interannual enso and interdecadal enso like variability in the southern hemisphere tropospheric circulation abstract recent work has identified variability in the pacific ocean sst with a structure qualitatively similar to enso but at lower frequencies than enso zhang et al have documented the atmospheric circulation anomalies in the tropics and northern hemisphere that are associated with decadal enso like variability and compared these anomalies to those associated with the interannual enso cycle here the authors extend the study of zhang et al to the southern hemisphere using the national centers for environmental prediction national center for atmospheric research reanalysis data for 1958 96 consistent with previous studies the southern hemisphere circulation anomalies associated with enso display a teleconnection pattern from the central tropical pacific into the far southeastern pacific ocean comparatively larger circulation anomalies are found in the southern hemisphere associated with the decadal enso like variability though aloft the structure of the anomalies emphasizes the polar vortex wit

about the role of westerly wind events in the possible development of an el nino in 2014 similarities between early 1997 and 2014 has prompted climate scientists to wonder if an el nino matching the 1997 el nino of the century could develop in 2014 until april 2014 the equatorial pacific exhibited positive heat content anomalies along with an eastward warm pool displacement similar to those found during the onset of strong el nino events yet in july 2014 the warm pool had retreated back to its climatological positions and equatorial temperature anomalies were much weaker than in mid 1997 dedicated oceanic simulations reveal that these weak interannual anomalies can be attributed to differences in westerly wind event wwe sequences in contrast with 1997 the lack of wwes from april to june significantly limited the growth of eastern pacific anomalies and the eastward warm pool displacement in 2014 with the absence of additional wwe activity prospects for a mature el nino in late 2014 are fading

origin of decadal el nino southern oscillation like variability in a coupled general circulation model 1 the origin of decadal el nino southern oscillation like variability hereinafter referred to as dev is analyzed in coupled general circulation model cgcm simulations the cgcm experiments test the null hypothesis for the existence of dev that is that dev is linear damped and stochastically forced by atmospheric internal dynamics in order to test this hypothesis we employ the interactive ensemble coupling strategy it is found that the spatially averaged variance of sea surface temperature anomaly ssta and heat content anomaly hca associated with the dev is linearly related to the amplitude of atmospheric internal dynamics this result suggests that the dev is primarily noise forced but that damped coupled feedbacks and or internal ocean dynamics enhance this variability the ssta variability associated with the dev appears to be of a basin type standing mode with a triangular shape however the decadal evolution of the hca associated with the dev shows a systematic westward propagation from the central north pacific and the eastern south pacific both a singular vector analysis and noise variance analysis based on the coupled simulation results support the argument that atmospheric noise in the subtropics leads to the excitation of the dev

subtropical dipole mode in the southern hemisphere a global view a global wavenumber 3 dipole sst mode is showed to exist in the southern hemisphere subtropical climate variability in austral summer a positive negative phase of the mode is characterized by cool warm sst anomalies in the east and warm cool sst anomalies in the southwest of the south indian pacific and atlantic oceans respectively this coherent dipole structure is largely a response of ocean mixed layer to the atmospheric forcing characterized by migration and modulation of the subtropical high pressures in which the latent heat flux play a leading role through wind induced evaporation although ocean dynamics may also be crucial in forming sst anomalies attached to the continents exploratory analyses suggest that this mode is strongly damped by the negative heat flux feedback with a persistence time about three months and no spectral peak at interannual to decadal time scales as the subtropical dipole mode is linearly independent of enso and sam whether it represents an additional source of climate predictability should be further studied citation wang f 2010 subtropical dipole mode in the southern hemisphere a global view geophys res lett 37 l10702 doi 10 1029 2010gl042750

westerly wind events in the tropical pacific 1986 95 abstract based on examination of 10 yr of 10 m winds and wind anomalies from european centre for medium range weather forecasts ecwmf analysis definitions for westerly wind events wwes of eight different types are proposed the authors construct a composite for each type of event show that a simple propagating gaussian model satisfactorily describes the evolution of zonal wind anomaly for each type of event and determine the scales of each composite event by fitting the model to each composite the authors discuss the wwes that occurred during the tropical oceans global atmosphere coupled ocean atmosphere response experiment toga coare intensive observing period iop and show the extent to which these composite events are able to reproduce the major westerly wind features of the iop the frequency of occurrence of each type of wwe for each year of this record and by calendar month are described the authors find several types of events are negatively correlated with the annual mean troup souther

high precision locations of the microseismicity preceding the 2002 2003 mt etna eruption 1 to recognize possible signals of intrusive processes leading to the last 2002 2003 flank eruption at mt etna we analyzed the spatial pattern of microseismicity between august 2001 and october 2002 and calculated 23 fault plane solutions fpss for shocks with magnitude greater than 2 5 by applying the double difference approach of waldhauser and ellsworth 2000 on 3d locations we found that most of the scattered epicentral locations further collapse in roughly linear features high precision locations evidenced a distribution of earthquakes along two main alignments oriented ne sw to ene wsw and nw se matching well both with the known tectonic and volcanic lineaments of etna and fpss results moreover microseismicity and swarms located along the nnw sse volcano genetic trend suggest together with geodetic data and volcanological evidence that progressive magma refilling has occurred since february 2002

the south pacific meridional mode as a thermally driven source of enso amplitude modulation and uncertainty abstractthis study seeks to identify thermally driven sources of enso amplitude and uncertainty as they are relatively unexplored compared to wind driven sources pacific meridional modes are argued to be wind triggers for enso events this study offers an alternative role for the south pacific meridional mode spmm in enso dynamics not as an enso trigger but as a coincident source of latent heat flux lhf forcing of enso ssta that if correctly incorrectly predicted could reduce increase enso prediction errors we utilize a coupled model simulation in which enso variability is perfectly periodic and each el nino experiences identical wind stress forcing differences in el nino amplitude are primarily thermally driven via the spmm when el nino occurs coincidentally with positive phase spmm the positive spmm lhf anomaly counteracts a fraction of the lhf damping of el nino allowing for a more intense el nino if the spmm phase is instead negative the spmm lhf amplifies the lhf damping of el nin

