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1.
It is generally accepted that altitude is the main variable governing the spatial distribution of precipitation in the mountains. This study mainly discusses the precipitation–altitude relationships on different timescales and at different individual precipitation magnitudes in the entire study period (April 2012 to September 2015), wet season (May to September), and dry season (October to April), and tries to find a threshold to determine whether the correlation between precipitation and altitude is significant. In this study, the half-hourly data, including precipitation, wind speed, and air temperature, from April 2012 to September 2015 are obtained by six automatic meteorological stations located on the north slope of Qilian Mountains, which range from 2980 to 4484 m a.s.l., and horizontal distance is approximately 7000 m. Results indicate that (i) if all samples in the entire study period are to be investigated, the individual precipitation had to reach about 30 or 40 mm, then the sample may pass the significance test at p < 0.05 or at p < 0.01, respectively. The thresholds in wet season are same as that during entire study period. The thresholds in dry season are about 10 and 15 mm (ii) with increasing timescale, the percentage of samples that pass the test increases. However, it is until the monthly scale whether it is wet or dry season or the entire study period, the precipitation–altitude relationships have statistical significance and using the monthly or yearly scale as the time unit can be better applied to the research, which is based on the precipitation–altitude relationships. 相似文献
2.
Summary Ground-based spectroradiometric measurements obtained in Athens have been used in order to derive the aerosol optical depth
and the ?ngstr?m parameters. Their derivation is achieved using three well-established and widely used techniques; the Volz
method, the direct method and the least-squares fit to the experimental aerosol optical depth values. This study aims at investigating
the ability of the different methods to derive similar ?ngstr?m turbidity coefficients and their dependence on the spectral
range used for their determination. In addition, the uncertainties revealed especially in the UV spectral band are highlighted.
The various techniques lead to different ?ngstr?m turbidity coefficients especially if narrow spectral bands at the shorter
wavelengths are used. It is also established that the ?ngstr?m turbidity coefficients derived by any of the three methods
at short wavelengths are not representative of the whole spectrum, while their derivation exhibits large uncertainties especially
under low turbidity conditions. Therefore, the comparison of α and β values obtained using the three above-mentioned techniques
in several spectral bands is not an easy task, since these values differ significantly. From the whole analysis it is established
that the least-squares method is the least imprecise, also exhibiting the least wavelength dependence.
Correspondence: Dimitris G. Kaskaoutis, Institute for Environmental Research and Sustainable Development, National Observatory
of Athens, Lofos Nymphon, P.O. Box 20048, 11810 Athens, Greece 相似文献
3.
Contributions of different time scales to extreme Paraná floods 总被引：1，自引：0，他引：1
4.
Climate Dynamics - Prospects for El Niño–Southern Oscillation (ENSO) predictability at long lead-times lie in the subsurface oceanic memory along the equatorial Pacific. Long considered... 相似文献
5.
Yeon-Soo Jang Daehyun Kim Young-Ho Kim Dong-Hoon Kim Masahiro Watanabe Fei-Fei Jin Jong-Seong Kug 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(2):193-199
Many recent studies have reported the presence of two types of El Niño events in observation: Cold Tongue (CT) El Niño and Warm Pool (WP) El Niño. We investigate the sensitivity of a model simulating two types of El Niño by changing a convective triggering parameter (Tokioka parameter). When deep convections are highly suppressed with a large Tokioka parameter, the model is capable of simulating distinct two-types of El Niño. However, the model has a problem in simulating two-types of El Niño distinctively when the Tokioka parameter is small, because the location of the maximum precipitation anomaly related to the CT El Niño is significantly shifted westward, leading to an atmospheric response pattern similar to that of the WP El Niño. Our results suggest that the mean precipitation over the eastern equatorial Pacific and the resultant zonal distribution in atmospheric feedback associated with ENSO can be one of the crucial factors for simulating two-types of El Niño. 相似文献
6.
The formation mechanism of diurnal rainfall in Taiwan is commonly recognized as a result of local forcings involving solar thermal heating and island-scale land–sea breeze (LSB) interacting with orography. This study found that the diurnal variation of the large-scale circulation over the East Asia-Western North Pacific (EAWNP) modulates considerably the diurnal rainfall in Taiwan. It is shown that the interaction between the two LSB systems—the island-scale LSB and the large-scale LSB over EAWNP—facilitates the formation of the early morning rainfall in western Taiwan, afternoon rainfall in central Taiwan, and nighttime rainfall in eastern Taiwan. Moreover, the post-1998 strengthening of a shallow, low-level southerly wind belt along the coast of Southeast China appears to intensify the diurnal rainfall activity in Taiwan. These findings reveal the role of the large-scale LSB and its long-term variation in the modulation of local diurnal rainfall. 相似文献
7.
