west florida continental shelf response to upwelling favorable wind forcing 2 dynamics dynamics analyses are presented for the west florida continental shelf response to upwelling favorable alongshore or offshore winds using a three dimensional time dependent primitive equation model these analyses complement the kinematics analyses of li and weisberg 1999 results are provided on four topics 1 the response evolutions to quasi steady states 2 the across shelf distributions of the vertically integrated alongshore and across shelf momentum balances 3 the three dimensional structures of the terms composing the momentum balance closures and 4 the model sensitivity to vertical friction parameterization the response evolution starts with a local wind driven acceleration and it transitions over the inner shelf into a primary balance between the pressure gradient coriolis and vertical friction terms thus the inner shelf spin up takes a classical ekman geostrophic route the middle shelf takes longer because it also depends on coastal boundary effects notably the partial closure of the domain in the south by the florida keys the outer shelf never achieves a steady state because of topographic wave effects coastline and isobath geometries result in fully three dimensional flow fields thus a two dimensional model that ignores alongshore variations cannot account for the results obtained the inner shelf is the transition region between ekman and ekman geostrophic balances where the surface slope results from mass adjustments through overlapping surface and bottom ekman layers across the inner shelf the vertically integrated momentum balance shows a gradual trade off between the coriolis pressure gradient and bottom friction terms and with the inner shelf frictionally determined its scale is sensitive to vertical friction parameterization

the frictional nearshore response to forcing by synoptic scale winds abstract an analytic barotropic model was used to study the nearshore frictional response to synoptic scale wind forcing the results depend only on the region where the surface and bottom ekman layers interact strongly and the water is consequently well mixed thus the conclusions apply even to shelves where baroclinic effects are not negligible father offshore the main findings are as follows i the blocking of the surface ekman flux which drives the shelf flow is a consequence of the interaction of ekwan layers in the nearshore region the interaction transfers progressively more of the surface stress directly to bottom stress as the depth decreases the consequent decrease in ekman flux toward the shore creates an ekman flux divergence which drives the interior flow ii the region over which the shelf is effectively forced is narrow it extends approximately from where the depth divided by the ekman layer e folding scale is 0 2 to where it is 2 5 iii simple equations for pressure and the

characterizing long island sound outflows from hf radar using self organizing maps abstract the surface outflows from the long island sound are examined from one year records of hf radar codar observations synoptic flow patterns are identified using manual classification empirical orthogonal function eof decomposition and self organizing maps som four characteristic flow patterns for the spring summer and fall winter seasons each are obtained through a 2 2 som array the som is confirmed by comparison with manual classification and is shown to be a significant improvement over eof classification it is suggested that the degrees of freedom of the leading eof modes can be used as a constraint on the otherwise arbitrary som dimension the relationship between the flow patterns and the winds also can be conveniently examined in som the outflows are shown to interact strongly with the ambient coastal currents both of which are under the influence of the winds this result challenges the conventional wisdom which often treats the outflows independent of the ambient currents the advantage of using som in synthesizing and interpreting synoptic hf radar observations is clearly demonstrated

characteristic atmospheric states during mid summer droughts over central america and mexico annual precipitation over central america and large areas of mexico is typically characterised by its bimodal distribution with a precipitation minimum in july to august that occurs between two separate maxima from may to july and august to october several theories have been proposed to explain this phenomenon which is often termed the mid summer drought msd but most fail to address the different characteristics associated with individual msd events here a regression based approach is used to detect and quantify the annual and climatological msd signature over central america and mexico this approach has been evaluated and shown to be robust for various datasets with different spatial resolutions it was found that in the southeast of the mexico central america region msds start earlier and end later than elsewhere and are thus longer in duration however the coast of the gulf of mexico cuba and large areas of central america exhibit climatologically stronger msds changes in precipitation brought about by the interaction between reversals of the onshore offshore winds and orographic forcing associated with the steep mountainous terrain have also been shown to be significant factors in the timing of msd occurrences offering support for a combined theory of large scale dynamics and regional forcing using self organising maps soms as an analysis tool it was found that msd events over the domain display strong spatial variability the msds over the domain also generate distinct signatures and may be forced by particular mechanisms we found that el nino southern oscillation enso could be a potential classifier for the som identified atmospheric states based on the correspondence of msd occurrences with enso phases

