scholarly journals Temporal dynamics of a jökulhlaup system

2009 ◽  
Vol 55 (192) ◽  
pp. 651-665 ◽  
Author(s):  
Felix Ng ◽  
Shiyin Liu
Keyword(s):  
Lake Level ◽  
Temporal Dynamics ◽  
Model Simulation ◽  
Threshold Model ◽  
Flood Events ◽  
The Past ◽  
Model Dynamics ◽  
Key Aspects ◽  
Time Sequences

AbstractRecurring jökulhlaups from ice-dammed lakes often form irregular time sequences that are seemingly unpredictable. Using the flood dates of Merzbacher Lake, Kyrgyzstan, as an example, we study these sequences through a model of lake filling and drainage where flood events initiate at a threshold water depth. Even with a constant threshold, model simulation can explain key aspects of the Merzbacher flood sequence. General analysis of model dynamics reveals a pacing mechanism that links one flood to the next, and which may be represented mathematically as an iterative map. This theory clarifies how environmental factors govern the long-term pattern of flood timings and their frequency distribution in the year. A reconstruction of the past level of Merzbacher Lake also suggests that its flood-initiation threshold decreases with the rate of lake-level rise. These results may help us understand how to forecast future outbursts from jökulhlaup lakes.

scholarly journals Long-term O<sub>3</sub>–precursor relationships in Hong Kong: field observation and model simulation

2017 ◽  
Vol 17 (18) ◽  
pp. 10919-10935 ◽  
Author(s):  
Yu Wang ◽  
Hao Wang ◽  
Hai Guo ◽  
Xiaopu Lyu ◽  
Hairong Cheng ◽  
...  
Keyword(s):  
Hong Kong ◽  
Model Simulation ◽  
Ground Level ◽  
Effective Control ◽  
Photochemical Pollution ◽  
Mixing Ratios ◽  
The Past ◽  
Total Volatile Organic Compounds

Abstract. Over the past 10 years (2005–2014), ground-level O3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e. nitrogen oxides (NOx =  NO + NO2), total volatile organic compounds (TVOCs), and carbon monoxide (CO). To explain the contradictory phenomena, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally produced O3 and regional transport. The simulation of locally produced O3 showed an increasing trend in spring, a decreasing trend in autumn, and no changes in summer and winter. The O3 increase in spring was caused by the net effect of more rapid decrease in NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease in NO titration. However, the decreased in situ O3 formation in autumn was overridden by the regional contribution, resulting in elevated O3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O3 formation was VOC-limited in all seasons, and that the long-term O3 formation was more sensitive to VOCs and less to NOx and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O3 formation decreased in all seasons of these years, particularly in autumn, probably due to the effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provide updated information on photochemical pollution and its impact in Hong Kong.

Early Medieval Great Hall Complexes in England: Temporality and Site Biographies

2020 ◽  
Vol 22 ◽  
pp. 50-67
Author(s):  
Christopher Scull ◽  
Gabor Thomas
Keyword(s):  
Social Action ◽  
Temporal Dynamics ◽  
Eighth Century ◽  
Short Term ◽  
The Past ◽  
Spatial And Temporal Dynamics ◽  
The Social ◽  
Elite Identity ◽  
Site History

This paper offers a critical reconsideration of the social, spatial and temporal dynamics of sixth- to eighth-century great hall complexes in England. The major interpretative issues and constraints imposed by the data are considered, and the sites are then subject to comparative analysis across long-term and short-term temporal scales. The former highlights persistence of antecedent activity and centrality, the latter the ways in which the built environment was perceived in the past, structured social action, and was a medium for the construction and consolidation of elite identity and authority. Within the broad similarity that defines the site-type there is evidence for considerable diversity and complexity of site history and afterlife.

scholarly journals Providing a long-term hydroclimatic perspective for the recent extreme decline of Lake Prespa (SW Balkans) through quantitative reconstruction of lake water-balance changes over the past 5000 years

2021 ◽  
Author(s):  
Tim van der Schriek ◽  
Christos Giannakopoulos
Keyword(s):  
Climate Change ◽  
Lake Water ◽  
Water Loss ◽  
Water Surface ◽  
Lake Level ◽  
Open Water ◽  
Water Levels ◽  
The Past ◽  
Lake Water Balance