Robust decision-making is being increasingly used to support environmental resources decisions and policy analysis under changing climate and society. In this context, a robust decision is a decision that is as much as possible insensitive to a large degree of uncertainty and ensures certain performance across multiple plausible futures. Yet, the concept of robustness is neither unique nor static. Multiple robustness metrics, such as maximin, optimism-pessimism, max regret, have been proposed in the literature, reflecting diverse optimistic/pessimistic attitudes by the decision maker. Further, these attitudes can evolve in time as a response to sequences of favorable (or adverse) events, inducing possible dynamic changes in the robustness metrics. In this paper, we explore the impact of alternative definitions of robustness and their evolution in time for a case of water resources system management under changing climate. We study the decisions of the Lake Como operator, who is called to regulate the lake by balancing irrigation supply and flood control, under an ensemble of climate change scenarios. Results show a considerable variability in the system performance across multiple robustness metrics. In fact, the mis-definition of the actual decision maker’s attitude biases the simulation of its future decisions and produces a general underestimation of the system performance. The analysis of the dynamic evolution of the decision maker’s preferences further confirms the potentially strong impact of changing robustness definition on the decision-making outcomes. Climate change impact assessment studies should therefore include the definition of robustness among the uncertain parameters of the problem in order to analyze future human decisions under uncertainty. 相似文献
8.
The contrast between the eastern and central responses of zonal and vertical circulation in the Pacific （EP- and CP-） E1 Nino is observed in the different tropics. To measure the different responses of the atmo- spheric circulation to the two types of E1 Nino, an eastern and a central Pacific southern oscillation index （EP- and CP-SOI） are defined based on the air-sea coupled relationship between eddy sea level pressure and sea surface temperature. Analyses suggest that while the EP-SOI exhibits variability on an interannual （2- 7-yr） time scale, decadal （10-15-yr） variations in the CP-SOI are more dominant; both are strongly coupled with their respective EP- and CP-E1 Nino patterns. Composite analysis suggests that, during EP-ENSO, the Walker circulation exhibits a dipole structure in the lower-level （850 hPa） and upper-level （200 hPa） velocity potential anomalies and exhibits a signal cell over the Pacific. In the case of CP-ENSO, however, the Walker circulation shows a tripole structure and exhibits double cells over the Pacific. In addition, the two types of ENSO events show opposite impacts on global land precipitation in the boreal winter and spring seasons. For example, seasonal precipitation across mainland China exhibits an opposite relationship with the EP- and CP-ENSO during winter and spring, but the rainfall over the lower reaches of the Yangtze River and South China shows an opposite relationship during the rest of the seasons. Therefore, the different relationships between rainfall and EP- and CP-ENSO should be carefully considered when predicting seasonal rainfall in the East Asian monsoon regions. 相似文献
9.
Both supply and demand side changes are necessary to achieve a sustainable food system. However, the weight accorded to these depends on one’s view of what the priority goals are for the food system and the extent to which production systems versus consumption patterns are open to change. Some stakeholders see the problem as one of ‘not enough food’ and focus on the need to sustainably increase supply, while others consider the resource demanding and ‘greedy’ consumption patterns of the Western world as the main problem and emphasize the need to shift diets. In this study global land use and greenhouse gas emissions are estimated for a set of scenarios, building on four ‘livestock futures’ reflecting these different perspectives. These scenarios are: further intensification of livestock systems; a transition to plant-based eating; a move towards artificial meat and dairy; and a future in which livestock production is restricted to the use of ‘ecological leftovers’ i.e. grass from pastures, food waste and food and agricultural byproducts. Two dietary variants for each scenario are modelled: 1) a projected diet following current trends and 2) a healthy diet with more fruits and vegetables and fewer animal products, vegetable oils and sugar. Livestock production in all scenarios (except the baseline scenario) was assumed to intensify to current levels of intensive production in North-Western Europe. For each scenario, several variant assumptions about yield increases and waste reductions were modelled. Results show that without improvements in crop productivity or reductions on today’s waste levels available cropland will only suffice if production of all protein currently supplied by animal foods is replaced by (hypothetical) artificial variants not requiring any land. With livestock intensities corresponding to current ones in North-Western Europe and with yield gaps closed by 50% and waste reduced by 50%, available cropland will suffice for all scenarios that include a reduction of animal products and/or a transition to poultry or aquaculture. However, in the scenario based on an extrapolation of current consumption patterns (animal product amounts and types consumed in proportions corresponding to the current average consumption in different world regions) and with livestock production based on feed from cropland, available cropland will not be enough. The scenario that makes use of pastures for ruminant production and food waste for pigs, uses considerably less cropland and could provide 40–56 kg per capita per year of red meat. However, such a livestock future would not reduce GHG emissions from agriculture on current levels. This study confirms previous research that to achieve a sustainable food future, action is needed on all fronts; improved supply and reduced demand and waste. 相似文献
10.