wind driven currents on the west florida shelf abstract three weeks of current meter wind and sea level data off cedar key florida are analyzed currents and sea level are found to be coherent with alongshore wind stress in the synoptic band 0 05 0 25 cycle per day and to lag it by approximately half a day little coherence is found with cross shelf wind stress at the inshore mooring 22 m depth currents are nearly barotropic for these winter 1978 data a linear parameterization of bottom stress in the barotropic alongshore current leads to a bottom friction parameter r of 0 01 0 02 cm s 1 using coastal wind stress no significant steady alongshore slope is found during this short interval the dominant momentum balance in the alongshore direction is between wind and bottom stress the offshore frictional length scale csanady 1978 is estimated to be 75 100 km which implies a seaward extent to a depth of about 30 m at the offshore mooring 44 m depth there is vertical shear between the currents at 9 and 39 m the upper cross shelf compon

seasonal modulation of the west florida continental shelf circulation velocity data from 28 n 84 w on the west florida continental shelf are presented the data were sampled from october 1993 through january 1995 at 1 m intervals between 3 m and 42 m in a total water depth of 47 m their monthly means suggest an annual cycle hypothesized to be driven by a seasonally varying shelf wide baroclinic structure motions at semi diurnal diurnal and synoptic time scales are seasonally modulated both by wind forcing and stratification that decouples fluid motions from the damping effects of bottom friction these motions are presented in the form of progressive vector plots with 16 months of data probability density and distribution functions for along shore and across shore particle displacements over specific time intervals are constructed for daily intervals particles are equally likely to travel approximately 5 km depending upon confidence interval in any direction for monthly intervals particles may travel a few hundred km primarily along shore

variability in satellite winds over the benguela upwelling system during 1999 2000 1 wind stress variability over the benguela upwelling system is considered using 16 months 01 august 1999 to 29 november 2000 of satellite derived quikscat wind data variability is investigated using a type of artificial neural network the self organizing map som and a wavelet analysis the som and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes the wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days with each region appearing to contain distinct periodicities to the north 10 23 5 s the majority of the power occurs during austral winter with a 4 16 day periodicity further investigation of national centers for environmental prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the angolan coast is linked with convective activity over equatorial west africa the summer activity appears to be linked with the intensification of the angolan heat low convective activity over the congo basin appears to impact upon wind stress variability off the angolan coast throughout the year farther south 24 35 s the majority of the power occurs in the summer here a bimodal distribution occurs with peaks of 4 12 and 25 50 days the southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones austral winter and mesoscale coastal lows austral summer at lower frequencies eastward propagating periodic wind events that originate over eastern south america appear to be important to the forcing of wind stress over the southern benguela

detecting decadal changes in enso using neural networks the present manuscript analyzes monthly equatorial pacific indices by using a specific neural algorithm the so called self organizing maps soms the main result is a change found in the nature of the transitions between cold to warm and warm to cold extreme events from 1950 to present around the late 1970s som is an unsupervised clustering technique which allows one to reduce high dimensional data space in this case three indices over 636 months in terms of a smaller set of three dimensional reference vectors 100 characterizing pertinent situations these reference vectors which are displayed on a two dimension map are closely related by a topological relationship leading us to discriminate la nina conditions from the opposite el nino conditions in a second step a hierarchical agglomerative clustering hac method is used to further group the reference vectors into a small number of clusters 12 whose spatial and temporal characteristics can be analyzed and interpreted in terms of physical parameters schematically these 12 clusters can be divided into two warm clusters six neutral or transition clusters and four cold clusters in each particular group warm neutral cold the clusters mainly differ from each other by the amplitude of the anomalies their spatial patterns and their temporal variability some clusters are found to be strongly linked to the boreal spring period while others have barely any records during that season other clusters are associated with records mainly observed either prior to or after 1980 this suggests that the method is able to identify changes in the variability of the tropical pacific basin observed on decadal time scales 1976 climate shift in our case each monthly record can be summarized by the cluster to which it belongs the temporal evolution of this value during extreme enso events shows similar patterns persistence in specific clusters and transition between groups of clusters associated with comparable el nino or la nina events the methodology described in the present study som plus hac is suggested to be useful both for seasonal enso predictability and for the detection of decadal changes in enso behavior

