TOGA Coupled Ocean-Atmosphere Response Experiment Research Articles

Horizontal Structure of the Upper Ocean Velocity and Density Fields in the Western Equatorial Pacific Warm Pool: Depth Range from 20 to 250 m*

Abstract Wavenumber spectra of velocity and density fields in the western equatorial Pacific warm pool on scales 6–120 km are estimated using the shipboard survey data collected during the TOGA Coupled Ocean–Atmosphere Response Experiment (COARE). The spectra are averaged over three depth intervals: 20–60, 60–110, and 110–250 m (corresponding to the Yoshida jet, the South Equatorial Current, and the southern edge of Equatorial Undercurrent). The velocity spectra are corrected for the mean flow shear advection, which is important under conditions of low gradient Richardson number (Ri). After that, both velocity and density spectra are consistent with an internal wave spectral model including a random component (equatorial version of the Garrett and Munk spectrum) and a tidal component (the Feng et al. tidal model). Tidal peaks, previously found by other COARE investigators as being prominent on the “moored” spectra (i.e., on the spectra derived from mooring data), appear to be much less significant on the ...

An Ensemble of Convective Systems on 11 February 1993 during TOGA COARE:Morphology, Rainfall Characteristics, and Anvil Cloud Interactions

Abstract An active day during the Coupled Ocean–Atmosphere Response Experiment (COARE) Intensive Observation Period (IOP) is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the Intensive Flux Array (IFA) within westerly wind burst conditions. The detailed genesis, morphology, and interactions between these cloud systems are documented from a radar and satellite perspective. One of these systems was a large and complex elliptical cluster, among the largest observed during the Tropical Ocean Global Atmosphere COARE. Multiple, parallel deep convective lines spaced 20–30 km apart and embedded within this system were initially oriented from north-northwest to south-southeast, oblique to the storm motion. Furthermore, the lines underwent counterclockwise realignment as the system moved eastward. The influence of strong lower-tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic,...

Subgrid Surface Fluxes in Fair Weather Conditions during TOGA COARE: Observational Estimates and Parameterization

Abstract Bulk aerodynamic formulas are applied to meteorological data from low-altitude aircraft flights to obtain observational estimates of the subgrid enhancement of momentum, sensible heat, and latent heat exchange at the atmospheric–oceanic boundary in light wind, fair weather conditions during TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment). Here, subgrid enhancement refers to the contributions of unresolved disturbances to the grid-box average fluxes at the lower boundary of an atmospheric general circulation model. The observed subgrid fluxes increase with grid-box area, reaching 11%, 9%, 24%, and 12% of the total sensible heat, latent heat, scalar wind stress, and vector wind stress magnitude, respectively, at a grid-box size of 2° × 2° longitude and latitude. Consistent with previous observational and modeling studies over the open ocean, most of the subgrid flux is explained by unresolved directional variability in the near-surface wind field. The auth...

Radiative Heating Errors in Naturally Ventilated Air Temperature Measurements Made from Buoys*

Abstract Solar radiative heating errors in buoy-mounted, naturally ventilated air temperature sensors are examined. Data from sensors with multiplate radiation shields and collocated, fan-aspirated air temperature sensors from three buoy deployments during TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment) and the Arabian Sea Mixed Layer Dynamics Experiment are used to describe the errors in the naturally ventilated measurements. The naturally ventilated sensors have mean daytime errors of 0.27°C and maximum instantaneous errors of 3.4°C. The errors are at times larger than the difference between the air and sea surface temperatures. These errors lead to mean daytime biases in sensible and latent heat fluxes of 1–4 W m−2 and instantaneous errors up to 22 W m−2. The heating errors increase with increasing shortwave radiation and diminish with increasing wind speed. The radiative heating is also found to be a function of sun elevation with maximum heating errors occur...

