direct correlation of millennial scale changes in western north american vegetation and climate with changes in the california current system over the past 60 kyr terrestrial pollen and marine climate proxies from seven sediment cores taken on the continental margin of western north america between 32 and 43 n show systematically related short term changes superposed on milankovitch scale oscillations of the past 60 kyr during oxygen isotope stage 3 brief warming events in california and oregon appear correlative with interstadial events in waters offshore as do the rapid climate oscillations of the last glacial transition 14 10 ka estimated temperature depression of the coastal lowlands ranges from 10 c in southern california to 5 c in oregon during the last glacial the absence of long distance migration of pacific coastal plant assemblages concurs with marine evidence that southward movement of the polar front during the last glacial maximum was limited correlative changes in terrestrial and marine ecosystems imply that broad reorganizations of circulation in the northeast pacific ocean were synchronous with reorganizations of atmospheric circulation over western north america

numerical simulations of tropical cyclone ocean interaction with a high resolution coupled model the tropical cyclone ocean interaction was investigated using a high resolution tropical cyclone ocean coupled model the model design consisted of the noaa geophysical fluid dynamics laboratory tropical cyclone prediction model which was coupled with a multilayer primitive equation ocean model coupling between the hurricane and the ocean models was carried out by passing into the ocean model the wind stress heat and moisture fluxes computed in the hurricane model the new sea surface temperature sst calculated by the ocean model was then used in the tropical cyclone model a set of idealized numerical experiments were performed in which a tropical cyclone vortex was embedded in both easterly and westerly basic flows of 2 5 5 and 7 5 m s 1 with a fourth experiment run with no basic flow specified initially the profile of the tangential wind for hurricane gloria at 1200 utc 22 september 1985 was used as the initial condition of the tropical cyclone for each of the experiments the model ocean was initially horizontally homogenous and quiescent to clarify the impact of the ocean response to the hurricane s behavior analogous experiments were also carried out with the sst kept constant control cases the experiments indicated that the cooling of the sea surface induced by the tropical cyclone resulted in a significant impact on the ultimate storm intensity due to the reduction of total heat flux directed into the tropical cyclone above the regions of decreased sst the sea surface cooling produced by the tropical cyclones was found to be larger when the storms moved slower in the experiments run without an initial basic flow the maximum sst anomaly was about 5 6 c with a resulting difference in the minimum sea level pressure and maximum surface winds of 16 4 hpa and 7 m s 1 respectively in contrast in the experiments run with the 7 5 m s 1 basic flow the maximum sst anomalies ranged from about 2 6 to 3 0 c with a difference in the minimum sea level pressure and maximum surface winds of about 7 3 hpa and 2 7 m s 1 the tropical cyclone ocean coupling significantly influenced the storm track only for the case with no basic flow and the 2 5 m s 1 easterly flow in these cases the storm with the ocean interaction turned more to the north and east no basic flow or the north 2 5 m s 1 easterly flow of the experiments with constant sst in the first case the storm by 72 hours was located over 70 km to the east southeast of the control case a possible explanation for this track deviation is related to a systematic weakening of the mean tangential flow at all radii of the storm due to the interaction with the ocean and resulting alteration of the beta drift

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

abrupt increase in greenland snow accumulation at the end of the younger dryas event the warming at the end of the last glaciation was characterized by a series of abrupt returns to glacial climate the best known of which is the younger dryas event1 despite much study of the causes of this event and the mechanisms by which it ended many questions remain unresolved1 oxygen isotope data from greenland ice cores2 4 suggest that the younger dryas ended abruptly over a period of about 50 years dust concentrations2 4 in these cores show an even more rapid transition 20 years this extremely short timescale places severe constraints on the mechanisms underlying the transition but dust concentrations can reflect subtle changes in atmospheric circulation which need not be associated with a large change in climate here we present results from a new greenland ice core gisp2 showing that snow accumulation doubled rapidly from the younger dryas event to the subsequent preboreal interval possibly in one to three years we also find that the accumulation rate change from the oldest dryas to the bo11ing allerod warm period was large and abrupt the extreme rapidity of these changes in a variable that directly represents regional climate implies that the events at the end of the last glaciation may have been responses to some kind of threshold or trigger in the north atlantic climate system

