annual net balance of north cascade glaciers 1984 94 annual net balance on eight north cascade glaciers during the 1984 94 period has been determined by measurement of total mass loss from firn and ice melt and of residual snow depth at the end of the summer season overall spatial density of measurement points is 200 points km 2 mean annual balance of north cascade glaciers from 1984 to 1994 has been 0 38 m a 1 the resulting 4 2 m loss in water equivalent thickness is significant since north cascade glaciers have an average thickness of 30 50 m cross correlation of annual net babance for eight glaciers ranges from 0 83 to 0 97 this indicates the mass balances of the eight glaciers have been responding similarly to climate conditions despite their range of topographic and geographic characteristics annual net balance of individual glaciers was correlated with climate records the highest ablation season correlation coefficient is mean may august temperature ranging from 0 63 to 0 84 the highest accumulation season correlation coefficient is total accumulation season precipitation ranging from 0 35 to 0 59

rocket triggered lightning propagation paths relative to preceding natural lightning activity and inferred cloud charge lightning mapping array lma data are used to compare the propagation paths of seven rocket triggered lightning flashes to the inferred charge structure of the thunderstorms in which they were triggered this is the first lma study of florida thunderstorm charge structure three sequentially within 16 min triggered lightning flashes whose initial stages were the subject of hill et al 2013 are reexamined by comparing the complete flashes to the preceding natural lightning to demonstrate that the three rocket triggered flashes propagated through an inferred negative charge region that decreased from about 6 8 to about 4 4 km altitude as the thunderstorm dissipated two other flashes were also sequentially triggered within 9 min in a thunderstorm that contained a convectively intense region ahead of a stratiform region with similar observed results finally two unique cases of triggered lightning flashes are presented in the first case the in cloud portion of the triggered lightning flash after ascending to and turning horizontal at 5 3 km altitude just above the 0 c level was observed to very clearly resemble the geometry of the in cloud portion of the preceding natural lightning discharges in the second case a flash was triggered relatively early in the storm s lifecycle that did not turn horizontal near the 0 c level as is usually the case for triggered lightning in dissipating storms but ascended to nearly 7 5 km altitude before exhibiting extensive horizontal branching

comparison of geodetic and glaciological mass balance techniques gulkana glacier alaska u s a the net mass balance on gulkana glacier alaska u s a has been measured since 1966 by the glaciological method in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier systematic errors can accumulate linearly with time in this method therefore the geodetic balance in which errors are less time dependent was calculated for comparison with the glaciological method digital elevation models of the glacier in 1974 1993 and 1999 were prepared using aerial photographs and geodetic balances were computed giving 6 0 0 7 m w e from 1974 to 1993 and 11 8 0 7 m w e from 1974 to 1999 these balances are compared with the glaciological balances over the same intervals which were 5 8 0 9 and 11 2 1 0 m w e respectively both balances show that the thinning rate tripled in the 1990s these cumulative balances differ by 6 for this close agreement the glaciologically measured mass balance of gulkana glacier must be largely free of systematic errors and be based on a time variable area altitude distribution and the photography used in the geodetic method must have enough contrast to enable accurate photogrammetry

vertical velocity characteristics of deep convection over darwin australia abstract continuous vertical velocity measurements using a 50 mhz wind profiler located at darwin in northern australia during periods of active convection have been analyzed this dataset is dominated by continental type convection numerous examples of shallow deep and decaying convection were seen and it is shown that only the deep systems have substantial tilts to the draft structure the most intense updrafts occur above the freezing level but shallow convection also produces large amplitude vertical motions the strength of these updrafts in this dataset is very similar to other tropical oceanic data that observation is consistent with the idea that the magnitude of the updrafts is much less in the tropics than for intense midlatitude convection because the convective available potential energy is distributed over a much deeper layer in the tropics although more intense updrafts may be present at other tropical locations such as the tiwi islands north of darwin the size of the cores however

a continuum model of melt pond evolution on arctic sea ice 1 during the northern hemisphere summer absorbed solar radiation melts snow and the upper surface of arctic sea ice to generate meltwater that accumulates in ponds the melt ponds reduce the albedo of the sea ice cover during the melting season with a significant impact on the heat and mass budget of the sea ice and the upper ocean we have developed a model designed to be suitable for inclusion into a global circulation model gcm which simulates the formation and evolution of the melt pond cover in order to be compatible with existing gcm sea ice models our melt pond model builds upon the existing theory of the evolution of the sea ice thickness distribution since this theory does not describe the topography of the ice cover which is crucial to determining the location extent and depth of individual ponds we have needed to introduce some assumptions we describe our model present calculations and a sensitivity analysis and discuss our results

pressure transients within mcs mesohighs and wake lows by animating enhanced coarse surface pressure observations of 12 1985 preliminary regional experiment for storm scale operational research meteorology pre storm mesoscale convective systems mcss the authors exposed 92 transitory highs and lows living within virtually all of the systems mesohighs and wake lows a quasi lagrangian feature following not material following analysis of the pressure fields produced five primary results first these transients with magnitudes of a few millibars horizontal dimensions of order 100 km and average lifetimes of about 2 h collectively composed spatial and temporal envelopes that contributed at least part of the total pressure field within mesohighs and wake lows transients did not apparently favor formation or dissipation in any location of the envelopes second as the mcss matured the difference between each complex s transitory highs mean pressure and transitory lows mean pressure increased in 78 of the conclusive cases apparently one frequent role of mcss is locally to magnify storm scale pressure gradients third transient paths reflect the frequent symmetric to asymmetric metamorphoses of the mcss fourth the temporal fluctuations of the numbers and apparent sizes of transients within a composite mcs partially support theories of mcs upscale evolution finally the composite s transient numbers and apparent sizes varied almost identically with time in a pattern that closely resembles the fluctuation of stratiform and convective volumetric rain rates of mcss

melt ponds on sea ice in the canadian archipelago 2 on the use of radarsat 1 synthetic aperture radar for geophysical inversion microwave scattering from a first year sea ice fyi melt ponded surface is examined using radarsat 1 synthetic aperture radar sar data collected during the 1997 collaborative interdisciplinary cryospheric experiment c ice 97 near resolute bay nunavut this paper 1 investigates the utility of time series of microwave scattering to detect melt pond formation and 2 investigates approaches toward geophysically inverting information on the physical and radiative properties of this surface we found melt pond formation to coincide with a sharp rise in the temporal evolution of the microwave scattering coefficient over fyi radarsat 1 incidence angle and surface wind speed explained 90 of the variation in radarsat 1 was sensitive r2 0 80 to the fractional coverage of melt ponds during windy conditions 5 3 m s 1 spatial and temporal coincident measurements of radarsat 1 and the integrated shortwave albedo revealed a strong negative statistical correlation r2 0 91 during windy conditions 5 3 m s 1 a weaker but strong negative relationship r2 0 78 was observed for less windy conditions 3 2 m s 1 and a very weak positive relationship r2 0 19 was found for low wind speed conditions 1 5 m s 1 all relationships were observed for melt pond fractions between 13 and 34

electrical structure in thunderstorm convective regions 1 mesoscale convective systems electric field e soundings through convective regions of mesoscale convective systems mcss are examined in this paper ten e soundings through updrafts in mcs convective regions and five soundings in mcs convective regions outside updrafts are used to show that a typical electrical structure exists in this region these 15 e soundings plus one other previously published sounding which is included in this analysis comprise all known soundings in the convective region of mcss the basic charge structure identified in mcs updrafts consists of four charge regions alternating in polarity with the lowest region positive and the highest region negative the basic charge structure outside updrafts in mcs convective regions has six charge regions alternating in polarity with a positive charge region lowest maximum e magnitudes of both polarities are larger and are located at lower heights in soundings outside updrafts compared to those within updrafts excepting the upper positive charge inferred charge regions are shallower and have larger charge densities outside updrafts the center of the main negative charge is lower and warmer outside updrafts 5 5 km 6 2 c than within updrafts 6 9 km 15 7 c these features inside and outside updrafts are incorporated in a new conceptual model of mcs convective region charge structure also an expanded conceptual model is developed using previously published data from other parts of mcss this more complete conceptual model shows the typical electrical charge airflow and reflectivity features in the stratiform region the transition zone and the convective region of midlatitude mesoscale convective systems

