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Predesigned complementary complexation of two 2,2':6',2?-terpyridine-based ligands was established by installing 2,6-dimethoxyphenyl substituents at the terpyridyl 6,6?-positions, which provided ancillary ion–dipole interactions in the coordination process and extra π-stacking stabilization in the resultant heteroleptic complex. The high-fidelity self-recognition ligation afforded facile access to the quantitative self-assembly of multicomponent triangle [Cd6L33L43] and ditrigon [Cd15L36L53] (that is, a hexagon with six 120° angles and two alternating edge lengths). It was found that the linear 6,6?-substituted ditopic motif (L3) would be directed by the ligand geometry of L5 to selectively incorporate into the parallel homoleptic connections in the bilayered framework. [ABSTRACT FROM AUTHOR]

Using multiple observational and model datasets, the authors document a strengthening relationship between boreal winter sea surface temperature anomalies (SSTAs) in the western North Pacific (WNP) and the development of the El Nino-Southern Oscillation (ENSO) in the following year. The increased WNP-ENSO association emerged in the mid-twentieth century and has grown through the present, reaching correlation coefficients as high as ∼0.70 in recent decades. Fully coupled climate experiments with the Community Earth System Model, version 1 (CESM1), replicate the WNP-ENSO association and indicate that greenhouse gases (GHGs) are largely responsible for this observed increase. The authors speculate that shifts in the location of the largest positive SST trends between the subtropical and tropical western Pacific impact the low-level circulation in a manner that reinforces the link between the WNP and the development of ENSO. A strengthened GHG-driven relationship with the WNP provides an example of how anthropogenic climate change may directly influence one of the most prominent patterns of natural climate variability, ENSO, and potentially improve the skill of intraseasonal-to-interannual climate prediction. [ABSTRACT FROM AUTHOR]

Here, we examine the dynamic properties associated with the recent increase in the Sahel rainfall using an ensemble of five global reanalysis datasets (1979-2010). The rainfall that has been observed to be increasing over the Sahel is accounted for by enhancements in both the tropical easterly jet and the African easterly jet, both of which are known to induce wet anomalies. Moreover, positional shifts in the African easterly jet and African easterly waves (AEWs) accompanied the northward migration of the Sahel rainband. Change in the African easterly jet and AEWs are coupled to a northward shift and amplification of convective activity; this signals an increased potential for the occurrence of flash floods along the northern Sahel. In addition, the result from a wave tracking analysis suggests that the change in AEWs is closely linked to increased activity of intense hurricanes in the North Atlantic. The synoptic concurrence of AEWs in driving the dynamics of the Sahel greening and the increase in tropical cyclogeneses over the North Atlantic is an important aspect in the evaluation of climate model projections. [ABSTRACT FROM AUTHOR]

Co-allocation architecture was developed to enable parallel transferring of files from multiple replicas stored in the different servers. Several co-allocation strategies have been coupled and used to exploit the different transfer rates among various client-server links and to address dynamic rate fluctuations by dividing files into multiple blocks of equal sizes. The paper presents a dynamic file transfer scheme, called dynamic adjustment strategy (DAS), for co-allocation architecture in concurrently transferring a file from multiple replicas stored in multiple servers within a data grid. The scheme overcomes the obstacle of transfer performance due to idle waiting time of faster servers in co-allocation based file transfers and, therefore, provides reduced file transfer time. A tool with user friendly interface that can be used to manage replicas and downloading in a data grid environment is also described. Experimental results show that our DAS can obtain high-performance file transfer speed and reduce the time cost of reassembling data blocks. [ABSTRACT FROM AUTHOR]

