scholarly journals Surface melt and the importance of water flow – an analysis based on high-resolution unmanned aerial vehicle (UAV) data for an Arctic glacier

2020 ◽  
Vol 14 (2) ◽  
pp. 549-563 ◽  
Author(s):  
Eleanor A. Bash ◽  
Brian J. Moorman
Keyword(s):  
Water Flow ◽  
Model Performance ◽  
Model Error ◽  
Two Dimensions ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Technological Advances ◽  
Flow Features ◽  
Surface Melt ◽  
The Difference

Abstract. Models of glacier surface melt are commonly used in studies of glacier mass balance and runoff; however, with limited data available, most models are validated based on ablation stakes and data from automatic weather stations (AWSs). The technological advances of unmanned aerial vehicles (UAVs) and structure from motion (SfM) have made it possible to measure glacier surface melt in detail over larger portions of a glacier. In this study, we use melt measured using SfM processing of UAV imagery to assess the performance of an energy balance (EB) and enhanced temperature index (ETI) melt model in two dimensions. Imagery collected over a portion of the ablation zone of Fountain Glacier, Nunavut, on 21, 23, and 24 July 2016 was previously used to determine distributed surface melt. An AWS on the glacier provides some measured inputs for both models as well as an additional check on model performance. Modelled incoming solar radiation and albedo derived from UAV imagery are also used as inputs for both models, which were used to estimate melt from 21 to 24 July 2016. Both models estimate total melt at the AWS within 16 % of observations (4 % for ETI). Across the study area the median model error, calculated as the difference between modelled and measured melt (EB = −0.064 m, ETI = −0.050 m), is within the uncertainty of the measurements. The errors in both models were strongly correlated to the density of water flow features on the glacier surface. The relation between water flow and model error suggests that energy from surface water flow contributes significantly to surface melt on Fountain Glacier. Deep surface streams with highly asymmetrical banks are observed on Fountain Glacier, but the processes leading to their formation are missing in the model assessed here. The failure of the model to capture flow-induced melt would lead to significant underestimation of surface melt should the model be used to project future change.

scholarly journals Assessing the performance of a distributed radiation-temperature melt model on an Arctic glacier using UAV data

2019 ◽  
Author(s):  
Eleanor A. Bash ◽  
Brian J. Moorman
Keyword(s):  
Water Flow ◽  
Model Error ◽  
Two Dimensions ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Technological Advances ◽  
Surface Water Flow ◽  
Flow Features ◽  
Surface Melt ◽  
The Difference

Abstract. Enhanced temperature index (ETI) models of glacier surface melt are commonly used in studies of glacier mass balance and runoff. With limited data available most models are validated based on ablation stakes and data from automatic weather stations (AWS). With the technological advances of unmanned aerial vehicles (UAVs) and structure-from-motion (SfM), it is possible to measure glacier surface melt in detail over larger portions of a glacier. In this study, we use melt measured using SfM processing of UAV imagery to assess the performance of an ETI melt model in two-dimensions. Imagery collected over a portion of the ablation zone of Fountain Glacier, NU, on July 21 and 24, 2016 was previously used to determine distributed surface melt. Incoming solar radiation and temperature measured at the AWS, along with albedo derived from UAV imagery, are used as inputs for the model which was used to estimate melt from July 21–24, 2016. Modelled melt agrees with melt measured at the AWS within ±0.010 m. Across the study area the median model error (−0.044 m), calculated as the difference between measured and modelled melt, is within the uncertainty of the measurements. A strong link was found between the model error and glacier surface aspect with higher errors linked to south aspects. The highest errors were also linked to the density of water flow features on the glacier surface. The relation between water flow and model error suggests that energy from surface water flow is contributing significantly to surface melt on Fountain Glacier. Deep surface streams with highly asymmetrical banks are observed on Fountain Glacier, but the processes leading to their formation are missing in the model assessed here. The failure of the model to capture flow-induced melt and to under-estimate melt on south aspects would lead to significant underestimation of surface melt should the model be used to project future change.

Temperate Alpine glacier surface dynamics linked to collapsing subglacial conduits

2021 ◽  
Author(s):  
Pascal Egli ◽  
Stuart Lane ◽  
James Irving ◽  
Bruno Belotti
Keyword(s):  
Three Dimensional ◽  
Swiss Alps ◽  
Glacier Retreat ◽  
Collapse Mechanism ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Alpine Glacier ◽  
Surface Loss ◽  
Ice Surface ◽  
Surface Melt