shear parallel moist convection over the tropical ocean a case study from 18 february 1993 toga coare abstract this paper describes a newly observed form of shear parallel rainbands that were observed on 18 february 1993 in tropical ocean global atmosphere coupled ocean atmosphere response experiment using the ncar eldora airborne doppler radar interesting features of these rainbands included their rapidly changing and highly cellular nature their complicated and layered kinematic structure and the effects of the rainbands on the tropical environment in their lower levels the rainbands consisted of east west elongated clusters of small convective cells aligned with the z 0 5 km shear vector strong low level convergence inflow from the north and enhanced westerly winds extended from the surface up to 5 km much of this air was vented out of the storm at midlevels exiting to the north in the 0 c stable layer at z 5 7 km this midlevel outflow fed an area of widespread stratiform precipitation lying to the north of the rainband the cold pool outflow emanating from this area of precipitation t

simulated convective lines with leading precipitation part ii evolution and maintenance abstract this article the second of two describing a study in which the authors used idealized numerical simulations to investigate front fed convective lines with leading stratiform precipitation ffls systems addresses the dynamics and sensitivities governing the systems evolution toward other structures and their sustenance despite the apparent contamination of their inflow by preline precipitation sensitivity tests show that the middle and upper tropospheric wind shear are important to the updraft tilt and overall structure of the simulated systems in time simulated ffls systems tend to evolve toward a convective line with trailing stratiform ts precipitation structure because they tend to decrease the line perpendicular vertical wind shear nearby this along with gradual increases in the system s cold pool strength contributes to more rearward sloping updrafts and may initiate a positive feedback mechanism that hastens transition toward ts structure however whereas the system s tendency

the 11 august 2006 squall line system as observed from mit doppler radar during the amma sop on the evening of 9 august 2006 a mesoscale convective system mcs having a north south oriented squall line organization formed over the border between chad and nigeria it propagated westward intensified over nigeria on 10 august and reached niamey niger at 0320 utc on 11 august its passage over niamey was accompanied by dust lifting and was well tracked by the massachusetts institute of technology mit doppler radar the three dimensional structure of the airflow and precipitation pattern is investigated from regular radar volume scans performed every ten minutes between 0200 and 0321 utc the 3d wind components are deduced from the multiple doppler synthesis and continuity adjustment technique muscat applied to a set of three volume scans obtained over a time period of one hour which are equivalent to a three radar observation of the squall line when considering a reference frame moving with the system and the hypothesis of a stationary field results of the wind synthesis reveal several features commonly observed in tropical squall lines such as the deep convective cells in front of the system fed by the monsoon air and extending up to 15 km altitude and the well marked stratiform rain region at the rear associated with mesoscale vertical motions forward and trailing anvils are clearly identified as resulting from the outflow of air reaching the tropopause and transported to this level by the sloping convective updraughts occurring in a sheared environment in the northern part a deeper and stronger front to rear flow at mid levels is found to contribute to the rearward deflection of the leading line and to promote a broader over 300 km stratiform cloud region eddy vertical transports of the cross line momentum mainly accounts for the mid level flow acceleration due to a momentum redistribution from low to higher levels the height distribution of hydrometeors and their associated production terms derived from a one dimensional microphysical retrieval model indicate the distinct roles of the convective and stratiform regions in the formation of graupel and rain and the respective contributions of cold riming and warm coalescence melting processes cooling from melting and heating cooling from condensation evaporation processes yield a net decrease and increase of the potential temperature at low and mid to upper levels respectively with respect to an environmental thermodynamic profile taken three hours ahead of the analysis finally the upper level rearward flow could convey the non negligible proportion of ice particles farther from the leading deep convection to the trailing stratiform region thereby favouring the extent of this region

the mechanisms of sea ice melt pond formation and evolution 1 a series of observations were made on melting first year landfast arctic sea ice near barrow alaska to explore the seasonal evolution of melt pond coverage observations of pond coverage albedo and ice properties are combined with terrestrial lidar measurements of surface topography and meltwater balance to quantitatively identify the timing and role of mechanisms driving pond coverage the formation of interposed fresh ice is found to eliminate meltwater percolation through early pond formation and allow widespread ponding well above sea level pond drainage to sea level occurs principally by horizontal meltwater transport over the ice surface to macroscopic flaws freeboard loss caused by buoyancy decline as the ice thins controls pond growth late in the melt season after percolation begins the majority of the macroscopic flaws that drain melt ponds to sea level are observed to develop from brine drainage channels within the ice a simple thermodynamic model of meltwater percolation illustrates that fresh meltwater inflow causes pores in the ice to either shrink and freeze shut or enlarge based on initial size and ice temperature this threshold behavior of pore diameter controls both the blockage of smaller pores with interposed ice and the enlargement of larger brine drainage channels to allow meltwater drainage the results identify links between the temporal evolution of pond coverage and ice temperature salinity and thickness providing new opportunities to realistically parameterize ponds and summer ice albedo within sea ice models

multisensor analysis of a squall line in the amazon region 1 mesoscale features of the 26 january 1999 squall line are described with measurements made during the field experiment in rondonia brazil in the wet season wet of the amazon region amc as part of the large scale biosphere atmosphere experiment in the amazon lba and the tropical rainfall measurement mission trmm henceforth referred to as the wet amc and trmm lba field experiment the squall line moved through the experiment area from northeast to southwest with high rainfall rates in its leading edge and a poorly defined trailing stratiform precipitating area polarimetric and doppler measurements from the portable polarimetric s band radar s pol were analyzed in conjunction with surface and upper level data satellite visible vis and infrared ir measurements these remote and local measurements of variables such as cloud spatial and temporal distribution pressure temperature moisture precipitation and wind fields are consistent with each other as well as with similar mesoscale dynamics and thermodynamics features measured analyzed and modeled elsewhere e g rotunno et al 1988 garstang et al 1994 houze et al 1990 this tropical squall line is similar to its cousins in the midlatitudes with finer scale structural and dynamic features such as rotation and divergence results suggest that the cold pool has its origins in midlevels between 400 and 600 hpa from where evaporative cooling and drop dragging bring down colder air to the surface the convective region is dominated by warm microphysics while the stratiform region is dominated by cold microphysics moreover both regions are characterized by monomodal drop spectra centered around 2 0 and 1 0 mm respectively horizontal circulation associated with strong updrafts tends to increase cloud growth efficiency in the leading edge of the squall line

geostrophic and ageostrophic circulations in midlatitude squall lines the eliassen transverse circulation equation is derived from the set of f plane semigeostrophic slab symmetric equations with the inclusion of both diabatic heating and ambient shear effects numerical integrations of this model in geostrophic coordinates are performed in the context of a typical midlatitude squall line characterized by a leading convective line and a trailing stratiform rain region some dynamical insights are provided by these integrations in conjunction with the theoretical framework which seem to be unavailable by primitive equation model simulations a more complete dynamical picture of a squall line circulation system is revealed from this study a balanced midlevel horizontal vortex coupled with an ageostrophic transverse circulation in the normalline plane this configuration suggests an interaction between two distinct dynamical scales that is the scales with geostrophic and ageostrophic like motions both of which play important roles in mesoscale convective systems the internal and external physical processes that affect the ageostrophic transverse circulation are further discussed

a study of two propagating heavy rainfall episodes near taiwan during sowmex timrex iop 8 in june 2008 part i synoptic evolution episode propagation and model control simulation abstractthis paper is the first of a two part study to investigate two rain producing episodes in the longitude time hovmoller space upstream from taiwan during the eighth intensive observing period iop 8 12 17 june 2008 of the southwest monsoon experiment terrain influenced monsoon rainfall experiment sowmex timrex with a goal to better understand the mechanism and controlling factors for their organization and propagation both in a prefrontal environment the first episode moved eastward and the second was a rare westward moving event and each caused heavy rainfall in taiwan on 14 and 16 june respectively in part ii the roles played by synoptic conditions and terrain effects are further examined through sensitivity tests with the aid from a successful simulation with a grid spacing of 2 5 km the structure and organization of convection embedded in the two episodes are shown to be different with stronger low level vertical wind shear in its environment the first episode consisted of well

