toxic dinoflagellate blooms in the kattegat north sea during the holocene data are presented on the temporal distribution of the toxic dinoflagellate gymnodinium catenatum in the kattegat region of the north sea based on dinoflagellate cyst and pollen analyses and a high resolution chronology a relationship between climatic and oceanographic variations and the blooming of g catenatum and other dinoflagellates is demonstrated gymnodinium catenatum first migrated into the kattegat about 6200 yr b p and had its first occurrence of high numbers at about 4300 4500 yr b p at about 4000 yr b p in connection with an oceanographic change and climatic deterioration the species decreased abruptly and subsequently disappeared it became re established again at about 2000 yr b p and occurred in massive blooms during the so called mediaeval warm epoch round about 700 800 yr b p 1200 1400 a d at the time of the so called little ice age approximately 300 yr b p 1500 1600 a d g catenatum again became extinct in the kattegat area this study clearly demonstrates that massive blooms of toxic dinoflagellates occur in the historical record before any anthropogenic impact on the environment

composite patterns of easterly disturbances over west africa and the tropical atlantic a climatology from the 1979 95 ncep ncar reanalyses the horizontal and vertical structure of the 3 5 day and 6 9 day easterly waves over west africa and tropical atlantic are investigated ncep ncar reanalyses are used for the period 1979 1995 to produce a 17 year climatology of both 3 5 day and 6 9 day easterly waves composite patterns of convection wind temperature and vertical velocity are analysed with respect to the following the modulation by 3 5 day and 6 9 day wave regimes the contrasts between the itcz 5 n 10 n and the sahelo saharan band 15 n 20 n the difference between land and ocean and seasonal variations similarities and differences in the characteristics of the two wave regimes are identified

water vapour transport over africa and the atlantic ocean during summer 1979 the water vapour transport over africa and the eastern atlantic ocean during the 1979 summer is studied the analysis is based on wind fields from the european centre for medium range weather forecasts and humidity fields derived from a three layer precipitable water data set the evolution of the bi weekly mean fields of water vapour flux in the surface to 850 mb layer shows the progressive penetration of moisture over west africa during the summer at low levels during the maximum activity of the african monsoon the southerly flow penetrates up to 20 n and there is a large belt of westerlies around 10 n the fluxes between 700 and 500 mb suggest the importance of the african easterly jet aej as a major artery for moisture for west africa vertically integrated fluxes across different sections have been analysed across the equator at the longitudes of the gulf of guinea the flux shows a decreasing trend due to the northward propagation of the intertropical discontinuity over west africa near 22 n the flux is mainly from the north at the beginning of the summer and becomes southerly during surges of the monsoon the flux from west africa toward the atlantic ocean is large indicating that moisture from the gulf is transported upward and advected westward by the aej the fluxes oscillate with two main periods around 3 5 days and 5 7 days water vapour budgets have been estimated for boxes located over the gulf of guinea and west africa the gulf of guinea is a source of water vapour transported northward and westward by the trade winds over west africa at low levels moisture comes from the gulf of guinea in the mid troposphere there is a strong easterly moisture flux associated with the aej and originating from central africa this moisture seems to come initially from the gulf of guinea because it is mainly divergent the mid tropospheric flux may have little influence on rainfall over west africa the budget study also emphasizes the importance of evapotranspiration over the belt north of the gulf of guinea where water vapour is recycled and transported northward

observations and predictability of a nondeveloping tropical disturbance over the eastern atlantic abstracta strong african easterly wave aew left the west african coast in early september 2014 and operational global numerical forecasts suggested a potential for rapid tropical cyclogenesis of this disturbance in the eastern atlantic despite the presence of a large region of dry air northwest of the disturbance analysis and in situ observations show that after leaving the coast the closed circulation associated with the aew trough was not well aligned vertically and therefore low level or midlevel dry air was advected below or above respectively areas of closed circulation gps dropwindsonde observations highlight the dry air undercutting the midlevel recirculation region in the southwestern quadrant this advection of dry air constrains the spatial extent of deep convection within the aew trough leading to the vortex decaying as the column continues to be displaced horizontally losing vertical alignment this enables increased horizontal advection of dry air into the system further limiting