the effect of relative flow on the asymmetric structure in the interior of hurricanes abstract asymmetric structure of tropical cyclones simulated by the geophysical fluid dynamics laboratory high resolution triply nested movable mesh hurricane model was analyzed emphasis was placed on the quasi steady component of the asymmetric structure in the region of the eyewall it was found that the asymmetry was primarily caused by the relative wind that is the flow entering and leaving the storm region relative to the moving storm a set of idealized numerical experiments was first performed both with a constant and a variable coriolis parameter f and the addition of basic flows that were either constant or sheared with height analysis was then made for one case of hurricane gilbert 1988 to demonstrate that the quasi steady asymmetric structure analyzed in the idealized studies could be identified in this real data case vorticity analysis in the variable f experiment indicated that quasi steady asymmetries resulted in the eyewall region through the effect of vorticity advection due to

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

on the geographic asymmetry of typhoon translation speed across the mountainous island of taiwan abstractthis paper examines the effect of topographically phase locked convection on the motion of typhoons across the island of taiwan data for 84 typhoons that reached taiwan s eastern coast from 1960 to 2010 are analyzed with motions compared to the long term average overland translation speed for 61 continuous track typhoons among all cases 77 of the slow moving tropical cyclones tcs made landfall on the northern end of taiwan s eastern coast while 60 of the fast storms had southeastern coastal landfalls this geographic asymmetry with respect to typhoon translation speeds widened after landfall as the slow movers typically decelerated during the overland period whereas the faster tcs sped up in particular the average overland duration was 16 h for the slow class compared to only 3 h for the fast moving typhoons the combination of slower translation with longer duration for the northern class of tcs led to large rainfall on the southwestern slope of the island s central mountain range we

glacial ventilation rates for the deep pacific ocean 1 a key constraint in attempts to reconstruct the patterns and rates of the ocean s thermohaline circulation during the last glacial period is the difference between the 14c to c ratio in surface and deep water while imperfect it is our best index of past deep sea ventilation rates in this paper we review published ventilation rate estimates based on the measured radiocarbon age difference between coexisting benthic and planktic foraminifera from glacial age pacific sediments we also present new results from a series of eastern equatorial pacific sediment cores the conclusion is that the scatter in these results is so large that the apparent 14c age of glacial deep pacific water could lie anywhere between double and half today s further it is not clear what is responsible for the wide scatter in the radiocarbon results

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

cluster analysis of post landfall tracks of landfalling tropical cyclones over china in this paper we apply finite mixture model based clustering algorithms to cluster post landfall tracks of tropical cyclones tcs making landfall over china because existing studies find that landfall surfaces or elevations affect post landfall tc movements we also take account of elevations in addition to time orders in this model our study reveals three clusters with cluster 1 making landfall in hainan province and moving across the western coast of guangdong province most of the tc tracks in cluster 1 move over the ocean and make secondary landfalls over yunnan province of china and vietnam cluster 1 finally dissipates inland and moves westward as a result of the westward shift subtropical high westward steering flow easterly vertical wind shear and strong mountainous blocking cluster 2 makes landfall over guangdong and fujian provinces tcs in cluster 2 subsequently move inland and disappear due largely to westward shift subtropical high easterly steering flow easterly vertical wind shear and relatively strong mountainous blocking cluster 3 makes landfall along the fujian and zhejiang coast and sustains a long period of time recurving mostly to the mid latitude region owing to the surrounding eastward shift subtropical high westerly vertical wind shear weak mountainous blocking and westerly steering flow because cluster 2 is significantly associated with la nina events tcs more likely make landfall over southeastern china coast and move westward or northwestward without recurving cluster 3 sustains a longer time than clusters 1 and 2 in spite of its weak horizontal and vertical water vapor supply tcs in cluster 3 interact actively with westerlies during the post landfall period however we cannot observe any analogous interactions with the mid latitude westerlies in clusters 1 and 2 tcs of clusters 1 and 2 are influenced by summer monsoon flows moreover summer monsoon exerts a greater influence on cluster 1 than cluster 2 the composite 200 hpa divergence of cluster 3 is stronger than that of clusters 1 and 2 this explains to some degree why cluster 3 sustains longer than clusters 1 and 2 after making landfall

