bluuebunny/crossref_metadata_2025 huggingface dataset:
Vertebrate retina and hypothalamus development
Authors: Byerly Mardi S. , Blackshaw Seth
Published: April 2009

The vertebrate retina and hypothalamus, which emerge from adjacent regions of the ventral diencephalon, provide accessible experimental systems for analysis of the molecular mechanisms by which neuronal subtype diversity is specified, and how this neuronal subtype diversity regulates perception and behavior. Although the retina emerges as a lateral extension of the hypothalamus prior to the onset of neurogenesis, the retina and hypothalamus go on to eventually be comprised of almost entirely different cell types, and differ extensively in the spatial organization, function, and connectivity of these cells. Despite these differences in cell composition, there are a number of mechanistic and molecular similarities in the process of cell fate specification in both organs, including a stereotyped temporal sequence in which major cell types are generated. Although a handful of genes have been identified in both systems that direct cell fate specification, many more remain to be characterized, and large numbers of candidate genes have been identified in recent high‐throughput screens, particularly in retina. Experimental challenges for the near future include functional analysis of the genes identified so far, and the use of the molecular pathways gained from analysis of the development of specific neuronal lineages to study the contribution of these cells to perception and behavior. Copyright © 2009 John Wiley & Sons, Inc.

This article is categorized under:

Developmental Biology > Developmental Processes in Health and Disease
Left–right axis determination
Authors: Ibañes Marta , Izpisúa Belmonte Juan Carlos
Published: April 2009

Vertebrates display left‐right (L‐R) asymmetric organ positioning and morphologies, which are established during embryonic development. These asymmetries are conserved among individuals and species. How, when and where do embryos first break the symmetry? Why is it broken in a consistent direction? How is the asymmetry transmitted to and coordinated within the whole embryo? Which of these elements are conserved between different organisms? These questions have been the focus of intense research during the last decade, and much has been learned. Nonetheless, our understanding of how tissue and organ L‐R differences are established during embryogenesis is scarce. A systems biology approach may enable us to better understand the dynamics of gene networks, epigenetics, cilia, fluids, and charged molecules as well as other processes involved in the generation of the vertebrate L‐R axis. Copyright © 2009 John Wiley & Sons, Inc.

This article is categorized under:

Developmental Biology > Stem Cell Biology and Regeneration
Signals controlling neural crest contributions to the heart
Authors: Scholl Ann Marie , Kirby Margaret L.
Published: April 2009

Cardiac neural crest cells represent a unique subpopulation of cranial neural crest cells that are specified, delaminate and migrate from the developing neural tube to the caudal pharynx where they support aortic arch artery development. From the caudal pharynx, a subset of these cells migrates into the cardiac outflow tract where they are needed for outflow septation. Many signaling factors are known to be involved in specifying and triggering the migration of neural crest cells. These factors have not been specifically studied in cardiac crest but are assumed to be the same as for the other regions of crest. Signaling factors like Ephs and semaphorins guide the cells into the caudal pharynx. Support of the cells in the pharynx is from endothelin, platelet‐derived growth factor (PDGF), and the transforming growth factor beta (TGFβ)/bone morphogenetic protein (BMP) signaling pathways. Mutants in the TGFβ/BMP pathway show abnormal migration or survival in the pharynx, whereas the migration of the neural crest cells into the outflow tract is orchestrated by semaphorin/plexin signaling. Although TGFβ family members have been well studied and show defective neural crest function in outflow septation, their mechanism of action remains unclear. Copyright © 2009 John Wiley & Sons, Inc.

This article is categorized under:

Developmental Biology > Lineages
Gridlock in the Government of the United States: Influence of Divided Government and Veto Players
Authors: Saeki Manabu
Published: April 2009

David Mayhew’s Divided We Govern significantly challenged the conventional wisdom of the adversarial effect of divided government on government effectiveness in the United States. While the post-Mayhewian literature has been centred on legislative productivity as a measure of gridlock, gridlock is here defined as an ‘inability to change policy’. In this study, the preferences of the legislators, such as the filibuster, override and House median veto players are plotted in Euclidean space. The analysis focuses on the influence of the area of the winset, which is an intersection overlapped by the veto players’ indifference curves. There is a substantial impact of the area of the winset on the change in policy output point, which is measured by the ADA scores and by Poole’s Mean Winning Coordinate. Yet divided government has marginal or no effect on policy swing. The conclusion is that the preferences of veto players, but not party control of the government, have a substantial impact on gridlock in the United States.
Sorapet Pinyoo and the status ofpleeng luuk tung
Authors: Mitchell James
Published: April 2009

Before 1997 a number of social, political and academic movements combined to present a more negative image ofluuk tung(Thai country music) than was warranted and as a result, the genre was understudied. This article identifies the forces that influenced the development ofluuk tung'sstatus in Thai society and demonstrates how the rising status ofluuk tungsince 1997 has influenced recent academic writing by Thai authors. This survey of the voices that speak onluuk tungis grounded by an analysis of the lyrics and melodies of Sorapet Pinyoo, a well-knownluuk tungartist.
Mixed up in power politics and the Cold War: The Americans, the ICFTU and Singapore's labour movement, 1955–1960
Authors: Long S.R. Joey
Published: April 2009

