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In 1976, a pilot experiment, called first Equatorial Mooring (EQUA-1), tested an innovative technique for anchoring a taut-line surface mooring at 0°, 150°W where the water depth is 4.5 km. The 36-day deployment contained a wind recorder and fixed-level current meters at 50 and 100 m in the Equatorial Undercurrent (EUC). The following year, in a second pilot experiment, named EQUA-2, a similar mooring was deployed at 0°, 125°W for 99 days. EQUA-2, with current meters at 10, 50, 100, 150, and 200 m, recorded a surge in EUC transport during April 1977 when 3-day-averaged eastward current speeds at 50-m depth reached 2 m s−1. The associated eastward transport per unit meridional width over the 50–200-m layer was 190 m2 s−1. Based on observations recorded in April 1980, the EQUA-2 pulse would correspond to a total EUC transport surge of about 38 Sv (1 Sv ≡ 106 m3 s−1) and would represent an equatorially trapped first-mode baroclinic Kelvin wave. This paper describes EQUA Project observations and why and how I created the high-risk-of-failure opportunity to record pioneering time series measurements at the equator. The enduring legacy of the EQUA Project is the sustained maintenance of in situ surface wind and upper-ocean current and temperature measurements at numerous sites in the equatorial oceans, starting in the Pacific to improve forecasts of the El Niño and La Niña phenomenon. For example, the 40-yr records of surface wind and upper-ocean current and temperature measurements at 0°, 110°W and 0°, 140°W are some of oceanography’s longest time series recorded far from land.

The impact of data assimilation on the transports of eastward-flowing Equatorial Undercurrent (EUC) and North Equatorial Countercurrent (NECC) in the Pacific Ocean from 145°E to 95°W during 2004–05 and 2009–11 was assessed. Two Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2), solutions were analyzed: one with data assimilation and one without. Assimilated data included satellite observations of sea surface temperature and ocean surface topography, in which the sampling patterns were approximately uniform over the 5 years, and in situ measurements of subsurface salinity and temperature profiles, in which the sampling patterns varied considerably in space and time throughout the 5 years. Velocity measurements were not assimilated. The impact of data assimilation was considered significant when the difference between the transports computed with and without data assimilation was greater than 5.5 × 106 m3 s−1 (or 5.5 Sv; 1 Sv ≡ 106 m3 s−1) for the EUC and greater than 5.0 Sv for the NECC. In addition, the difference of annual-mean transports computed from 3-day-averaged data was statistically significant at the 95% level. The impact of data assimilation ranged from no impact to very substantial impact when data assimilation increased the EUC transport and decreased the NECC transport. The study’s EUC results had some correspondence with other studies and no simple agreement or disagreement pattern emerged among all studies of the impact of data assimilation. No comparable study of the impact of data assimilation on the NECC has been made.

Interannual variations of the Somali Jet in the Arabian Sea during 1988-99 were linked to El Nino and La Nina episodes and to India west coast rainfall.

The European Center for Medium-Range Weather Forecasts (ECMWF) and Institut Francais Pour la Recherche et 1'Exploitation de la Mer (IFREMER) European Remote-Sensing Satellite (ERS-1), named IFR2, surface wind velocity data products are compared during July 1995 over the Arabian Sea.

Although the distribution of sunshine is symmetrical about the equator, the earth's climate is not. Climatic asymmetries are prominent in the eastern tropical Pacific and Atlantic Oceans where the regions of maximum sea surface temperature, convective cloud cover, and rainfall are north of the equator. This is the result of two sets of factors: interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry, and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located. 'The Ocean-atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions. The thermocline happens to shoal in the eastern equatorial Pacific and Atlantic, but not in the eastern Indian Ocean, because easterly trade winds prevail over the tropical Atlantic and Pacific wher...

The origin of the Tropical Oceans-Global Atmosphere (TOGA) Program was closely related to the response of global atmospheric circulation to sea surface temperature variations in the tropical Pacific Ocean, which is evident by the El Nino phenomenon. During the two decades before the 1985 start of TOGA, advancements in scientific understanding of the tropical ocean and global atmosphere and advancements in technology provided strong foundations for TOGA. By the early 1980s, research had demonstrated a strong linkage between tropical SST variations and global atmospheric circulation, and discussions of an international ocean-atmosphere program had begun. Probably the single most important event leading to the creation of TOGA was the unannounced arrival in 1982 of the largest El Nino in a century.

