Interdecadal change of the linkage between the North Atlantic Oscillation and the tropical cyclone frequency over the western North Pacific

The relationship between the North Atlantic Oscillation(NAO) and the tropical cyclone frequency over the western North Pacific(WNPTCF) in summer is investigated by use of observation data. It is found that their linkage appears to have an interdecadal change from weak connection to strong connection. During the period of 1948–1977, the NAO was insignificantly correlated to the WNPTCF. However, during the period of 1980–2009, they were significantly correlated with stronger(weaker) NAO corresponding to more(fewer) tropical cyclones in the western North Pacific. The possible reason for such a different relationship between the NAO and the WNPTCF during the former and latter periods is further analyzed from the perspective of large-scale atmospheric circulations. When the NAO was stronger than normal in the latter period, an anomalous cyclonic circulation prevailed in the lower troposphere of the western North Pacific and the monsoon trough was intensified, concurrent with the eastward-shifting western Pacific subtropical high as well as anomalous low-level convergence and high-level divergence over the western North Pacific. These conditions favor the genesis and development of tropical cyclones, and thus more tropical cyclones appeared over the western North Pacific. In contrast, in the former period, the impact of the NAO on the aforementioned atmospheric circulations became insignificant, thereby weakening its linkage to the WNPTCF. Further study shows that the change of the wave activity flux associated with the NAO during the former and latter periods may account for such an interdecadal shift of the NAO–WNPTCF relationship.     

Global Terrestrial Water Storage Changes and Connections to ENSO Events

Improved data quality of extended record of the Gravity Recovery and Climate Experiment (GRACE) satellite gravity solutions enables better understanding of terrestrial water storage (TWS) variations. Connections of TWS and climate change are critical to investigate regional and global water cycles. In this study, we provide a comprehensive analysis of global connections between interannual TWS changes and El Niño Southern Oscillation (ENSO) events, using multiple sources of data, including GRACE measurements, land surface model (LSM) predictions and precipitation observations. We use cross-correlation and coherence spectrum analysis to examine global connections between interannual TWS changes and the Niño 3.4 index, and select four river basins (Amazon, Orinoco, Colorado, and Lena) for more detailed analysis. The results indicate that interannual TWS changes are strongly correlated with ENSO over much of the globe, with maximum cross-correlation coefficients up to ~0.70, well above the 95% significance level (~0.29) derived by the Monte Carlo experiments. The strongest correlations are found in tropical and subtropical regions, especially in the Amazon, Orinoco, and La Plata basins. While both GRACE and LSM TWS estimates show reasonably good correlations with ENSO and generally consistent spatial correlation patterns, notably higher correlations are found between GRACE TWS and ENSO. The existence of significant correlations in middle–high latitudes shows the large-scale impact of ENSO on the global water cycle.     

Interhemispheric contrasts in the ionospheric convection response to changes in the interplanetary magnetic field and substorm activity: a case-study

Interhemispheric contrasts in the ionospheric convection response to variations of the interplanetary magnetic field (IMF) and substorm activity are examined, for an interval observed by the Polar Anglo-American Conjugate Experiment (PACE) radar system between 1600 and 2100 MLT on 4 March 1992. Representations of the ionospheric convection pattern associated with different orientations and magnitudes of the IMF and nightside driven enhancements of the auroral electrojet are employed to illustrate a possible explanation for the contrast in convection flow response observed in radar data at nominally conjugate points. Ion drift measurements from the Defence Meteorological Satellite Program (DMSP) confirm these ionospheric convection flows to be representative for the prevailing IMF orientation and magnitude. The location of the fields of view of the PACE radars with respect to these patterns suggest that the radar backscatter observed in each hemisphere is critically influenced by the position of the ionospheric convection reversal boundary (CRB) within the radar field of view and the influence it has on the generation of the irregularities required as scattering targets by high-frequency coherent radar systems. The position of the CRB in each hemisphere is strongly controlled by the relative magnitudes of the IMF B_z and B_y components, and hence so is the interhemispheric contrast in the radar observations.     