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

modeling the effects of land sea roughness contrast on tropical cyclone winds abstract the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 is used to simulate tropical cyclone tc wind distribution near landfall on an f plane at 15 n the effects of the different surface roughness between the land and sea on the wind asymmetry is examined under a strong constraint of a dry atmosphere and time invariant axisymmetric mass fields the winds are found to adjust toward a steady state for prelandfall 50 100 and 150 km offshore landfall and postlandfall 50 100 and 150 km inland tc positions the tc core is asymmetric even when it lies completely offshore or inland the surface 10 m wind asymmetry at the core for pre post landfall position is apparently related to the acceleration deceleration of the flow that has just moved over the sea land as a response to the sudden change of surface friction for prelandfall tc positions the resulted strong surface inflow to the left and front left relative

radar observations of intense orographic precipitation associated with typhoon xangsane 2000 abstract with measurements from two ground based doppler radars located in northern taiwan this study documents the detailed aspects of intense orographic precipitation associated with typhoon xangsane 2000 as it moved northward immediately off the eastern coast of taiwan bringing strong low level northeasterly to north northeasterly winds impinging on the mountainous northern coast with relatively good persistent coverage of radar echoes on both inland and upstream regions this particular event provides a unique description of the orographic precipitation and its relationship with orographic geometry strong upstream oncoming flow and the precipitation inherently associated with typhoon circulations in this case the heaviest precipitation was observed to occur primarily over two coastal mountain barriers mount da tun dt and the nangang keelung range nkr barrier dt is an approximately 3d mountain barrier and the nkr adjacent to the southeast of dt is a relatively lower narrower 2d moun

a fast and easy method to derive highest resolution time series datasets from drillcores and rock samples abstract we present a fast method to obtain highest resolution greyvalue datasets from digital core images these datasets are processed using a software package developed by us artificially introduced trends in the datasets are corrected disturbances i e cracks voids are eliminated to reduce the high level noise in data we have developed a vector filter that effectively removes such noise application of the method to odp drillcores from the santa barbara basin allowed exact correlation of two drillcores from the same basin the influence of the termination of the last glacial cold period on the flux rates in the basin are reflected in the greyvalue datasets we found a transitional period of about 3000 yr between the end of the last glacial cold period and the onset of post glacial climatic oscillation in the basin fourier analyses show that the high resolution greyvalue time series record climatic cycles with frequencies as high as 1 cycle yr varves

numerical simulation of typhoon gladys 1994 and its interaction with taiwan terrain using the gfdl hurricane model abstract numerical integrations using the geophysical fluid dynamics laboratory gfdl hurricane model were performed to study the evolution of typhoon gladys 1994 and its interaction with the taiwan terrain consistent with most previous studies the taiwan topography results in the deceleration of gladys s translation speed and southward deviation as it approaches taiwan on the other hand gladys accelerates northwestward while passing taiwan which is likely to be related to the moist processes and differs from the track pattern in the dry model of lin et al although the gfdl hurricane model forecast underestimates gladys s intensity the model can capture the evolution of gladys s intensity especially its weakening during landfall which is primarily due to the cutoff of the water vapor supply in the boundary layer as gladys approached the taiwan terrain other mesoscale phenomena including the pattern of heavy precipitation and the formation of secondary lows are well simulated by the model

monsoonal influence on typhoon morakot 2009 part ii numerical study abstractin the second part of this study numerical experiments are conducted to investigate the influences of multi time scale monsoonal flows on the track change of typhoon morakot 2009 while the control simulation captures the slowing and northward deflections in the vicinity of taiwan island the highly asymmetric rainfall structure and the associated rainfall pattern sensitivity experiments suggest that the westward movement prior to the landfall on taiwan and the subsequent northward shifts in the vicinity of taiwan were closely associated with the interaction between morakot and multi time scale monsoonal flows prior to the landfall on taiwan morakot moved westward directly toward taiwan because of a synoptic wave train like pattern which consisted of goni over mainland china morakot and a cyclone over the western north pacific with an anticyclone to the west of morakot numerical simulation suggests that strong northerly winds between morakot and the anticyclone reduced the northward stee