Mike Hulme 《Climatic change》2012,113(1):5-21
Articulated initially by physical scientists, the idea of anthropogenic global climate change has been subject to increasingly diverse examinations in recent years. The idea has been appropriated by economists, worked with by engineers and, more recently, scrutinised by social scientists and humanities scholars. Underlying these examinations are different, yet rarely exposed, presumptions about what kind of ??thing?? climate is: a physical abstraction, a statistical construct, an imaginative idea. If the ontological status of climate is rarely made explicit it becomes difficult to know whether the different epistemologies used to reveal climates ?? and their changing properties ?? are appropriate. This study offers one way in which the different worlds inhabited by the idea of climate may be revealed. It does so by examining a heatwave: a powerful meteorological phenomenon one would think and one which scientific accounts of climate change tell us will become more frequent in the future. The heatwave in question occurred in July 1900 in the county of Norfolk, England. This heatwave inhabits three very different worlds: the imaginative world of L P Hartley in his novel The Go Between; the historical world of late Victorian Norfolk; and the digital world of the climate sciences. The traces of the heatwave left in these different worlds are varied and access to them is uneven. Constructing an adequate interpretation of this singular climatic event and its meaning is challenging. The study suggests that grasping the idea of climate may be harder than we think. Climates may be ineffable. Yet the approach to the study of climate illustrated here opens up new ways of thinking about the meaning and significance of climate change. 相似文献
11.
The present study is focused on examination of the physical processes of convective cell evolved from a MCS occurred on 4 November 2011 over Genoa, Italy. The Quantitative Precipitation Forecasts (QPF) have been performed using WRF v3.6 model under different configurations and cloud permitting simulations. The results indicate underestimation of the amount of precipitation and spatial displacement of the area with a peak 24-h accumulated rainfall in (mm). Our main objective in the research is to test the cloud model ability and performance in simulation of this particular case. For that purpose a set of sensitivity experiments under different model initializations and initial data have been conducted. The results also indicate that the merging process apparently alters the physical processes through low- and middle-level forcing, increasing cloud depth, and enhancing convection. The examination of the microphysical process simulated by the model indicates that dominant production terms are the accretion of rain by graupel and snow, probabilistic freezing of rain to form graupel and dry and wet growth of graupel. Experiment under WRF v3.6 model initialization has shown some advantage in simulation of the physical processes responsible for production and initiation of heavy rainfall compared to other model runs. Most of the precipitation came from ice-phase particles-via accretion processes and the graupel melting at temperature T0 ≥ 0°C. The rainfall intensity and accumulated rainfall calculated by the model closely reflect the amount of rainfall recorded. Thus, the main benefit is to better resolve convective showers or storms which, in extreme cases, can give rise to major flooding events. In such a way, this model may become major contributor to improvements in weather analysis and small-scale atmospheric predictions and early warnings of such subscale processes. 相似文献
12.
