Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

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Climate Change 2007: The Physical Science Basis.

The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Glacial melting in the Tibetan Plateau affects the water resources of millions of people. This study finds that—partly owing to changes in atmospheric circulations and precipitation patterns—the most intensive glacier shrinkage is in the Himalayan region, whereas glacial retreat in the Pamir Plateau region is less apparent.

Different glacier status with atmospheric circulations in Tibetan Plateau and surroundings

[1] Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

Expression of active tectonics in erosional landscapes

Here we present the first results of quality assessment of height retrieval by CryoSat­2 over the snow and ice covered Karakoram region. We simulate the successive areas tracked by CryoSat in SARIN mode, compare them to glacier regions and estimate the region of interest covered by CS2.

https://hal.archives-ouvertes.fr/hal-00973393/document

Evaluation of CryoSat-2 for height retrieval over the Himalayan range

In this paper, we process TanDEM-X scenes, acquired between May 2012 and November 2013, with the use of a high-resolution DEM obtained from Pleiades images, to derive 5 new DEMs in the Mont Blanc area, by mean of differential radar interferometry (D-InSAR). The vertical precision of the DEMs estimated off ice is in the range 1.92–3.10 m. The comparison between the DEMs derived from optical and radar sensors at close dates allows use to estimate the penetration of the radar signal into snow and ice. It can reach 7 m in dry snow and ice, for elevations higher than 3500 m in October and 2500 m in February. This difference must be taken into account when deriving glaciers mass balance, especially over short periods.

Elevation changes and X-band ice and snow penetration inferred from TanDEM-X data of the Mont-Blanc area

Dynamic flood topographies in the Terai region of Nepal

Terrestrial Radar Interferometry (TRI) has several advantages for measuring glacier velocity. These ground-based systems alleviate problems associated with the long revisit times of satellites, and provide higher spatial sampling compared to GPS-based approaches. TRI is the technique of choice for rapidly moving glaciers, especially their terminal zones, which tend to exhibit high spatial and temporal variability. In this study, we use the Gamma Portable Radar Interferometer (GPRI) to measure the velocity of Breidamerkurjokull, a marine-terminating outlet glacier on the southeastern coast of Iceland, and compare it to TerraSAR-X data taken shortly after. We document significant temporal and spatial variability of ice velocity within 800 meters of the calving front.

Monitoring a glacier in southeastern Iceland with the portable Terrestrial Radar Interferometer

. Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson
ice shelves have undergone speedup, thinning, and rapid grounding-line
retreat in recent years, leaving them in a state likely conducive to future
retreat. We conducted a suite of numerical model simulations of these
glaciers and compared the results to observations to determine the processes
controlling their recent evolution. The model simulations indicate that the
state of these glaciers in the 1990s was not inherently unstable, i.e., that
small perturbations to the grounding line would not necessarily have caused
the large retreat that has been observed. Instead, sustained, elevated melt
at the grounding line was needed to cause the observed retreat. Weakening of
the margins of Crosson Ice Shelf may have hastened the onset of
grounding-line retreat but is unlikely to have initiated these rapid changes
without an accompanying increase in melt. In the simulations that most
closely match the observed thinning, speedup, and retreat, modeled
grounding-line retreat and ice loss continue unabated throughout the
21st century, and subsequent retreat along Smith Glacier's trough
appears likely. Given the rapid progression of grounding-line retreat in the
model simulations, thinning associated with the retreat of Smith Glacier may
reach the ice divide and undermine a portion of the Thwaites catchment as
quickly as changes initiated at the Thwaites terminus.

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Noel Gourmelen

Papers

Evaluation of CryoSat-2 for height retrieval over the Himalayan range

Elevation changes and X-band ice and snow penetration inferred from TanDEM-X data of the Mont-Blanc area

Dynamic flood topographies in the Terai region of Nepal

Monitoring a glacier in southeastern Iceland with the portable Terrestrial Radar Interferometer

Melt at grounding line controls observed and future retreat of Smith, Pope, and Kohler glaciers