soil co2 degassing along tectonic structures of mount etna sicily the pernicana fault abstract carbon dioxide emissions from the soil have been investigated along lines of equally spaced sampling points perpendicular to the pernicana fault on mt etna anomalous values of soil co2 have been found not only along the fault plane but also along directions parallel to it both to the n and to the s of the main fault the acquired data seem to reveal a shallow step like geometry of the pernicana fault system with parallel faults being generally not deeper than the interface between etna s volcanic cover and its sedimentary basement a few hundred meters the distribution of the anomalous co2 emissions has also revealed that the pernicana fault continues at least as far as the ionian sea in an area where only sedimentary rocks crop out this finding would suggest that the main structure is deeper than the base of the volcanic cover thus cutting at least the uppermost portion of etna s sedimentary basement isotopic analyses of c carried out in samples from locations of high co2 seem to indicate that the emitted co2 is a mixture of an organic shallow component and a minor deeper magmatic one both chemical and isotopic data on soil gases emitted in the easternmost part of the studied area distinguished another tectonic structure which seems to be much deeper than the pernicana fault and is roughly directed nne ssw this direction being coincident with an important structural trend of eastern sicily

intrusive mechanisms at mt etna forerunning the july august 2001 eruption from seismic and ground deformation data in this work we present seismological and ground deformation evidence for the phase preparing the july 18 to august 9 2001 flank eruption at etna the analysis performed through data from the permanent seismic and ground deformation networks highlighted a strong relationship between seismic strain release at depth and surface deformation this joint analysis provided strong constraints on the magma rising mechanisms we show that in the last ten years after the 1991 1993 eruption an overall accumulation of tension has affected the volcano then we investigate the months preceding the 2001 eruption in particular we analyse the strong seismic swarm on april 20 24 2001 comprising more than 200 events mmax 3 6 with prevalent dextral shear fault mechanisms in the western flank the swarm showed a ca ne sw earthquake alignment which in agreement with previous cases can be interpreted as the response of the medium to an intrusive process along the approximately nnw sse volcano genetic trend these mechanisms leading to the july 18 to august 9 2001 flank eruption are analogous to ones observed some months before the 1991 1993 flank eruption and more recently in january 1998 before the february november 1999 summit eruption

origin and subglacial erosion of part of the coastal highland of east antarctica the origin and erosional history of the eastern end of the coastal highlands of east antarctica within mac robertson kemp and enderby lands 50 64 e has been investigated using 13 000 km of ice thickness radar traversing the highlands are interpreted as the residual of widespread 1 km altitude crust within gondwanaland the low altitude of the adjacent coastal lowlands as due to crustal thinning caused by continental breakup and the low altitude of the areas inland as due to depression caused by the weight of the present ice sheet the coastal highlands are therefore a normal continental edge feature of a large ice sheet the highlands have an important influence on preserving the ice sheet and on ice sheet dynamics the topography and present day ice base temperatures of the highland and coastal lowland are consistent with a model containing three zones of glacial erosion proposed by sugden from exposed rocks in greenland in this model there is glacial erosion only on those rock surfaces where th

north american rainfall and temperature prediction response to the diversity of enso research has shown that there is significant diversity in the location of the maximum sea surface temperature anomaly ssta associated with the el nino southern oscillation enso in one extreme warm ssta peak near the south american coast often referred to as eastern pacific of ep el nino and at the other extreme warm ssta peak in the central pacific central pacific or cp el nino due to the differing tropical pacific ssta and precipitation structure there are differing extratropical responses particularly over north america recent work involving the north american multi model ensemble nmme system for intra seasonal to inter annual prediction on prediction of the differences between el nino events found excess warming in the eastern pacific during cp el nino events this manuscript investigates the ensemble and observational agreement of the nmme system when forecasting the north american response to the diversity of enso focusing on regional land based 2 meter temperature and precipitation nmme forecasts of north american precipitation and t2m agree with observations more often during ep events ensemble agreement of nmme forecasts is regional for instance ensemble agreement in southeast north america demonstrates a strong connection to nino3 precipitation and ssta amplitude during warm enso events ensemble agreement in northwest north america demonstrates a weak connection to nino4 precipitation and ssta amplitude during warm enso events still other regions do not show a strong connection between ensemble agreement and strength of warm enso events

tomographic images and 3d earthquake locations of the seismic swarm preceding the 2001 mt etna eruption evidence for a dyke intrusion 1 on july 12 2001 mt etna experienced a sudden increase of seismic activity heralding one of the most intense eruptions of the past 30 years between july 12 and july 18 when the eruption started thousands of small magnitude earthquakes occurred and were recorded by a dense seismic network run by the istituto nazionale di geofisica e vulcanologia sezione di catania ingv ct hypocentral depths of earthquakes were very shallow mostly located above 3 km b s l and clustered near the summit area the high quality seismic dataset gives us the unique opportunity to study the process of magma migration before the eruption in this study we present the three dimensional earthquake locations and the velocity structure obtained by a tomographic inversion the shallowness of seismicity allowed us to enhance the details of the structure beneath the summit craters in a volume poorly defined by previous tomographic studies the presence of a high vp body previously observed at mt etna is confirmed at shallow depth beneath the southeastern part of the summit area the earthquakes preceding the eruption onset concentrated at its western border a low vp vs anomaly is found at 0 1 km depth just at the top of the volume where the magma intruded before the eruption this anomalous zone can be considered as molten material wealthy in gas the relocated seismicity occurs in a cylinder below the vents activated along the fracture system and exhibited an upward migration until the eruption all these results show evidence for the emplacement of a near vertical dyke striking about n s and a few kilometres south of the summit craters

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

contributions of the north pacific meridional mode to ensemble spread of enso prediction abstractseasonal prediction of el nino southern oscillation enso employs the ensemble method which samples the uncertainty in initial conditions while much attention has been given to the ensemble mean the ensemble spread limits the reliability of the forecast spatiotemporal coevolution of intermember anomalies of sea surface temperature sst and low level winds over the pacific is examined in ensemble hindcasts two types of evolution of intermember sst anomalies in the equatorial pacific are identified the first features an apparent southwestward propagation of the sst spread from the subtropical northeastern pacific southeast of hawaii to the central equatorial pacific in boreal winter spring indicative of the precursor effect of the north pacific meridional mode npmm on enso variability extratropical atmospheric variability generates ensemble spread in enso through wind evaporation sst wes in the subtropical northeastern pacific and then bjerknes feedback on the equator in the second ty

composite ground deformation pattern forerunning the 2004 2005 mount etna eruption 1 after the end of the 2002 2003 eruption mount etna activity was characterized only by gentle degassing at the summit craters and some earthquake swarms suddenly an eruption started on 7 september 2004 in complete absence of summit crater volcanic activity seismicity or seismic tremor and ground deformation this is the first time that magma poured out passively without preeruptive and coeruptive volcanic and or geophysical phenomena the primary key to understanding this event is represented by the ground deformation pattern recorded through gps measurements during the year before the eruption the ground deformation shows inflation superimposed by a predominant eastward movement of the eastern sector at a rate never observed before in a noneruptive period the images from satellite radar interferometry confirmed this pattern the deformation field clearly shows that the maximum tension in the eastern sector of the volcano caused the opening of the eruptive fracture which favored the silent pouring out of already resident magma