tropical cyclone motion in response to land surface friction abstract numerical experiments are performed with the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 to study the effects of surface moisture flux and friction over land on the movement of tropical cyclones tcs on an f plane the tcs are initially placed 150 km due east of a north south oriented coastline in an atmosphere at rest it is found that a tc could drift toward land when the roughness length is 0 5 m over land with an average drift speed of 1 m s 1 friction but not surface moisture flux over land is apparently essential for the movement toward land the friction induced asymmetry in the large scale flow is the primary mechanism responsible for causing the tc drift the mechanism responsible for the development of the large scale asymmetric flow over the lower to midtroposphere 900 600 hpa appears to be the creation of asymmetric vorticity by the divergence term in the vorticity equation horizontal advection then rotates t

geographic coherence of millennial scale climate cycles during the holocene varve thickness measurements and variation in sediment texture have been compiled for an intermittently varved sequence of holocene sediments at odp site 893 in the santa barbara basin sbb off california a varve based age model is generated from the varve counts using interpolation across homogeneous intervals with this age model the varve thickness and sediment texture time series are compared to published gisp2 stable oxygen isotope and aerosol data as well as to the atmospheric 14c record variation in sediment texture at site 893 shows the presence of a 1000 year cycle which is attributed to fluctuations in the degree of ventilation of the basin cross spectral analysis shows that this cycle is coherent with the gisp2 18o record and with atmospheric 14c throughout the holocene the correlation with the 14c record indicates that this 1000 year cycle is related to solar cycles which appear to have a noticeable impact especially on circum north atlantic climate the presence of the 1000 year cycle in the sbb is attributed to a tele connection with the northern high latitudes most likely via intermediate water formation in the north pacific in contrast the gisp2 aerosol record and variation in varve thickness at odp site 893 show a coherent 2750 year cycle which does not correlate with the 1000 year cycle varve thickness in sbb has been shown to correlate with annual rainfall which occurs mainly during winter when prevailing winds slacken both the gisp2 aerosol and sbb varve thickness records are therefore interpreted as a measure for a combination of wind stress and aridity the correlation is negative in that thick varves wet climate in sbb occur during times that the aerosol load is high at gisp2 dry the presence of two distinct patterns of millennial scale variation points to regional trends in climate change during the holocene however the fact that both patterns occur at two distant localities suggest that they represent differential behaviour of supra regional climate systems of which the effects can be traced over large parts of the globe

a numerical study of the effects of land proximity and changes in sea surface temperature on hurricane tracks a three layer shallow water model with a convection parametrization is used to study the track deflections of slow moving hurricanes on a plane as they approach straight coastlines of different orientations with respect to north or as they cross to a cooler or warmer body of water in the landfall experiments the land surface is level and is characterized by an abrupt increase of the drag coefficient and zero evaporation the tracks of a 72 h integration on a plane are compared with an ocean control experiment it is found that the divergent flow in the boundary layer in regions of offshore winds is responsible for the observed track deflections in this region middle layer air descends into the boundary layer and increases the positive potential vorticity anomaly in the middle layer in the case of land conditions to the west of the vortex the maximum potential vorticity anomaly extends less to the north of the vortex centre and results in a more southerly track than in the ocean control case if land conditions are specified in the north the positive potential vorticityasymmetry maximum extends more to the north west and results in a northward deflection of the track on the other hand land conditions to the north west of the initial vortex centre do not significantly change the location of the asymmetry and therefore the track deflection is small the magnitude of the track deflections as well as the drift speed increases when the roughness of the land is increased it is significant that track deflections commence about 20 h before landfall reaching a value of about 150 km at the time of landfall compared with landfalling hurricanes track deflections of model hurricanes which drift into a region of different sea surface temperature sst are smaller and are a result of intensity changes of the vortex circulation the maximum wind speed at the time of landfall increases if a region of higher sst is located adjacent to the coastline

