winter cascading of cold water in lake geneva 1 during the winters of 1998 and 1999 observations were made of the cascading of cold water from the nearshore shallow shelf zones and down the sloping sides of lake geneva cascading starts on the average 10 hours after the onset of surface cooling the draining cold water descends like a gravity current and the downslope speed of the head of these slugs of cold water u has a mean value of 5 2 cm s 1 with slugs persisting on the average for 8 hours when the monin obukov length scale at the water surface l is negative implying convection occurs and d over bar lg 1 where d is the mean shelf depth the nondimensionalized speed of the front of slugs u b 1 3 is found to be 1 3 0 4 where b is the surface buoyancy flux integrated over the time period from one slug to the next each slug is unsteady the head being followed by several fronts in which the temperature of the current decreases and its thickness increases these fronts travel faster than the mean flow by a factor of r 1 38 0 3 dynamical similarities are found with roll waves observed in turbulent open channel flows the circulation induced by the cascade is found to give a positive skewness to the time derivatives of near surface temperature in shallow waters in contrast with negative values close to the slope the volume of cold water carried by a slug increases with downslope distance as a consequence of turbulent entrainment and the contribution of convectively unstable plumes from the surface the average volume carried by the slug across the 21 m depth contour is about 1 9 times the volume of water in shallower water i e that on the shelf between shore and a depth of 21 m implying that cascading is an efficient means of flushing shelf water integrated around the lake the mean total volume flux amounts to 11 5 the average winter river inflow

response of vietnam coastal upwelling to the 1997 1998 enso event observed by multisensor data abstract in this paper we examine the behavior of the vietnam coastal upwelling during the 1997 1998 el nino southern oscillation enso event the baseline is 4 years of national oceanic and atmospheric administration noaa satellite advanced very high resolution radiometer avhrr sea surface temperature sst data taken from 1997 to 2000 comparison of upwelling images to simultaneous ers 2 european remote sensing satellite wind fields indicates that the summer monsoon winds constitute a major generation forcing during the 1997 el nino the monsoon winds enhanced the upwelling and induced the upwelling center to move southward during the 1998 la nina the monsoon winds weakened the upwelling in contrast with the tropical pacific in the study area la nina implies a warm event and el nino a cold event we use empirical orthogonal function eof methods to analyze the spatial and temporal variance of the upwelling the three principal modes account for 37 15 and 8 of the total variance respectively the first eof modes reveal that the sst variance in the north and south subregions underwent a positive negative sign switch in summer 1997 the second eof modes represent the monthly evolution in normal years the third modes seem to be sensitive to the 1998 la nina event simultaneous topex poseidon and ers 2 altimeter data provide further evidence for our analysis comparison with california coastal upwelling and mid atlantic bight mab coastal upwelling indicates that the vietnam coastal upwelling is the most intensive one

a three dimensional model of the mean and seasonal circulation of the gulf of california 1 the mean and seasonal circulation of the gulf of california is simulated with a three dimensional numerical model forced by the pacific ocean through specifying the sea level the temperature and the salinity fields at its entrance at the sea surface the wind and the heat and freshwater fluxes are specified the model reproduces the observed mean and seasonal variability of sea level of heat and salt balances and the sea surface temperature sst climatology it also reproduces the general surface circulation of the northern gulf which consists of a seasonally reversing basin wide gyre it is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the sst tides provide the mixing to upwell the cooler subsurface waters in the large islands area and the heating from the surface raises the sst the general circulation of the southern part of the gulf is due to the wind and the pacific forcing in the ekman layer two periods of anticyclonic circulation and one cyclonic per year occur below this layer two cyclonic periods develop in the northern part the tides play an important role in producing mean residual currents and both tides and winds compete against the pacific forcing to produce a cyclonic and anticyclonic circulation once a year contrary to conclusions of previous studies the thermohaline circulation is found to be unimportant in the gulf