Observation of large diurnal warming events in the near-surface layer of the western equatorial Pacific warm pool

Because of the relatively calm winds which prevail over the western Pacific warm pool, the diurnal cycle of temperature in the near-surface layer of the ocean is often quite pronounced. During the TOGA Coupled Ocean-Atmosphere Response Experiment (COARE), very high resolution measurements of near-surface thermohaline and turbulence structures were made using bowmounted probes and a free-rising profiler. Experimental data demonstrate a strong dependence of near-surface thermal structure on weather conditions, In calm weather, SST was observed to exceed 33.25°C; this was associated with a diurnal warming of more than 3°C in the top I m of the ocean. A 1-D model of transilient type reproduces the diurnal cycle at low wind speeds and the evening deepening of the diurnal thermocline. Precipitation influenced the diurnal cycle by trapping heat in the near-surface region. During daytime evaporation, surface salinity increased slightly, but deep convection was inhibited by the strong vertical temperature gradient. Contour plots calculated using observations from bow sensors “scanning” the upper meters of the ocean due to ship's pitching in some cases revealed strong horizontal variability of the shallow diurnal thermocline with amplitude ∼ 2°C on scales of 0.2–6 km.

Surface Buoyancy Forcing and the Mixed Layer of the Western Pacific Warm Pool: Observations and 1D Model Results

The broad, shallow body of warm (>29°C) water found in the western tropical Pacific Ocean plays an important role in the coupled ocean-atmosphere dynamics and thermodynamics associated with the El Niño-Southern Oscillation phenomenon. Thus, it is important to understand the processes that maintain and perturb that warm pool. Measurements from a buoy moored in the center of the warm pool during the TOGA Coupled Ocean-Atmosphere Response Experiment show that the exchange of mass between the ocean and atmosphere is as important as the exchange of heat. Rain forms a shallow, buoyant layer that does not mix with the water below except during infrequent strong wind events. Using a one-dimensional mixed layer model, it is demonstrated that the rate of local precipitation governs the mixed layer depth and can thus alter the rates of change in sea surface temperature during both warming and cooling periods. The observed mixed layer depth in the warm pool is at a depth that allows for maximum warming by capturing a significant portion of the shortwave radiation, but is shallow enough to avoid entrainment cooling. Either increased rain rates or reduced wind forcing yields a shallow mixed layer, which may be associated with cooling of the sea surface temperature in spite of a net positive heat flux at the sea surface because penetrating shortwave radiation is lost across the base of the shallow, fresh mixed layer. Decreased rain rates or increased wind forcing can turn on entrainment cooling of the surface mixed layer.

Scale Dependence of Air-Sea Fluxes over the Western Equatorial Pacific

Abstract The goal of this study is to examine the horizontal scale dependence of vertical eddy flux in the tropical marine surface boundary layer and how this scale dependence of flux relates to the bulk aerodynamic relationship and the parameterization of subgrid-scale flux. The fluxes of heat, moisture, and momentum are computed from data collected from 27 NCAR Electra flight legs in TOGA COARE (The Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment) with flight elevations lower than 40 m and flight runs longer than 60 km. The dependence of the fluxes on two length scales are studied: the cutoff length scale, defining the averaging length over which mean components are obtained in order to partition field variables into mean and perturbation components; and the flux averaging length scale, defining the length over which products of perturbations are averaged in order to estimate vertical fluxes. Based on the characteristics of the scale dependence of fluxes, the total flux of ...

Surface Meteorology and Air-Sea Fluxes in the Western Equatorial Pacific Warm Pool during the TOGA Coupled Ocean-Atmosphere Response Experiment

Abstract A major goal of the Coupled Ocean-Atmosphere Response Experiment (COARE) was to achieve significantly more accurate and complete descriptions of the surface meteorology and air-sea fluxes in the western equatorial warm pool region. Time series of near-surface meteorology from a buoy moored near the center of the COARE Intensive Flux Array (IFA) are described here. The accuracies of the measurements and the derived fluxes are quantified; agreement between average net heat fluxes at the buoy and two nearby research ships is better than 10 W m−2 during three intercomparisons. Variability in the surface meteorology and fluxes associated with westerly wind bursts, periods of low winds, and short-lived, deep convective events characteristic of the region was large compared to the 4-month means. The ECMWF (European Centre for Medium-Range Weather Forecasts) analysis and prediction fields differed most from the buoy data during periods of short-lived, deep convective events, when several day averages of ...