Monthly mean, 2.5 deg - x 2.5 deg-resolution, 10-m height wind speeds from the Special Sensor Microwave Imager (SSMI) instrument and the European Center for Medium-Range Weather Forecasts (ECMWF) forecast-analysis system are compared between 60 deg S and 60 deg N during 1988-1991. The SSMI data were uniformly processed while numerous changes were made to the ECMWF forecast-analysis system. The SSMI measurements, which were compared with moored-buoy wind observations, were considered to be a reference data set to evaluate the influence of the changes made to the ECMWF system upon the ECMWF surface wind speed over the ocean. A demonstrable yearly decrease of the difference between SSMI and ECMWF wind speeds occurred in the 10 deg S - 10 deg N region, including the 5 deg S - 5 deg N zone of the Pacific Ocean, where nearly all of the variations occurred in the 160 deg E - 160 deg W region. The apparent improvement of the ECMWF wind speed occurred at the same time as the yearly decrease of the equatorial Pacific SSMI wind speed, which was associated with the natural transition from La Nina to El Nino conditions. In the 10 deg S - 10 deg N tropical Atlantic, the ECMWF wind speed had a 4-year trend, which was not expected nor was it duplicated with the SSMI data. No yearly trend was found in the difference between SSMI and ECMWF surface wind speeds in middle latitudes of the northern and southern hemispheres. The magnitude of the differences between SSMI and ECMWF was 0.4 m s^(-1) or 100 percent larger in the northern than in the southern hemisphere extratropics. In two areas (Arabian Sea and North Atlantic Ocean) where ECMWF and SSMI wind speeds were compared to ship measurements, the ship data had much better agreement with the ECMWF analyses compared to SSMI data. In the 10 deg S - 10 deg N area the difference between monthly standard deviations of the daily wind speeds dropped significantly from 1988 to 1989, but remained constant at about 30 percent for the remaining years. y.

Simulations with the UCLA atmospheric general circulation model (AGCM) using two different global sea surface temperature (SST) datasets for January 1979 are compared. One of these datasets is based on Comprehensive Ocean-Atmosphere Data Set (COADS) (SSTs) at locations where there are ship reports, and climatology elsewhere; the other is derived from measurements by instruments onboard NOAA satellites. In the former dataset (COADS SST), data are concentrated along shipping routes in the Northern Hemisphere; in the latter dataset High Resolution Infrared Sounder (HIRS SST), data cover the global domain. Ensembles of five 30-day mean fields are obtained from integrations performed in the perpetual-January mode. The results are presented as anomalies, that is, departures of each ensemble mean from that produced in a control simulation with climatological SSTs. Large differences are found between the anomalies obtained using COADS and HIRS SSTs, even in the Northern Hemisphere where the datasets are most similar to each other. The internal variability of the circulation in the control simulation and the simulated atmospheric response to anomalous forcings appear to be linked in that the pattern of geopotential height anomalies obtained using COADS SSTs resembles the first empirical orthogonal function (EOF 1) in the control simulation. The corresponding pattern obtained using HIRS SSTs is substantially different and somewhat resembles EOF 2 in the sector from central North America to central Asia. To gain insight into the reasons for these results, three additional simulations are carried out with SST anomalies confined to regions where COADS SSTs are substantially warmer than HIRS SSTs. The regions correspond to warm pools in the northwest and northeast Pacific, and the northwest Atlantic. These warm pools tend to produce positive geopotential height anomalies in the northeastern part of the corresponding oceans. Both warm pools in the Pacific produce large-scale circulation anomalies with a pattern that resembles that obtained using COADS SSTs as well as EOF 1 of the control simulation; the warm pool in the Atlantic does not. These results suggest that the differences obtained with COADS SSTs and HIRS SSTs are mostly due to the differences in the datasets over the northern Pacific. There was a blocking episode near Greenland in late January 1979. Both simulations with warm SST anomalies over the northwest and northeast Pacific show a tendency toward increased incidence of North Atlantic blocking; the simulation with warm SST anomalies over the northwest Atlantic shows a tendency toward decreased incidence. These results suggest that features in both SST datasets that do not have a counterpart in the other dataset contribute signficantly to the differences between the simulated and observed fields. The results of this study imply that uncertainties in current SST distributions for the world oceans can be as important as the SST anomalies themselves in terms of their impact on the atmospheric circulation. Caution should be exercised, therefore, when linking anomalous circulation and SST patterns, especially in long-range prediction.