<p>If tongues of temperate Alpine glaciers are subjected to high temperatures their topography may change rapidly due to the effects of differential melt related to aspect and debris cover. Independent of local surface melt, the position of subglacial conduits may have an important influence on ice creep and so on changes in topography at the ice surface. This reflects analyses that suggest that subglacial conduits at glacier margins may not be permanently pressurised; and that creep closure rates are insufficient to close subglacial conduits completely. Rapid climate warming may exacerbate this process, due both to surface-melt driven glacier thinning and over-enlargement of conduits due to high upstream melt rates. Over-enlarged conduits that are not permanently pressurised would lead to the development of structural weaknesses and eventual collapse of the ice surface into the conduits. We hypothesise that this collapse mechanism could represent an important and alternative driver of rapid glacier retreat.</p><p>In this paper we combine: (1) an extensive survey of glacier margin collapse in the Swiss Alps with (2) intensive monitoring of the dynamics of such collapse at the Otemma Glacier in the south-western Swiss Alps. Daily UAV surveys were undertaken at a high spatial resolution and with precise and accurate ground control. These datasets were used to generate surface change information using SfM-MVS photogrammetry. Surfaces of difference showed surface loss that could not be related to ablation alone. Combining them with three-dimensional ground-penetrating radar (GPR) surveys in the same zone showed that the surface loss was coincident spatially with the positions of sub-glacial conduits, for ice thicknesses between 20 m and 50 m. We show that this form of subglacial conduit collapse is also happening for several other glaciers in the Swiss Alps, and that this mechanism of snout collapse and glacier retreat has become more common than has hitherto been the case. It also leads to temporal patterns of glacier margin retreat that differ from those that might be expected due to glacier mass balance and ice mass flux effects alone.</p>

Quality of life in Hungarian polio survivors

2021 ◽  
Author(s):  
Erika Viktória Miszory ◽  
Melinda Járomi ◽  
Annamária Pakai
Keyword(s):  
Quality Of Life ◽  
Mental Health ◽  
Sample Selection ◽  
Cross Sectional Study ◽  
Two Dimensions ◽  
Cross Sectional ◽  
Emotional Role ◽  
The Difference ◽  
Polio Survivors

Abstract Aim The number of Hungarian polio patients can be estimated at approximately 3000. Polio infection is currently affecting people 56–65 years of age. The aim of the study was to reveal the quality of life of patients living with polio virus in Hungary. Subject and methods The quantitative cross-sectional study was conducted in January–April 2017 among polyomyelitis patients living in Hungary. In the non-random, targeted, expert sample selection, the target group was composed of patients infected with poliovirus (N = 268). We have excluded those who refused to sign the consent statement. Our data collection method was an SF-36 questionnaire. Using the IBM SPSS Statistics Version 22 program, descriptive and mathematical statistics (χ2-test) were calculated (p < 0.05). Results The mean age of the members of the examined population is 63.5 years; 68.1% were women and 31.90% were men. The majority of the respondents were infected by the polyovirus in 1956 (11.9%), 1957 (24.3%), and 1959 (19.5%). Polio patients, with the exception of two dimensions (mental health, social operation), on the scale of 100 do not reach the “average” quality of life (physical functioning 23 points, functional role 36 points, emotional role 47 points, body pain 48 points, general health 42 points, vitality 50 points, health change 31 points). Conclusion The quality of life of polio patients is far below the dimensions of physical function, while the difference in mental health compared to healthy people is minimal. It would be important to educate health professionals about the existing disease, to develop an effective rehabilitation method.

scholarly journals Application of an improved surface energy balance model to two large valley glaciers in the St. Elias Mountains, Yukon

2020 ◽  
pp. 1-16
Author(s):  
Tim Hill ◽  
Christine F. Dow ◽  
Eleanor A. Bash ◽  
Luke Copland
Keyword(s):  
Energy Balance ◽  
Surface Energy ◽  
Surface Energy Balance ◽  
Shortwave Radiation ◽  
Balance Model ◽  
Landsat 8 ◽  
Glacier Surface ◽  
Ice Dynamics ◽  
Surface Melt

Abstract Glacier surficial melt rates are commonly modelled using surface energy balance (SEB) models, with outputs applied to extend point-based mass-balance measurements to regional scales, assess water resource availability, examine supraglacial hydrology and to investigate the relationship between surface melt and ice dynamics. We present an improved SEB model that addresses the primary limitations of existing models by: (1) deriving high-resolution (30 m) surface albedo from Landsat 8 imagery, (2) calculating shadows cast onto the glacier surface by high-relief topography to model incident shortwave radiation, (3) developing an algorithm to map debris sufficiently thick to insulate the glacier surface and (4) presenting a formulation of the SEB model coupled to a subsurface heat conduction model. We drive the model with 6 years of in situ meteorological data from Kaskawulsh Glacier and Nàłùdäy (Lowell) Glacier in the St. Elias Mountains, Yukon, Canada, and validate outputs against in situ measurements. Modelled seasonal melt agrees with observations within 9% across a range of elevations on both glaciers in years with high-quality in situ observations. We recommend applying the model to investigate the impacts of surface melt for individual glaciers when sufficient input data are available.