Development of a stochastic weather generator for the sub-polar North Atlantic

The article presents an approach for creating a computationally efficient stochastic weather generator. In this work the method is tested by the stochastic simulation of sea level pressure over the sub-polar North Atlantic. The weather generator includes a hidden Markov model, which propagates regional circulation patterns identified by a self organising map analysis, conditioned on the state of large-scale interannual weather regimes. The remaining residual effects are propagated by a regression model with added noise components. The regression step is performed by one of two methods, a linear model or artificial neural networks and the performance of these two methods is assessed and compared. The resulting simulations express the range of the major regional patterns of atmospheric variability and typical time scales. The long term aims of this work are to provide ensembles of atmospheric data for applied regional studies and to develop tools applicable in down-scaling large-scale ocean and atmospheric simulations.     

外热带大气扰动对ENSO的影响

合成分析了20世纪80年代以来5次主要的ENSO事件,发现外热带大气扰动通过经向风异常不仅对ENSO的发生起到重要的触发作用,而且影响到ENSO的发展和衰减. 因此,尽管ENSO对外热带大气扰动有影响,但同时外热带大气扰动又与ENSO有相互作用. 在ENSO发生前,南印度洋中纬度为反气旋异常,并通过Rossby波的频散作用加强了澳大利亚附近的反气旋异常;同时,澳大利亚东部沿海的南风异常与菲律宾附近的北风异常在赤道辐合,促进了赤道西太平洋西风异常的爆发和其后ENSO的发生. 在ENSO发生之后,东南太平洋上的气旋异常及相关的南风异常进一步增强了赤道中东太平洋的西风异常和ENSO的发展. 当ENSO达到成熟时,澳大利亚东部的反气旋异常东移,使东南太平洋的气旋异常减弱,南方涛动型环流异常亦随之减弱;同时,阿留申气旋异常加强,尤其是副热带北太平洋的风场异常可加强赤道中东太平洋海水的涌升,使该地区海表温度降低,加速ENSO的消亡.     

Comparative influence of land and sea surfaces on the Sahelian drought: a numerical study

The aim of this work is to compare the relative impact of land and sea surface anomalies on Sahel rainfall and to describe the associated anomalies in the atmospheric general circulation. This sensitivity study was done with the Météo-France climate model: ARPEGE. The sensitivity to land surface conditions consists of changes in the management of water and heat exchanges by vegetation cover and bare soil. The sensitivity to ocean surfaces consists in forcing the lower boundary of the model with worldwide composite sea surface temperature (SST) anomalies obtained from the difference between 4 dry Sahel years and 4 wet Sahel years observed since 1970. For each case, the spatiotemporal variability of the simulated rainfall anomaly and changes in the modelled tropical easterly jet (TEJ) and African easterly jet (AEJ) are discussed. The global changes in land surface evaporation have caused a rainfall deficit over the Sahel and over the Guinea Coast. No significant changes in the simulated TEJ and an enhancement of the AEJ are found; at the surface, the energy budget and the hydrological cycle are substantially modified. On the other hand, SST anomalies induce a negative rainfall anomaly over the Sahel and a positive rainfall anomaly to the south of this area. The rainfall deficit due to those anomalies is consistent with previous diagnostic and sensitivity studies. The TEJ is weaker and the AEJ is stronger than in the reference. The composite impact of SST and land surfaces anomalies is also analyzed: the simulated rainfall anomaly is similar to the observed mean African drought patterns. This work suggests that large-scale variations of surface conditions may have a substantial influence on Sahel rainfall and shows the importance of land surface parameterization in climate change modelling. In addition, it points out the interest in accurately considering the land and sea surfaces conditions in sensitivity studies on Sahel rainfall.     