relation between the mass balance of western canadian mountain glaciers and meteorological data le bilan de masse les bilans d ete et d hiver et l altitude de la ligne d equilibre de 3 glaciers canadiens sont compares avec les donnees meteorologiques de stations avoisinantes pour la periode 1966 1984 presentation de reconstructions statistiques pour les 3 glaciers sur la base des equations de regression avec les enregistrements meteorologiques depuis 1938

microphysical characteristics of squall line stratiform precipitation and transition zones simulated using an ice particle property evolving model abstracta quasi idealized 3d squall line case is simulated using a novel bulk microphysics scheme called the ice spheroids habit model with aspect ratio evolution ishmael in ishmael the evolution of ice particle properties e g mass shape maximum diameter density and fall speed are predicted during vapor growth sublimation riming and melting allowing ice properties to evolve from various microphysical processes without needing separate unrimed and rimed ice categories ishmael produces both a transition zone and an enhanced stratiform precipitation region and ice particle properties are analyzed to determine the characteristics of ice that lead to the development of these squall line features rimed particles advected rearward from the convective region produce the enhanced stratiform precipitation region the transition zone results from hydrometeor sorting the evolution of ice particle properties in the convective region leads to fall speeds that favor ice advecting rearward of the tran

evolution of the total lightning structure in a leading line trailing stratiform mesoscale convective system over houston texas 1 line normal vertical cross sections of houston lightning detection and ranging ldar vhf radiation sources and radar reflectivity provide new insights into the three dimensional total lightning structure and evolution of a leading line trailing stratiform llts mesoscale convective system mcs over houston texas on 31 october 2005 previous research examining only the mature stage of an mcs showed that the overwhelming majority of vhf lightning sources occurred in the convective region with a lightning pathway extending rearward and descending in altitude into the stratiform region this descending pathway was most likely associated with small charged ice particles advected from the convective line unlike previous research the lightning pathway observed during the evolution of the mcs on 31 october 2005 initially extended rearward 40 km at a nearly constant height of 9 10 km in less than an hour the lightning pathway evolved into a sloped pathway similar to that found by previous research with a horizontal extent between 50 to 60 km and downward descent of 4 to 5 km during the lightning pathway evolution radar analysis showed an increase of reflectivity in the midlevels of the stratiform region consistent with increased depositional and aggregational growth above the melting layer broadening increased range of values of radar reflectivity above the melting layer was most likely an indication of a strengthening mesoscale updraft in the stratiform region this strengthening updraft may have contributed to an increase in the growth of the small charge carrying ice crystals giving them a greater fall speed in addition the mesoscale updraft may have promoted an environment conducive to local stratiform region charge generation in the mixed phase region just above the melting layer

high resolution observations and numerical simulations of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 abstract this paper examines the three dimensional flow and dynamics of easterly gap flow through the strait of juan de fuca on 9 10 december 1995 using high resolution observations and model simulations the observations were obtained during the fourth intensive observing period during the second phase of the coastal observation and simulation with topography field experiment one of the most important data sources was the noaa p 3 aircraft which provided flight level data reflectivity and doppler winds as it flew down the strait of juan de fuca below 900 m the flow accelerated from 7 to 14 m s 1 at the entrance to the strait with a significant cross gap component and confluence over the eastern sections of the strait below 500 m the easterly flow approaching the western exit of the strait accelerated from 15 to 20 m s 1 as the 900 m deep easterly flow exited the gap it decreased in depth and accelerated to 25 m s 1 creating a shallow swath of diffluent winds below 300 m later in the event whe

test of a convective wake parameterization in the single column version of ccm3 abstract a convective wake parameterization incorporated into the single column scm version of the ncar community climate model ccm3 is tested using observational data from 12 squall line cases to determine whether it can successfully reproduce convectively driven wakes in a global climate model the key spatial thermodynamic and kinematic properties of the modeled versus the observed wakes are examined as these features determine the effects of the wakes on surface fluxes and the initiation of convection effects that should be simulated correctly in general circulation models if deep convection and the resulting earth atmosphere energy exchanges are to be adequately represented results from these simulations indicate that while the scm convective wake scheme combination generally produced long lasting squall wake systems the wakes were often too shallow too warm and too moist these differences occurred despite the ability of ccm3 s standard cumulus parameterization to provide the wake scheme

dynamics of the stratiform sector of a tropical cyclone rainband abstractairborne doppler radar documented the stratiform sector of a rainband within the stationary rainband complex of hurricane rita the stratiform rainband sector is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow beneath downward transport is organized into descending radial inflow in response to two regions of latent cooling in the outer upper regions of the rainband sublimational cooling introduces horizontal buoyancy gradients which produce horizontal vorticity and descending inflow similar to that of the trailing stratiform region of a mesoscale convective system within the zone of heavier stratiform precipitation melting cooling along the outer rainband edge creates a midlevel horizontal buoyancy gradient across the rainband that drives air farther inward beneath the brightband the organi

the evolution of the 10 11 june 1985 pre storm squall line initiation development of rear inflow and dissipation abstract mesoscale analysis of surface observations and mesoscale modeling results show that the 10 11 june squall line contrary to prior studies did not form entirely ahead of a cold front the primary environmental features leading to the initiation and organization of the squall line were a low level trough in the lee of the rocky mountains and a midlevel short wave trough three additional mechanisms were active a southeastward moving cold front formed the northern part of the line convection along the edge of cold air from prior convection over oklahoma and kansas formed the central part of the line and convection forced by convective outflow near the lee trough axis formed the southern portion of the line mesoscale model results show that the large scale environment significantly influenced the mesoscale circulations associated with the squall line the qualitative distribution of along line velocities within the squall line is attributed to the larger scale circulations associated with the le

relationships between lightning location and polarimetric radar signatures in a small mesoscale convective system abstract on 19 june 2004 the thunderstorm electrification and lightning experiment observed electrical microphysical and kinematic properties of a small mesoscale convective system mcs the primary observing systems were the oklahoma lightning mapping array the koun s band polarimetric radar two mobile c band doppler radars and balloonborne electric field meters during its mature phase this mcs had a normal tripolar charge structure lightning involved a midlevel negative charge between an upper and a lower positive charge and flash rates fluctuated between 80 and 100 flashes per minute most lightning was initiated within one of two altitude ranges 3 6 or 7 10 km msl and within the 35 dbz contours of convective cells embedded within the convective line the properties of two such cells were investigated in detail with the first lasting approximately 40 min and producing only 12 flashes and the second lasting over an hour and producing 105 flashes in both lightning was initiated in or nea

kinematic and precipitation structure of the 10 11 june 1985 squall line abstract high frequency 90 min rawinsonde data from a special mesoscale network 26 sites have been combined with wind profiler dense automated surface network data 80 stations spaced 50 km apart and a series of high resolution dual doppler radar analyses in a common framework attached to a moving squall line system to form a comprehensive dataset describing the mature phase of the 10 11 june 1985 squall line observed during pre storm the dual doppler radar analyses covered a 200 300 km2 area from the leading edge of the convective line to the back edge of the trailing stratiform precipitation region thus providing high resolution wind information over a very broad portion of the storm system the comprehensive analysis is used to resolve several aspects of the trailing stratiform region that had remained unclear from previous studies first a difference in the horizontal scale was found between the mesoscale updraft which at upper levels was on the scale of the trailing stratiform cloud a

systematic variation of drop size and radar rainfall relations time histories of the characteristics of the drop size distribution of surface disdrometer measurements collected at kapingamarangi atoll were partitioned for several storms using rain rate r reflectivity factor z and median diameter of the distribution of water content d0 this partitioning produced physically based systematic variations of the drop size distribution dsd and z r relations in accord with the precipitation types viewed simultaneously by a collocated radar wind profiler these variations encompass the complete range of scatter around the mean z r relations previously reported by tokay and short 1996 for convective and stratiform rain and demonstrate that the scatter is not random the systematic time or space variations are also consistent with the structure of mesoscale convective complexes with a sequence of convective transition and stratiform rain described by various authors there is a distinct inverse relation between the coefficient a and the exponent of the z r relations which has been obscured in prior work because of the lack of proper discrimination of the rain types contrary to previous practice it is evident that there is also a distinct difference in the dsd and the z r relations between the initial convective and the trailing transition zones the previously reported z r relation for convective rain is primarily representative of the transition rain that was included in the convective class the failure of present algorithms to distinguish between the initial convective and the trailing transition rains causes an erroneous apportionment of the diabatic heating and cooling and defeats the primary intent of discriminating stratiform from convective rains

