Jost von Hardenberg

INO - Istituto Nazionale di Ottica, Florens, Tuscany, Italy

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Publications (102)232.93 Total impact

  • No preview · Article · Feb 2016 · Journal of Hydrometeorology
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    ABSTRACT: Turbulent Rayleigh–Bénard convection is characterized by the presence of intense coherent structures called plumes. With additional system rotation along an axis parallel to gravity, individual plumes can merge together to form larger thermal structures. In this paper, we propose an efficient way to quantify plume merging using three accessible statistics: plume vorticity, plume number and plume area. Using this approach, we show that plume merging is more intense for moderate values of the Rossby number, around . Merging is spatially localized near boundary layers, determining what we call the “merging region”. Inside this region, vertical heat transport by individual plumes is enhanced. Outside the merging region, on the other hand, rotating plumes transport less heat than in the non-rotating case. Since the total heat transport is enhanced by rotation in the turbulent regime explored here, this implies that outside the merging region the vortical structures of background turbulence transport heat more effectively than in the non-rotating case.
    No preview · Article · Feb 2016
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    Full-text · Article · Oct 2015 · Ecological Entomology
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    Full-text · Article · Sep 2015 · Ecological Entomology
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    Paolo Davini · Jost von Hardenberg · Susanna Corti
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    ABSTRACT: Atlantic Multidecadal Variability (AMV) is known for influencing the mid-latitude climate variability, especially over the European region. This letter assesses the impact of the wintertime AMV in a group of 200-year atmospheric-only numerical experiments, in which the atmosphere is forced with positive and negative AMV-like sea surface temperatures (SSTs) and sea ice concentration patterns. Anomalies are applied separately to the whole North Atlantic ocean, to the extratropics (north of 30° N) and to the tropics (between 0° and 30° N). Results show that AMV anomalies considerably affect the North Atlantic Oscillation (NAO), the jet stream variability and the frequency of atmospheric blocking over the Euro-Atlantic sector, resulting in a negative (positive) NAO during positive (negative) AMV. It is found that the bulk of the signal is originated in the tropics and it is associated with a Gill-like response—an anomalous upper tropospheric streamfunction dipole over the tropical Atlantic driven by the SST anomalies—and with the subsequent structural change of the upper-tropospheric jet, which affects the propagation of Rossby waves in the North Atlantic. Conversely, the NAO response is almost negligible when the AMV anomalies are applied only to the extratropics, suggesting that the relevance of SST anomalies along the North Atlantic frontal zone may be overestimated.
    Full-text · Article · Sep 2015 · Environmental Research Letters
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    ABSTRACT: A coupled aerosol-atmosphere–ocean-sea ice climate model is used to explore the interaction between aerosols and the Indian summer monsoon precipitation on seasonal-to-interannual time scales. Results show that when increased aerosol loading is found on the Himalayas slopes in the pre-monsoon period (April-May), intensification of early monsoon rainfall over India and increased low-level westerly flow follow, in agreement with the Elevated-Heat-Pump mechanism. The increase in rainfall during the early monsoon season has a cooling effect on the land surface. In the same period, enhanced surface cooling may also be amplified through solar dimming by more cloudiness and aerosol loading, via increased dust transported by low-level westerly flow. The surface cooling causes subsequent reduction in monsoon rainfall in July-August over India. The time-lagged nature of the reasonably realistic response of the model to aerosol forcing suggests that absorbing aerosols, besides their potential key roles in impacting monsoon water cycle and climate, may influence the seasonal variability of the Indian summer monsoon.
    No preview · Article · Aug 2015 · Journal of Geophysical Research Atmospheres
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    Elisa Palazzi · Jost von Hardenberg · Silvia Terzago · Antonello Provenzale
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    ABSTRACT: This work analyzes the properties of precipitation in the Hindu-Kush Karakoram Himalaya region as simulated by thirty-two state-of-the-art global climate models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5). We separately consider the Hindu-Kush Karakoram (HKK) in the west and the Himalaya in the east. These two regions are characterized by different precipitation climatologies, which are associated with different circulation patterns. Historical model simulations are compared with the Climate Research Unit (CRU) and Global Precipitation Climatology Centre (GPCC) precipitation data in the period 1901–2005. Future precipitation is analyzed for the two representative concentration pathways (RCP) RCP 4.5 and RCP 8.5 scenarios. We find that the multi-model ensemble mean and most individual models exhibit a wet bias with respect to CRU and GPCC observations in both regions and for all seasons. The models differ greatly in the seasonal climatology of precipitation which they reproduce in the HKK. The CMIP5 models predict wetter future conditions in the Himalaya in summer, with a gradual precipitation increase throughout the 21st century. Wetter summer future conditions are also predicted by most models in the RCP 8.5 scenario for the HKK, while on average no significant change can be detected in winter precipitation for both regions. In general, no single model (or group of models) emerges as that providing the best results for all the statistics considered, and the large spread in the behavior of individual models suggests to consider multi-model ensemble means with extreme care.
