potential vorticity diagnosis of the severe convective regime part ii the impact of idealized pv anomalies abstract idealized numerical experiments are conducted to understand the effect of upper tropospheric potential vorticity pv anomalies on an environment conducive to severe weather anomalies are specified as a single isolated vortex a string of vortices analogous to a negatively tilted trough and a pair of string vortices analogous to a position error in a negatively tilted trough the anomalies are placed adjacent to the tropopause along a strong upper level jet at a time just prior to a major tornado outbreak and inverted using the nonlinear balance equations in addition to the expected destabilization beneath and adjacent to a cyclonic pv anomaly the spatial pattern of the inverted balanced streamfunction and height fields is distorted by the presence of the horizontal pv gradient along the upper tropospheric jet stream streamfunction anomalies are elongated in the cross jet direction while height and temperature anomalies are elongated in the along jet direction the amplitude of the inverted

on the frequency distribution of net annual snow accumulation at the south pole the frequency distribution of stratigraphic layer thickness in cores and a snowmine at south pole is not compatible with a significant number 1 of missing layers associated with zero accumulation years inferred from pole height measurements a reconciliation of these data sets is needed if observed stratigraphic records are to be used as reliable paleoclimate indicators three explanations for the discrepancy are offered namely i during a significant number of years a visible stratigraphic horizon does not form or is not identified ii the true distribution is characterized by two maxima with a secondary maximum centered around zero layer thickness or iii the pole height measurements are misinterpreted and there are very few zero accumulation years at south pole with the currently available data it is not possible to discriminate among these three possibilities

potential vorticity diagnosis of the severe convective regime part i methodology observational and modeling studies have shown that shear and instability are powerful predictors of the likelihood of severe weather and tornadoes to the extent that upper tropospheric forecast errors can be described as potential vorticity pv anomalies on the forecasted pv field knowing and being able to quantify the effects of such errors on shear and instability would allow forecasters to anticipate the effects of those errors on the likely mode of severe weather to test the sensitivity of the severe convective environment to pv fluctuations a pv inversion framework is adopted that utilizes nonlinear balance the observed pv field is modified in a way that mimics realistic perturbations of trough intensity location or shape soundings including moisture profiles are reconstructed from the balanced geopotential height field assuming that air parcels conserve mixing ratio while their isentropic surfaces are displaced upward or downward by the addition of anomalous pv unperturbed balanced soundings agree reasonably well with full unbalanced soundings and differences are attributable to departures from nonlinear balance in areas of strong vorticity or acceleration balanced vertical wind profiles do not include the effects of friction so the vertical shear of the balanced wind departs unacceptably from total shear within the lowest 1 km of the troposphere the balanced wind perturbations are added to the total analyzed shear profile to estimate the effect of pv perturbations on shear and storm relative helicity by this process the importance of typical or hypothesized upper tropospheric forecast errors may be addressed in an idealized case study or operational context

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

convective destabilization by upper level troughs the approach of an upper level trough is accompanied by a local ascent of the isentropic surfaces in the troposphere the associated cooling and moistening destabilizes the atmosphere to convection in this paper we attempt to quantify the maximum amount of destabilization as a function of the amplitude and horizontal scale of the trough the trough is represented by an elongated potential temperature perturbation on the tropopause its structure including the isentrope displacement it produces is calculated from the balanced shear line solutions of juckes these solutions are used to estimate the amount by which mid and lower tropospheric air masses are lifted when an upper tropospheric trough passes overhead on the assumption that isentropic potential vorticity anomalies are localized in the upper troposphere the amount of destabilization is characterized by the maximum change in convective available potential energy cape and convective inhibition cin brought about by the passage of the trough the calculations seek to isolate one aspect of the interaction between an upper level trough and a tropical cyclone we show that the changes in cape are significant in the tropics up to 83 for the soundings examined and even more so in the middle latitudes up to 130 and that the cin may be completely removed

