Coastal Front Research Articles

Bio‐optical modeling of photosynthetic production in coastal waters

A physiological‐based bio‐optical model is used to estimate vertical profiles of instantaneous, diurnal, and integrated daily rates of in situ primary production throughout the water column at three stations across a coastal front. The model makes use of an empirical relationship between photosynthesis, quantum yield, and photosynthetically absorbed radiation and is a full spectral model with all relevant parameters determined as a function of wavelength. In the prior application of this bio‐optical model, parameters used to estimate quantum yield as a function of irradiance were wavelength‐independent and held constant. Here, the model is recast so that quantum yield is estimated with wavelength‐dependent photosynthesis‐irradiance parameters, Pmax the maximum rate of phytoplankton photosynthesis, and Ik the P‐I saturation parameter, which are allowed to vary with depth and time of day. Both Pmax‐dependent (assumed to be λ‐independent) and Ik‐dependent (known to be λ‐dependent) estimates of temporal/spatial changes in quantum yield were assessed. The model was tested in water masses where a net‐to‐nanoplankton transition was occurring in phytoplankton communities dominated by diatoms and prymnesiophytes. At each station there is close agreement between 14C productivity estimates derived from knowledge of diurnal patterns in P‐I parameters and productivity estimates derived from two variants of the bio‐optical model based on knowledge of spectral irradiance and phytoplankton pigmentation. The 14C and bio‐optical estimates of primary production also show similar vertical patterns for either instantaneous or daily integrated values. When compared with 14C estimates, Ik‐dependent bio‐optical estimates of photosynthetic rates give a closer match than bio‐optical estimates that are Pmax‐dependent. The model permits calculation of primary production from shipboard observations and may be useful for predicting production rates from bio‐optical data provided by untended buoys.

The large-scale atmospheric structure accompanying New England coastal frontogenesis and associated North American east coast cyclogenesis

An eleven-case composite is constructed of the large-scale flow configuration accompanying wintertime New England coastal frontogenesis events which are associated with Atlantic coast cyclogenesis in the United States. The pre-coastal-front environment is dominated by anticyclonic activity in the lower troposphere over the eastern Great Lakes. The cold anticyclone moves eastward north of New England while slowly strengthening, and is eventually responsible for the cold south-easterly flow that participates in the developing coastal front circulation. Coastal frontogenesis commences in an increasingly favourable synoptic-scale environment for ascending motion and pressure falls with both the passage of the 500 mb ridge axis and the onset of strong 850 mb warm air advection beneath the entrance region of a broad confluence zone at 500 mb. The synoptic-scale forcing for ascent over the developing coastal front is maximized from the cyclonic shear side of the jet in the base of the 500 mb trough to the anticyclonic shear side of the jet entrance region in the downstream confluence zone. Clearly identifiable departures in both the global-scale (wavenumbers 0–3) and large synoptic-scale (wavenumbers 4–8) waves from the long term climatological mean 1000–500 mb thickness field are observed during the evolution of the Atlantic coast cyclogenesis event. The major deviations from climatology in the wavenumbers 0–3 thickness deviation fields are negative anomalies in eastern Asia, the northern Soviet Union and the United States, and positive anomalies over Alaska and Greenland. The global-scale thickness waves show substantial evolution in their transience and amplitude characteristics following the onset of the cyclogenesis event. The wavenumbers 4–8 thickness anomaly analyses reveal initially quasi-stationary amplification during the onset of cyclogenesis. As Atlantic coast cyclone development proceeds, however, a pronounced positive thickness anomaly is generated in the western Atlantic and extends into New England. Similarly, wavenumbers 4–8 thickness anomalies from eastern North America to western Europe amplify and become more progressive.

