Climatic Data Oceanic Observations

CLIMATIC OCEANIC OBSERVATIONS are marine meteorological and deep ocean observations that are performed for a long time (at least over a few decades) using specialized oceanographic vessels, volunteer merchant ships, buoy arrays, floats, and drifters. Marine meteorological observations are performed over a few centuries. Voluntary observations by merchant ships (volunteer observing systems, or VOS) report most of these data. Standard marine meteorological observations include sea-level pressure, air and sea-surface temperatures, humidity, cloudiness, velocity, and direction of wind.

Marine meteorological observations have been collected and generalized in the Comprehensive Ocean-Atmosphere Data Sets (COADS). However, the differences in instruments and observation techniques, and construction and size of various ships, reduce the compatibility of different data for analysis of climate variability and change. One of the most comprehensive analyses of this problem has been done at the CLIMAR 99 WMO workshop.

Between 1948 and 1984, the Ocean Weather Station (OWS) network operated in the North Atlantic and Pacific Oceans. The principal goal of this network was to get oceanic meteorological and aero-logical data for improvement of the weather forecast in North America, Europe, the North Atlantic Ocean, and the Pacific Ocean. At the same time, OWS performed deep-ocean hydrographic casts and soundings. This network provided long-term and compatible deep-ocean time series of temperature and salinity, and aerological data on wind, pressure, temperature, and humidity within air columns up to about 19 mi. (30 km.). The OWS network initially consisted of 13 stations in the North Atlantic and nine stations in the Pacific. After 1973 (when a world economic crisis occurred), funding was cut off, and in 1984 (soon after beginning of the satellite era in meteorology), OWS observations ceased (with the exception of one Norwegian station in the North Atlantic that is still in operation).

Deep-sea hydrographic observations have been performed since 1872. Pre-1970s hydrographic casts were performed using Nansen bottles, and were the main source of deep-sea hydrographic data. Then, the expandable bathythermograph (XBT) and conductivity-temperature-depth (CTD) soundings replaced the Nansen bottles' measurements. However, the routine oceanographic observations are too sparse and noisy for the reliable detection of low-frequency (long-term) changes of the oceanic fields in the deep ocean (below 2,625 ft. [800 m.]), except near a few standard oceanographic sections and some specific regions with strong oceanographic activity.

Long-term buoy arrays have been deployed in a few key regions of the world's oceans, such as the tropical Pacific and Atlantic, since early 1990s. The Tropical Ocean-Global Atmosphere-Tropical Atmosphere Ocean (TOGA-TAO) and Pilot Research Moored Array in the Tropical Atlantic (PIRATA) mooring networks are in operation. They perform marine meteorological observations and subsurface oceanographic measurement in approximately the first 984 ft. (300 m.), and regularly transmit information to the satellite.

The Rapid Climate Change (RAPID) mooring array has monitored the meridional circulation in the North Atlantic along 26.5 degrees N since March of 2004. First results published by Stuart Cunningham, et al., showed that meridional overturning could be observed with errors smaller than 1.5 Sv (one Sv equals a flow of ocean water of 106 cu. m. per second). This shows the beginning of thermohaline catastro-phy (which occurs when meridional overturning in the North Atlantic Ocean shuts down) at the early stage and superimposed high-magnitude interannual variability of meridional circulation.

Surface and subsurface drifters are numerous and effective tools for long-term monitoring, as shown, for instance, by David Fratantoni. They are based on a Lagrange principle of current measurement. Since the late 1980s, they have been the principal source of global data on ocean circulation. Now, ARGO technology is used as a key element of the Global Ocean Observing System (GOOS). This is a subsurface drifter that typically drifts at 1-1.25 mi. (1.5-2 km.) in depth, floats to the surface every 10 days, registers the profiles of temperature and salinity, transmits its information to the satellite, and then sinks back into the depths. The lifetime of each ARGO float is about two to four years. At the moment, there are about 3,000 ARGO floats on the world's oceans. This provides a density of observa tions of about one float per 776 sq. mi. (300 sq. km.) of water surface all over the globe.

SEE ALSO: Climatic Data, Sea Floor Records; Meridional Overturning Circulation; Ocean Component of Models; Oceanic Changes; Thermohaline Circulation.

BIBLIOGRApHY. Stuart Cunningham, et al., "Temporal Variability of the Atlantic Meridional Overturning Circulation at 26.5°N," Science (v.317/5840, 2007); David Fratantoni, "North Atlantic Surface Circulation during the 1990s Observed with Satellite-Tracked Drifters," Journal of Geophysical Research (v.106/C10, 2001); Joint WMO/IOC Commission for Oceanography and Marine Meteorology, WMO TD-N 1062, JCOMM technical report (n.10, 2003); Alexander Polonsky, Role of the Ocean in the Climate Change (Naukova Dumka, 2007); Proceedings of CLIMAR 99 WMO Workshop on Advances in Marine Climatology (Vancouver, Canada, September 8-15, 1999).

Alexander Boris Polonsky Marine Hydrophysical Institute, Sevastopol

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