Equatorward Wind Research Articles

Flow around a coastal bend: A model of the Santa Barbara Channel eddy

A steady, equatorward wind stress is applied over a two‐layer ocean (infinitely deep lower layer) west of an otherwise straight meridional coast with a right‐angle bend. Initial (t ≈ 10 days) response consists of an equatorward current (Kelvin wave) that triggers a cyclone around the bend through viscous production and advection of vorticity, a process akin to eddy shedding in flows without rotation. The response at large times is governed by a Kelvin wave forced by the equatorward weakening of the (assumed positive) wind stress curl, which produces a poleward current near the coast. Application to the Santa Barbara Channel cyclone is discussed, and the cyclone‐formation process is further demonstrated with a three‐dimensional model with topography and stratification.

Ionospheric irregularities and storm-induced equatorial and high-latitude effects at the anomaly crest region

IEC information received through VHF RB measurements has been analyzed over the anomaly crest region of Guwahati (92° E, 26° N, 15° N geo.mag) along with a few low/low-mid latitude observations for understanding the roles of influx of plasma to anomaly crest regions, from equatorward and poleward processes during geomagnetically disturbed situations. The conditions leading to inflow of plasma to equatorial anomaly crest region or inhibition of such processes have been described in the paper through systematic analysis of disturbed day (free from sudden commencements) ionospheric electron content (IEC) variations at different temporal situtions. The storm-induced effects in relation to the development of the above conditions have also been examined for moderate and moderately severe isolated storm cases. Finally the paper deals with a few severe storms. The storm-triggered IEC features indicate inhibition or suppression of plasma dumping process at anomaly crests, through equatorial anomaly phenomenon. During winter and many equinoxial storms, the compression effect pushes this station away from the region where effective dumping of ionization from the equator is expected. Diffusion of plasma from the polar region to the crest area has also been observed through penetration of the eastward electric field during many disturbed situations. Depletion of noontime density during winter and equinoxial months and enhancement of the same during summer geomagnetically active situations are examined through anomaly compression (or inhibition) process as well as plasma replenishment through the equatorward wind.

Atmospheric humidity variations associated with westerly wind bursts during Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean Atmosphere Response Experiment (COARE)

Precipitable water determined from special sensor microwave/imager brightness temperatures is used to examine westerly wind bursts (WWBs) in the equatorial western Pacific. Six microwave satellite water vapor retrieval algorithms are tested for their performance in the tropics. The study of two major WWB events and several localized and short‐lived wind perturbations in the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) domain unveils the relationship between precipitable water field and anomalous wind regimes. WWBs are found to be accompanied by a drastic drop in the precipitable water amount. The decrease is partly explained by the transition between easterly and westerly wind regimes. A few days before the westerly wind is established, the transitional equatorward wind introduces the dry air from the subtropics. When the westerly wind eventually weakens, a transitional equatorward wind regime once again occurs and lasts for several days before the easterlies take over. The strongest WWB event during TOGA COARE is found to be consistent with midlatitude cold surge. This provides evidence for the midlatitude forcing of WWBs. While the interaction with higher latitudes explains the reduction in precipitable water in WWB events, it is not clear what region is responsible for feeding extra moisture to the western Pacific.

Seasonal variations of equatorial night-time thermospheric meridional winds

Using h'F data at two equatorial stations, night-time equatorial thermospheric meridional winds have been deduced for a period of two years to study their seasonal characteristics. It has been found that the thermospheric wind shows trans-equatorial flow from summer to winter hemisphere. During equinoxes the flow is mainly equatorward with a reversal to poleward direction around midnight hours. The abatement and reversal of equatorward wind which is weaker in summer compared to equinoxes is attributed to Midnight Temperature Maximum (MTM). The results of the present investigation are compared with those at other equatorial stations and also with the empirical model of Hedin et al. (1991).

A numerical study of the effects of wind forcing on the Chile Current System

A high-resolution, multi-level, primitive equation ocean model is used to examine the response of the coastal region from 22.5°S to 35°S of the Chile Current System to both equatorward and climatological wind forcing. The results from both types of forcing show that an equatorward surface current, a poleward undercurrent, upwelling, meanders, filaments and eddies develop in response to the predominant equatorward wind forcing. When climatological wind forcing is used, an offshore branch of the equatorward surface current is also generated. These features are consistent with available observations of the Chile Current System. The model results support the hypothesis that wind forcing is an important mechanism for generating currents, eddies and filaments in the Chile eastern boundary current system and in other eastern boundary current regions which have predominantly equatorward wind forcing.

