Why do the dark and light ogives of Forbes bands have similar surface mass balances?

ABSTRACTBand ogives are a striking and enigmatic feature of Mer de Glace glacier flow. The surface mass balances (SMBs) of these ogives have been thoroughly investigated over a period of 12 years. We find similar cumulative SMBs over this period, ranging between −64.1 and −66.2 m w.e., on the dark and light ogives even though the dark ogive albedo is ~40% lower than that of the light ogives. We, therefore, looked for another process that could compensate for the large difference of absorbed short-wave radiation between dark and light ogives. Based on in situ roughness measurements, our numerical modeling experiments demonstrate that a significant difference in turbulent flux over the dark and light ogives due to different surface roughnesses could compensate for the difference in radiative forcing. Our results discard theories for the genesis of band ogives that are based on the assumption of a strong ice ablation contrast between dark and light ogives. More generally, our study demonstrates that future roughness changes are as important to analyze as the radiative impacts of a potential increase of aerosols or debris at the surface of glaciers.

Download Full-text

Long-range terrestrial laser scanning measurements of annual and intra-annual mass balances for Urumqi Glacier No. 1, eastern Tien Shan, China

The Cryosphere ◽

10.5194/tc-13-2361-2019 ◽

2019 ◽

Vol 13 (9) ◽

pp. 2361-2383 ◽

Cited By ~ 8

Author(s):

Chunhai Xu ◽

Zhongqin Li ◽

Huilin Li ◽

Feiteng Wang ◽

Ping Zhou

Keyword(s):

Mass Balance ◽

Long Range ◽

Tien Shan ◽

Glacier Mass Balance ◽

Surface Mass Balance ◽

Mass Balances ◽

Surface Mass ◽

Mass Conversion ◽

Geodetic Mass Balance

Abstract. The direct glaciological method provides in situ observations of annual or seasonal surface mass balance, but can only be implemented through a succession of intensive in situ measurements of field networks of stakes and snow pits. This has contributed to glacier surface mass-balance measurements being sparse and often discontinuous in the Tien Shan. Nevertheless, long-term glacier mass-balance measurements are the basis for understanding climate–glacier interactions and projecting future water availability for glacierized catchments in the Tien Shan. Riegl VZ®-6000 long-range terrestrial laser scanner (TLS), typically using class 3B laser beams, is exceptionally well suited for repeated glacier mapping, and thus determination of annual and seasonal geodetic mass balance. This paper introduces the applied TLS for monitoring summer and annual surface elevation and geodetic mass changes of Urumqi Glacier No. 1 as well as delineating accurate glacier boundaries for 2 consecutive mass-balance years (2015–2017), and discusses the potential of such technology in glaciological applications. Three-dimensional changes of ice and firn–snow bodies and the corresponding densities were considered for the volume-to-mass conversion. The glacier showed pronounced thinning and mass loss for the four investigated periods; glacier-wide geodetic mass balance in the mass-balance year 2015–2016 was slightly more negative than in 2016–2017. Statistical comparison shows that agreement between the glaciological and geodetic mass balances can be considered satisfactory, indicating that the TLS system yields accurate results and has the potential to monitor remote and inaccessible glacier areas where no glaciological measurements are available as the vertical velocity component of the glacier is negligible. For wide applications of the TLS in glaciology, we should use stable scan positions and in-situ-measured densities of snow–firn to establish volume-to-mass conversion.

Download Full-text

Atmospheric ionization and cloud radiative forcing

Scientific Reports ◽

10.1038/s41598-021-99033-1 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Henrik Svensmark ◽

Jacob Svensmark ◽

Martin Bødker Enghoff ◽

Nir J. Shaviv

Keyword(s):

Radiative Forcing ◽

Cloud Condensation Nuclei ◽

Short Wave ◽

Satellite Observations ◽

Cloud Formation ◽

Wave Radiation ◽

Substantial Impact ◽

Radiative Balance ◽

Cloud Radiative Forcing ◽

Atmospheric Ionization

AbstractAtmospheric ionization produced by cosmic rays has been suspected to influence aerosols and clouds, but its actual importance has been questioned. If changes in atmospheric ionization have a substantial impact on clouds, one would expect to observe significant responses in Earth’s energy budget. Here it is shown that the average of the five strongest week-long decreases in atmospheric ionization coincides with changes in the average net radiative balance of 1.7 W/m$$^2$$ 2 (median value: 1.2 W/m$$^2$$ 2 ) using CERES satellite observations. Simultaneous satellite observations of clouds show that these variations are mainly caused by changes in the short-wave radiation of low liquid clouds along with small changes in the long-wave radiation, and are almost exclusively located over the pristine areas of the oceans. These observed radiation and cloud changes are consistent with a link in which atmospheric ionization modulates aerosol's formation and growth, which survive to cloud condensation nuclei and ultimately affect cloud formation and thereby temporarily the radiative balance of Earth.