palynomorph distribution in recent sediments from the labrador sea surface sediments from the labrador sea and baffin bay have been examined for their palynomorph content pollen and spore assemblages reflect the vegetation zones of eastern canada although long distance atmospheric transport results in over representation of pinus and spores a linear decrease of pollen input is observed with distance from the source vegetation the abyssal domain receives less than 2 of the initial input the abundance of dinoflagellate cysts reflects a relatively high primary productivity in surface water masses which seems proportional to the benthic productivity as shown by the concentrations of organic linings of foraminifers the relative abundance of dinoflagellate cyst taxa and principal component analysis led to the definition of three assemblages that can be related to sea surface conditions and current pattern the modern distribution of dinoflagellate cysts was used to interpret assemblages recovered in five box cores from the deep labrador sea results reveal important ch

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

climatology and structures of southwest vortices in the ncep climate forecast system reanalysis abstractthe southwest vortex swv is a meso scale cyclonic low pressure system originating in southwest china it is a high impact precipitation generating weather system in this region and a large downstream area a climatology of the swv over 1979 2010 is presented here results indicate that the swv is a common regional weather system with about 73 annual occurrences two primary genesis regions are identified one in the sichuan basin and another one in the southeast flank of the tibetan plateau swv genesis displays seasonality with a spring summer preference and diurnal variations the average life cycle horizontal dimension and translation speed are 15 1 h 435 km and 8 6 m s 1 respectively swvs are classified into four types that show regional and seasonal contrasts in structure in type i the winter spring elevated dry vortex in the basin is vertically confined to a shallow layer between 850 and 600 hpa and tilts northeastward the low level vortex has a cold center and the middle to up

mesoscale interactions in tropical cyclone genesis with the multitude of cloud clusters over tropical oceans it has been perplexing that so few develop into tropical cyclones the authors postulate that a major obstacle has been the complexity of scale interactions particularly those on the mesoscale which have only recently been observable while there are well known climatological requirements these are by no means sufficient a major reason for this rarity is the essentially stochastic nature of the mesoscale interactions that precede and contribute to cyclone development observations exist for only a few forming cases in these the moist convection in the preformation environment is organized into mesoscale convective systems each of which have associated mesoscale potential vortices in the midlevels interactions between these systems may lead to merger growth to the surface and development of both the nascent eye and inner rainbands of a tropical cyclone the process is essentially stochastic but the degree of stochasticity can be reduced by the continued interaction of the mesoscale systems or by environmental influences for example a monsoon trough provides a region of reduced deformation radius which substantially improves the efficiency of mesoscale vortex interactions and the amplitude of the merged vortices further a strong monsoon trough provides a vertical wind shear that enables long lived midlevel mesoscale vortices that are able to maintain or even redevelop the associated convective system the authors develop this hypothesis by use of a detailed case study of the formation of tropical cyclone oliver observed during toga coare 1993 in this case two dominant mesoscale vortices interacted with a monsoon trough to separately produce a nascent eye and a major rainband the eye developed on the edge of the major convective system and the associated atmospheric warming was provided almost entirely by moist processes in the upper atmosphere and by a combination of latent heating and adiabatic subsidence in the lower and middle atmosphere the importance of mesoscale interactions is illustrated further by brief reference to the development of two typhoons in the western north pacific

a model for the exchange of water and salt between the baltic and the skagerrak abstract a model for the exchange of salt and water between the baltic and the sea the skagerrak is presented because of strong inter basin interactions in the baltic entrance area the model must include the kattegat and the belt sea these are modeled by horizontally homogeneous two layer sub models the most prominent dynamical properties of the sub models are wind driven entrainment flows and rotational baroclinic hydraulic controls the model is driven by a meteorologically forced barotropic transport qh calculated from the freshwater supply to the baltic qf and the sea level fluctuations in the kattegat and turbulent entrainment flows coupled to the wind speed w and in the belt sea also to the barotropic transport the most important bathymetric features of the basins are included the model equations are integrated numerically for a test period of 1 years the stratification in the kattegat as well as in the belt sea is quite well predicted it is found that approximately one half of