The Formation of New England Coastal Fronts

Abstract Coastal fronts are a frequent late fall and early winter feature of eastern New England weather. Data from a mesoscale observing network is used to describe the process of coastal frontogenesis and to determine the causes of formation. Three distinct types of coastal frontogenesis are found to occur in New England, and examples of each are presented using mesoscale surface maps and time series. Type a coastal fronts form during cold air outbreaks as winds veer from offshore to onshore. Type B coastal fronts form in the evening as air temperatures over land fall below air temperatures over water. Both types of fronts represent thermally direct circulations which are created by heating from the warm sea surface, often in combination with radiational cooling over land. Type C coastal fronts are caused by upstream blocking when a stable region of warm advection, such as warm front, approaches the Appalachian Mountains from the south. Type A and Type B fronts are described in terms of land and sea bre...

The large‐scale atmospheric structure accompanying New England coastal frontogenesis and associated North American east coast cyclogenesis

AbstractAn eleven‐case composite is constructed of the large‐scale flow configuration accompanying wintertime New England coastal frontogenesis events which are associated with Atlantic coast cyclogenesis in the United States.The pre‐coastal‐front environment is dominated by anticyclonic activity in the lower troposphere over the eastern Great Lakes. The cold anticyclone moves eastward north of New England while slowly strengthening, and is eventually responsible for the cold south‐easterly flow that participates in the developing coastal front circulation. Coastal frontogenesis commences in an increasingly favourable synoptic‐scale environment for ascending motion and pressure falls with both the passage of the 500 mb ridge axis and the onset of strong 850 mb warm air advection beneath the entrance region of a broad confluence zone at 500 mb. The synoptic‐scale forcing for ascent over the developing coastal front is maximized from the cyclonic shear side of the jet in the base of the 500 mb trough to the anticyclonic shear side of the jet entrance region in the downstream confluence zone.Clearly identifiable departures in both the global‐scale (wavenumbers 0–3) and large synoptic‐scale (wavenumbers 4–8) waves from the long term climatological mean 1000–500 mb thickness field are observed during the evolution of the Atlantic coast cyclogenesis event. The major deviations from climatology in the wavenumbers 0–3 thickness deviation fields are negative anomalies in eastern Asia, the northern Soviet Union and the United States, and positive anomalies over Alaska and Greenland. The global‐scale thickness waves show substantial evolution in their transience and amplitude characteristics following the onset of the cyclogenesis event. The wavenumbers 4–8 thickness anomaly analyses reveal initially quasi‐stationary amplification during the onset of cyclogenesis. As Atlantic coast cyclone development proceeds, however, a pronounced positive thickness anomaly is generated in the western Atlantic and extends into New England. Similarly, wavenumbers 4–8 thickness anomalies from eastern North America to western Europe amplify and become more progressive.

Distribution and diversity of recurrent groups of demersal fishes in the South China Sea off Viet Nam.

The distribution and diversity of demersal fish communities were described in the South China Sea off Viet Nam from December 1968 to July 1969. The first recurrent group including lizardfish as a principal member was located dispersedly along coastal front from winter to summer. Snapper which was a principal member of the second recurrent group coexisted with largeeyed bream at 40-60m depth in winter. However, snapper coexisted with grunt in the shallow region less than 40m depth in summer. Diversity was relatively high in southeastern area, and was low off the Mekong delta.

