sensitivity of extratropical cyclone characteristics to horizontal resolution in the ecmwf model the sensitivity to horizontal resolution of northern hemisphere extratropical cyclone characteristics during the wintertime december march is investigated using a set of seasonal forecasts 1982 2001 with the european centre for medium range weather forecasts ecmwf model three different horizontal resolutions tl95 tl159 and tl255 are employed in order to test the realism of the simulations the model results are compared with those obtained from era 40 re analysis data the cyclone tracking is accomplished by applying an automatic tracking scheme to six hourly mean sea level pressure data it is shown that many of the key characteristics of extratropical cyclones in the ecmwf model are highly sensitive to horizontal resolution with the low resolution version tl95 for example simulating only about 60 of the re analysed total number of extratropical cyclones regions found to be particularly sensitive include the northern pacific the arctic baffin bay and the labrador sea as well as the mediterranean sea for the latter region it is shown that even the relatively high resolution version of the model tl255 significantly underestimates the number of cases of genoa cyclogenesis furthermore it is shown that in some regions such as the entrance regions of the major northern hemisphere storm tracks model deficits are insensitive to increases in horizontal resolution the same analysis has been repeated for the high resolution operational ecmwf analysis 2000 2004 truncated at different total wave numbers tl95 tl159 tl255 and tl511 in order to separate dynamical effects of differences in resolution from those due to pure spectral truncation it is found that the dynamical effect of changing horizontal resolution dominates over the truncation effect for intense cyclones whereas the truncation effect dominates for shallow cyclones copyright 2006 royal meteorological society

low latitude zonal and vertical ion drifts seen by de 2 horizontal and vertical ion drift data from the de 2 spacecraft have been used to determine average zonal and vertical plasma flow electric field characteristics in the plus minus 26 degree dip latitude region during a time of high solar activity the data base consists of over 800 equatorial passes horizontal ion drift data were projected along magnetic field lines to the magnetic equator using a dipole model to yield their apex height dependence the average data local time profile for an apex height bin centered at 400 km indicates westward plasma flow from 0600 to 1900 solar local time slt with a maximum westward velocity of 80 m s in the early afternoon there is a sharp change to eastward flow at approximately 1900 hours with an early evening peak of 170 m s a secondary nighttime maximum exists a 0430 slt preceeding the reversal to westward flow this profile is in good agreement with jicamarca radar measurements made under similar solar maximum conditions harmonic analysis indicates a net superrotation which is strongest at lower apex altitudes the diurnal term is dominant but higher order terms through th quatradiurnal are significant vertical ion data taken at low plus minus 5 degree dip latitudes while possessing greatermore scatter generally agree wtih jicamarca values copyright american geophysical union 1989 less

equatorial zonal plasma drifts measured by the c nofs satellite during the 2008 2011 solar minimum 1 we use the measurements by the vector electric field investigation vefi on board the communication navigation outage forecasting system c nofs satellite to study the local time and seasonal and longitudinal dependent climatology of equatorial f region zonal plasma drifts during 2008 2011 these drifts are essentially westward during the day and eastward at night over jicamarca radio observatory the satellite measurements are in good agreement with incoherent scatter radar drifts our data show strong longitudinal variations particularly in the south american sector during the solstices the equinoctial data exhibit short lived and largely enhanced westward drifts near sunrise and wave 4 structures from the early afternoon to late night equinoctial periods the nighttime eastward drifts are largest near the western american sector at all seasons the june solstice postmidnight eastward drifts decrease sharply at longitudes of about 310 and have much smaller values in the entire eastern hemisphere we also briefly discuss the relationship between the longitude dependent vertical and zonal plasma drifts

exploring the role of humans and climate over the balkan landscape 500 years of vegetational history of serbia abstract we present the first well dated high resolution record of vegetation and landscape change from serbia which spans the past 500 years biological proxies pollen spores and charcoal geochemical analysis through x ray fluorescence xrf and a detailed chronology based on ams 14c dating from a western serbian sinkhole core suggest complex woodland grassland dynamics and strong erosional signals throughout the little ice age lia an open landscape with prominent steppe vegetation e g poaceae chenopodiaceae and minor woodland exists during 1540 1720 ce early lia while the late lia 1720 1850 ce in this record shows higher tree percentages possibly due to increased moisture availability the post lia era 1850 2012 ce brings a disturbed type of vegetation with the presence of weedy genera and an increase in regional woodland anthropogenic indicators for agricultural pastoral and fire practices in the region together attest to the dominant role of humans in shaping this balkan landscape throughout the interval the changing nature of human interference potentially as a response to underlying climatic transitions is evident through large scale soil depletion resulting from grazing and land clearance during the early lia and stabilization of arable lands during the late and post lia eras

annual climate variability in the holocene interpreting the message of ancient trees abstract over vast areas of the world s landmasses where climate beats out a strong seasonal rhythm tree growth keeps unerring time in their rings trees record many climate melodies played in different places and different eras recent years have seen a consolidation and expansion of tree ring sample collections across the traditional research areas of north america and europe and the start of major developments in many new areas of eurasia south america and australasia from such collections are produced networks of precisely dated chronologies records of various aspects of tree growth registered continuously year by year across many centuries their sensitivities to different climate parameters are now translated into ever more detailed histories of temperature and moisture variability across expanding dimensions of time and space with their extensive coverage high temporal resolution and rigid dating control dendroclimatic reconstructions contribute significantly to our knowledge of late holocene climates most importantly on timescales ranging from 1 to 100 years in special areas of the world where trees live for thousands of years or where subfossil remnants of long dead specimens are preserved work building chronologies covering many millennia continues apace very recently trees have provided important new information about major modes of general circulation dynamics linked to the el nino southern oscillation and the north atlantic oscillation and about the effect of large volcanic eruptions as for assessing the significance of 20th century global warming the evidence from dendroclimatology in general supports the notion that the last 100 years have been unusually warm at least within a context of the last two millennia however this evidence should not be considered equivocal the activities of humans may well be impacting on the natural growth of trees in different ways making the task of isolating a clear climate message subtly difficult