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

relationship of temperature and light ring formation at subarctic treeline and implications for climate reconstruction abstract during the past 8 centuries light rings lrs have occasionally formed in black spruce picea mariana at treeline near bush lake northern quebec l filion s payette l gauthier and y boutin 1986 quaternary research 26 272 279 a delwaide l filion and s fayette 1991 canadian journal of forest research 21 1828 1832 new analyses of climate data compiled during the period of overlapping tree ring and instrumental records show that years of lr formation at bush lake have unusually cool may june august and september temperatures the analyses also show that august september temperatures strongly correlate with may july temperatures thus late spring and entire growing season temperatures influence lr formation at subarctic treeline lrs formed in at least 5 of the trees at bush lake when may september mean temperatures at inukjuak fell below 4 2 c and august september mean temperatures fell below 6 7 c these threshold temperature lr relationships can be used to infer limiting summer temperatures during the period preceding instrumental records for example the lr record suggests that may september temperatures at northern quebec treeline dropped below 4 2 c in a d 1601 after a major volcanic eruption of unknown source visual assessments of lr occurrence provide a new approach for extracting quantitative paleoclimatic information from tree rings

air sea interaction in the gulf of guinea at intraseasonal time scales wind bursts and coastal precipitation in boreal spring the role of air sea interaction in the boreal spring precipitation of the west african monsoon is explored through the wind variability in the gulf of guinea linear regressions are performed in may june during the decade 2000 2009 to investigate the origin and effect of the surface wind strengthening north of the equator it appears that the equatorial sea surface temperature cooling intensifies a surface wind equatorial divergence coastal convergence circulation and generates a cross equatorial pressure gradient which both strengthen the southerlies north of the equator this increases subsidence above the ocean and convection in the northern gulf of guinea in addition an abrupt change is observed in the surface wind pattern in the eastern equatorial atlantic eea between april and july to investigate the transition mechanisms a reference date is defined as the date when the surface wind north of the equator becomes and remains stronger than south of the equator thus the maintenance of strong southerlies north of the equator is linked to a coincident installation of a deep circulation on the whole troposphere and a northward shift of the low atmospheric local circulation the resulting sharp seasonal transition coincides each year with a southeasterly wind burst suggesting that the equatorial sst cooling plays a role in the precipitation along the african coast during boreal spring copyright 2012 royal meteorological society

analysis of strengthening and dissipating mesoscale convective systems propagating off the west african coast abstracta large number of atlantic tropical depressions are generated in the eastern basin in relation to the african easterly wave aew and embedded mesoscale convective systems mcss coming from the african continent in this paper the structures of strengthening and dissipating mcss evolving near the west african coast are analyzed including the role of the ocean surface conditions in their evolution satellite infrared brightness temperature and meteorological radar data over seven summer seasons between 1993 and 2006 are used to subjectively select 20 cases of strengthening and dissipating mcss in the vicinity of the senegal coast with these observed mcss a lagged composite analysis is then performed using interim ecmwf re analysis era interim and climate forecast system reanalysis cfsr it is shown that the strengthening mcs is generally preceded by prior passage of an aew near the west african coast this previous wave trough is associated with a convective cyclonic circulation in the low a

large scale influences on tropical cyclogenesis in the western north pacific abstract objectively analyzed data from the european centre for medium range weather forecasts are used to examine the large scale aspects of the formation of tropical cyclones it is hypothesized that tropical cyclogenesis occurs when external atmospheric forcing on the synoptic or larger scale provides uplift through a deep layer enhancing convection in a region with environmental conditions favorable for genesis emphasis is placed on the roles of upper level troughs low level wind surges preexisting tropical cyclones and propagating wave disturbances in triggering tropical cyclogenesis composites of the 200 hpa and 850 hpa flows reveal the presence of both upper level troughs and low level wind surges respectively prior to genesis in the composites the wind surges also appear to be related to the presence of a prior circulation located approximately 2000 km to the west of the genesis location an examination of the individual cases demonstrates that approximately 85 of all storms had either