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

changes in arctic melt season and implications for sea ice loss the arctic wide melt season has lengthened at a rate of 5 days decade 1 from 1979 to 2013 dominated by later autumn freezeup within the kara laptev east siberian chukchi and beaufort seas between 6 and 11 days decade 1 while melt onset trends are generally smaller the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer the additional heat stored in the upper ocean of approximately 752 mj m 2 during the last decade increases sea surface temperatures by 0 5 to 1 5 c and largely explains the observed delays in autumn freezeup within the arctic ocean s adjacent seas cumulative anomalies in total absorbed solar radiation from may through september for the most recent pentad locally exceed 300 400 mj m 2 in the beaufort chukchi and east siberian seas this extra solar energy is equivalent to melting 0 97 to 1 3 m of ice during the summer

a numerical study of the along line variability of a frontal squall line during pre storm despite considerable progress in the understanding of two dimensional structures of squall lines little attention has been paid to the along line variability of these convective systems in this study the roles of meso and larger scale circulations in the generation of along line variability of squall lines are investigated using an 18 h prediction of a frontal squall line that occurred on 26 27 june 1985 during pre storm preliminary regional experiment for stormscale operational research meteorology it is shown that the canadian regional finiteelement rfe model reproduces reasonably well a number of surface and vertical circulation structures of the squall system as verified against available network observations these include the initiation propagation and dissipation of the squall system surface pressure perturbations and cold outflow boundaries a midlevel mesolow and an upper level mesohigh a front to rear ftr ascending flow overlying an intense rear to front rtf flow and a leading convective line followed by stratiform precipitation regions it is found that across line circulations at the northern segment of the squall line differ significantly from those at its southern segment including the different types of precipitation the absence of the rtf flow and midlevel mesolow and the early dissipation of organized convection in the northern part the along line variability of the squall s circulations results primarily from the interaction of convectively generated perturbations with a midlevel baroclinic trough the large scale trough provides an extensive rtf flow component in the southern portion of the squall system and an ftr flow component in the north whereas the midlevel mesolow tends to enhance the rtf flow to the south and the ftr flow to the north of the mesolow during the mature to decaying stages the along line variability of the squall s circulations appears to be partly responsible for the generation of different weather conditions along the line such as the development of an upper level stratiform region in the southern segment and a midlevel cloud region in the northern portion of the squall line

flash propagation and inferred charge structure relative to radar observed ice alignment signatures in a small florida mesoscale convective system a series of vertical cross sections taken through a small mesoscale convective system mcs observed over florida by the dual polarimetric smart radar were combined with vhf radiation source locations from a lightning mapping array lma to examine the lightning channel propagation paths relative to the radar observed ice alignment signatures associated with regions of negative specific differential phase kdp additionally charge layers inferred from analysis of lma sources were related to the ice alignment signature it was found that intracloud flashes initiated near the upper zero kdp boundary surrounding the negative kdp region the zero kdp boundary also delineated the propagation path of the lightning channel with the negative leaders following the upper boundary and positive leaders following the lower boundary very few lma sources were found in the negative kdp region we conclude that rapid dual polarimetric radar observations can diagnose strong electric fields and may help identify surrounding regions of charge

a real time automated convective and stratiform precipitation segregation algorithm in native radar coordinates a new convective stratiform c s precipitation segregation algorithm was developed for applications with single radar volume scan data and in its native spherical coordinates the new algorithm consists of two parts the first is to find convective rainfall cores based on physical characteristics of different rainfall types and the second is to delineate the full convective area through seeded region growing the new scheme takes into account radar sampling characteristics and a variety of precipitation scenarios where the c s delineation was relatively challenging the new c s delineation scheme has two impacts on radar quantitative precipitation estimation qpe i correctly separate convective and stratiform regions such that appropriate ze r relationships can be applied ii correctly define the stratiform area such that a vertical profile of reflectivity vpr correction can be applied the vpr correction is very important to reduce overestimation errors in radar qpes associated with bright band the new algorithm was tested on many events and showed improved performance over previous schemes especially when handling strong bright band and melting graupels in stratiform precipitation the new scheme was also tested in radar quantitative precipitation estimation qpe and it consistently reduced the root mean square error and mean absolute bias in the radar qpe when compared with gauges

the development and structure of an oceanic squall line system during the south china sea monsoon experiment abstract a primary goal of the south china sea monsoon experiment scsmex a major field campaign of the tropical rainfall measuring mission trmm is to define the initiation structure evolution and dynamics of precipitation processes associated with the onset of the south china sea scs summer monsoon in this study dual doppler and dual polarimetric radar analysis techniques are used to investigate the development and structure of a squall line system observed on 24 may 1998 the focus is the linkage between the airflow and the microphysical fields through the system the squall line system including three distinct lines persisted from 1200 utc 24 may to the following day a detailed study was performed on the structure of the second and most intense line lasting for over 10 h compared to tropical squall lines observed in other regions this narrow squall line system had some interesting features including 1 maximum reflectivity as high as 55 dbz 2 relatively little stratiform rainfall th

analysis of a small vigorous mesoscale convective system in a low shear environment part ii evolution of the stratiform precipitation and mesoscale flows abstract the evolution of the mesoscale flow and precipitation distribution are investigated for a small mesoscale convective system mcs that evolved in a nearly barotropic environment exhibiting moderate instability and weak wind shear observations primarily from a single doppler radar detail the growth of the mcs from the merger of several clusters and lines of vigorous convective cells into a mature state consisting of a weaker convective line trailed by an expanding stratiform precipitation region analysis of radar reflectivity reveals that this stratiform region formed in situ in the presence of weak mesoscale updraft as decaying convective cores coalesced rather than through rearward advection of ice particles directly from the convective region in the absence of sufficient low level shear the mcs collapsed rapidly as it assumed the structure of the archetypal convective line and trailing stratiform precipitation region velocity azimuth displays reveal mesoscale updrafts of about 70 cm s 1 d

a wintertime gulf coast squall line observed by edop airborne doppler radar abstract an extensive wintertime squall line on 13 january 1995 occurring along the u s gulf of mexico coastline is examined using airborne radar observations combined with conventional data analysis flight tracks with the er 2 doppler radar edop mounted on the high altitude 20 km er 2 aircraft provided a unique view of the vertical structure of this line in this paper the authors document the squall line structure and compare and contrast this structure with other published cases the squall line had several prominent features that differ from previous studies 1 the stratiform region was wide in comparison to more typical systems that are 50 100 km wide 2 the trailing stratiform region consisted of two to three separate embedded trailing bands rather than one continuous band 3 vertical motions in the trailing stratiform region were nearly twice as strong as previously reported values with mean values approaching 1 m s 1 between 7 and 9 km altitude and larger values 1 5 m s 1 in the em

multiscale convective overturning in mesoscale convective systems reconciling observations simulations and theory abstract an analysis of how parameterized convection interacts with hydrostatic explicitly resolved precipitation processes to represent multiscale convective overturning in a mesoscale resolution numerical simulation is presented critically important ingredients of the successful simulation are identified and the degree to which simulations are consistent with observations and theoretical considerations is examined of particular concern is how convective parameterization routines reconcile the deep moist absolutely unstable structures that form in mesoscale convective systems it is found that these structures arise primarily from resolvable scale vertical motion and that the model responds to these structures not only by maintaining parameterized convection but also by developing a hydrostatic manifestation of convective overturning on its smallest resolvable horizontal scales the strongest and most distinctive mesoscale perturbations develop in regions where the mesoscale contribution to convectiv