Cloud-to-Ground Lightning Observations from TOGA COARE: Selected Results and Lightning Location Algorithms

Abstract Recently, observations of electrified oceanic convection and associated cloud-to-ground (CG) lightning were obtained over the tropical western Pacific Ocean during TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment). During COARE, observations of convection were made using a variety of instrument platforms including ship and airborne Doppler radars, an advanced lightning direction finder (ALDF) network, and a shipborne inverted electric field mill. This study focuses on data collected by the COARE ALDF network, fusion of those data with observations, and the methods used to calculate accurate CG return stroke locations. Analysis of CG lightning data and Doppler radar data indicates that lightning-producing oceanic convection is characterized by deep, vertically developed convective cells with radar reflectivities exceeding 30-dBZ above the height of the −10°C level. In several cases a peak in CG frequency occurred coincident with the descent of precipitation...

TOGA COARE Aircraft Mission Summary Images: An Electronic Atlas

An electronic atlas of research aircraft missions in TOGA COARE (Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment) has been prepared and is available on the Internet via WorldWide Web browsers such as Mosaic. These maps are in the form of time sequences of color imagery assembled using the NCAR Zebra software. Initial versions of these maps were prepared in the field at the TOGA COARE Honiara Operations Center to aid in the evaluation of each aircraft mission immediately after it was flown. The maps prepared in the field have been updated, corrected, and remapped at standard scales and with common color schemes. They show the meteorological setting of sampling by all seven aircraft participating in TOGA COARE - the two NOAA WP-3D aircraft, the NCAR Electra, the FIAMS C-340, the UK C-130, and the NASA DC-8 and ER-2 - by overlaying flight tracks, GMS satellite infrared data, and NOAA WP-3D airborne radar images. The map sequences are combined with text of scientists` notes and other background information on the research flights to form a summary of each aircraft mission. The resulting aircraft mission summaries are intended as a road map to the COARE aircraft dataset. They indicate where andmore » when data were collected and the meteorological context for those data. As an electronic document, the atlas of aircraft mission summaries is available on demand, and it is dynamic: as further information becomes available, the mission summaries will continue to be added to and updated as appropriate, and new release will be issued periodically. 9 refs., 9 figs.« less

The large-scale context for the TOGA Coupled Ocean-Atmosphere Response Experiment

The TOGA Coupled Ocean-Atmosphere Response Experiment (COARE) concentrated a variety of observational systems in the warm pool of the western equatorial Pacific for an Intensive Observation Period (IOP) November 1992 through February 1993. In this paper, aspects of the largescale variations of the tropical atmosphere and Pacific Ocean surrounding the observations of air-sea interaction in the Intensive Flux Array (IFA) during the IOP are described, with the objective of providing a context for the future analyses of these observations.

Satellite Observations during TOGA COARE: Large-Scale Descriptive Overview

Abstract The 1992/93 Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (COARE) was specifically designed to monitor multiscale interactions between the atmosphere and ocean over the western Pacific warm pool. To help meet this objective, satellite observations were used to augment the enhanced COARE conventional data array in both space and time. In this paper the authors present a descriptive overview of convective cloud variability and sea surface temperature during the four-month intensive observational period (IOP) as revealed by satellite. Time series of Geostationary Meteorological Satellite infrared brightness temperatures are evaluated at selected equatorial locations in the western Pacific and eastern Indian Oceans. Intraseasonal modes of transient convection/cloudiness are revealed, with two eastward-propagating Madden-Julian oscillations identified. Spectral analysis on the time series data indicates that higher-frequency variations in regional convective activity ar...

TOGA COARE takes to the field

Field research for a 4‐month multinational study of the interactions between the tropical ocean and the global atmosphere will begin on November 1. The massive Coupled Ocean‐Atmosphere Response Experiment (COARE) will involve over 700 scientists and support staff from 19 nations. “An experiment on this scale that couples meteorology and oceanography has not taken place for about 20 years,” said Roger Lukas of the University of Hawaii, Honolulu, chief scientist on the R/V Wecoma, which will be taking towed ocean temperatures, salinity, and velocity measurements for the project.