long lived mesoconvective vortices and their environment part ii induced thermodynamic destabilization in idealized simulations abstract idealized numerical simulations are used to quantify the effect of quasi balanced lifting arising from the interaction of the ambient vertical shear with midtropospheric cyclonic vortices mcvs generated by mesoscale convective systems on thermodynamic destabilization over a range of ambient vertical shear strengths and vortex characteristics observed in part i maximum upward displacements occur beneath the midtropospheric potential vorticity anomaly near the radius of maximum tangential vortex winds the location of the region of upward displacements relative to the ambient vertical shear vector depends on the relative strength of the vortex tangential flow and the ambient vertical shear and ranges from downshear for vortices of moderate strength in strong ambient vertical shear to 90 to the left of downshear for strong vortices in weak ambient vertical shear although significant upward displacements occur most rapidly with small vortices in strong ambient vertical shear maximum upward di

convective destabilization by a tropopause fold diagnosed using potential vorticity inversion there is observational evidence to suggest that at the time tropopause folds in extra tropical cyclones are descending into the mid troposphere there is frequently a destablization of the lower troposphere to moist convection here we consider the dynamical reasons for such a linkage using so called potential vorticity pv attribution concepts in particular pv inversion is used to find the wind shear attributable to the tropopause fold itself then this shear is used to quantify the tendency to generate regions of potential instability for an observed case of a modest tropopause fold it is found that the pv anomaly contained in the tropopause fold contributed substantially to the instantaneous convective destabilization in the sense of increasing the potential instability indeed at some locations it overcame a tendency to stabilize by the atmosphere without the fold on the other hand only a fraction of the region with increased potential instability experienced sufficient large scale ascent to lead to convection and it remains to be seen whether folds in general make a significant contribution to the generation of potential instability that can actually be realized the importance of tropopause folds or indeed of tropopause depressions in general in the context of convection is that their small horizontal scale has the potential to focus and amplify any convective destabilization locally this may account for the localization of outbreaks of severe convective weather which it is important to forecast accurately currently numerical weather prediction models often do not handle these small scales very accurately

rapid thinning of parts of the southern greenland ice sheet aircraft laser altimeter surveys over southern greenland in 1993 and 1998 show three areas of thickening by more than 10 centimeters per year in the southern part of the region and large areas of thinning particularly in the east above 2000 meters elevation the ice sheet is in balance but thinning predominates at lower elevations with rates exceeding 1 meter per year on east coast outlet glaciers these high thinning rates occur at different latitudes and at elevations up to 1500 meters which suggests that they are caused by increased rates of creep thinning rather than by excessive melting taken as a whole the surveyed region is in negative balance

using tropopause maps to diagnose midlatitude weather systems the use of potential vorticity pv allows the efficient description of the dynamics of nearly balanced atmospheric flow phenomena but the distribution of pv must be simply represented for ease in interpretation representations of pv on isentropic or isobaric surfaces can be cumbersome as analyses of several surfaces spanning the troposphere must be constructed to fully apprehend the complete pv distribution following a brief review of the relationship between pv and nearly balanced flows it is demonstrated that the tropospheric pv has a simple distribution and as a consequence an analysis of potential temperature along the dynamic tropopause here defined as a surface of constant pv allows for a simple representation of the upper tropospheric and lower stratospheric pv the construction and interpretation of these tropopause maps which may be termed isertelic analyses of potential temperature are described in addition techniques to construct dynamical representations of the lower tropospheric pv and near surface potential temperature which complement these isertelic analyses are also suggested case studies are presented to illustrate the utility of these techniques in diagnosing phenomena such as cyclogenesis tropopause folds the formation of an upper trough and the effects of latent heat release on the upper and lower troposphere