The upper-ocean temperature distribution along the Pacific equator from 139 to 103 deg W was observed in January 1992 with temperature profiles recorded from a ship and inferred from an ocean general circulation model calculation involving data assimilation (i.e., hindcast). An El Nino episode was in progress. The l00-m-thick mixed layer depth, the mixed-layer temperature, and the depth-averaged temperature below the thermocline were similar in both data products. Considerable differences occurred in the representation of the 15-25 C thermocline, such as the depth-averaged temperatures above and below the 20 C isotherm, the east-west slope of the 20 C isotherm, and a 1000-km-wide depression. The longitudinal-averaged root-mean-square difference between the hindcast and observed depths of the center of the thermocline was 17 m. Most of the disparities could be attributed to a high wavenumber transient event that the model-based assimilation system was not intended to resolve.

Measurements of wind at 5 m height, currents at 7.6, 15.4. 21.4 and 27.5 m depths, and temperature at 19 depths between 0.4 and 43.3 m depths were made from 19 August to 12 September 1974 at 8°41′N, 23°10′W (Site E3 of the GATE C-scale Oceanographic Experiment). In the uppermost 30 m where the temperature was isothermal to within 0.1°C m−1, the 24-day mean wind-driven trans-port represented ∼20% of the total transport and the geostrophic transport was 80%. Time variations of the current records were dominated by near-inertial period and semidiurnal tidal period motions with rms amplitudes of 0.05-0.08 m s−1 and 0.05 m s−1, respectively. Throughout the frequency range the currents were coherent with zero phase difference between 7.6 and 27.5 M. Several squalls occurred in which the wind stress was greater than 0.1 N m−2 and the temperature records did not indicate entrainment of cold water into the mixed layer from the upper thermo-cline. The upper pycnocline was very strongly stratified. The vigo...

Depth-averaged current shears computed from shipboard acoustic Doppler current profiler (ADCP) and moored Savonius rotor and vane vector-averaging current meter (VACM) measurements are compared at 35, 62.5, 100 and 140 m depths within 7 km of each other near 0 deg, 140 deg W during a 12-day interval in November 1984. The agreement between the VACM and ADCP shears was excellent. The average root-mean-square difference of hourly shear values was small, approximately 0.0021/s, and the average correlation coefficient was 0.90. Spectral estimates were equivalent to within a 95 percent significance level and the VACM and ADCP shears were 95 percent statistically coherent with zero phase difference for frequencies below 0.2 cycles per hour.

Measurements of winds, currents and temperature are used to describe the response of the upper ocean in the northeast Pacific to the passage of an August 1971 synoptic-scale meteorological disturbance. The experiment was designed so that at the beginning of the 32-day study the uppermost two current meters were located in the upper isothermal layer, a third current meter was placed at the top of the seasonal thermocline, and the fourth current meter was located near the bottom of the seasonal thermocline. Thermistors attached to a multi-conductor cable were placed in the mixed layer and in the thermocline region. Before the onset of the storm the thickness of the mixed layer was about 15 m. The storm produced a more homogeneous temperature distribution above 20 m with a lower average temperature, higher temperature values below 20 m, and a thicker (25 m) mixed layer. The heat content of the upper layer changed little (

Measurements from a Savonius rotor and vane vector-averaging current meter (VACM) and dual orthogonal propeller vector-measuring current meter (VMCM) placed 1 m apart beneath a surface-following buoy moored on the Pacific equator for 6-month intervals are described. Experiments at 13, 98, 120 and 160 m depths were completed in light winds (≈5 m s−1), small surface wave heights (1–2 m), strong current speeds (monthly averaged speeds ≈65 cm s−1) and large current shears (0.0 1 s−1). Excellent coherence was found between each VACM-VMCM doublet's data. As expected, the near-surface VACM recorded slightly larger speeds (≈10% for monthly mean 15-min vector-averaged values) than the VMCM. The only kinetic energy density mismatch at the 95% confidence level was between the 13-14 m dyad and occurred above 1.3 cph. The most striking feature of them intercomparison tests was that the VACM and VMCM observations were virtually identical below the new-surface layer. Below 98 m the average rms amplitude differe...