&lt;p&gt;Ancient lakes throughout the Mediterranean are at risk of disappearing due to a combination of climate change and human impacts. The growing imbalance between water availability and demand is creating unprecedented ecological problems. There is an urgent need for better understanding the patterns of natural lake water variability to improve water resource management and conservation. The incorporation of long-term cycles is particularly important for assessing low frequency &amp;#8211; high magnitude trends in lake water levels.&lt;/p&gt;&lt;p&gt;The Ohrid-Prespa Lake system is amongst the oldest permanent lake systems in Europe, with an age of &gt;1 million years, and hosts a globally significant biodiversity. The closed-basin Prespa Lakes are particularly sensitive to climatic variability with long-term water level changes informing on the dynamic balance between [1] runoff and precipitation supplying water to the lakes, and [2] water loss from the lakes by evaporation and underground karst outflow.&lt;/p&gt;&lt;p&gt;The large, ongoing, fall of the Prespa Lakes that started in 1987 threatens the biodiversity and water resources of the interconnected lake system. This decline is caused by climate change, specifically by decreases of 10% in precipitation and 25% in runoff, amplified by water abstraction. There is no precedent for this water level fall in the observational record (1951-present), although geological archives indicate equally low water levels at least twice over the past five millennia.&amp;#160;&lt;/p&gt;&lt;p&gt;Here we present the first quantified estimates of changes in the lake water balance over time that are based on the strong relationship between open water surface area and water loss. This quantification allows direct comparison of lake low- and highstand events across time and assessing magnitudes of regional hydro-climatic changes. This study uses a novel approach that reconstructs absolute lake levels and related open water surface areas for different past periods, using the landform-sediment record.&lt;/p&gt;&lt;p&gt;The hydro-climate of the Prespa catchment shows a drying trend of since the mid Holocene. The recent (2001-2018) lake lowstand is the most significant over the past 700 years in terms of water loss changes. A lake lowstand period of a similar magnitude occurred about 2000 years ago. The most extreme lowstand period over the past 5000 years occurred between 1100-800 years ago during the Medieval Climate Anomaly, when water loss changes were &gt;50% higher compared to the present lowstand. However, the renewed decline in lake level and surface area since 2019 requires close monitoring; if lake level falls a further 2m to 840m.a.s.l. it would become the largest recorded fall over the entire Holocene, with unknown impacts for the wider system.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Multiple Modern Methods of Blood Pressure Measurement and the 2018 European Society of Hypertesion Guidelines

2020 ◽  
Vol 16 (1) ◽  
pp. 126-132
Author(s):  
V. M. Gorbunov ◽  
E. Y. Fedorova ◽  
E. V. Platonova
Keyword(s):  
Blood Pressure ◽  
Blood Pressure Measurement ◽  
Measurement Methods ◽  
The Past ◽  
Measurement Methodology ◽  
Evidence Source ◽  
Esc Guidelines ◽  
Long Term Observation ◽  
Key Aspects

The new international guidelines on hypertension management have been issued in the past few years. The AHA (2017) and ESH (2018) Guidelines are similar in many key aspects. However, they differ substantially in the area of blood pressure (BP) measurement methodology. In this article, we aim to explain the ESC Guidelines position, specifically the conservative BP thresholds and a wider use of ambulatory BP measurement methods. In our opinion, the main reason behind this position is the introduction and a relatively widespread use of automatic office BP measurement (AOBP). On one hand, this method has questioned the results of the SPRINT trial – the key evidence source for the AHA Guidelines. On the other hand, AOBP has challenged the concept of “traditional office BP measurement”. Therefore, it is important to be aware of the current multiplicity of BP measurement methods and respective threshold values recommended for each method. It is essential to perform the office BP measurement correctly and thoroughly. Throughout all stages of the hypertensive patient management (diagnosis, antihypertensive treatment choice, and long-term observation), the use of out-of-clinic BP measurement is strongly advisable.

scholarly journals The response of diatom assemblages in a Jamaican coastal lagoon to hurricane and drought activity over the past millennium

The Holocene ◽  
2021 ◽  
pp. 095968362110190
Author(s):  
Charlotte A Heller ◽  
Neal Michelutti ◽  
Michael J Burn ◽  
Suzanne E Palmer ◽  
John P Smol
Keyword(s):  
Coastal Lagoon ◽  
Lake Level ◽  
Rainfall Variability ◽  
Diatom Assemblages ◽  
Chl A ◽  
Lake Level Changes ◽  
The Past ◽  
Hurricane Activity ◽  
Past Millennium