the volume and shape of the 1991 1993 lava flow field at mount etna sicily the 1991 1993 lava flow is the most voluminous flow erupted at mount etna sicily in over 300 years estimates of the volume obtained by various methods range from 205 106 m3 tanguy 1996 to over 500 106 m3 barberi et al 1993 this paper describes the results of an electronic distance measurement edm based field survey of the upper surface of the 1991 1993 flow field undertaken in 1995 the results were digitised interpolated and converted into a digital elevation model and then compared with a pre eruption digital elevation model constructed from a 1 25 000 contour map of the area based on 1989 aerial photographs our measurements are the most accurate to date and show that the 1991 1993 lava flow occupies a volume of 231 29 106 m3

continuous soil radon monitoring during the july 2006 etna eruption 1 continuous soil radon monitoring was carried out near the southeast crater sec of mt etna during the 10 day july 2006 strombolian effusive eruption this signal was compared with simultaneously acquired volcanic tremor and thermal radiance data the onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4 5 orders of magnitude which we interpret as precursors minor changes in eruptive behavior did not produce significant variations in the monitored parameters the remarkably high radon concentrations we observed are unprecedented in the literature we interpret peaks in radon activity as due primarily to microfracturing of uranium bearing rock these observations suggest that radon measurements in the summit area of etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions citation neri m b behncke m burton g galli s giammanco e pecora e privitera and d reitano 2006 continuous soil radon monitoring during the july 2006 etna eruption geophys res lett 33 l24316 doi 10 1029 2006gl028394

magma storage eruptive activity and flank instability inferences from ground deformation and gravity changes during the 1993 2000 recharging of mt etna volcano abstract a long recharging period characterized mount etna volcano during 1993 2000 before the main explosive effusive 2001 and 2002 2003 flank eruptions the joint analysis of ground deformation and gravity data over the recharge period reveals that different phenomena occurred within etna s plumbing system and clearly indicates two phases spanning 1993 1997 and 1997 2000 respectively the first phase was characterized by magma storage and accumulation at an intermediate depth 2 6 km below sea level which provoked overall inflation and positive gravity changes during the second phase the magma started to rise and intrude at shallower levels favoring the movement of the unstable eastern flank which accelerated its sliding toward the east the shallower magma accumulation also caused the gas exsolution associated with increasing explosive activity at the summit craters negative gravity changes were detected during this phase the gravity measurements independent of the same result obtained by geochemical studies suggest that only 20 30 of the magma volumes supplied in the plumbing system were then erupted the complex dynamics of rising magma beneath mount etna makes ground deformation and gravity measurements complementary being able to detect different effects of magma emplacements beneath the surface our results also highlight how the joint use of ground deformation and gravity observations may be crucial in identifying the nature and rate of an impending period of volcanic eruptions

the 2004 2005 etna eruption implications for flank deformation and structural behaviour of the volcano the development of the 2004 2005 eruption at etna italy is investigated by means of field surveys to define the current structural state of the volcano in 2004 2005 a fracture swarm associated with three effusive vents propagated downslope from the se summit crater towards the se such a scenario is commonly observed at etna as a pressure increase within the central conduits induces the lateral propagation of most of the dikes downslope nevertheless some unusual features of this eruption slower propagation of fractures lack of explosive activity and seismicity oblique shear along the fractures suggest a more complex triggering mechanism a detailed review of the recent activity at etna enables us to better define this possible mechanism in fact the nw se trending fractures formed in 2004 2005 constitute the southeastern continuation of a n s trending fracture system which started to develop in early 1998 to the east of the summit craters the overall 1998 2005 deformation pattern therefore forms an arcuate feature whose geometry and kinematics are consistent with the head of a shallow flank deformation on the e summit of etna similar deformation patterns have also been observed in analogue models of deforming volcanic cones in this framework the 2004 2005 eruption was possibly induced by a dike resulting from the intersection of this incipient fracture system with the se crater a significant acceleration of this flank deformation may be induced by any magmatic involvement the central conduit of the volcano is presently open constantly buffering any increase in magmatic pressure and any hazardous consequence can be expected to be limited a more hazardous scenario may be considered with a partial or total closing of the central conduit in this case magmatic overpressure within the central conduit may enhance the collapse of the upper eastern flank triggering an explosive eruption associated with a landslide reaching the eastern lower slope of the volcano

long term record of co2 degassing along mt etna s flanks and its relationship with magma dynamics and eastern flank instability a record of soil co2 flux data on the lower flanks of mt etna measured from 1989 to 2008 is discussed in the framework of multidisciplinary observations including seismicity ground deformations and flank instability a huge increase in soil co2 fluxes appears to be related to the dynamics of magma ascent in the upper portions of the volcano 0 3 km and the intrusion of dykes along the southern rift as mainly observed before the 1991 93 eruption even after the 1991 93 eruption the recharge of the shallow central reservoir was accompanied by a long term increase in soil co2 degassing mainly in the southwestern area the 2001 eruption marked dramatic changes in the areal distribution of seismicity the deformation pattern and the soil co2 degassing indeed while the soil co2 degassing showed background values in the southwestern area it progressively increased in the eastern sector and along the pernicana fault this has been related to the marked sliding of the eastern flank since the 2002 03 eruption and the associated seismicity this study provides evidence that the extent of soil co2 degassing on the lower flanks of mt etna is controlled by 1 the volume of involved magma 2 the intrusion of dykes in the upper parts of the volcano and 3 fault movement and seismicity this implies that different degassing structures must be monitored simultaneously when attempting to understand the behavior of the volcano as a whole

predictability of a coupled model of enso using singular vector analysis part i optimal growth in seasonal background and enso cycles the fastest initial error growth optimal growth in the zebiak and cane zc forecast model for the el nino southern oscillation enso is analyzed by singular value decomposition of a forward tangent model along a trajectory in a reduced eof space in this paper part i of ii optimal growth about the seasonally varying background and enso cycles from a long model run are discussed among the many forms of nonlinearity in zc the discontinuity of the slope in subsurface temperature at zero thermocline depth and the nonlinear advection of sst are the most significant that positive perturbations grow much faster than negative perturbations around the seasonally varying background is first attributable to the discontinuity and second attributable to nonlinear advection about the seasonally varying background 6 month optimal growth is largest for early boreal spring starts which is related to the enhanced atmospheric heating due to equatorward movement of the itcz one dominant growing structure is found characterized by north south and east west sst dipoles convergent winds on the equator in the eastern pacific and a deepened thermocline in the whole equatorial belt this structure is insensitive to start month and optimization time optimal growth about enso cycles in a long model run is generally much smaller than that about the seasonally varying background as before one dominant growing structure insensitive to start time and optimization time is found during the warm phase of enso optimal growth is modulated by season as is that about the seasonal varying background during the onset and mature phases of enso the final pattern of the optimal structure in 6 months is confined to the eastern pacific during the decay phase of enso it spreads to the western pacific as well during the cold phase of enso optimal growth has two maxima in a year early spring and fall the optimal perturbation propagates westward associated with surface layer wind interaction the authors also compare the singular vector analysis in eof space and the standard one in physical space the importance of norm definition to optimal growth and optimal structure is discussed