The vertical structure of low frequency velocity and temperature variability in the eastern equatorial Pacific Ocean is examined using surface and subsurface moored current meter data from 0°, 110°W between 20 and 3027 m depths over the period 30 March 1980 to 2 February 1981. Three methods of analysis are employed: vertical coherence, empirical orthogonal functions, and linear least-squares dynamical mode decompositions. Direct evidence is given for the existence of first baroclinic mode Kelvin waves in the east component of velocity and vertical displacement (estimated from temperature) in that the vertical displacement is coherent and in phase over the water column and the upper-ocean east component of velocity varies out of phase with the vertical displacement over the water column. Near-surface modifications due to advection, nonadiabatic processes, and local forcing are also noted.

This paper describes the temporal and spatial variations of the wind stress (computed from the square of the wind velocity vector) and wind-stress curl recorded during July and August 1973 at two moored buoy stations, one 13 km and the other 120 km from the Oregon coast, along 45°15′N. Some facets of the relationship between wind stress and the physical oceanography over the continental shelf off 0regon are discussed.

Data obtained at a time-series station during intense coastal upwelling off Oregon were applied to a model of heat conservation for the upper 8 m, and a thermal eddy diffusivity (horizontal) of 300 M2s−1 was computed. Horizontal advection and horizontal diffusion both appeared to be more important than surface heat exchange in producing changes in heat content. Hourly changes in heat content were quite large, and it appears that advection and diffusion varied appreciably in conjunction with changing tidal currents.

Moored buoy wind measurements were made at 15 min intervals at 3.5 m height at 6, 7 and 8°N along 150°W in the central equatorial Pacific from November 1977 to March 1978. During November, December and January the Intertropical Convergence Zone occurred near 8, 7 and 6°N, respectively, indicating a southward movement of ∼3 km day−1. The east and north spectra of each record did not contain any significant (at the 95% confidence level) peaks and the spectral estimates decreased with increasing frequency with a slope of about −1.5. Wind fluctuations at frequencies

Prominent oscillations of the meridional current, with a mean period of approximately 20 days, have been observed in the upper ocean over several years from May 1979 to October 1985 using moored current measurements along the Pacific equator at 95°, 110°, 124°,140°W and 152°W, as well as off (but near) the equator at 110° and 140°W. The fluctuations are relatively narrowband (±0.005 cpd) in frequency. A 95% statistically significant peak in power spectra of meridional current occurred at 110°, 124° and 140°W, but not at 95° and 152°W where the spectral peaks were smaller. The dominant wave period decreased by about 4% from 110° to 140°W. Maximum amplitude was measured at 124°W; the amplitude above 80 m was maximum at the equator and decreased poleward from the equator. At 15 m the annual averaged root-mean-square amplitude was about 20.5 cm s−1, and individual peak-to-trough values reached 150 cm s−1. The wave amplitude decreased with depth and the wave was essentially confined to the upper 80 m....

Moored buoy wind measurements made at 3 m height at three sites (8°27′N, 150°45′W; 0°, 150°W; 0°, 125°W) in the central equatorial Pacific during 1976 and 1977 were compared with satellite-derived low-level (∼1 km) cloud motion vectors within a 5° square centered on each buoy site. The satellite winds were determined on a routine basis by NOAA's National Environmental Satellite Service and the buoy wind measurements were made by NOAA's Pacific Marine Environmental Laboratory. To compare satellite and buoy wind measurements, 3 h vector averages of the buoy data were computed at times of satellite wind observations. The number of pairs of buoy winds and winds derived from infrared satellite imagery was 265. Directions of the low-level cloud motion vectors were similar to the buoy wind directions. The average satellite wind speed was 8.0 m s−1, which was 3.3 m s−1 or 70% greater than the average buoy wind speed. At the 0°, 125°W site where 190 satellite-buoy wind pairs were obtained, the average win...