The United States had a hand in shaping Singapore's labour developments between the period 1955 and 1960. Utilising materials from archives in Britain, the Netherlands and the United States, this study details the impetus for, the nature of, and the outcome of the US attempt to strengthen non-communist labour institutions in Singapore.
Singapore and the Vietnam war
Authors: Guan Ang Cheng
Published: April 2009

This article attempts to fill two gaps in two sets of inter-related historiographies, that of the diplomatic history of Singapore and that of the Vietnam war. For a number of reasons, not much had been published about the foreign policy of Singapore from the historical perspective. The Southeast Asian dimension of the Vietnam war is also starkly missing from the voluminous literature on the war. This article thus tries to describe and explain Singapore's attitude towards the war as it evolved over the ten years — from 1965, when the war really began and which coincided with the year that Singapore became independent, to 1975, a period which overlaps with the first ten years of Singapore's independence. Hopefully, this study will provide an understanding of one aspect of Singapore's foreign policy in its first 10 years as well as offer one Southeast Asian perspective on the Vietnam war.
Revisiting the rice deltas and reconsidering modern Southeast Asia's economic history
Authors: Montesano Michael J.
Published: April 2009

The rise of the three great rice-producing and -exporting deltas of mainland Southeast Asia numbers among the most familiar chapters in the modern history of the region. On a macro level, it exemplifies the integration of the region into the North Atlantic-centered world economy during the age of high imperialism and the consequent shock of the depression of the 1930s. On a micro level, that rise has offered historians an opportunity to examine the responses of Southeast Asian cultivators to market signals; the variation in the allocation of factors of production across the Irrawaddy, Chao Phraya and Mekong deltas; and the implications of those responses and that allocation for reactions to the shock of the inter-war crisis. The principal features of the history of the mainland rice economies between 1850 and the 1930s have indeed grown so familiar as to make that history seem like yesterday's topic. Occasional attempts to propose significant revision to the story have had little impact. And the need for a major monograph on the economic history of the Mekong delta during the French colonial period remains unmet.
Fragments of utopia: Popular yearnings in East Timor
Authors: Kammen Douglas
Published: April 2009

Six months after the historic August 1999 referendum in which the people of East Timor voted to reject Indonesia's offer of broad autonomy, the newly appointed chief of the United Nations Transitional Administration in East Timor, Sérgio Vieira de Mello, commented to CNN on the enormous challenge of setting the territory on the road to independence: ‘It is a test case, therefore it is even a laboratory case where we can transform utopia into reality. But I think we can try and get it right in the case of Timor.’ After 24 years of brutal military occupation, the suggestion that East Timor was to be a laboratory case for the United Nations might have seemed insulting, the notion of utopia absurd. Hundreds of thousands of people were without housing. Basic infrastructure lay in ruins. Commodities were scarce and those goods available were sold at grossly inflated prices. Eleven thousand foreign troops had arrived to restore security. Tens of thousands of refugees were still living in squalid camps across the border in Indonesian West Timor, many against their will. Nevertheless, Vieira de Mello's statement neatly captured the twin aspirations of the time — the independence long-dreamed of by East Timorese and the opportunity for the United Nations literally to build a state from the ground up. In the same CNN report, East Timorese Nobel Laureate José Ramos-Horta emphasised precisely this point: ‘This is the first instance in the history of the UN that the UN has managed completely an entire country; and they have a [Timorese pro-independence] movement that is very cooperative, they have an exceptional people that's cooperating with them, so they cannot fail. They are condemned to succeed because failure would be disastrous for the credibility of the UN, so they simply cannot afford to fail.’ Utopia, it seems, had become a necessity.
Impact of growth patterns and early diet on obesity and cardiovascular risk factors in young children from developing countries
Authors: Corvalán Camila , Kain Juliana , Weisstaub Gerardo , Uauy Ricardo
Published: April 2009

Non-communicable chronic diseases are now a worldwide epidemic. Diet and physical activity throughout life are among its main determinants. In countries undergoing the early stages of the nutrition transition weight gain from birth to 2 years of life is related to lean mass gain, while ponderal gain after age 2 years is related to adiposity and later diabetes and CVD risk. Evidence from developing countries undergoing the more advanced stages of the nutrition transition is limited. The early growth patterns of a cohort of Chilean children born in 2002 with normal birth weight who at 4 years had a high prevalence of obesity and CVD risk factors have been assessed. Results indicate that BMI gain in early life, particularly from 6 months to 24 months, is positively associated with adiposity and CVD risk status at 4 years. These results together with existing evidence suggest that actions to prevent obesity and nutrition-related chronic diseases in developing countries should start early in life, possibly after 6 months of age. This approach should consider assessing the effect of mode of feeding and the amount and type of energy fed, as well as the resulting growth patterns. The challenge for researchers addressing the nutrition transition is to define the optimal nutrition in early life, considering not only the short- and long-term health consequences but also taking into account the stage of the nutritional transition for the given population of interest. The latter will probably require redefining optimal postnatal growth based on the context of maternal size and fetal growth.
Pennington Lecture Teams, strategies and networks: developments in nutritional support; a personal perspective
Authors: Powell-Tuck J.
Published: April 2009