Physical processes responsible for the abnormally wet condition in the Central Intermountain West (CIW) of the United States in June 2009 were investigated. It was illustrated that persistent rainy conditions over the CIW during June 2009 were associated with a pronounced circumglobal teleconnection pattern, which is characterized as a short Rossby wave train along the jet stream waveguide with a wave number 5 structure. The ascending motion and moisture flux convergence over the CIW associated with the cyclonic action center over the US West Coast in the teleconnection wave train could be essential for the persistent local rainfall during June 2009. Further analysis suggested that the June 2009 circulation pattern is consistent with a prevailing mode of the summer circumglobal teleconnection pattern. The findings in this study provide information for improved understanding of the early summer rainfall regime in the CIW. [ABSTRACT FROM AUTHOR]

Using a composite procedure, North American Mesoscale Model (NAM) forecast and observed environments associated with zonally oriented, quasi-stationary surface fronts for 64 cases during July–August 2006–08 were examined for a large region encompassing the central United States. NAM adequately simulated the general synoptic features associated with the frontal environments (e.g., patterns in the low-level wind fields) as well as the positions of the fronts. However, kinematic fields important to frontogenesis such as horizontal deformation and convergence were overpredicted. Surface-based convective available potential energy (CAPE) and precipitable water were also overpredicted, which was likely related to the overprediction of the kinematic fields through convergence of water vapor flux. In addition, a spurious coherence between forecast deformation and precipitation was found using spatial correlation coefficients. Composite precipitation forecasts featured a broad area of rainfall stretched parallel to the composite front, whereas the composite observed precipitation covered a smaller area and had a WNW–ESE orientation relative to the front, consistent with mesoscale convective systems (MCSs) propagating at a slight right angle relative to the thermal gradient. Thus, deficiencies in the NAM precipitation forecasts may at least partially result from the inability to depict MCSs properly. It was observed that errors in the precipitation forecasts appeared to lag those of the kinematic fields, and so it seems likely that deficiencies in the precipitation forecasts are related to the overprediction of the kinematic fields such as deformation. However, no attempts were made to establish whether the overpredicted kinematic fields actually contributed to the errors in the precipitation forecasts or whether the overpredicted kinematic fields were simply an artifact of the precipitation errors. Regardless of the relationship between such errors, recognition of typical warm-season environments associated with these errors should be useful to operational forecasters. [ABSTRACT FROM AUTHOR]

A recent study by Gillies and others of persistent inversion events in the Intermountain West of the United States found a substantive linkage between the intraseasonal oscillation (ISO) and the development of persistent inversion events. Given that NCEP’s Climate Forecast System (CFS) has demonstrated skill in the prediction of the ISO as far out as 1 month, it was decided to examine the CFS forecast’s capability in the prediction of such winter persistent inversions. After initial analysis, a simple regression scheme is proposed that is coupled to the CFS output of geopotential height as a way to predict the occurrence of persistent inversion events for Salt Lake City, Utah. Analysis of the CFS hindcasts through the period 1981–2008 indicates that the regression coupled with the CFS can predict persistent inversion events with lead times of up to 4 weeks. The adoption of this coupled regression–CFS prediction may improve the forecasting of persistent inversion events in the Intermountain West, which is currently restricted to the more limited time span (∼10 days) of medium-range weather forecast models. [ABSTRACT FROM AUTHOR]

Persistent winter inversions result in poor air quality in the Intermountain West of the United States. Although the onset of an inversion is relatively easy to predict, the duration and the subsequent breakup of a persistent inversion event remains a forecasting challenge. For this reason and for this region, historic soundings were analyzed for Salt Lake City, Utah, with reanalysis and station data to investigate how persistent inversion events are modulated by synoptic and intraseasonal variabilities. The results point to a close linkage between persistent inversions and the dominant intraseasonal (30 day) mode that characterizes the winter circulation regime over the Pacific Northwest. Meteorological variables and pollution (e.g., particulate matter of ≤2.5- μm diameter, PM2.5) revealed coherent variations with this intraseasonal mode. The intraseasonal mode also modulates the characteristics of the synoptic (6 day) variability and further influences the duration of persistent inversions in the Intermountain West. The interaction between modes suggests that a complete forecast of persistent inversions is more involved and technically beyond numerical weather prediction models intended for the medium range (∼10 day). Therefore, to predict persistent inversions, the results point to the adoption of standard medium-range forecasts with a longer-term climate diagnostic approach. [ABSTRACT FROM AUTHOR]