２０世紀の寒冷期・温暖期・変動期における東アジア地上気圧配置の季節内変動と特異性

Surface weather charts have been analyzed nearly for one century on a hemisphere scale. The present study tries to demonstrate characteristics of the occurrence frequency of pressure patterns in the global cold, warm, and recent variable periods, which correspond to or are responsible for anomalies in air temperature and precipitation, and to investigate the intraseasonal variations and singularities of pressure patterns over East Asia. This study defines the period from 1906 to 1920 as a cold period, that from 1936 to 1950 as a warm period, and that from 1971 to 1985 as a recent variable period. According to the classification of pressure pattern types by Yoshino (1968), a calendar of pressure patterns during the periods 1906-1920 and 1936-1940 was originally made on the basis of “Daily Synoptic Series, Historical Weather Maps, Northern Hemisphere Sea Level”. The statistics of this study are also based on the calendars for the periods 1941-1950 (Yoshino and Kai, 1974), 1971-1980 (Yoshino and Yamakawa, 1985) and 1981-1985 (original).The results of this paper are summarized as follows : The annual frequency of the typical winter type (type W) of west high and east low does not reveal much difference between the cold and warm periods. However, in the warm period, the duration of Type W appearance is shorter, but it occurs more frequently in January than in that of the cold period. The typical summer type (Type S), south high and north low, is most distinguished in August, though it is perceptible from July, in the warm period. The temperate migratory high type (Type H) (excluding highs passing North Japan) is clearly eminent throughout the year in the warm period. Particularly in April, Type H accounts for 43% (13% more than that of the cold period); in October it forms 37% (16% more). In the warm period, singularities of Type H are recorded five times in spring and autumn seasons, respectively. The north high type (Type N), which includes migratory highs in North Japan, southern coastal lows and southern coastal fronts, appears with low frequency in the warm period. The difference in occurrence frequency of Type N between the both periods is large in spring (April, May) and autumn (Sept., Oct.). In the cold period when the onset and end of the Baiu season are quite clear, the frontal zone type, consisting of Types N and L, appears with very high frequency (about 90%) throughout the Baiu season. With regard to the typhoon type (Type T), it tends to appear more frequently in August and September of the cold period ; in October of the warm period. Type T appears less frequently in both the summer and autumn seasons of the recent variable periods. Ratios of anticyclonic singularities to cyclonicones are 43 to 57 in the cold period, 54 to 46 in the warm period and 42 to 58 in the recent variable period. In the last period there are many identical singularities with those in the warm period. Especially from mid-August (Aug. 14-18) to mid-September (Sept. 8-12), a series of common singularities-Types T, S, L, S, L and L-are recognized in this order both in the warm and recent variable periods.

Long, nonlinear oscillations of density fronts

Abstract A new nonlinear mode of a density front is presented and we show that long, finite deviations from a steady state of the free streamlines of the coupled front of zero potential vorticity lead to oscillations of these streamlines about their initial locations. The amplitude and frequency of such oscillations are computed and it is found that the frequency depends on the initial displacement and is always higher than the inertial frequency. The results found for the free streamline behavior are also applicable to the coastal front in which the potential vorticity is zero and the along-stream velocity vanishes at the coast.

Genesis of Atlantic Lows Experiment (GALE): An Overview

The field phase of the Genesis of Atlantic Lows Experiment (GALE) was conducted from 15 January to 15 March 1986. The objectives of GALE were to study mesoscale and air-sea interaction processes in East Coast winter storms, with particular emphasis on their contributions to cyclogenesis. The project area, special observing systems, and field operations are described. There were thirteen special observing periods during the field phase including eight cases of cyclogenesis. Meteorological and oceanographic phenomena on which special observations were collected include: cyclogenesis, rainbands, cold fronts, coastal fronts, cold-air damming, jet streaks, tropopause folding, low-level jets, cold-air outbreaks, lightning and marine boundary layer interactions with Gulf Stream and mid-shelf oceanic fronts. Preliminary research findings and operational implications are presented. GALE data documents are listed. The GALE data set is open to all interested scientists.

The Genesis of Atlantic Lows Experiment: The Planetary-Boundary-Layer Subprogram of GALE

Abstract The Genesis of Atlantic Lows Experiment (GALE), focused an intensive data-gathering effort along the mid-Atlantic coast of the United States from 15 January through 15 March 1986. Here, the general objectives and experimental layout are described with special emphasis on the planetary-boundary-layer (PBL) component of GALE. Instrumentation is described for buoys, ships, research aircraft, and towers. The networks of the cross-chain long range aid to navigation (LORAN) atmospheric sounding system (CLASS) and the portable automated mesonet (PAM II) are described and their impact on the operation of GALE is outlined. Special use of dual-Doppler radar to obtain detailed wind measurements in the PBL is discussed. Preliminary analyses for a selected observational period are given. Detailed observations of the offshore coastal front reveal direct mesoscale circulations imbedded in the frontal zone. Later in the period, during an intense cold-air outbreak, sensible-heat and latent-heat fluxes over the co...