genesis of typhoon chanchu 2006 from a westerly wind burst associated with the mjo part ii roles of deep convection in tropical transition abstractin this study the life cycles of a series of four major mesoscale convective systems mcss during genesis and their roles in transforming a vertically tilted vortex associated with a westerly wind burst hereafter the wwb vortex into typhoon chanchu 2006 are examined using 11 day cloud resolving simulations presented in part i it is found that the tilted wwb vortex at early stages is characterized by an elevated cold core layer about 200 hpa thick below and a weak warm column above with large vertical wind shear across the layer which extends over a horizontal distance of about 450 km between the vortex s 400 and 900 hpa centers during the final two days of the genesis process the upper level warm column increases in depth and intensity as a result of the absorption of convectively generated vortices cgvs including a mesoscale convective vortex mcv causing more rapid amplification of cyclonic vorticity in the middle than the lower troposphere the commencement of sustained intens

evolution of mesoscale convective system organizational structure and convective line propagation abstractthis study examines organizational changes and periods of rapid forward propagation in an mcs on 6 july 2015 in south dakota the mcs case was the focus of a plains elevated convection at night pecan iop data from the sioux falls wsr 88d and a high resolution wrf simulation are analyzed to examine two periods of rapid forward propagation or surges and organizational changes during the first surge surge a the northern portion of the convective line propagates eastward faster than the southern portion and the northern portion of the leading line transitions from a single convective core to a multicellular structure as it merges with convection initiation radar reflectivity factor z and graupel concentrations decrease above the melting layer while at lower altitudes z increases the mcs cold pool also intensifies and deepens beneath an expanded region of high rainwater content and subsaturated air throughout surge a a mesoscale circulation with strong rear to front near surface flow and

evidence for a nimbostratus uncinus in a convectively generated mixed phase stratiform cloud shield abstractthe structure of a melting layer associated with a mesoconvective system is examined using a combination of in situ aircraft measurements and a unique doppler radar operated by the u s navy that has a range resolution as fine as 0 5 m interest in this case was motivated by ground based all sky camera images that captured the transient development of midlevel billow cloud structures within a precipitating trailing stratiform cloud shield associated with a passing deep convective system a sequence of high fidelity time height radar measurements taken of this storm system reveal that the movement of the billow cloud structure over the radar site corresponded with abrupt transitions in the observed low level precipitation structure of particular note is an observed transition from stratiform to more periodic and vertically slanted rain shaft structures that both radar and aircraft measurements indicate have the same temporal periodicity determined to arise visually between successive billow cloud

sub surface melting in a seasonal snow cover the ability of solar radiation to penetrate into a snow cover combined with the low thermal conductivity of snow can lead to a sub surface temperature maximum this elevated sub surface temperature allows a layer of wet snow to form below the surface even on days when the air temperature remains subfreezing a high resolution frequency modulated continuous wave fmcw radar has been used to detect the onset of sub surface melting in a seasonal snow cover the experimental observation of sub surface melting is shown to be in good agreement with the predictions of a one dimensional mass and energy balance model the effects of varying snow characteristics and solar extinction parameters on the sub surface melt characteristics are investigated using model simulations

serial soundings of electric field through a mesoscale convective system five partial balloon soundings of electric field and thermodynamics were made in a mesoscale convective system mcs in 1998 data were gathered in an updraft and outside updrafts within the convective region in the transition zone and in the stratiform cloud region in the first sounding the maximum and average inferred updraft speeds 27 and 15 m s 1 are the largest found to date in soundings through mcs convection as in previous measurements the electric field profile is simpler and fewer charge regions are inferred within the updraft than elsewhere together the first four soundings support in most details a previously published conceptual model of mcs electrical structure from the convective region updraft to the transition zone two exceptions within the soundings were found these involve opposite polarity of the lowest two charge regions in the transition zone cloud and additional complexity above the main negative charge region the earlier conceptual model also showed possible connections between charge regions across an mcs but those were based on soundings through many different mcss the first four soundings presented herein provide stronger evidence for three to five similar charge regions across the front of this mcs the sounding through the stratiform cloud region was atypical and does not fit the conceptual model and no connections to charge regions in the rest of the mcs are obvious two soundings presented from a second mcs indicate that the upper three charge regions in the transition zone are connected to the stratiform cloud as depicted in earlier conceptual models

new long term mass balance series for the swiss alps in this study we present 19 new or re analysed series of glacier wide seasonal mass balance for the swiss alps based on direct measurements the records partly start around 1920 and continue until today previously unpublished and unevaluated observations of point winter and annual balance are compiled from various sources and archives these highly valuable datasets have not yet been consistently evaluated and were thus unavailable to the scientific community using distributed modelling for spatial interpolation and extrapolation and homogenization of the point measurements we infer continuous series of area averaged mass balance the results are validated against independent decadal ice volume changes from photogrammetric surveys six of the new seasonal series cover 60 years and more and add a substantial amount of information on the variations of regional glacier mass change this will strengthen the worldwide collection of glacier monitoring data especially for the data sparse period before the 1980s we compare our results to existing long term series and present an updated assessment of mass balance variability and glacier sensitivity throughout the european alps

correlation of late quaternary moraines impact of climate variability glacier response and chronological resolution abstract the last decade has seen a global surge in the number and resolution of well dated geomorphological reconstructions of mountain glacier fluctuations and former ice sheet extents this has been facilitated by the widespread deployment of large samples of terrestrial cosmogenic nuclide dating tcnd allowing more sophisticated probability analyses for reducing the statistical uncertainty of moraine ages and testing of correlations at local regional and hemispheric scales geochronological advances in the field laboratory and on model calibration have taken place in parallel with modelling of palaeoclimate based on glacier reconstructions and of glacier sensitivity to temperature and precipitation forcing in spite of these advances basic conceptual issues remain this review questions whether the technical leap forward in dating has encouraged us to over reach our interpretive limits particularly in terms of the concept and practice of correlation we propose that to enable reliable correlation glacier chronologies should first be examined for their climatic integrity spatial coherence and chronological robustness even with excellent dating interpretive complexity remains due to complex climate signals and glacier response characteristics and to erosion censoring of the landform record all are issues which must be addressed to avoid either spurious lumping correlation or splitting differentiation of glacier chronologies and thus misinterpretation of the climatic significance of reconstructed glacier advances we suggest that the reliability of correlation is no better than the weakest link in the chain of reasoning which connects climatic fluctuations with dated landforms and sediments improved dating means that poor chronological resolution is less likely to be the limiting factor for correlation but shifts the focus onto other less quantifiable sources of uncertainty these conceptual statements are exemplified with reference to holocene glacial chronologies of contrasting mid latitude environments in southern norway iceland and new zealand

evolution and structure of the mesoscale convection and its environment a case study during the early onset of the southeast asian summer monsoon abstract the evolution and structure of mesoscale convection in the south china sea scs region are documented for the first time mainly using the dual doppler radar dataset collected during the south china sea monsoon experiment scsmex in 1998 in particular this study focuses on the convection associated with a subtropical frontal passage during the early onset of the southeast asian monsoon seam for the case of 15 may 1998 interaction between the tropical monsoon flow and frontal circulation played an important role in the evolution and structure of mesoscale convection in the prefrontal region the southwesterly monsoon flow converged with the southwesterly frontal flow to generate northeast to southwest oriented convection in the postfrontal region the southwesterly monsoon flow converged with the northerly frontal flow to produce a wide convective line with an east to west orientation in addition the convergence between the southerly monsoon flow and the northerly postfrontal flow gener

melt detection in antarctic ice shelves using scatterometers and microwave radiometers ku band dual polarization radar backscatter measurements from the seawinds on quikscat scatterometer are used to determine periods of surface freeze and melt in the antarctic ice shelves the normalized horizontal polarization radar backscatter sigmao and backscatter polarization ratio are used in maximum likelihood estimation of the ice state this method is used to infer the daily ice surface conditions for 25 study locations located on the ronne ross larsen amery shackleton and other ice shelves the temporal and spatial variations of the radar response are observed for various neighborhood sizes surrounding each given location during the study period criteria for determining the dates of melt onset and freeze up for each austral summer are presented validation of the ice state and melt onset date estimates is performed by analyzing the corresponding brightness temperature tb measurements from special sensor microwave imager ssm i radiometers quikscat sigmao measurements from 1999 to 2003 are analyzed and found to be effective in determining periods of melt in antarctic ice sheets at high temporal and spatial resolutions these estimates can be used in studies of the climatic effects of the seasonal and interannual melting of the antarctic ice sheets