The lake level elevation of the Great Salt Lake (GSL), a large closed basin lake in the arid western United States, is characterized by a pronounced quasi-decadal oscillation (QDO). The variation of the GSL elevation is very coherent with the QDO of sea surface temperature anomalies in the tropical central Pacific (also known as the Pacific QDO). However, such coherence denies any direct association between the precipitation in the GSL watershed and the Pacific QDO because, in a given frequency, the precipitation variation always leads the GSL elevation variation. Therefore, the precipitation variation is phase shifted from the Pacific QDO. This study investigates the physical mechanism forming the coherence between the GSL elevation and the Pacific QDO. Pronounced and coherent quasi-decadal signals in precipitation, streamflow, water vapor flux, and drought conditions are found throughout the Great Basin. Recurrent atmospheric circulation patterns develop over the Gulf of Alaska during the warm-to-cool and cool-to-warm transition phases of the Pacific QDO. These circulation patterns modulate the water vapor flux associated with synoptic transient activities over the western United States and, in turn, lead to the QDO in the hydrological cycle of the Great Basin. As the GSL integrates the hydrological responses in the Great Basin, the hydrological QDO is then transferred to the GSL elevation. Because the GSL elevation consistently lags the precipitation by a quarter-phase (about 3 yr in the quasi-decadal time scale), these processes take an average of 6 yr for the GSL elevation to eventually respond to the Pacific QDO. This creates a half-phase delay of the GSL elevation from the Pacific QDO, thereby forming the inverse, yet coherent, relationship between them. Tree-ring reconstructed precipitation records confirm that the quasi-decadal signal in precipitation is a prominent feature in this region. [ABSTRACT FROM AUTHOR]

Typhoon passages across Taiwan can generate sudden surface warming in downslope regions. Special characteristics and mechanisms for 54 such warming events that were identified during the 1961–2007 period are examined. Preferred warming regions were identified in northwest Taiwan, where warming is generated by downslope flow from east or northeast winds in westward-moving typhoons, and in southeast Taiwan, where it is generated by downslope flow from west or northwest winds in northwestward-moving typhoons. In addition to the orographic effect, warmings occurred exclusively within nonprecipitation zones of typhoons. Most northwest (southeast) warmings occur during the day (night) with an average lifetime of 4 (5) h, which roughly corresponds to the average time a nonprecipitation zone remains over a station. During the period examined, three typhoons generated warming events in both northwest and southeast Taiwan, and only Typhoon Haitang (2005) generated warmings with comparable magnitudes (∼12-K increase) in both regions. For Typhoon Haitang as an example, diagnostic analyses with two different approaches reveal that the majority of the warming is contributed by downslope adiabatic warming, but the warming associated with the passage of a nonprecipitation zone is not negligible. Similar results were found when these two diagnostic approaches were applied to the other warming events. The diurnal mode of the atmospheric divergent circulation over East Asia–western North Pacific undergoes a clockwise rotation. The vorticity tendency generated by this diurnal divergent circulation through vortex stretching may modulate the arrival time of typhoons to cause daily (nighttime) warming in the northwest (southeast). [ABSTRACT FROM AUTHOR]

