasu.Finally,the physical mechanism of binary TC interaction was preliminarily proposed.

Western North Pacific Tropical Cyclone Intensity Guidance Evaluations Using an Alternative Verification Technique

In this study,six intensity forecast guidance techniques from the East China Regional Meteorological Center are verified for the 2008 and 2009 typhoon seasons through an alternative forecast verification technique.This technique is used to verify intensity forecasts if those forecasts call for a typhoon to dissipate or if the real typhoon dissipates.Using a contingency table,skill scores,chance,and probabilities are computed.It is shown that the skill of the six tropical cyclone intensity guidance techniques was highest for the 12-h forecasts,while the lowest skill of all the six models did not occur in 72-h forecasting.For both the 2008 and 2009 seasons,the average probabilities of the forecast intensity having a small error(6 m s-1) tended to decrease steadily.Some of the intensity forecasts had small skill scores,but the associated probabilities of the forecast intensity errors > 15 m s-1 were not the highest.

EFFECTS OF VERTICAL WIND SHEAR ON TROPICAL CYCLONE INTENSITY CHANGE

The effects of vertical wind shear on tropical cyclone(TC) intensity change are examined based on the TC data from the China Meteorological Administration and the NCEP reanalysis daily data from 2001 to 2006.First,the influence of wind shear between different vertical levels and averages in different horizontal areas are compared.The results indicate that the effect of wind shear between 200 and 850 hPa averaged within a 200-800 km annulus on TC intensity change is larger than any other calculated vertical wind shear.High-latitude and intense TCs tend to be less sensitive to the effects of VWS than low-latitude and weak TCs.TCs experience time lags between the imposition of the shear and the weakening in TC intensity.A vertical shear of 8-9 m/s(9-10 m/s) would weaken TC intensity within 60 h(48 h).A vertical shear greater than 10 m/s would weaken TC intensity within 6 h.Finally,a statistical TC intensity prediction scheme is developed by using partial least squares regression,which produces skillful intensity forecasts when potential predictors include factors related to the vertical wind shear.Analysis of the standardized regression coefficients further confirms the obtained statistical results.

Preliminary Study of Sensitive Areas for Several Tropical Cyclone Track Prediction Cases in 2007

Conditional nonlinear optimal perturbation (CNOP) obtained by the ensemble-based calculation method is employed to find possible sensitive areas for improving 48-h or more than 48-h tropical cyclone (TC) track predictions in several cases affecting China in 2007. These sensitive areas are examined by observing system simulation experiments (OSSEs). Results show that these sensitive areas improve TC track predictions for 48 h or more to different extents. Further analysis is performed to determine the distribution characteristics of sensitive areas in these cases. Results show that areas south of Luzon and over surrounding oceans are significant for 48-h or more than 48-h TC track predictions, especially 60-h to 72-h track predictions. Areas over oceans north or east to Taiwan Island seem to be secondary sensitive for 48-h or more than 48-h TC track predictions.

IMPACT OF SEA SPRAY ON TROPICAL CYCLONE STRUCTURE AND INTENSITY CHANGE

In this paper,the effects of sea spray on tropical cyclone(TC)structure and intensity variation are evaluated through numerical simulations using an advanced sea-spray parameterization from the National Oceanic and Atmospheric Administration/Earth System Research Laboratory(NOAA/ESRL),which is incorporated in the idealized Advanced Research version of the Weather Research and Forecast (WRF-ARW)model.The effect of sea spray on TC boundary-layer structure is also analyzed.The results show that there is a significant increase in TC intensity when its boundary-layer wind includes the radial and tangential winds,their structure change,and the total surface wind speed change.Diagnosis of the vorticity budget shows that an increase of convergence in TC boundary layer enhances TC vorticity due to the dynamic effect of sea spay.The main kinematic effect of the friction velocity reduction by sea spray produces an increment of large-scale convergence in the TC boundary layer,while the radial and tangential winds significantly increase with an increment of the horizontal gradient maximum of the radial wind, resulting in a final increase in the simulated TC intensity.The surface enthalpy flux enlarges TC intensity and reduces storm structure change to some degree,which results in a secondary thermodynamic impact on TC intensification.Implications of the new interpretation of sea-spray effects on TC intensification are also discussed.

A STUDY ON THE IMPACTS OF LATENT HEAT PARAMETERIZATION SCHEME ON PREDICTION SKILL OF ENSO WITH A SIMPLE OCEAN-ATMOSPHERE COUPLED MODEL

This study revises Weare's latent heat parameterization scheme and conducts an associated theoretic analysis.The revised Weare's scheme is found to present potentially better results than Zebiak's scheme.The Zebiak-Cane coupled ocean-atmosphere model,initialized by the National Centers for Environmental Prediction and the National Center for Atmospheric Research(NCEP/NCAR) reanalysis of wind stress anomaly at 925 hPa,is referred to as the ZCW coupled model.The atmosphere models of the ZCW coupled model that use Zebiak's scheme and the revised Weare's scheme are referred to as the ZCW0 and ZCWN atmosphere models,respectively.The coupled ocean-atmosphere models that use Zebiak's scheme and the revised Weare's scheme are referred to as the ZCW0and ZCWN coupled models,respectively.The simulations between the ZCW0 and ZCWN atmosphere models and between the ZCW0 and ZCWN coupled models are analyzed.The results include:(1) The evolution of heat,meridional wind and divergence anomalies simulated by similar ZCW0 and ZCWN atmosphere models,although the magnitudes of the former are larger than those of the latter;(2) The prediction skill of the Nio3 index from 1982 to 1999 by the ZCWN coupled model shows improvement compared with those by the ZCW0 coupled model;(3) The analysis of El Nio events in 1982/1983,1986/1987,and 1997/1998 and La Nia events in 1984/1985,1988/1989,and 1998/2000 suggests that the ZCWN coupled model is better than the ZCW0 coupled model in predicting warm event evolution and cold event generation.The results also show the disadvantage of the ZCWN coupled model for predicting El Nio.