internal structure of sst features in the central gulf of california abstract closely spaced xbt and ctd data were used to study the sub surface structure of features observed in satellite avhrr sea surface temperature sst images of the gulf of california gc such as fronts jets and gyres the lowest ssts in the gc are found around the midriff islands and especially over the sills because of strong mixing from tidal currents and breaking internal waves this minimum sst area is limited to the south and north by sharp sst fronts which frequently show convolutions gyres and filaments a vertical section of temperature along the gulf length shows that about 300 km south of the sills the isotherms begin to spread out in the vertical reducing stratification the thermocline isotherms begin surfacing about 100 km south of the sill forming the sst minimum area which has a maximum temperature difference of 6 c with waters to the south and a horizontal sst gradient of 0 05 c km 1 the evolution and subsurface structure of a cool filament apparently originated as an instability of the sst front was intensely sampled satellite images show that its head advanced due south at about 0 5 ms 1 along the edge of a pool of warm surface water about 110 km in diameter the thermocline below the warm pool was raised at its edge and some isotherms reached the surface producing the cool filament the tilt of the temperature salinity and density isolines at the edge of the warm pool produced a geostrophic jet adjacent to the cool filament and just inside the warm pool with maximum speed 0 5 ms 1 and extending down to 80 m the filament lasted about 10 days its width was 30 km and it reached a maximum length of 120 km the volume transport of the jet in the top 100 m was around 0 7 sv

tidal and atmospheric forcing of the upper ocean in the gulf of california 1 sea surface temperature variability two years of satellite infrared imagery 1984 1986 are used to examine the sea surface temperature sst variability in the northern gulf of california empirical orthogonal functions eofs of the temporal and spatial sst variance for 20 monthly mean images show that the dominant sst patterns are generated by spatially varying tidal mixing in the presence of seasonal heating and cooling these patterns are modified in the fall and winter when shelf temperatures south of tiburon island cool in response to upwelling favorable winds these same winds bring cold dry air from off the continental united states causing local cooling of the shallow northern shelf during the rest of the year the broad shallow shelves are warmer than offshore the seasonally reversing temperature patterns are consistent with recent hydrographic observations which show a cyclonic surface circulation in the summer and a weaker anticyclonic circulation during the rest of the year atmospheric forcing of the northern gulf appears to occur over large spatial scales area averaged ssts for the guaymas basin island region and northern basin show significant fluctuations which are highly correlated these fluctuations in sst correspond to similar fluctuations in the air temperature which are related to synoptic weather events over the gulf during periods of particularly low wind speeds the air temperature over the gulf increases dramatically by afternoon intense heating of the sea surface results in the appearance of warm sst anomalies in the satellite data these ssts are approximately 2 c warmer than surrounding ssts and most likely occur as a result of a spatially varying wind field a regression analysis of the sst relative to the fortnightly tidal range shows that tidal mixing occurs over the sills in the island region as well as on the shallow norther shelf mixing over the sills however occurs as a result of large breaking internal waves or internal hydraulic jumps which mix water over the upper 300 500 m this mixing pumps heat away from the surface deep into the water column there by maintaining the cool ssts since mixing occurs over greater depths in the island region the temperatures there are much colder than those generated by tidal mixing on the shallow shelves resulting in the persistent pool of cool water evident in the satellite data this cooler water is mixed horizontally by the basin scale circulation lowering the ssts over much of the northern gulf these reduced ssts have a large impact on the surface heat flux by lowering the saturation vapor pressure of the air as a result the amount of heat lost to the atmosphere through the latent or evaporative heat flux is reduced this may explain why the gulf of california gains heat on an annual average rather than losing heat as occurs in the mediterranean and red seas where tidal mixing is not significant

on the three dimensional numerical modeling of the deep circulation around angel de la guarda island in the gulf of california a three dimensional nonlinear baroclinic model is used to model the circulation in the ballenas channel gulf of california mexico which was inferred from current meter observations over three sills that surround the area the suggested circulation consists of deep inflow that follows two paths the first one is a direct spill of water through san lorenzo sill into ballenas channel the second one a larger route that starts at san esteban sill then flows north of the island passing over tiburon and delfin basins and then turns to the south reaching the north ballenas channel sill and then spills into ballenas channel following the latter result a previous modeling effort to reproduce the circulation was partially obtained the long path was not reproduced and it was believed that finer horizontal resolution was needed in this work the bathymetric resolution was increased by a factor of three and the full path of this deep circulation is now obtained and corroborated