Chris Pennington was an archetypal team player, strategist and networker. Clinical nutritional support has progressed remarkably since the 1970s and it has been a privilege to work in this field over this period during which teamwork, strategy development and networking have been crucial. British experience has been characterised by groups of individuals of differing professions and specialties coming together to enable progress to be made. This approach was initially in the form of nutrition support teams orientated to patient-centred ward-based care, then as hospital strategic committees and the concept of the ‘patient journey’. Indeed, the formation of the British Association for Parenteral and Enteral Nutrition (now known as BAPEN) in 1992 required the statesmanlike burying of jealousies as societies came together into a multiprofessional association. With the understanding that disease-related malnutrition was highly prevalent it became apparent that it must be managed on a broad and organised clinical front. In the Organisation of Food and Nutritional Support in Hospitals a group of professionals developed for BAPEN concepts of hospital-wide organisation to tackle malnutrition that were based on previous reports, both national and international, and were made easily accessible from the BAPEN website, especially the ‘Malnutrition Universal Screening Tool’ and the National Institute for Health and Clinical Excellence nutrition guidelines. The coming together of six national clinical societies to develop evidence-based consensus guidelines for intravenous saline therapy (also on the BAPEN website) has shown that BAPEN can catalyse opinion well beyond its own nutritional constituency. In England Chris Pennington's Scottish lead is being followed by developing a patient-centred strategic framework for a managed home parenteral nutrition and intestinal failure national network. In research, education or clinical practice the engines of progress have been teams, strategies and networks.
The 2-year prognosis of panic episodes in the general population
Authors: Batelaan N. M. , de Graaf R. , Penninx B. W. J. H. , van Balkom A. J. L. M. , Vollebergh W. A. M. , Beekman A. T. F.
Published: April 2009

Background

Panic disorder (PD) is generally considered to be a chronic or intermittent disorder. This view may be biased because of a lack of general population studies investigating panic from the onset of an episode onwards. Data regarding the course of subthreshold panic disorder (sub-PD) and predictors of its course are lacking.

Method

Using data from a large community-based survey, the Netherlands Mental Health and Incidence Study (NEMESIS), that retrospectively assessed the 2-year course of panic with a Life Chart Interview (LCI), this study investigated remission, chronicity and recurrence in subjects with new episodes of PD or sub-PD. Predictor variables of remission consisted of sociodemographics, psychobiological, environmental, psychiatric and panic-related factors.

Results

In PD, remission of panic attacks occurred in 64.5% of subjects, mean time to remission was 5.7 months, and the remission rate was 5.8/100 person-months. In 43.3% of subjects panic was still present after 1 year. Recurrence of panic attacks occurred in 21.4% of those with PD who had achieved remission and for whom sufficient follow-up time was available. In general, the course of sub-PD was more favourable. Predictors of remission were female gender, the absence of ongoing difficulties, subthreshold panic and a low initial frequency of attacks.

Conclusions

These results suggest that the course of panic is diverse in the general population, thereby underlining the need for accurate predictors. This requires further research including biological data and additional psychological data. In addition, given the large proportion with a relapse, relapse prevention should be part of any treatment programme.
A psychometric evaluation of the DSM-IV borderline personality disorder criteria: age and sex moderation of criterion functioning
Authors: Aggen S. H. , Neale M. C. , Røysamb E. , Reichborn-Kjennerud T. , Kendler K. S.
Published: April 2009

Background

Despite its importance as a paradigmatic personality disorder, little is known about the measurement invariance of the DSM-IV borderline personality disorder (BPD) criteria; that is, whether the criteria assess the disorder equivalently across different groups.

Method

BPD criteria were evaluated at interview in 2794 young adult Norwegian twins. Analyses, based on item-response modeling, were conducted to test for differential age and sex moderation of the individual BPD criteria characteristics given factor-level covariate effects.

Results

Confirmatory factor analytic results supported a unidimensional structure for the nine BPD criteria. Compared to males, females had a higher BPD factor mean, larger factor variance and there was a significant age by sex interaction on the factor mean. Strong differential sex and age by sex interaction effects were found for the ‘impulsivity’ criterion factor loading and threshold. Impulsivity related to the BPD factor poorly in young females but improved significantly in older females. Males reported more impulsivity compared to females and this difference increased with age. The ‘affective instability’ threshold was also moderated, with males reporting less than expected.

