Modelling variable glacier lapse rates using ERA‐Interim reanalysis climatology: an evaluation at Vestari‐ Hagafellsjökull, Langjökull, Iceland

Hodgkins, Richard; Carr, Simon; Pálsson, Finnur; Guðmundsson, Snævarr; Björnsson, Helgi

doi:10.1002/joc.3440

Cited by 10 publications

(15 citation statements)

References 27 publications

(72 reference statements)

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“…This lends credence to the suggestion that TIMs are sensitive to lapse rate values and demands longer‐term analyses of lapse rates with respect to air temperatures (e.g. Gardner and Sharp, ; Gardner et al ., ; Hodgkins et al ., ). Such interannual contrasts in synoptic influences will certainly define the relationship between melt and T a because clouds and inversions both have marked influence on longwave radiation fluxes (Zhang et al ., ; Zhang et al ., ).…”

Section: Discussionmentioning

confidence: 99%

Examination of a physically based, high‐resolution, distributed Arctic temperature‐index melt model, on Midtre Lovénbreen, Svalbard

Irvine‐Fynn

Hanna

Barrand

et al. 2012

Hydrological Processes

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Improvements in our ability to model runoff from glaciers remain an important scientific goal. This paper describes a new temperature-radiation-index glacier melt model specifically enhanced for use in High-Arctic environments, utilising high temporal and spatial resolution datasets while retaining relatively modest data requirements. The model employs several physically constrained parameters and was tuned using a lidar-derived surface elevation model of Midtre LovÃ©nbreen, meteorological data from sites spanning ~70 of the glacier's area-altitude distribution and periodic ablation surveys during the 2005 melt season. The model explained 80 of the variance in observed ablation across the glacier, an improvement of ~40 on a simplified energy balance model (EBM), yet equivalent to the performance of a full EBM employed at the same location. Model performance was assessed further by comparing potential and measured runoff from the catchment and through application to an earlier (2004) melt season. The additive model form and consideration of a priori parameters for the Arctic locality were shown to be beneficial, with a planimetry correction eliminating systematic errors in potential runoff. Further parameterisations defining modelled incident radiation failed to yield significant improvements to model output. Our results suggest that such enhanced melt models may perform well for singular melt seasons, yet are highly sensitive to the choice of lapse rates, and their transferability to different locations and seasons may be limited. While modelling ablation requires detailed consideration of the transition between snow and ice melt, our study suggests that description of the ratio between radiative and turbulent heat fluxes may provide a useful step towards dynamic parameterisation of melt factors in temperature-index models. Â© 2012 John Wiley & Sons, Ltd

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Section: Discussionmentioning

confidence: 99%

Examination of a physically based, high‐resolution, distributed Arctic temperature‐index melt model, on Midtre Lovénbreen, Svalbard

Irvine‐Fynn

Hanna

Barrand

et al. 2012

Hydrological Processes

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“…The four lapse rates used are as follows (also summarized in Table ): MLR: the measured lapse rate between the calibration AWS, 597 and 998 m a.s.l. (this rate is variable). SALR: the MMLR over the entire interval April to October, which is close enough to be indistinguishable from the saturated adiabatic rate, 0.60 °C 100 m –1 (this rate is constant). mean summer lapse rate (MSLR): the MMLR for the interval June to August only, 0.47 °C 100 m –1 (this rate is constant) VLR: a modelled VLR following the method of Gardner et al (), adapted for Vestari‐Hagafellsjökull by Hodgkins et al () using 750 hPa ERA‐Interim temperature, converted to daily, standardized anomalies (750 T ; see section on Data sources for details on ERA‐Interim reanalysis data and Hodgkins et al , , for full details of the lapse‐rate model). In this case, the model is calibrated using the measured lapse rate between the 597‐ and the 998‐m AWS in the 37‐day interval 25 April to 31 May (i.e.…”

Section: Methodsmentioning

confidence: 98%

“…The range of near‐surface lapse rates that has been used in recent energy‐ and mass‐balance studies at Icelandic glaciers is 0.45 to 0.70 °C 100 m –1 (Jóhannesson et al , ; Jóhannesson, ; Flowers et al , , ; Aðalgeirsdóttir et al , ; Guðmundsson et al , ; Hodgkins et al , ). Most lapse‐rate values have either been assumed (in which case 0.60 °C 100 m –1 is the modal choice) or determined through model calibration, rather than directly measured.…”

Section: Methodsmentioning

confidence: 99%

“…This relationship was used to develop regression‐based VLR models predicting lapse rates from daily, standardized anomalies in 750 hPa reanalysis temperature. Hodgkins et al () applied the same approach to temperature series from Vestari‐Hagafellsjökull, after finding that the 750‐hPa temperature anomalies derived from ERA‐Interim climatology were also significantly correlated with near‐surface temperatures there: overestimation of cumulative June–September positive degree days (PDDs, sometimes called daily positive temperatures) for a validation season was reduced by 11% when a VLR model was used to extrapolate temperatures from 1100 to 500 m a.s.l. on the glacier, compared with an SALR model.…”