melt inclusion record of the conditions of ascent degassing and extrusion of volatile rich alkali basalt during the powerful 2002 flank eruption of mount etna italy 1 two unusual highly explosive flank eruptions succeeded on mount etna in july august 2001 and in october 2002 to january 2003 raising the possibility of changing magmatic conditions here we decipher the origin and mechanisms of the second eruption from the composition and volatile h2o co2 s cl content of olivine hosted melt inclusions in explosive products from its south flank vents our results demonstrate that powerful lava fountains and ash columns at the eruption onset were sustained by closed system ascent of a batch of primitive volatile rich 4 wt basaltic magma that rose from 10 km depth below sea level bsl and suddenly extruded through 2001 fractures maintained opened by eastward flank spreading this magma the most primitive for 240 years probably represents the alkali rich parental end member responsible for etna lavas evolution since the early 1970s few of it was directly extruded at the eruption onset but its input likely pressurized the shallow plumbing system several weeks before the eruption this latter was subsequently fed by the extrusion and degassing of larger amounts of the same but slightly more evolved magma that were ponding at 6 4 km bsl in agreement with seismic data and with the lack of preeruptive so2 accumulation above the initial depth of sulphur exsolution 3 km bsl we find that while ponding this magma was flushed and dehydrated by a co2 rich gas phase of deeper derivation a process that may commonly affect the plumbing system of etna and other alkali basaltic volcanoes

modulation of equatorial pacific westerly easterly wind events by the madden julian oscillation and convectively coupled rossby waves synoptic wind events in the equatorial pacific strongly influence the el nino southern oscillation enso evolution this paper characterizes the spatio temporal distribution of easterly ewes and westerly wind events wwes and quantifies their relationship with intraseasonal and interannual large scale climate variability we unambiguously demonstrate that the madden julian oscillation mjo and convectively coupled rossby waves crw modulate both wwes and ewes occurrence probability 86 of wwes occur within convective mjo and or crw phases and 83 of ewes occur within the suppressed phase of mjo and or crw 41 of wwes and 26 of ewes are in particular associated with the combined occurrence of a crw mjo far more than what would be expected from a random distribution 3 wind events embedded within mjo phases also have a stronger impact on the ocean due to a tendency to have a larger amplitude zonal extent and longer duration these findings are robust irrespective of the wind events and mjo crw detection methods while wwes and ewes behave rather symmetrically with respect to mjo crw activity the impact of enso on wind events is asymmetrical the wwes occurrence probability indeed increases when the warm pool is displaced eastward during el nino events an increase that can partly be related to interannual modulation of the mjo crw activity in the western pacific on the other hand the ewes modulation by enso is less robust and strongly depends on the wind event detection method the consequences of these results for enso predictability are discussed

contrasting triggering mechanisms of the 2001 and 2002 2003 eruptions of mount etna italy abstract mount etna produced two significant eruptions in 2001 and 2002 2003 which we have analysed using geological seismic and deformation data these eruptions showed some similarities such as the activating of two magmatic plumbing systems central lateral and eccentric but they differed in their triggering mechanisms while the 2001 eruption was largely the result of the emplacement of a n s eccentric dike independent from the central conduits consistent with e w regional extension the 2002 2003 eruption occurred in response to a major flank slip on the eastern and southeastern sides of the volcano this is demonstrated by the spatial and temporal distribution of seismicity and deformation preceding and accompanying the two eruptions during the months prior to the 2001 eruption most epicenters were concentrated on the southern flank at depths of 5 15 km below sea level during the 4 days before the eruption earthquake hypocenters migrated to shallower levels from 5 km bsl upward indicating the emplacement of the eccentric dike this is confirmed by the patterns of ground fracturing observed in the field and deformation documented by electronic distance measurements edm in contrast the months before the 2002 2003 eruption were characterised by shallower seismicity mainly concentrated along the active faults bordering the slipping flank sector flank slip accelerated in september 2002 and a second more vigorous acceleration of flank slip occurred on 26 27 october 2002 accompanying the opening of eruptive vents the very short 2 h seismic crisis preceding the onset of eruptive activity stands in neat contrast with the 4 days of intense seismicity before the 2001 eruption subsequently flank slip deformation extended all over the eastern and southeastern flanks of the volcano causing serious damage in this sector the events of 2001 2003 can be seen as a continuous chain of intimately interacting processes including regional tectonics magma accumulation and eruption and flank instability in this scenario the 2001 eruption led to increased flank instability that subsequently accelerated and culminated with the massive flank slip which in turn facilitated the 2002 2003 eruption this sequence of events points to a long term feedback mechanism between magmatism and flank instability at etna

faulting on the western flank of mt etna and magma intrusions in the shallow crust surface deformations on the western flank of mt etna volcano spanning 1980 2004 have been analysed as they pertain to stress interactions between magma intrusions within the shallow crust along the s se rift and faulting sensitivity during this period an accurate analysis of strain parameters computed by inversion of sw electro optical distance data suggested that the observed strong displacements on this flank of the edifice can also be related to dextral shear movements along a roughly ne sw buried fault crossing the area covered

interannual variations of atlantic tropical instability waves 1 observations are used to develop metrics for interannual tropical instability wave tiw variability in the atlantic and to relate that variability to larger scale processes the analysis is partitioned into different latitude bands to distinguish between off equatorial 5 s 2 n and 5 n and near equatorial 2 s and 0 tiws tiw metrics based on sea surface temperature sst and sea level anomaly sla fluctuations are compared against interannual anomalies of sst in the cold tongue region to examine the role of barotropic shear instabilities in modulating the intensity of a tiw season wind stress and near surface current indices are developed in regions where the shear between the equatorial undercurrent euc and the northern branch of the south equatorial current nsec and between the nsec and the north equatorial countercurrent necc are expected to be largest good agreement is found between the sst and sla tiw metrics along the off equatorial latitude bands and interannual variations of both metrics can largely be attributed to barotropic shear instabilities in particular years with low high tiw variance along the off equatorial latitude bands are associated with anomalously warm cold ssts in the cold tongue region weak strong wind stress divergence and curl in the euc nsec region and weak strong zonal current shear in the nsec necc region in contrast in the near equatorial latitude bands poor agreement is found between interannual tiw activity based on the sst and sla metrics and near equatorial tiw variability cannot be explained by the large scale sst wind stress divergence and curl and current shear indices

