443 research outputs found
Large-scale SST anomalies associated with subtropical fronts in the western North Atlantic during FASINEX
We describe the large-scale variability of sea surface temperature (Ts) and fronts in the western North Atlantic Subtropical Convergence Zone from January–June 1986 within an approximately 11° longitude by 10° latitude domain. Fronts were primarily found within interconnected bands separated by \u3c500 km that tended to be located on the periphery of anisotropic Ts spatial anomaly features that propagated westward at about 3 km day–1. Relatively weak and strong (small or large |∇Ts|) segments of the dominant zonally-oriented frontal band (the Subtropical Frontal Zone, or SFZ) shifted westward with these anomaly features, which had characteristic peak-to-peak space scales of up to ≈800 km in the minor axis direction (NW-SE) and time scales of up to ≈275 days, both larger than the scales of mesoscale eddies observed during earlier experiments. Both the main and seasonal thermoclines tended to be elevated (depressed) by several tens of meters beneath cold (warm) anomaly features, suggesting that the influence of eddies on Ts and fronts extends to larger space and longer time scales than those resolved in earlier studies. Because of the very limited spatial and temporal coverage of available subsurface data, however, this relationship could not be verified conclusively. Properties of the anomaly features were consistent with the dispersion of lowest-mode internal Rossby waves, and they were apparently not generated or significantly influenced by wind-driven Ekman transport. A much longer data set, including altimetry and subsurface data, will be required to verify that eddies influence Ts and fronts at these large scales, and if so, to determine the physical processes behind this influence
Large-Scale SST Variability in the Western North Atlantic Subtropical Convergence Zone during FASINEX. Part II: Upper Ocean Heat Balance and Frontogenesis
We analyzed the influence of wind-deriven horizontal heat advection on the large-scale [O(1000) km wavelength] variability of both the upper-ocean mixed-layer heat content and the subtropical frontal zone (SFZ) within an 11° by 10° domain in the western North Atlantic Ocean during FASINEX (January through June 1986). By estimating heat advection due to both Ekman transport and interior geostrophic (Sverdrup minus Ekman) transport from a slab mixed layer heat balance equation using satellite-derived sea surface temperature (Ts) and wind analysis maps, it was found that these processes could not account for the observed variability in either beat content or the SFZ. The annual cycle of surface vertical heat flux had the dominant influence on the heat content. Even when the average heat balance was analyzed during a 4-month time interval when the net influence of the annual cycle was nearly zero (mid-January to mid-May 1986), westward-propagating Ts spatial anomaly features with peak-to-peak scales of several hundred kilometers apparently had the dominant influence on heat content. The influence of Ekman transport appeared to become marginally detectable only when terms in the heat equation were zonally averaged across the entire analysis domain, apparently reducing the influence of the propagating anomaly features. Ekman transport did act to maintain the SFZ during the 4-month interval, and thus may have been ultimately responsible for its existence, but the large-amplitude variability in heat content and the SFZ driven by other processes made this impossible to prove conclusively in the FASINEX region
Westward-propagating SST Anomalies and Baroclinic Eddies in the Sargasso Sea
Previous studies have documented the existence of a zonal band of strong, persistent, westward-propagating sea surface temperature (Ts) anomalies with zonal wavelengths of ≈800 km and periods of ≈200 days that are confined to the subtropical convergence zone (STCZ, roughly 26°–32°N). Two years of satellite-derived sea surface temperature (Ts) and sea surface elevation anomaly (η) maps of the Sargasso Sea (22.5°–33.5°N, 71.5°–59.5°W) are analyzed to determine how these anomalies are forced and why they an confined to the STCZ. A simple anomaly model forced by horizontal eddy currents and damped by a linear feedback mechanism explains many properties of the anomaly response. At wavelengths exceeding several hundred kilometers, forcing by horizontal eddy currents becomes less important relative to atmospheric forcing with increasing wavelength. The anomalies are confined to the STCZ partly because the large mean Ts gradient there enables the horizontal eddy currents to be relatively effective at forcing anomalies. Also, the eddies that force these anomalies, wavelike features with wavelengths of ∼800 km and periods of ∼200 days, are themselves confined to the STCZ. These wavelike eddies were not detecting during earlier experiments such as MODE because the domains within which they were conducted were too small. Within the STCZ, zonal dispersion properties of the eddy field are consistent with baroclinic Rossby wave variability. To the north and south of the STCZ, however, zonal dispersion properties differ substantially from the properties observed within the STCZ. The eddy dispersion properties change abruptly across transition zones 1–2 degree wide centered at 32.5° and 25.5°N. A simple linearized reduced-gravity model is used to demonstrate that interaction between eddies and zonal mean currents can qualitatively account for the change is dispersion properties south of the STCZ, but not to the north within the Gulf Stream recirculation region
Westward-propagating SST Anomaly Features in the Sargasso Sea, 1982–88