Reconstructing pre-industrial hurricane activity and aridity from natural archives places modern trends within the context of long-term natural variability. The first reconstruction of Atlantic hurricane activity in Jamaica was based on a sediment record previously obtained from a coastal lagoon. Specifically, an Extended Hurricane Activity (EHA) index was developed from high-resolution geochemical data that linked fluctuations in lake-level changes to rainfall variability associated with hurricane activity. Here, we analyse the same sediment core from which the EHA index was developed to assess the response of biological indicators, namely fossil diatom assemblages and sediment chlorophyll a (chl- a) concentrations, to hydrometeorological events (tropical cyclone-induced precipitation and droughts) over the past ~1500 years. The diatom assemblages responded sensitively to changes in salinity associated with lake-level changes driven by the balance of precipitation and evaporation. Aquatic production (inferred from sediment chl- a, which includes its main diagenetic products) and salinity (inferred from ITRAXTM µXRF chlorine counts) vary inversely following ca. 1300 CE, likely due to enhanced nutrient delivery from freshwater runoff during periods of elevated precipitation. Although the temporal resolution of our biological data is less-well resolved than that of the geochemical record, it generally tracks long-term trends in rainfall variability inferred by the EHA index over the past millennium. This further demonstrates the potential of using biological proxies from coastal lagoons to track past hurricane activity and aridity.

scholarly journals How I treat acquired aplastic anemia

Blood ◽  
2012 ◽  
Vol 120 (6) ◽  
pp. 1185-1196 ◽  
Author(s):  
Phillip Scheinberg ◽  
Neal S. Young
Keyword(s):  
Aplastic Anemia ◽  
Recent Literature ◽  
Bone Marrow Failure ◽  
Hematopoietic Stem ◽  
Blood Institute ◽  
The Past ◽  
National Heart Lung ◽  
Key Aspects ◽  
Practical Implications

Abstract Survival in severe aplastic anemia (SAA) has markedly improved in the past 4 decades because of advances in hematopoietic stem cell transplantation, immunosuppressive biologics and drugs, and supportive care. However, management of SAA patients remains challenging, both acutely in addressing the immediate consequences of pancytopenia and in the long term because of the disease's natural history and the consequences of therapy. Recent insights into pathophysiology have practical implications. We review key aspects of differential diagnosis, considerations in the choice of first- and second-line therapies, and the management of patients after immunosuppression, based on both a critical review of the recent literature and our large personal and research protocol experience of bone marrow failure in the Hematology Branch of the National Heart, Lung, and Blood Institute.

Early Medieval Great Hall Complexes in England: Temporality and Site Biographies

2020 ◽  
Vol 22 ◽  
pp. 50-67
Author(s):  
Neil Faulkner ◽  
Eleanor Blakelock
Keyword(s):  
Social Action ◽  
Temporal Dynamics ◽  
Eighth Century ◽  
Short Term ◽  
The Past ◽  
Spatial And Temporal Dynamics ◽  
The Social ◽  
Elite Identity ◽  
Site History

This paper offers a critical reconsideration of the social, spatial and temporal dynamics of sixth- to eighth-century great hall complexes in England. The major interpretative issues and constraints imposed by the data are considered, and the sites are then subject to comparative analysis across long-term and short-term temporal scales. The former highlights persistence of antecedent activity and centrality, the latter the ways in which the built environment was perceived in the past, structured social action, and was a medium for the construction and consolidation of elite identity and authority. Within the broad similarity that defines the site-type there is evidence for considerable diversity and complexity of site history and afterlife.

scholarly journals Long term O<sub>3</sub>-precursor relationships in Hong Kong: Field observation and model simulation

2017 ◽  
Author(s):  
Yu Wang ◽  
Hao Wang ◽  
Hai Guo ◽  
Xiaopu Lyu ◽  
Hairong Cheng ◽  
...  
Keyword(s):  
Hong Kong ◽  
Model Simulation ◽  
Ground Level ◽  
Effective Control ◽  
Photochemical Pollution ◽  
Mixing Ratios ◽  
The Past ◽  
Total Volatile Organic Compounds