Download Full-text

Monitoring glacier albedo as a proxy to derive summer and annual surface mass balances from optical remote-sensing data

The Cryosphere ◽

10.5194/tc-12-271-2018 ◽

2018 ◽

Vol 12 (1) ◽

pp. 271-286 ◽

Cited By ~ 8

Author(s):

Lucas Davaze ◽

Antoine Rabatel ◽

Yves Arnaud ◽

Pascal Sirguey ◽

Delphine Six ◽

...

Keyword(s):

Mass Balance ◽

Surface Albedo ◽

In Situ Measurements ◽

Surface Mass Balance ◽

Mass Balances ◽

Equilibrium Line Altitude ◽

Surface Mass ◽

Minimum Surface ◽

Summer Minimum

Abstract. Less than 0.25 % of the 250 000 glaciers inventoried in the Randolph Glacier Inventory (RGI V.5) are currently monitored with in situ measurements of surface mass balance. Increasing this archive is very challenging, especially using time-consuming methods based on in situ measurements, and complementary methods are required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, on board the TERRA satellite. Recent studies revealed substantial relationships between summer minimum glacier-wide surface albedo and annual surface mass balance, because this minimum surface albedo is directly related to the accumulation–area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance data are available, our study conducted on the period 2000–2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. For the ablation season, the integrated summer surface albedo is significantly correlated with the summer surface mass balance of the six glaciers seasonally monitored. These results are promising to monitor both annual and summer glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images. A sensitivity study on the computed cloud masks revealed a high confidence in the retrieved albedo maps, restricting the number of omission errors. Albedo retrieval artifacts have been detected for topographically incised glaciers, highlighting limitations in the shadow correction algorithm, although inter-annual comparisons are not affected by systematic errors.

Download Full-text

Snow farming: conserving snow over the summer season

The Cryosphere ◽

10.5194/tc-12-385-2018 ◽

2018 ◽

Vol 12 (1) ◽

pp. 385-400 ◽

Cited By ~ 10

Author(s):

Thomas Grünewald ◽

Fabian Wolfsperger ◽

Michael Lehning

Keyword(s):

Laser Scanning ◽

Short Wave ◽

Heat Fluxes ◽

Wave Radiation ◽

Measured Quantity ◽

Wind Speeds ◽

Air Temperatures ◽

Physically Based ◽

The Difference ◽

The One

Abstract. Summer storage of snow for tourism has seen an increasing interest in the last years. Covering large snow piles with materials such as sawdust enables more than two-thirds of the initial snow volume to be conserved. We present detailed mass balance measurements of two sawdust-covered snow piles obtained by terrestrial laser scanning during summer 2015. Results indicate that 74 and 63 % of the snow volume remained over the summer for piles in Davos, Switzerland and Martell, Italy. If snow mass is considered instead of volume, the values increase to 83 and 72 %. The difference is attributed to settling and densification of the snow. Additionally, we adapted the one-dimensional, physically based snow cover model SNOWPACK to perform simulations of the sawdust-covered snow piles. Model results and measurements agreed extremely well at the point scale. Moreover, we analysed the contribution of the different terms of the surface energy balance to snow ablation for a pile covered with a 40 cm thick sawdust layer and a pile without insulation. Short-wave radiation was the dominant source of energy for both scenarios, but the moist sawdust caused strong cooling by long-wave emission and negative sensible and latent heat fluxes. This cooling effect reduces the energy available for melt by up to a factor of 12. As a result only 9 % of the net short-wave energy remained available for melt. Finally, sensitivity studies of the parameters thickness of the sawdust layer, air temperature, precipitation and wind speed were performed. We show that sawdust thickness has a tremendous effect on snow loss. Higher air temperatures and wind speeds increase snow ablation but less significantly. No significant effect of additional precipitation could be found as the sawdust remained wet during the entire summer with the measured quantity of rain. Setting precipitation amounts to zero, however, strongly increased melt. Overall, the 40 cm sawdust provides sufficient protection for mid-elevation (approx. 1500 m a.s.l.) Alpine climates and can be managed with reasonable effort.

