crustal structure evolution and volcanic unrest of the alban hills central italy the alban hills a quaternary volcanic center lying west of the central apennines 15 25 km southeast of rome last erupted 19 ka and has produced approximately 290 km3 of eruptive deposits since the inception of volcanism at 580 ka earthquakes of moderate intensity have been generated there at least since the roman age modern observations show that intermittent periods of swarm activity originate primarily beneath the youngest features the phreatomagmatic craters on the west side of the volcano results from seismic tomography allow identification of a low velocity region perhaps still hot or partially molten more than 6 km beneath the youngest craters and a high velocity region probably a solidified magma body beneath the older central volcanic construct thirty centimeters of uplift measured by releveling supports the contention that high levels of seismicity during the 1980s and 1990s resulted from accumulation of magma beneath these craters the volume of magma accumulation and the amount of maximum uplift was probably at least 40 106 m3 and 40 cm respectively comparison of newer levelings with those completed in 1891 and 1927 suggests earlier episodes of uplift the magma chamber beneath the western alban hills is probably responsible for much of the past 200 ka of eruptive activity is still receiving intermittent batches of magma and is therefore continuing to generate modest levels of volcanic unrest bending of overburden is the most likely cause of the persistent earthquakes which generally have hypocenters above the 6 km deep top of the magma reservoir in this view the most recent uplift and seismicity are probably characteristic and not precursors of more intense activity

saltation and wind flow interaction in a variable slope wind tunnel abstract in a 15 m long horizontal wind tunnel we studied the internal boundary layer over fixed arrays with roughness z0 similar to the roughness of saltation of a sand bed utilizing turbulence spires the logarithmic overlap layer is at least 75 mm thick some 5 m downwind of the entry this permits a precise determination of u from wind profile data over a sand bed in a variable slope wind tunnel with a 6 m long working section we studied how slope grain size and friction speed influence bed roughness owen 1964 proposed that z 0 c u 2 2 g where c is a constant but we found that c depends in a complex manner on grain size and friction speed c increases from very low values near the threshold to an apparently limiting value at large friction speeds for an almost uniform 125 m sand the limiting value of c is 0 06 the limiting value decreases however with particle size for a uniform 544 m sand c only approaches 0 03 for friction speeds as high as 1 m s with the measured values of friction speed corrected for the effects of slope our results appear to show that the limiting values of c do not depend on the slope angle even though the slope affects the individual shapes of particle trajectory c is perhaps independent of slope angle because the roughness height and therefore c is more directly related to the amount of momentum extracted from the air by the particles i e the shear stress rather than to the manner of extraction particle trajectory shapes

clarifying ambiguity in intraseasonal southern hemisphere climate modes during austral winter the relative importance of annular and nonannular characteristics in the wintertime southern hemisphere circulation is investigated using reanalysis data between 1978 and 2010 weekly averaged data are chosen to capture the typically short time scale of intraseasonal atmospheric variability in existing studies the southern annular mode sam has been shown to exhibit significant nonannular behavior in the western southern hemisphere during austral winter variability in this region is also characterized by wave like disturbances and this overlap in nonannular behavior between different climate modes has led to a lack of consensus when defining and measuring impact from these wave like disturbances a number of approaches are adopted including empirical orthogonal function analysis teleconnection correlation analysis and the application of a vector autoregression model to isolate directions of causality and wave propagation austral winter variability is shown to be dominated by nonannular wavelike disturbances rather than a seesaw pattern between high and middle latitudes the wavelike disturbances have the largest amplitude in the western southern hemisphere are quasistationary and exhibit eastward propagation of information this suggests that the dominant pattern of western southern hemisphere intraseasonal variability during austral winter which is commonly associated with the sam is in fact a wave like mode of variability supporting material

southern hemisphere circulation features associated with el nino southern oscillation events abstract composite seasonal mean and anomaly fields prepared from operational numerical analyses have been used to describe the southern hemisphere sh circulation features associated with el nino southern oscillation enso events the period of analyses available 1972 83 has limited the composites to include only three enso events the reliability and stability of the composites has been tested using multiple permutation methods and by comparison with the results obtained using a longer period 1950 79 of sh rawinsonde station data in the sh winter a weak equivalent barotropic wavetrain pattern of anomalies extends over australia and the south pacific ocean to south america this wavetrain pattern is quite variable in amplitude and location between enso events although it is more stable over the subtropical pacific in the sh summer the circulation anomalies are more zonally symmetric with increased height at low and high latitudes and decreased height in middle latitudes the circulation anoma