three dimensional structure and dynamics of african easterly waves part i observations the mean structure of african easterly waves aews over west africa and the adjacent atlantic is isolated by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered satellite derived outgoing longwave radiation these results are compared with previous studies and an idealized modeling study in a companion paper which provides evidence that the waves bear a close structural resemblance to the fastest growing linear normal mode of the summertime basic state flow over africa there is a significant evolution in the three dimensional structure of aews as they propagate along 10 n across west africa at this latitude convection occurs in northerly flow to the east of the greenwich meridian then shifts into the wave trough and finally into southerly flow as the waves propagate offshore into the atlantic itcz in contrast to the north of the african easterly jet along 15 n convection remains in southerly flow throughout the waves trajectory along 10 n over west africa the location of convection is consistent with the adiabatic dynamical forcing implied by the advection of perturbation vorticity by the mean thermal wind in the zonal direction as in the companion paper offshore and along 15 n the relationship between the convection and dynamics is more complex and not as easily explained in terms of dynamical forcing alone

a mesoscale convective complex generated inertially stable warm core vortex abstract a long lived mesoscale convectively generated vortex mcv associated with a mesoscale convective complex mcc is documented the mcv with a rossby number of approximately 0 5 is investigated as a feature intrinsic to the organization of the mcc on 6 7 july 1982 a particularly large and intense mcc developed in a region of high convective available potential energy cape but weak vertical wind shear bulk richardson number 150 and weak advection of temperature and vorticity convection initially was organized in a narrow line with elements propagating relative to the mean environmental flow these elements subsequently developed a large semicircular area of stratiform precipitation and a surface mesolow to the rear heavy rain fell over a broad area amounts as great as 10 9 cm accompanied by flooding were reported in central oklahoma as the large semicircular rain area dissipated a three layered structure became evident a large upper tropospheric anticyclone a rain cooled mesoscale h

synoptic scale influence of the saharan air layer on tropical cyclogenesis over the eastern atlantic abstract the formations of hurricane andrew tropical storm ernesto and hurricane luis which occurred respectively during the 1992 1994 and 1995 hurricane seasons over the eastern atlantic have been investigated by utilizing the european centre for medium range weather forecasts ecmwf gridded data analyses these cases were selected to illustrate the contrasting influences of the saharan air layer sal on tropical cyclogenesis analyses results show that tropical storm ernesto 1994 and hurricane luis 1995 formed from the merger of the low level 925 hpa and midlevel 700 hpa vortices over the eastern atlantic within the monsoon trough enhanced by surges in the trades midlevel vortices associated with each case appear to evolve from african wave troughs enhanced by cyclonic shear vorticity of the midtropospheric jet which existed to the south of an sal anticyclonic eddy as an elongated wind maximum vorticity budget calculations suggest that vortex stretching dominated the enhancement of

intraseasonal variability of tropical atlantic sea surface temperature air sea interaction over upwelling fronts tropical atlantic sea surface temperatures ssts maximum intra seasonal variability isv and their interaction with local surface winds are investigated applying statistical analysis to observations and to a recent coupled reanalysis over the 2000 2009 decade five cores of strong isv emerge with standard deviation reaching about 1 c in frontal areas of the three main upwelling systems equatorial angola benguela and senegal mauritania the southern side of the canary upwelling west of 10 w along the equator a 20 60 day peak caused by tropical instability waves is shown to generate surface wind anomalies through the adjustment of the horizontal surface pressure gradient in addition to the modification of near surface atmospheric stratification east of 10 w along the equator an intense biweekly oscillation increases the ocean and atmosphere isv in the two coastal upwelling fronts intraseasonal sst anomalies resemble each other they are shown to be influenced by coastal kelvin waves in addition to large scale wind forcing over the angola benguela upwelling coastal wind bursts controlling the sst isv are associated with anomalously strong pressure patterns related to the madden julian oscillation the st helena anticyclone and the antarctic oscillation in the senegal mauritania upwelling the wind anomalies mainly linked to the azores anticyclone in the southern front during november to may appear to be connected to the saharan heat low in the northern front from june to september in all five regions and as expected for such upwelling regimes vertical oceanic mixing represents the dominant term in the mixed layer heat budget in the equatorial band as found in previous studies horizontal advection is equally important while it appears surprisingly weak in coastal fronts finally a striking result is the general lack of surface wind signal related to the sst isv in the coastal upwellings