Conclusions

The results suggest the DSM-IV BPD ‘impulsivity’ and ‘affective instability’ criteria function differentially with respect to age and sex, with impulsivity being especially problematic. If verified, these findings have important implications for the interpretation of prior research with these criteria. These non-invariant age and sex effects may be identifying criteria-level expression features relevant to BPD nosology and etiology. Criterion functioning assessed using modern psychometric methods should be considered in the development of DSM-V.
Preterm babies grown up: understanding a hidden public health problem
Authors: Allin M. P. G.
Published: April 2009

Even when they have grown up, the survivors of preterm birth are at increased risk of psychiatric illness. As the incidence of preterm birth is increasing, there is now a growing population of adults whose mental health needs have been neglected.
Macrosecuritisation and security constellations: reconsidering scale in securitisation theory
Authors: BUZAN BARRY , WÆVER OLE
Published: April 2009

The Copenhagen school's theory of securitisation has mainly focused on the middle level of world politics in which collective political units, often but not always states, construct relationships of amity or enmity with each other. Its argument has been that this middle level would be the most active both because of the facility with which collective political units can construct each other as threats, and the difficulty of finding audiences for the kinds of securitisations and referent objects that are available at the individual and system levels. This article focuses on the gap between the middle and system levels, and asks whether there is not more of substance there than the existing Copenhagen school analyses suggests. It revisits the under-discussed concept of security constellations in Copenhagen school theory, and adds to it the idea of macrosecuritisations as ways of getting an analytical grip on what happens above the middle level. It then suggests how applying these concepts adds not just a missing sense of scale, but also a useful insight into underlying political logics, to how one understands the patterns of securitisation historical, and contemporary.
Securitising Threats without the State: A case study of misgovernance as a security threat in Bangladesh
Authors: BARTHWAL-DATTA MONIKA
Published: April 2009

This article provides a critique of the securitisation framework around its ability to provide a comprehensive security analysis when applied in a developing socio-political context. It argues that the framework's conditionalities around who can securitise and how, and its assumptions around the nature of the state restrict its ability to consider the role of non-state actors in raising existential threats to societal security. Through a case study of newspapers in Bangladesh raising ‘misgovernance’ as a security threat to its citizens, it explores how the securitisation framework can become more perceptive to security dynamics in contexts which differ from the one within which the framework has evolved.
Misreading in IR theory and ideology critique: Morgenthau, Waltz and neo-realism
Authors: BEHR HARTMUT , HEATH AMELIA
Published: April 2009

This article is interested in the hegemony which neo-realism accomplished during the second half of the 20th century in both the academic field and policy making of I/international R/relations. Our examination posits the argument that neo-realism can be seen as an ideology rather than a theory of international politics. While this view can connect to individual voices from the 1960s as well as to an emerging body of critical literature since the 1990s, we propose an ideology critique to explore this argument. To unfold this approach we will elaborate some neo-realist misreadings which we think manipulate intellectual history (among others, the writings of Hans J. Morgenthau) and represent an ideological impact intrinsic in the development of IR. An ideology critical approach – which is inherent in Morgenthau's thoughts on international theory themselves and thus helps to reveal profound discrepancies at the heart of an ostensible ‘realist’-neo-realist ‘unity’ – has, firstly, to problematise those discrepancies and, secondly, to focus on hegemonic strategies applied to ideologise and mainstream the academic field. The first part of such an agenda is what we present here; the second part is what we outline methodologically and suggest for further studies in, and of, IR.
Noam Chomsky and the realist tradition
Authors: OSBORN RONALD
Published: April 2009

This article examines the assumptions that underlie Noam Chomsky's politics and argues that his analysis of US foreign policy since World War II may best be situated within the realist tradition in international relations. Chomsky's left realism has not been adequately understood or addressed by IR scholars for both political and disciplinary reasons. In opposition to most classical realists, he has insisted that intellectuals should resist rather than serve national power interests. In contrast to most political scientists, he has also refused to theorize, critiquing much of the enterprise of social science in terms of what he sees as highly suspect power interests within the academy. Hostility to Chomsky's normative commitments has consequently prevented IR scholars from discerning key aspects of his project, as well as important historical and theoretical continuities between radical and realist thought.
Pigs can't fly, or can they? Ontology, scientific realism and the metaphysics of presence in international relations
Authors: MICHEL TORSTEN
Published: April 2009

In recent debates in IR theory a specific trend has evolved which advocates a renewed focus on matters of ontology as a way to overcome or at least to reconceptualise the divides within the field of IR that we encounter especially after the considerable widening of scope after the end of the Cold War. Responding to these claims the article sets out to provide a closer look at the different arguments presented for a renewed concern with ontology and its ramifications. With this task in mind, three particular complexes will be addressed. First, we have to identify the central claims of these new ontological approaches and assess them in respect to coherence and analytic rigour. Secondly, then, we will proceed with identifying the underlying reasons for their shortcomings which as will be shown lie with the misguided concept of ontology. If this conception is properly reworked, can indeed bring new light into otherwise protracted or even deadlocked debates.
Multi-nodal politics: globalisation is what actors make of it
Authors: CERNY PHILIP G.
Published: April 2009