Conceptual model about the interaction between El Ni?o/Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

Interaction between the Quasi-Biennial Oscillation in far west equatorial Pacific (QBOWP) and the El Ni?o/Southern Oscillation (ENSO) is studied using a new conceptual model. In this conceptual model, the QBOWP effects on ENSO are achieved through two ways: (1) the oceanic Kelvin wave along equatorial Pacific, and (2) the Atmospheric Walker Circulation anomaly, while ENSO effects on QBOWP can be accomplished by the atmospheric Walker Circulation anomaly. Diagnosis analysis of the model results shows that the Atmospheric bridge (Walker circulation) plays a more important role in interaction between the ENSO and QBOWP than the oceanic bridge (oceanic Kelvin wave along equatorial Pacific); It is found that by the interaction of the ENSO and QBOWP, a free ENSO oscillation with 3–5 years period could be substituted by a oscillation with the quasi-biennial period, and the dominant period of SST anomaly and wind anomaly in the far west equatorial Pacific tends to be prolonged with enhanced ENSO forcing. Generally, the multi-period variability in the coupled Atmosphere-Ocean System in the Tropical Pacific can be achieved through the interaction between ENSO and QBOWP.     

Improved ENSO simulation in regional coupled GCM using regressive correction method

A regressive correction method is presented with the primary goal of improving ENSO simulation in regional coupled GCM. It focuses on the correction of ocean-atmosphere exchanged fluxes. On the basis of numerical experiments and analysis, the method can be described as follows: first, driving the ocean model with heat and momentum flux computed from a long-term observation data set; the pro-duced SST is then applied to force the AGCM as its boundary condition; after that the AGCM’s simula-tion and the corresponding observation can be correlated by a linear regressive formula. Thus the re-gressive correction coefficients for the simulation with spatial and temporal variation could be obtained by linear fitting. Finally the coefficients are applied to redressing the variables used for the calculation of the exchanged air-sea flux in the coupled model when it starts integration. This method together with the anomaly coupling method is tested in a regional coupled model, which is composed of a global grid-point atmospheric general circulation model and a high-resolution tropical Pacific Ocean model. The comparison of the results shows that it is superior to the anomaly coupling both in reducing the coupled model ‘climate drift’ and in improving the ENSO simulation in the tropical Pacific Ocean.     

Developing configuration of WRF model for long-term high-resolution wind wave hindcast over the North Atlantic with WAVEWATCH III

The spatial resolution of wind forcing fields is critical for modeling ocean surface waves. We analyze here the performance of the non-hydrostatic numerical weather prediction system WRF-ARW (Weather Research and Forecasting) run with a 14-km resolution for hindcasting wind waves in the North Atlantic. The regional atmospheric model was run in the domain from 20° N to 70° N in the North Atlantic and was forced with ERA-Interim reanalysis as initial and boundary conditions in a spectral nudging mode. Here, we present the analysis of the impact of spectral nudging formulation (cutoff wavelengths and depth through which full weighting from reanalysis data is applied) onto the performance of the modeled 10-m wind speed and wind wave fields for 1 year (2010). For modeling waves, we use the third-generation spectral wave model WAVEWATCH III. The sensitivity of the atmospheric and wave models to the spectral nudging formulation is investigated via the comparison with reanalysis and observational data. The results reveal strong and persistent agreement with reanalysis data during all seasons within the year with well-simulated annual cycle and regional patterns independently of the nudging parameters that were tested. Thus, the proposed formulation of the nudging provides a reliable framework for future long-term experiments aiming at hindcasting climate variability in the North Atlantic wave field. At the same time, dynamical downscaling allows for simulation of higher waves in coastal regions, specifically near the Greenland east coast likely due to a better representation of the mesoscale atmospheric dynamics in this area.     

Conceptual model about the interaction between El Ni(n)o/ Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

Interaction between the Quasi-Biennial Oscillation in far west equatorial Pacific (QBOWP) and the El Nino/Southern Oscillation (ENSO) is studied using a new conceptual model. In this conceptual model, the QBOWP effects on ENSO are achieved through two ways: (1) the oceanic Kelvin wave along equatorial Pacific, and (2) the Atmospheric Walker Circulation anomaly, while ENSO effects on QBOWP can be accomplished by the atmospheric Walker Circulation anomaly. Diagnosis analysis of the model results shows that the Atmospheric bridge (Walker circulation) plays a more important role in interaction between the ENSO and QBOWP than the oceanic bridge (oceanic Kelvin wave along equatorial Pacific); It is found that by the interaction of the ENSO and QBOWP, a free ENSO oscillation with 3-5 years period could be substituted by a oscillation with the quasi-biennial period, and the dominant period of SST anomaly and wind anomaly in the far west equatorial Pacific tends to be prolonged with enhanced ENSO forcing. Generally, the multi-period variability in the coupled Atmosphere-Ocean System in the Tropical Pacific can be achieved through the interaction between ENSO and QBOWP.     