meteorologically forced subinertial flows through the strait of gibraltar the observed transport due to subinertial flows with periods ranging from days to a few months through the strait of gibraltar reaches values up to 106 m3 s 1 and is well correlated with atmospheric pressure fluctuations over the mediterranean sea this transport is barotropic and accounts for 84 of the variance observed at these frequencies a second mode accounts for 12 of the variance and is characterized by a node zero amplitude located at the mean depth of the interface between atlantic and mediterranean waters this baroclinic mode is modulated by the spring neap tidal cycle corresponding to an increased exchange of waters between atlantic and mediterranean at neap tides a simple model of the mediterranean which includes two basins and two straits indicates that the system has two resonant frequencies at periods of 1 2 and 5 6 days the 1 2 day resonance corresponds to the eastern and western basins oscillating through the strait of sicily while that at 5 6 days is the resonance of the mediterranean sea with the north atlantic ocean a good approximation to the observed flows is obtained when this model is forced with the most energetic mode of the atmospheric pressure over the eastern and the western mediterranean and a friction term is included to limit the flow through the strait of gibraltar restricting the flow through the strait of sicily does not improve the agreement between the model and the observations for the flows at gibraltar

two overflows in the northern gulf of california 1 two overflows originating at sills in the northern gulf of california are marked by strong average downstream slopes of 17 and 4 near bottom stratification upstream of both sills is relatively strong but the near bottom water is very well mixed downstream of the sills the homogenization of a thick bottom layer downstream albeit close to the sills is indicative of very strong mixing waters in the downstream basins are well ventilated with relatively high oxygen concentrations these hydrographic patterns were observed during three different seasons time series of temperature salinity and potential density show that water flowing over the sills is essentially subsurface subtropical water from the pacific ocean the time series also indicate that water is nearly always denser at the sills compared to water in the downstream basins despite the two fold 800 m and more than three fold 1500 m increase in depth the long term more than a year average current at both sills is bottom intensified with maximum average speeds of 33 and 17 cm s there are also strong tidal currents at the sills although the subinertial currents near the bottom are quite persistent with nearly no flow reversals transports estimated exclusively with the mean flow are about 0 08 and 0 09 sv 1 sv 1 106 m3 s which agree well with previous estimates based on shorter time series and a lower vertical resolution these results indicate that the deep water at both downstream basins are renewed by these overflows which enter at sill depths 400 m and are capable of reaching the deepest part of both basins the overflows appear to be responsible for the main mechanisms that transform subsurface subtropical water into gulf of california water

thermohaline circulation in the gulf of california the gulf of california a narrow semienclosed sea is the only evaporative basin of the pacific ocean as a result of evaporative forcing salinities in the gulf are 1 to 2 higher than in the adjacent pacific at the same latitude this paper examines the thermohaline structure of the gulf and the means by which thermohaline exchange between the pacific and the gulf occurs over time scales of months to years in addition to evaporative forcing air sea heat fluxes and momentum fluxes are important to thermohaline circulation in the gulf from observations presented here it appears that the gulf gains heat from the atmosphere on an annual average unlike the mediterranean and red seas which have comparable evaporative forcing as a result outflow from the gulf tends to be less dense than inflow from the pacific winds over the gulf change direction with season blowing northward in summer and southward in winter this same seasonal pattern appears in near surface transports averaged across the gulf the thermohaline circulation then consists of outflow mostly between about 50 m and 250 m inflow mostly between 250 m and 500 m and a surface layer in which the direction of transport changes with seasonal changes in the large scale winds using hydrographic observations from a section across the central gulf total transport in or out of the northern gulf is estimated to be 0 9 sv heat gain from the atmosphere is estimated to be 20 to 50 w m 2 and evaporation is estimated to be 0 95 m yr 1 these estimates are annual averages based on cruises from several years seasonal variations in thermohaline structure in the gulf are also examined and found to dominate the variance in temperature and density in the top 500 m of the water column salinity has little seasonal variability but does exhibit more horizontal variablility than temperature or density major year to year variations in thermohaline structure may be attributable to el nino southern oscillation events