Section: Methodsmentioning

confidence: 99%

“…A range of studies (Greuell and Böhm, ; Braun and Hock, ; Hanna et al , ; Klok et al , ; Marshall et al , ; Gardner and Sharp, ; Gardner et al , ; Hodgkins et al , ) have now shown that near‐surface lapse rates measured over melting glacier surfaces tend to be lower than saturated adiabatic values, primarily as a result of the lower near‐surface temperature sensitivity to free‐atmosphere temperature change in the presence of melting (Gardner et al , ). The American Meteorological Society convention is followed below: near‐surface lapse rate is deemed positive when air temperature decreases as elevation increases.…”

Section: Introductionmentioning

confidence: 99%

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Sensitivity analysis of temperature‐index melt simulations to near‐surface lapse rates and degree‐day factors at Vestari‐Hagafellsjökull, Langjökull, Iceland

Hodgkins

Carr

Pálsson

et al. 2012

Hydrological Processes

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Abstract:The performance of temperature-index melt models is particularly affected by the choice of near-surface lapse rate used to determine the sum of positive daily temperatures at different elevations, and by the choice of factor used to relate this sum to the rate of melting. Data from the Langjökull ice cap are used in this study to quantify the influence of lapse-rate and degree-day factor variation on temperatureindex melt simulations. The lapse rate was significantly lower during summer than in spring or autumn, as a result of diabatic cooling, reducing boundary-layer sensitivity to free-air temperature change. The summer lapse rate was also significantly lower than the saturated adiabatic lapse rate. A sensitivity of approximately 600 mm water equivalent (w.e.) cumulative June-August melt per 0.1 C 100 m -1 change in lapse rate was found across a 500-m altitude range. The sensitivity to a 1-mm w.e. C -1 day -1 change in degree-day factors varied more: from approximately 500 mm w.e. cumulative summer melt at low elevation to approximately 200 mm w.e. at high elevation, reflecting the decline in melt rates associated with the greater persistence of snow with increasing altitude. The determination of a degreeday factor for snow is complicated by the densification of the ageing snowpack, but the application of a parameterization for near-surface density on the basis of albedo helped account for the development of snow water equivalence. Lapse rate was parameterized as a function of standardized anomalies in 750 hPa reanalysis temperature and significantly improved the simulation of cumulative summer melt compared with models applying the saturated adiabatic lapse rate.

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Dyke to sill deflection in the shallow heterogeneous crust during glacier retreat: part I

Drymoni,

Tibaldi,

Bonali

et al. 2023

Bull Volcanol

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Dykes and sills occupy Mode I (extension), Mode II (shear), or hybrid mode fractures and most of the time transport and store magma from deep reservoirs to the surface. Subject to their successful propagation, they feed volcanic eruptions. Yet, dykes and sills can also stall and become arrested as a result of the crust’s heterogeneous and anisotropic characteristics. Dykes can become deflected at mechanical discontinuities to form sills, and vice versa. Although several studies have examined dyke propagation in heterogeneous and anisotropic crustal segments before, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear. Here, we coupled field observations with 2D FEM numerical modelling to explore the mechanical conditions that encourage (or not) dyke-sill transitions in volcanotectonic or glacial settings. We used as a field example the Stardalur cone sheet-laccolith system, which lies on the Esja peninsula, close to the western rift zone, NW of the southern part of the Icelandic rift. The laccolith is composed of several vertical dykes that transition into sills and form a unique stacked sill ‘flower’ structure. Here, we investigate whether the Stardalur laccolith was formed under the influence of stresses caused by glacial retreat due to thickness variations (0–1 km) in addition to regional and local tectonic stresses (1–3 MPa extension or compression) and varied magma overpressure (1–30 MPa), as well as the influence of the mechanical properties of the lava/hyaloclastite contact. Our results show that the observed field structure in non-glacial regimes was formed as a result of either the mechanical (Young’s modulus) contrast of the lava/hyaloclastite contact or a compressional regime due to pre-existing dykes or faulting. In the glacial domain, the extensional stress field below the ice cap encouraged the formation of the laccolith as the glacier became thinner (subject to a lower vertical load). In all cases, the local stress field influenced dyke to sill deflection in both volcanotectonic regimes.

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Modelling variable glacier lapse rates using ERA‐Interim reanalysis climatology: an evaluation at Vestari‐ Hagafellsjökull, Langjökull, Iceland

Cited by 10 publications

References 27 publications

Examination of a physically based, high‐resolution, distributed Arctic temperature‐index melt model, on Midtre Lovénbreen, Svalbard

Examination of a physically based, high‐resolution, distributed Arctic temperature‐index melt model, on Midtre Lovénbreen, Svalbard

Sensitivity analysis of temperature‐index melt simulations to near‐surface lapse rates and degree‐day factors at Vestari‐Hagafellsjökull, Langjökull, Iceland

Dyke to sill deflection in the shallow heterogeneous crust during glacier retreat: part I

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