http://hdl.handle.net/2122/175 2013-05-23T21:55:08Z http://hdl.handle.net/2122/8437 Title: Combining model and geostationary satellite data to reconstruct the hourly SST field over the Mediterranean Sea Authors: Marullo, S.; Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile, ENEA; Santoleri, R.; CNR Istituto di Scienze dell'Atmosfera e del Clima; Ciani, D.; CNR Istituto di Scienze dell'Atmosfera e del Clima; Le Borgne, P.; Meteo-France/DP/CMS; Pere, S.; Meteo-France/DP/CMS; Pinardi, N.; Dipartimento di Scienze Ambientali, Universita' di Bologna; Tonani, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Nardone, G.; Istituto Superiore per la Protezione e la Ricerca Ambientale Abstract: This work focuses on the Sea Surface Temperature diurnal cycle reconstruction over the Mediterranean Sea by combining numerical model analyses and geostationary satellite measurements. Our approach is to take advantage of geostationary satellite observations as the diurnal signal source to produce gap‐free optimally interpolated (OI) hourly SST fields using model analyses as first guess. The work is focused on summer 2011 including all the data and model output from June 1st to August 31st 2011. The OI interpolation estimate, the model first guess (provided by an operational forecasting model) and the SEVIRI data (provided by O&SI SAF) were evaluated using drifter and mooring data as a references. Special attention was devoted to the analysis of Diurnal Warming (DW) events that were particularly frequent during this period. Results suggest the following: 1) the model reproduces quite well the Mediterranean SST diurnal cycle with the exclusion of intense DW events but the amplitude of the model cycle is often less intense than the corresponding SEVIRI and drifter observations, due to the different thickness of the surface ocean layer they represent. Time shifts between model and data warming/cooling phases of the day are also discussed. 2) The Diurnal OI SST field (DOISST), resulting from the blending of model and SEVIRI data via optimal interpolation, well reproduces the diurnal cycle (including DW events) leaving substantially unchanged the statistics of the difference between SEVIRI and drifter measurements also in data void positions where the interpolation operates. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8193 Title: Global response to solar radiation absorbed by phytoplankton in a coupled climate model Authors: Patara, L.; CMCC; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Fogli, P. G.; CMCC; Manzini, E.; MPI Abstract: The global climate response to solar radiation absorbed by phytoplankton is investigated by performing multi-century simulations with a coupled ocean–atmosphere-biogeochemistry model. The absorption of solar radiation by phytoplankton increases radiative heating in the near-surface ocean and raises sea surface temperature (SST) by overall ~0.5°C. The resulting increase in evaporation enhances specific atmospheric humidity by 2–5%, thereby increasing the Earth’s greenhouse effect and the atmospheric temperatures. The Hadley Cell exhibits a weakening and poleward expansion, therefore reducing cloudiness at subtropical-middle latitudes and increasing it at tropical latitudes except near the Equator. Higher SST at polar latitudes reduces sea ice cover and albedo, thereby increasing the high-latitude ocean absorption of solar radiation. Changes in the atmospheric baroclinicity cause a poleward intensification of mid-latitude westerly winds in both hemispheres. As a result, the North Atlantic Ocean meridional overturning circulation extends more northward, and the equatorward Ekman transport is enhanced in the Southern Ocean. The combination of local and dynamical processes decreases upper-ocean heat content in the Tropics and in the subpolar Southern Ocean, and increases it at middle latitudes. This study highlights the relevance of coupled ocean–atmosphere processes in the global climate response to phytoplankton solar absorption. Given that simulated impacts of phytoplankton on physical climate are within the range of natural climate variability, this study suggests the importance of phytoplankton as an internal constituent of the Earth’s climate and its potential role in participating in its long-term climate adjustments. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8190 Title: Layered structures in the upper Ligurian Sea Authors: Carniel, S.; CNR-ISMAR; Kantha, L.; Univ. of Colorado; Bergamasco, A.; CNR-ISMAR; Prandke, H.; ISW; Small, R. J.; NCAR; Sclavo, M.; CNR-ISMAR Abstract: During the dedicated sea-truth cruise LIGURE2007, a part of the intensive observational campaign Ligurian Sea Air-Sea Interaction Experiment (LASIE) performed in the eastern Ligurian Sea (Italy) from 16th to 23rd June in 2007, the R/V Urania carried out an intensive microstructure measurement program. Most of these measurements were made between 17th and 20th, in the vicinity of a spar buoy anchored 60 km off the coast in a region with a water column depth of approximately 1500 m; the prevailing light wind conditions and intense solar radiation limited the depth of the upper mixed layer to about 10–15m. We carried out measurements of the structure of the upper water column to a depth exceeding about 200 m. Interestingly, the microstructure measurements revealed multiple layers of relatively elevated dissipation and diffusivity rates around a depth of about 100 m. Since the water column is shown not to be not conducive to double-diffusion, these layered structures must have been produced by small-scale shear due to other processes, such as breaking internal waves. In this paper, we describe the oceanographic conditions prevailing at the time of the measurements, as well as the general turbulent properties in the upper part of the water column. In particular, the layered structures below the mixed layer are discussed in detail, with suggestions as to the likely origin and possible ways of investigating these processes. 