biostratigraphic and sedimentological evidence of hydrographic changes in the kattegat during the later part of the holocene abstract detailed sedimentological and micropaleontological investigations complemented with 14 c analyses were made in a large number of cores from the kattegat in general the holocene in the kattegat is represented by sediments deposited since 4000 yrs b p resting directly upon glacial sediments sediments formed between the younger dryas and 4000 yrs b p are found in restricted areas near the coast at present day water depths of less than 20 25 m the cores yield evidence of one pronounced hydrographic shift at 4000 yrs b p and two minor changes at 2000 and at about 300 yrs b p these three hydrographic shifts are in addition to sedimentological changes also characterized by the following biostratigraphic markers 1 at 4000 yrs b p the benthic foraminifers nonion labradoricum a different variety of ammonia batavus and a benthic microforaminiferal fauna became established 2 at 2000 yrs b p a pronounced appearance of an algal cyst occurred called here varia type a and 3 at about 300 yrs b p varia type a peaked and subsequently vanished the hydrographic shifts are attributed to changes in the inflow outflow regime between the north sea and the skagerrak kattegat baltic and tentatively to changes in the large scale circulation patterns of the north atlantic

tropical storm development from african easterly waves in the eastern atlantic a comparison of two successive waves using a regional model as part of nasa amma 2006 abstract two successive african easterly waves aews from august 2006 are analyzed utilizing observational data the european centre for medium range weather forecasts reanalysis and output from the national center for atmospheric research national oceanic and atmospheric administration weather research and forecasting model wrf to understand why the first wave does not develop over the eastern atlantic while the second wave does the first aew eventually forms hurricane ernesto over the caribbean sea but genesis does not occur over the eastern atlantic the second wave although weaker than the first over land leaves the west african coast and quickly intensifies into tropical storm debby west of the cape verde islands this study shows that the environmental conditions associated with the first aew s passage inhibited development these conditions include strong low and midtropospheric vertical wind shear owing to a stronger than normal african easterly jet lower than normal relative humidity a

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

relation between tropical easterly waves convection and tropical cyclogenesis a lagrangian perspective abstractin this study a wave following lagrangian framework was used to examine the evolution of tropical easterly wave structure circulation and convection in the days leading up to and including tropical cyclogenesis in the atlantic and east pacific basins after easterly waves were separated into northerly southerly trough and ridge phases using the national centers for environmental prediction national center for atmospheric research reanalysis 700 hpa meridional wind waves that developed a tropical cyclone developing waves dws and waves that never developed a cyclone nondeveloping waves ndws were identified day zero d0 was defined as the day on which a tropical depression was identified for dws or the day the waves achieved maximum 850 hpa vorticity for ndws both waves types were then traced from five days prior to d0 d 5 through one day after d0 results suggest that as genesis is approached for dws the coverage by convection and cold cloudiness e g fractional coverage by

atlantic tropical systems of 1994 and 1995 a comparison of a quiet season to a near record breaking one abstract totals of 70 and 63 tropical waves also known as african or easterly waves were counted in the atlantic basin during the 1994 and 1995 hurricane seasons these waves led to the formation of 9 of the 12 total number of tropical cyclones in 1994 and 19 of the 21 total number of tropical cyclones in 1995 tropical waves contributed to the formation of 75 of the eastern pacific tropical cyclones in 1994 and 73 in 1995 upper and lower level prevailing wind patterns observed during the below normal season of 1994 and the very active one of 1995 are discussed tropical wave characteristics between the two years are compared

comparison between two case studies of developing and nondeveloping african easterly waves during namma and amma sop 3 absolute vertical vorticity budget abstract two west african disturbances observed in august and september 2006 during the national aeronautics and space administration african monsoon multidisciplinary analysis namma and the special observing period 3 amma sop 3 have been simulated using the meso nh numerical model with explicit convection the first disturbance spawned hurricane helene 2006 off the west african coast and the second one referred to as perturbation d though relatively intense failed to develop over the continent each case was associated with a well defined african easterly wave aew trough with embedded growing and decaying convective activity of various size duration and intensity the aim of this work is to investigate the contribution of these convective systems in the generation and maintenance of cyclonic vorticity associated with the aew trough with respect to the synoptic scale processes the absolute vorticity budgets are analyzed during the continental and oceanic transition stages of these aew