internal waves in the gulf of california observations from a spaceborne radar pronounced signatures of internal waves were detected repeatedly in the gulf of california by the seasat synthetic aperture radar sar a series of nine images with exactly repeating ground coverage was used to study the temporal variability of the internal wave field in the area it was found that the number of observed wave groups was highly correlated with the strength of the local tides the maximum number occurred during spring tides and the minimum number occurred during neap tides indicating that the internal waves were tidally forced most of the wave activity was found to the north of 28 n where the tides were the strongest in the gulf the application of a simple nonlinear internal wave model to the observations indicated that the peak to peak amplitude of the observed waves was about 50 m with an uncertainty of a factor of 2 the estimated upper bound for the rate of the loss of tidal energy to internal waves was about 5 1015 erg s representing only 10 of the rate of the dissipation of the dominant m2 tide in the gulf

on the variability of tidal fronts on a macrotidal continental shelf northern patagonia argentina abstract tidal fronts are associated with the transition between homogeneous and vertically stratified water and are characterized by the simultaneous availability of light and nutrients that enhance the growth of marine productivity we study the variability in the position of two tidal fronts located in patagonia argentina the san matias and valdes fronts the rate of tidal dissipation in these regions is among the highest of the world oceans the study is based on the analysis of over 1200 satellite derived sea surface temperature images the results indicate that the mean monthly position of both fronts is strongly linked to the characteristics of the bottom topography in response to increasing surface heat flux the fronts displace toward shallower areas similarly a slight displacement towards deeper waters is observed when the heat flux decreases high frequency variability is revealed by the standard deviation around monthly averages at the mouth of the san matias gulf the front location variability in the spring neap cycle is around 10 km while east of the valdes peninsula the fortnightly cycle is masked by high frequency fluctuations 30 km governed by meanders and meso scale filaments a simple conceptual model is proposed which suggests that the mean frontal position is determined by the bottom topography while its seasonal variability is driven by the surface heat flux and the front intensity is modulated by the spring neap transition

summer sea surface temperature variability off vancouver island from satellite data satellite sensed advanced very high resolution radiometer avhrr sea surface temperature sst data over eight summers 1984 1991 were used to analyze the summer sst patterns of variability off the west coast of vancouver island empirical orthogonal function eof analysis of the spatial variance for 133 nearly cloud free summer images was performed the first eof mode which resembled the mean of all images showed a strong cool water band located at the northwest comer of vancouver island a cool tongue extending seaward from the strait of juan de fuca and a warm patch off barkley sound the second mode revealed topographically controlled upwelling cool water over the shelf region with its seaward boundary roughly following the 200 m depth contour plus a cold eddy located just north of the juan de fuca canyon the third mode displayed cool water extending southwestward off brooks peninsula while the fourth mode showed a cool water plume extending off cape scott at the northern tip of vancouver island these four modes accounted for 33 12 10 and 5 of the sst variance respectively the temporal amplitude of these eof modes revealed how the sst features changed as summer progressed from these images we also constructed an overall seasonal coolness index which revealed the summers of 1986 and 1991 to have the coolest coastal water with both summers immediately preceding an e1 nifio

tidal dissipation and stratification in the gulf of california the effect of tidal mixing upon the distribution of stratification and sea surface temperature sst in the gulf of california is studied by direct observation and by numerical modeling data from conductivity temperature depth surveys made in september and december of 1986 are used to describe the distribution of stratification and sst a vertically integrated finite differences numerical model was used to obtain the geographical distribution of available turbulent kinetic energy tke from the m2 tide the following three areas were found to be strongly affected by tidal mixing the shallow coastal area at the head of the gulf the shelf south of tiburon island and the area of the midgulf archipelago the first two are vertically well mixed and are therefore similar to other shelf sea frontal areas dissipation occurs all around the islands of the archipelago and the sills are foci of the most intense tidal dissipation stratification in this area was reduced with respect to the background but complete vertical mixing does not occur therefore the strong sst fronts that occur in this area do not mark the boundary between well mixed and stratified water the simpson hujiter criterion simpson and hunter 1974 for stratification and frontal position produced 2 75 crit 3 0 for the frontal position in the shallow northern gulf this value of crit is larger than in other shelf sea fronts which may be due to horizontal advection which is not included in the criterion we found that the effect of advection may be of the same order of magnitude as that of buoyancy flux in the area over the sills criti the available tke is not enough to produce complete mixing over the 400 m of water over the sills