Download Full-text

Geodetic point surface mass balances: a new approach to determine point surface mass balances on glaciers from remote sensing measurements

The Cryosphere ◽

10.5194/tc-15-1259-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1259-1276

Author(s):

Christian Vincent ◽

Diego Cusicanqui ◽

Bruno Jourdain ◽

Olivier Laarman ◽

Delphine Six ◽

...

Keyword(s):

Remote Sensing ◽

Mass Balance ◽

Mass Balances ◽

New Approach ◽

Surface Mass ◽

Assess Climate Change ◽

Satellite Sensors ◽

Aerial Vehicle ◽

Velocity Changes

Abstract. Mass balance observations are very useful to assess climate change in different regions of the world. As opposed to glacier-wide mass balances which are influenced by the dynamic response of each glacier, point mass balances provide a direct climatic signal that depends on surface accumulation and ablation only. Unfortunately, major efforts are required to conduct in situ measurements on glaciers. Here, we propose a new approach that determines point surface mass balances from remote sensing observations. We call this balance the geodetic point surface mass balance. From observations and modelling performed on the Argentière and Mer de Glace glaciers over the last decade, we show that the vertical ice flow velocity changes are small in areas of low bedrock slope. Therefore, assuming constant vertical velocities in time for such areas and provided that the vertical velocities have been measured for at least 1 year in the past, our method can be used to reconstruct annual point surface mass balances from surface elevations and horizontal velocities alone. We demonstrate that the annual point surface mass balances can be reconstructed with an accuracy of about 0.3 m of water equivalent per year (m w.e. a−1) using the vertical velocities observed over the previous years and data from unmanned aerial vehicle images. Given the recent improvements of satellite sensors, it should be possible to apply this method to high-spatial-resolution satellite images as well.

Download Full-text

The Body Temperature of Tenebrionid Beetles in the Namib Desert of Southern Africa

Journal of Experimental Biology ◽

10.1242/jeb.55.1.253 ◽

1971 ◽

Vol 55 (1) ◽

pp. 253-272

Author(s):

E. B. EDNEY

Keyword(s):

Heat Balance ◽

Muscular Activity ◽

Selective Advantage ◽

Short Wave ◽

The Body ◽

Wave Radiation ◽

Consistent Difference ◽

Angle Of Incidence ◽

Lethal Temperatures ◽

The Difference

1. In direct sunshine the abdomen of living Onymacris brincki, which is covered by white elytra, was 3-4 °C cooler than its thorax, while in the same conditions the abdomen and thorax of O. rugatipemtis, which is an entirely black beetle, had the same temperature. Since similar effects were observed in dead beetles, the warmer thorax was not due to muscular activity. When the white elytra of brincki were covered with carbon black, its abdominal temperature rose to equal that of rugatipenntis. Models, made of pieces of black and white elytra, showed similar effects. 2. The smaller species Stenocara eburnea (with white elytra) showed a smaller and less consistent temperature depression when compared with the similar-sized species S. depressa (which is black). Abdomens of O. rugatipennis, O. laeviceps and Physosterna cribripes (all large black beetles) were from 3-5 °C wanner than O. brincki, but showed no consistent difference among themselves. 3. When O. rugatipennis was oriented head-on to the sun in its natural environment its thorax was about 4 °C cooler than when its long axis was normal to the sun's rays. Beetles exposed to sunshine were 12-15 °C warmer than they were in the shade. When transferred from one to the other, the greater part of temperature equilibration occurred in about 2 min and equilibration was complete in about 4 min. 4. Observation suggested that beetles thermoregulate by moving between sunshine and shade. Measurements showed that a beetle exposed to alternating periods of 10 sec in sunshine and 30 sec in shade reached a steady temperature of about 33 °C, while the reverse conditions (10 sec in the shade and 30 sec in sunshine) led to a temperature of about 38 °C. In continuous alternations thoracic temperatures remained constant within about 1 °C. 5. Laboratory experiments in which the angle of incidence of the sun's rays was varied through 180° confirmed the field results and showed that white elytra lower the abdominal temperature of living and dead beetles. 6. Upper lethal temperatures for 30 min in saturated air varied from 50 °C for the desert tenebrionid Onymacris plana to 42.5 °C for the mesic species Trigonopus capicola. In general, upper lethal temperatures correlated well with habitat and habit. 7. Making certain assumptions, analysis of the heat balance of beetles during one exposure in sunshine suggests that the difference between the white elytra of brincki and the black ones of rugatipennis as regards the amount of short-wave radiation reflected is 0.227 cal cm-2 min-1, and further, that the reflectivities of the two surfaces are 79% and 38% respectively. 8. The selective advantage of white elytra probably has little to do with heat balance; the vivid contrast between white and black suggests that the pattern may be aposematic.

