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Thirty-one GPS geodetic measurements of crustal uplift in southernmost South America determined extraordinarily high trend rates (> 35 mm/yr) in the north-central part of the Southern Patagonian Icefield. These trends have a coherent pattern, motivating a refined viscoelastic glacial isostatic adjustment model to explain the observations. Two end-member models provide good fits: both require a lithospheric thickness of 36.5 ± 5.3 km. However, one end-member has a mantle viscosity near =1.6 ×10 18 Pa s and an ice collapse rate from the Little Ice Age (LIA) maximum comparable to a lowest recent estimate of 1995-2012 ice loss at about −11 Gt/yr. In contrast, the other end-member has much larger viscosity: = 8.0 ×10 18 Pa s, half the post-LIA collapse rate, and a steadily rising loss rate in the twentieth century after AD 1943, reaching −25.9 Gt/yr during 1995-2012.

RESUMENSe presenta una sintesis de la investigacion glaciologica realizada en Chile durante las ultimas decadas, incluyendo los inventarios existentes, los balances de masa y las variaciones de glaciares, todo lo cual se analiza con relacion a los cambios climaticos que han afectado el pais. En Chile se han medido variaciones frontales historicas para casi 100 glaciares, que representan el 5,6% del total de glaciares inventariados hasta ahora en el pais. De ellos, solo el 6% ha presentado un estado neto de avance en los periodos estudiados, destacando el del glaciar Pio XI con un promedio de +206 m a-l para el periodo 1945-1 997. Un 7 % de los glaciares estudiados no han experimentado un cambio significativo, mientras que cerca de un 87 %, han tenido tasas de variacion negativas, desde pocos metros por ano, hasta un maximo de -278 m a-1 en el glaciar Amalia para el periodo 1945-1 986. No obstante existir comportamientos de glaciares que obedecen a factores no climaticos, se confirma que la mayoria de las fluctuaciones de los glaciares son generadas por los aumentos de temperatura detectados en numerosas estaciones de Chile, algunas de las cuales muestran para las ultimas tres decadas, aumentos de casi el doble de la tendencia secular. Tambien han incidido significativamente en las variaciones de los glaciares, los ciclos interanuales con anomalias pluviometricas extremas y la tendencia de algunas estaciones que han experimentado un descenso de los montos totales anuales de precipitacion. Finalmente, la mayor frecuencia de fenomenos El Nino / Oscilacion del Sur (ENOS), han tenido un rol significativo en la variabilidad interanual de las precipitaciones y temperaturas, generando respuestas distintas a nivel regional. Frente a dichas tendencias climaticas, se espera que el retroceso de glaciares continue, que los balances de masa mantengan sus tendencias negativas y que los adelgazamientos aumenten, todo lo cual impactara la dotacion y disponibilidad de recursos hidricos en el pais.Palabras claves: Glaciares, cambio climatico, ENOS, balance de masa. Recent glacier variations in Chile ABSTRACTA synthesis of glaciological research carried out in Chile during the last decades is presented, including existing inventories, mass balance and glacier variations, which are related to the regional climate change. In Chile, almost 100 glaciers have been measured in terms of their historical frontal variations. They represent 5,6% of the total inventoried glaciers of the country. Only 6% of the inventoried glaciers show a net advance during the study penod, especially glaciar Pio XI with an average of 206 m a-1 between 1945-1997. A 7 % of the studied glaciers show no significant change, while 87% show a negative rate of variation, ranging from a few meters per year to a maximum of 278 m a-1 at glaciar Amalia for the period 1945-1986. Although there are some glaciers with variations related to non-climatic effects, most of the glacier variations are driven by the temperature increase which has been detected in several stations ...

