http://hdl.handle.net/2122/89 Mon, 20 May 2013 12:02:01 GMT 2013-05-20T12:02:01Z http://hdl.handle.net/2122/8592 Title: Influence of ENSO and of the Indian Ocean dipole on the Indian summer monsoon variability Authors: Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: Indian summer monsoon (ISM) variability is forced from external factors (like the El Nino Southern Oscillation, ENSO) but it contains also an internal component that tends to reduce its potential for predictability. Large-scale and local monsoon indices based on precipitation and atmospheric circulation parameters are used as a measure of ISM variability. In a 9-members ensemble of AMIP-type experiments (with same boundary SST forcing and different initial conditions) their potential predictability is comparable using both local and large-scale monsoon indices. In the sample analyzed, about half of more predictable monsoon years coincide with El Nino and/or positive Indian Ocean Dipole (IOD) events. Summer monsoon characteristics during ENSO and IOD years are analyzed through composites computed over a three years period (i.e. one year before and one year after the event peak) to investigate the mutual relationship between the events lagged in time. The connection between ISM and IOD is mostly confined in the summer and autumn, while that with ENSO is stronger and extends more in time. In the coupled model results the IOD influence on the monsoon is large, even because in the model IOD events are intense and easily reproduced due to a strong air-sea feedback in the eastern side of the basin. Monsoon seasons preceding or following an El Nino or a La Nina event are not exactly symmetric, even in terms of their biennial character. In most of the cases, both in reanalysis and model, El Nino and positive IOD events tend to co-occur with larger anomalies either in the Indo-Pacific ocean sector or over India, while La Nina and negative IOD do not. From the observed record, the ENSO-IOD correlation is positive strong and significant since mid-60s and it may correspond with either strong or weak ENSO-monsoon relationship and with strong or weak IOD-monsoon relationship. A main difference between those periods is the relationship between Indian monsoon rainfall and SST in other ocean basins rather than the Indo-Pacific sector alone. Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2122/8592 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8266 Title: ENSO and its effects on the atmospheric heating processes Authors: Miyakoda, K.; Princeton University; Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Ploshay, J.; GFDL, NJ, USA Abstract: El Nino-Southern Oscillation (ENSO) is an important air-sea coupled phenomenon that plays a dominant role in the variability of the tropical regions. Observations, atmospheric and oceanic reanalysis datasets are used to classify ENSO and non-ENSO years to investigate the typical features of its periodicity and atmospheric circulation patterns. Among non-ENSO years, we have analyzed a group, called type-II years, with very small SST anomalies in summer that tend to weaken the correlation between ENSO and precipitation in the equatorial regions. A unique character of ENSO is studied in terms of the quasi-biennial periodicity of SST and heat content (HC) fields over the Pacific-Indian Oceans. While the SST tends to have higher biennial frequency along the Equator, the HC maximizes it into two centers in the western Pacific sector. The north-western center, located east of Mindanao, is strongly correlated with SST in the NINO3 region. The classification of El Nino and La Nina years, based on NINO3 SST and north-western Pacific HC respectively, has been used to identify and describe temperature and wind patterns over an extended-ENSO region that includes the tropical Pacific and Indian Oceans. The description of the spatial patterns within the atmospheric ENSO circulation has been extended to tropospheric moisture fields and low-level moisture divergence during November–December–January, differentiating the role of El Nino, when large amounts of condensational heat are concentrated in the central Pacific, from La Nina that tends to mainly redistribute heat to Maritime Continents and higher latitudes. The influence of the described mechanisms on equatorial convection in the context of the variability of ENSO on longer timescales for the end of the 20th century is questioned. However, the inaccuracy of the atmospheric reanalysis products in terms of precipitation and the shorter time length of more reliable datasets hamper a final conclusion on this issue. Tue, 28 Feb 2012 23:00:00 GMT http://hdl.handle.net/2122/8266 2012-02-28T23:00:00Z http://hdl.handle.net/2122/7943 Title: Strato-mesospheric ozone measurements using ground-based millimeter-wave spectroscopy at Thule, Greenland Authors: Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cesaroni, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Fiorucci, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Smith, A. K.; Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, Colorado, USA; Froidevaux, L.