scholarly journals THE VALUE OF ROBUST STATISTICAL FORECASTS IN THE COVID-19 PANDEMIC

2021 ◽  
Vol 256 ◽  
pp. 19-43
Author(s):  
Jennifer L. Castle ◽  
Jurgen A. Doornik ◽  
David F. Hendry
Keyword(s):  
Structural Change ◽  
Measurement Errors ◽  
Epidemiological Models ◽  
Short Term ◽  
Data Measurement ◽  
Policy Interventions ◽  
Changing Trends ◽  
Technological Advances ◽  
The Difference ◽  
The Uk

The Covid-19 pandemic has put forecasting under the spotlight, pitting epidemiological models against extrapolative time-series devices. We have been producing real-time short-term forecasts of confirmed cases and deaths using robust statistical models since 20 March 2020. The forecasts are adaptive to abrupt structural change, a major feature of the pandemic data due to data measurement errors, definitional and testing changes, policy interventions, technological advances and rapidly changing trends. The pandemic has also led to abrupt structural change in macroeconomic outcomes. Using the same methods, we forecast aggregate UK unemployment over the pandemic. The forecasts rapidly adapt to the employment policies implemented when the UK entered the first lockdown. The difference between our statistical and theory based forecasts provides a measure of the effect of furlough policies on stabilising unemployment, establishing useful scenarios had furlough policies not been implemented.

Non-linear dynamics, chaos, complexity and enclaves in granitoid magmas

1996 ◽  
Vol 87 (1-2) ◽  
pp. 217-223 ◽  
Author(s):  
James Flinders ◽  
John D. Clemens
Keyword(s):  
Deterministic Chaos ◽  
Interfacial Area ◽  
Two Dimensions ◽  
Mixing Processes ◽  
Nd Isotope ◽  
Natural Systems ◽  
Non Linear ◽  
The Difference ◽  
Magma System ◽  
Isotope Systematics

ABSTRACT:Most natural systems display non-linear dynamic behaviour. This should be true for magma mingling and mixing processes, which may be chaotic. The equations that most nearly represent how a chaotic natural system behaves are insoluble, so modelling involves linearisation. The difference between the solution of the linearised and ‘true’ equation is assumed to be small because the discarded terms are assumed to be unimportant. This may be very misleading because the importance of such terms is both unknown and unknowable. Linearised equations are generally poor descriptors of nature and are incapable of either predicting or retrodicting the evolution of most natural systems. Viewed in two dimensions, the mixing of two or more visually contrasting fluids produces patterns by folding and stretching. This increases the interfacial area and reduces striation thickness. This provides visual analogues of the deterministic chaos within a dynamic magma system, in which an enclave magma is mingling and mixing with a host magma. Here, two initially adjacent enclave blobs may be driven arbitrarily and exponentially far apart, while undergoing independent (and possibly dissimilar) changes in their composition. Examples are given of the wildly different morphologies, chemical characteristics and Nd isotope systematics of microgranitoid enclaves within individual felsic magmas, and it is concluded that these contrasts represent different stages in the temporal evolution of a complex magma system driven by nonlinear dynamics. If this is true, there are major implications for the interpretation of the parts played by enclaves in the genesis and evolution of granitoid magmas.

scholarly journals An alternative way to evaluate chemistry-transport model variability

2017 ◽  
Vol 10 (3) ◽  
pp. 1199-1208 ◽  
Author(s):  
Laurent Menut ◽  
Sylvain Mailler ◽  
Bertrand Bessagnet ◽  
Guillaume Siour ◽  
Augustin Colette ◽  
...  
Keyword(s):  
Transport Model ◽  
Model Performance ◽  
Error Statistics ◽  
Chemistry Transport Model ◽  
Temporal Correlations ◽  
Time Period ◽  
The Difference ◽  
Model Variability ◽  
Spatial Locations ◽  
Statistical Indicators

Abstract. A simple and complementary model evaluation technique for regional chemistry transport is discussed. The methodology is based on the concept that we can learn about model performance by comparing the simulation results with observational data available for time periods other than the period originally targeted. First, the statistical indicators selected in this study (spatial and temporal correlations) are computed for a given time period, using colocated observation and simulation data in time and space. Second, the same indicators are used to calculate scores for several other years while conserving the spatial locations and Julian days of the year. The difference between the results provides useful insights on the model capability to reproduce the observed day-to-day and spatial variability. In order to synthesize the large amount of results, a new indicator is proposed, designed to compare several error statistics between all the years of validation and to quantify whether the period and area being studied were well captured by the model for the correct reasons.