Abstract. Over the past ten years (2005–2014), ground-level O3 in Hong Kong has consistently increased in all seasons except winter, despite the yearly reduction of its precursors, i.e., nitrogen oxides (NOx = O + NO2), total volatile organic compounds (TVOCs) and carbon monoxide (CO). To explain the contradictory phenomenon, an observation-based box model (OBM) coupled with CB05 mechanism was applied in order to understand the influence of both locally-produced O3 and regional transport. The simulation of locally-produced O3 showed an increasing trend in spring, a decreasing trend in autumn and no changes in summer and winter. The O3 increase in spring was caused by the net effect of more rapid decrease of NO titration and unchanged TVOC reactivity despite decreased TVOC mixing ratios, while the decreased local O3 formation in autumn was mainly due to the reduction of aromatic VOC mixing ratios and the TVOC reactivity and much slower decrease of NO titration. However, the decreased in-situ O3 formation in autumn was overridden by the regional contribution, resulting in elevated O3 observations. Furthermore, the OBM-derived relative incremental reactivity indicated that the O3 formation was VOC-limited in all seasons, and the long-term O3 formation was more sensitive to VOCs and less to NOx and CO in the past 10 years. In addition, the OBM results found that the contributions of aromatics to O3 formation decreased in all seasons of these years, particularly in autumn, likely due to effective control of solvent-related sources. In contrast, the contributions of alkenes increased, suggesting a continuing need to reduce traffic emissions. The findings provided updated information on photochemical pollution and its impact in Hong Kong.

scholarly journals A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps

2016 ◽  
Author(s):  
Bruno Wilhelm ◽  
Hendrik Vogel ◽  
Flavio S. Anselmetti
Keyword(s):  
Lake Sediment ◽  
Seismic Data ◽  
Flood Events ◽  
Italian Alps ◽  
Regional Seismicity ◽  
The Past ◽  
Event Layers ◽  
Regional Earthquake ◽  
Precipitation Events

Abstract. Mediterranean Alpine populations are particularly exposed to natural hazards like floods and earthquakes because of both the close Mediterranean humidity source and the seismically active Alpine region. Knowledge of long-term variability in flood and earthquake occurrences is of high value since it can be useful to improve risk assessment and mitigation. In this context, we explore the potential of a lake-sediment sequence from Lago Inferiore de Laures in Valle d'Aosta (Northern Italy) as a long-term record of past floods and earthquakes. The high-resolution sedimentological study revealed 77 event layers over the last ca. 270 years; 8 are interpreted as most probably induced by earthquakes and 68 by flood events. Comparison to historical seismic data suggests that the recorded earthquakes are strong (epicentral MSK intensity of VI–IX) and/or close to the lake (distance of 25–120 km). Compared to other lake-sediment sequences, Lago Inferiore de Laures sediments appear to be regionally the most sensitive to earthquake shaking, offering a great potential to reconstruct the past regional seismicity further back in time. Comparison to historical and palaeoflood records suggests that the flood signal reconstructed from Lago Inferiore de Laures sediments well represents the regional and (multi-)decennial variability of summer–autumn floods, in connection to Mediterranean mesoscale precipitation events. Overall, our results reveal the high potential of Lago Inferiore de Laures sediments to extend the regional earthquake and flood catalogues far back in time.

scholarly journals Long-term variations in the net inflow record for Lake Malawi

2016 ◽  
Vol 48 (3) ◽  
pp. 851-866 ◽  
Author(s):  
K. Sene ◽  
B. Piper ◽  
D. Wykeham ◽  
R. T. McSweeney ◽  
W. Tych ◽  
...  
Keyword(s):  
Lake Level ◽  
Lake Malawi ◽  
Flood Events ◽  
Lake Levels ◽  
Hydropower Generation ◽  
Unobserved Component ◽  
Periodic Behaviour ◽  
Component Approach ◽  
Long Term Trends

Lake Malawi is the third largest lake in Africa and plays an important role in water supply, hydropower generation, agriculture and fisheries in the region. Lake level observations started in the 1890s and anecdotal evidence of variations dates back to the early 1800s. A chronology of lake level and outflow variations is presented together with updated estimates for the net inflow to the lake. The inflow series and selected rainfall records were also analysed using an unobserved component approach and, although there was little evidence of long-term trends, there was some indication of increasing interannual variability in recent decades. A weak quasi-periodic behaviour was also noted with a period of approximately 4–8 years. The results provide useful insights into the severity of drought and flood events in the region since the 1890s and the potential for seasonal forecasting of lake levels and outflows.

Sign in / Sign up

Export Citation Format

Share Document