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA; Mlynczak, M. G.; NASA Langley Research Center, Hampton, Virginia, USA Abstract: On January 2009 a ground-based millimeter-wave spectrometer (GBMS) was installed at Thule Air Base (76.5ºN, 68.8ºW), Greenland, for long-term winter monitoring of several stratospheric and mesospheric trace gases in the framework of the Network for the Detection of Atmospheric Composition Change. This work is aimed at characterizing the GBMS O3 vertical profiles between 35 and 80 km altitude obtained by applying the optimal estimation method to O3 pressure-broadened spectral line measurements carried out during three winters. In this altitude range, GBMS O3 retrievals are highly sensitive to variations of the atmospheric state, and their accuracy is estimated to be the larger of 11% or 0.2 ppmv. Comparisons of GBMS O3 profiles with colocated satellite-based measurements from Aura Microwave Limb Sounder (MLS) and Thermosphere Ionosphere Mesosphere Energetics and Dynamics Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) show a good agreement below 65 km altitude once the known 10%–20% high bias of SABER O3 profiles is considered, with the GBMS displaying an averaged low bias of 9% and 17% with respect to MLS and SABER. In the nighttime mesosphere, the GBMS detects the ozone tertiary maximum within 0.1 ppmv (6%) on average with respect to the convolved MLS, SABER, and global 3-D ROSE model profiles but shifts its position to lower altitudes by 4–5 km compared to the height obtained by the other three data sets. In the 50–80 km altitude range, estimates of mesospheric O3 diurnal variation obtained from the GBMS and the convolved satellite measurements agree well within the ±1 standard deviation (~ 0.6 ppmv) of the GBMS mean profile. Thu, 12 Apr 2012 22:00:00 GMT http://hdl.handle.net/2122/7943 2012-04-12T22:00:00Z http://hdl.handle.net/2122/7410 Title: Intercomparison between Aura MLS and ground-based millimeter-wave observations of stratospheric O3 and HNO3 from Thule (76.5° N, 68.7° W) Authors: Fiorucci, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Froidevaux, L.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA; Santee, M.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA; Manney, G. L.; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA USA Abstract: The Ground-Based Millimeter-wave Spectrometer (GBMS) measures rotational emission spectra of middle atmospheric trace gases, with a spectral window of 600 MHz tunable between approximately 230 and 280 GHz and a resolution of up to 65 kHz. It was designed and built at the State University of New York at Stony Brook in the early 90’s and since then has been regularly upgraded and operated at a variety of sites in both hemispheres, at polar and mid-latitudes. In view of a growing need for long-term data sets of stratospheric constituents, in January 2009 we resolved to establish a long-term GBMS observation site at the Arctic station of Thule Air Base (76.5°N, 68.8°W), Greenland, in order to track the long- and short-term interactions between the changing climate and the seasonal processes tied to the ozone depletion phenomenon. Since then three winter campaigns were carried out from Thule during the period January-March 2009, 2010 and 2011. Observations of O3, HNO3, CO and N2O were performed, mostly on a daily basis, except during periods characterized by poor weather conditions. In this study we compare GBMS stratospheric O3 and HNO3 measurements obtained during these three winter periods at Thule with colocated satellite observations from the Aura Microwave Limb Sounder (MLS) experiment. The Version 3.3 Aura MLS O3 and HNO3 data sets have a resolution of about 2.5 km and 3-4 km, respectively, in the stratosphere. The MLS precisions range from 0.1 to 0.6 ppmv for O3 and about 0.6-0.7 ppbv for HNO3 throughout the stratosphere. Based on preliminary comparisons with correlative data sets and on results obtained for v2.2, systematic uncertainties are estimated to lead to HNO3 measurements biases that vary between ±0.5 and ±2 ppbv and multiplicative errors of ±5 –15% throughout most of the stratosphere. Similarly, a systematic uncertainty of the order of 5-10% has been assessed for O3 data. As for the GBMS, the O3 pure rotational transition line at 276.923 GHz is observed with a ~1.5-hour integration, while the weaker HNO3 spectrum, represented by a cluster of superimposed emission lines centered at 269.1 GHz, needs about 4 hours of integration. Taking advantage of the dependence of the line broadening on atmospheric pressure, inversion techniques allow the retrieval of vertical profiles from approximately 15 to 50 km. In the past, GBMS O3 and HNO3 spectra were deconvolved using a Chahine-Twomey (C-T) and an iterative constrained Matrix Inversion (MI) technique, respectively. More recently, the GBMS retrieval algorithm has been