Buoy observations of the atmosphere along the west coast of the United States, 1981–1990

The distribution of statistical properties of the meteorological and sea surface temperature fields along the west coast of the United States is described based on 10‐yearlong observations from buoys deployed by the National Data Buoy Center. The observations suggest that properties vary differently in each of three different regions along the coast: the Southern California Bight which remains sheltered from strong wind forcing throughout the year; the central and northern California coast up to Cape Mendocino, the site of persistent equatorward winds; and the Oregon‐Washington coast, where traveling cyclones and anticyclones produce vigorous and variable forcing. Over most of the region the variance in the wind speed is roughly equally divided between the annual cycle and the synoptic forcing, corresponding to periods between 5 and 50 cycles per year. Two seasons, summer and winter, are sufficient to describe the annual cycle. During the summer, two distinct wind speed maxima occur along the coast, one near Point Conception and the other off northern California, between Point Reyes and Point Arena. In the winter a single maximum occurs, located near Point Conception. The atmospheric pressure generally increases with latitude along the coast, but the annual cycle of atmospheric pressure has a different phase, depending on location; off the coast of California, highest pressures are found during the winter, while off Oregon and Washington, the highest pressures occur during the summer. Fluctuations in air and sea temperature are highly correlated, and the sea temperature is usually higher than the air temperature, in the winter. Examination of vertical soundings of the atmosphere at Oakland, Vandenberg Air Force Base and San Diego during the same period of time reveals that a well‐defined inversion separates the marine boundary layer (MBL) from the free atmosphere above nearly 90% of the time during the summer and half the time during the winter. Station soundings consistently overestimate the MBL thickness, but the results do suggest that the MBL is supercritical part of the time in the vicinity of the three sites. An attempt is made to examine the interannual variability and compare it to the Southern Oscillation index, although the results are limited because the record length is short compared with interannual timescales. Spatially averaged temperature anomalies increase during winter 1982–1983, coincident with the large El Niño event.

Wind-Related Features and Processes on Venus: Summary of Magellan Results

A search of Magellan synthetic aperture radar images covering ∼98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation with respect to local slope, and type of landform with which it is associated. In addition, streaks occurring in association with parabolic ejects deposits were designated type P streaks, which constitute about 31% of the data base. Wind streak azimuths were analyzed to assess wind patterns at the time of their formation. Both hemispheres show strong westward and equatorward trends in azimuths, consistent with Hadley circulation and inferred upper atmospheric westward zonal winds. When type P streaks (those considered to result from transient impact events) were removed, the westward component was greatly reduced, suggesting that the upper zonal winds do not extend to the surface. The presence of equator-oriented streaks at high latitudes suggests that Hadley circulation extends to the poles. A field of possible yardangs found southwest of Mead Crater strikes NE-SW and occupies plains situated in a shallow topographic depression. Analysis of non-type P streaks in the area suggests that equatorward winds are funneled through the depression and are responsible for the erosion of the terrain to form the yardangs. Dune deposits are limited on Venus. Two dune fields were identified (Aglonice and Fortuna-Meshkenet) which total in area about 18,300 Km 2. Microdunes are proposed for some southern hemisphere areas which show distinctive radar reflectivities. Bragg scattering and/or subpixel reflections from the leeward faces of microdune bedforms could account for the unusual radar backscatter cross sections.

Daytime F2-layer positive storm effect at middle and lower latitudes

Abstract. Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N2] absolute concentrations, while (N2/O)storm/(N2/O)quiet\\approx1 at F2-layer heights, are shown to contribute largely to the background NmF2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional NmF2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N2] concentrations.

