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Cherchi, Annalisa
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Cherchi, Annalisa
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annalisa.cherchi@ingv.it
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staff
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Y-6684-2019
45 results
Now showing 1 - 10 of 45
- PublicationEmbargoClimate sensitivity to changes in ocean heat transport(2011)
; ; ; ;Barreiro, M.; Universidad de la Republica, Uruguay ;Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; Using an atmospheric general circulation model coupled to a slab ocean we study the effect of ocean heat transport (OHT) on climate prescribing OHT from zero to two times the present-day values. In agreement with previous studies an increase in OHT from zero to present-day conditions warms the climate by decreasing the albedo due to reduced sea-ice extent and marine stratus cloud cover and by increasing the greenhouse effect through a moistening of the atmosphere. However, when the OHT is further increased the solution becomes highly dependent on a positive radiative feedback between tropical low clouds and sea surface temperature. We found that the strength of the low clouds-SST feedback combined with the model design may produce solutions that are globally colder than Control mainly due to an unrealistically strong equatorial cooling. Excluding those cases, results indicate that the climate warms only if the OHT increase does not exceed more than 10% of the present-day value in the case of a strong cloud-SST feedback and more than 25% when this feedback is weak. Larger OHT increases lead to a cold state where low clouds cover most of the deep tropics increasing the tropical albedo and drying the atmosphere. This suggests that the present-day climate is close to a state where the OHT maximizes its warming effect on climate and pose doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today.202 22 - PublicationOpen AccessA coupled model study on the Atlantic Meridional Overturning Circulation under extreme atmospheric CO2 conditionsThis study investigates the climate sensitivity to a strong CO2 atmospheric forcing focusing on the North Atlantic Ocean (NA). The analysis is based on a set of 600 years long experiments performed with a state-of-the-art coupled general circulation model (CGCM) with the 1990 reference value of atmospheric CO2 multiplied by 4, 8 and 16. Extreme increases in atmospheric CO2 concentration have been applied to force the climate system towards stable states with different thermo-dynamical properties and analyze how the different resulting oceanic stratification and diffusion affect the Atlantic Meridional Overturning Circulation (AMOC). The AMOC weakens in response to the induced warming with distinctive features in the extreme case: a southward shift of convective sites and the formation of a density front at mid-latitudes. The analysis of the density fluxes reveals that NA loses density at high latitudes and gains it southward of 40°N mainly due to the haline contribution. Our results indicate that the most important processes that control the AMOC are active in the high latitudes and are related to the stability of the water column. The increased ocean stratification stabilizes the ocean interior leading to a decreased vertical diffusivity, a reduction in the formation of deep water and a weaker circulation. In particular, the deep convection collapses mainly in the Labrador Sea as a consequence of the water column stratification under high latitudes freshening.
65 18 - PublicationOpen AccessClimate forcings and climate sensitivities diagnosed from atmospheric global circulation models(2010-12)
; ; ; ; ; ; ; ;Anderson, B. T.; Department of Geography and Environment, Boston University, Boston, MA ;Knight, J. R.; Met Office Hadley Centre, Exeter, UK ;Ringer, M. A.; Met Office Hadley Centre, Exeter, UK ;Deser, C.; National Center for Atmospheric Research, Boulder, CO, USA ;Phillips, A. S.; National Center for Atmospheric Research, Boulder, CO, USA ;Yoon, J.; Cooperative Institute for Climate and Satellites, Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA ;Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ;; ; ; ; Understanding the historical and future response of the global climate system to anthropogenic emissions of radiatively active atmospheric constituents has become a timely and compelling concern. At present, however, there are uncertainties in: the total radiative forcing associated with changes in the chemical composition of the atmosphere; the effective forcing applied to the climate system resulting from a (temporary) reduction via ocean-heat uptake; and the strength of the climate feedbacks that subsequently modify this forcing. Here a set of analyses derived from atmospheric general circulation model simulations are used to estimate the effective and total radiative forcing of the observed climate system due to anthropogenic emissions over the last 50 years of the twentieth century. They are also used to estimate the sensitivity of the observed climate system to these emissions, as well as the expected change in global surface temperatures once the climate system returns to radiative equilibrium. Results indicate that estimates of the effective radiative forcing and total radiative forcing associated with historical anthropogenic emissions differ across models. In addition estimates of the historical sensitivity of the climate to these emissions differ across models. However, results suggest that the variations in climate sensitivity and total climate forcing are not independent, and that the two vary inversely with respect to one another. As such, expected equilibrium temperature changes, which are given by the product of the total radiative forcing and the climate sensitivity, are relatively constant between models, particularly in comparison to results in which the total radiative forcing is assumed constant. Implications of these results for projected future climate forcings and subsequent responses are also discussed.164 204 - PublicationRestrictedMoisture variability over the Indo-Pacific region and its influence on the Indian summer monsoon rainfall(2016)