storm tracks in the southern hemisphere abstract from 1979 to 1989 global european centre for medium range weather forecasts ecmwf analyses of many meteorological variables important in baroclinic storms have been bandpass filtered to highlight fluctuations on 2 to 8 day time scales in order to illuminate the relationships among the variables in baroclinic storm track regions because of the greater zonal symmetry in the southern hemisphere sh versus the northern hemisphere nh it is possible to examine these relationships over a zonal sector without being dominated by local effects associated with jet stream entrance and exit regions of the storm tracks the bandpassed variance of geopotential height is used to define the storm track and its meridional profile has a pronounced midlatitude maximum in the sh the locations of the jet stream and the variance maxima of meridional and zonal velocity components vorticity vertical motion specific humidity and temperature all bear a distinctive relationship to the storm track but the lat

the association of australian winter climate with ocean temperatures to the west abstract two general circulation model experiments have been conducted with a view toward determining the sensitivity of australian winter circulation and precipitation to the imposition of idealized sea surface temperature anomalies around the western half of australia in the first a positive anomaly was imposed to the northwest of the continent and a negative anomaly to the southwest while in the second this pattern was reversed in the former major changes were simulated in the circulation over the australian sector and significant precipitation increases were induced over more than half of the continent by contrast the responses to the forcing in the latter experiment were considerably less particularly for precipitation over the continent which showed virtually no change of significance the results taken in concert with those of simmonds suggest the important role played by warm ocean temperatures to the northwest of australia in influencing winter rainfall the results suggest that the a

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

austral summer teleconnections of indo pacific variability their nonlinearity and impacts on australian climate abstractin austral summer el nino southern oscillation enso covaries with the indian ocean basin mode iobm and with the southern annular mode sam the present study addresses how the iobm and the sam modulate the impact of enso on australia the authors show that the modulating effect of the sam is limited in particular the sam does not modify the enso teleconnection pattern however the iobm extends enso induced convection anomalies westward over northern australia and over the eastern indian ocean whereby extending the enso tropical teleconnection to the northwest of australia the iobm also generates an equivalent barotropic rossby wave train through convection anomalies over northern australia the wave train shares an anomaly center over the tasman sea latitudes with the pacific south american psa pattern shifting the anomaly center of the psa pattern to within a closer proximity to australia there is a strong asymmetry in the iobm modulating effect during an iobm negative phase whic

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

observed relationships between the el nino southern oscillation and the extratropical zonal mean circulation abstract there is increasing evidence indicating that the climate response to variations in the el nino southern oscillation enso includes not only thermally forced zonal wind anomalies in the subtropics but also eddy driven zonal wind anomalies that extend into the mid high latitudes of both hemispheres in this study new insights into the observed seasonally varying signature of enso in the extratropical zonal mean circulation are provided and the associated linkages with the dominant patterns of extratropical variability are examined the zonal mean extratropical atmospheric response to enso is characterized by two principal features an equivalent barotropic dipole in the southern hemisphere sh zonal mean zonal flow with centers of action located near 40 and 60 during austral summer and a weaker but analogous dipole in the northern hemisphere nh with centers of action located near 25 and 45 during early and late boreal winter both structures are accompanied by eddy momentum flux ano

different modes of variability over the tasman sea implications for regional climate abstracta new approach is used to detect atmospheric teleconnections without being bound by orthogonality such as empirical orthogonal functions this method employs negative correlations in a global dataset to detect potential teleconnections one teleconnection occurs between the tasman sea and the southern ocean it is related to el nino southern oscillation enso the indian ocean dipole iod and the southern annular mode sam this teleconnection is significantly correlated with sam during austral summer fall and winter with iod during spring and with enso in summer it can thus be described as a hybrid between these modes given previously found relationships between iod and enso and iod s proximity to the teleconnection centers correlations to iod are generally stronger than to enso increasing pressure over the tasman sea leads to higher lower surface temperature over eastern australia the southwestern pacific in all seasons and is related to reduced surface temperature over wilkes