    Full-text · Article · Jul 2015 · Climate Dynamics
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    ABSTRACT: We explore the impact of different resolutions, convective closures, and microphysical parameterizations on the representation of precipitation statistics (climatology, seasonal cycle, and intense events) in 20-yr-long simulations over Europe with the regional climateWeather Research and Forecasting (WRF) Model. The simulations are forced in the period 1979-98, using as boundary conditions the ERA-Interim fields over the European region. Special attention is paid to the representation of precipitation in the Alpine area. We consider spatial resolutions ranging from 0.118 to 0.0378, allowing for an explicit representation of convection at the highest resolution. Our results show that while there is a good overall agreement between observed and modeled precipitation patterns, the model outputs display a positive precipitation bias, particularly in winter. The choice of the microphysics scheme is shown to significantly affect the statistics of intense events. High resolution and explicitly resolved convection help to considerably reduce precipitation biases in summer and the reproduction of precipitation statistics.
    Full-text · Article · May 2015 · Journal of Hydrometeorology
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    Marco Turco · Elisa Palazzi · Jost von Hardenberg · Antonello Provenzale
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    ABSTRACT: We quantify climate change hot-spots from observations, taking into account the differences in precipitation and temperature statistics (mean, variability and extremes) between 1981-2010 and 1951-1980. Areas in the Amazon, the Sahel, tropical West Africa, Indonesia and central eastern Asia emerge as primary observed hot-spots. The main contributing factors are the global increase in mean temperatures, the intensification of extreme hot-season occurrence in low-latitude regions and the decrease of precipitation over central Africa. Temperature and precipitation variability have been substantially stable over the past decades, with only a few areas showing significant changes against the background climate variability. The regions identified from the observations are remarkably similar to those defined from projections of global climate models under a “business-as-usual” scenario, indicating that climate change hot-spots are robust and persistent over time. These results provide a useful background to develop global policy decisions on adaptation and mitigation priorities over near-time horizons.
    Full-text · Article · Apr 2015 · Geophysical Research Letters
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    P. Davini · J. von Hardenberg · L. Filippi · A. Provenzale
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    ABSTRACT: We show that the absence of the Greenland ice sheet would have important consequences on the North Atlantic Ocean circulation, even without taking into account the effect of the freshwater input to the ocean from ice melting. These effects are investigated in a 600-year long coupled ocean–atmosphere simulation with the high-resolution global climate model EC-Earth 3.0.1. Once a new equilibrium is established, a cooling of Eurasia and of the North Atlantic and a poleward shift of the subtropical jet are observed. These hemispheric changes are ascribed to a weakening of the Atlantic Meridional Overturning Circulation (AMOC) by about 12%. We attribute this slowdown to a reduction in salinity of the Arctic basin and to the related change of the mass and salt transport through the Fram Strait – a consequence of the new surface wind pattern over the lower orography. This idealized experiment illustrates the sensitivity of the AMOC to local surface winds.
    Full-text · Article · Feb 2015 · Geophysical Research Letters
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    J. von Hardenberg · D. Goluskin · A. Provenzale · E. A. Spiegel
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    ABSTRACT: We simulate three-dimensional, horizontally periodic Rayleigh-B\'enard convection between free-slip horizontal plates, rotating about a horizontal axis. When both the temperature difference between the plates and the rotation rate are sufficiently large, a strong horizontal wind is generated that is perpendicular to both the rotation vector and the gravity vector. The wind is turbulent, large-scale, and vertically sheared. Horizontal anisotropy, engendered here by rotation, appears necessary for such wind generation. Most of the kinetic energy of the flow resides in the wind, and the vertical turbulent heat flux is much lower on average than when there is no wind.
    Full-text · Article · Jan 2015 · Physical Review Letters
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    ABSTRACT: The mountain regions of the Hindu Kush, Karakoram and Himalaya (HKKH) are the ‘‘third pole’’ of our planet, and the glaciers in this area are ‘‘water towers’’ of Asia. Recent studies postulated the existence of a ‘‘Karakoram anomaly’’, i.e. with substantially unchanged ice cover during the last decade, against noticeable area loss worldwide. Yet, recent major floods occurring in Pakistan and the Karakoram area, may represent an effect of modified climate in the area, carrying heavier precipitation in the Monsoon season, and possibly faster ice melting. We present here the results of the SHARE-Paprika project of the EvK2CNR Committee of Italy, aiming at evaluating the impact of climate change on the hydrology of the upper Indus river. We focus here on a particular watershed, the Shigar river closed in Shigar, with an area of about 7,000 km2 and fed by seasonal melt from two major glaciers (Baltoro and Biafo). Based upon data gathered during three field campaigns we set up a semidistributed, altitude belt based hydrological model, providing acceptable depiction of in stream flows, and snow and ice cover dynamics. We then project the future (until 2,100) hydrological cycle in the area by feeding the hydrological model with future precipitation and temperature (plus downscaling, whenever necessary) from a number of climate models, under different RCP scenarios.