average equatorial zonal and vertical ion drifts determined from san marco d electric field measurements san marco d electric field measurements have been averaged in terms of their equivalent ion drift to produce an average pattern of equatorial zonal and vertical ion drifts variations with season solar activity kp lunar phase and longitude have been analyzed similarities and some differences from previous jicamarca de 2 and ae e results are seen confirmation is given of the dominance of the f region dynamo in the 1900 2100 local time region the daytime zonal ion drift is larger for high f10 7 values than that for low values there is little variation between high and low values of kp superrotation is evident in this data set and is larger at equinox compared to solstice at the june solstice there are significant differences between the average ion drifts in the longitude sector where the geomagnetic equator is north of the geographic equator indian sector and the sector where the geomagnetic equator is south of the geographic equator peruvian sector the daytime upward velocity is larger in the indian sector than in the peruvian sector and it reverses later in the evening in the indian sector daytime westward zonal velocities are larger and the nighttime eastward velocities are smaller in the indian sector a presunrise enhancement is seen in the downward velocity in the indian sector but not in the peruvian sector significant variations are also seen with the phase of the moon in light of current theory the lunar variations suggest a complex interaction of e and f region dynamo sources with conductivity changing in phase and character with latitude

greenland s pressure drag and the atlantic storm track abstract some effects of greenland on the northern hemisphere wintertime circulation are discussed inviscid pressure drag on greenland s slopes calculated from reanalysis data is related to circulation patterns greenland lies north of the core of the tropospheric westerly winds yet strong standing waves which extend well into the stratosphere produce a trough ridge system with jet stream lying close to greenland mean icelandic low in its wake and storm track that interacts strongly with its topography in the lower troposphere dynamic height anomalies associated with strongly easterly pressure drag on the atmosphere are quite localized in space and relatively short lived compared to upper levels yet they involve a hemispheric scale dislocation of the stratospheric polar vortex it is a two scale problem however the high pass time filtered part of the height field responsible for 73 of the pressure drag is quite different and expresses propagating cyclonic development in the atlantic storm

empirical models of storm time equatorial zonal electric fields ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes we describe initially a methodology for the study of storm time dependent ionospheric electric fields we present empirical models of equatorial disturbance zonal electric fields obtained using extensive f region vertical plasma drift measurements from the jicamarca observatory and auroral electrojet indices these models determine the plasma drift perturbations due to the combined effects of short lived prompt penetration and longer lasting disturbance dynamo electric fields we show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the rice convection model for comparable changes in the polar cap potential drop we also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns when the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects the measured and modeled drift velocities are generally in good agreement however our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency and in the high latitude potential and energy deposition patterns which are not accounted for in the model these case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields

southern ocean mesocyclones and polar lows from manually tracked satellite mosaics a new reference dataset of mesocyclone activity over the southern ocean has been developed from the manual analysis of high resolution infrared satellite mosaics for winter 2004 of the total 1735 mesocyclones which were identified and analyzed about three quarters were classified as being polar lows i e intense systems see rasmussen and turner 2003 the dataset includes mesocyclone track size associated cloud vortex type and background synoptic conditions maxima in track density were observed over the bellingshausen sea and around east antarctica and are highly correlated with cyclogenesis regions a comparison against quikscat and reanalyses wind characteristics shows that the reanalyses while capturing mesocyclone events tend to considerably underestimate their wind speed by up to 10 ms 1 this mesocyclone dataset is available as a reference for further analysis of mesocyclones and for the evaluation and development of cyclone tracking algorithms

an objective cyclone climatology for the southern hemisphere abstract an objective method is developed and used to derive a climatology of centers of cyclonic vorticity for the southern hemisphere based on twice daily european centre for medium range weather forecasts ecmwf 1000 hpa analyses during 1980 86 these centers were computed as local minima of geostrophic relative vorticity g extending previous studies based on pressure minima this use of g avoids a bias favoring slower and or deeper cyclones that occurs when pressure is used and includes a large number of additional mobile vorticity centers in the 45 55 s band that are missed where a local pressure minimum cannot be found an automated tracking algorithm similar to that of murray and simmonds is used to match predicted location pressure and g from previous track history with available centers large numbers of g centers were found south of 60 s and near the midlatitude continents as in previous studies these were a mixture of migratory centers and other fixed topographic features the maxi

lightning generated whistler waves observed by probes on the communication navigation outage forecast system satellite at low latitudes 1 direct evidence is presented for a causal relationship between lightning and strong electric field transients inside equatorial ionospheric density depletions in fact these whistler mode plasma waves may be the dominant electric field signal within such depletions optical lightning data from the communication navigation outage forecast system c nofs satellite and global lightning location information from the world wide lightning location network are presented as independent verification that these electric field transients are caused by lightning the electric field instrument on c nofs routinely measures lightning related electric field wave packets or sferics associated with simultaneous measurements of optical flashes at all altitudes encountered by the satellite 401 867 km lightning generated whistler waves have abundant access to the topside ionosphere even close to the magnetic equator

borehole climate reconstructions spatial structure and hemispheric averages 1 ground surface temperature gst reconstructions determined from temperature profiles measured in terrestrial boreholes when averaged over the northern hemisphere estimate a surface warming of 1 k during the interval ad 1500 2000 other traditional proxy based estimates suggest less warming during the same interval mann et al 2003a have raised two issues with regard to borehole based reconstructions the first focuses on the need for spatial gridding and area weighting of the ensemble of borehole based gst reconstructions to yield an average hemispheric reconstruction the second asserts that application of optimal detection techniques show that the gst only weakly displays the spatial structure of the surface air temperature sat we demonstrate the consistency of gst warming estimates by showing that over a wide range of grid element area and occupancy weighting schemes the five century gst change falls in the range of 0 89 1 05 k we examine the subhemispheric spatial correlation of gst and sat trends at various spatial scales in the 5 degree grid employed for optimal detection we find that the majority of grid element means are determined from three or fewer boreholes a number that is insufficient to suppress site specific noise via ensemble averaging significant spatial correlation between sat and gst emerges in a 5 degree grid if low occupancy grid elements are excluded and also in a 30 degree grid in which grid element means are better determined through higher occupancy reconstructions assembled after excluding low occupancy grid elements show a five century gst change in the range of 1 02 1 06 k index terms 1645 global change solid earth 1699 global change general or miscellaneous 3309 meteorology and atmospheric dynamics climatology 1620 3322 meteorology and atmospheric dynamics land atmosphere interactions 3344 meteorology and atmospheric dynamics paleoclimatology keywords boreholes paleoclimate spatial analysis surface temperature