comparing and contrasting the behaviour of arctic and antarctic sea ice over the 35 year period 1979 2013 we examine the evolution of sea ice extent sie over both polar regions for 35 years from november 1978 to december 2013 as well as for the global total ice arctic plus antarctic our examination confirms the ongoing loss of arctic sea ice and we find significant p 0 001 negative trends in all months seasons and in the annual mean the greatest rate of decrease occurs in september and corresponds to a loss of 3 x 10 6 km 2 over 35 years the antarctic shows positive trends in all seasons and for the annual mean p 0 01 with summer attaining a reduced significance p 0 10 based on our longer record which includes the remarkable year 2013 the positive antarctic ice trends can no longer be considered small and the positive trend in the annual mean of 15 29 3 85 x 10 3 km 2 a 1 is almost one third of the magnitude of the arctic annual mean decrease the global annual mean sie series exhibits a trend of 35 29 5 75 x 10 3 km 2 a 1 p

severe heat waves in southern australia synoptic climatology and large scale connections this paper brings a new perspective on the large scale dynamics of severe heat wave hw events that commonly affect southern australia through an automatic tracking scheme the cyclones and anticyclones associated with hws affecting melbourne adelaide and perth are tracked at both the surface and upper levels producing for the first time a synoptic climatology that reveals the broader connections associated with these extreme phenomena the results show that a couplet or pressure dipole formed by transient cyclones and anticyclones can reinforce the hw similarly to what is observed in cold surges cs with an obvious opposite polarity our results show that there is a large degree of mobility in the synoptic signature associated with the passage of the upper level ridges before they reach australia and the blocking is established with hw associated surface anticyclones often initiating over the west indian ocean and decaying in the eastern pacific in contrast to this result the 500 hpa anticyclone tracks show a very small degree of mobility responding to the dominance of the upper level blocking ridge an important feature of hws is that most of the cyclones are formed inland in association with heat troughs while in cs the cyclones are typically maritime often explosive associated with a strong cold front hence the influence of the cyclone is indirect contributing to reinforce the blocking ridge through hot and dry advection on the ridge s western flank additional insights are drawn for the record adelaide case of march 2008 with fifteen consecutive days above 35 c breaking the previous record by 7 days sea surface temperatures suggest a significant air sea interaction mechanism with a broad increase in the meridional temperature gradient over the indian ocean amplifying the upstream rossby waves that can trigger hw events a robust cooling of the waters close to the australian coast also contributes to the maintenance of the blocking highs locally which is a fundamental ingredient to sustain the hws

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

sidewall effects of a wind tunnel on wind velocity and mass flux in aeolian sand transport abstract the sidewall effects of a wind tunnel on aeolian sand transport were investigated experimentally a wind tunnel was used to conduct the experiments with a given channel height of 120 cm and varying widths b of 40 60 80 100 and 120 cm both vertical profiles of wind velocity and sand mass flux were measured at different locations across the test section the results show that the wind velocity with saltation first increases and then decreases to a minimum from the sidewall to the central line of the wind tunnel the discrepancy among wind velocities at different locations of the transverse section decreases with decreasing tunnel width the wind friction velocity across the wind tunnel floor with the exception of the region closest to the sidewalls does not deviate strongly in wide wind tunnels from that along the central line whereas it does vary in narrow tunnels the sand mass fluxes with the exception of some near bed regions are larger along the central line of the wind tunnel than they are at the quarter width location from the sidewall unlikely previously reported results the dimensionless sand transport rate qg u 3 where q is the total sand transport rate g is the gravitational acceleration constant is the air density and u is the wind friction velocity first decreases and then increases with the dimensionless friction velocity u u t where u t is the threshold friction velocity the above differences may be attributed to the sidewall effects of the wind tunnel a dimensionless parameter f b u gb 1 2 is defined to reflect the sidewall effects on aeolian sand transport the flows with f b of 0 33 or less may be free from the sidewall effects of the wind tunnel and can ensure accurate saltation tunnel simulation

observed southern hemisphere eddy statistics at 500 mb frequency and spatial dependence abstract nearly eight years of daily southern hemisphere analyses at 500 mb have been used to define the spatial dependence of the variance fields of geopotential height and the two geostrophic wind components the corresponding covariance fields and the transient kinetic energy the fields are further examined in the frequency domain by using lorenz 1979 poor man s spectral analysis technique in view of the small variation in eddy statistics as a function of the time of the year in the sh this study removes the first four harmonies of the annual cycle and then considers all data together so that contributions from all time scales from 2 to 4096 days 11 years can be resolved the main results are based on analyses from may 1972 january 1978 but are verified with analyses from the relatively data rich fgge period results for the zonal mean statistics are compared with those from previous studies the zonal means of the geopotential height and westerly wind component have spectra which roughly