equatorial wave sequence associated with warm pool displacements during the 1986 1989 el nino la nina in the pacific equatorial band the zonal displacement of the eastern edge of the warm pool subject to insignificant seasonal variations is dominated by strong interannual variations almost in phase with the southern oscillation index over the 1971 1973 el nino la nina period gill 1983 suggested that such displacement was caused solely by horizontal advection by zonal current anomaly basin wide geosat derived zonal surface current anomalies are available during the 1986 1989 period and they agree quite well with observed equatorial currents in the western and central pacific within the 4on 4 s equatorial band the cumulative contribution of first baroclinic kelvin and first symmetric m 1 rossby modes to surface zonal equatorial current anomalies account for most of the geosat derived current variability from these geosat derived currents it is demonstrated that the eastward westward displacement of the eastern edge of the warm pool was primarily due to horizontal advection by zonal current anomalies during the 1986 1987 el nino 1988 1989 la nina as a corollary the el nino la nina warm cold sea surface temperature sst anomaly in the central western pacific was the result of anomalous zonal advection the 1986 1989 displacement of the warm pool appeared as a low frequency movement resulting from high frequency forcing i e a succession of local wind forcing and its remote kelvin and m 1 rossby wave responses in the equatorial waveguide in the central western pacific a in 1 downwelling rossby wave issued from the eastern pacific shifted the displacement from eastward to westward and therefore seems to have been the cause for el nino to turn to la nina in boreal fall 1987 in the eastern pacific the simultaneous occurrence of free propagating downwelling upwelling kelvin waves with the seasonal sst warming cooling appeared necessary for the development of local el nino la nina sst anomaly over most of the equatorial pacific slow migration of sst anomalies clearly showed up distinct during el nino and la nina these zonal migrations appeared to result from the delayed association of two phenomena the zonal advection in the central western pacific and the arrival of downwelling upwelling kelvin waves into the eastern pacific synchronous with the seasonal sst warming cooling albeit different in terms of equatorial wave action as compared to the delayed action oscillator theory our results suggest that zonal advection and wave dynamics were both important for the generation and migration of el nino southern oscillation sst anomalies in 1986 1989 finally our observational results about warm pool displacements equatorial wave sequence the shift from el nino to la nina and the slow sst migrations are presented in a schematic form involving sequential ocean atmosphere coupling which appears continuously over the november 1986 to a

why the southern hemisphere enso responses lead enso 1 analysis of observational estimates indicates that the el nino southern oscillation enso forced pattern in the extratropical southern hemisphere sh somewhat surprisingly leads the peak phase of enso by one season a rossby wave source rws analysis indicates that the tropical and extratropical rws in the sh develops before the enso peak season and abruptly weakens thereafter further analysis shows that anomalous divergence convergence and corresponding irrotational wind anomalies are sensitive to local seasonality numerical experiments in which the tropical pacific is prescribed with perfectly periodic enso while all other oceans are simulated as a slab mixed layer model coupled to agcm also show similar features additional numerical experiments in which enso forcing is shifted by 6 months i e the enso peak in the southern winter season indicate that the northern hemisphere atmosphere rather than the sh atmosphere precedes enso this result supports the hypothesis that the enso forced pattern in the extratropics is strongly limited by local seasonality rather than by the temporal phase of tropical remote forcing

magma movements in etna volcano associated with the major 1991 1993 lava eruption evidence from gravity and deformation the 1991 1993 eruption was probably the largest on mt etna for 300 years since then the volcano has entered an unusually quiescent period a comprehensive record of gravity and ground deformation changes presented here bracket this eruption and give valuable insight into magma movements before during and after the eruption the gravity and deformation changes observed before the eruption 1990 1991 record the intrusion of magma into the summit feeder and the sse trending fracture system which had recently been active in 1978 1979 1983 and 1989 creating the feeder dyke for the 1991 1993 eruption in the summit region gravity changes between 1992 and 1993 spanning the end of the eruption reflect the withdrawal of magma from the conduit followed more recently 1993 1994 by the re filling of magma in the conduit up to pre eruption levels in contrast in the vicinity of the fracture zone gravity has remained at the 1991 1992 level indicating that no withdrawal has occurred here rather magma has solidified in the fracture system and sealed it such that the 1993 1994 increase in magma level in the conduit was not accompanied by further intrusion into the flanks mass calculations suggest that a volume of at least 107 m3 of magma has solidified within the southeastern flank of the volcano

sea surface cooling at the equator by subsurface mixing in tropical instability waves changes in the sea surface temperature of equatorial waters have critical effects on the large scale atmospheric circulation shipboard measurements of turbulence kinetic energy dissipation rate indicate that seasonal surface cooling in the central equatorial pacific may be largely caused by mixing induced by tropical instability waves

eastern equatorial pacific response to three composite westerly wind types it has been suggested recently that episodes of westerly wind near the international date line in the western pacific tend to fall into one of four types three of the types have enough equatorial zonal wind variation to be able to induce an eastern pacific response by forcing equatorial waves in this note we examine the central and eastern pacific waveguide response to idealized representations of these three types of westerly wind episodes using a combination of linear theory and results from an ocean general circulation model the idealized westerly wind types are the c type maximum anomalies centered on the equator the n type maximum anomalies just north of the equator and the s type maximum anomalies just south of the equator the composite c type event excites equatorially trapped kelvin pulses that alter sea surface temperature in the central and eastern pacific warm anomalies caused by the c type episode have approximately equal contributions from a zonal advection of heat by the kelvin pulses and a meridional advection of heat by an altered instability wave field because the center of forcing of the s type event is displaced off of the equator the kelvin pulses excited by the s type episode have smaller amplitude than those of the c type episode even though the maximum wind anomaly is the same in the two cases the s type anomaly also excites weak rossby gravity waves that can propagate into the eastern pacific because the rossby gravity waves are dispersive their amplitude diminishes as the waves propagate into the eastern pacific the n type episode as observed in winds from the western tropical pacific is much weaker and of shorter duration than the c and s types and therefore excites only a very weak eastern pacific response although all types of westerly wind excite a local western pacific response only the c and s type events excite a significant eastern pacific response