nao signal recorded in the stable isotopes of greenland ice cores 1 the winter 18o signal is extracted from 7 greenland ice cores covering the past 700 years to filter out noise and local variations in the 7 isotope records a principal component analysis is carried out on the ice core data a comparison between the time series of the first principal component pc1 with 67 years of winter december to march temperature measurements from 3 southern greenland synoptic stations shows highly significant correlations southern greenland winter temperatures are known to be greatly influenced by the north atlantic oscillation nao a good proxy for southern greenland temperatures is therefore expected to reveal at least parts of the nao signal it is shown that the pc1 time series indeed is significantly correlated to the nao during the winter months the inclusion of ice core winter season 18o time series in future multiproxy nao reconstructions is therefore recommended

drought reconstructions for the continental united states abstract the development of a 2 lat 3 long grid of summer drought reconstructions for the continental united states estimated from a dense network of annual tree ring chronologies is described the drought metric used is the palmer drought severity index pdsi the number of grid points is 154 and the reconstructions cover the common period 1700 1978 in producing this grid an automated gridpoint regression method called point by point regression was developed and tested in so doing a near optimal global solution was found for its implementation the reconstructions have been thoroughly tested for validity using pdsi data not used in regression modeling in general most of the gridpoint estimates of drought pass the verification tests used in addition the spatial features of drought in the united states have been faithfully recorded in the reconstructions even though the method of reconstruction is not explicitly spatial in its design the drought reconstructions show that the 1930s dust bow

last millennium summer temperature variations in western europe based on proxy data we present a method of multiproxy reconstruction of the climate of europe during the last millennium the proxies used comprise long tree ring width series grape harvest dates greenland ice oxygen isotope series and temperature indices based on historical documents the proxies are calibrated using gridded april to september mean temperatures for western europe i e between 10 degrees w and 20 degrees e and between 35 degrees n and 55 degrees n they are calibrated also using the long instrumental summer temperature series of the marseilles observatory of longchamp which begins in the mid eighteenth century the method is a combination of an analogue technique which is able to deal with missing data an artificial neural network technique for an optimal non linear calibration and a bootstrap technique for calculating error bars on the reconstruction about 70 of the temperature variance is reconstructed the amplitude of the past temperature variations is particularly well reconstructed which is important when considering whether the recent temperature trend is or is not within the natural variability it appears that the temperature of the last decade of the twentieth century was reached only 14 times during the last millennium the reconstruction is discussed with respect to other multiproxy and borehole temperature reconstructions we conclude that a reconstruction such ours with a specific regional focus as opposed to the larger northern hemisphere is more reliable and is in better agreement with borehole results even allowing for the fact that only a part of the long term variance is reconstructed little ice age c ad 1560 1930 summers were 0 2 0 5 degrees c cooler than the 1961 1990 period borehole temperatures indicate a cooling of 0 4 degrees c which falls in the 95 confidence interval of our reconstructions

c nofs observations of deep plasma depletions at dawn 1 the communication navigation outage forecasting system c nofs satellite was launched in 2008 during solar minimum conditions an unexpected feature in the c nofs plasma density data is the presence of deep plasma depletions observed at sunrise at all satellite altitudes ionospheric irregularities are often embedded within these dawn depletions their frequencies strongly depend on longitude and season dawn depletions are also observed in coincident satellite passes such as dmsp and champ in one example the depletion extended 50 14 in the n s and e w directions respectively these depletions are caused by upward plasma drifts observed in c nofs and ground based measurements the reason for these upward drifts is still unresolved we discuss the roles of dynamo electric fields over shielding and tidal effects as sources for the reported depletions

climate variability in se europe since 1450 ad based on a varved sediment record from etoliko lagoon western greece to achieve deeper understanding of climate variability during the last millennium in se europe we report new sedimentological and paleoecological data from etoliko lagoon western greece the record represents the southernmost annually laminated i e varved archive from the balkan peninsula spanning the little ice age allowing insights into critical time intervals of climate instability such as during the maunder and dalton solar minima after developing a continuous ca 500 year long varve chronology high resolution xrf counts stable isotope data measured on ostracod shells palynological including pollen and dinoflagellate cysts and diatom data are used to decipher the season specific climate and ecosystem evolution at etoliko lagoon since 1450 ad our results show that the etoliko varve record became more sensitive to climate change from 1740 ad onwards we attribute this shift to the enhancement of primary productivity within the lagoon which is documented by an up to threefold increase in varve thickness this marked change in the lagoon s ecosystem was caused by i increased terrestrial input of nutrients ii a closer connection to the sea and human eutrophication particularly from 1850 ad onwards and iii increasing summer temperatures integration of our data with those of previously published paleolake sediment records tree ring based precipitation reconstructions simulations of atmospheric circulation and instrumental precipitation data suggests that wet conditions in winter prevailed during 1740 1790 ad whereas dry winters marked the periods 1790 1830 ad dalton minimum and 1830 1930 ad the latter being sporadically interrupted by wet winters this variability in precipitation can be explained by shifts in the large scale atmospheric circulation patterns over the european continent that affected the balkan peninsula e g north atlantic oscillation the transition between dry and wet phases at etoliko points to longitudinal shifts of the precipitation pattern in the balkan peninsula during the little ice age