What has been traditionally conceptualised as ‘the international’ has been undergoing a fundamental transformation in recent decades, usually called ‘globalisation’. Globalisation is a highly contested concept, and even among those who accept that some sort of globalisation process is occurring, attempts to analyse it have focused on a range of structural explanations: the expansion of economic transactions; the development of transnational or global social bonds; and the emergence and consolidation of a range of semi-international, semi-global political institutions. In all of these explanations, the role of actors as agents strategically shaping change has been neglected. In this article I argue that structural variables alone do not determine specific outcomes. Indeed, structural changes are permissive and can be the source of a range of potential multiple equilibria. The interaction of structural constraints and actors’ strategic and tactical choices involves a process of ‘structuration’, leading to wider systemic outcomes. In understanding this process, the concepts of ‘pluralism’ and ‘neopluralism’ as used in traditional ‘domestic’-level Political Science can provide an insightful framework for analysis. This process, I argue, has developed in five interrelated, overlapping stages that involve the interaction of a diverse range of economic, social and political actors. Globalisation is still in the early stages of development, and depending on actors’ choices in a dynamic process of structuration, a range of alternative potential outcomes can be suggested. There is a tide in the affairs of menWhich, taken at the flood, leads on to fortune;Omitted, all the voyage of their lifeIs bound in shallows and in miseries.On such a full sea are we now afloat,And we must take the current when it serves,Or lose our ventures.(William Shakespeare, Julius Caesar, IV.ii.269–276)
Variegated neo-liberalism: transnationally oriented fractions of capital in EU financial market integration
Authors: MACARTNEY HUW
Published: April 2009

This article develops a twofold critique: on the one hand it addresses those accounts commonly associated with the Varieties of Capitalism literature and their associated understanding of neo-liberalism to argue that there is a dominant tendency to collapse into a binary analysis that asserts either we are witnessing convergence or we are experiencing path dependency. On the other hand it addresses ‘neo-Gramscian’ accounts which tend to overemphasise processes of transnational convergence and the emergence of a transnational capitalist class at the expense of the embeddedness of capital in national-domestic contexts. On this basis, it is argued that several contributions within political geography pose meaningful questions about the premise that neo-liberalism is inherently variegated. Principally, this involves developing the notion of variegated neo-liberalism to analyse the dynamics of a contingent neo-liberal consensus between transnationally-oriented fractions that both drives EU reform in a neo-liberal direction and reinforces domestic linkages organic to the national context. As a result, the article suggests we therefore reject the notion of a transnational capitalist class somehow detached from the national.
A description of hydrometeor layer occurrence statistics derived from the first year of merged Cloudsat and CALIPSO data
Authors: Mace Gerald G. , Zhang Qiuqing , Vaughan Mark , Marchand Roger , Stephens Graeme , Trepte Chip , Winker Dave
Published: April 2009

The occurrence statistics of hydrometeor layers covering the Earth's surface is described using the first year of millimeter radar data collected by Cloudsat merged with lidar data collected by CALIPSO (July 2006 to June 2007). These satellites are flown in a tight orbital configuration so that they probe nearly the same volumes of the atmosphere within 10–15 s of each other. This configuration combined with the capacity for millimeter radar to penetrate optically thick hydrometeor layers and the ability of the lidar to detect optically thin clouds has allowed us to characterize the vertical and horizontal structure of hydrometeor layers with unprecedented precision. We find that the global hydrometeor coverage averages 76% and demonstrates a fairly smooth annual cycle with a range of 3% peaking in October 2006 and reaching a minimum in March 2007. The geographic distribution of hydrometeor layers defined in terms of layer base, layer top, and layer thickness is described. The predominance of geometrically thin boundary layer clouds is illustrated as is the spatial distribution of upper tropospheric ice clouds in the tropics. The cooccurrence of multiple layers is shown to be a strong function of latitude and geography with cooccurring middle‐level (3 km < layer base < 6 km) and high‐level (base > 6 km) layers being predominant over the continents. Cloud layer overlap is also examined, and a bias due to an assumption of maximum fractional overlap in coarse resolution models is quantified and shown to be on the order of −5 to −7% globally maximizing over the high‐latitude continents of the Northern Hemisphere.
A technique for short‐term warning of solar energetic particle events based on flare location, flare size, and evidence of particle escape
Authors: Laurenza M. , Cliver E. W. , Hewitt J. , Storini M. , Ling A. G. , Balch C. C. , Kaiser M. L.
Published: April 2009