updated to an Optimal Estimation Method (OEM) in order to conform to the standard of the NDACC microwave group, and to easily provide retrievals with a set of averaging kernels that grants more straightforward comparisons with other data sets. The nominal vertical resolution of the retrieved profiles (defined as the FWHM of averaging kernels) is ~8 km for O3 and ~ 12 km for HNO3, although the inversion technique locates the maximum of the mixing ratio profile of both species with a much better accuracy (i.e., ~ ±1 km). The 1σ uncertainty of O3 and HNO3 mixing ratio vertical profiles depends on altitude and is estimated at ~15% or 0.3 ppbv, whichever is larger. Each GBMS profile is compared to the closest MLS profile, with coincidence criteria of ±10° longitude, ±2.5° latitude and ±12 h. In order to avoid of severely compromising the comparison between GBMS and Aura MLS observations due to the much higher resolution of the satellite-derived data sets, we ‘convolved’ the MLS profiles using the GBMS averaging kernels before directly comparing the two data sets. For both species a fairly good agreement between MLS and GBMS profiles is observed, with the GBMS showing, however, a ~10-15% low bias at the mixing ratio peak. Sun, 06 Nov 2011 23:00:00 GMT http://hdl.handle.net/2122/7410 2011-11-06T23:00:00Z http://hdl.handle.net/2122/7325 Title: Global and regional ocean carbon uptake and climate change: sensitivity to a substantial mitigation scenario Authors: Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Manzini, E.; MPI, Hamburg; Fogli, P. G.; CMCC; Alessandri, A.; ENEA; Patara, L.; CMCC; Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: Under future scenarios of business-as-usual emissions, the ocean storage of anthropogenic carbon is anticipated to decrease because of ocean chemistry con- straints and positive feedbacks in the carbon-climate dynamics, whereas it is still unknown how the oceanic carbon cycle will respond to more substantial mitigation scenarios. To evaluate the natural system response to pre- scribed atmospheric ‘‘target’’ concentrations and assess the response of the ocean carbon pool to these values, 2 cen- tennial projection simulations have been performed with an Earth System Model that includes a fully coupled carbon cycle, forced in one case with a mitigation scenario and the other with the SRES A1B scenario. End of century ocean uptake with the mitigation scenario is projected to return to the same magnitude of carbon fluxes as simulated in 1960 in the Pacific Ocean and to lower values in the Atlantic. With A1B, the major ocean basins are instead projected to decrease the capacity for carbon uptake globally as found with simpler carbon cycle models, while at the regional level the response is contrasting. The model indicates that the equatorial Pacific may increase the carbon uptake rates in both scenarios, owing to enhancement of the biological carbon pump evidenced by an increase in Net Community Production (NCP) following changes in the subsurface equatorial circulation and enhanced iron availability from extratropical regions. NCP is a proxy of the bulk organic carbon made available to the higher trophic levels and potentially exportable from the surface layers. The model results indicate that, besides the localized increase in the equatorial Pacific, the NCP of lower trophic levels in the northern Pacific and Atlantic oceans is projected to be halved with respect to the current climate under a sub- stantial mitigation scenario at the end of the twenty-first century. It is thus suggested that changes due to cumulative carbon emissions up to present and the projected concen- tration pathways of aerosol in the next decades control the evolution of surface ocean biogeochemistry in the second half of this century more than the specific pathways of atmospheric CO2 concentrations. Sat, 30 Apr 2011 22:00:00 GMT http://hdl.handle.net/2122/7325 2011-04-30T22:00:00Z http://hdl.handle.net/2122/7104 Title: Societal need for improved understanding of climate change, anthropogenic impacts, and geo-hazard warning drive development of ocean observatories in European Seas Authors: Ruhl, H. A.; NOCS; Andrè, M.; UPC; Beranzoli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Çagatay, M. N.; ITU; Colaço, A.; Univ. Azores; Cannat, M.; IPGP; Dañobeitia, J. J.; CSIC-UTM; Favali, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Géli, L.; IFREMER; Gillooly, M.; IMI; Greinert, J.; NIOZ; Hall, P. O. J.; Univ. Goteborg; Huber, R.; MARUM; Karstensen, J.; Univ. Kiel; Lampitt, R. S.; NOCS; Larkin, K. E.; NOCS; Lykousis, V.; HCMR; Mienert, J.; Univ. Tromsø; Miranda, J. M.; Univ. Lisboa; Person, R.; IFREMER; Priede, I. G.; Univ. Aberdeen; Puillat, I.; IFREMER; Thomsen, L.; Jacobs Univ. Bremen; Waldmann, C.; MARUM Abstract: Society’s needs for a network of in situ ocean observing systems cross many areas of earth and marine science. Here we review the science themes that benefit from data supplied from ocean observatories. Understanding