Conceptual model about the interaction between El Nio/Southern Oscillation and Quasi-Biennial Oscillation in far west equatorial Pacific

In the tropical Pacific region, El Ni?o/Southern Os- (COADS SST from 1945 to 1993) in the eastern cillation (ENSO) and the Quasi-Biennial Oscillation in (150°W-90°W, 5°S-5°N) and the observed SST far west equatorial Pacific (QBOWP) are two most and zonal wind in the far western equatorial Pacific prominent interannual variation phenomena. The for- (120°-140°E, 0°-10°N) (Fig.1), in the eastern Pa- mer is characterized by coupled SST-wind variability cific the period of S…     

Die Abweichungen der Oberflächentemperatur des Ozeans bei den nordatlantischen Wetterschiffen 1951–1953

Zusammenfassung Die Abweichungen der Meerestemperatur vom Normalwert bei den zehn nordatlantischen Wetterschiffen während der 38 Monate November 1950 bis Dezember 1953 werden dazu benutzt, die angenäherte thermische Anomalie der Oberfläche des Gesamtozeans in diesem Zeitraum festzustellen. Sie beträgt im Mittel der drei Jahre 1951–1953 etwa +0,6°. Das Verhältnis von positiven zu negativen Abweichungen war im Durchschnitt von 380 Fällen (10 Wetterschiffe 38 Monate) etwas größer als 31. Die positive thermische Anomalie des Nordatlantischen Ozeans hatte in dem betrachteten Zeitraum ihr Hauptmaximum im Winter, ein Nebenmaximum im Sommer.Das winterliche Maximum zeigte sich in auffälliger Weise auch in den Anomalien der Lufttemperatur an der Ostküste Nordamerikas. Es läßt sich weitgehend erklären durch die Besonderheit der mittleren atmosphärischen Zirkulation in den Jahren 1951 bis 1953: Das Abströmen von Kaltluft über die amerikanische Ostküste auf den Ozean war erheblich unternormal.Die Lufttemperatur über dem Nordatlantischen Ozean selbst zeigt im ganzen ähnliche Änderungstendenzen wie die Oberflächentemperatur des Meeres, wobei die Änderungen der Lufttemperatur als das Primäre erscheinen. Die Anomalien der Lufttemperatur an der Westküste Europas (übergreifende Vierteljahrmittel) schwangen im Zeitraum 1951–53 oft entgegengesetzt zu denen an der Ostküste Nordamerikas und wurden von der Wassertemperaturanomalie des Gesamtozeans in überraschend geringem Maße beeinflußt. Die mittleren jährlichen Abweichungen der Lufttemperatur amerikanische plus europäische Küste stimmten aber in den Jahren 1951 bis 1953 mit den mittleren Abweichungen der Wassertemperatur des Nordatlantischen Ozeans recht genau überein (Durchschnitt +0,60:+0,59°).Die Bedeutung der Überwärmung des Ozeans wäre besser abzuschätzen bei Kenntnis der Tiefenerstreckung der positiven thermischen Anomalie. Nach Tiefenmessungen der japanischen Wetterschiffe Tango und Extra dürfte eine Reichweite der längeren unperiodischen Änderungen von der Oberfläche bis 200 m Tiefe nicht unwahrscheinlich sein. Unter der Annahme, daß zur Zeit der Nordatlantische Ozean von 0 bis 200 m Tiefe 0,5° wärmer ist als normal, bestände pro cm² eine Zusatzspeicherung von 10000 gcal: ein Wert, dessen Größe sich an Hand der ozeanischen Strahlungsbilanz erläutern läßt.Zum Schluß werden die Jahresanomalien der Oberflächentemperatur für die einzelnen zehn Wetterschiffe mitgeteilt, nachdem an einem Beispiel gezeigt wurde, wie die Umstellungen der atmosphärischen Zirkulation auf die Entwicklung der Anomalien einwirken.