Aircraft observations of wind and temperature collected by airport surveillance radars [Mode-S Enhanced Surveillance (Mode-S EHS)] were assimilated in the Consortium for Small-Scale Modeling Kilometre-scale Ensemble Data Assimilation (COSMO-KENDA), which couples an ensemble Kalman filter to a 40-member ensemble of the convection permitting COSMO-DE model. The number of observing aircrafts in Mode-S EHS was about 15 times larger than in the AMDAR system. In the comparison of both aircraft observation systems, a similar observation error standard deviation was diagnosed for wind. For temperature, a larger error was diagnosed for Mode-S EHS. With the high density of Mode-S EHS observations, a reduction of temperature and wind error in forecasts of 1 and 3 hours was found mainly in the flight level and less near the surface. The amount of Mode-S EHS data was reduced by random thinning to test the effect of a varying observation density. With the current data assimilation setup, a saturation of the forecast error reduction was apparent when more than 50% of the Mode-S EHS data were assimilated. Forecast kinetic energy spectra indicated that the reduction in error is related to analysis updates on all scales resolved by COSMO-DE.

An idealized convective test bed for the local ensemble transform Kalman filter (LETKF) is set up to perform storm-scale data assimilation of simulated Doppler radar observations. Convective systems with lifetimes exceeding 6 h are triggered in a doubly periodic domain. Perfect-model experiments are used to investigate the limited predictability in precipitation forecasts by comparing analysis schemes that resolve different length scales. Starting from a high-resolution reference scheme with 8-km covariance localization and observations with 2-km resolution on a 5-min cycle, an experimental hierarchy is set up by successively choosing a larger covariance localization radius of 32 km, observations that are horizontally averaged by a factor of 4, a coarser resolution in the calculation of the analysis weights, and a cycling interval of 20 min. After 3 h of assimilation, the high-resolution analysis scheme is clearly superior to the configurations with coarser scales in terms of RMS error and field-oriented measures. The difference is associated with the observation resolution and a larger localization radius required for filter convergence with coarse observations. The high-resolution analysis leads to better forecasts for the first hour, but after 3 hours, the forecast quality of the schemes is indistinguishable. The more rapid error growth in forecasts from the high-resolution analysis appears to be associated with a limited predictability of the small scales, but also with gravity wave noise and spurious convective cells. The latter suggests that the field is in some sense less balanced, or less consistent with the model dynamics, than in the coarser-resolution analysis.

Patriot Hills is located at 80˚18’ S, 81˚22’W, at the southernmost end of the Heritage Range, Ellsworth Mountains, West Antarctica. A comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996–97 is presented. Ablation/accumulation rates measured at a network of stakes in Horseshoe Valley show average accumulation of 70 kg m–2 a–1 in the central part of the valley, and a maximum ablation of ∼170 kg m–2 a–1 at the edge of the blue-ice area, close to Patriot Hills. Changes in the surface elevation of the glacier measured at 81 stakes in the period 1995–97 show a mean thickening of +0.43±0.42ma–1, which, considering the uncertainties, indicates that the ice sheet around Patriot Hills is in near steady state. Surface velocities, in combination with ice thicknesses obtained by ground-based radio-echo sounding, are used to compute the ice flux across the Horseshoe Valley transect. A total outflow of 0.44 ±0.08km3 a–1 is obtained. Considering a catchment area for Horseshoe Valley of 1087 km2 upstream from the flow transect, and a net accumulation rate of 100 kg m–2 a–1, a total input of 0.11 ±0.04km3 a–1 by snow accumulation is obtained. Accepting a near-equilibrium condition for the ice sheet, the flux difference, i.e. 0.33 km3 a–1, must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the Heritage Range. If Horseshoe Valley is not in steady state but is thickening, the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet. New data are needed to elucidate this.

Glaciar Pio XI, the largest glacier in South America, has experienced an advance during the 20th century, unlike virtually all other glaciers in Patagonia, which are retreating rapidly. Climatological records of the last 80 years are analyzed together with ice-velocity and meteorological measurements collected during November 1995 near the tidewater front of Glaciar Pio XI. Ice speeds of up to 50 m d−1 were measured, the maximum occurring during a period when air temperatures were high.