We have developed a technique to provide short‐term warnings of solar energetic proton (SEP) events that meet or exceed the Space Weather Prediction Center threshold of J (>10 MeV) = 10 pr cm−2 s−1 sr−1. The method is based on flare location, flare size, and evidence of particle acceleration/escape as parameterized by flare longitude, time‐integrated soft X‐ray intensity, and time‐integrated intensity of type III radio emission at ∼1 MHz, respectively. In this technique, warnings are issued 10 min after the maximum of ≥M2 soft X‐ray flares. For the solar cycle 23 (1995–2005) data on which it was developed, the method has a probability of detection of 63% (47/75), a false alarm rate of 42% (34/81), and a median warning time of ∼55 min for the 19 events successfully predicted by our technique for which SEP event onset times were provided by Posner (2007). These measures meet or exceed verification results for competing automated SEP warning techniques but, at the present stage of space weather forecasting, fall well short of those achieved with a human (aided by techniques such as ours) making the ultimate yes/no SEP event prediction. We give some suggestions as to how our method could be improved and provide our flare and SEP event database in the auxiliary material to facilitate quantitative comparisons with techniques developed in the future.
Determining ion production rates near Saturn's extended neutral cloud from ion cyclotron wave amplitudes
Authors: Cowee M. M. , Omidi N. , Russell C. T. , Blanco‐Cano X. , Tokar R. L.
Published: April 2009

Recent Cassini observations of active venting of water molecules from Enceladus indicate that the moon is the primary source of Saturn's extended neutral cloud. Ionization of the neutrals through charge exchange creates a population of newborn ions with a velocity space distribution, which is highly unstable to the generation of electromagnetic ion cyclotron waves. Cassini observed such ion cyclotron waves, finding spatial and temporal variability in the wave amplitudes throughout the extended neutral cloud region. Since the amount of energy in the ion cyclotron waves is proportional to the number of newborn ions generating them, it is possible to infer the ion production rate in the region. To do so, we use two‐dimensional electromagnetic hybrid (kinetic ions, fluid electrons) simulations to investigate the growth and nonlinear evolution of ion cyclotron waves. We focus on conditions near Enceladus' L shell and compare the simulated and observed ion cyclotron wave amplitudes to estimate the neutral densities and ion production rates. Our simulation results find a relatively linear relation between ion production rate and quasisteady wave energy level (δB2). For conditions near Enceladus' L shell, we find that water group ion production rates of 0.007–0.014/cc/s (which yield wave amplitudes of ∼0.1–0.3 nT) are appropriate. For ion production within an annulus volume from 3.9 to 4 RS, we obtain ion production rates of 3.8 × 1026 to 7.6 × 1026 ions/s or 10.2–20.4 kg/s.
Cause of different local time distribution in the postsunset equatorial ionospheric irregularity occurrences between June and December solstices
Authors: Su S.‐Y. , Chao C. K. , Liu C. H.
Published: April 2009

Global averaged postsunset equatorial ionospheric density irregularity occurrences observed by ROCSAT during the moderate to high solar activity years of 1999 to 2004 indicate a different local time distribution between June and December solstices. The irregularity occurrences during the December solstice show a faster increase rate to peak at 2100–2200 local time, while the irregularity occurrences during the June solstice have a slower increase rate and peak one hour later in local time than that in the December solstice. The cause of such different local time distributions is attributed to a large contrast in the time of zonal drift reversal and the magnitude of postsunset vertical drift observed by ROCSAT at longitudes of large magnetic declination in the two solstices. That is, a delay in the zonal drift reversal in association with a smaller postsunset vertical drift observed at longitudes of positive magnetic declination has greatly inhibited the irregularity occurrences during the June solstice in contrast to an earlier zonal drift reversal together with a large vertical drift occurring at longitudes of negative magnetic declination to accelerate the irregularity occurrences during the December solstice. We think that the different geomagnetic field strengths that existed between the longitudes of positive and negative magnetic declinations have played a crucial role in determining the different local time distributions of irregularity occurrences for the two solstices.
Acceleration mechanism of high‐speed neutral wind observed in the polar lower thermosphere
Authors: Tsuda T. T. , Nozawa S. , Oyama S. , Motoba T. , Ogawa Y. , Shinagawa H. , Nishitani N. , Hosokawa K. , Sato N. , Lester M. , Fujii R.
Published: April 2009

We analyzed data obtained with the European incoherent scatter (EISCAT) Svalbard Radar (ESR) at Longyearbyen (78.2°N, 16.0°E in geographic coordinates, 75.2°Λ in invariant latitude) to advance our understanding of the acceleration mechanism of the lower thermospheric neutral wind when the ionospheric convection becomes enhanced. The Advanced Composition Explorer satellite observed a southward turning in the interplanetary magnetic field at 0843 UT on 16 June 2005. At 0900 UT, the F region ion velocity and the lower thermospheric neutral wind (at 118‐km altitude) observed with the ESR began to accelerate significantly in the westward and northwestward directions, respectively. The neutral wind was remarkably accelerated within 1 hour from 0900 UT, and its speed became a value of ∼500 m s−1 at 1000 UT. The wind speed was significantly higher than a typical wind speed at 118 km. We evaluated the ion drag contribution on the generation of the high‐speed neutral wind. Our evaluation verifies that the ion drag force could not generate the high‐speed neutral wind within such a short time (∼1 hour). This result implies that the major driving force was the horizontal pressure gradient force induced by the Joule heating. We deduced the contribution of the pressure gradient force based on a quantitative estimation of the Joule‐heating‐induced pressure gradient from the ESR and the Super Dual Auroral Radar Network data. We concluded that the pressure gradient force was the most probable force in this event.
Experimental investigation of frictional melting of argillite at high slip rates: Implications for seismic slip in subduction‐accretion complexes
Authors: Ujiie Kohtaro , Tsutsumi Akito , Fialko Yuri , Yamaguchi Haruka
Published: April 2009