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Departures from the normal values of sea surface temperatures in the vicinity of the North Atlantic weather ships

Summary The departures from the normal values of sea temperature in the vicinity of the ten North Atlantic weather ships during the 38 months from November, 1950 to December, 1953 are used as a means of determining the approximate thermic anomaly of the whole ocean surface during this period. The mean value of this anomaly for the three years from 1951 to 1953 is about +0,6°. The average ratio of positive to negative departures is found to be somewhat greater than 3 1. The positive thermal anomaly of the North Atlantic ocean during the period in question reached its main maximum in winter and a maximum of secondary importance in summer.The winter maximum likewise appears in a striking manner in the anomalies of air temperatures on the east coast of North America. It may be chiefly explained by the peculiarity of the mean atmospheric circulation throughout the years from 1951 to 1953 when the flow of cold air across the east coast of America towards the ocean was considerably below normal.On the whole, the air temperature over the North Atlantic ocean tends to vary similarly to the temperature of the ocean surface, the variations of the air temperatures apparently being the primary phenomenon. The anomalies of the air temperature on the west coast of Europe (overlapping three months' means) during the period from 1951 to 1953 often show variations contrasting to those on the east coast of North America; they are to a surprisingly small degree influenced by the anomalies of the water temperature of the whole ocean area. Throughout the years 1951–1953, the mean annual departures of the sums of air temperature American plus European coast were, however, in good conformity with the mean departures of water temperatures in the North Atlantic ocean (annual mean values: +0,60:+0,59°).The influence of the superheating of the ocean might be more accurately estimated if the depth range of the positive thermal anomaly were known. From measurements made by the Japanese weather ships Tango and Extra it would not appear improbable that the long aperiodic variations may reach as far down as 200 m below the surface. Supposing that at present in the surface layer between 0 and 200 m the water temperature of the North Atlantic Ocean may be 0,5° above normal, this would mean an additional storage of heat of 10000 gcal per cm², a value which may be explained by the oceanic radiation balance.Finally, after having shown by an example how the variations in the atmospheric circulation reflect on the anomalies of water temperature, the annual anomalies of surface temperature in the neighbourhood of the ten weather ships are given.

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Écarts à la normale de la température superficielle de l'Atlantique près de l'emplacement des frégates météorologiques de l'Atlantique Nord

Résumé On utilise les écarts à la normale de la température de la mer près de l'emplacement des dix frégates météorologiques pendant les 38 mois du novembre 1950 au décembre 1953 pour en dériver les anomalies thermiques approximatives de la surface de l'océan entier pendant cette période. La valeur moyenne de cette anomalie s'élève à + 0,6° pour les trois ans susmentionnés. On trouve que la proportion moyenne des écarts positifs aux écarts negatifs est un peu plus forte que 3 1. Pendant la période en question, l'anomalie thermique positive de l'Atlantique Nord atteignait son principal maximum en hiver et un maximum secondaire en été.Le maximum hivernal se montre également d'une manière frappante dans les anomalies des températures de l'air sur la côte d'est de l'Amérique du Nord. La particularité de la circulation atmosphérique moyenne pendant la période de 1951 à 1953 nous en donne une explication assez suffisante, car le courant vers l'océan d'air froid à travers la côte d'est de l'Amerique était sensiblement inférieur à sa valeur normale.A tout prendre, la température de l'air sur l'Atlantique Nord et la température de la surface montrent des tendances analogues, et on peut supposer que la variation de température de l'air en est probablement le phénomène primaire. Pendant l'époque de 1951 à 1953, les anomalies de la température de l'air sur la côte d'ouest de l'Europe (moyennes de trois mois superposés) variaient souvent en raison inverse de celles observées sur la côte d'est de l'Amérique du Nord; elles ne subissaient qu'une influence bien faible de l'anomalie de la température de l'Océan entier. Les écarts moyens mensuels de la température de l'air côte américaine plus côte européenne s'accordèrent, cependant, très exactement pendant la période de 1951 à 1953 avec les écarts moyens de la température de l'eau de l'océan Atlantique (moyenne: +0,60: + 0,59°).L'influence du surchauffage de l'océan pourrait être estimée plus exactement si l'on mieux connaissait l'étendue en profondeur des anomalies thermiques positives. D'après des mesures des températures de profondeur recueillies par les frégates météorologiques japonaises Tango et Extra il ne semble pas être improbable que les longues variations apériodiques s'étendent de la surface jusqu'à 200 m de profondeur. Supposant qu'à présent la température entre 0 et 200 m dans l'Atlantique Nord soit supérieur à sa valeur normale de 0,5°, il y aurait une accumulation supplémentaire de chaleur de 10 000 goal par cm², valeur qui se laisse expliquer à l'aide du bilan de rayonnement océanique.Après avoir fourni un exemple montrant de quelle manière les variations de la circulation atmosphérique agissent sur le développement des anomalies de la température de la mer l'auteur présente un tableau des anomalies annuelles de la température superficielle pour chacune des dix frégates météorologiques.