artificial neural networks and dendroclimatic reconstructions an example from the front range colorado usa the feasibility of reconstructing total spring precipitation for the south platte river basin from tree ring chronologies using artificial neural networks is explored the use of artificial neural networks allows a comparison of reconstructions resulting from both linear and nonlinear models both types of models produced reconstructions that explained more than 40 of the variation in spring precipitation and were well verified with independent data although the nonlinear models produced higher r2 values than did the linear model for the calibration period they performed less well in the independent period this result and other model evaluation statistics suggest that in this study the nonlinear models contain a greater degree of overfit than the linear model and thus do not offer a clear improvement over the linear model for the reconstruction of spring precipitation in this region however neural networks offer an alternative approach to linear regression techniques and may provide improved den

longitudinal variations in the equatorial vertical drift in the topside ionosphere 1 the vertical ion drift is important for understanding and modeling the electrodynamics at low latitudes measurements from the ion drift meter on the defense meteorological satellite program dmsp f15 are used to examine longitudinal variations in the vertical ion drift at the dip equator in the topside ionosphere local time was restricted to 0930 and the data were organized by month for 2001 and 2002 two features were found contributing to the longitudinal variations in the electrodynamics meridional winds contribute to the equatorial vertical ion drift at the 830 km magnetic apex due to their dynamo action at the foot points of the magnetic field lines in the f region at magnetic latitudes near 15 electric fields producing a downward perturbation drift at 0930 are produced by hemispheric differences in the dynamo current due primarily to the different orientation of the magnetic meridian relative to the terminator this produces the seasonally dependent variation as a function of longitude that is observed a wavenumber 4 longitudinal variation also appears to be present throughout the year but is more influential during equinox conditions this variation also shows a seasonal cycle shifting east during northern summer and west during northern winter further analysis would be required to isolate the characteristics of a wavenumber 4 driver from the wavenumber 4 component of the fourier series used here to fit the data

proxy based northern hemisphere surface temperature reconstructions sensitivity to method predictor network target season and target domain abstract results are presented from a set of experiments designed to investigate factors that may influence proxy based reconstructions of large scale temperature patterns in past centuries the factors investigated include 1 the method used to assimilate proxy data into a climate reconstruction 2 the proxy data network used 3 the target season and 4 the spatial domain of the reconstruction estimates of hemispheric mean temperature are formed through spatial averaging of reconstructed temperature patterns that are based on either the local calibration of proxy and instrumental data or a more elaborate multivariate climate field reconstruction approach the experiments compare results based on the global multiproxy dataset used by mann and coworkers with results obtained using the extratropical northern hemisphere nh maximum latewood tree ring density set used by briffa and coworkers mean temperature reconstructions are compared for the full nh tropics and extratropics land and ocean and ext

five hundred years of gridded high resolution precipitation reconstructions over europe and the connection to large scale circulation we present seasonal precipitation reconstructions for european land areas 30 w to 40 e 30 71 n given on a 0 5 0 5 resolved grid covering the period 1500 1900 together with gridded reanalysis from 1901 to 2000 mitchell and jones 2005 principal component regression techniques were applied to develop this dataset a large variety of long instrumental precipitation series precipitation indices based on documentary evidence and natural proxies tree ring chronologies ice cores corals and a speleothem that are sensitive to precipitation signals were used as predictors transfer functions were derived over the 1901 1983 calibration period and applied to 1500 1900 in order to reconstruct the large scale precipitation fields over europe the performance quality estimation based on unresolved variance within the calibration period of the reconstructions varies over centuries seasons and space highest reconstructive skill was found for winter over central europe and the iberian peninsula precipitation variability over the last half millennium reveals both large interannual and decadal fluctuations applying running correlations we found major non stationarities in the relation between large scale circulation and regional precipitation for several periods during the last 500 years we identified key atmospheric modes for southern spain northern morocco and central europe as representations of two precipitation regimes using scaled composite analysis we show that precipitation extremes over central europe and southern spain are linked to distinct pressure patterns due to its high spatial and temporal resolution this dataset allows detailed studies of regional precipitation variability for all seasons impact studies on different time and space scales comparisons with high resolution climate models as well as analysis of connections with regional temperature reconstructions

interannual variations and future change of wintertime extratropical cyclone activity over north america in ccsm3 climatology and interannual variations of wintertime extratropical cyclone frequency in ccsm3 twentieth century simulation are compared with the ncep ncar reanalysis during 1950 1999 ccsm3 can simulate the storm tracks reasonably well although the model produces slightly less cyclones at the beginning of the pacific and atlantic storm tracks and weaker poleward deflection over the pacific as in the reanalysis frequency of cyclones stronger than 980 hpa shows significant correlation with the pacific north america pna teleconnection pattern over the pacific region and with the north atlantic oscillation nao in the atlantic sector composite maps are constructed for opposite phases of el nino southern oscillation enso and the nao and all anomalous patterns coincide with observed one ccsm3 twenty first century a1b scenario realization indicates there is significant increase in the extratropical cyclone frequency on the us west coast and decrease in alaska meanwhile cyclone frequency increases from the great lakes region to quebec and decreases over the us east coast suggesting a possible northward shift of the atlantic storm tracks under the warmer climate the cyclone frequency anomalies are closely linked to changes in seasonal mean states of the upper troposphere zonal wind and baroclinicity in the lower troposphere due to lack of 6 hourly outputs we cannot apply the cyclone tracking algorithm to the other eight ccsm3 realizations based on the linkage between the mean state change and the cyclone frequency anomalies it is likely a common feature among the other ensemble members that cyclone activity is reduced on the east coast and in alaska as a result of global warming

reconstruction of precipitation in morocco since 1100 a d based on cedrus atlantica tree ring widths annual october through september precipitation from 1100 a d to modern times is reconstructed for morocco using cedrus atlantica endl carriere tree ring chronologies both multiple regression on principal components and the bootstrap method are used to calibrate tree ring width with precipitation precipitation variation is reconstructed for three climatically distinct areas the humid subhumid and arid regions of morocco a series of successive wet and dry periods is identified for the past 1000 years the maximum length of the 13 dry periods during which precipitation was at least 1 sigma below normal is six years twenty one years are identified during which precipitation fell more than 2 sigma below normal there is no significant correspondence in climatic variation in morocco europe and the sahel during this time period