    No preview · Book · Jan 2015
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    ABSTRACT: In what follows, we present the study of different configurations of the Weather Research and Forecast model restricted to the EURO-CORDEX area at different spatial resolutions from 0.44°× 0.44° down to 0.04° × 0.04°. Our numerical model is forced at the boundaries by ERA-interim re-analysis data. Monthly and daily statistics for the year 1979 are compared in order to set the best configuration for rainfall predictions. Precipitation climatologies are then derived and particular attention is paid to the Alpine region. Our results show that local precipitation patterns are well reproduced by the regional model while highlighting the need of grid-resolved convection to avoid artificial additive precipitation and to reduce the rainfall rate bias especially of regions with complex orography.
    No preview · Article · Jan 2015
  • Silvia Terzago · Jost von Hardenberg · Elisa Palazzi · Antonello Provenzale
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    ABSTRACT: The Hindu Kush, Karakoram, and Himalaya (HKKH) mountain ranges feed the most important Asian river systems, providing water to about 1.5 billion people. As a consequence, changes in snow dynamics in this area could severely impact water availability for downstream populations. Despite their importance, the amount, spatial distribution, and seasonality of snow in the HKKH region are still poorly known, owing to the limited availability of surface observations in this remote and high-elevation area. This work considers global climate models (GCM) participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) and analyzes how they represent current and future snowpack in the HKKH region in terms of snow depth and snow water equivalent. It is found that models with high spatial resolution (up to 1.25 degrees) simulate a spatial pattern of the winter snowpack in greater agreement with each other, with observations, with reanalysis datasets, and with the orographic features of the region, compared to most lower-resolution models. The seasonal cycle of snow depth displays a unimodal regime, with a maximum in February-March and almost complete melting in summer. The models generally indicate thicker [in Hindu Kush-Karakoram (HKK)] or comparable (in the Himalayas) snow depth and higher snow water equivalent compared to the reanalyses for the control period 1980-2005. Future projections, evaluated in terms of the ensemble mean of GCM simulations, indicate a significant reduction in the spatial average of snow depth over the HKK and an even stronger decrease in the Himalayas, where a reduction between 25% and 50% is expected by the end of the twenty-first century.
    No preview · Article · Dec 2014 · Journal of Hydrometeorology
  • Luca Filippi · Elisa Palazzi · Jost von Hardenberg · Antonello Provenzale
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    ABSTRACT: Winter precipitation over the Hindu Kush-Karakoram (HKK) range in the western Himalayas is generated by westerly perturbations whose dynamics is affected by the North Atlantic Oscillation (NAG). Larger precipitation is typically recorded during the positive NAO phase. In this work, the relationship between the NAO and winter precipitation in the HKK is explored further, using an ensemble of precipitation datasets and the 40-yr ECMWF Re-Analysis (ERA-40) and Twentieth Century Reanalysis (20CR) data. The mechanisms underlying this relationship are discussed, with a focus on the secular variations that occurred in the last century. The NAO exerts its control on HKK precipitation by altering the intensity of westerly winds in the region of the Middle East jet stream (MEJS). Results indicate that evaporation from the Persian Gulf, the northern Arabian Sea, and the Red Sea plays an important role. During positive NAO phases, westerlies are strengthened and enhanced evaporation occurs from these basins owing to higher surface wind speed. The extra moisture combines with stronger westerlies and results in enhanced moisture transport toward the HKK. Precipitation datasets covering the twentieth century show an alternation of periods of strong and weaker influence of the NAO on precipitation in the HKK. It is found that these variations are associated with changes in the spatial pattern of the NAO: the relative position of the two centers of action of the NAO determines to what extent it can modulate the MEJS, affecting precipitation in the HKK.
    No preview · Article · Oct 2014 · Journal of Climate
  • Francesco Paparella · Jost von Hardenberg
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    ABSTRACT: Fingering convection is a convective instability that occurs in fluids where two buoyancy-changing scalars with different diffusivities have a competing effect on density. The peculiarity of this form of convection is that, although the transport of each individual scalar occurs down-gradient, the net density transport is up-gradient. In a suitable range of non-dimensional parameters, solutions characterized by constant vertical gradients of the horizontally averaged fields may undergo a further instability, which results in the alternation of layers where density is roughly homogeneous with layers where there are steep vertical density gradients, a pattern known as “doubly-diffusive staircases”. This instability has been interpreted in terms of an effective negative diffusivity, but simplistic parameterizations based on this idea, obviously, lead to ill-posed equations. Here we propose a mathematical model that describes the dynamics of the horizontally-averaged scalar fields and the staircase-forming instability. The model allows for unstable constant-gradient solutions, but it is free from the ultraviolet catastrophe that characterizes diffusive processes with a negative diffusivity.