on polarimetric radar signatures of deep convection for model evaluation columns of specific differential phase observed during mc3e abstractthe representation of deep convection in general circulation models is in part informed by cloud resolving models crms that function at higher spatial and temporal resolution however recent studies have shown that crms often fail at capturing the details of deep convection updrafts with the goal of providing constraint on crm simulation of deep convection updrafts ground based remote sensing observations are analyzed and statistically correlated for four deep convection events observed during the midlatitude continental convective clouds experiment mc3e since positive values of specific differential phase observed above the melting level are associated with deep convection updraft cells so called columns are analyzed using two scanning polarimetric radars in oklahoma the national weather service vance wsr 88d kvnx and the department of energy c band scanning atmospheric radiation measurement arm precipitation radar c sapr kvnx and c sapr volumes and columns are then statistically

seasonal evolution of melt ponds on arctic sea ice the seasonal evolution of melt ponds has been well documented on multiyear and landfast first year sea ice but is critically lacking on drifting first year sea ice which is becoming increasingly prevalent in the arctic using 1 m resolution panchromatic satellite imagery paired with airborne and in situ data we evaluated melt pond evolution for an entire melt season on drifting first year and multiyear sea ice near the 2011 applied physics laboratory ice station aplis site in the beaufort and chukchi seas a new algorithm was developed to classify the imagery into sea ice thin ice melt pond and open water classes on two contrasting ice types first year and multiyear sea ice surprisingly melt ponds formed 3 weeks earlier on multiyear ice both ice types had comparable mean snow depths but multiyear ice had 0 5 cm deep snow covering 37 of its surveyed area which may have facilitated earlier melt due to its low surface albedo compared to thicker snow maximum pond fractions were 53 3 and 38 3 on first year and multiyear ice respectively aplis pond fractions were compared with those from the surface heat budget of the arctic ocean sheba field campaign aplis exhibited earlier melt and double the maximum pond fraction which was in part due to the greater presence of thin snow and first year ice at aplis these results reveal considerable differences in pond formation between ice types and underscore the importance of snow depth distributions in the timing and progression of melt pond formation

vertical variability of cloud hydrometeors in the stratiform region of mesoscale convective systems and bow echoes abstract during the bow echo and mesoscale convective vortex experiment the noaa p 3 research aircraft executed 17 spiral descents to the rear of convective lines to document the vertical variability of hydrometeors above within and below the stratiform melting layer ten spirals were behind lines that exhibited bowing at some stage in their evolution although quick descents on some spirals forced sampling of different particle zones clear trends with respect to temperature were seen for 16 spirals the ambient relative humidity with respect to ice was in the range of 100 4 at temperatures between 10 c and the melting layer but exhibited steady decreases below the melting layer to an average relative humidity with respect to water of 77 15 at 9 c in contrast one spiral conducted on 29 june 2003 directly behind a developing bow echo had a relative humidity with respect to ice averaging 85 at heights above the 0 c level and relative humidity with respect to ice further decreased below the

seven doppler radar and in situ analysis of the 25 26 june 2015 kansas mcs during pecan abstractthis case study analyzes a nocturnal mesoscale convective system mcs that was observed on 25 26 june 2015 in northeastern kansas during the plains elevated convection at night pecan pro

interaction of an upper tropospheric jet with a squall line originating along a cold frontal boundary abstracton 8 june 2003 an expansive squall line along a surface cold frontal boundary was sampled during the bow echo and mesoscale convective vortex experiment the naval research laboratory p 3 aircraft and the national oceanic and atmospheric administration p 3 aircraft simultaneously sampled the leading and trailing edge of this squall line respectively with x band doppler radars data from these two airborne radar systems have been synthesized to produce a pseudo quad doppler analysis of the squall line yielding a detailed three dimensional kinematic analysis of its structure a simulation of the squall line was carried out using the weather research and forecasting model to complement the pseudo quad doppler analysis the simulation employed a 3 km convection allowing nested domain centered over the pseudo quad doppler domain along with a 9 km parent domain to capture the larger synoptic scale cyclone the pseudo quad doppler analysis reveals that the convective line was embedded within the up

microphysical and thermodynamic structure and evolution of the trailing stratiform regions of mesoscale convective systems during bamex part i observations abstract this study used airborne and ground based radar and optical array probe data from the spiral descent flight patterns and horizontal flight legs of the noaa p 3 aircraft in the trailing stratiform regions tsrs of mesoscale convective systems mcss observed during the bow echo and mesoscale convective vortex experiment bamex to characterize microphysical and thermodynamic variations within the tsrs in the context of the following features the transition zone the notch region the enhanced stratiform rain region the rear anvil region the front to rear flow the rear to front flow and the rear inflow jet axis one spiral from the notch region nine from the enhanced stratiform rain region and two from the rear anvil region were analyzed along with numerous horizontal flight legs that traversed these zones the spiral performed in the notch region on 29 june occurred early in the mcs life cycle and exhibited subsaturated conditions throughout its depth the nine spirals performed within the

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

an observational and numerical study of a cold front interacting with the olympic mountains during coast iop5 abstract this paper documents the three dimensional flow and precipitation structures associated with a weak cold front interacting with the olympic mountains and the subsequent development of a puget sound convergence zone this study utilizes data collected during coast iop5 the fifth intensive observing period of the coastal observation and simulation with topography field experiment that took place on 11 12 december 1993 one of the most important data sources was a noaa p 3 aircraft which provided flight level data radar reflectivity and doppler winds as it circumnavigated the olympics initially frontal passage along the western foothills of the olympics was accompanied by a 2 3 c temperature drop a rapid wind shift to northwesterlies and an intense line of precipitation 35 45 dbz however the wind shift and associated precipitation structures attenuated when the front began to ascend the windward slopes of the olympics surface and p 3 observations document the deformation of the front

the vertical vorticity structure within a squall line observed during bamex banded vorticity features and the evolution of a bowing segment abstracta quasi linear convective line with a trailing stratiform region developed during the bow echo and mesoscale convective vortex experiment bamex while being sampled by two airborne doppler radars the finescale reflectivity and doppler velocities recorded by the radars documented the evolution of the convective line bands of positive and negative vertical vorticity oriented parallel to the convective line were resolved in the analysis this type of structure has rarely been reported in the literature and appears to be a result of the tilting and subsequent stretching of ambient horizontal vorticity produced by the low level wind shear vector with a significant along line component the radar analysis also documented the evolution of an embedded bow echo within the convective line embedded bow echoes have been documented for a number of years however a detailed analysis of their kinematic structure has not been previously reported in the literature the counterrotating circulation patterns tha

statistical modelling of the surface mass balance variability of the morteratsch glacier switzerland strong control of early melting season meteorological conditions in this study we analyse a 15 year long time series of surface mass balance smb measurements performed between 2001 and 2016 in the ablation zone of the morteratsch glacier complex engadine switzerland for a better understanding of the smb variability and its causes multiple linear regressions analyses are performed with temperature and precipitation series from nearby meteorological stations up to 85 of the observed smb variance can be explained by the mean may june july temperature and the total precipitation from october to march a new method is presented where the contribution of each month s individual temperature and precipitation to the smb can be examined in a total sample of 2 24 16 8 million combinations more than 90 of the observed smb can be explained with particular combinations in which the may june july temperature is the most recurrent followed by october temperature the role of precipitation is less pronounced but autumn winter and spring precipitation are always more important than summer precipitation our results indicate that the length of the ice ablation season is of larger importance than its intensity to explain year to year variations the widely used june july august temperature index may not always be the best option to describe smb variability through statistical correlation

structure and evolution of the 22 february 1993 toga coare squall line aircraft observations of precipitation circulation and surface energy fluxes abstract this study documents the precipitation and kinematic structure of a mature eastward propagating oceanic squall line system observed by instrumented aircraft during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare doppler radar and low level in situ observations are used to show the evolution of the convection from an initially linear nnw sse oriented convective line to a highly bow shaped structure with an embedded low to midlevel counterclockwise rotating vortex on its northern flank in addition to previously documented features of squall lines such as highly upshear tilted convection on its leading edge a channel of strong front to rear flow that ascended with height over a rear inflow that descended toward the convective line and a pronounced low level cold pool apparently fed from convective and mesoscale downdrafts from the convective line rearward the observations of this system showed distinct multiple maxima in updraft strength with