Atmospheric Water Vapor Characteristics at 70°N

Using an extensive rawinsonde archive, characteristics of Arctic water vapor and its transports at 70°N are examined for the period 1974–1991. Monthly-mean profiles and vertically integrated values of specific humidity and meridional vapor fluxes are computed for land stations north of 65°N for the surface up to 300 mb using once to twice daily soundings. Mean values at 70°N for these and other variables, including temperature and meridional winds, are obtained through an objective analysis of the monthly station means. The annual zonal mean specific humidity at 70°N ranges from 2.4 g kg−1 at the surface to 0.02 g kg−1 at 300 mb. Zonal-mean precipitable water ranges from 2.9 mm in February and March to 16.2 mm in July. For all months, over 95% of water vapor is found below 500 mb. Although mean winds are equatorward up to about 400 mb, the tendency for poleward winds to transport more water vapor results in a poleward annual-mean flux at all levels except at the surface, peaking at 1.5 g kg−1 m s−1 at 850 mb. Whereas over 85% of the integrated zonal-mean meridional flux is found below 500 mb for all months, a smaller percentage is found at lower levels during summer due to stronger equatorward winds. The flux convergence across 70°N is positive in all months, peaking in September at an equivalent monthly water depth of 22.1 mm averaged over the region north of 70°N. Aerological estimates of precipitation minus evaporation (P - E) for the area north of 70°N that account for changes in water storage also peak in September (26.1 mm), with the annual total of 163 mm larger than previous estimates by up to 36%. Integrated vapor transports exhibit marked longitudinal variations, with maximum annual poleward transports of 16–25 kg s−1 m−1 found over the Norwegian Sea and Baffin Bay. The Canadian Arctic archipelago is the only sector where mean integrated transports are equatorward, ranging from 1 to 10 kg s−1 m−1 depending on longitude. The September peak in P - E results from a circulation shift yielding poleward fluxes along a broad zone from near the prime meridian to 15O°E.

The effect of oblateness and gravity darkening on the radiation driving in winds from rapidly rotating B stars

We calculate the radiative driving force for winds around rapidly rotating oblate B stars, and we estimate the impact these forces should have on the production of a wind compressed disk. The effects of limb darkening, gravity darkening, oblateness, and an arbitrary wind velocity field are included in the computation of vector 'oblate finite disk' (OFD) factors, which depend on both radius and colatitude in the wind. The impact of limb darkening alone, with or without rotation, can increase the mass loss by as much as 10% over values computed using the standard uniformly bright spherical finite disk factor. For rapidly rotating stars, limb darkening makes 'sub-stellar' gravity darkening the dominant effect in the radial and latitudinal OFD factors, and lessens the impact of gravity darkening at other visible latitudes (nearer to the oblate limb). Thus, the radial radiative driving is generally stronger over the poles and weaker over the equator, following the gravity darkening at these latitudes. The nonradial radiative driving is considerably smaller in magnitude than the radial component, but is directed both away from the equatorial plane and in a retrograde azimuthal direction, acting to decrease the effective stellar rotation velocity. These forces thus weaken the equatorward wind compression compared to wind models computed with nonrotating finite disk factors.

Daytime F2-layer positive storm effect at middle and lower latitudes

<strong class="journal-contentHeaderColor">Abstract.</strong> Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N₂] absolute concentrations, while (N₂/O)<i>_storm</i>/(N₂/O)<i>_quiet</i>\approx1 at F2-layer heights, are shown to contribute largely to the background N<i>_m</i>F2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional N<i>_m</i>F2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N₂] concentrations.

Mean thermospheric winds observed from Halley, Antarctica

Abstract. Thermospheric winds on a total of 237 nights have been studied for the effects due to geomagnetic activity, solar flux, and season. The observations have been made from 1988 to 1992 by a Fabry-Perot interferometer (FPI) operating at Halley (75.5°S, 26.6°W), Antarctica. This is the first statistical study of thermospheric winds near the southern auroral zone. The main factor affecting the wind velocities is the geomagnetic activity. Increases in activity cause an increase in the maximum equatorward wind, and cause the zonal wind in the evening to become more westward. Smaller changes in the mean wind occur with variations in season and solar flux. The small variation with solar flux is more akin to the situation found at mid-latitudes than at high latitudes. Since the geomagnetic latitude of Halley is only 61°, it suggests that the variability of the wind with solar flux may depend more on geomagnetic than geographic latitude. These observations are in good agreement with the empirical Horizontal Wind Model (HWM90). However, comparisons with predictions of the Vector Spherical Harmonic Model (VSH) show that for low geomagnetic activity the predicted phases of the two components of the wind closely resemble the observations but the modelled amplitudes are too small by a factor of two. At high geomagnetic activity the major differences are that modelled zonal velocity is too westward in the evening and too eastward after 04 UT. The modelled ion densities at the F-region peak are a factor of up to 9 too large, whilst the predicted mean value and diurnal variation of the altitude of the peak are significantly lower than those observed. It is suggested that these differences result from the ion loss rate being too low, and an inaccurate model of the magnetic field.