This article is a case study of the Mitigation Action Plans and Scenarios programme (MAPS) which worked in climate change mitigation and development policy-making spaces in Brazil, Chile, Colombia, Peru and South Africa from 2010–2015. The MAPS programme was focused on achieving change in the commitment of southern decision makers to mitigate against climate change through government-mandated, stakeholder processes which generated evidence making a case for a low carbon transition. The article draws on reflective materials generated in the last year of the project. The value of MAPS was found in the well-tested data and evidence-driven scenario building; locally specific and country-driven processes; a culture of knowledge sharing through facilitated communities of practice; the role of professional facilitation in process design and in conducting stakeholder processes; shared experiences of working in the south, and particularly with cultural differences and conflict; and new ways of working south–south with each other, and with donors. These MAPS programme experiences stood in contrast to previous north–south knowledge sharing involvements. Theoretically, the article asks whether MAPS represents southern theory-making (after Connell, 2007). It concludes that through the action-oriented, facilitated co-production way of working on climate change in the south, MAPS represents an understanding of southern theory that challenges the orthodoxy of global knowledge production. MAPS emphasizes the need for theorizing in, and of, the south, and connecting policy and practices.
Key policy insights
Climate change mitigation work in the south faces poorly resourced, fragmented, under-capacitated governance structures, often in conflicted settings.
Given conflicted settings, skilled facilitation is an integral part of knowledge-making processes.
Strong local communities of practice, who undertake learning-by-doing and are connected to ‘stubborn’ development realities, are also key to knowledge-making.
Intentional co-production of data and evidence enable peer-to-peer learning and the trust-building which is vital to strong communities of practice.
13.
Juan Carlos Linares Antonio Delgado-Huertas Jos�� Antonio Carreira 《Climatic change》2011,105(1-2):67-90
The projected temperature rise, rainfall decrease and concentration of rainfall in extreme events could induce growth decline and die-off on tree populations located at the geographical distribution limit of the species. Understanding of adaptive capacity and regional vulnerability to climate change in Mediterranean forests is not well developed and requires more focused research efforts. We studied the relationships between spatiotemporal patterns of temperature and precipitation along the southwestern edge of the Betic range (southern Spain) and measured basal area increment (BAI) and carbon isotope (??) in tree ring series of Abies pinsapo and Pinus halepensis, two Mediterranean conifer trees with contrasting drought adaptive capacity. Climatic information was obtained from a network covering a wide range of elevations and distances from the Atlantic and Mediterranean coasts. Temperature trends were tested by the Mann?CKendall test, and precipitation was thoroughly analyzed by quantile regression. Climatic data showed a warming trend, enhanced since the 1970s, while quantile regressions revealed that drought events worsened during the course of the twentieth century. Long-term decrease of A. pinsapo BAI was related to regional warming and changing precipitation patterns, suggesting increasing drought stress on this species. Both temperature and precipitation in the summer influenced wood ?? in P. halepensis, whereas negative correlation between wood ?? and current autumn temperature was yielded for A. pinsapo. Increased intrinsic water use efficiency was inferred from wood ?? in both species; however, A. pinsapo showed sudden growth reductions under drier conditions, while pine trees were able to maintain almost constant BAI values and lower water costs under increasing long-term water stress. 相似文献
14.
Does public policy support or undermine climate change adaptation? Exploring policy interplay across different scales of governance 总被引：4，自引：0，他引：4
Policy makers have now recognised the need to integrate thinking about climate change into all areas of public policy making. However, the discussion of ‘climate policy integration’ has tended to focus on mitigation decisions mostly taken at international and national levels. Clearly, there is also a more locally focused adaptation dimension to climate policy integration, which has not been adequately explored by academics or policy makers. Drawing on a case study of the UK, this paper adopts both a top-down and a bottom-up perspective to explore how far different sub-elements of policies within the agriculture, nature conservation and water sectors support or undermine potential adaptive responses. The top-down approach, which assumes that policies set explicit aims and objectives that are directly translated into action on the ground, combines a content analysis of policy documents with interviews with policy makers. The bottom-up approach recognises the importance of other actors in shaping policy implementation and involves interviews with actors in organisations within the three sectors. This paper reveals that neither approach offers a complete picture of the potentially enabling or constraining effects of different policies on future adaptive planning, but together they offer new perspectives on climate policy integration. These findings inform a discussion on how to implement climate policy integration, including auditing existing policies and ‘climate proofing’ new ones so they support rather than hinder adaptive planning. 相似文献
15.