potential vorticity diagnosis of the severe convective regime part iii the hesston tornado outbreak nonlinear balance potential vorticity pv inversion is used to diagnose the sensitivity of the severe convective parameter space to the amplitude of a subsynoptic scale pv anomaly on 13 march 1990 a day on which a significant tornado outbreak impacted the great plains pv surgery is used to both amplify and remove the pv anomaly and the contemporaneous impact on various convective parameters is subsequently quantified by using piecewise pv inversion to compute the changes in those parameters attributable to each pv alteration it is found that amplifying the anomaly increases the cape by amounts typically ranging from 20 to 30 within the atmospheric columns experiencing the maximum pv increase ascent is increased slightly downshear of the pv anomaly consistent with extant conceptual models governing synoptic scale forcing for vertical motion amplifying the pv anomaly increases deep layer shear over the southern half of the outbreak region and reduces storm relative helicity over the northern half primarily through changes in the estimated storm motion vector removing the anomaly produces complementary changes of the opposite sign thresholds of several commonly used convective parameters are chosen on the basis of prior empirical studies and the horizontal displacement of these threshold contours produced by the pv alterations reveals that relatively modest subsynoptic scale pv changes would not likely change the predominant convective mode during the hesston outbreak

glaciological investigations in the crete area central greenland a search for a new deep drilling site the results of the 1984 85 post gisp campaigns in central greenland are presented eight ice cores were obtained some spanning up to 360 years we present i geographical positions and elevations at the drill sites

thickening of the western part of the greenland ice sheet nasa s program for arctic regional climate assessment parca includes measurements of ice velocity and ice thickness along the 2000 m elevation contour line in the western part of the ice sheet here we use these measurements together with published estimates of snow accumulation rates to infer the mass balance or rate of thickening thinning of the ice sheet catchment area inland from the velocity traverse within the accuracy to which we know snow accumulation rates the entire area is in balance but localized regions inland from upernavik isstrom and jakobshavn isbrae both appear to be thickening by about 10 cm a 1

confluence and intersection of interacting conjugate faults a new concept based on analogue experiments abstract examination of the interaction area of conjugate faults yields evidence of a yet unknown structural pattern analogue experiments revealed the evolution of this pattern during the interaction process a fault propagating towards the highly active section of another conjugate fault becomes increasingly deflected towards the obtuse angle side of the conjugate system while approaching until joining it during this process the tip of the curved propagating fault retains its shear sense until immediately before joining with the highly active fault a process called confluence in this report under constant remote stress the deflected fault now becomes dominant a fault branch splits off at the point where deflection commences propagating straight ahead of the original direction and may dissect the former master fault alternating activity at both of the faults finally produces the known intersection patterns further studies of the proposed concept on natural examples are recommended due to the close geometric similarity of the evolutionary structural stages and natural fault patterns

sensitivity of central oklahoma convection forecasts to upstream potential vorticity anomalies during two strongly forced cases during mpex abstractthe role of upstream subsynoptic forecast errors on forecasts of two different central oklahoma severe convection events 19 and 31 may 2013 characterized by strong synoptic forcing during the mesoscale predictability experiment mpex are evaluated by applying the ensemble based sensitivity technique to wrf ensemble forecasts with explicit convection during both cases the forecast of the timing and intensity of convection over central oklahoma is modulated by the southward extent of upstream midtropospheric potential vorticity anomalies that are moving through the base of a larger scale upstream trough but pass by central oklahoma prior to convective initiation in addition the convection forecasts are also sensitive to the position of lower tropospheric boundaries such that moving the boundaries in a manner that would lead to increased equivalent potential temperature over central oklahoma prior to convective initiation leads to more precipitation statistical pv inversion and correlation c

thermal versus dynamical tropopause in upper tropospheric balanced flow anomalies this paper systematically investigates differences between the thermal and the dynamical tropopause for upper tropospheric balanced flow anomalies idealized cyclonic and anticyclonic anomalies are considered which are either axisymmetric or plane symmetric given a distribution of potential vorticity pv the inversion problem is solved numerically to obtain the corresponding balanced flow i e wind and temperature the control parameter is the aspect ratio of the pv anomaly which governs the partitioning into a thermal and a dynamical anomaly for pv anomalies of intermediate and tall aspect ratios the location of the thermal tropopause differs significantly from the location of the dynamical tropopause the thermal tropopause is rather indistinct for intermediate aspect ratios while it is sharp and well defined for both tall and shallow anomalies a barotropic deformation flow field superimposed on a plane symmetric anomaly induces an ageostrophic wind which modifies the static stability throughout the pv anomaly such that the thermal and dynamical tropopauses evolve differently recent observations concerning the correlation between the thermal and ozone tropopauses can be interpreted consistently in terms of the present results