Upper-ocean current and temperature records from neat 0°, 110°W are compared with Galapagos Island sea level measurements (0°3′S, 91°28′W) for the period March 1980 to July 1981. Low-frequency (periods greater than 30 days) near surface zonal currents (20 and 50 m) were well correlated with local wind, but deeper currents (100 and 150 m) and sea level were not. Response to the local wind was studied in terms of linear dynamics. Periods where zonal acceleration was in phase with zonal wind stress were found; however, overall these two series were uncorrelated. The direct relation of low-frequency wind stress and surface current (rather than acceleration) suggests a quasi equilibrium response on these time scales. The response at deeper levels was investigated by comparing the zonal transport per unit width (vertically averaged zonal Velocity) in the upper 200 m with sea level. These series were significantly correlated (with 95% confidence) at a lag of 10.5 d indicating eastward phase propagation ...

Measurements of winds and of near-surface temperatures and currents made during March and April 1974 on the continental shelf off northwest Africa were extremely time-dependent. Alternating land and sea breezes were well-developed and produced temperature and current fluctuations in the uppermost 15 m. Time-averaged speed of the surface current (28 an s−1) was much larger than the geostrophic current computed from the density field over the shelf. Approximately 60% of the variance of the current measurements occurred at frequencies less than the inertial period. Inertial and tidal period currents were large. Water stratification was very weak and tidal internal gravity wave motions were not detected. During a coastal upwelling event the Ekman transport, the offshore transport and the onshore transport were nearly equivalent, and the vertical eddy viscosity coefficient over the upper 10 m was about 125 cm2 s−1.

The heat budget of a small region (∼2 km×2 km) near the coast of northwest Africa was investigated during a 3-day period in March 1974 when light winds (∼2 m s−1) occurred. Horizontal advection and diffusion of heat were negligible, and the local change in heat content resulted from the net radiative and evaporative flux at the sea surface. Diurnal heating produced surface temperature ranges of 0.9, 1.1 and 1.4°C for each of the 3 days. The exponential decrease of the diurnal heat wave with depth was used to estimate the vertical eddy thermal conductivity of the upper 10 m; values of approximately 10−3 m−2 s−1 were obtained.

Moored surface wind measurements were recorded along the Pacific equator at 140, 124, 110, and 95 deg W during portions of 1980-1985. Minimum record length is one year. The annual mean and monthly mean westward speeds at 110 deg W were about 1.5 m/s higher during the year preceding the 1982-1983 El Nino than in the year following this event. The annual cycle, which moved westward at about 0.8 m/s, consisted of weak westward and northward speeds in February-April and vice versa in September-October. The spectral slope between 5-day and 0.05-day periods was -1.5. The rms amplitude of the 95-percent statistically significant diurnal period oscillation was 0.3 m/s, and the meridional component was nearly twice as large as the zonal component. The diurnal period wave was coherent (at the 95-percent confidence level) between 95 and 124 deg W, with westward phase propagation of about 138 m/s. No statistically significant spectral peak was found in the 40- to 50-day intraseasonal period band. The surface zonal ocean current component, which reached approximately 0.5 and -0.5 m/s in April and October, respectively at 110 deg W, influenced the surface wind stress computed from the quadratic bulk aerodynamic formulation by 10-20 percent.

In this paper, yearlong in situ wind measurements at a 3.8-m height, obtained at three sites along the Pacific equator (95, 110, and 152 deg W), were used to estimate the number of random observations required per month for monthly mean wind speeds accurate to 1.0 m/s and 0.5 m/s. Wind measurements were made with a vector-averaging wind recorder mounted on a surface-following toroid float, which measured speed continuously, and direction nearly continuously. For equatorial Pacific winds in the 95 to 152 deg W region, the typical numbers of random wind observations required per month were found to be about nine for a 1.0 m/s accuracy, and 35 for a 0.5 m/s accuracy. The corresponding number of ship winds would likely be greater. The number of random observations required increased westward and was highly correlated with monthly mean standard deviations.