Response of the thermosphere and ionosphere to geomagnetic storms

Four numerical simulations have been performed, at equinox, using a coupled thermosphere‐ionosphere model, to illustrate the response of the upper atmosphere to geomagnetic storms. The storms are characterized by an increase in magnetospheric energy input at high latitude for a 12‐hour period; each storm commences at a different universal time (UT). The initial response at high latitude is that Joule heating raises the temperature of the upper thermosphere and ion drag drives high‐velocity neutral winds. The heat source drives a global wind surge, from both polar regions, which propagates to low latitudes and into the opposite hemisphere. The surge has the character of a large‐scale gravity wave with a phase speed of about 600 m s−1. Behind the surge a global circulation of magnitude 100 m s −1 is established at middle latitudes, indicating that the wave and the onset of global circulation are manifestations of the same phenomena. A dominant feature of the response is the penetration of the surge into the opposite hemisphere where it drives poleward winds for a few hours. The global wind surge has a preference for the night sector and for the longitude of the magnetic pole and therefore depends on the UT start time of the storm. A second phase of the meridional circulation develops after the wave interaction but is also restricted, in this case by the buildup of zonal winds via the Coriolis interaction. Conservation of angular momentum may limit the buildup of zonal wind in extreme cases. The divergent wind field drives upwelling and composition change on both height and pressure surfaces. The composition bulge responds to both the background and the storm‐induced horizontal winds; it does not simply rotate with Earth. During the storm the disturbance wind modulates the location of the bulge; during the recovery the background winds induce a diurnal variation in its position. Equatorward winds in sunlight produce positive ionospheric changes during the main driving phase of the storm. Negative ionospheric phases are caused by increases of molecular nitrogen in regions of sunlight, the strength of which depends on longitude and the local time of the sector during the storm input. Regions of positive phase in the ionosphere persist in the recovery period due to decreases in mean molecular mass in regions of previous downwelling. Ion density changes, expressed as a ratio of disturbed to quiet values, exhibit a diurnal variation that is driven by the location of the composition bulge; this variation explains the ac component of the local time variation of the observed negative storm phase.

The equatorial ionospheric anomaly in electron content from solar minimum to solar maximum for South East Asia

Abstract. Median hourly, electron content-latitude profiles obtained in South East Asia under solar minimum and maximum conditions have been used to establish seasonal and solar differences in the diurnal variations of the ionospheric equatorial anomaly (EIA). The seasonal changes have been mainly accounted for from a consideration of the daytime meridional wind, affecting the EIA diffusion of ionization from the magnetic equator down the magnetic field lines towards the crests. Depending upon the seasonal location of the subsolar point in relation to the magnetic equator diffusion rates were increased or decreased. This led to crest asymmetries at the solstices with (1) the winter crest enhanced in the morning (increased diffusion rate) and (2) the same crest decaying most rapidly in the late afternoon (faster recombination rate at lower ionospheric levels). Such asymmetries were also observed, to a lesser extent, at the equinoxes since the magnetic equator (located at about 9°N lat) does not coincide with the geographic equator. Another factor affecting the magnitude of a particular electron content crest was the proximity of the subsolar point, since this increased the local ionization production rate. Enhancements of the EIA took place around sunset, mainly during the equinoxes and more frequently at solar maximum, and also there was evidence of apparent EIA crest resurgences around 0300 LST for all seasons at solar maximum. The latter are thought to be associated with the commonly observed, post-midnight, ionization enhancements at midlatitudes, ionization being transported to low latitudes by an equatorward wind. The ratio increases in crest peak electron contents from solar minimum to maximum of 2.7 at the equinoxes, 2.0 at the northern summer solstice and 1.7 at northern winter solstice can be explained, only partly, by increases in the magnitude of the eastward electric field E overhead the magnetic equator affecting the [E×B] vertical drifts. The most important factor is the corresponding increase in ionization production rate due to the increase in solar radiation flux. The EIA crest asymmetries observed at solar maximum were less significant, and this is probably due to the corresponding increase in ionization densities leading to an increase of the retarding effect of ion-drag on the daytime meridional winds.