Discovery of pseudotachylytes from exhumed accretionary complexes indicates that frictional melting occurred along illite‐rich, argillite‐derived slip zones during subduction earthquakes. We conducted high‐velocity friction experiments on argillite at a slip rate of 1.13 m/s and normal stresses of 2.67–13.33 MPa. Experiments show slip weakening followed by slip strengthening. Slip weakening is associated with the formation and shearing of low‐viscosity melt patches. The subsequent slip strengthening occurred despite the reduction in shear strain rate due to the growth (thickening) of melt layer, suggesting that the viscosity of melt layer increased with slip. Microstructural and chemical analyses suggest that the viscosity increase during the slip strengthening is not due to an increase in the volume fraction of solid grains and bubbles in the melt layer but could be caused primarily by dehydration of the melt layer. Our experimental results suggest that viscous braking can be efficient at shallow depths of subduction‐accretion complexes if substantial melt dehydration occurs on a timescale of seismic slip. Melt lubrication can possibly occur at greater depths within subduction‐accretion complexes because the ratio of viscous shear to normal stress decreases with depth. Argillite‐derived natural pseudotachylytes formed at seismogenic depths in subduction‐accretion complexes are more hydrous than the experimentally generated pseudotachylytes and may be evidence of nearly complete stress drop.
Exploring the initial errors that cause a significant “spring predictability barrier” for El Niño events
Authors: Duan Wansuo , Liu Xinchao , Zhu Keyun , Mu Mu
Published: April 2009

Within the Zebiak‐Cane model, we identify two types of initial errors that have significant season‐dependent evolutions related to the spring predictability barrier (SPB) for El Niño events. One type includes the sea surface temperature anomaly (SSTA) errors that have a zonal dipolar pattern with positive anomalies in the central equatorial Pacific and negative ones in the eastern equatorial Pacific; the other type consists of the SSTA errors with a spatial structure opposite to that of the former type, the zonal dipolar pattern shows negative anomalies in the central equatorial Pacific and positive anomalies in the eastern equatorial Pacific. The patterns of these two types of errors are nearly opposite of each other. The former causes the El Niño event to be underpredicted, and the latter causes the El Niño event to be overpredicted. For strong El Niño events the former tends to have a larger effect on the predictions than the latter, but for weak El Niño events, it is very difficult to determine which type of initial errors results in worse predictions. It is thought that strong (weak) El Niño events could be affected by strong (weak) nonlinearities. There are also other initial errors; however, they do not yield considerable season‐dependent evolutions nor can a common characteristic be extracted from their patterns. The two types of initial errors suggest two dynamical behaviors of error growth related to the SPB: in one case, the initial errors grow in a manner similar to the El Niño events; in the other case, the initial errors develop with a tendency opposite to the El Niño events. The two types of initial errors may capture the errors that exhibit significant season‐dependent evolutions related to the SPB. In addition, they may provide information regarding the “sensitive area” of ENSO predictions because of their localized regions. Therefore, if these types of initial errors exist in the realistic El Niño–Southern Oscillation (ENSO) predictions and if a data assimilation or a target method can filter them, the ENSO forecast skill may be improved. For ensemble forecast studies, different signs of prediction errors caused by the two types of initial errors could illustrate why the ensemble mean offers a better forecast than a single prediction.
Eddy overturning across a shelf edge front: Kongsfjorden, west Spitsbergen
Authors: Tverberg V. , Nøst O. A.
Published: April 2009

Eddy overturning across a shelf edge front has been investigated in a simplified model setup comprising an along‐slope uniform shelf and slope with a slope current. Results from three model runs are presented, each initiated with and nudged toward a sharp shelf edge front in temperature, salinity, density, and velocity. Data collected off Kongsfjorden at Spitsbergen were used for initiating the model runs. Three distinctly different density fronts were used to initialize the model runs, one with a negative cross‐frontal density gradient toward the shelf, one with a positive density gradient, and one with a combination of negative density gradient in the upper water column and a positive in the lower water column. The model results indicate that the initial cross‐frontal density gradients determine the eddy overturning direction, acting toward flattened or terrain‐following isopycnals. The steady state modeled fronts resemble quite well the observed front structures, as well as temperature and salinity fields. This indicates that eddy overturning plays an important role in cross‐frontal exchange of water masses along the shelf edge front off west Spitsbergen. The Eulerian mean cross‐slope flow is close to zero, and the corresponding fluxes do not describe the correct vertical distribution.
Numerical simulations of submesoscale balanced vertical velocity forcing unsteady nutrient‐phytoplankton‐zooplankton distributions
Authors: Viúdez Álvaro , Claret Mariona
Published: April 2009