Sea surface temperature (Ts) maps of the region from 59.5° to 75.5°W, 22.5° to 33.5°N containing the western North Atlantic Subtropical Convergence Zone (STCZ) were derived from AVHRR/2 images. The 7- year mean annual cycle was removed and the maps were filtered in space and time to represent anomaly variability with wavelengths ≥ 220 km and periods ≥ 50 days. Warm and cold anomaly features were observed cast of 71°W between 26° and 32°N that propagated westward at 3–4 km day−1 and that occasionally exceeded ±1°C in amplitude. They are generally strong and persistent from fall to spring and are only marginally detectable during summer. During 1981–82, 1982–83, and 1985–86, individual features could be followed through the entire fall-spring interval. During 1983–84,1986–87,and 1987–88,they could typically be followed for 2–4 months, and during 1984–85, for only 1–2 months. The features were anisotropic during all fall-spring intervals except 1986–87, and they had characteristic wavelengths of ∼800 km in the minor axis direction and periods of ∼200 days. Local forcing by synoptic atmospheric variability alone could not amount for the existence of these features. Anomaly features propagated westward in a manner consistent with theoretical zonal dispersion properties of first-mode baroclinic Rossby waves, suggesting that the anomalies may be coupled to a field of wavelike eddies. Since the anomalies were confined to the zonal hand of large mean meridional Ts gradients associated with the STCZ, where meridional eddy currents are relatively effective at forcing anomalies these eddy currents could be largely responsible for their existence. In one case, however, the influence of eddies an vertical heat flux at the mixed layer base appeared to be important. The relatively strong and persistent 1985–86 anomaly features appeared during a several-day interval at the onset of relatively stormy fall weather and (presumably) rapid mixed-layer deepening
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The Code large-scale meteorological, sea surface temperature, and coastal sea level data set, 1980-84
Meteorological, sea surface temperature, and coastal sea level data were collected along the west coast of North America from northern Baja California to the Alaska/British Columbia border from 1980 to mid-1984 for the large-scale component of the Coastal Ocean Dynamics Experiment (CODE). This report presents statistical summaries and plots of selected meteorological
variables, sea surface temperature, and coastal sea level from this data set
Descriptive oceanography during the Frontal Air‐Sea Interaction Experiment: Medium‐ to large‐scale variability
Medium‐ and large‐scale oceanographic variability in the Sargasso Sea is examined during the Frontal Air‐Sea Interaction Experiment (FASINEX), focusing primarily on processes that influence the formation of subtropical fronts. From Fall to Spring the mean meridional gradient of meridional Ekman transport in the Subtropical Convergence Zone (STCZ) enhances the meridional sea surface temperature (Ts) gradients between 26° and 32°N. In the presence of this enhanced mean gradient, baroclinic eddies with zonal wavelengths of ≈800 km and periods of ≈200 days exert the dominant influence on the formation of subtropical fronts at medium and large scales. These eddies generate westward propagating Ts anomaly features with the same dominant wavelengths and periods. They are confined between 26° and 32°N and have amplitudes that occasionally exceed ±1°C. Ts fronts tend to be found within bands ≈200 km wide that roughly follow the periphery of these anomaly features. Deformation in the horizontal eddy current field is primarily responsible for the existence of these frontal bands. The migration of the strong front originally bracketed by the FASINEX moored array was related to the westward propagation of the larger‐scale eddy/anomaly/frontal‐band pattern. The moored array was located within a warm‐anomaly feature during most of the experiment, which produced exceptionally warm conditions in the upper ocean. These anomalies are confined between 26° and 32°N, not only because the relatively large seasonal mean Tsy there allows horizontal eddy currents to force strong anomalies, but also because the baroclinic eddies with wavelengths of ≈800 km and periods of ≈200 days are confined to the STCZ. Large meridional variability exists in many properties of the eddy field, much of which can be traced to the influence of the Sargasso Sea mean current field on eddy variability
CODE-1 : moored array and large-scale data report
The Coastal Ocean Dynamics Experiment
(CODE) was undertaken to identify and study
the important dynamical processes which
govern the wind-driven motion of coastal
water over the continental shelf. The
initial effort in this multi-year, multi-institutional
research program was to obtain
high-quality data sets of all the
relevant physical variables needed to construct
accurate kinematic and dynamic descriptions
of the response of shelf water
to strong wind forcing in the 2 to 10 day
band. A series of two small-scale, densely-instrumented
field experiments of approximately
four months duration (called CODE-1
and CODE-2) were designed to explore and
to determine the kinematics and momentum
and heat balances of the local wind-driven
flow over a region of the northern California shelf which is characterized by both
relatively simple bottom topography and
large wind stress events in both winter
and summer. A more lightly instrumented,
long-term, large-scale component was designed
to help separate the local wind-driven
response in the region of the small-scale
experiments from motions generated either offshore by the California Current
system or in some distant region along the
coast, and also to help determine the seasonal
cycles of the atmospheric forcing,
water structure, and coastal currents over
the northern California shelf.