Hydrographic variability off the Rías Baixas (NW Spain) during the upwelling season

During the Galicia X cruise, from May to October 1989 an intensive collection of hydrographic data was carried out at a single station on the shelf off the western coast of Galicia. It allows us to follow the response of the water column to the intermittent equatorward wind stress during the upwelling season. Upwelling events occur with biweekly periodicity, bringing Eastern North Atlantic Water (ENAW) to the subsurface layer at our station. A trend of the thermohaline properties of the upwelled water to increase in time was observed. This seems to be mostly due to the southwestward displacement of the origin of this water mass during the year. Although the saltier and warmer ENAW is less nutrient‐rich, nutrient levels increase because of the rapid remineralization of organic matter from the Rías, which takes place in the bottom water on the shelf.

The Leeuwin Current south of Western Australia

Satellite images as well as data collected in situ were used to follow the seasonal changes of the Leeuwin Current south of Western Australia (WA) in 1986-87. The current has two major sources: salty subtropical water from west of WA, and fresher tropical water from north of WA. In summer, the tropical waters are excluded by the strong equatorward wind stress. In autumn and winter, this wind stress is reduced and tropical waters flood southward to dominate the flow. Nevertheless, salty subtropical water is entrained en route, and so, whatever the season, the Leeuwin Current is more saline than the 'local' subantarctic waters off southern WA. From a research vessel, observations were made on the current and one of its offshoots in June 1987. The Leeuwin Current had a maximum surface speed of more than 1 m s-1 just beyond the shelf edge. Its warm, low-salinity surface core rode on a sheath of higher-salinity subtropical water that it had entrained upstream. The first survey of the offshoot showed it to be 50 km across and 130 m deep (for water warmer than 17�C), and it extended 200 km seaward (as deduced from a satellite image). Velocities in the offshoot ranged up to 1 m s-1 southward and 1 m s-1 north-eastward on the western and eastern sides, respectively. Richardson numbers were, in places, as low as 0.25. On a second survey two days later, the offshoot was found to have pinched off and the remnant bulge on the edge of the parent stream to have moved 30 km eastward. The flow around this bulge reached 1.6 m s-'. The offshoot/bulge was possibly first formed in April, and it kept its identity at least until August. During this time, it moved eastward at speeds between 2 and 15 km day-1. In June, the offshoot was estimated to contain water equivalent to five days' transport of the parent current.

Observations of the geostrophic current and water mass characteristics off Point Sur, California, from May 1988 through November 1989

The Point Sur transect (POST) has been occupied 6–8 times per year since 1988 to resolve the flow in the California Current system at seasonal and interannual time scales. The POST extends offshore, normal to bottom topography, along 36°20′N, to 123°01.7′W where it doglegs southwest along the California Cooperative Fisheries Investigation (CalCOFI) line 67. Hydrographic observations from seven cruises over 2 years have been used to study variations of alongshore geostrophic velocities and water mass characteristics within these time scales. The California Undercurrent was a prominent feature in six of the seven sections analyzed and was very weak during a period of strong equatorward wind stress. The position of the undercurrent core varied from 12 to 42 km from shore while its strength varied from less than 5 cm s−1 to 35 cm s−1, with the maximum flow occurring in winter. The undercurrent (core) over the continental slope was found from 70 to 460 m depth throughout these seven cruises. The nature of the alongshore geostrophic velocities and the location and spatial extent of the California Undercurrent appear strongly related to specific wind events, both local and remote. Remote wind forcing from the south was believed to cause anomalous, strong poleward flow throughout the entire water column above 1000 dbar during a period of local equatorward wind stress.