storm time dependence of equatorial disturbance dynamo zonal electric fields we use jicamarca radar observations of f region vertical plasma drifts and auroral electrojet indices during 1968 1988 to study the characteristics and temporal evolution of equatorial disturbance dynamo zonal electric fields these electric fields result from the dynamo action of storm time winds and or thermospheric composition changes driven by enhanced energy deposition into the high latitude ionosphere during geomagnetically active conditions the equatorial vertical drift perturbations last for periods of up to 30 hours after large increases in the high latitude currents on the average this process can be described by two basic components with time delays of about 1 12 hours and 22 28 hours between the high latitude current enhancements and the equatorial velocity perturbations our data indicate strong coupling between dynamo processes with different timescales the short term disturbance dynamo drives upward equatorial drifts eastward electric fields at night with largest amplitudes near sunrise and small downward drifts during the day these perturbation drifts are in good agreement with results from the blanc richmond disturbance dynamo theory the dynamo process with time delays of about a day drives upward drift velocities at night with largest values near midnight and downward drifts in the sunrise noon sector in this case the amplitudes of the disturbance drifts maximize during geomagnetically quiet times preceded by strongly disturbed conditions we also present results of a new equatorial storm time dependent empirical model which illustrate the characteristics of the vertical disturbance dynamo drifts

equatorial longitude and local time variations of topside magnetic field aligned ion drifts at solar minimum 1 in the topside ionosphere the high mobility of the plasma along the magnetic field allows field aligned ion drifts to occur readily as a result of field aligned gravitational forces collisional forces or pressure gradients therefore variations in the field aligned ion drifts can be used to explore the influence of thermospheric electrodynamic and chemical processes on the ionosphere longitude and local time variations in the field aligned ion drifts near the magnetic equator are presented using observations from the coupled ion neutral dynamics investigation on board the communications navigation outage forecast system satellite these observations were obtained during the period of extremely low solar activity present in 2008 and 2009 allowing the seasonal local time and longitudinal variations to reveal the relative importance of the processes responsible for topside field aligned plasma drifts during solar minimum this investigation found that the low altitude winds and tides the net ionization or loss and the meridional e b drift were all influential in creating longitudinal and local time variations in the field aligned drift though the strength of the influence seen by each driver was found to vary with season local time and longitude

1200 years of decadal scale variability of mediterranean vegetation and climate at pantelleria island italy a new sedimentary sequence from lago di venere on pantelleria island located in the strait of sicily between tunisia and sicily was recovered the lake is located in the coastal infra mediterranean vegetation belt at 2 m a s l pollen charcoal and sedimentological analyses are used to explore linkages among vegetation fire and climate at a decadal scale over the past 1200 years a dry period from ad 800 to 1000 that corresponds to the medieval warm period wmp is inferred from sedimentological analysis the high content of carbonate recorded in this period suggests a dry phase when the ratio of evaporation precipitation was high during this period the island was dominated by thermophilous and drought tolerant taxa such as quercus ilex olea pistacia and juniperus a marked shift in the sediment properties is recorded at ad 1000 when carbonate content became very low suggesting wetter conditions until ad 1850 1900 broadly this period coincides with the little ice age lia which was charact

low frequency temperature variations from a northern tree ring density network we describe new reconstructions of northern extratropical summer temperatures for nine subcontinental scale regions and a composite series representing quasi northern hemisphere temperature change over the last 600 years these series are based on tree ring density data that have been processed using a novel statistical technique age band decomposition designed to preserve greater long timescale variability than in previous analyses we provide time dependent and timescale dependent uncertainty estimates for all of the reconstructions the new regional estimates are generally cooler in almost all precalibration periods compared to estimates obtained using earlier processing methods particularly during the 17th century one exception is the reconstruction for northern siberia where 15th century summers are now estimated to be warmer than those observed in the 20th century in producing a new northern hemisphere series we demonstrate the sensitivity of the results to the methodology used once the number of regions with data and the reliability of each regional series begins to decrease we compare our new hemisphere series to other published large regional temperature histories most of which lie within the 1 confidence band of our estimates over most of the last 600 years the 20th century is clearly shown by all of the palaeoseries composites to be the warmest during this period

high resolution palaeoclimatology of the last millennium a review of current status and future prospects this review of late holocene palaeoclimatology represents the results from a pages clivar intersection panel meeting that took place in june 2006 the review is in three parts the principal high resolution proxy disciplines trees corals ice cores and documentary evidence emphasizing current issues in their use for climate reconstruction the various approaches that have been adopted to combine multiple climate proxy records to provide estimates of past annual to decadal timescale northern hemisphere surface temperatures and other climate variables such as large scale circulation indices and the forcing histories used in climate model simulations of the past millennium we discuss the need to develop a framework through which current and new approaches to interpreting these proxy data may be rigorously assessed using pseudo proxies derived from climate model runs where the answer is known the article concludes with a list of recommendations first more raw proxy data are required from the diverse disciplines and from more locations as well as replication for all proxy sources of the basic raw measurements to improve absolute dating and to better distinguish the proxy climate signal from noise second more effort is required to improve the understanding of what individual proxies respond to supported by more site measurements and process studies these activities should also be mindful of the correlation structure of instrumental data indicating which adjacent proxy records ought to be in agreement and which not third large scale climate reconstructions should be attempted using a wide variety of techniques emphasizing those for which quantified errors can be estimated at specified timescales fourth a greater use of climate model simulations is needed to guide the choice of reconstruction techniques the pseudo proxy concept and possibly help determine where given limited resources future sampling should be concentrated

statistical analysis and updated climatology of explosive cyclones abstract a statistical analysis of 12 and 24 hour deepening rates for all surface lows analyzed on at least two successive nmc 12 hourly front half hemispheric surface charts was performed for one year of data both 12 and 24 hour deepening distributions showed statistically significant at the 5 level departures from normality with the largest deviations occurring along the tail of the distribution associated with most rapid deepening the sum of two normal curves of different means and standard deviations was successfully fitted to the deepening distributions suggesting that most cases of explosive cyclogenesis are the result of some additional physical mechanism distinct from ordinary baroclinic instability the climatology of explosive cyclones sanders and gyakum was updated to include the 1979 82 cold seasons and compared to the previous three year sample in addition a climatology of formation positions maximum deepening positions and dissipation positions for all cyclones in a one year d