Diurnal patterns of size-fractioned primary productivity across a coastal front

In July 1985, diurnal patterns of photosynthesis and pigmentation were characterized for whole water (>0.4 μm) and size-fractioned (>5 μm and 0.4 to 5 μm) communities from three light depths sampled across a coastal thermal front in the Southern California Bight. Samples were collected predawn and held for 20 h in deck incubators. Variations in chlorophyll a and accessory pigment-to-chlorophyll a ratios showed no obvious diurnal trends. Timing of peak photosynthetic potential (P max) and its coincidence with variations in light-limited rates of photosynthesis (alpha), as well as diurnal amplitudes in P max and alpha, often differed between size fractions sampled within the same community. The same was true for identical size fractions collected from different depths and stations transecting the front. Primary productivity was 20-fold greater on the cold water side, where >5 μm diatoms dominated the mixed layer and accounted for 80% of daytime productivity. Diatoms collected from the top and bottom of the upper mixed layer displayed nearly identical diurnal patterns in P max and alpha, with midday peaks exceeding predawn values by four-fold and two-fold respectively. Above the pycnocline, the 0.4 to 5 μm fraction had lower assimilation rates than the >5 μm fraction and smaller diurnal amplitudes in P max and/or alpha, with daytime patterns often characterized by two peaks interspersed by a short period of photoinhibition. Within the front, the 0.4 to 5 μm fraction accounted for two-thirds of plant biomass and >90% of primary production. Pigment analyses by high-performance liquid chromatography revealed enrichment in 19′-hexanoyloxyfucoxanthin, indicative of enhanced numbers of prymnesiophtes. Photosynthetic activity in confined surface communities was susceptible to daytime photoinhibition, but subsurface communities exhibited midday P max peaks that were three-to seven-fold predawn values. In the warm-water mass, both algal size fractions contributed equally to photosynthesis and chlorophyll a in surface waters, with the 0.4 to 5 μm fraction becoming dominant at the base of the euphotic zone. At all depths, peak P max of the 0.4 to 5 μm fraction occurred before noon, while P max of the >5 μm fraction was clearly evident in the afternoon. Elevated chlorophyll b-, 19′hexanoyloxyfucoxanthin- and zeaxanthin-to-chlorophyll a ratios indicated a mixture of algal groups, including chlorophytes, cyanobacteria and prymnesiophytes.

Optical characterization of primary productivity across a coastal front

Methods for the remote estimation of phytoplankton biomass and production rates using multiplatform sampling strategies are essential for the better understanding of oceanic bio-geochemical cycles. Recent advances in remote sensing of ocean color have made synoptic estimation of phytoplankton biomass attainable. While considerable success has been achieved in the estimation of plant biomass, the synoptic estimation of phytoplankton rates of production has been inadequate. Rapid shipboard estimates of the vertical distribution of primary productivity, on mesoscale spatial scales and event-time scales, are needed to provide both surface validation and data for the development of bio-optical models linking production to the optical characteristics of the water column. This study details the primary productivity and optical properties of a frontal region in July 1985 along 35°50′N in the Southern California Bight which is shown to be consistent with the concurrent high-performance liquid-chromatography pigment-analysis. We describe here a “quasi-synoptic” shipboard bio-optical sampling strategy across a frontal region as an example of time-corrected data for assessing phytoplankton production in highly variable ocean regions.

Estuary Plumes and Fronts in Shelf Waters: A Layer Model

Abstract A layer model that treats fronts as discontinuities is developed to study the steady state behavior of shallow estuary plumes on the continental shelf. The complete range of earth rotation effect is evaluated from small-scale or nonrotating plumes (Kelvin number equal zero) to large-scale, rotating plumes (Kelvin number equal order one). Supercritical flow is assumed in the outlet channel and the method of characteristics is used to compute the flow downstream. Nonrotating plumes have strong boundary fronts and concentrate their greatest layer depth and mass transport offshore near the front, but form no coastal current. Rotating plumes have boundary fronts that weaken soon after discharge, form a turning region where Coriolis action deflects the flow toward shore, and subsequently set up a coastal current. Soon after its formation this coastal current is bounded offshore by a strong front called the coastal front, across which the momentum balance changes from nearly inertial in the turning regi...