greenland ice sheet high elevation balance and peripheral thinning aircraft laser altimeter surveys over northern greenland in 1994 and 1999 have been coupled with previously reported data from southern greenland to analyze the recent mass balance of the greenland ice sheet above 2000 meters elevation the ice sheet is in balance on average but has some regions of local thickening or thinning thinning predominates at lower elevations with rates exceeding 1 meter per year close to the coast interpolation of our results between flight lines indicates a net loss of about 51 cubic kilometers of ice per year from the entire ice sheet sufficient to raise sea level by 0 13 millimeter per year approximately 7 of the observed rise

annual accumulation at two sites in northwest greenland during recent centuries during summer 1995 150 m firn and ice cores were drilled to determine annual accumulation rates at two greenland sites 73 84 n 49 49 w nasa u site and 78 53 n 56 83 w humboldt glacier site annual layers were identified in the cores using multiple parameters 18 o and concentrations of dust h 2 o 2 nh 4 ca 2 and no 3 using all parameters together to define annual layers resulted in a 350 year record for the nasa u core with no dating uncertainty for the lower accumulation humboldt core the dating uncertainty is about 5 years over the 852 year period of record with no uncertainty over the past 200 years annual accumulation over the periods of record at the two sites averaged about 0 34 and 0 14 m water equivalent respectively a set of 20 m firn cores drilled near the main 150 m cores showed that interannual variability of accumulation exceeded spatial variability at nasa u the humboldt cores showed equal spatial and interannual variability the accumulation rates at both sites showed a low frequency variation of about 100 years and both sites showed 200 year cumulative fluctuations of about 2 m from mean accumulation rates compared to central greenland and to nasa u the humboldt core showed higher annual accumulation rates around 1760 1810 possibly indicating a changed circulation pattern for the more northern part of greenland in that period

occurrence frequency of thickness of annual snow accumulation layers at south pole this paper describes the frequency analysis of 2000 annual snow accumulation layers at the south pole it proposes application of this analysis to objective extraction of meteorological parameters from the south pole snow accumulation record we have compared the 200 year snow mine accumulation record of giovinetto and schwerdtfeger and a 2000 layer pit and core record obtained in 1982 frequency analysis of the number of occurrences of layers with respect to thickness or mass of the layer showed the logarithms of thickness or mass to be normally distributed this lognormality is quite robust arbitrary partitioning of the data by depth or systematic partition of the data by densification or firn ice transition does not destroy the lognormality of the accumulation series the geometric standard deviation of the mass of annual layers was the same as the geometric standard deviation of the thickness of these same layers as the layers densified from firn to ice this agrees with kapteyn s theory of transformability of lognormal distributions we have also compared the snow accumulation and marine aerosol sodium accumulation in recent annual layers with the station meteorological record and the surface aerosol record the amounts of snow and sodium accumulated are proportional to the number of warmings salt storms in most years of this short record the accumulation record may be transformable to provide an index of this meridional transport we propose that the magnitude of snow accumulation with respect to frequency of that accumulation provides an objective criterion for comparing individual years of meteorological history and that the geometric standard deviation of accumulation provides an objective index for estimation of climatic fluctuation during the period of accumulation

synoptic scale disturbances with circular symmetry abstract ate balanced flow structure of various classic synopitc scale disturbances is reviewed using the invertibility principle for isentropic potential vorticity ipv distributions complete solutions are shown for cold and warm core structures of various types the basic model imagines the tropopause to be the interface between the lower potential vorticity of the troposphere and the approximately six fold larger value typical of the lower stratosphere the sensitivity of the structure of the potential temperature variation along the tropopause and at the surface is described results are presented in diagrammatic form to allow easy diagnosis of the vortex structure from synoptic data available at perhaps only a few levels the point is made that upper air ipv and surface potential temperature distributions are often the most crucial in accounting for the balanced flow structure