diagnostic investigation of impulsive pressures induced by plunging breakers impinging on gravel beaches abstract this paper presents an integrated investigation of physical processes generating impulsive pressures under the action of plunging breakers impinging on gravel beaches this work is an extension of a recent investigation which suggested that wave impacts from plunging breakers acting on gravel beaches may be a key mechanism to enhance sediment mobilisation in particular comparisons of full scale laboratory measurements against model results from a well validated phase depth resolving numerical model based on the reynolds averaged navier stokes rans equations are presented this represents the first attempt at comparison with such a tool against observed hydrodynamics on steep slope 1 8 gravel beaches at prototype scale in order to understand how impulsive pressures are generated under plunging waves the numerical model is used to carry out a detailed investigation to examine the role of each of the acceleration terms in the momentum balance consistent with prior studies numerical results show that under plunging breakers the local acceleration u t alone cannot be used as a proxy for pressure gradients however the contribution of the third term w u z of total acceleration is recognized for the first time and indicates that this term has an important role in both the induced pressure gradient and sediment mobilisation as induced by this particular type of breaking furthermore results suggest that a parameterisation of the pressure gradient in terms of u t u u x may not suffice when dealing with plunging breakers and hence there is a lack of a suitable parameterisation of this process in the present literature thus for different types of breaking it may be necessary to consider a different characterisation of the pressure gradient toward the parameterisation of sediment transport inside the surf zone

diurnal cycle of surface flows during 2004 name and comparison to model reanalysis abstract during the north american monsoon experiment name an unprecedented surface dataset was collected over the core monsoon region observations from 157 surface sites in this region along with twice daily quick scatterometer quikscat oceanic winds were quality controlled and processed into a gridded dataset covering the domain 15 40 n 90 120 w at 1 h 0 25 resolution for the period from 1 july to 15 august using this dataset the mean temporal variability and diurnal characteristics of the monsoon surface flow are documented with detail not previously possible being independent of model data over land these objectively analyzed surface products are compared to similar analyses from a special north american regional reanlysis for name narr name that was produced for the same period observed surface fields indicate that a robust land sea breeze circulation is present over most of the gulf of california goc region in response to the strong diurnal heating of landmasses on both sides

summer generation of the southern gulf of california eddy train 1 ocean color and sea surface temperature satellite observations show the existence of a series of anticyclonic eddies along the axis of the southern gulf of california sgoc to investigate the summer generation of these eddies a regional version of the hybrid coordinate ocean model hycom has been configured for the goc and has been nested inside the global model a suite of experiments using the nested goc model was developed and used to isolate the effects of the local wind and the effects of the oceanic remote forcing on the generation of the sgoc eddies the results indicate that the local wind is not essential for the generation of these eddies rather it is the oceanic remote forcing in the sgoc the monthly variability of the currents and sea surface height is mainly due to the deterministic near coastal poleward eastern boundary currents pebc the interaction of the pebc with the topographic irregularities the capes at topolobampo and cabo lobos and the ridges extending offshore from the entrance of the san lorenzo and sinaloa rivers generates the sgoc eddies the northward upper ocean transport induced by the pebc includes two maximums one in may june and the other in december during the summers of 1999 and 2004 the pebc were intensified by the arrival of equatorially originated downwelling coastally trapped waves ctws which contributed to the generation of the sgoc eddies the summer 2004 ctw increased the northward upper ocean transport by 2 sv this particular ctw was measured by several tide gauges located along the coast

surface heat flux in the northern gulf of california recent coastal meteorological data 1979 1986 are used to evaluate the seasonal cycle of surface heat fluxes in the northern gulf of california although net heat loss occurs from october to january the annual mean of the net surface heat flux was found to be into the sea 69 w m 2 near the coast and 83 w m 2 offshore with a mean evaporation rate 0 9 m yr 1 these results require an oceanic export of heat and salt out of the northern gulf to achieve a balance and imply that the annual mean thermohaline circulation must have an inflowing component at depth thus enriching the central and northern parts of the gulf these results differ from previous meteorological estimates which suggested a net surface heat loss but confirm those based on hydrographic data