seasonal and interannual changes of the kuroshio intrusion onto the east china sea shelf an advanced artificial neural network classification algorithm is applied to 20 years of multisatellite geostrophic velocity data to study the kuroshio intrusion onto the southern shelf of the east china sea the results suggest that the on shelf intrusion may occur year round but winter intrusion events are more frequent than summer events both stronger intrusion which is closely correlated to surface heat flux gradient and weaker intrusion which is correlated to wind forcing occur during wintertime but the former dominates in late winter while the latter prevails in early winter there is a significant year to year variation of the winter on shelf intrusion although on shelf intrusion is the major characteristic of the region during wintertime seldom intrusion events have been identified in the winters of 1997 1998 and 2002 2003 two conditions are responsible for the cause of the nonintrusion events during the two nonintrusion winters the upstream kuroshio transport anomaly is insignificant the kuroshio is not weakened and no significant winter cooling off northeast taiwan thus the kuroshio tends to flow along the shelf break following the 200 m isobath and on shelf intrusion ceases those two nonintrusion events take place during the winters when both the nino 3 4 index and the pdo index are large and positive

variability of current temperature and bottom pressure across the west florida continental shelf winter 1981 1982 observations are analyzed from four current meter moorings deployed on the broad continental shelf in the northeastern gulf of mexico from november 29 1981 to february 8 1982 71 days consistent with recent modeling studies the shelf circulation responds within an inertial period to the alternating up and down coast synoptic scale wind forcing average response to a 0 5 dyn cm 2 alongshore wind stress as measured at the coast is 20 cm s 1 off cedar key and 40 cm s 1 in the north where the shelf narrows off cape san bias lower layer currents veer counterclockwise with depth as in a bottom ekman layer e folding scale 8 m the pressure field decays offshore e folding scale 160 km and yields a geostrophic current in good agreement with the observed alongshelf flow cross shelf and vertical variations of the tidal signals compare nicely with results from barotropic theory calculations indicate that most of the shoreward propagating tidal energy must be dissipated in depths of 20 m within 50 km of shore

small scale variations of the wind driven coastal sea level response in the west florida bight abstract records from a number of temporary tide gage stations spaced an average of 20 km apart new cedar key florida are used to examine the alongshore pressure gradient over length scales much smaller than before possible in agreement with previous studies an alongshore stress of 1 dyn cm 2 will produce a large scale over distances of several hundred kilometers alongshore sea level gradient on the order of 10 6 sea level rising downwind however cross shore stress is also important and at short periods 3 5 days can be the more coherent forcing estimates of small scale level slope do appear to show systematic deviations from the larger scale slope some of which seem to be related to alongshore variations in nearshore bathymetry

pyrrhotite as a tracer for denudation of the taiwan orogen 1 the use of pyrrhotite as an index mineral to delineate metamorphic isograds has long been proposed however details of the occurrence of pyrrhotite in different metamorphic facies and its implications have rarely been explored here by simple characterization of magnetic properties and mineral identification we demonstrate that pyrrhotite is widely distributed in low grade metamorphic terranes of taiwan s central range and in sediments derived therefrom by coupling the distribution of pyrrhotite in rocks with that in dated sediment strata we have studied the denudation history of taiwan s orogen from a source to sink perspective we suggest that pyrrhotite is a potential tracer for studying surface processes in orogens with high denudation rates similar to that in taiwan

surface current patterns in the northeastern chukchi sea and their response to wind forcing we measured northeastern chukchi sea surface currents using high frequency radar systems hfr during the ice free periods of august to october from 2010 2014 we analyzed these data along with regional winds using self organizing maps som to develop a set of surface current wind patterns temporal changes in the som patterns consist predominantly of two patterns comprising northeastward and southwestward surface currents a third pattern represents a transitional stage established during the onset of strong northeasterly winds these patterns are analogous to the first two eigenmodes of an empirical orthogonal function analysis of the hfr data the first principal component pc1 is significantly correlated 0 8 to that of the winds and is directly related to the time series of som derived patterns the sign of pc1 changes when the speed of local northeasterly winds exceeds 6 m s 1 at which point the northeastward surface currents reverse to the southwest this finding agrees with previous models and observations that suggest this wind threshold is needed to overcome the pressure gradient between the pacific and arctic oceans the transitional stage is characterized by alongshore currents bifurcating in the vicinity of icy cape and wind driven ekman currents north of 71 5 n its development is a manifestation of interactions amongst the poleward pressure gradient wind stress and geostrophic flow due to the coastal setdown