little ice age proxy glacier mass balance records reconstructed from tree rings in the mt waddington area british columbia coast mountains canada the intention of this research was to explore whether dendroclimatological relationships could be used to reconstruct long term proxy records of little ice age glacier mass balance changes in the southern coast mountains of british columbia tree ring width chronologies from the mt waddington area were used in concert with historical glacier records to construct models spanning the past 450 years the approach was to build models that were based on derived relationships between tree ring growth and glacier mass balance 1 warmer temperatures in the summer positively influence tree growth but are detrimental to glacier health 2 colder temperatures during the winter and deeper snowpack have a negative impact on tree growth whereas they are related to greater accumulation on the glacier during the winter season stepwise regression analyses were applied to tree ring chronologies to predict glacier mass balance at local and regional scales the models of net annual balance for the region regional data set show that periods of positive mass balance occurred in the ad 1750s 1820s to 1830s and 1970s peaks of winter balance correspond closely to these periods showing a sharp drop in winter mass balance towards the end of the nineteenth century wavelet analyses suggest that glacial mass balance regimes in the region respond synchronously to pacific ocean circulation systems such as the el nino southern oscillation and the pacific decadal oscillation

little ice age glacial activity in strathcona provincial park vancouver island british columbia canada dendroglaciological and lichenometric techniques are used to establish the little ice age lia history of two glaciers colonel foster and septimus in strathcona provincial park vancouver island british columbia our lichenometric investigations were preceded by the development of a locally calibrated rhizocarpon geographicum growth curve 1708 1998 a d documentation of a 3 4 year ecesis interval for both trees and lichen greatly reduces one of the main uncertainties in using geobotanical methods for dating lia landforms the moraine dates provided therefore give a good approximation of the shift in climate conditions that lead to the retreat of the glaciers and subsequent moraine stabilization geobotanical evidence records three synchronous episodes of lia moraine deposition at both glaciers two prominent moraines at each site are dated to the early 1700s and late 1800s with a third smaller moraine dated to the mid 1930s moraines deposited prior to 1397 a d were also recorded at colonel foster glacier however precise dating of these moraines was not possible the moraine records from strathcona provincial park suggest two possible modes of glacier response i synchronous responses to larger scale climatic forcing and ii asynchronous responses to local factors such as microclimate topography and glacier geometry the vancouver island lia record was evaluated in the context of lia results from the pacific north american pna cordillera it compares well with regional moraine records from coastal british columbia washington alaska and the canadian rocky mountains suggesting a regional response of pna glaciers to climate change associated with the lia

surface and melt pond evolution on landfast first year sea ice in the canadian arctic archipelago the evolution of landfast sea ice melt pond coverage surface topography and mass balance was studied in the canadian arctic during may june 2011 and 2012 using a terrestrial laser scanner snow and sea ice sampling and surface meteorological characterization initial melt pond formation was not limited to low lying areas rather ponds formed at almost all premelt elevations the subsequent evolution of melt pond coverage varied considerably between the 2 years owing to four principle temporally variable factors first the range in premelt topographic relief was 0 5 m greater in 2011 rougher surface than in 2012 smoother surface such that a seasonal maximum pond coverage of 60 and maximum hydraulic head of 204 mm were reached in 2011 versus 78 and 138 mm in 2012 a change in the meltwater balance production minus drainage caused the ponds to spread or recede over an area that was almost 90 larger in 2012 than in 2011 second modification of the premelt topography was observed during mid june due to preferential melting under certain drainage channels some of the lowest lying premelt areas were subsequently elevated above these deepening channels and unexpectedly became drained later in the season third ice interior temperatures remained 1 2 c colder later into june in 2012 than in 2011 even though the ice was 0 35 m thinner at melt onset thereby delaying permeability increases in the ice that would allow vertical meltwater drainage to the ocean finally surface melt was estimated to account for approximately 62 of the net radiative flux to the sea ice cover during the melt season

convection permitting simulations of the environment supporting widespread turbulence within the upper level outflow of a mesoscale convective system abstract widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system mcs on 17 june 2005 a noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection i e large reflectivity regions of the mcs herein the mcs life cycle and the turbulence environment in its upper level outflow are studied using rapid update cycle ruc analyses and cloud permitting simulations with the weather research and forecast model wrf it is demonstrated that strong vertical shear beneath the mcs outflow jet is critical to providing an environment that could support dynamic e g shearing type instabilities conducive to turbulence comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the l

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

effects of under resolved convective dynamics on the evolution of a squall line abstractsimulations of a squall line observed on 20 may 2011 during the midlatitude continental convective clouds experiment mc3e using 750 and 250 m horizontal grid spacing are performed the h

visible and near infrared reflectivity during the ablation period on peyto glacier alberta canada models for calculating glacier mass balance are sensitive to surface reflectivity variation fieldwork carried out on peyto glacier alberta canada contributes to the data set available for ice reflectivity parameterization in such models hemispherical reflectivity in the visible and near infrared parts of the solar spectrum was obtained for rock snow and three contrasting glacier surfaces to examine temporal and spatial variations glacier ice near infrared reflectivity displays only minor spatial variation 0 12 0 17 in comparison with the visible range 0 23 0 40 the latter being influenced primarily by surface impurity content surface roughness is of minor importance compared with impurities temporal variation of reflectivity was weak at all glacier ice and rock locations slight variations observed were due to changes in either solar zenith angle or cloud amount snow reflectivity displayed pronounced diurnal asymmetry and a larger response to cloud cover the minimal temporal variation in glacier ice reflectivity simplifies its parameterization this behaviour is additionally useful for satellite based measurements of the reflectivity field on larger glaciers as images obtained within a 6 h window centred on solar noon are likely to yield values which are within 2 3 of daily mean values

the kinematics of a midlatitude continental mesoscale convective system and its mesoscale vortex the authors present a unique scale discriminating study of the environment relative circulations within a mesoscale convective system mcs and mesoscale convective vortex mcv the mcs a leading convective line and trailing stratiform region that became asymmetric passed through the national oceanic and atmospheric administration noaa profiler network npn in kansas and oklahoma on 1 august 1996 the mcv appeared in the mcs s stratiform region just prior to the system s mature stage and grew to a depth of over 12 km as the mcs dissipated the mcv did not apparently survive to the next day a spatial bandpass filter was used to divide observed wind into a component that was predominantly synoptic background wind and a component that was predominantly a mesoscale perturbation on that background wind a mesoscale updraft mesoscale downdraft and divergent outflows in the lower and upper troposphere were evident after the synoptic background wind was removed so these four circulations were internal and fundamental to the mcs the mesoscale perturbation in wind in the middle troposphere extended farther behind the mcs than ahead of it consistent with analytic studies and numerical simulations of gravity waves generated by heat sources characteristic of mcss with leading convective lines and trailing stratiform regions deepening of the mcv appeared to be reflected in the vertical wind shear at the vortex s center as the mcv strengthened the mesoscale shear through its lower part decreased perhaps as wind became more vortical at increasing altitudes mesoscale and synoptic vertical shears were of similar magnitude so an average of environmental soundings outside an mcs probably does not accurately represent the shear that affects an mcv this suggests the need to reevaluate how the kinematical settings of mcvs are diagnosed

the effects of interannual climate variability on the moraine record valley glacier moraines are commonly used to infer past mean annual precipitation and mean melt season temperature however recent research has demonstrated that even in steady climates multi decadal kilometer scale fluctuations in glacier length occur in response to stochastic year to year variability in mass balance when interpreting moraine sequences it is important to include the effect of interannual weather variability on glacier length moraines record advances that are forced either by interannual variability or by a combination of climate change and interannual variability we address this issue for the last glacial maximum lgm glaciers of the colorado front range united states using a linear glacier model that allows thorough exploration of parameter uncertainties supplemented by a shallow ice flowline model our analyses suggest that 1 glacial standstills longer than 50 years were unlikely 2 mean glacier lengths are 10 15 up valley from maximum glacier lengths and 3 individual lgm terminal moraines were formed by a combination of a climate change and interannual variability forced advances