In the U.S. northern plains, summer progressive convective storms that occur in weakly forced environments are often coupled with short-wave perturbations that are embedded in the midlevel northwesterly flow. These midtropospheric perturbations (MPs) are capable of inducing propagating convection that contributes to a majority of the rainfall over the northern plains during July and August. There is a possibility that the difficulties of numerical weather prediction models in forecasting summer convective rainfall over the northern plains are partly attributed to their deficiency in forecasting MPs. The present study tests this possibility through examining operational forecasts by the North American Mesoscale (NAM) model during the summers of 2005 and 2006. Forecasted MPs exhibit slower propagation speeds and weaker relative vorticity than the observations leading to systematic position errors. Underpredicted vorticity magnitudes weaken horizontal vorticity advection that influences the vorticity tendency throughout the MP life cycle and, in turn, slows the propagation speed of MPs. Moreover, biases of weak ambient flow speed and vortex stretching contribute to the magnitude and propagation speed errors of MPs. Skill scores of precipitation forecasts associated with MPs are low, but can be considerably improved after removing the MP position error that displaces the rainfall pattern. The NAM also tends to underpredict precipitation amounts. A modified water vapor budget analysis reveals that the NAM insufficiently generates atmospheric humidity over the central United States. The shortage of moisture in the forecast reduces the water vapor flux convergence that is part of the precipitation process. The precipitation bias may feed back to affect the MP growth through the bias in heating, thus further slowing the perturbation. [ABSTRACT FROM AUTHOR]

The seasonal rainfall over the U.S. central plains features a late-spring maximum. A spring–fall annual mode revealed from the empirical orthogonal function analysis on rainfall delineates a maximum center over the central plains that coincides with the large late-spring rainfall. This paper examines the large-scale dynamical and hydrological processes in forming the rainfall center. The NCEP–Department of Energy (DOE) reanalysis 2 data reveal that the baroclinic structure of the continental-scale circulation during late spring (May and June) induces a vertically out-of-phase divergent circulation forming strong convergence of water vapor flux over the central plains. Such circulation features generate concentrated convective activity in this region. The upper-level anticyclone development with the North American monsoon in July replaces the late-spring baroclinic structure and, in turn, reduces the convective activity. The Great Plains low-level jet (LLJ) plays a role in the downscaling process that connects the continental-scale circulation to rainfall. The LLJ coupled with approaching baroclinic waves leads to stronger moisture convergence in the central plains than that occurring under the upper-level anticyclone. The former type of the LLJ occurs most frequently in late spring and contributes to more than 60% of the rainfall. During midsummer (July and August), such a coupling is hindered by the well-developed upper-level anticyclone, subsequently decreasing the rainfall. [ABSTRACT FROM AUTHOR]

The life cycle of the Southeast Asian–western North Pacific monsoon circulation is established by the northward migrations of the monsoon trough and the western Pacific subtropical anticyclone, and is reflected by the intraseasonal variations of monsoon westerlies and trade easterlies in the form of an east–west seesaw oscillation. In this paper, an effort is made to disclose the influence of this monsoon circulation on tropical cyclone tracks during its different phases using composite charts of large-scale circulation for certain types of tracks. A majority of straight-moving (recurving) tropical cyclones appear during weak (strong) monsoon westerlies and strong (weak) trade easterlies. The monsoon conditions associated with straight-moving tropical cyclones are linked to the intensified subtropical anticyclone, while that associated with recurving tropical cyclones is coupled with the deepened monsoon trough. The relationship between genesis locations and track characteristics is evolved from the intraseasonal variation of the monsoon circulation reflected by the east–west oscillation of monsoon westerlies and trade easterlies. Composite circulation differences between the flows associated with the two types of tropical cyclone tracks show a vertically uniform short wave train along the North Pacific rim, as portrayed by the Pacific–Japan oscillation. During the extreme phases of the monsoon life cycle, the anomalous circulation pattern east of Taiwan resembles this anomalous short wave train. A vorticity budget analysis of the strong monsoon condition reveals a vorticity tendency dipole with a positive zone to the north and a negative zone to the south of the deepened monsoon trough. This meridional juxtaposition of vorticity tendency propagates the monsoon trough northward. The interaction of a tropical cyclone with the monsoon trough intensifies the north–south juxtaposition of the vorticity tendency and deflects the tropical cyclone northward. In contrast, during weak monsoon conditions, the interaction between a tropical cyclone and the subtropical high results in a northwestward motion steered by the intensified trade easterlies. The accurate prediction of the monsoon trough and the subtropical anticyclone variations coupled with the monsoon life cycle may help to improve the forecasting of tropical cyclone tracks. [ABSTRACT FROM AUTHOR]