2009-12-31T23:00:00Z http://hdl.handle.net/2122/7629 Title: Marine biogeochemical responses to the North Atlantic Oscillation in a coupled climate model Authors: Patara, L.; CMCC; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Visbeck, M.; IFM-Kiel; Krahmann, G.; IFM-Kiel; Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: In this study a coupled ocean‐atmosphere model containing interactive marine biogeochemistry is used to analyze interannual, lagged, and decadal marine biogeochemical responses to the North Atlantic Oscillation (NAO), the dominant mode of North Atlantic atmospheric variability. The coupled model adequately reproduces present‐day climatologies and NAO atmospheric variability. It is shown that marine biogeochemical responses to the NAO are governed by different mechanisms according to the time scale considered. On interannual time scales, local changes in vertical mixing, caused by modifications in air‐sea heat, freshwater, and momentum fluxes, are most relevant in influencing phytoplankton growth through light and nutrient limitation mechanisms. At subpolar latitudes, deeper mixing occurring during positive NAO winters causes a slight decrease in late winter chlorophyll concentration due to light limitation and a 10%–20% increase in spring chlorophyll concentration due to higher nutrient availability. The lagged response of physical and biogeochemical properties to a high NAO winter shows some memory in the following 2 years. In particular, subsurface nutrient anomalies generated by local changes in mixing near the American coast are advected along the North Atlantic Current, where they are suggested to affect downstream chlorophyll concentration with 1 year lag. On decadal time scales, local and remote mechanisms act contemporaneously in shaping the decadal biogeochemical response to the NAO. The slow circulation adjustment, in response to NAO wind stress curl anomalies, causes a basin redistribution of heat, freshwater, and biogeochemical properties which, in turn, modifies the spatial structure of the subpolar chlorophyll bloom. 2010-12-31T23:00:00Z http://hdl.handle.net/2122/2369 Title: Enhanced rainfall in the western Mediterranean during deposition of sapropel S1: stalagmite evidence from Corchia Cave (Central Italy) Authors: Zanchetta, G.; 1Dipartimento di Scienze della Terra, University of Pisa,; Drysdale, R. N.; School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia; Hellstrom, J. C.; School of Earth Sciences, University of Melbourne, Parkville, Victoria 3010 Australia; Fallick, A. E.; Scottish Universities Environmental Research Centre, East Kilbride, G75 0GF Glasgow, UK; Isola, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia; Gargan, M.; Research School of Earth Sciences, The Australian National University, Canberra ACT 0600, Australia; Pareschi, M. T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia Abstract: A stable isotope record from a stalagmite collected from Antro del Corchia cave (Apuan Alps, Central Italy), supported by 17 uranium-series ages, indicates enhanced regional rainfall between ca. 8.9 and 7.3 kyr cal. BP at the time of sapropel S1 deposition. Within this phase, the highest rainfall occurred between 7.9 and 7.4 kyr cal. BP. Comparison with different marine and lake records, and in particular with the Soreq Cave record (Israel), suggests substantial in-phase occurrence of enhanced rainfall between the Western and Eastern Mediterranean basins. There is no convincing evidence for major climatic change at the time of the “8.2 ka event”. 2005-12-31T23:00:00Z http://hdl.handle.net/2122/753 Title: Scale interactions on diurnal toseasonal timescales and their relevanceto model systematic errors Authors: Slingo, J.; NCAS Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, U.K.; Inness, P.; NCAS Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, U.K.; Neale, R.; NCAS Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, U.K.; Woolnough, S.; NCAS Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, U.K.; Yang, G.; NCAS Centre for Global Atmospheric Modelling, Department of Meteorology, University of Reading, U.K. Abstract: Examples of current research into systematic errors in climate models are used to demonstrate the importance of scale interactions on diurnal,intraseasonal and seasonal timescales for the mean and variability of the tropical climate system. It has enabled some conclusions to be drawn about possible processes that may need to be represented, and some recommendations to be made regarding model improvements. It has been shown that the Maritime Continent heat source is a major driver of the global circulation but yet is poorly represented in GCMs. A new climatology of the diurnal cycle has been used to provide compelling evidence of important land-sea breeze and gravity wave effects, which may play a crucial role in the heat and moisture budget of this key region for the tropical and global circulation. The role of the diurnal cycle has also been emphasized for intraseasonal variability associated with the Madden Julian Oscillation (MJO). It is suggested that the diurnal cycle in Sea Surface Temperature (SST) during the suppressed phase of the MJO leads to a triggering of cumulus congestus clouds, which serve to moisten the free troposphere and hence precondition the atmosphere for the next active phase. It has been further shown that coupling between the ocean and atmosphere on intraseasonal timescales leads to a more realistic simulation of the MJO. These results stress the need for models to be able to simulate firstly, the observed tri-modal distribution of convection, and secondly, the coupling between the ocean and atmosphere on diurnal to intraseasonal timescales. It is argued, however, that the current representation of the ocean mixed layer in coupled models is not adequate to represent the complex structure of the observed mixed layer, in particular the formation of salinity barrier layers which can potentially provide much stronger local coupling between the atmosphere and ocean on diurnal to intraseasonal timescales. 2002-12-31T23:00:00Z