quasi stationarity of centennial northern hemisphere midlatitude winter storm tracks the winter storm activity on the northern hemisphere during the last one thousand years in a global climate simulation was analyzed by determining all midlatitude storms and their tracks then consecutively clustering them for hundred years segments storm track clusters with longest lifetime and largest deepening rates are found over the oceans the numbers of extratropical winter storms exhibit notable yearly variability but hardly any variability on centennial time scales the clusters of these storm tracks also show only small differences between the centuries the numbers of members in neighboring oceanic clusters are negatively correlated a linear relationship was found between the numbers of members per storm track clusters over the pacific or atlantic ocean and seasonal mean atmospheric circulation patterns by a canonical correlation analysis

tree ring width and density data around the northern hemisphere part 2 spatio temporal variability and associated climate patterns patterns of summer temperature over the northern hemisphere obtained from a calibration of a treering network are presented for every year from 1600 to 1877 the network of tree ring density chronologies is shown to exhibit spatially coherent modes of variability these modes closely match summer half year tempera ture variations in terms of similar spatial patterns and similar temporal evolution during the instrumental period they can therefore be considered to be proxies for the temperature patterns and time series for the eight most dominant patterns are presented back to the late seventeenth century the first pattern represents spatially coherent warming or cooling and it appears to respond to climate forcings especially volcanic erup tions most other patterns appear to be related to atmospheric pressure anomalies and they can be partially explained by heat advection associated with anomalous atmospheric circulation this provides the potential for reconstructing past variations in atmospher

identification and climatology of southern hemisphere mobile fronts in a modern reanalysis abstractpresented here is an objective approach to identify characterize and track southern hemisphere mobile fronts in hemispheric analyses of relatively modest resolution such as reanalyses among the principles in its design were that it should be based on broadscale synoptic considerations and be as simple and easily understood as possible the resulting eulerian scheme has been applied to the european centre for medium range weather forecasts ecmwf re analysis era interim and a climatology of frontal characteristics at both the 10 m and 850 hpa levels derived for the period 1 january 1989 28 february 2009 the knowledge of the character of these features is central to understanding weather and climate over the hemisphere in both summer and winter the latitude belt 40 60 s hosts the highest frequency of frontal points but there are significant zonal asymmetries within this band the climatology reveals that the longest fronts are in the indian ocean where mean lengths exceed 2000 km the me

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

observations of dc electric fields in the low latitude ionosphere and their variations with local time longitude and plasma density during extreme solar minimum 1 dc electric fields and associated e b plasma drifts detected with the double probe experiment on the c nofs satellite during extreme solar minimum conditions near the june 2008 solstice are shown to be highly variable with weak to moderate ambient amplitudes of 1 2 mv m 25 50 m s average field or drift patterns show similarities to those reported for more active solar conditions i e eastward and outward during day and westward and inward at night however these patterns vary significantly with longitude and are not always present daytime vertical drifts near the magnetic equator are largest in the prenoon sector observations of weak to nonexistent prereversal enhancements in the vertical drifts near sunset are attributable to reduced dynamo activity during solar minimum as well as seasonal effects enhanced meridional drifts are observed near sunrise in certain longitude regions precisely where the enhanced eastward flow that persisted from earlier local times terminates the nightside ionosphere is characterized by larger amplitude structured electric fields dominated by horizontal scales of 500 1500 km even where local plasma densities appear relatively undisturbed data acquired during successive orbits indicate that plasma drifts and densities are persistently organized by longitude the high duty cycle of the c nofs observations and its unique orbit promise to expose new physics of the low latitude ionosphere

tree ring based drought reconstruction for the central tien shan area in northwest china 1 a robust ring width chronology developed from two sites of picea schrenkiana in the central tien shan area of northwest china was employed to study regional drought variability our analyses demonstrate both temperature and precipitation have significant effects on tree growth thus both should be considered for climate reconstruction regional drought history 1675 2002 a d was therefore reconstructed by calibrating with the palmer drought severity index pdsi our reconstruction not only captured well those extreme drought events recorded in local historical archives but also revealed the long term pattern of drought variability especially the trend of increasing moisture during the 20th century multi taper method spectral analysis indicates the existence of some low and high frequency cycles 146 171 11 5 10 6 9 7 6 1 3 9 3 4 3 2 2 4 and 2 1 yr overall our study indicates the feasibility of combining tree rings and the pdsi to reconstruct large scale drought patterns over this area

on the statistical analysis of cyclone deepening rates abstract statistical analysis of cyclone deepening rates has been used in the past to infer distinctions between physical processes operative in cases of explosive cyclogenesis and lesser storms this note attempts to qualify the conclusions of the previous study by analyzing cyclone deepening data from a new prospective the results suggest that the debate concerning the relative normality of these distributions is essentially irrelevant significant statistical evidence is provided to suggest that midlatitude maritime cyclogenesis exhibits a fundamentally different character from continental events and that this distinction is evident across a wide spectrum of storm intensities

seasonality variations in the central mediterranean during climate change events in the late holocene abstract holocene rapid climate change rcc events such as the little ice age lia are thought to have influenced average annual temperatures only marginally but to have affected winter temperatures relatively strongly with summer temperatures relatively unaffected reconstructing climate change at a seasonal resolution is crucial to fully capture holocene climate variability mediterranean climate is highly seasonal being influenced by the subtropical high pressure belt in summer and the mid latitude westerlies combined with outbreaks of polar winds in winter we identified events of high and low detrital input to the gulf of taranto central mediterranean sea anticipated to be linked to humid and dry conditions respectively and thereby potentially reflecting seasonal contrasts these events represent the bronze age ba roman humid period rhp medieval climate anomaly mca lia and present day and were selected for the analysis of single specimen globigerinoides ruber white carbonate chemistry mg ca 18o and 13c the dynamic range found for these parameters for the measured single individuals in the most recent interval reflects the present day seasonal contrasts in temperature and precipitation albeit with a bias towards the summer season these results are compared with high resolution 15 years sample sea surface temperature sst and bottom water temperature bwt reconstructions based on the 18o of g ruber white and mg ca of benthic foraminifer hyalinea balthica although the seasonal temperature contrast remains relatively stable significant winter cooling is observed during the ba and lia connections between high latitude climate winter conditions and low latitude climate summer conditions appear not straightforward during rcc events this results in changes in the moisture balance and in shifts in seasonal dominance between rccs during the lia winter like conditions cold and humid prevail throughout the year in contrast winters are dry and cold during the ba and are accompanied by dry and warm summers suggesting year round aridity and a relatively high seasonal temperature contrast this could have had a profound impact on early agriculture in southern italy