On the Effects of Coastline Perturbations on Coastal Currents and Fronts

Abstract Surface stress-driven coastal currents and upwelling were produced around the outer edge of a cylindrical tank having a conical bottom and a protuberance representing a cape. A large-standing wave formed at a distance Dsw ≈ 2Rcθ0.4*(λs/Rc)0.2 downstream of the cape, where Dsw is the distance between the wave trough and tip of the cape, Rc is the radius of the cape, and θ* = g′h0/u*fλs (where g′ = gδρ0 is the reduced gravity, h0 is the initial depth of the top layer, u* is the friction velocity applied to the top surface of the fluid, f is the Coriolis parameter and λs is the distance of the stationary position of the upwelling front at the surface from the wall of the tank). The extreme offshore extent of this stable wave trough (as seen from particle streaks) was Asw ≈ 3.4Rc. However, at low values of θ* after many rotation periods, the standing wave often grew in amplitude, producing a cyclone which detached from the wave trough. Unstable baroclinic waves formed at the upwelled front upstream o...

A Numerical Study of Appalachian Cold-Air Damming and Coastal Frontogenesis

The mesoscale structures of the wedge-shaped pressure ridge and the coastal front associated with the Appalachian ice storm of January 13-14, 1980 is analyzed using a mesoscale model. The characteristic features of the mesoscale model, which uses 15 vertical levels, 50-km grid length, and multilevel, boundary-layer parameterization, are described. The simulation of the surface layer winds and temperature, the evolution of the vertical temperature structure of the wedge-ridge region, and model simulations of the low-level jets and the coastal front are examined. Trajectories based on the 24-hr simulation of the winds are discussed.

Demographic Structure of Ceanothus Megacarpus Chaparral in the Long Absence of Fire

Wildfires have had a major influence on the struc? tural and functional adaptations that have evolved in species of mediterranean-type ecosystems. In Califor? nia chaparral, for example, shrubs regenerate after fires from basal sprouts or seed germination cued to the first postfire season. Certain species of Ceanothus and Arctostaphylos produce abundant seed throughout their lifespan, and the seeds lie dormant in the soil for many years until germination is stimulated by fire. These species do not resprout after fire, and thus are often referred to as obligate seeding shrubs. In the absence of fire, these species neither rejuvenate their canopy from basal sprouts as sprouting shrubs do, nor do they recruit new seedlings. The demographic patterns for one such species, Ce? anothus megacarpus Nutt. ssp. megacarpus, have been documented in studies by Schlesinger and Gill (1978, 1980). This shrub is distributed on the coastal front of the Coast Ranges from Santa Barbara County to San Diego County, often forming nearly pure, even-aged stands dating back to a previous fire. As with other obligate-seeding species, seedling populations are high in the first postfire year, but nil in later years. Mortality in the 1st yr is typically quite high. The causes of mor? tality probably include drought, predation, and com? petition from the dense herbaceous vegetation. After the 1st yr, mortality is relatively low during the first decade. However, as the shrub canopy closes in, Schle? singer and Gill (1978) found another sharp increase in mortality, and they attributed this stand-thinning to increased competition for water (Schlesinger and Gill 1980). After stand-thinning in the second decade, mortality in Ceanothus megacarpus was shown to level offonce again. Schlesinger and Gill's studies, however, did not extend much beyond the second decade. It is not known what happens after this time. Anecdotal observations in the literature suggest that after ?30-40 yr another sharp increase in mortality is to be expected due to stand senescence.