from existing studies is fragmented to the extent that it lacks the coherent long-term monitoring needed to address questions at the scales essential to understand climate change and improve geo-hazard early warning. Data sets from the deep sea are particularly rare with long-term data available from only a few locations worldwide. These science areas have impacts on societal health and well-being and our awareness of ocean function in a shifting climate. Substantial efforts are underway to realise a network of open-ocean observatories around European Seas that will operate over multiple decades. Some systems are already collecting high-resolution data from surface, water column, seafloor, and sub-seafloor sensors linked to shore by satellite or cable connection in real or near-real time, along with samples and other data collected in a delayed mode. We expect that such observatories will contribute to answering major ocean science questions including: How can monitoring of factors such as seismic activity, pore fluid chemistry and pressure, and gas hydrate stability improve seismic, slope failure, and tsunami warning? What aspects of physical oceanography, biogeochemical cycling, and ecosystems will be most sensitive to climatic and anthropogenic change? What are natural versus anthropogenic changes? Most fundamentally, how are marine processes that occur at differing scales related? The development of ocean observatories provides a substantial opportunity for ocean science to evolve in Europe. Here we also describe some basic attributes of network design. Observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in European Seas adding needed certainty to estimates of future oceanic conditions. Observatory data can be analysed along with other data such as those from satellites, drifting floats, autonomous underwater vehicles, model analysis, and the known distribution and abundances of marine fauna in order to address some of the questions posed above. Standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit. The connection of ocean observatory effort into larger frameworks including the Global Earth Observation System of Systems (GEOSS) and the Global Monitoring of Environment and Security (GMES) is integral to its success. It is in a greater integrated framework that the full potential of the component systems will be realised. Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2122/7104 2010-12-31T23:00:00Z http://hdl.handle.net/2122/7076 Title: Revising the retrieval technique of a long-term stratospheric HNO3 data set: from a constrained matrix inversion to the optimal estimation algorithm Authors: Fiorucci, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Muscari, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; de Zafra, R. L.; Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY, USA Abstract: The Ground-Based Millimeter-wave Spectrometer (GBMS) was designed and built at the State University of New York at Stony Brook in the early 1990s and since then has carried out many measurement campaigns of stratospheric O3, HNO3, CO and N2O at polar and mid-latitudes. Its HNO3 data set shed light on HNO3 annual cycles over the Antarctic continent and contributed to the validation of both generations of the satellite-based JPL Microwave Limb Sounder (MLS). Following the increasing need for long-term data sets of stratospheric constituents, we resolved to establish a long-term GMBS observation site at the Arctic station of Thule (76.5 N, 68.8 W), Greenland, beginning in January 2009, in order to track the long- and short-term interactions between the changing climate and the seasonal processes tied to the ozone depletion phenomenon. Furthermore, we updated the retrieval algorithm adapting the Optimal Estimation (OE) method to GBMS spectral data in order to conform to the standard of the Network for the Detection of Atmospheric Composition Change (NDACC) microwave group, and to provide our retrievals with a set of averaging kernels that allow more straightforward comparisons with other data sets. The new OE algorithm was applied to GBMS HNO3 data sets from 1993 South Pole observations to date, in order to produce HNO3 version 2 (v2) profiles. A sample of results obtained at Antarctic latitudes in fall and winter and at mid-latitudes is shown here. In most conditions, v2 inversions show a sensitivity (i.e., sum of column elements of the averaging kernel matrix) of 100±20% from 20 to 45 km altitude, with somewhat worse (better) sensitivity in the Antarctic winter lower (upper) stratosphere. The 1 uncertainty on HNO3 v2 mixing ratio vertical profiles depends on altitude and is estimated at 15% or 0.3 ppbv, whichever is larger. Comparisons of v2 with former (v1) GBMS HNO3 vertical profiles, obtained employing the constrained matrix inversion method, show that v1 and v2 profiles are overall consistent. The main difference is at the HNO3 mixing ratio maximum in the 20–25 km altitude range, which is smaller in v2 than v1 