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

monsoonal influence on typhoon morakot 2009 part i observational analysis abstracttyphoon morakot made landfall on taiwan with a record rainfall of 3031 5 mm during 6 13 august 2009 while previous studies have emphasized the influence of southwesterly winds associated with intraseasonal oscillations and monsoon surges on moisture supply the interaction between morakot and low frequency monsoon flows and the resulting influence on the slow movement and asymmetric precipitation structure of the typhoon were examined observationally embedded in multi time scale monsoonal flows morakot generally moved westward prior to its landfall on taiwan and underwent a coalescence process first with a cyclonic gyre on the quasi biweekly oscillation time scale and then with a cyclonic gyre on the madden julian oscillation time scale the coalescence enhanced the synoptic scale southwesterly winds of morakot and thus decreased its westward movement and turned the track northward leading to an unusually long residence time in the vicinity of taiwan the resulting slow movement and collocation

a simulation study of the landfall of tropical cyclones abstract by use of a triply nested movable mesh model several ideal simulations of tropical cyclone landfall were performed for a strong zonal flow of 10 m s 1 the integration domain was a 37 45 channel with the innermost mesh having a 22 22 point resolution of 1 6 general characteristics similar to observed landfalling tropical cyclones are obtained in the primary simulation experiment including an abrupt change in the low level 68 m winds at the coastline and a decay of the tropical cyclone at it moves inland additional interesting features subject to model and experimental limitations include little noticeable track change of the model storm when compared to a control experiment with an ocean surface only a possible temporary displacement or the center of the surface wind circulation from the surface pressure center at landfall and a distinct decrease in kinetic energy generation and precipitation a few hours after landfall the sensitivity to the specified land surface conditions was

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

the impact of ocean coupling on hurricanes during landfall the impact of ocean coupling on landfalling hurricanes is studied using a coupled hurricane ocean model with idealized atmospheric and oceanic conditions we focus here on coastal sea surface temperature responses and their effects on hurricanes during landfall we find that given the ocean thermal stratification the hurricane induced sea surface cooling is nearly independent of the ocean depth as long as the ocean is considerably deeper than the mixed layer after the storm center moves inland the near surface processes around the storm core area are influenced by the sea surface cooling behind and on the right side of the storm track via reduction of near surface entropy advection into this area the impact of ocean coupling is generally limited to the early times after landfall and nearly disappears after the hurricane center reaches about 200 km inland

climatically related millennial scale fluctuations in strength of california margin oxygen minimum zone during the past 60 k y a strong oxygen minimum zone omz currently exists along the california margin because of a combination of high surface water productivity and poor intermediate water ventilation however the strength of this omz may have been sensitive to late quaternary ocean circulation and productivity changes along the margin although sediment lamination strength has been used to trace ocean oxygenation changes in the past oxygen levels on the open margin are not sufficiently low for laminations to form in these regions benthic foraminifera are highly sensitive monitors of omz strength and their fossil assemblages can be used to reconstruct past fluctuations benthic foraminiferal assemblages from ocean drilling program site 1017 off point conception exhibit major and rapid faunal oscillations in response to late quaternary millennial scale climate change dansgaard oeschger cycles on the open central california margin these faunal oscillations can be correlated to and are apparently synchronous with those reported from santa barbara basin together they represent major fluctuations in the strength of the omz which were intimately associated with global climate change weakening perhaps disappearing during cool periods and strengthening during warm periods these rapid major omz strength fluctuations were apparently widespread on the northeast pacific margin and must have influenced the evolution of margin biota and altered biogeochemicalmore cycles with potential feedbacks to global climate change less

the conundrum of coal bed thickness a theory for stacked mire sequences maximum thicknesses for modern peats have been documented only up to about 20 m whereas coal beds can often be as much as 90 m thick since peat is expected to compact appreciably during burial there appears to be no modern analogue for the processes which formed thick coal beds and this seems to challenge the law of uniformitarianism however the conundrum of coal bed thickness can be resolved by identification of discontinuities in coal beds coal beds are generally treated as single entities created by a continuous process of peat deposition it is more likely however that most thick coal beds are composed of multiple paleo peat bodies stacked one upon another rather than a single paleo peat body it is suggested that there are three types of bounding surfaces seen in modern peat bodies that can be used to distinguish individual paleo peats in coal beds these bounding surfaces can be recognized both in the field and microscopically each of these surfaces represents cessation or at least ext