tidal mixing signatures in the indonesian seas from high resolution sea surface temperature data the presence of significant tidal mixing in the indonesian seas is well established from both observations and numerical modeling one indicator is a clear spring neap cycle in satellite sea surface temperature sst measurements as first shown by ffield and gordon their early results are here updated with sst data of considerably higher spatial and temporal resolution the largest fortnightly signals are found to be localized to relatively small straits channels and sills while the deep basin of the banda sea displays little significant signal a broader region of somewhat enhanced signal surrounds the seram sea the high resolution of the modern sst data is especially critical for mapping the complex fortnightly signals that arise in and especially south of the major straits of the lesser sunda island chain

lagrangian observations of the circulation in the northern gulf of california argos drifters deployed in the northern gulf of california in september 1995 showed the presence of a cyclonic gyre while a second deployment in march 1996 revealed an anticyclonic gyre a circulation pattern consisting of a seasonally reversing gyre had been proposed before on the basis of satellite images geostrophic calculations and numerical models but so far no direct observations have been made to test its existence in september the gyre was cyclonic baroclinic very well defined stable and strong its mean speed and rotation time were 0 3 m s21 and 7 days in march the gyre had the same mean speed but it was anticyclonic and displaced to the northwest of the summer position the march gyre has barotopic and baroclinic characteristics but the observed speeds are stronger than in numerical simulations these data and a data bank analysis suggest that the summer gyre is a persistent summer feature but the winter spring situation remains ill defined and requires further research

the lower atmosphere over the gulf of california automated meteorological observations at coastal and island stations instrumented aircraft flights and coastal soundings were made between july 1983 and june 1985 to define the variations of the lower atmosphere over the northern half of the gulf of california during the two important climatic seasons the mid latitude winter and the subtropical summer a marine layer is well defined over water during both seasons but dissipates within a few kilometers inland the winter large scale pressure field is dominated by the great basin high over the southwestern united states modulated by upper level synoptic activity it causes 3 to 6 days events of northwesterly winds 8 12 m s 1 directed along the gulf s axis which are coherent over basin scales and bring cool dry desert air over the gulf the vertical scale of these winds is 700 1000 m over land on the western side of the gulf close to the height of the baja california mountains but only 100 400 m over water defined by the wintertime inversion cross gulf winds related to topographic effects during upper level trough passages over baja california are particularly intense in the northwestern portion of the gulf the winter marine layer is defined by a 1 to 4 5 c temperature inversion and a dew point temperature of 6 11 c a moisture content of 6 8 g kg 1 weak subsidence reduces dew point values to 4 c above the inversion winter winds above the marine layer are coherent 0 8 across the width of the gulf the summer large scale pressure field is dominated by a thermal low over the southwestern united states and drives weak 2 5 m s 1 southeasterly winds also directed primarily along the gulf which are less spatially uniform than winter winds air temperature and moisture content are rather constant and topographic effects are absent the summer marine layer is on the order of 200 300 m thick with dew point temperatures of 26 28 c 21 24 g kg 1 and capped by a weak temperature inversion 1 2 c over water aloft the dew point temperature is 17 21 c and winds are weak and uncorrelated across the width of the gulf during june and early july 1984 four week long pulses of southeasterly winds 10 m s 1 support the existence reported previously of moisture surges from the gulf into the sonoran desert a dynamical analysis of subdiurnal motions shows that the cross gulf momentum balance is geostrophic the along gulf balance is ageostrophic with the along gulf pressure gradient opposed by friction at the surface these results are consistent with a scale analysis of the equations of motion in the marine layer over the gulf of california