; ; ; ; ; ; ;Ratna, S. B.; CMCC ;Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Joseph, P. V.; Nansen Environmental Research Centre (India), Kochi, India ;Behera, S.; Application Laboratory, JAMSTEC, Yokohama, Japan ;Abish, B.; Nansen Environmental Research Centre (India), Kochi, India ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; The Indo-Pacific Ocean (i.e. region between 30E and 150E) has been experiencing a spread warming since the 1950s. At the same time the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea is related with the Indo-Pacific Ocean warming and how this could affect the variability of the Indian summer monsoon rainfall. We performed the analysis for the period 1951-2012 based on observed precipitation, sea surface temperature and atmospheric reanalysis products and we verified the robustness of the result by comparing different datasets. The decreasing trend of moisture over the East Africa/Arabian Sea coincides with an increasing trend of moisture over the western Pacific region. This is accompanied by the strengthening (weakening) of the upward motion over the western Pacific (East Africa/Arabian Sea) that, consequently, contributes in strengthening the western Pacific-Indian Ocean Walker circulation. Associated with it, the low-level westerlies are weakening over the peninsular India, thus contributing to the reduction of moisture transport towards India. Therefore, rainfall has decreased over the Western Ghats and central-east India. Differently from previous decades, since 2003 moisture over the East Africa/Arabian Sea started to increase and this is accompanied by the strengthening of convection due to increased warming of sea surface temperature over the western Arabian Sea. Despite this moisture increase over the Arabian sea, we found that moisture transport is still weakening over the Indian landmass in the very recent decade and still contributing to the decreased precipitation over the northeast India and southern part of the Western Ghats.402 92 - ProductOpen Access
84 53 - PublicationOpen AccessHeatwaves in Europe: areas of homogeneous variability and links with the regional to large-scale atmospheric and SSTs anomalies(2007-06-28)
; ; ; ; ;Carril, A. F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;; ; This work presents a methodology to study the interannual variability associated with summertime months in which extremely hot temperatures are frequent. Daily time series of maximum and minimum temperature fields (T max and T min, respectively) are used to define indexes of extreme months based on the number of days crossing thresholds. An empirical orthogonal function (EOF) analysis is applied to the monthly indexes. EOF loadings give information about the geographical areas where the number of days per month with extreme temperatures has the largest variability. Correlations between the EOF principal components and the time series of other fields allow plotting maps highlighting the anomalies in the large scale circulation and in the SSTs that are associated with the occurrence of extreme events. The methodology is used to construct the “climatology” of the extremely hot summertime months over Europe. In terms of both interannual and intraseasonal variability, there are three regions in which the frequency of the extremely hot days per month homogeneously varies: north-west Europe, Euro-Mediterranean and Eurasia region. Although extremes over those regions occur during the whole summer (June to August), the anomalous climatic conditions associated with frequent heatwaves present some intraseasonal variability. Extreme climate events over the north-west Europe and Eurasia are typically related to the occurrence of blocking situations. The intraseasonal variability of those patterns is related to the amplitude of the blocking, the relative location of the action centre and the wavetrain of anomalies downstream or upstream of the blocking. During June and July, blocking situations which give extremely hot climate conditions over north-west Europe are also associated with cold conditions over the eastern Mediterranean sector. The Euro-Mediterranean region is a transition area in which extratropical and tropical systems compete, influencing the occurrence of climate events: blockings tend to be related to extremely hot months during June while baroclinic anomalies dominate the variability of the climate events in July and August. We highlight that our method could be easily applied to other regions of the world, to other fields as well as to model outputs to assess, e.g. the potential change of extreme climate events in a warmer climate.154 2975 - PublicationOpen AccessThe INGV-CMCC Seasonal Prediction System: improved ocean initial conditions(2010)