impact of the south and north pacific meridional modes on the el nino southern oscillation observational analysis and comparison abstractan interannual variability mode in the southeast pacific with a physical interpretation similar to that of the pacific meridional mode pmm in the north pacific was recently identified both modes have been shown to influence the subsequent development of el nino southern oscillation enso events this study investigates the relationship between enso and the two pmms using observational and reanalysis data the results show that the south pacific meridional mode spmm mainly favors the development of sea surface temperature anomalies sstas in the eastern equatorial pacific whereas the north pacific meridional mode npmm mainly favors the development of sstas in the central equatorial pacific both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of enso when considering different flavors of enso neither the npmm nor the spmm can be precluded as accurate indicators when forecasting particular flavors of enso

deformation and eruptions at mt etna italy a lesson from 15 years of observations this work was partly funded by ingv and the italian dpc and was supported by asi the preview project and crdc amra dpc ingv flank project providing the funds for the publication fees

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

insights into fluid circulation across the pernicana fault mt etna italy and implications for flank instability article i nfo we conducted geophysical geochemical measurements on a 2k m n s profile cutting across the pernicana fault one of the most active tectonic features on the ne flank of mt etna the profile passes from the unstable e flank of the volcano to the south to the stable n flank and significant fluctuations in electrical resistivity self potential and soil gas emissions co2 rn and th are found the detailed multidisciplinary analysis reveals a complex interplay between the structural setting uprising hydrothermal fluids meteoric fluids percolating downwards ground permeability and surface topography in particular the recovered fluid circulation model highlights that the southern sector is heavily fractured and faulted allowing the formation of convective hydrothermal cells although the existence of a hydrothermal system in a volcanic area does not surprise these results have great implications in terms of flank dynamics at mt etna indeed the hydrothermal activity interacting with the pernicana fault activity could enhance the flank instability our approach should be further extended along the full extent of the boundary between the stable and unstable sectors of etna for a better evaluation of the geohazard in this active tectonic area

the pacific meridional mode as a trigger for enso in a high resolution coupled model 1 this study investigates el nino precursors in a high resolution version of ccsm3 5 first using an empirical orthogonal function analysis of all non enso tropical pacific variability we find that the pacific meridional mode pmm acts as an enso trigger 7 9 months prior to large el nino events in the model which is consistent with previous model and observational studies however because not every pmm event triggers an enso event we also find that pmm appears to be an effective trigger when the western to central pacific is preconditioned i e anomalously high sea surface heights or heat content second this study looks at the contribution of western pacific variability namely westerly wind bursts wwbs as well as all other non enso variability in the tropical pacific we find that the relative importance of low frequency climate variability associated with pmm dominates over other non enso variability between 15 n and 15 s including high frequency atmospheric variability and wwbs in acting as a precursor to el nino events

petrology of lavas from the 2004 2005 flank eruption of mt etna italy inferences on the dynamics of magma in the shallow plumbing system following the 2001 and 2002 2003 flank eruptions activity resumed at mt etna on 7 september 2004 and lasted for about 6 months this paper presents new petrographic major and trace element and sr nd isotope data from sequential samples collected during the entire 2004 2005 eruption the progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits the compositional variability of products erupted up to 24 september is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002 2003 eruption the progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 september to 15 october after 15 october the contribution from the new magma gradually becomes predominant and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of mt etna during a flank eruption furthermore they confirm that the 2004 2005 activity at etna was triggered by regional movements of the eastern flank of the volcano they caused the opening of a complex fracture zone extending ese which drained a magma stored at shallow depth since the 2002 2003 eruption this process favored the ascent of a different magma in the central conduits which began to be erupted on 24 september without any significant change in eruptive style deformation and seismicity until the end of eruption

continuous soil co2 and discrete plume so2 measurements at mt etna italy during 1997 2000 a contribution to volcano monitoring continuous monitoring of soil co2 dynamic concentration which is proportional to the co2 flux through the soil was carried out at a peripheral site of mt etna during the period november 1997 september 2000 using an automated station the acquired data were compared with so2 flux from the summit craters measured two to three times a week during the same period the high frequency of data acquisition with both methods allowed us to analyze in detail the time variations of both parameters anomalous high values of soil co2 dynamic concentration always preceded periods of increased flux of plume so2 and these in turn were followed by periods of summit eruptions the variations were modeled in terms of gas efflux increase due to magma ascent to shallow depth and its consequent depressurization and degassing this model is supported by data from other geophysical and volcanological parameters the rates of increase both of soil co2 dynamic concentration and of plume so2 flux are interpreted to be positively correlated both to the velocity of magma ascent within the volcano and to lava effusion rate once magma is erupted at the surface low rates of the increase were recorded before the nine month long 1999 subterminal eruption higher rates of increase were observed before the violent summit eruption of september november 1999 and the highest rates were observed during shorter and very frequent spike like anomalies that preceded the sequence of short lived but very violent summit eruptions that started in late january 2000 and continued until late june of the same year furthermore the time interval between the peaks of co2 and so2 in a single sequence of gas anomalies is likely to be controlled by magma ascent velocity

continuous monitoring of soil co2 flux on mt etna the 2004 2005 eruption and the role of regional tectonics and volcano tectonics 1 the soil co2 flux on mt etna as recorded by the etnagas network an automatic system for measuring soil co2 flux and meteorological parameters started to increase strongly about 5 months prior to the onset of the 2004 2005 eruption and decreased a few months before the end of the eruption time delays in the occurrences of anomalies in soil co2 flux at different sites in the geochemical network constrain the relationship between soil co2 flux distributions and the tectonic framework of etna volcano the anomalies observed before the 2004 2005 eruption support the intrusion of new undegassed magma into the upper feeding system of the volcano 20 km below sea level magma subsequently rose slowly in the volcano conduits thereby triggering the onset of the 2004 2005 eruption the time delays in the occurrences of anomalies in combination with spectral analysis indicate the importance of tectonic and volcanotectonic structures in driving the ascent of deep gases within the crust moreover greatest amplitude pulsations of the low frequency components of the co2 flux signals were correlated with the paroxystic activities of the 2004 2005 eruption this study confirms that co2 flux variation is a useful indicator for volcanic activity in the surveillance of the mt etna and similar basaltic volcanoes

rates of carbon dioxide plume degassing from mount etna volcano 1 we report here on the real time measurement of co2 and so2 concentrations in the near vent volcanic gas plume of mount etna acquired by the use of a field portable gas analyzer during a series of periodic field surveys on the volcano s summit during the investigated period september 2004 to september 2005 the plume co2 so2 ratio ranged from 1 9 to 10 8 with contrasting composition for northeast and voragine crater plumes scaling the above co2 so2 ratios by uv spectroscopy determined so2 emission rates we estimate co2 emission rates from the volcano in the range 0 9 67 5 kt d 1 average 9 kt d 1 about 2 kt of co2 were emitted daily on average during quiescent passive degassing whereas co2 emission rates from etna s summit were 10 40 times larger during the 2004 2005 effusive event with a cumulative co2 release of 3800 kt during the 6 months of the eruption such a syneruptive increase ascribed to the replenishment of the shallow 6 km volcanic plumbing system by co2 rich 0 25 wt more primitive magmas supports the potential of co2 output rates as key parameters for volcanic hazard assessment