A numerical study of wind stress curl effects on eddies and filaments off the northwest coast of the Iberian Peninsula

A high-resolution, multi-level, primitive equation ocean model is used to examine the response to the particular conditions of anticyclonic (negative) wind stress curl and equatorward (upwelling favorable) winds along the eastern ocean boundary off the northwest coast of the Iberian Peninsula in the vicinity of the highly productive rias. A band of steady equatorward winds, which are uniform alongshore but contain zonal variability (i.e., anticyclonic wind stress curl), results in an equatorward coastal surface current nearshore and a poleward surface current offshore. In time, the currents become unstable and lead to the development of anticyclonic warm core eddies. In addition, cold core filament formation occurs in areas where the anticyclones advect the upwelled coastal water offshore. The results from the experiments support the hypothesis that wind forcing, particularly the combination of anticyclonic (negative) wind stress curl and equatorward (upwelling favorable) winds, is an important mechanism for generating opposing alongshore surface currents, anticyclonic eddies, and filaments off the northwest coast of the Iberian Peninsula. In a sensitivity study, the results from three numerical experiments are examined to understand, in a limited way, the dependence of the generation of the surface currents on the boundary conditions (free slip and no slip), the use of wind band forcing and the imposed wind stress curl distribution. Results show that, regardless of whether free-slip or no-slip boundary conditions or wind band forcing are used, opposing alongshore surface currents are generated. Because such currents do not develop when there is no wind stress curl, the opposing currents are generated by the anticyclonic wind stress curl.

How the effects of winds and electric fields in F2-layer storms vary with latitude and longitude: A theoretical study

The effects of thermospheric winds and electric fields on the ionospheric F2-layer are controlled by the geometry of the magnetic field, and so vary with latitude and longitude. We adopt a simple model of the daytime F2-layer and study the effects at midlatitudes (25°–65° geographic) of three processes that accompany geomagnetic storms: (i) thermospheric changes due to auroral heating; (ii) equatorward winds that tend to cancel the quiet-day poleward winds; and (iii) the penetration of magnetospheric electric fields. At ± 65°, the effects of heating and electric fields are strongest in the longitudes towards which the geomagnetic dipole is tilted, i.e. the North American and the South Indian Ocean sectors. Because of the proximity of the geomagnetic equator to the East Asian and South American sectors, the reverse is true at ± 25°.

Coastal upwelling in the modern ocean

Abstract During the past decade several major physical oceanographical experiments were performed over the continental margins along the ocean’s eastern boundaries. The studies extended farther seaward than the continental shelf and extended over the seasons. As a result, our understanding of the processes and phenomena associated with coastal upwelling and affecting the ocean farther seaward has increased. The Coastal Ocean Dynamics Experiment investigated the dynamics controlling the currents over a continental shelf exposed to strong upwelling favourable winds; the experiment was more intensive and completely instrumented than any previous shelf experiment. The Coastal Transition Zone experiment investigated the cool ‘filaments’ conspicuous in satellite images of SST off northern California during the coastal upwelling seasons. Associated with the cool filaments are jets along the boundary between the cooler recently upwelled water and the warmer adjacent ocean water; as the jets meander equatorward and offshore (several hundred km), the upwelled water extends over greater distances offshore than previously thought likely. One experiment (SuperCODE) looked at the large alongshore scale, from 35°N to 50°N off the west coast of north America, defined the seasonal cycle, and found that the tendency for subsurface poleward flow over the continental shelf and slope increased at lower latitudes in spite of the increased equatorward mean wind. The ubiquitous poleward currents, usually subsurface over the inner slope and outer shelf, have been observed in all the experiments off the west coasts of the Americas, in spite of equatorward winds. Unlike the jets of the coastal transition zone, the poleward undercurrents are trapped to the continental slope and shelf. The Leeuwin Current Interdisciplinary Experiment took place off Western Australia, the only major eastern boundary without coastal upwelling in spite of strong equatorward winds. The alongshore pressure gradient along the west coast of Australia is large, perhaps because of the free connection to the western Pacific, and dominates the opposing equatorward wind stress, suppressing upwelling and causing poleward flow (the Leeuwin Current) at the surface over the slope and outer shelf.