The first small-scale experiment
(CODE-1) was conducted between April and
August, 1981 as a pilot study in which
primary emphasis was placed on characterizing
the wind-driven "signal" and the
"noise" from which this signal must be
extracted. In particular, CODE-1 was
designed to identify the key features of
the circulation and its variability over
the northern California shelf and to
determine the important time and length
scales of the wind-driven response. This
report presents a basic description of the
moored array data and some other Eulerian
data collected during CODE-1. A brief
description of the CODE-1 field program is
presented first, followed by a description
of the common data analysis procedures used
to produce the various data sets presented
here. Then basic descriptions of the following
data sets are presented: (a) the
coastal and moored meteorological measurements,
(b) the moored current measurements,
(c) the moored temperature and conductivity
observations, (d) the bottom pressure measurements,
and (e) the wind and adjusted
coastal sea level observations obtained as
part of the CODE-1 large-scale component.Prepared for the National Science
Foundation under Grant OCE 80-14941
CODE-2 : moored array and large-scale data report
The Coastal Ocean Dynamics Experiment
(CODE) was undertaken to identify and study
the important dynamical processes which
govern the wind-driven motion of coastal
water over the continental shelf. The
initial effort in this multi-year, multi-institutional
research program was to obtain
high-quality data sets of all the
relevant physical variables needed to construct
accurate kinematic and dynamic descriptions
of the response of shelf water
to strong wind forcing in the 2 to 10 day
band. A series of two small-scale, densely-
instrumented field experiments of approximately
four months duration (called CODE-1
and CODE-2) were designed to explore and
to determine the kinematics and momentum
and heat balances of the local wind-driven
flow over a region of the northern California
shelf which is characterized by both
relatively simple bottom topography and
large wind stress events in both winter
and summer. A more lightly instrumented,
long -term, large-scale component was
designed to help separate the local wind-driven
response in the region of the small-scale
experiments from motions generated
either offshore by the California Current
system or in some distant region along the
coast, and also to help determine the seasonal
cycles of the atmospheric forcing,
water structure, and coastal currents over
the northern California shelf.
The first small-scale experiment
(CODE-1) was conducted between April and
August, 1981 as a pilot study in "which
primary emphasis was placed on characterizing
the wind-driven "signal" and the
"noise" from which this signal must be
extracted. In particular, CODE-1 was
designed to identify the key features of
the circulation and its variability over
the northern California shelf and to
determine the important time and length
scales of the wind-driven response. The
second small-scale experiment (CODE-2) was
conducted between April and August, 1982
and was designed to sample more carefully
the mesoscale horizonta1 variability
observed in CODE-1. This report presents a
basic description of the moored array data
and some other Eulerian data collected
during CODE-2. A brief description of the
CODE-2 field program is presented first,
followed by a description of the common
data analysis procedures used to produce
the various data sets presented here. Then
basic descriptions of the following data
sets are presented: (a) the coastal and
moored meteorological measurements, (b)
the moored current measurements, (c) array
plots of the surface wind stress and near-surface
current measurements, (d) the
moored temperature and conductivity observations,
(e) the bottom pressure measurements,
and (f) the wind and adjusted
coastal sea level observations obtained as
part of the CODE-2 large-scale component.This work has
been supported by the National Science
Foundation
The Representation of an Action: Tragedy between Kant and Hegel
Hegel's theory of tragedy has polarized critics. In the past, many philosophers have claimed that Hegel's theory of tragedy removes Kant's critical insights and returns to pre-critical metaphysics. More recently, several have argued that Hegel does not break faith with tragic experience but allows philosophy to be transformed by tragedy. In this paper I examine the strength of this revised position. First I show that it identifies Hegel's insightful critique of Kant's theoretical assumptions. Yet I then argue that it fails to note the practical importance of Kant's separation of knowledge and aesthetics. I propose an alternative approach to tragedy that builds from the revised view and yet maintains the autonomy of aesthetics. Tragedy represents an action, a set of events that are internally unified and yet cannot be reduced to theory. This is to say that tragedy confronts us with an aesthetic sphere of making and doing that, while constrained, is incessantly open and free
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