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

degassing of so2 and co2 at mount etna sicily as an indicator of pre eruptive ascent and shallow emplacement of magma abstract we studied soil co 2 emissions together with crater so 2 fluxes from mt etna during the period july 1997 to march 1999 this period was characterized by high levels of volcanic activity and ended with the onset of a 10 month long sub terminal eruption on february 4 1999 soil co 2 degassing was measured at two sites p39 on the lower sw flank of etna and p78 on the e flank known for being connected to deep faults that allow the escape of magmatic gas site p39 is inferred to drain gas from a deep 15 km magma reservoir whereas site p78 is connected to a shallower 5 10 km reservoir based on the temporal variations of measured soil co 2 and crater so 2 data five intervals of anomalous degassing were recognized each of them is interpreted as due to massive gas release from a magma batch that is moving toward the surface the time lag between the occurrence of degassing anomalies of co 2 and those of so 2 agrees well with the different depth of exsolution of the two gases our data also indicate a step like migration of magma to the surface which bears on the existence of at least three different temporary storage levels within etna s feeder system lastly the observed anomalies preceded by months to weeks increases in the summit activity of mt etna including the february 4 1999 eruption comparison between the amounts of degassing magma during each interval of anomalous degassing based on so 2 fluxes and erupted volumes of lava during the same periods seems to indicate that the 1999 eruption was largely fed by magma that started entering the upper feeder system of etna about 1 year earlier

modulation of westerly wind bursts by sea surface temperature a semistochastic feedback for enso abstract westerly wind bursts wwbs in the equatorial pacific are known to play a significant role in the development of el nino events they have typically been treated as a purely stochastic external forcing of enso recent observations however show that wwb characteristics depend upon the large scale sst field the consequences of such a wwb modulation by sst are examined using an ocean general circulation model coupled to a statistical atmosphere model i e a hybrid coupled model an explicit wwb component is added to the model with guidance from a 23 yr observational record the wwb parameterization scheme is constructed such that the likelihood of wwb occurrence increases as the western pacific warm pool extends a semistochastic formulation which has both deterministic and stochastic elements the location of the wwbs is parameterized to migrate with the edge of the warm pool it is found that modulation of wwbs by sst strongly affects the characteristics of enso in particular coupled fe

on the joint role of subtropical atmospheric variability and equatorial subsurface heat content anomalies in initiating the onset of enso events abstract previous research has shown that seasonal mean variations in both the subtropical extratropical sea level pressures over the central north pacific and the subsurface heat content anomalies in the western equatorial pacific are significantly related to the state of the el nino southern oscillation enso 12 18 months later here we find that positive negative subsurface temperature anomalies in the western equatorial pacific during boreal summer fall followed by negative positive anomalies in the sea level pressure fields over the subtropical central north pacific during boreal winter tend to result in positive negative mature enso events 12 15 months later i e during the following boreal winter when the intervening sea level pressure anomalies are of the same sign as the preceding heat content anomalies the correlation between the heat content anomalies and the following boreal winter enso state disappears there is still some relation between the boreal winter sea level pressure an

geochemical investigations applied to active fault detection in a volcanic area the north east rift on mt etna sicily italy geochemical investigations were performed on the northeast rift of mt etna a prominent volcanic structure of this volcano low temperature fumaroles were found on the upper part of this area and the isotopic compositions of c co2 and he suggest a likely magmatic origin of the emitted gases on the contrary very low degassing was found in the lower part of the ne rift with co2 concentrations generally very close to those in air this pattern is probably due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing high soil co2 concentrations were also found in an elongated area parallel to the ne rift and located immediately to the east of it the geometry of these anomalies suggests the existence of several hidden faults sub parallel to the ne rift and likely connected to the pernicana fault system this latter structure seems to merge with the ne rift at the altitude where the fumarole emissions are located the hidden structures together with the pernicana system and the ne rift represent the western and northern boundaries of a large eastward collapsing sector of mt etna

structural features of an active strike slip fault on the sliding flank of mt etna italy abstract the strike slip pernicana fault system pfs was activated along the eastern flank of mt etna during an earthquake in september 2002 and one month later during the eruption of the ne rift structural and volcanological data suggest that the pfs was activated as a result of the slide of the ne flank of etna this activation produced surface fracturing on walls and on paved and unpaved roads the segments of the pfs arranged in a right stepping en echelon configuration show a an inverse proportion between length and frequency b fractal behavior over scales of 10 2 10 1 m between their length overstep and overlap c consistent strike with regard to their fault array and d a progressive eastward decrease in the displacement along the smallest faults the consistent geometric and kinematic features of the pfs related to the sector collapse of etna are similar to those of faults in strike slip settings

thermodynamic coupled modes in the tropical atmosphere ocean an analytical solution the present study provides a consistent and unified solution for the two types of thermodynamical coupled modes in the atmosphere ocean climate system the tropical meridional mode and the subtropical dipole mode the solution is derived analytically from a linear model that couples a simple atmosphere to a slab ocean via the wind evaporation sst wes feedback for a mean zonal wind the results show that the wind hence latent heat flux anomaly and the sst anomaly differ in phase such that the tropical mode propagates downwind and the subtropical modes propagate upwind with both modes being damped by the sst driven component of latent heat flux despite the existence of positive wes feedback the large scale subtropical modes are always stable while the tropical mode can become unstable only when the air sea coupling is strong and the mean wind is easterly furthermore the mean meridional winds break the equatorial symmetry and enable the coupled modes to intensify in the southern northern hemisphere for a southerly northerly component for realistic parameter values these thermodynamical coupled modes have periods and damping time scales in years hence they may play important roles in the tropical interannual to decadal climate variability

equatorial signatures of the pacific meridional modes dependence on mean climate state extratropical atmospheric variability can impact tropical climate in the pacific sector via the pacific meridional modes pmms the south pmm spmm has a larger equatorial signature than the north pmm npmm for the same amount of extratropical variability here we explain this interhemispheric asymmetry using an atmospheric general circulation model coupled to a slab ocean model by imposing an anomalous interhemispheric heating gradient we strengthen the northeasterly trades and weaken the southeasterly trades shifting the intertropical convergence zone south of the equator as a result the spmm no longer influences the equatorial region while the npmm shows strengthened linkages to the central western equatorial pacific by demonstrating that background winds determine the propagation of the wind evaporation sea surface temperature feedback fundamental for the pmms we conclude that the interhemispheric asymmetry between the pmms is largely attributed to the asymmetric mean trades in the pacific the results have implications for both paleoclimate studies and model development