Perception of Risk as Related to Choice in a Two-Dimensional Risk Situation

1978 ◽  
Vol 43 (3_suppl) ◽  
pp. 1059-1062 ◽  
Author(s):  
John W. Dickson
Keyword(s):  
Risky Choice ◽  
Expected Value ◽  
Two Dimensions ◽  
Choice Situation ◽  
Two Dimensional ◽  
Objective Risk ◽  
Subjective Risk ◽  
Risk Situation ◽  
The Difference ◽  
Two Alternatives

A risky choice was created by manipulating two dimensions of risk for 21 managers attending a conference. The first dimension varied risk by altering the difference in expected value between two alternatives of widely differing variance. The second dimension varied the expectancy of achieving a particular outcome. Whereas choice was significantly related to both dimensions of risk, it was not significantly related to estimates of the subjective risk inherent in the choice situation. It appears that subjective risk does not mediate between objective risk and choice.

scholarly journals Woody species do not differ in dormancy progression: differences in time to budbreak due to forcing and cold hardiness

2021 ◽  
Author(s):  
Al Kovaleski
Keyword(s):  
Maximum Rate ◽  
Path Length ◽  
Cold Hardiness ◽  
Woody Species ◽  
Two Dimensions ◽  
Spring Phenology ◽  
Wide Range ◽  
The Difference ◽  
Response To Temperature ◽  
Phenological Phases

AbstractBudbreak is one of the most observed and studied phenological phases in perennial plants. Two dimensions of exposure to temperature are generally used to model budbreak: accumulation of time spent at low temperatures (chilling); and accumulation of heat units (forcing). These two effects have a well-established negative correlation: the more chilling, the less forcing required for budbreak. Furthermore, temperate plant species are assumed to vary in amount of chilling required to complete endodormancy and begin the transition to breaking bud. Still, prediction of budbreak remains a challenge. The present work demonstrates across a wide range of species how bud cold hardiness must be accounted for to study dormancy and accurately predict time to budbreak. Cold hardiness defines the path length to budbreak, meaning the difference between the cold hardiness buds attain during the winter, and the cold hardiness at which deacclimated buds are predicted to open. This distance varies among species and throughout winter within a species. Increases in rate of cold hardiness loss (deacclimation) measured throughout winter show that chilling controls deacclimation potential – the proportion of the maximum rate response attained at high chill accumulation – which has a sigmoid relationship to chilling accumulation. For forcing, rates of deacclimation increase non-linearly in response to temperature. Comparisons of deacclimation potential show a dormancy progresses similarly for all species. This observation suggests that comparisons of physiologic and genetic control of dormancy requires an understanding of cold hardiness dynamics and the necessity for an update of the framework for studying dormancy and its effects on spring phenology.

scholarly journals Comparison of direct and geodetic mass balances on a multi-annual time scale

2010 ◽  
Vol 4 (3) ◽  
pp. 1151-1194
Author(s):  
A. Fischer
Keyword(s):  
Mass Balance ◽  
Direct Method ◽  
Mean Difference ◽  
Published Data ◽  
Glacier Mass Balance ◽  
Mass Balances ◽  
Direct Data ◽  
The Mean ◽  
The Difference ◽  
Geodetic Mass Balance

Abstract. Glacier mass balance is measured with the direct or the geodetic method. In this study, the geodetic mass balances of six Austrian glaciers in 19 periods between 1953 and 2006 are compared to the direct mass balances in the same periods. The mean annual geodetic mass balance for all periods is −0.5 m w.e./year. The mean difference between the geodetic and the direct data is −0.7 m w.e., the minimum −7.3 m w.e. and the maximum 5.6 m w.e. The accuracy of geodetic mass balance resulting from the accuracy of the DEMs ranges from 2 m w.e. for photogrammetric data to 0.002 m w.e. for LIDAR data. Basal melt, seasonal snow cover and density changes of the surface layer contribute up to 0.7 m w.e. for the period of 10 years to the difference to the direct method. The characteristics of published data of Griesgletscher, Gulkana Glacier, Lemon Creek glacier, South Cascade, Storbreen, Storglaciären, and Zongo Glacier is similar to these Austrian glaciers. For 26 analyzed periods with an average length of 18 years the mean difference between the geodetic and the direct data is −0.4 m w.e., the minimum −7.2 m w.e. and the maximum 3.6 m w.e. Longer periods between the acquisition of the DEMs do not necessarily result in a higher accuracy of the geodetic mass balance. Specific glaciers show specific trends of the difference between the direct and the geodetic data according to their type and state. In conclusion, geodetic and direct mass balance data are complementary, but differ systematically.

Sign in / Sign up

Export Citation Format

Share Document