climatology of surface cyclone tracks associated with large central and eastern u s snowstorms 1950 2000 abstract the 241 largest snowstorms over the eastern two thirds of the united states during 1950 2000 exhibited considerable temporal variability ranging from 1 storm in three winters to 10 storms in 1993 94 the peak decadal frequency was 55 storms 1950s and the minimum was 45 storms 1970s and 1980s the east north central region experienced the greatest number of large snowstorms 148 followed by the west north central 136 and central 133 regions regional trends were different assessment of surface cyclone tracks associated with the large snowstorms identified three primary tracks one was located from the leeward side of the south central rocky mountains east northeast toward the great lakes a second was from the lower mississippi river basin northeastward toward the great lakes and a third was along the coastal mid atlantic region northeast toward maine temporal differences in the frequency of certain surface cyclone tracks were related to the decadal trends in regional large snowstorm

more intense more frequent and longer lasting heat waves in the 21st century a global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves model results for areas of europe and north america associated with the severe heat waves in chicago in 1995 and paris in 2003 show that future heat waves in these areas will become more intense more frequent and longer lasting in the second half of the 21st century observations and the model show that present day heat waves over europe and north america coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases indicating that it will produce more severe heat waves in those regions in the future

impact of increased horizontal resolution in coupled and atmosphere only models of the hadgem1 family upon the climate patterns of south america this study investigates the impact of increased horizontal resolution in coupled and atmosphere only global climate models on the simulation of climate patterns in south america sa we analyze simulations of the hadgem1 model family with three different horizontal resolutions in the atmosphere n96 135 km at 50 n n144 90 km and n216 60 km and two different resolutions in the ocean 1 and 1 3 in general the coupled simulation with the highest resolution 60 km in the atmosphere and 1 3 in the ocean has smaller systematic errors in seasonal mean precipitation temperature and circulation over sa than the atmosphere only model at all resolutions the models both coupled and atmosphere only properly simulate spatial patterns of the seasonal shift of the intertropical convergence zone itcz the formation and positioning of the south atlantic convergence zone sacz and the subtropical atlantic and pacific highs however the models overestimate rainfall especially in the itcz and over the western border of high elevation areas such as southern chile the coupling combined with higher resolution result in a more realistic spatial pattern of rain particularly over the atlantic itcz and the continental branch of the sacz all models correctly simulate the phase and amplitude of the annual cycle of precipitation and air temperature over most of south america the overall results show that despite some problems increasing the resolution in the hadgem1 model family results in a more realistic representation of climate patterns over south america and the adjacent oceans

penetration of magnetospheric electric fields to the equator during a geomagnetic storm 1 penetration of the magnetospheric electric field to the equatorial ionosphere was examined for the geomagnetic storm on 6 november 2001 by analyzing the difference in magnitude of the geomagnetic storm recorded at the dayside geomagnetic equator yap 0 3 gml and low latitude okinawa 14 47 gml the penetrated electric field caused the dp2 currents at the equator i e eastward currents during the main phase of the storm while the overshielding currents i e westward currents dominated during the recovery phase it is shown that the ring current started to develop simultaneously with the onset of the equatorial dp2 within the temporal resolution of a few minutes these results imply prompt transmission of the dawn to dusk convection electric field to the inner magnetosphere as well as to the equatorial ionosphere it is found that the equatorial dp2 started to decrease one hour after the onset of the ring current development indicating shielding effects becoming effective at the equator during the latter half of the storm main phase the dp2 was then overwhelmed by the overshielding which resulted in the counter electrojet cej in the beginning of the storm recovery phase the image magnetometer chain data indicate that the westward auroral electrojet aej in the dawn sector was driven over midlatitude centered at 57 corrected geomagnetic latitude cgml during the main phase while the aej shifted rapidly poleward to the auroral latitude centered at 67 cgml in the beginning of the recovery phase the overshielding must be caused by the abrupt poleward shift of the rl facs as inferred from the poleward shift of the aej in addition to the decrease in their magnitude due to the decrease in magnitude of the southward imf the geomagnetic storm at the dayside geomagnetic equator was enhanced in amplitude with the ratio of 2 7 as compared with the geomagnetic storm at low latitude this amplification is a result of both effects of the dp2 currents and the cej associated with the main and recovery phases respectively it is suggested that the electric field associated with the dp2 currents contributed to the development of the ring current during the main phase while the overshielding electric field may contribute to cease developing the ring current during the recovery phase

a 1052 year tree ring proxy for alpine summer temperatures a june august alpine temperature proxy series is developed back to ad 951 using 1 527 ring width measurements from living trees and relict wood the reconstruction is composed of larch data from four alpine valleys in switzerland and pine data from the western austrian alps these regions are situated in high elevation alpine environments where a spatially homogenous summer temperature signal exists in an attempt to capture the full frequency range of summer temperatures over the past millennium from inter annual to multi centennial scales the regional curve standardization technique is applied to the ring width measurements correlations of 0 65 and 0 86 after decadal smoothing with high elevation meteorological stations since 1864 indicate an optimal response of the rcs chronology to june august mean temperatures the proxy record reveals warm conditions from before ad 1000 into the thirteenth century followed by a prolonged cool period reaching minimum values in the 1820s and a warming trend into the twentieth century this latter trend and the higher frequency variations compare well with the actual high elevation temperature record the new central alpine proxy suggests that summer temperatures during the last decade are unprecedented over the past millennium it also reveals significant similarities at inter decadal to multi centennial frequencies with large scale temperature reconstructions however deviating during certain periods from h h lamb s european north atlantic temperature history