The effect of submesoscale balanced (void of waves) vertical velocity on initially steady nutrient‐phytoplankton‐zooplankton (NPZ) distributions is investigated numerically. First, steady vertical NPZ profiles, continuous but not continuously differentiable at several depths, are found as analytical solutions to the NPZ equations in the absence of flow. These solutions admit numerical equivalents that are continuously differentiable in the numerical sense, here meaning convergence of the vertical derivative with respect to increasing vertical resolution. These NPZ solutions require, however, large vertical resolutions, with a grid size of few centimeters, to be properly discretisized. The ecological model is next coupled to a nonhydrostatic Boussinesq f plane physical model that explicitly conserves potential vorticity on isopycnals. Then the NPZ solutions are used as steady initial ecosystem conditions to investigate the role of submesoscale balanced vertical velocity in forcing NPZ anomalies in an idealized case of a baroclinic unstable jet. The results show that the baroclinic flow rapidly develops balanced vertical velocity that in turn favors NPZ anomalies. A large cancelation between the local change and the horizontal advection occurs in the ecosystem variables. This particularly occurs for zooplankton anomalies that therefore behave as better passive tracers of the horizontal flow than phytoplankton anomalies. However, once phytoplankton and zooplankton anomalies develop locally, forced by vertical velocity, they are horizontally advected away from the upwelling or downwelling regions so that spatial distributions of vertical velocity and ecological fields become eventually uncorrelated.
Development and testing of Polar Weather Research and Forecasting model: 2. Arctic Ocean
Authors: Bromwich David H. , Hines Keith M. , Bai Le‐Sheng
Published: April 2009

A version of the state‐of‐the‐art Weather Research and Forecasting model (WRF) has been developed for polar applications. The model known as “Polar WRF” is tested over the Arctic Ocean with a western Arctic grid using 25‐km resolution. The model is based upon WRF version 2.2, with improvements to the Noah land surface model and the snowpack treatment. The ocean surface treatment is modified to include fractional sea ice. Simulations consist of a series of 48‐h integrations initialized daily at 0000 UTC. The initial 24 h are taken as model spin‐up time for the atmospheric hydrology and boundary layer processes. Arctic conditions are simulated for the selected months: January 1998, June 1998, and August 1998 representing midwinter, early summer, and late summer conditions, respectively, from the Surface Heat Budget of the Arctic (SHEBA) study. The albedo of sea ice is specified as a function of time and latitude for June and as a function of time for August. Simulation results are compared with observations of the drifting ice station SHEBA in the Arctic ice pack. Polar WRF simulations show good agreement with observations for all three months. Some differences between the simulations and observation occur owing to apparent errors in the synoptic forecasts and the representation of clouds. Nevertheless, the biases in the simulated fields appear to be small, and Polar WRF appears to be a very good tool for studies of Arctic Ocean meteorology.
Development and assessment of broadband surface albedo from Clouds and the Earth's Radiant Energy System Clouds and Radiation Swath data product
Authors: Rutan David , Rose Fred , Roman Miguel , Manalo‐Smith Natividad , Schaaf Crystal , Charlock Tom
Published: April 2009

We describe a method to determine broadband albedo globally over land viewed by the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometers on board the TRMM, Terra, and Aqua satellites. This albedo is used as a surface boundary condition for a fast radiation transfer code in the Surface and Atmospheric Radiation Budget (SARB) subsystem of the CERES processing scheme. Cloudy sky surface albedo is estimated from derived clear sky values. Clear sky surface albedo is assessed by comparing the CERES/SARB‐based surface albedo with the bidirectional reflectance distribution function (BRDF)–based surface albedo supplied by the MODIS land surfaces group. The SARB method employs broadband observations at the top of atmosphere (TOA) and assumes relative spectral shape of surface albedo. The MODIS group uses higher spatial resolution observations in several shortwave window channels to retrieve spectral surface albedos and then scales up to broadband surface albedo. Comparisons over snow‐free land show good agreement between the two independent products on the scale of the CERES footprint. Biases run approximately 0.005 absolute or 0.02 relative with SARB albedo, generally lower than MODIS. We find little dependence on view geometry and slight functional dependence on aerosol optical depth. The value selected for a priori surface spectral albedo is important, but not critical, when retrieving broadband surface albedo with broadband TOA data. However, based on calculations, aerosol forcing to TOA flux changes in spectral albedo shape can affect aerosol forcing for as much as would a 15% absolute change in the original broadband surface albedo.