; ; ; ; ; ; ; ;Alessandri, A.; Centro Euro-Mediterraneo per i cambiamenti Climatici, Bologna, Italy ;Borrelli, A.; Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Di Pietro, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; ; The development of the INGV (Istituto Nazionale di Geofisica e Vulcanologia)-CMCC (Centro Euro-Mediterraneo per i Cambiamenti Climatici) Seasonal Prediction System (SPS) is documented. In this SPS the ocean initial conditions estimation includes a Reduced Order Optimal Interpolation procedure for the assimilation of temperature and salinity profiles at the global scale. Nine member ensemble forecasts have been produced for the period 1991-2003 for two starting dates per year in order to assess the impact of the subsurface assimilation in the ocean for initialization. Comparing the results with control simulations (i.e.: without assimilation of subsurface profiles during ocean initialization), we showed that the improved ocean initialization increases the skill in the prediction of tropical Pacific SSTs in our system for boreal winter forecasts. Considering the forecast of the El Ni˜no 1997-1998, the data assimilation in the ocean initial conditions leads to a considerable improvement in the representation of its onset and development. Our results indicate a better prediction of global scale surface climate anomalies for the forecasts started in November, probably due to the improvement in the tropical Pacific. For boreal winter, in both tropics and extra tropics, we show significant increases in the capability of the system to discriminate above normal and below normal temperature anomalies.401 498 - PublicationOpen AccessHow will climate change affect the isotope composition of meteoric water in the Mediterranean area?The relationship between the isotopic composition of precipitation in the Mediterranean Sea, the atmospheric circulation patterns over the region and groundwater properties has been topic of investigation in recent years. Overall, the link between the isotopic composition of precipitation and the Mediterranean climate raises the question of how future climate change could affect the isotope ratios of precipitation and groundwater. Past and future atmospheric properties (i.e. humidity, evaporation, precipitation and winds) over the Mediterranean region can be used to investigate the past and possibly understand future characteristics of meteoric water isotope composition. In order to evaluate how the climate change will affect the isotope composition of meteoric water, we re-evaluated previous rain events in light of well-defined climate framework. The main objective is to retrieve information on the atmospheric circulation systems based on ERA5 reanalysis and relate climate features with the isotope composition of selected rain events. This will allow to identify the most appropriate parameters needed to constrain the circulation systems responsible for those events and their isotope composition. Preliminary results to infer scenario-based considerations on the evolution of the meteoric recharge will be shown and discussed.
21 1 - PublicationOpen AccessChanges in the future summer Mediterranean climate: contribution of teleconnections and local factors(2020)
; ; ; ; ; ; ; ; ; ; ; The realistic simulation of the summer Mediterraneanclimaterequires not only refined spatial scales, but also an adequate representation of land-atmosphere interactions andteleconnections. Addressing all of these issues remains a challenge for most of the CMIP3/CMIP5 generation models. In this study we analyze high-24resolution (~0.5° lat x lon) RCP8.5 future projections of the Geophysical Fluid Dynamics Laboratory CM2.5 model with anew incorporatedland model (LM3). The simulated regional future changes suggest pronounced warming and drying over mostparts of the Mediterranean. However the changes aredistinctivelyless radical when compared with the CMIP5 multimodel ensemble. Moreover, changes over the Southeast (off the coast area of the Balkans) and Central Europe indicate not only a very modest warming, compared to the CMIP5 projections, but also wetting tendencies. The difference of CM2.5 projections of future changes over previous-generation modelshighlights the mportance of a) a correctlyprojectedmagnitude of changes of the North Atlantic Oscillation and its regional impacts, which have thecapacity to partly offset the anthropogenicwarming and drying over the western andcentral Mediterranean; b) a refined representation of land surface-atmospheric interactions, whichare a governing factor for thermal-and hydro-climate over Central and SoutheasternEurope. The CM2.5 projections also indicate a maximum of warming (Levant) and drying (Asia Minor) over the eastern Mediterranean. The changes derived in this region indicate a decreasing influence of atmospheric dynamics in maintaining the regional temperature and precipitation balance and instead an increasing influence of local surface temperature on the local surface atmospheric circulation.90 69 - PublicationOpen AccessThe typhoon-induced drying of the Maritime Continent(2020-02-10)
; ; ; ; ; ; ; ; ; ; ; ; ; The Maritime Continent plays a role in the global circulation pattern, due to the energy released by convective condensation over the region which influences the global atmospheric circulation. We demonstrate that tropical cyclones contribute to drying the Maritime Continent atmosphere, influencing the definition of the onset of the dry season. The process was investigated using observational data and reanalysis. Our findings were confirmed by numerical experiments using low- and high-resolution versions of the CMCC-CM2 General Circulation Model contributing to the HighResMIP CMIP6 effort.55 26