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

tectonic control on the eruptive dynamics at mt etna volcano sicily during the 2001 and 2002 2003 eruptions abstract the eruptive events of the july august 2001 and october 2002 january 2003 at mt etna provide new insights for reconstructing the complex geometry of the feeding system and their relationship to regional tectonics the 2001 eruption took place mainly on the upper southern sector of the volcano the eruption was preceded by a large earthquake swarm for a few days before its onset and accompanied by ground deformation and fracturing the development of surface cracking along with the seismic pattern has allowed us to recognize three distinct eruptive systems the sw ne nnw sse and n s systems which have been simultaneously active such eruptive systems are only the upper portions of a complex feeding system that was fed at the same time by two distinct magmas the sw ne and nnw sse systems connected with the se crater conduit were fed by magma coming from depth whereas the n s system served instead as an ascending pathway for an amphibole bearing magma residing in a shallow reservoir the eruptive activity started again on october 2002 on the ne rift zone where about 20 eruptive vents were aligned between 2500 and 1900 m a s l and on the southern flank from the central crater to the montagnola the onset of eruptive activity was accompanied by a seismic swarm as in the 2001 eruptive event two independent feeding systems formed characterized by distinct magmas the sw ne system controlled the feeding of the northeast rift and was accommodated by left lateral displacement along the wnw ese trending pernicana fault the n s system fed the eruptions on the southern flank moreover the associated crustal deformation triggered seismic reactivation of tectonic structures in the eastern flank of the volcano and offshore these two last eruptions indicate that at mt etna the ascent of magma as well as the accommodation of deformation is strongly dominated by local extensional structures that are connected to a regional tectonic regime

total volatile flux from mount etna 1 the total volatile tv flux from mount etna volcano has been characterised for the first time by summing the simultaneously evaluated fluxes of the three main volcanogenic volatiles h2o co2 and so2 so2 flux was determined by routine doas traverse measurements while h2o and co2 were evaluated by scaling multigas sensed h2o so2 and co2 so2 plume ratios to the uv sensed so2 flux the time averaged tv flux from etna is evaluated at 21 000 t day 1 with a large fraction accounted for by h2o 13 000 t day 1 h2o dominates 70 the volatile budget during syn eruptive degassing while co2 and h2o contribute equally to the tv flux during passive degassing the co2 flux was observed to be particularly high prior to the 2006 eruption suggesting that this parameter is a good candidate for eruption prediction at basaltic volcanoes

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

the extreme el nino of 2015 2016 the role of westerly and easterly wind bursts and preconditioning by the failed 2014 event at the beginning of 2015 as one year earlier in 2014 the scientific community anticipated that el nino conditions could develop in the tropical pacific by year end such projections were related to the occurrence of westerly wind bursts during winter spring of each year that generated strong downwelling kelvin waves indicative of an emerging el nino however the event s progression quickly stalled in 2014 but actively continued in 2015 leading to an extreme warm event comparable to 1997 or 1982 here we compare climate evolution during these two years using satellite observations and numerical simulations we show that during 2014 el nino development was interrupted mid year by an exceptionally strong easterly wind burst whereas during the second year it continued through the summer further we show that the failed 2014 event created favorable conditions for el nino development during the next year as it kept ocean heat content recharged and the western pacific warm pool extended eastward subsequently the winter spring westerly wind bursts in 2015 were followed by a series of state dependent westerly bursts as part of a strong positive bjerknes feedback analogue simulations with a coupled gcm wherein we superimpose the observed sequences of westerly and easterly wind bursts support these conclusions stressing the role of the failed 2014 event in preconditioning the ocean atmosphere system for the development of an extreme el nino in our simulations the probability of an extreme event following early year westerly wind bursts increases from 14 to nearly 60 due to this preconditioning thus the interplay between westerly and easterly wind bursts shapes el nino development and diversity

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

pacific meridional mode and el nino southern oscillation 1 we present intriguing evidence that the majority of el nino events over the past four decades are preceded by a distinctive sea surface warming and southwesterly wind anomaly in the vicinity of the intertropical convergence zone itcz during the boreal spring this phenomenon known as the meridional mode mm is shown to be intrinsic to the thermodynamic coupling between the atmosphere and ocean the mm effectively acts as a conduit through which the extratropical atmosphere influences enso modeling results further suggest that the mm plays a vital role in the seasonal phase locking behavior of enso the findings provide a new perspective for understanding the important role of thermodynamic ocean atmosphere feedback in enso and may have profound implications for enso prediction particularly the unresolved issue of the spring predictability barrier citation chang p l zhang r saravanan d j vimont j c h chiang l ji h seidel and m k tippett 2007 pacific meridional mode and el nino southern oscillation geophys res lett 34 l16608 doi 10 1029 2007gl030302

the south pacific meridional mode a mechanism for enso like variability in this study the authors investigate the connection between the south pacific atmospheric variability and the tropical pacific climate in models of different degrees of coupling between the atmosphere and ocean a robust mode of variability defined as the south pacific meridional mode spmm is identified in a multimodel ensemble of climate model experiments where the atmosphere is only thermodynamically coupled to a slab ocean mixed layer the physical interpretation of the spmm is nearly identical to the north pacific meridionalmode npmm withtheoff equatorialsoutheasttradewindvariabilityalteringthelatentheatflux and sea surface temperature sst and initiating a wind evaporation sst feedback that propagates signals into the tropics the authors also show that a positive cloud feedback plays a role in the development of this mode butthiseffectismodeldependent whilephysicallyanalogoustothenpmm thespmmhasastronger expression in the equatorial pacific and directly perturbs the zonal gradients of sst and sea level pressure slp on the equator thus leading to enso like variability despite the lack of ocean atmosphere dynamical coupling further analysis suggests that the spmm is also active in fully coupled climate models and observations this study highlights the important role of the southern hemisphere in tropical climate variability and suggests that including observations from the data poor south pacific could improve the enso predictability