salt precipitation in sea ice and its effect on albedo with application to snowball earth during the initial freezing of the tropical ocean on snowball earth the first ice to form would be sea ice which contains salt within inclusions of liquid brine at temperatures below 23 c significant amounts of the salt begin to crystallize with the most abundant salt being hydrohalite nacl 2h2o these crystals scatter light increasing the ice albedo in this paper we present field measurements of the albedo of cold sea ice and laboratory measurements of hydrohalite precipitation precipitation of salt within brine inclusions was observed on windswept bare ice of mcmurdo sound at the coast of antarctica 78 s in early austral spring salinity and temperature were measured in ice cores spectral albedo was measured on several occasions during september and october the albedo showed a gradual increase with decreasing temperature consistent with salt precipitation laboratory examination of thin sections from the ice cores showed that the precipitation process exhibits hysteresis with hydrohalite precipitating over a range of temperatures between 28 c and 35 c but dissolving at about 23 c the causes of the hysteresis were investigated in experiments on laboratory grown sea ice with different solute mixtures all mixtures showed hysteresis suggesting that it may be an inherent property of hydrohalite precipitation within brine inclusions rather than being due to biological macromolecules or interactions between various salts in seawater this article is protected by copyright all rights reserved

diagnosis of hydrometeor profiles from area mean vertical velocity data a simple one dimensional microphysical retrieval model is developed for estimating vertical profiles of liquid and frozen hydrometeor mixing ratios from observed vertical profiles of area mean vertical velocity in regions of convective and or stratiform precipitation the mean vertical velocity profiles can be obtained from doppler radar single and dual or other means the one dimensional results are shown to be in good agreement with two dimensional microphysical fields from a previous study sensitivity tests are performed

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

tracer studies of pathways and rates of meltwater transport through arctic summer sea ice 1 at the surface heat budget of the arctic ocean sheba program s field site in the northern chukchi sea snow and ice meltwater flow was found to have a strong impact on the heat and mass balance of sea ice during the summer of 1998 pathways and rates of meltwater transport were derived from tracer studies h218o 7be and release of fluorescent dyes complemented by in situ sea ice permeability measurements it was shown that the balance between meltwater supply at the surface averaging between 3 5 and 10 5 mm d 1 and ice permeability between 10 9 m2 determines the retention and pooling of meltwater which in turn controls ice albedo we found that the seasonal evolution of first year and multiyear ice permeability and surface morphology determine four distinct stages of melt at the start of the ablation season stage 1 ponding is widespread and lateral melt flow dominates several tens of cubic meters of meltwater per day were found to drain hundreds to thousands of square meters of ice through flaws and permeable zones significant formation of underwater ice composed between 50 of meteoric water formed at these drainage sites complete removal of snow cover increase in ice permeability and reductions in hydraulic gradients driving fluid flow mark stage 2 concurrent with a reduction in pond coverage and albedo during stage 3 maximum permeabilities were measured with surface meltwater penetrating to 1 m depth in the ice and convective overturning and desalination found to dominate the lower layers of first year and thin multiyear ice enhanced fluid flow into flaws and permeable zones was observed to promote ice floe breakup and disintegration concurrent with increases in pond salinities and 7be advective heat flows of several tens of watts per square meter were derived promoting widening of ponds and increases in pond coverage stage 4 corresponds to freeze up roughly 40 of the total surface melt was retained by the ice cover within the ice matrix as well as in surface and under ice ponds with a total net retention of 15 based on this work areas of improvement for fully prognostic simulations of ice albedo are identified calling for parameterizations of sea ice permeability and the integration of ice topography and refined ablation schemes into atmosphere ice ocean models

topography climate and ice masses a review topography acts as a filter between regional climate and the consequent response of a glacier or ice sheet it influences the mass and energy inputs and modifies the ice dynamics the evolution of the ice sheet surface and over longer time scales of the bed topography modulates the climatic forcing until we have a better understanding of these topographic linkages the use of geophysical signals from former ice masses to determine palaeoclimates must be regarded as fundamentally flawed

the evolution of lake effect convection during landfall and orographic uplift as observed by profiling radars abstracta pronounced snowfall maximum occurs about 30 km downwind of lake ontario over the 600 m high tug hill plateau hereafter tug hill a region where lake effect convection is affected by mesoscale forcing associated with landfall and orographic uplift profiling radar data from the ontario winter lake effect systems field campaign are used to characterize the inland evolution of lake effect convection that produces the tug hill snowfall maximum four k band profiling micro rain radars mrrs were aligned in a transect from the ontario coast onto tug hill additional observations were provided by an x band profiling radar xpr analysis is presented of a major lake effect storm that produced 6 4 cm liquid precipitation equivalent lpe snowfall over tug hill this event exhibited strong inland enhancement with lpe increasing by a factor of 1 9 over 15 km horizontal distance mrr profiles reveal that this enhancement was not due to increases in the depth or intensity of lake effect convection with

lightning location relative to storm structure in a leading line trailing stratiform mesoscale convective system 1 horizontal and line normal vertical cross sections and composite images of dallas fort worth lightning detection and ranging ldar ii vhf radiation sources and radar reflectivity over a 30 min period provide a unique perspective on lightning pathways within a leading line trailing stratiform llts mesoscale convective system mcs on 16 june 2002 the overwhelming majority of vhf lightning sources occurred within the leading convective line in a bimodal pattern in the vertical assuming that vhf source density maxima were most likely associated with positive charge then the ldar ii observations suggest that the gross charge structure of the convective region of the mcs was characterized by a tripole with net positive charge centered at 4 5 km agl 3 c and 9 5 km agl 35 c and net negative charge centered roughly in the relative minimum of the vhf source density maximum at 7 km agl 17 c a persistent lightning pathway and inferred positive charge zone sloped rearward by 40 50 km and downward by 4 5 km from the upper vhf source maximum in the convective line through the transition zone and into the radar bright band of the stratiform region in the stratiform region vhf lightning sources and inferred positive charge were concentrated in three layers centered at 4 5 6 and 9 km agl 2 c 11 c and 31 c respectively consistent with past electric field studies of symmetric llts mcss positive cloud to ground lightning flashes in the stratiform region were initiated in the convective line and followed the slanting pathway from the top of convective cores to the stratiform precipitation where they were horizontally extensive layered and highly branched the sloping lightning pathway was identical to hypothetical trajectories taken by snow particles these observations provide further support for the advection of charge on snow along the sloping pathway and the in situ generation of charge in the horizontal lightning layers as primary contributors to electrification and positive lightning production rearward of the convective line

evolution of microphysical structure of a subtropical squall line observed by a polarimetric radar and a disdrometer during opacc in eastern china the evolution of the microphysical structures of a subtropical squall line observed during the observation prediction and analysis of severe convection of china opacc field campaign in eastern china is documented in this paper the data collected from a c band polarimetric doppler radar reflectivity z differential reflectivity zdr and specific differential phase kdp and a disdrometer are used to investigate the variations of microphysical characteristics within the convective region during the formative intensifying and mature stages of the squall line the microphysical characteristics of the squall line are noticeably different among these three stages when the squall line develops from the formative stage to the mature stage its radar derived drop size distribution dsd in the convective region evolves from continental like convection to more maritime like convection contrary to previous studies the dsd characteristics of a convective line may not be simply locked to a geographical location but varied extensively throughout its life cycle the polarimetric radar derived liquid water content below the freezing level in the convective region is three times higher than the ice water content above the freezing level this in conjunction with a low cloud base 0 68 km and a high freezing level 5 km indicates a deep warm cloud layer and the dominance of the warm rain process within this squall line

a model of melt pond evolution on sea ice a one dimensional thermodynamic and radiative model of a melt pond on sea ice is presented that explicitly treats the melt pond as an extra phase a two stream radiation model which allows albedo to be determined from bulk optical properties and a parameterization of the summertime evolution of optical properties is used heat transport within the sea ice is described using an equation describing heat transport in a mushy layer of a binary alloy salt water the model is tested by comparison of numerical simulations with sheba data and previous modeling the presence of melt ponds on the sea ice surface is demonstrated to have a significant effect on the heat and mass balance sensitivity tests indicate that the maximum melt pond depth is highly sensitive to optical parameters and drainage