Located in northern Taiwan, Taipei is a metropolis surrounded by hills and mountains that form a basin in which two river valleys funnel the surface airflow of this basin to the open sea. Because of the southwest monsoon, summer is a dry season in northern Taiwan but is the season of maximum rainfall in the Taipei basin. This unusual summer rainfall maximum in Taipei is largely produced by afternoon/evening thunderstorms—in particular, on the downwind side and slopes of mountains south of the city. The population in the city of Taipei and the county in which this city is located has more than tripled during the past four decades while land use for building and surface construction increased by a factor of 3. This urbanization may contribute to an increase of 1.5°C in daily mean temperature, a decrease of 1°C in daily temperature range, an increase of more than 67% in the frequency of afternoon/evening thunderstorms, and an increase of 77% in rainfall generated by thunderstorms. These findings may explain the reduction in the water supply deficit to the Taipei metropolitan area and the ground subsidence of the Taipei basin caused by the excessive use of groundwater. Results of this study also provide important information for urban planning and pollution control and for management of the increasing traffic hazards caused by the enhanced thunderstorm activity and rainfall. [ABSTRACT FROM AUTHOR]

An effort was made to search for relationships between interannual variations of population, lifetime, genesis locations, and intensity of named typhoons and numbered tropical depressions in the western North Pacific during the 1979–2002 period. To support this research task, climatological relationships of tropical cyclone characteristics were also investigated for these cyclones. Major findings of this study are summarized as follows: : Climatology: Measured by the intensity scale of the Japan Meteorological Agency, three groups of tropical cyclones were identified in terms of population versus intensity: Group 1 [tropical depression (TD) + typhoon (TY)], Group 2 (strong + very strong TY), and Group 3 (catastrophic TY). This group division coincides with that formed in terms of lifetime of tropical cyclones versus intensity. Weak cyclones (Group 1) have a larger population than strong cyclones (Group 3), while the former group has shorter lifetime than the latter group. For genesis locations, the monsoon trough is established as a favorable region of tropical cyclone genesis because it provides an environment of large vorticity. Therefore, the northward latitudinal displacement of the maximum genesis frequency in the three groups of tropical cyclones follows that of the monsoon trough. : Interannual variation: Any mechanism that can modulate the location and intensity of the monsoon trough affects the genesis location and frequency of tropical cyclones. In response to tropical Pacific sea surface temperature anomalies, a short wave train consisting of east–west oriented cells emanates from the Tropics and progresses along the western North Pacific rim. Population of the Group-1 tropical cyclones varies interannually in phase with the oscillation of the anomalous circulation cell northeast of Taiwan and south of Japan in this short wave train, while that of Group 3 fluctuates coherently with the tropical cell of this short wave train. Because these two anomalous circulation cells exhibit opposite polarity, the out-of-phase interannual oscillation between these two cells results in the opposite interannual variation of genesis frequency between tropical cyclones of Groups 1 and 3. [ABSTRACT FROM AUTHOR]

The south-southeast periphery of a monsoon gyre in the western North Pacific (WNP) is a favorable region for tropical cyclone/tropical depression (TC/TD) genesis. The TC genesis frequency is interannually modulated by the WNP monsoon circulation in response to a change in tropical Pacific sea surface temperature (SST). These findings from previous studies lead to the hypothesis that the effect of tropical Pacific SST changes on the WNP TC/TD genesis frequency is accomplished through a modulation of the monsoon gyre activity by WNP monsoon circulation variations. The 6-h TC/TD track records and NCEP–NCAR reanalysis data for the period of 1979–2002 were analyzed to test this hypothesis. Results show that roughly 70% of WNP TC/TD geneses are linked to monsoon gyres. The interannual variation of these geneses is highly correlated (with a correlation coefficient of 0.89) with that of monsoon gyre activity, which is out-of-phase with the interannual variation of SST over the NOAA Niño-3 region. [ABSTRACT FROM AUTHOR]