Analysis of biological and chemical associations near a turbid coastal front during winter 1982 : Wiseman, W.J. Jr., R.E. Turner, F.J. Kelly, L.J. Rouse Jr. and R.F. Shaw, 1986. Contr. mar. Sci. Univ. Texas, 29:141–151

Analysis of biological and chemical associations near a turbid coastal front during winter 1982 : Wiseman, W.J. Jr., R.E. Turner, F.J. Kelly, L.J. Rouse Jr. and R.F. Shaw, 1986. Contr. mar. Sci. Univ. Texas, 29:141–151

Mesoscale Structure in the Megalopolitan Snowstorm of 11–12 February 1983. Part III: A Large-Amplitude Gravity Wave

A large-amplitude singular gravity wave is studied through the analysis of hourly observations, radar and satellite data and observations of cloud to ground lightning flashes. The wave activity was initiated just ahead of, and to the left of the track of, the major Atlantic Coast cyclone of 11–12 February 1983. The initial wave of depression was followed by a wave of elevation and finally a wake depression. Pressure amplitudes were several millibars. The system propagated northeastward at 15 m s−1 accelerating to more than 25 m s−1 against increasing northeasterly flow in the lower troposphere. Surface northeasterlies increased and became gusty with the approach of the first pressure falls, reaching a maximum at the pressure trough, then abruptly weakening and backing as strong pressure increases were observed. Strong fluctuations in column total condensation rate and radar reflectivity occurred with the passage of the wave. Clustered lightning activity accompanied wave passage, principally near the intersection of the gravity wave and the east–west oriented escarpment of deep, high cloud along the north edge of the dry intrusion. A unique aspect was that lightning from clouds with relatively warm tops in the northern periphery of the dry intrusion lowered primarily positive charge to ground. Disorganized wave activity developed in the presence of modest midtropospheric convection and beneath a shear zone in advance of a propagating jet streak. The singular appearing large amplitude wave organized subsequently in a transient zone of strong frontogenetical forcing. The wave appeared as the northern extension of a coastal front. Overall, the system represented a ducted gravity wave propagating in a layer of large stability beneath an elevated layer of small Richardson number containing a critical level. Whether the accompanying convection and enhancement of condensation heating represented a forcing effect on the wave is unknown.

Measurements in the marine boundary layer near a coastal front

Measurements taken from aboard ship and from nearby fixed sites during a March 1985 research cruise near Cape Hatteras document some interesting boundary layer features of the coastal front which have been largely unexplored. The front, although commonly associated with the development of coastal cyclones is nevertheless shallow and often difficult to detect due to the scarcity of routinely available observations offshore.During the particular case described, the coastal front, undetected by routine analyses, divides air masses of quite different character. To the east of the surface wind shift line a warm, statically unstable boundary layer is associated with strong fluxes of latent heat from the sea surface. To the west, however, the boundary layer is cold and stable with negligible air‐sea heat exchange. A low‐level jet in the frontal zone carries the warm moist air westward toward eastern North Carolina. Subsequent moderate precipitation and cyclone passage may be associated with the frontal boundary.

A numerical simulation of the distribution of water temperature and salinity in the Seto Inland Sea

Constant flows, as well as oscillatory tidal flow, play an important role in the long-term dispersion of water in the Seto Inland Sea. Two kinds of numerical model (1-line and 2-line models) of the Seto Inland Sea have been developed to determine the role of density-induced currents, one type of the constant flow, in water dispersion in the Inland Sea. The seasonal variations of temperature, salinity and density fields are simulated and the density-induced current field is predicted at the same time. It is found that the most appropriate value of the longitudinal eddy diffusion coefficient,K x, is 5×106−7×106 cm2sec−1. The value of the overall mean dispersion coefficient is of the order of 107cm2sec−1 (Hayami and Unoki, 1970). Consequently, it is suggested that 50–70% of the total dispersion in the Seto Inland Sea can be attributed to currents other than density-induced currents,i.e., tidal currents, tide-induced currents and wind-driven currents. In winter, both density and velocity fields, calculated using the 1-line model, satisfy the conditions for the existence of a coastal front in Kii Channel and in the eastern Iyo-nada.

Thermal satellite imagery applied to a littoral macrobenthos investigation in the Gulf of Maine

Abstract The application of satellite imagery to oceanographic problems has grown in recent years. Its use in biological oceanography, however, has been largely limited to studies of primary productivity. The ability of thermal satellite imagery to identify coastal oceanic fronts suggests that there may be an application to macrobenthos investigations. This communication describes how thermal satellite imagery was applied to the study of sand-beach community distribution in the Gulf of Maine.