calibration and multi source consistency analysis of reconstructed precipitation series in portugal since the early 17th century a calibration of reconstructed winter spring and autumn precipitation series in portugal from 1600 onwards is undertaken in the present study using new instrumental sources for the period of 1815 2012 as summer precipitation in portugal is scarce and irregular it is not considered a consistency analysis of the calibrated time series is then undertaken using 1 precipitation indices for portugal in 1675 1799 2 teleconnections between seasonal precipitation and large scale atmospheric flow 3 two paleoclimatic experiments erik1 and erik2 generated from a global regional climate model chain echo g mm5 and 4 tree ring records from oak trees in portugal serra do bucaco these are the first multi centennial records of tree ring growth in portugal the earliest series begin in 1675 general agreement is found between indices and calibrated precipitation for their common period on an annual basis overall the atmospheric teleconnection patterns are dynamically coherent between the instrumen

mediterranean drought fluctuation during the last 500 years based on tree ring data a 2 5 x 2 5 degrees gridded summer april september drought reconstruction over the larger mediterranean land area 32 5 degrees 47 5 degrees n 10 degrees w 50 degrees e 152 grid points is described based on a network of 165 tree ring series the drought index used is the self calibrated palmer drought severity index and the period considered is 1500 2000 the reconstruction technique combines an analogue technique for the estimation of missing tree ring data with an artificial neural network for optimal non linear calibration including a bootstrap error assessment tests were carried out on the various sources of error in the reconstructions errors related to the temporal variations of the number of proxies were tested by comparing four reconstructions calibrated with four different sized regressor datasets representing the decrease in the number of available proxies over time errors related to the heterogeneous spatial density of predictors were tested using pseudo proxies provided by the global climate model echo g finally the errors related to the imperfect climate signal recorded by tree ring series were tested by adding white noise to the pseudo proxies reconstructions pass standard cross validation tests nevertheless tests using pseudo proxies show that the reconstructions are less good in areas where proxies are rare but that the average reconstruction curve is robust finally the noise added to proxies which is by definition a high frequency component has a major effect on the low frequency signal but not on the medium frequencies the comparison of the low frequency trends of our mean reconstruction and the gcm simulation indicates that the detrending method used is able to preserve the long term variations of reconstructed pdsi the results also highlight similar multi decadal pdsi variations in the central and western parts of the mediterranean basin and less clear low frequency changes in the east the sixteenth and the first part of the seventeenth centuries are characterized by marked dry episodes in the west similar to those observed in the end of the twentieth century in contrast the eighteenth and nineteenth centuries little ice age are characterized by dominant wet periods in the eastern part of the mediterranean basin the observed strong drought period of the end of the twentieth century seems to be the strongest of the last 500 years

representation of extratropical cyclones blocking anticyclones and alpine circulation types in multiple reanalyses and model simulations abstractatmospheric circulation types blockings and cyclones are central features of the extratropical flow and key to understanding the climate system this study intercompares the representation of these features in 10 reanalyses and in an ensemble of 30 climate model simulations between 1980 and 2005 both modern full input reanalyses and century long surface input reanalyses are examined modern full input reanalyses agree well on key statistics of blockings cyclones and circulation types however the intensity and depth of cyclones vary among them reanalyses with higher horizontal resolution show higher cyclone center densities and more intense cyclones for blockings no strict relationship is found between frequency or intensity and horizontal resolution full input reanalyses contain more intense blocking compared to surface input reanalyses circulation type classifications over central europe show that both versions of the twentieth century reanalysis dataset contain more easterlies and

little ice age glacier variations in jotunheimen southern norwvay a study in regionally controlled lichenometric dating of recessional moraines with implications for climate and lichen growth rates a new approach to regional lichenometric dating is developed and applied to little ice age moraine ridge sequences on 16 glacier forelands in jotunheimen southern norway lichenometric dating curves based on the rhizocarpon subgenus are constructed independently for west central and east jotunheimen although there are differences between the subregions a composite regional moraine chronology for jotunheimen identifies 12 episodes of moraine formation in ad 1743 1750 the regional little ice age glacier maximum 1762 1771 1782 1790 1796 1802 1811 1818 1833 1838 1845 1854 1860 1868 1871 1879 1886 1898 1915 1922 and 1927 1934 spatial and temporal patterns in glacier behaviour between the subregions and between jotunheimen and the neighbouring jostedalsbreen are explained in terms of the interaction of annual to decadal variations in summer temperature and winter precipitation glacier advances and moraine formation events driven primarily by winter precipitation variations exhibit subregio

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

a radius depth model for midlatitude cyclones in reanalysis data and simulations geometric properties of winter djf and summer jja midlatitude cyclones are analysed in reanalysis data present day and global warming simulations cyclone centres are identified by the minima of the 1000 hpa geopotential height fitting an azimuthally symmetric gaussian function to the surrounding height field provides cyclone depth difference between the cyclone centre and the synoptic environment radius standard deviation geostrophic wind and vorticity analysing era 40 reanalysis data of different resolutions and intergovernmental panel on climate change ipcc scenario simulations by the coupled atmosphere ocean general circulation model echam5 mpi om yields mean radii of 300 500 km in winter and 300 400 km in summer depth maxima occur in the storm tracks determined by the bandpass filtered variance of the geopotential height and the smallest radii characterize oceanic cyclogenesis regions the geostrophic vorticity derived from the fitted gaussian model agrees reasonably well with the observed relative vorticity future warmer climate scenarios exhibit smaller radii and weaker depths during winter and summer an intense growth of the depth is found during the 2 10 day cyclone life cycles while the radii reveal negligible growth compositing depths with respect to normalized total lifetime leads to rescaled depth life cycles which collapse to a simple universal function a 1 a for relative cyclone age a copyright 2010 royal meteorological society