estuarine versus transient flow regimes in juan de fuca strait 1 residual currents in juan de fuca strait are observed to switch between two fundamental states estuarine and transient the estuarine regime which prevails roughly 90 of the time in summer and 55 of the time in winter has a fortnightly modulated three layer structure characterized by strong 50 cm s 1 outflow above 60 15 m depth moderate 25 cm s 1 inflow between 60 and 125 m depth and weak 10 cm s 1 inflow below 125 10 m depth rotation increases the upper layer depth by 40 m on the northern side of the channel and upwelling favorable coastal winds augment inflow in the bottom layer by as much as 5 cm s 1 rotation combined with modulation of the estuarine currents by tidal mixing in the eastern strait leads to fortnightly variability in the along channel velocity and cross channel positioning of the core flow regions transient flows which occur roughly 10 of the time in summer and 45 of the time in winter are rapidly evolving horizontally and vertically sheared reversals in the estuarine circulation generated during poleward wind events along the outer coast major events can persist for several weeks force a net inward transport and give rise to an o 10 km wide surface intensified o 100 cm s 1 inflow along the southern olympic peninsula boundary of the strait this olympic peninsula countercurrent is typically accompanied by an abrupt decrease in salinity indicating that it is a buoyancy flow originating with low density water on the northern washington shelf

west florida shelf response to local wind forcing april 1998 we compare west florida shelf velocity and sea level data with a model simulation for april 1998 responses for three upwelling and three downwelling favorable wind events are documented along shelf jets accompanied by oppositely directed upper and lower layer across shelf flows with connecting vertical velocity comprise the fully three dimensional inner shelf responses which are sensitive to stratification with an initial density field representative of april 1998 the model simulates velocity and sea level variations in general agreement with the observations whereas substantial mismatches occur without stratification despite the winds being the primary motive agent for the inner shelf the stratification dependence requires that model density fields be maintained through a combination of adequate initial conditions surface offshore and land derived buoyancy inputs and data assimilation dynamical analyses define the inner shelf as the region where the surface and bottom boundary layers are important in the momentum balance kinematically this is where surface ekman layer divergence fed by the bottom ekman layer convergence or conversely sets up the across shelf pressure gradient stratification causes a response asymmetry wherein the offshore scale and magnitude of the upwelling responses are larger than those for the downwelling responses this asymmetry is attributed to thermal wind effects across the bottom ekman layer buoyancy torque by isopycnals bending into the bottom adds constructively destructively with planetary vorticity tilting under upwelling downwelling favorable winds and this may have important implications for nutrients and other material property distributions on the shelf

patterns of the loop current system and regions of sea surface height variability in the eastern gulf of mexico revealed by the self organizing maps the self organizing map som an unsupervised learning neural network is employed to extract patterns evinced by the loop current lc system and to identify regions of sea surface height ssh variability in the eastern gulf of mexico gom from 23 years 1993 2015 of altimetry data spatial patterns are characterized as different lc extensions and different stages in the process of lc eddy shedding the temporal evolutions and the frequency of occurrences of these patterns are obtained and the typical trajectories of the lc system progression on the som grid are investigated for an elongated northwest extended or west positioned lc it is common for the lc anticyclonic eddy lce to separate and propagate into the western gom while an initially separated lce in close proximity to the west florida continental slope often reattaches to the lc and develops into an elongated lc or reduces intensity locally before moving westward as a smaller eddy regions of differing ssh variations are also identified using the joint som wavelet analysis along the general axis of the lc ssh exhibits strong variability on time scales of 3 months to 2 years also with energetic intraseasonal variations which is consistent with the joint empirical orthogonal function eof wavelet analysis in the more peripheral regions the ssh has a dominant seasonal variation that also projects across the coastal ocean the som when applied to both space and time domains of the same data provides a powerful tool for diagnosing ocean processes from such different perspectives