    No preview · Article · Aug 2014 · Acta Applicandae Mathematicae
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    ABSTRACT: We analyse the observed climate-driven changes in summer wildfires and their future evolution in a typical Mediterranean environment (NE Spain). By analysing observed climate and fire data from 1970 to 2007, we estimate the response of fire number (NF) and burned area (BA) to climate trends, disentangling the drivers responsible for long-term and interannual changes by means of a parsimonious Multi Linear Regression model (MLR). In the last forty years, the observed NF trend was negative. Here we show that, if improvements in fire management were not taken into account, the warming climate forcing alone would have led to a positive trend in NF. On the other hand, for BA, higher fuel flammability is counterbalanced by the indirect climate effects on fuel structure (i.e. less favourable conditions for fine-fuel availability and fuel connectivity), leading to a slightly negative trend. Driving the fire model with A1B climate change scenarios based on a set of Regional Climate Models from the ENSEMBLES project indicates that increasing temperatures promote a positive trend in NF if no further improvements in fire management are introduced.
    Full-text · Article · Aug 2014 · Climatic Change
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    ABSTRACT: The mysterious ‘fairy circles’ are vegetation‐free discs that cover vast areas along the pro‐Namib Desert. Despite 30 yr of research their origin remains unknown. Here we adopt a novel approach that focuses on analysis of the spatial patterns of fairy circles obtained from representative 25‐ha aerial images of north‐west Namibia. We use spatial point pattern analysis to quantify different features of their spatial structures and then critically inspect existing hypotheses with respect to their ability to generate the observed circle patterns. Our working hypothesis is that fairy circles are a self‐organized vegetation pattern. Finally, we test if an existing partial‐differential‐equation model, that was designed to describe vegetation pattern formation, is able to reproduce the characteristic features of the observed fairy circle patterns. The model is based on key‐processes in arid areas such as plant competition for water and local resource‐biomass feedbacks.
    Full-text · Article · May 2014 · Ecography
  • D. D'Onofrio · E. Palazzi · J. von Hardenberg · A. Provenzale · S. Calmanti
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    ABSTRACT: Precipitation extremes and small-scale variability are essential drivers in many climate change impact studies. However, the spatial resolution currently achieved by global climate models (GCMs) and regional climate models (RCMs) is still insufficient to correctly identify the fine structure of precipitation intensity fields. In the absence of a proper physically based representation, this scale gap can be at least temporarily bridged by adopting a stochastic rainfall downscaling technique. In this work, a precipitation downscaling chain is introduced where the global 40-yr ECMWF Re-Analysis (ERA-40) (at about 120-km resolution) is dynamically downscaled using the Protheus RCM at 30-km resolution. The RCM precipitation is then further downscaled using a stochastic downscaling technique, the Rainfall Filtered Autoregressive Model (RainFARM), which has been extended for application to long climate simulations. The application of the stochastic downscaling technique directly to the larger-scale reanalysis field at about 120-km resolution is also discussed. To assess the ability of this approach in reproducing the main statistical properties of precipitation, the downscaled model results are compared with the precipitation data provided by a dense network of 122 rain gauges in northwestern Italy, in the time period from 1958 to 2001. The high-resolution precipitation fields obtained by stochastically downscaling the RCM outputs reproduce well the seasonality and amplitude distribution of the observed precipitation during most of the year, including extreme events and variance. In addition, the RainFARM outputs compare more favorably to observations when the procedure is applied to the RCM output rather than to the global reanalyses, highlighting the added value of reaching high enough resolution with a dynamical model.
    No preview · Article · Mar 2014 · Journal of Hydrometeorology
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    Full-text · Dataset · Nov 2013

Publication Stats

2k Citations
232.93 Total Impact Points


  • 2008-2015
    • INO - Istituto Nazionale di Ottica
      Florens, Tuscany, Italy
  • 2008-2013
    • Italian National Research Council
      • Institute of Atmospheric Sciences and Climate ISAC
      Oristany, Sardinia, Italy
  • 2001-2010
    • Ben-Gurion University of the Negev
      • Department of Physics
      Beersheba, Southern District, Israel
  • 2004-2007
    • CIMA Research Foundation
      Savona, Liguria, Italy
  • 2005-2006
    • Università degli Studi della Basilicata
      Potenza, Basilicate, Italy
  • 2004-2006
    • Università degli Studi di Genova
      Genova, Liguria, Italy
  • 2002-2003
    • University of Oxford
      • Mathematical Institute
      Oxford, England, United Kingdom
    • ISI Foundation
      Torino, Piedmont, Italy