Gyrlene Aparecida Mendes da Silva Anita Drumond T��rcio Ambrizzi 《Theoretical and Applied Climatology》2011,106(3-4):307-319
In austral summer, the observed El Ni?o (EN) events during warm Pacific Decadal Oscillation (PDO) phases (PDO(+)) exhibited large anomalous upper level wave patterns in response to larger Sea Surface Temperature (SST) anomalies in the Equatorial Pacific and Atlantic Oceans compared with SST anomalies in EN events during cold PDO phases (PDO(?)). The precipitation anomalies in PDO(+) EN are increased over Southeastern South America (SESA) associated with the intensification of the moisture flux convergence in this region. The PDO(?) EN events exhibit positive precipitation anomalies only over southern SESA, while negative anomalies were observed in the north. Downward motion and anomalous divergence over central eastern Brazil may have contributed to the weakening of the northwesterly moisture flux convergence associated with the South American Low Level Jet (SALLJ) over the subtropics. The extratropical cyclones showed higher frequency and lower central pressures in southern Brazil, Uruguay, northeastern Argentina, and Southwest Atlantic Ocean during the PDO(+) EN events compared with the PDO(?) EN events. Such increase in the frequency and intensity of cyclogenesis cases seems to be in accordance with the anomalous moisture flux convergence over the SESA and associated reduction in the Sea Level Pressure observed during PDO(+) EN events. In order to investigate the impact of a canonical El Ni?o event over South America under different PDO phases, two numerical experiments were done with an Atmospheric General Circulation Model. Global SST and ice sea fields average over years characterized by (a) PDO(+) and (b) PDO(?) were considered as climatologically fields, and a composite of anomalies of SST of all El Ni?o events observed in 1950?C1999 was added in the region 20oS?C20oN;120oW?C175oW of both ??climatologies.?? The differences in experiments suggest that a canonical EN may produce significant different anomalous atmospheric patterns associated with distinct PDO climatologies. The more significant differences are simulated over extreme northern and eastern Brazil. Additional numerical experiments isolating the observed variability of SST over several oceanic basins during different PDO phases will be conducted to study their particular role on the South American climate. 相似文献
16.
Garcia-Villada Laurence P. Donat Markus G. Angélil Oliver Taschetto Andréa S. 《Climate Dynamics》2020,55(9-10):2351-2376
Climate Dynamics - El Niño-Southern Oscillation (ENSO) is the dominant mode of climate variability, affecting climate conditions over large areas of the globe. There are, however, substantial... 相似文献
17.
Over the last decades there have been a considerable number of deforestation studies in Latin America reporting lower rates compared with other regions; although these studies are either regional or local and do not allow the comparison of the intraregional variability present among countries or forest types. Here, we present the results obtained from a systematic review of 369 articles (published from 1990 to 2014) about deforestation rates for 17 countries and forest types (tropical lowland, tropical montane, tropical and subtropical dry, subtropical temperate and mixed, and Atlantic forests). Drivers identified as direct or indirect causes of deforestation in the literature were also analysed. With an overall annual deforestation rate of −1.14 (±0.092 SE) in the region, we compared the rates per forest type and country. The results indicate that there is a high variability of forest loss rates among countries and forest types. In general, Chile and Argentina presented the highest deforestation rates (−3.28 and −2.31 yearly average, respectively), followed by Ecuador and Paraguay (−2.19 and −1.89 yearly average, respectively). Atlantic forests (−1.62) and tropical montane forests (−1.55) presented the highest deforestation rates for the region. In particular, tropical lowland forests in Ecuador (−2.42) and tropical dry forests in Mexico (−2.88) and Argentina (−2.20) were the most affected. In most countries, the access to markets and agricultural and forest activities are the main causes of deforestation; however, the causes vary according to the forest types. Deforestation measurements focused at different scales and on different forest types will help governments to improve their reports for international initiatives, such as reducing emissions from deforestation and forest degradation (REDD+) but, more importantly, for developing local policies for the sustainable management of forests and for reducing the deforestation in Latin America. 相似文献
18.