patterns of ocean current variability on the west florida shelf using the self organizing map 1 patterns of ocean current variability are examined on the west florida shelf by a neural network analysis based on the self organizing map som using time series of moored velocity data that span the interval october 1998 september 2001 three characteristic spatial patterns are extracted in a 3 4 som array spatially coherent southeastward and northwestward flow patterns with strong currents and a transition pattern of weak currents on the synoptic weather timescale the variations of these patterns are coherent with the local winds on the seasonal timescale the variations of the patterns are coherent with both the local winds and complementary sea surface temperature patterns the currents are predominantly southeastward during fall winter months from october to march and northwestward during summer months from june to september the spatial patterns extracted by the nonlinear som method are asymmetric a feature that is not captured by the linear empirical orthogonal function method thus we find for the synoptic weather and longer timescales that 1 southeastward currents are generally stronger than northwestward currents 2 the coastal jet axis is located further offshore for southeastward currents than for northwestward currents and 3 the velocity vector rotations with depth are larger in shallower water when the currents are southeastward relative to when the currents are northwestward

wind induced sea surface slopes on the west florida shelf abstract tidal and meteorological records at stations in the eastern gulf of mexico have been studied the sea level response is a maximum for winds along the coast and varies symmetrically with angle the coherence is maximum at periods of 4 10 days the horizontal coherence of sea level is high out to 500 km for 4 10 day periods the horizontal coherence for wind measured at coastal stations is high out to at least 500 km the amplitude of the response of sea level to winds is larger by a factor of 4 here on a broad shelf than on the oregon coast which is more narrow by about the same ratio a response of 16 cm is induced by 4 m s 1 wind this response or transfer function is uniform over the spectral range 4 100 days the sea level response to the longshore wind stress is not linear but to the power 0 8 0 1 and is attributed to the relatively low tidal currents in this region the large horizontal coherences of wind and sea level imply broad longshore flows extending 500 km or more along

coastal ocean wind fields gauged against the performance of an ocean circulation model 1 atmosphere model derived flux fields are used to force coastal ocean models coarse resolution and incomplete boundary layer dynamics limit the accuracy of these forcing fields and hence the performance of the ocean models we address this limitation for the west florida shelf using optimal interpolation to blend winds measured in situ with winds produced by model analyses by improving the coastal wind field we improve the fidelity between currents modeled and currents observed comparisons between momentum analyses performed independently from the model and the data demonstrate the fidelity to be of a correct dynamical basis we conclude that the primary limitation to coastal ocean model performance lies with the boundary conditions

wind forced sea level variability along the west florida shelf winter 1978 abstract coastal tide gage and meteorological records from pensacola to key west for the period january april 1978 have been examined for low frequency fluctuations the dominant 6 day period signals in sea level alongshore wind stress and atmospheric pressure were coherent over the entire shelf and propagated southward consistent with the movement of cold fronts through the area sea level response tagged the local wind stress by 18 h in the north to 9 h in the south in response to a 1 dyn cm 2 alongshore stress sea level amplitudes were largest 60 cm where the shelf is widest 200 km and undergoes an abrupt bend and were 30 cm elsewhere large transient alongshore sea level slopes on the order of 10 6 were thus set up a linear steady state shelf circulation model hsueh 1980 is used to explore the sea level distribution that is in frictional equilibrium with a wind stress of given orientation for a bottom resistance coefficient of 0 014 cm s 1 a value suggested by an analysis of fe

mapping of decadal middle adriatic oceanographic variability and its relation to the bios regime we analyzed long term time series of temperature salinity and dissolved oxygen do concentrations collected along the palagru a sill transect middle adriatic between 1952 and 2010 the data have been mostly collected on seasonal basis allowing for extraction of seasonal signal from the series by applying self organizing maps som method a kind of unsupervised neural network method the processes on a decadal time scale emerged as the most relevant for changes of oceanographic properties in the middle adriatic area sensitivity studies revealed that oceanographic patterns obtained by som were not sensitive to shortening of time series to removal of data from one station or to removal of do from the analysis simultaneous som based mapping of sea surface heights in the northern ionian sea with these heights serving as a proxy for the adriatic ionian bimodal oscillating system bios revealed asymmetry between anticyclonic and cyclonic bios patterns and correlated the decadal oscillations in the middle adriatic with the reversals in the bios circulation regimes these reversals are found to either rapidly change oceanographic properties in the middle adriatic e g during the eastern mediterranean transient or to change them with a time lag of 2 3 years the mapped connections may be used for a short time a few years forecasting of the adriatic oceanographic properties or for mapping future climate decadal oscillations as seen by ocean climate models