profiles by up to 2 ppbv at mid-latitudes and during the Antarctic fall. This difference suggests a better agreement of GBMS HNO3 v2 profiles with both UARS/ and EOS Aura/MLS HNO3 data than previous v1 profiles. Tue, 26 Jul 2011 22:00:00 GMT http://hdl.handle.net/2122/7076 2011-07-26T22:00:00Z http://hdl.handle.net/2122/7063 Title: Tropical Pacific-North Pacific teleconnection in a coupled GCM: Remote and local effects Authors: Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: The connection between Tropical Pacific and North Pacific variability is investigated in a state-of-the art coupled ocean-atmosphere model, comparing two 20th century simulations at T30 and T106 atmospheric horizontal resolutions. Despite a better simulation of the frequency and the spatial distribution of the Tropical Pacific anomalies associated with the El Nino Southern Oscillation (ENSO) in the high-resolution experiment, the response in the North Pacific is scarcely different from the low-resolution experiment where the ENSO variability is weaker and at higher than observed frequency. In the North Pacific, the response of surface atmospheric fields to the variability in the Tropical Pacific appears to be affected by local coupling processes significantly different in the two experiments. The coupling between sea level pressure (SLP) and sea surface temperature (SST) in the North Pacific as well as the influence of the Tropical Pacific SST has been measured here by means of the ‘coupled manifold’ technique. In the low-resolution case the SLP variances linked to the fraction of North Pacific SST not influenced by the Tropical Pacific are weak suggesting that the remote influence is strong, consistently with the observations. On the contrary, in the high-resolution experiment the fractions and the patterns of the SLP variances due to the Tropical Pacific SST and those linked to the North Pacific SST are comparable. In the latter case, model systematic errors in the northwestern Pacific influences the local coupling processes thus triggering the remote response. We conclude that an increased atmospheric horizontal resolution does not reduce the coupled model systematic errors in the representation of the teleconnection between the North and the Tropical Pacific and that the validation of coupled models has to consider both remote and local processes. Sat, 31 Dec 2011 23:00:00 GMT http://hdl.handle.net/2122/7063 2011-12-31T23:00:00Z http://hdl.handle.net/2122/7062 Title: Climate sensitivity to changes in ocean heat transport Authors: 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 Abstract: 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. Fri, 31 Dec 2010 23:00:00 GMT http://hdl.handle.net/2122/7062 2010-12-31T23:00:00Z http://hdl.handle.net/2122/7061 Title: Effects of increased CO2 levels on monsoons Authors: Cherchi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Alessandri, A.; ENEA, Rome, Italy; Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia Abstract: Increased atmospheric carbon dioxide concentration provided warmer atmospheric temperature and higher atmospheric water vapor content, but not necessarily more precipitation. A set of experiments performed with a state-of-the-art coupled general circulation model forced with increased atmospheric CO2 concentration (2, 4 and 16 times the present-day mean value) were analyzed and compared with a control experiment to evaluate the effect of increased CO2 levels on monsoons. Generally, the monsoon precipitation responses to CO2 forcing are largest if extreme concentrations of carbon dioxide are used, but they are not necessarly proportional to the forcing applied. In fact, despite a common response in terms of an atmospheric water vapor increase to the atmospheric warming, two out of the six monsoons studied simulate less or equal summer mean precipitation in the 16xCO2 experiment compared to the intermediate sensitivity experiments. The precipitation differences between CO2 sensitivity experiments and CTRL have been investigated specifying the contribution of thermodynamic and purely dynamic processes. As a general rule, the differences depending on the atmospheric moisture content changes (thermodynamic component) are large and positive, and they tend to be damped by the dynamic component associated with the changes in the vertical velocity. However, differences are observed among monsoons in terms of the role played by other terms (like moisture advection and evaporation) in shaping the precipitation changes in warmer climates. The precipitation increase, even if weak, occurs despite a weakening of the mean circulation in the monsoon regions (‘‘precipitation-wind paradox’’). In particular, the tropical east-west Walker circulation is reduced, as found from velocity potential analysis. The meridional component of the monsoon circulation is changed as well, with larger (smaller) meridional (vertical) scales. Thu, 30 Jun 2011 22:00:00 GMT http://hdl.handle.net/2122/7061 2011-06-30T22:00:00Z