Download Full-text

Comparison between the change in total corneal astigmatism and actual change in refractive astigmatism in transepithelial photorefractive keratectomy (tPRK), laser in situ keratomileusis (LASIK) and femtosecond laser assisted laser in situ keratomileusis (FsLASIK)

European Journal of Ophthalmology ◽

10.1177/11206721211059327 ◽

2021 ◽

pp. 112067212110593

Author(s):

Maja Bohac ◽

Alma Biscevic ◽

Violeta Shijakova ◽

Ivan Gabric ◽

Kresimir Gabric ◽

...

Keyword(s):

Corneal Astigmatism ◽

Laser In Situ Keratomileusis ◽

Significant Difference ◽

Actual Change ◽

The Difference ◽

Induced Changes ◽

Surgically Induced ◽

Refraction Data ◽

Total Corneal Astigmatism

Purpose To compare changes in astigmatism by refraction and total corneal astigmatism after tPRK, LASIK and FsLASIK. Setting Specialty Eye Hospital Svjetlost, Zagreb, Croatia. Design Partially masked, semi-randomized, prospective, case-by-case, interventional, clinical study. Methods Patients with a stable refraction (-0.75DS to −8.00DS, astigmatism ≤1.00DC) underwent tPRK, LASIK or FsLASIK without complication. Astigmatism was measured at both corneal surfaces over the central 3.2 mm zone (approximately using Pentacam HRTM) preoperatively and 3 months postoperatively. Pentacam and refraction data were subjected to vector analysis to calculate the surgically induced changes in i) total corneal astigmatism (SIATCA) ii) any astigmatism by refraction (SIAR) and the vectorial difference (DV) between SIATCA and SIAR. Results Reporting key findings (p < .01), there was a significant difference between mean SIATCA and SIAR powers after tPRK (75eyes) but not after LASIK (100eyes) or FsLASIK (100eyes). Mean (±sd,95% CIs) values for DV powers were, tPRK −1.13DC(±0.71, −1.29 to −0.97), LASIK −0.39DC(±0.23,-0.44 to −0.34), FsLASIK −0.55DC(±0.38,-0.62 to −0.47). The differences were significant. For the tPRK and FsLASIK cases, linear regression revealed significant associations between I) SIATCA (x) &DV (z) powers (tPRK z = 1.586x-0.179, r = 0.767, p < .01; FsLASIK z = 0.442x-0.303, r = .484,p < .01), II) sines of SIATCA (x1) &DV (z1) axes (tPRK, z1 = 0.523 × 1 + 0.394, r = .650,p < .01; FsLASIK z1 = 0.460 × 1-0.308, r = .465,p < .01). Conclusions tPRK is more prone to unintended changes in astigmatism. The difference between SIATCA & SIAR after tPRK or FsLASIK is mediated by SIATCA. Photoablating deeper regions of the cornea reduces the gap between SIATCA & SIAR.

Download Full-text

Elevation change, mass balance, dynamics and surging of Langjökull, Iceland from 1997 to 2007

Journal of Glaciology ◽

10.1017/jog.2016.55 ◽

2016 ◽

Vol 62 (233) ◽

pp. 497-511 ◽

Cited By ~ 3

Author(s):

ALLEN POPE ◽

IAN C. WILLIS ◽

FINNUR PÁLSSON ◽

NEIL S. ARNOLD ◽

W. GARETH REES ◽

...

Keyword(s):

Mass Balance ◽

Source Area ◽

Lapse Rate ◽

Balance Model ◽

Mass Balances ◽

Elevation Change ◽

Ice Dynamics ◽

Surface Mass ◽

Ice Caps

ABSTRACTGlaciers and ice caps around the world are changing quickly, with surge-type behaviour superimposed upon climatic forcing. Here, we study Iceland's second largest ice cap, Langjökull, which has both surge- and non-surge-type outlets. By differencing elevation change with surface mass balance, we estimate the contribution of ice dynamics to elevation change. We use DEMs, in situ stake measurements, regional reanalyses and a mass-balance model to calculate the vertical ice velocity. Thus, we not only compare the geodetic, modelled and glaciological mass balances, but also map spatial variations in glacier dynamics. Maps of emergence and submergence velocity successfully highlight the 1998 surge and subsequent quiescence of one of Langjökull's outlets by visualizing both source and sink areas. In addition to observing the extent of traditional surge behaviour (i.e. mass transfer from the accumulation area to the ablation area followed by recharge of the source area), we see peripheral areas where the surge impinged upon an adjacent ridge and subsequently retreated. While mass balances are largely in good agreement, discrepancies between modelled and geodetic mass balance may be explained by inaccurate estimates of precipitation, saturated adiabatic lapse rate or degree-day factors. Nevertheless, the study was ultimately able to investigate dynamic surge behaviour in the absence of in situ measurements during the surge.

Download Full-text

Monitoring of glacier albedo from optical remote-sensing data: application to seasonal and annual surface mass balances quantification in the French Alps for the 2000–2015 period

10.5194/tc-2017-49 ◽

2017 ◽

Author(s):

Lucas Davaze ◽

Antoine Rabatel ◽

Yves Arnaud ◽

Pascal Sirguey ◽

Delphine Six ◽

...

Keyword(s):

Mass Balance ◽

Surface Albedo ◽

In Situ Measurements ◽

Surface Mass Balance ◽

Mass Balances ◽

Surface Mass ◽

French Alps ◽

Minimum Surface ◽

Summer Minimum

Abstract. Less than 0.25 % of the 250,000 glaciers inventoried in the Randolph Glacier Inventory (RGI V.5) are currently monitored with in situ measurements of surface mass balance. Increasing this archive is very challenging, especially using time-consuming methods based on in situ measurements, and complementary methods are required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, onboard of TERRA satellite. Recent studies revealed substantial relationships between summer minimum glacier-wide surface albedo and annual surface mass balance, because this minimum surface albedo is directly related to the accumulation-area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance are available, our study conducted on the period 2000–2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. At the seasonal scale, the integrated summer surface albedo is significantly correlated with the summer surface mass balance of the six glaciers seasonally monitored. For the winter season, four of the six glaciers showed a significant correlation when linking the winter surface mass balance and the integrated winter surface albedo, using glacier-dependent thresholds to filter the albedo signal (threshold from 0.53 to 0.76). These results are promising to monitor both annual and seasonal glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images. A sensitivity study on the computed cloud masks revealed a high confidence in the retrieved albedo maps, restricting the number of omission errors. Albedo retrieval artifacts have been detected for topographically incised glaciers, highlighting limitations in the shadows correction algorithm, although inter-annual comparisons are not affected by systematic errors.

Download Full-text

Mapping radiation transfer through sea ice using a remotely operated vehicle (ROV)

The Cryosphere Discussions ◽

10.5194/tcd-6-3613-2012 ◽

2012 ◽

Vol 6 (5) ◽

pp. 3613-3646 ◽

Cited By ~ 1

Author(s):

M. Nicolaus ◽

C. Katlein

Keyword(s):

Sea Ice ◽

Primary Source ◽

Short Wave ◽

Wave Radiation ◽

Spectral Radiance ◽

Data Sets ◽

Polar Regions ◽

Remotely Operated Vehicle ◽

Data Set

Abstract. Light (solar short-wave radiation) transmission into and through sea ice is of high importance for various processes in Polar Regions. The amount of energy transferred through the ice determines formation and melt of sea ice and finally contributes to warming of the uppermost ocean. At the same time the amount and distribution of light, as the primary source of energy, is of critical importance for sea-ice associated organisms and bio-geochemical processes. However, our current understanding of these processes and their interdisciplinary interactions is still sparse. The main reason is that the under-ice environment is difficult to access and measurements require large logistical and instrumental efforts. Particularly, it was not possible to map light conditions under sea ice over larger areas. Here we present a detailed methodical description of operating spectral radiometers on a remotely operated vehicle (ROV) in the Central Arctic under sea ice. This new measurement concept resulted in a~most comprehensive data set of spectral radiance and irradiance under and above sea ice, complemented through various additional in-situ measurements of sea-ice, snow, and surface properties. Finally, such data sets allow quantifying the spatial variability of light under sea ice, especially highlighting differences between ponded and white ice as well as different ice types.

Download Full-text