are the north atlantic oscillation and the northern annular mode distinguishable this study addresses the question of whether persistent events of the north atlantic oscillation nao and the northern annular mode nam teleconnection patterns are distinguishable from each other standard daily index time series are used to specify the amplitude of the nao and nam patterns the above question is examined with composites of sea level pressure and 300 and 40 hpa streamfunction along with tests of field significance a null hypothesis is specified that the nao and nam persistent events are indistinguishable this null hypothesis is evaluated by calculating the difference between time averaged nao and nam composites it is found that the null hypothesis cannot be rejected even at the 80 confidence level the wave breaking characteristics during the nam life cycle are also examined both the positive and negative nam phases yield the same wave breaking properties as those for the nao the results suggest that not only are the nao and nam persistent events indistinguishable but that the nao nam events are neither confined to the north atlantic nor are they annular

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

the north pacific oscillation west pacific teleconnection pattern mature phase structure and winter impacts abstract the north pacific oscillation npo in sea level pressure and its upper air geopotential height signature the west pacific wp teleconnection pattern constitute a prominent mode of winter midlatitude variability the npo wp its mature phase expression is identified from principal component analysis of monthly sea level pressure variability as the second leading mode just behind the pacific north american variability pattern npo wp variability primarily on subseasonal time scales is characterized by a large scale meridional dipole in slp and geopotential height over the pacific and is linked to meridional movements of the asian pacific jet and pacific storm track modulation the hemispheric height anomalies at upper levels resemble the climatological stationary wave pattern attributed to transient eddy forcing the npo wp divergent circulation is thermal wind restoring pointing to independent forcing of jet fluctuations intercomparison of sea level pressure geopotential height and zonal

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

vertical profiles of aeolian sand mass flux abstract vertical profiles of the horizontal mass flux of blown sand are investigated experimentally using a passive vertical array in a wind tunnel considering lower sampling efficiency of the sand trap in the near bed region this investigation is complemented by the measurements of the longitudinal profiles of mass flux made using a horizontal sand trap the experiments were conducted with two test sands and five different stream velocities in the upper part of the vertical profile the measured data exhibit an exponential decay distribution with a positive deviation occurring in the near bed region the measured longitudinal profiles are similar to the measured vertical profiles linking both profiles and the modes of sand transport it is possible that saltating sand grains give rise to the well known exponential decay distribution of mass flux and that creeping and reptating grains force a deviation from it a simple equation applicable for both the vertical and the longitudinal sand mass flux variations is introduced and the parameters are estimated from experimental data

on the midlatitude thermal response to tropical warmth 1 observations reveal a global scale thermal response to el nino and la nina featuring a band of tropospheric anomalies opposite in sign to those in the tropics when an idealized dynamical model is forced by increased tropical heating a similar response with an enhanced subtropical thermal gradient results in the idealized model this response is produced by changes in transient eddy fluxes of heat and momentum and consequent changes in the mean meridional circulation the similarity between the two level model results and those from observations as well as the zonally averaged behavior of a gcm suggests that the same dynamics operate in nature this represents a tropical midlatitude teleconnection distinct from and in addition to that mediated by stationary rossby wave trains

seasonal evolutions of atmospheric response to decadal sst anomalies in the north pacific subarctic frontal zone observations and a coupled model simulation abstractpotential impacts of pronounced decadal scale variations in the north pacific sea surface temperature sst that tend to be confined to the subarctic frontal zone safz upon seasonally varying atmospheric states are investigated by using 48 yr observational data and a 120 yr simulation with an ocean atmosphere coupled general circulation model cgcm sst fields based on in situ observations and the ocean component of the cgcm have horizontal resolutions of 2 0 and 0 5 respectively which can reasonably resolve frontal sst gradient across the safz both the observations and cgcm simulation provide a consistent picture between sst anomalies in the safz yielded by its decadal scale meridional displacement and their association with atmospheric anomalies correlated with sst anomalies persistent in the safz from fall to winter a coherent decadal scale signal in the wintertime atmospheric circulation over the north pacific starts emerging in november and develops into an equivalent barotropic an