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Für die Aufbereitung, Tabellierung und rechnerische Auswertung des Grundmaterials dieser Studie sei den Herren J. Greiter, P. Otto und G. Schindler vom Seewetteramt, Hamburg, besonders gedankt.     

南印度洋副热带偶极模在ENSO事件中的作用

南印度洋副热带偶极模（Subtropical Dipole Pattern,SDP）是印度洋存在的另一种很明显的偶极型海温差异现象,在年际和年代际尺度上均有十分明显的表现.而目前有关印度洋海气相互作用的研究主要集中在赤道印度洋地区,针对南印度洋地区的工作还比较少,特别是有关南印度洋海温与ENSO（El NiDo-Southern Oscillation）事件关系的研究.本文初步探讨了年际尺度上南印度洋副热带偶极型海温变化差异与ENSO事件的关系,发现SDP与ENSO事件有密切的联系,SDP事件就像连接正负ENSO位相转换的一个中间环节,SDP事件前后期ENSO的位相刚好完全相反.进一步,本文通过分析SDP事件前后期海温、高低层风、低层辐合辐散、高空云量和辐射等的变化特征研究了南印度洋偶极型海温异常在ENSO事件中的作用,结果表明：SDP在ENSO事件中的作用不仅涉及海气相互作用的正负反馈过程,还与热带和副热带大气环流之间的相互作用有关,特别是与东南印度洋海温变化所引起的异常纬向风由赤道印度洋向赤道太平洋传播的过程等有十分直接的关系;同时,SDP对ENSO事件的影响在很大程度上还依赖于大尺度平均气流随季节的变换.     

Effects of Arctic Sea Ice Decline on Weather and Climate: A Review

The areal extent, concentration and thickness of sea ice in the Arctic Ocean and adjacent seas have strongly decreased during the recent decades, but cold, snow-rich winters have been common over mid-latitude land areas since 2005. A review is presented on studies addressing the local and remote effects of the sea ice decline on weather and climate. It is evident that the reduction in sea ice cover has increased the heat flux from the ocean to atmosphere in autumn and early winter. This has locally increased air temperature, moisture, and cloud cover and reduced the static stability in the lower troposphere. Several studies based on observations, atmospheric reanalyses, and model experiments suggest that the sea ice decline, together with increased snow cover in Eurasia, favours circulation patterns resembling the negative phase of the North Atlantic Oscillation and Arctic Oscillation. The suggested large-scale pressure patterns include a high over Eurasia, which favours cold winters in Europe and northeastern Eurasia. A high over the western and a low over the eastern North America have also been suggested, favouring advection of Arctic air masses to North America. Mid-latitude winter weather is, however, affected by several other factors, which generate a large inter-annual variability and often mask the effects of sea ice decline. In addition, the small sample of years with a large sea ice loss makes it difficult to distinguish the effects directly attributable to sea ice conditions. Several studies suggest that, with advancing global warming, cold winters in mid-latitude continents will no longer be common during the second half of the twenty-first century. Recent studies have also suggested causal links between the sea ice decline and summer precipitation in Europe, the Mediterranean, and East Asia.     