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

asymmetric distribution of convection associated with tropical cyclones making landfall along the south china coast this study examines the convection distribution associated with 18 tcs that made landfall along the south china coast during 1995 and 2005 cloud top temperatures from high resolution satellite imageries of the geosynchronous meteorological satellite 5 are used as proxy of strong convection it is found that convection tends to be enhanced on the western side of the tc as it makes landfall in 10 of the cases in agreement with the conclusion of some previous studies four cases have stronger convection on the eastern side this deviation from the general rule appears to be related to the tcs being more slow moving or their interaction of the tc with another land surface prior to its making landfall along the south china coast for the remaining cases in which no significant asymmetries in convection can be identified the vertical wind shear appears to enhance convection on the east side

forcing of the antarctic circumpolar wave by el nino southern oscillation teleconnections we address several issues regarding the antarctic circumpolar wave acw these include the extent to which the acw is related to el nino southern oscillation enso cycles and the need to reconcile differences between the observed zonal wavenumber 2 pattern and the wavenumber 3 pattern found in coupled ocean atmosphere models in the present study we revisit the sea surface temperature sst signal of the observed acw we find that the associated sst variations may be decomposed into several empirical orthogonal functions eofs that are linearly independent the first four eofs describe 84 of the total variance on timescales of 3 7 years and superposition of sst signals of the four eofs reproduces sst signals of the observed acw given that eof analysis can only describe standing oscillations we then employ complex eof ceof analysis suitable for studying propagating waves the first two ceofs denoted ceofsst1 and 2 account for 70 of the total variance and the sst variability reconstructed from them again reproduces the observed acw the real part of ceofsst1 44 of the total variance is similar to the first real eof eofsst1 both eofsst1 and ceofsst1 may be identified with enso and have a wavenumber 2 zonal pattern in the southern middle to high latitudes ceofsst1 is the major constituent of the acw in the period of 1981 1997 the associated atmospheric circulation displays a pacific south america psa pattern statistical analyses demonstrate that the psa pattern teleconnected to enso is the major mechanism that forces this principal constituent of the acw ceofsst2 26 of the total variance has a zonal wavenumber 3 pattern in the same latitude band similar to that simulated by several coupled models we suggest that if enso is not adequately resolved in coupled models but structures with zonal wavenumber 3 pattern are then the modeled acw would appear to have a zonal wavenumber 3 pattern

a high resolution prediction study of two typhoons at landfall abstract the landfall on the china coast of two typhoons has been studied using both observational diagnostics and a 30 km 19 level prediction system the typhoons vary in size and in the amount of rainfall they produced after landfall use is made of a synthetic typhoon insertion scheme and the relatively dense observational network around china to provide objective analyses the authors illustrate that in the forecast model as the typhoon s outer circulation impinges on the china coast an outer cloud band develops offshore parallel to the coast extending cyclonically north and east during this time the inner circulation weakens as the outer cloud band strengthens the center of the circulation approaches it from the east and there is a short term intensification of both the inner region vertical motion and vorticity following landfall rapid dissipation of the core occurs using detailed diagnostics from the model integration the changing thermal structure of the forecast vortex is illustrated

sediment fluxes and varve formation in santa barbara basin offshore california results from a year long sediment trap study provide the first direct observations of seasonal variability in sediment fluxes to the sea floor in santa barbara basin offshore california and are used to evaluate varve formation in this basin sediment fluxes throughout the year are dominated by lithogenic material biogenic sediments primarily silica are of secondary importance we conclude that the combination of high lithogenic fluxes and low biogenic fluxes during the fall winter period results in the deposition of dark laminae the onset of upwelling and high surface productivity in the spring results in high biogenic silica fluxes that last into the summer the relative contribution of silica to the total sediment flux is highest during this spring summer period and we suggest that light laminae are formed at that time this is consistent with previous suggestions that sediment input is the primary factor controlling varve formation in this basin