Rainfall variation of the East Asian summer monsoon has long been believed to be caused by the transition of weather regimes in company with the evolution of monsoon circulation. However, this claim was neither comprehensively analyzed nor convincingly demonstrated. Four datasets [Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) rainfall, NCEP–NCAR reanalysis data, Japan Meteorological Agency (JMA) 6-h surface analysis maps, and Joint Typhoon Warning Center (JTWC) 6-h tropical cyclone tracks] were used to depict the climatology of the monsoon rainfall variation and to explore the cause of this variation, particularly through the relationship between the seasonal evolution of the monsoon circulation and the associated synoptic disturbance activity. The monsoon life cycle in the southern part of East Asia is basically developed by the sequential passages of the mei-yu rainband in early summer, the western Pacific subtropical high in midsummer, and the tropical cyclone activity in late summer. Although the monsoon onset in the northern part of East Asia, particularly Japan, is triggered by the mei-yu/baiu rainband, the monsoon break follows the rainband's dissipation caused by the northward-migrating subtropical high, and the monsoon revival accompanies the arrival of the midlatitude frontal activity. In view of the role played by the subtropical high in developing the monsoon break, the phase lag of the monsoon life cycle between the south and north is a result of this subtropical high's northward progression. Two rainfall maxima in the revival phase of the Japanese monsoon are generated by different mechanisms: the first is a result of the collaborative contribution of the frontal and tropical cyclone activity, but the second is primarily due to the midlatitude frontal activity. Despite the vertical phase reversal of monsoon circulation in the middle troposphere, two intraseasonal (10–24- and 30–60-day) monsoon modes propagating across East Asia do not undergo a vertical phase reversal until 200–250 mb. The vertical structure of these two intraseasonal modes causes monsoon rainfall to fluctuate intraseasonally between the low plains and the tallest East Asian mountain (Yu Shan, ∼4 km above sea level) in Taiwan. In addition to these new findings, further research efforts are needed to explore the modulations of the frontal and tropical cyclone activity by intraseasonal modes and the monsoon revival in northeast Asia by the interannual climate mode of the summer monsoon circulation through the tropical cyclone and midlatitude frontal activity. [ABSTRACT FROM AUTHOR]

Being restricted in their vertical development by the Tibetan high, monsoon depressions propagate westward against monsoon westerlies embedded in the Indian monsoon trough. The cause of this peculiar propagation has not been well explained. Special characteristics of individual depressions were revealed from observations of previous studies; particularly, the major rainfall of a depression occurs over its west–south-west sector. The latent heat released by this rainfall forms east–west differential heating across the depression in developing an east–west asymmetric circulation. Because this east–west circulation is a part of the depression's divergent circulation, a spatial quadrature relationship exists between this divergent circulation and the depression. Based on these characteristics, a westward propagation mechanism of the depression is introduced. The depression's rainfall is supported by the convergence of water vapor transported by the low-level divergent circulation. In turn, the divergent circulation is maintained through a feedback of the latent heat released by the rainfall. The upward branch of the east–west circulation coupled with the convergent center of the low-level divergent circulation generates a negative streamfunction tendency. The depression is propagated westward by a dynamic interaction between rainfall/convection and this monsoon disturbance through the negative streamfunction tendency. The spatial quadrature relationship between a depression and its east–west (divergent) circulation rejuvenates the water vapor supply maintaining diabatic heating and the divergent circulation, and perpetuating the generation of negative streamfunction tendency ahead of the depression. The entire process from the maintenance of east–west differential heating to the generation of negative streamfunction tendency west of a depression will not diminish until the cessation of water vapor supply. Budget analyses of heat, water vapor, velocity potential, and streamfunction for 143 depressions identified over 24 summers (1979–2002) were performed with ERA-40 reanalyses and three daily rainfall data sources. The westward propagation mechanism of monsoon depressions was illustrated/confirmed in terms of these budget analyses. [ABSTRACT FROM AUTHOR]