atlantic sea surface temperatures and tropical cyclone formation abstract it has long been accepted that interannual fluctuations in sea surface temperature sst in the atlantic are associated with fluctuations in seasonal atlantic basin tropical cyclone frequency to isolate the physical mechanism responsible for this relationship a singular value decomposition svd is used to establish the dominant covarying modes of tropospheric wind shear and sst as well as horizontal sst gradients the dominant svd mode of covarying vertical shear and sst gradients which comprises equatorially confined near zonal vertical wind shear fluctuations across the atlantic basin is highly correlated with both equatorial eastern pacific sst anomalies associated with el nino and west african sahel rainfall while this mode is strongly related to tropical storm hurricanes and major hurricane frequency in the atlantic it is not associated with any appreciable atlantic sst signal by contrast the second svd mode of covarying vertical shear and horizontal sst gradient variability wh

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

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

analysis of african easterly wave structures and their role in influencing tropical cyclogenesis abstract composite structures of african easterly waves aews that develop into named tropical cyclones in the atlantic are compared and contrasted with nondeveloping aews using the 40 yr ecmwf re analysis era 40 data and satellite brightness temperature between 1979 and 2001 developing aews are characterized by a more distinctive cold core structure two days before reaching the west african coast as they move westward the convective activity increases further in the vicinity of the guinea highlands region at the same time the aew trough increases its vorticity at low levels consistent with a transformation toward a more warm core structure before it reaches the ocean as the aew moves over the ocean convection is maintained in the trough consistent with the observed tropical cyclogenesis the nondeveloping aew has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the guinea highlands region the nondeveloping aew composite

trains of african easterly waves and their relationship to tropical cyclone genesis in the eastern atlantic abstractin this study the relationship between trains of african easterly waves aews and downstream tropical cyclogenesis is studied based on 19 summer seasons july september from 1990 to 2008 of era interim reanalysis fields and brightness temperature from the cloud user archive the signature of aew troughs and embedded convection are tracked from the west african coast to the central atlantic the tracked systems are separated into four groups i systems originating from the north zone of the midtropospheric african easterly jet aej ii those coming from the south part of aej iii systems that are associated with a downstream trough located around 2000 km westward termed duo systems and iv those that are not associated with such a close downstream trough termed solo systems by monitoring the embedded 700 hpa filtered relative vorticity and 850 hpa wind convergence anomaly associated with these families along their trajectories it is shown that the duo generally have stronger dynam

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

variations in surface water mass conditions in the norwegian sea evidence from holocene coccolith and dinoflagellate cyst assemblages coccolith and dinoflagellate cyst assemblages have been investigated in five sediment cores from the norwegian sea and fram strait both fossil groups are characterized by similar patterns of composition the assemblages contain high proportions of single species the coccolith flora is of low diversity and consists almost entirely of coccolithus pelagicus and emiliania huxleyi the dinoflagellate cysts are generally dominated by operculodinium centrocarpum and nematosphaeropsis labyrinthus other species especially bitectatodinium tepikiense peridinium faeroense and impagidinium pallidum sometimes contribute considerably to the assemblages based on the abundance of the assemblages and the ratio change between the dominating species it has been possible to establish three intervals of distinct major changes in surface water mass conditions sparse occurrences of coccoliths and dinoflagellate cysts have been observed before 10 000 yrs b p indicating harsh environmental conditions with a distinct influence of meltwater and temporarily very slight inflow of atlantic water the modern surface water circulation pattern was reinitiated during termination ib the assemblages suggest slightly cooler and probably less saline surface water conditions than are present today until 7500 yrs b p solar insolation may have caused a first temperature peak which is responsible for the early holocene productivity maximum a considerable change in the composition of dinocyst and coccolith assemblages occurs corresponding approximately to the onset of the holocene climatic optimum this change was most probably linked to an almost synchronous reorganization of the hydrographic properties in the entire north atlantic realm after the ice sheets had vanished since 6000 yrs b p the norwegian current with its modern oceanographic and ecological properties has been fully established