K. Slezakova J. C. M. Pires M. C. Pereira F. G. Martins M. C. Alvim-Ferraz 《Journal of Atmospheric Chemistry》2008,60(3):221-236
In urban areas traffic is the major contributor to atmospheric particulate matter and exposure to these particles currently
represents a serious risk to human health. The attention has been recently focused more on the particles of smaller sizes
(PM2.5) which penetrate deeper in respiratory system causing severe health effects. Therefore, more information on PM2.5 should be provided, namely concerning morphological and chemical characterization. Aiming further evaluation of the impact
of traffic emissions on public health, this work evaluated the influence of traffic on the chemical and morphological characteristics
of PM10 and PM2.5, collected at one site influenced by traffic emissions and at one reference site. Chemical and morphological characteristics
of 1,000 individual particles were determined by scanning electron microscopy combined with energy dispersive spectrometer
(SEM–EDS). Cluster analysis (CA) was used to identify different types of particles that occurred in PM, aiming the identification
of the respective emission sources. Traffic PM2.5 were dominated by particles composed of Fe oxides and alloys (67%) which were related to traffic emissions (this percentage
was 3.7 times higher than at the background site); in PM2.5–10 the abundance of Fe oxides and alloys were 20% and 0% for the traffic and background sites, respectively. Background PM2.5 were mainly constituted by aluminum silicates (63%) related to natural sources (this percentage was 2.5 times higher than
at the traffic site); the abundances of aluminum silicates in PM2.5–10 were 74% and 73% for traffic and background sites, respectively. It was concluded that traffic emissions were mainly present
in PM2.5 (the percentage of particles associated to these emissions was 3.4 times higher than in PM2.5–10), while coarse particles were dominated by material of natural origin (the percentage of particles associated was 1.2 and
3.0 times higher than in PM2.5 for traffic and background sites, respectively). Previous results obtained by proton induced X-ray emission (PIXE) were consistent
with SEM–EDS analysis that showed to be very useful to complement elemental analysis of different PM2.5 and PM2.5–10. 相似文献
19.
People vary considerably in terms of their knowledge, beliefs, and concern about climate change. Thus, an important challenge for climate change communicators is how to most effectively engage different types of audiences. This study aimed to identify distinct audience segments that vary in terms of their values, beliefs, and responses to climate change and determine for each segment which specific message attributes increased motivation to engage in climate adaptation. A sample of 1031 Australian residents (aged 18–66 years) completed an online survey assessing their values, beliefs, and behaviors related to climate change, and recording their responses to a broad range of climate change adaptation messages. Latent profile analysis identified three distinct audience segments: alarmed (34.4%), uncommitted (45.2%), and dismissive (20.3%). Sixty climate change adaptation messages were coded in terms of the presence/absence of six attributes: explicit reference to climate change, providing specific adaptation advice, strong negative emotive content, emphasis on collective responsibility, highlighting local impacts, and underscoring financial impacts. Participants viewed a random sample of six messages and rated the extent to which each message motivated them to seek out more information and immediately respond to the climate change threat portrayed in the message. Multilevel modeling indicated messages that included strong negative emotive content or provided specific adaptation advice increased adaptation intentions in all three audience segments. Omitting any mention of climate change and emphasizing local impacts increased adaptation intentions in dismissive audiences. Implications for tailoring and targeting climate change adaptation messages are discussed. 相似文献
20.
Reanalysis datasets have been very popular for understanding the general circulation as well as verifying general circulation models. The most recent versions of global reanalysis datasets prepared by ECMWF (“ERA-40”) and NCEP (“NDRa2”) are examined in this article. The NDRa2 data are regridded to the resolution (2.5° × 2.5° longitude and latitude) of the ERA-40 public data. Primary variables that both relate to the atmosphere's general circulation and are readily available are compared and contrasted. Significant differences are found in the primary circulation variables and energetics. The zonal mean Hadley cells are stronger in ERA-40, but differences in temperature and moisture make the poleward heat transport by the cells more similar in the two datasets. The subtropical and polar night jet streams are stronger in ERA-40 data as is kinetic energy. The surface energy budgets differ in that ERA-40 data have greater sensible heat flux into the air, while NDRa2 data have greater latent heat flux. The result is NDRa2 has more moisture in the subtropics; ERA-40 data have more moisture in the tropics. Geographically, the two datasets have notable differences in their treatment of the intertropical convergence zone (ICZ). The ICZ over the Atlantic and eastern Pacific is narrower and stronger in ERA-40 data. The ICZ over the western Pacific and Indian oceans is generally stronger in NDRa2 data, one consequence is a stronger tropical easterly jet in NDRa2 data over the Indian Ocean in JJA. Both datasets have a double ICZ in the western half of the Pacific in DJF; in JJA ERA-40 retains that double ICZ but NDRa2 largely does not. Beyond the handling of the ICZ, the datasets differ in tropical zonal mean zonal wind, ERA-40 data in DJF has zonal mean upper troposphere tropical westerlies where NDRa2 data have easterlies; this difference may imply a different amount of interhemispheric communication. The datasets also have strong disagreements in regions of large-scale higher topography. 相似文献