interannual variations of snow accumulation on the greenland ice sheet 1985 1996 new observations versus model predictions newly measured time series of net water equivalent accumulation from ice cores are reported for 11 sites located near the 2000 m contour of the greenland ice sheet many of these sites are located in regions where accumulation has not been previously measured we compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range because ice core accumulation records include both regional and local accumulation components we used adjacent ice core records at six multiple core sites to estimate the local component and extrapolated these results to the five single core sites we investigated the impact of this short scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation although sealers were required to match the 12 year mean modeled precipitation to the mean observed accumulation a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations the need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed although very encouraging a more spatially distributed array of ice core accumulation measurements spanning the same time period as the precipitation modeling is necessary for continued model improvement and validation in agreement with earlier studies the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation

invigoration and capping of a convective rainband ahead of a potential vorticity anomaly abstractdeep convection frequently occurs on the eastern side of upper level troughs or potential vorticity pv anomalies this is consistent with uplift ahead of a cyclonic pv anomaly and consequent reduction in static stability and increase of convective available potential energy cape nevertheless the causal link between upper level pv and deep convection has not been proven and given that lift moisture and instability must all be present for deep convection to occur it is not clear that upper level forcing is sufficient in this paper a convective rainband that intensified ahead of a cyclonic pv anomaly in an environment with little cape 10 j kg 1 is examined to determine the factors responsible for its intensification the key feature was a low level convergence line arising from the remnants of an occluded front embedded in the low level cyclonic flow the rainband s intensity and morphology was influenced by the remnants of a tropopause fold that capped convection at midlevels in the

the balanced dynamical nature of a rapidly intensifying oceanic cyclone abstract aided with a numerical simulation the authors diagnose the synoptic scale evolution of an intense extratropical cyclone over the western atlantic ocean from the perspective of balanced dynamics using potential vorticity inversion techniques the authors show that even during the period of largest growth rate early in the life cycle the balance equations capture much of the nondivergent wind irrotational wind and height tendency fields the structure of the cyclone evolves from a maximum amplitude at the tropopause to a maximum amplitude at the surface as the system moves offshore the vertical phase structure remains slightly upshear tilted throughout less than one quarter wavelength cyclogenesis is interpreted in terms of a baroclinic wave propagating through a varying basic state in which surface development is rapid because of the sudden response of the wave structure to a changing environment the mature cyclone structure strongly resembles cases of continental cyclones except that t

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

precipitation over greenland and its relation to the north atlantic oscillation the equation method based on an equivalent isobaric geopotential height in coordinates has been used to retrieve the precipitation over greenland this approach is designed to accurately represent the topographic effects of the greenland ice sheet on atmospheric motion and precipitation the 11 year mean precipitation from 1985 to 1996 over all of greenland is 376 mm yr 1 which is close to the long term mean precipitation of 346 mm yr 1 estimated from glaciological data the precipitation over all of greenland shows that the largest value in 1986 is 472 mm yr 1 and the smallest value in 1995 is 309 mm yr 1 the major interannual variability of the atmospheric circulation in the north atlantic can be represented by the variation of the north atlantic oscillation nao index which is most pronounced during winter it is found that if the nao index increases the total precipitation over greenland decreases and vice versa the correlation coefficient between these two series for 1985 1995 is 0 75 the mean precipitation over southern greenland where the majority of precipitation falls is more closely related to the nao index in winter and their correlation coefficient is 0 80 this relationship can be understood from the composite maps of sea level pressure and greenland precipitation for the high and low index months during months of high nao index values the icelandic low is strong during months of low nao index values the monthly mean low is located to the southwest of greenland over the labrador sea precipitation amounts over the southeast coast of greenland are about 100 mm larger during the low nao index months than the high nao index months precipitation over all of greenland during the low nao index months is higher there are significant downward trends in annual precipitation from 1985 1995 for all of greenland and its southern and central west coastal regions amounting to about 3 per year

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet