Rapid loss of firn pore space accelerates 21st century Greenland mass loss

in Geophysical Research Letters (2013), 40

Mass loss from the two major ice sheets and their contribution to global sea level rise is accelerating. In Antarctica, mass loss is dominated by increased flow velocities of outlet glaciers, following ... [more ▼]

Mass loss from the two major ice sheets and their contribution to global sea level rise is accelerating. In Antarctica, mass loss is dominated by increased flow velocities of outlet glaciers, following the thinning or disintegration of coastal ice shelves into which they flow. In contrast, ∼55% of post‒1992 Greenland ice sheet (GrIS) mass loss is accounted for by surface processes, notably increased meltwater runoff. A subtle process in the surface mass balance of the GrIS is the retention and refreezing of meltwater, currently preventing ∼40% of the meltwater to reach the ocean. Here we force a high‒resolution atmosphere/snow model with a mid‒range warming scenario (RCP4.5, 1970–2100), to show that rapid loss of firn pore space, by >50% at the end of the 21st century, quickly reduces this refreezing buffer. As a result, GrIS surface mass loss accelerates throughout the 21st century and its contribution to global sea level rise increases to 1.7 ±0.5 mm yr−1, more than four times the current value. [less ▲]

Bursty magnetic reconnection at Saturn's magnetosphere

in Geophysical Research Letters (2013)

Measurement and modeling of ablation of the bottom of supraglacial lakes in western Greenland

in Geophysical Research Letters (2012), 39(L02502), 5

We report measurements of ablation rates of the bottom of two supraglacial lakes and of temperatures at different depths collected during the summers of 2010 and 2011 in west Greenland. To our knowledge ... [more ▼]

We report measurements of ablation rates of the bottom of two supraglacial lakes and of temperatures at different depths collected during the summers of 2010 and 2011 in west Greenland. To our knowledge, this is the first time that such data sets are reported and discussed in the literature. The measured ablation rates at the bottom of the two lakes are of the order of ∼6 cm/day, versus a rate of ∼2.5–3 cm/day in the case of bare ice of surrounding areas. Though our measurements suggest the presence of a vertical temperature gradient, it is not possible to draw final conclusions as the measured gradient is smaller than the accuracy of our temperature sensors. In-situ measurements are compared with the results of a thermodynamic model forced with the outputs of a regional climate model. In general, the model is able to satisfactorily reproduce the measured quantities with RMSE of the order of 3–4 cm for the ablation and ∼1.5°C in the case of water temperature. Our results confirm that the ablation at the bottom of supraglacial lakes plays an important role on the overall lake volume with the ablation in the case of ice covered by a lake being 110–135% of that over bare ice at nearby locations. Beside ice sheet hydrological implications, melting at the bottom of a supraglacial lake might affect estimates of lake volume from spaceborne visible and near-infrared measurements. [less ▲]

Morphometric dating of the fluvial landscape response to a tectonic perturbation

in Geophysical Research Letters (2012), 39

Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low ... [more ▼]

Despite constant progress in numerical and field studies of landscape evolution, time evolution is still poorly constrained in many uplifted areas where low denudation rates prevent the use of low temperature thermochronology, especially outside high relief mountainous areas. Here, I show that regional statistics of the landscape metric R involving hypsometric integrals at three nested levels of a catchment are able to isolate the time effect on landscape geometry during the latter’s transient response to a tectonic perturbation. Analysis of 210 catchments from 9 regions of known uplift age worldwide shows that the regionally characteristic, R-derived SR index is in inverse power law relation with the time elapsed since a base level lowering. Suggesting a response time of 5 My, this finding has important implications for quantifying the rate of landform evolution and determining whether a landscape has reached steady-state form. [less ▲]

Quasi-periodic polar flares at Jupiter: A signature of pulsed dayside reconnections?

in Geophysical Research Letters (2011), 38

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds ... [more ▼]

The most dynamic part of the Jovian UV aurora is located inside the main auroral oval. This region is known to regularly show localized but dramatic enhancements on timescales of several tens of seconds, called polar flares. They have often been associated with the polar cusp, based on their location in the polar cap. The present study is based on the longest high-time resolution image sequences ever acquired by the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. We report the first observations of a regularity in the occurrence of these flares, with a timescale of 2-3 minutes. We use a magnetic flux mapping model to identify the region corresponding to these emissions in the equatorial plane: the radial distance ranges from 55 to 120 Jovian radii and the local times are between 10: 00 and 18: 00. The analogy with similar phenomena observed at Earth suggests that these quasi-periodic auroral flares could be related to pulsed reconnections at the dayside magnetopause. Indeed, the flares' projected location in the equatorial plane and their rate of re-occurrence show some similarities with the properties of the flux transfer events observed by the Pioneer and Voyager probes. [less ▲]

Venus OH nightglow distribution based on VIRTIS limb observations from Venus Express

in Geophysical Research Letters (2010), 37

The full set of VIRTIS‐M limb observations of the OH Venus nightglow has been analyzed to determine its characteristics. Based on 3328 limb profiles, we find that the mean peak intensity along the line of ... [more ▼]

The full set of VIRTIS‐M limb observations of the OH Venus nightglow has been analyzed to determine its characteristics. Based on 3328 limb profiles, we find that the mean peak intensity along the line of sight of the OH(deltaV = 1 sequence) is 0.35 MR and is located at 96.4 ± 5 km. The emission is highly variable and no dependence of the airglow layer altitude versus the antisolar angle is observed. The peak brightness appears to decrease away from the antisolar point even if the variability at a given location is very strong. Some correlation between the intensity of the OH and the O2(a1Delta) emissions is also observed, resumably because atomic oxygen is a common precursor to the formation of O2(a1Delta) and O3, whose reaction with H produces excited OH. Comparing our results with predictions from a photochemical model, a constant H flux does not match the simultaneous OH and O2 airglow observations. [less ▲]

Evaluation of sinks and sources of CO2 in the global coastal ocean using a spatially-explicit typology of estuaries and continental shelves

in Geophysical Research Letters (2010), 37

The exchange of CO2 between the atmosphere and the global coastal ocean was evaluated from a compilation of air-water CO2 fluxes scaled using a spatially-explicit global typology of inner estuaries ... [more ▼]

The exchange of CO2 between the atmosphere and the global coastal ocean was evaluated from a compilation of air-water CO2 fluxes scaled using a spatially-explicit global typology of inner estuaries (excluding outer estuaries such as large river deltas) and continental shelves. The computed emission of CO2 to the atmosphere from estuaries (+0.27 +/- 0.23 PgC yr(-1)) is similar to 26% to similar to 55% lower than previous estimates while the sink of atmospheric CO2 over continental shelf seas (-0.21 +/- 0.36 PgC yr(-1)) is at the low end of the range of previous estimates (-0.22 to -1.00 PgC yr(-1)). The air-sea CO2 flux per surface area over continental shelf seas (-0.7 +/- 1.2 molC m(-2) yr(-1)) is the double of the value in the open ocean based on the most recent CO2 climatology. The largest uncertainty of scaling approaches remains in the availability of CO2 data to describe the spatial variability, and to capture relevant temporal scales of variability. Citation: Laruelle, G. G., H. H. Durr, C. P. Slomp, and A. V. Borges (2010), Evaluation of sinks and sources of CO2 in the global coastal ocean using a spatially-explicit typology of estuaries and continental shelves, Geophys. Res. Lett., 37, L15607, doi:10.1029/2010GL043691. [less ▲]

Correction to ``Equatorward diffuse auroral emissions at Jupiter: Simultaneous HST and Galileo observations''

in Geophysical Research Letters (2009), 36

<A href="/journals/gl/gl0909/2009GL038676/">Abstract Available</A> from <A href="http://www.agu.org">http://www.agu.org</A>

Observations of Jovian polar auroral filaments

in Geophysical Research Letters (2009), 36

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ... [more ▼]

In this paper we report a phenomenon hitherto unobserved in Jupiter's ultraviolet polar auroras, specifically thin (~0.6° wide), long-lived quasi-sun-aligned polar auroral filaments (PAFs) of brightness ~100 kR spanning the highly variable region poleward of the main oval. This observation, made using Hubble Space Telescope images, is significant since no coherent structures have previously been observed in Jupiter's very high latitude auroral region, and it may help shed light on the dynamics of Jupiter's under-explored magnetotail. PAFs have been observed in 4 sets of observations over 6 days in 2007, and their occurrence appears to be independent of impinging solar wind conditions. The feature comprises two components: the section toward noon remains fixed in orientation toward the sun, while the anti-sunward section rotates. We estimate overall rotation rates of ~0--45% of corotation, values which may indicate the rotation rate of Jupiter's polar ionosphere and tail lobes. [less ▲]

Altitude of Saturn's aurora and its implications for the characteristic energy of precipitated electrons

in Geophysical Research Letters (2009), 36

Images of Saturn's aurora at the limb have been collected with the Advanced Camera for Surveys on board the Hubble Space Telescope. They show that the peak of Saturn's nightside emission is generally ... [more ▼]

Images of Saturn's aurora at the limb have been collected with the Advanced Camera for Surveys on board the Hubble Space Telescope. They show that the peak of Saturn's nightside emission is generally located 900-1300 km above the 1-bar level. On the other hand, methane and H[SUB]2[/SUB] columns overlying the aurora have been determined from the analysis of FUV and EUV spectra, respectively. Using a low-latitude model, these columns place the emission layer at or above 610 km. One possibility to solve this apparent discrepancy between imaging and spectral observations is to assume that the thermospheric temperature in the auroral region sharply increases at a higher pressure level than in the low-latitude regions. Using an electron transport code, we estimate the characteristic energy of the precipitated electrons derived from these observations to be in the range 1-5 keV using a low latitude model and 5-30 keV in case of the modified model. [less ▲]