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

an analysis of errors in sea surface temperature in a series of infrared images from noaa 6 as part of the coastal ocean dynamics experiment 58 infrared satellite images were analyzed for the magnitude and source of their errors in predicting sea surface temperature comparisons with near surface thermistors on moorings and differences between images from consecutive days showed that a two channel atmospheric correction using the 3 7 m and the 11 m channels was ineffective in reducing errors large systematic errors which have the form of a constant over an image were found in both channels a simple viewing angle correction reduced fluctuations in the area mean 11 m channel temperature from 0 74 to 0 45 c a satisfactory correction could not be found for the larger fluctuations in the 3 7 m channel which appears to be degraded by reflected or scattered solar radiation by taking account of the known dependence of atmospheric effects on viewing angle geometry it was possible to isolate the primary causes of error to estimate typical magnitudes and to correct for them the 11 m channel temperature error from the northern california atmosphere was found to be nearly constant in time over a 100 day period but to vary slowly with distance from the coast

water mass formation in the gulf of california the gulf of california is a long narrow marginal sea lying between the baja california peninsula and the mainland of mexico air sea fluxes of heat and moisture in the gulf are enhanced because of geographical isolation from the pacific provided by the mountainous baja california peninsula in the northern gulf annual evaporation rates are about 1 m y 1 unlike most evaporative basins however the gulf gains heat from the atmosphere at an annual average rate of 20 to 80 w m 2 bray 1988 given the unusual air sea forcing of the gulf what form or forms should water mass formation take the annual moisture loss and heat gain require that high salinity surface water be transported downward to an intermediate depth and that cold fresh inflow be transported upward to an intermediate depth this is accomplished through several mechanisms 1 winter convection this occurs only in a limited geographical region the wagner basin of the far northern gulf except in el nino southern oscillation years when convection appears to be more widespread 2 dispersion of convected water in small eddylike features this occurs within a large scale southward transport possibly driven by the large scale density gradient associated with atmospheric fluxes 3 an anticyclonic circulation in the northern gulf this is found south of the convection region and transports high salinity water off the shallow shelves and to substantial depths where it may mix with water of central gulf origin 4 tidal mixing most of the energy available for mixing in the northern gulf derives from the tides in particular tidal mixing over the sill in the island region is responsible for the substantial reduction in salinity of northern gulf waters as they enter the central gulf

shelf circulation in the gulf of california a description of the variability the first long term measurements 1983 1984 of winds temperature bottom pressure and currents made in the gulf of california are used to describe the dynamically important spatial and temporal scales and to compare and contrast the shelf circulation on opposite sides of the guaymas basin in addition a qualitative assessment of possible forcing mechanisms of gulf shelf circulation and an account of an energetic coastal trapped wave event are presented winds over the gulf are weak and variable with maximum wind speeds of 10 15 m s and sustained wind events of less than a week low frequency 3 cpd fluctuations in the dominant along gulf component of the wind field which are largely coherent over the study area are directed upgulf during summer and downgulf for the remainder of the year low frequency winds are not significantly correlated 95 confidence level with currents temperature and pressure in part because of weak local winds and nonlocally forced coastal trapped waves on longer time scales seasonal upwelling on both sides of the gulf and guaymas basin mean currents are related to local winds low frequency current fluctuations on the two facing shelf regions guaymas on the mexican mainland and santa rosalia on the baja california peninsula are not significantly correlated along gulf currents in the basin however are negatively correlated with alongshelf currents at guaymas 0 54 due to sporadically occurring eddylike features and santa rosalia 0 61 due to seasonal flow patterns low frequency fluctuations on the mainland shelf are significantly correlated during the summer e g 0 67 in temperature between topolobampo and guaymas separation of 375 km such that topolobampo leads guaymas by approximately 1 5 days this lagged signal is associated with coastal trapped waves that are generated by tropical storms and hurricanes south of the gulf and propagate poleward along the mainland shelf at speeds of 200 250 km day near guaymas current speeds of approximately 50 cm s were measured at the 100 m isobath on the mainland shelf during an event with a 20 cm coastal sea level rise the offshore decay of these waves is of the order of 50 km on the guaymas shelf low frequency temperature or equivalently density and sea level fluctuations are correlated 0 78 such that a 10 cm rise in sea level corresponds to a 20 m drop in isotherm depths over much of the water column this sea surface isotherm relationship is such that the amplitude of pressure fluctuations decays rapidly with depth e folding scale 160 m a similar relationship is only weakly apparent correlation 0 39 on the santa rosalia shelf cross gulf geostrophy is observed with 35 of the along gulf current averaged across the gulf related to dp dx measured between guaymas and santa rosalia on the guaymas and santa rosalia shelves dp dx measured across each shelf explains approximately 20 of the variability in alongshelf currents in the alongshelf momentum balance dp dy accounts for approximately 40 of the low frequency variability in dv dt at the guaymas shelf break consistent with the dynamics of freely propagating coastal trapped waves the same balance is only weakly apparent 10 of variance explained at santa rosalia at higher frequencies temperature fluctuations at guaymas are coherent and in phase to 200 m depth coherent 0 74 with the alongshelf near surface current at the shelf break m8 and exhibit a spring neap modulation consistent with internal tides