Influence of the El Niño/Southern Oscillation on South Korean streamflow variability

Deciphering the mechanisms through which the El Niño/Southern Oscillation (ENSO) affects hydrometeorological parameters in the tropics and extratropics is of great interest. We investigate climatic teleconnections between warm or cold phases of ENSO and streamflow patterns over South Korea using an empirical methodology designed to detect regions showing a strong and consistent hydroclimatic signal associated with ENSO. We calculate not only spatial coherence values by monthly streamflow composite formed over 2‐year ENSO cycle and the first harmonic fit to detect candidate regions but also temporal consistency rates by aggregate composite and index time series to determine core regions. As a result, the core regions, namely, the Han river basin and the Nakdong river basin, are detected with a high level of response of ENSO phenomena to streamflow patterns. The ENSO composites for both core regions indicate drier (wetter) conditions in early autumn of the warm (cold) episode years and wetter (drier) conditions from winter to spring of the following year. For both regions, the spatial coherences are over 92% (82%) and the temporal consistencies are 71% (75%) during the El Niño (La Niña) events. In addition, for the core regions identified by composite‐harmonic analysis for both extreme episodes, the results of comparative analyses by using correlation, annual cycle, and Wilcoxon rank sum test indicate that 2 opposite phases‐streamflow relationships have a tendency of sign reversal of the streamflow anomaly. Also, the positive departures during the El Niño years show more coherent and strong responses than the negative anomalies in the La Niña events. In conclusion, South Korea experiences climatic teleconnection between ENSO forcing and midlatitude streamflow patterns.     

Impacts of thermodynamic processes over the Tibetan Plateau on the Northern Hemispheric climate

We here report our recent research results on the climatic features of Tibetan thermodynamic functions and their impacts on the regional climates of the Northern Hemisphere. The results show that the thermodynamic processes over the Tibetan Plateau not only strongly influence the Asian monsoon and precipitation, but also modulate the atmospheric circulation and climate over North America and Europe through stimulating the large-scale teleconnections such as the Asian-Pacific oscillation and affect the atmospheric circulation over the southern Indian Ocean. The Tibetan climate may be affected by sea surface temperatures over the tropical Pacific. On the other hand, the Tibetan climate also affects the atmosphere-ocean interactions in the tropics and mid-latitudes of the Pacific by the atmospheric circulation over the North Pacific. In spring and summer, the thermodynamic anomalies on the plateau affect the subtropical high pressure, the Hadley circulation, and the intertropical convergence zone over the Pacific, and then modulate the development of the El Niño/Southern Oscillation (ENSO). It is necessary to study the forecasting methods for the development of ENSO from the Tibetan climate anomaly. This result also embodies the essence of interactions among land, atmosphere, and ocean over the Northern Hemisphere. Since the previous studies focused on impacts of the plateau on climates in the Asian monsoon regions, it is essential to pay more attention to studying the roles of the plateau in the Northern Hemispheric and even global climates.     

A theoretical investigation of the tropical Indo-Pacific tripole mode

The El Ni o-Southern Oscillation(ENSO)phenomenon in the tropical Pacific has been a focus of ocean and climate studies in the last few decades.Recently,the short-term climate variability in the tropical Indian Ocean has attracted increasingly more attention,especially with the proposition of the Indian Ocean Dipole(IOD)mode.However,these phenomena are often studied separately without much consideration of their interaction.Observations reveal a striking out-of-phase relationship between zonal gradients of sea surface height anomaly(SSHA)and sea surface temperature anomaly(SSTA)in the tropical Indian and Pacific Oceans.Since the two oceans share the ascending branch of the Walker cells over the warm pool,the variation within one of them will affect the other.The accompanied zonal surface wind anomalies are always opposite over the two basins,thus producing a tripole structure with opposite zonal gradients of SSHA/SSTA in the two oceans.This mode of variability has been referred to as Indo-Pacific Tripole(IPT).Based on observational data analyses and a simple ocean-atmosphere coupled model,this study tries to identify the characteristics and physical mechanism of IPT with a particular emphasis on the relationships among ENSO,IOD,and IPT.The model includes the basic oceanic and atmospheric variables and the feedbacks between them,and takes into account the inter-basin connection through an atmospheric bridge,thus providing a valuable framework for further research on the short-term tropical climate variability.     

青藏高原春季积雪在南海夏季风爆发过程中的作用

本文应用欧洲中期预报中心（ECMWF,European Centre for Medium\|Range Weather Forecasts—ERA\|40）资料和美国国家环境预测中心和国家大气研究中心(NCEP/NCAR, National Centers for Environmental Prediction/National Center for Atmospheric Research)资料,研究了青藏高原雪深变化对南海夏季风爆发的影响和ENSO对青藏高原降雪的影响.结果表明：（1）ECMWF的雪深资料是可信的,可以用来研究青藏高原雪深变化对南海夏季风爆发的影响;（2）青藏高原的积雪异常影响到500 hPa以上的温度异常和印度洋与大陆间的气温对比,一方面使上层的南亚高压移动速度发生变化,另一方面也影响到低层大气的运动和东西向风异常,在青藏高原少雪年,东印度洋产生西风异常和一个气旋对,而在青藏高原多雪年,东印度洋产生东风异常和一个反气旋对;（3）ENSO与青藏高原春季积雪关系密切.东太平洋SST正异常时,东印度洋和南海气压偏高,从而导致该区海陆经向压强梯度增强和西风异常.另外,此时青藏高原北部气压偏高,北风偏强,副热带锋面增强,同时,印度洋的SST偏高,为青藏高原降雪提供了水汽保障,这些都有利于青藏高原的降雪.     

风应力桥梁作用下热带太平洋和热带大西洋相互作用的数值试验

利用中等复杂程度热带大气和海洋模式研究了热带太平洋和大西洋SST通过风应力桥梁的相互作用.利用1958～1998年NCEP分析的海表面温度场（SST）强迫大气模式得到的表面风应力与NCEP分析的同期热通量共同驱动海洋模式,作为控制试验;和控制试验平行,但强迫大气模式的SST在某一海盆取为多年气候平均值的试验作为敏感性试验;比较控制试验与敏感性试验模拟,则可反映风应力桥梁作用下热带某海盆SST异常对其他海盆的影响.结果表明,热带某一海盆SST暖（冷）异常总是引起局地海盆表面西部西（东）风异常和东部东（西）风异常;热带太平洋SST暖（冷）异常导致的该海盆东部表面东（西）风异常可以扩展到热带大西洋,从而导致热带大西洋SST冷（暖）异常;热带大西洋SST暖（冷）异常导致的该海盆西部表面西（东）风异常可以扩展到热带太平洋,从而导致热带太平洋SST暖（冷）异常.     

Long-term relationships between climate oscillation and basin-scale hydrological variability during rainy season in eastern Northeast Brazil

ABSTRACT

The high variability in the hydrological regime of the Eastern Hydrological Region (EHR) of Northeast Brazil often results in floods and droughts, leading to serious socio-economic issues. Therefore, this work aimed to investigate connections between spatiotemporal hydrological variability of the EHR and large-scale climate phenomena. Multivariate statistical techniques were applied to relate climate indices with hydrological variables within two representative river basins in the EHR. The results indicated a multi-annual relationship between the state of the sea surface temperature of the Atlantic and Pacific oceans and anomalous hydrological variability in the basins. In addition, the northern Tropical Atlantic conditions were shown to play an important role in modulating the long-term variability of the hydrological response of the basins, whilst only extreme ENSO anomalies seemed to affect the rainy season. This knowledge is an important step towards long-term prediction of hydrological conditions and contributes to the improvement of water resources planning and management in the EHR.