satellite derived sea surface temperature variability off california during the upwelling season abstract an empirical orthogonal function analysis of an advanced very high resolution radiometer sea surface temperature data set encompassing the spring summer period during 1991 1993 was used to examine patterns of temperature variability off northern and central california this analysis decomposed the spatial variability of remotely sensed sea surface temperature in 124 images that covered an offshore distance of 200 km and an alongshore distance of 500 km the first mode empirical orthogonal function described 65 of the spatial variability in the data set the spatial amplitude pattern of the first mode which closely resembled the mean of all the images revealed a strong cross shore gradient with much cooler water nearshore and warmer water offshore these areas of cool waters were associated with known upwelling locales and the large scale temperature structure compared favorably to that derived from historical california cooperative oceanographic fisheries investigation calcofi climatology the mode 1 temporal amplitude function representing the temporal modulation of this spatial pattern was coupled with changes in the alongshore component of the coastal wind field interannual variations in the timing of the spring transition were reflected in this temporal amplitude time series the second mode empirical orthogonal function described 11 of the variability in the data set the spatial pattern revealed a north south structure that appeared to be related to regional spatial variations in the strength of upwelling favorable wind the third empirical orthogonal function described only 3 of the data variability and the spatial structure suggested a meandering of the coastal surface flow the results of this investigation indicate that the empirical orthogonal function method was effective at characterizing from the satellite data the dominant nearshore surface properties of the california current system related to upwelling and wind and by extension suggest that it is a suitable approach for remotely investigating other less well known eastern boundary current systems

decadal climate variability is there a tidal connection abstract a possible connection between oceanic tides and climate variability arises from modulations in tidally induced vertical mixing the idea is reexamined here with emphasis on near decadal time scales occasional extreme tides caused by unusually favorable alignments of the moon and sun are unlikely to influence decadal climate since these tides are of short duration and in fact are barely larger than the typical spring tide near lunar perigee the argument by keeling and whorf in favor of extreme tides is further handicapped by an insufficiently precise catalog of extreme tides a more plausible connection between tides and near decadal climate is through harmonic beating of nearby tidal spectral lines the 18 6 yr modulation of diurnal tides is the most likely to be detectable possible evidence for this is reviewed some of the most promising candidates rely on temperature data in the vicinity of the north pacific ocean where diurnal tides are large but definitive detection is hindered by t

observations of the coastal upwelling region near 34 30 n of california spring 1981 abstract coordinated meteorological and oceanographic ctd measurements were made near point conception california during march april 1981 the goal of the observations was to study coastal upwelling and the local characteristics of the assumed wind driving results showed substantial topographically induced spatial structure in the near surface winds with weaker winds generally occurring within the santa barbara channel the 1981 spring transition event was monitored by mews of hydrographic and sea level measurements the details of the event suggest that it was not entirely driven by lead wind stress the mean sea surface temperature pattern suggests the existence of an upwelling center between points arguello and conception the individual sea surface temperature charts are all dominated by patchiness on a scale of 5 15 km the nature of these structures is not well understood but on the one occasion when a patch was isolated by a ctd survey its structure penetrated to at 1east 50 db

ocean color observations of eddies during the summer in the gulf of california 1 using seawifs ocean color satellite images collected during 1997 2001 a series of eddies have been observed in the gulf of california these eddies are not clearly seen in the summertime sea surface temperature images the surface circulation between the midriff islands and the mouth of the gulf appears to be dominated by this series of eddies that have an alternating sense of rotation an eddy pair is observed to extend from cabo lobos in each of the three years suggesting that the eddies are topographically locked the formation mechanism of the eddies remains unknown however we suspect the most likely mechanism includes baroclinic instabilities along the coast produced by interactions between coastally trapped waves and local wind driven currents