An Introduction to Atmospheric and Oceanographic Datasets

7. ATMOSPHERE-OCEAN COMPOSITION

Some important atmosphere/ocean constituents include:

• Water vapor (i.e., the gaseous phase of water) is a very important greenhouse gas because it strongly absorbs outgoing long-wave radiation and, of course, is essential to life itself. Atmospheric water vapor is very important in large-scale thermally driven circulations due to the release of latent heat when the water vapor condenses. Specific (or relative) humidity is a variable commonly (but poorly) observed by both conventional observations (Chapter 3) and satellites (Chapter 5) and is available on analyzed grids (Chapter 6). The distribution of water vapor is known to within (+- 20%).

• Ozone is present in abundance between 10 and 40 kilometers above the earth's surface. This region of the stratosphere contains about 90% of the world's ozone. One reason for the importance of ozone is that it absorbs dangerous ultraviolet (UV) radiation from the sun. In fact, ozone absorbs nearly all solar radiation between 0.2 and 0.3 um. Decreases in ozone in the upper atmosphere (e.g., ``the ozone hole''; possibly induced by humans) allow more ultra-violet radiation to reach the surface of the earth which could alter the chemistry of the troposphere and expose plants, animals and humans to dangerous side-effects. Additionally, variations in ozone amounts, which are very sensitive to variations in solar radiation, affect the distribution of temperature and wind in the stratosphere, which could affect the dynamical interactions between the stratosphere and troposphere.

• It is also an important component of smog near the surface and some communities have occasional `ozone alerts'.

• Observational records from both Mauna Loa (Hawaii) and the South Pole indicate that the amount of carbon dioxide in the atmosphere has been steadily increasing. Much of this increase is due to the burning of fossil fuels. Carbon dioxide plays an important role in greenhouse warming scenarios because it absorbs outgoing long-wave radiation and, thereby, warms the lower atmosphere.

• Salinity is a measure of the total dissolved salts in sea water. Combined sodium and chloride make up about 85% of the principal ionic constituents in sea water. Although salinity varies throughout the ocean, the relative proportion of constituents remains very nearly constant, with the exception of ocean water directly impacted by river runoff. This relationship is important and is exploited by instruments designed to determine salinity. Salinity has a major influence on the physical properties of sea water. Ocean water density is determined by temperature and salinity; and density variations affect water flow (ocean currents) much in the same way atmospheric density variations cause wind. Some other properties that are influenced by variations in salinity are: the freezing point of sea water, the speed of sound, electrical conductivity, and specific heat capacity.

• The distribution of oceanic dissolved nutrients and oxygen strongly influences the distribution of biological ecosystems in the marine environment. The primary nutrients are nitrate, nitrite, phosphate, and silicate. The many complex relationships between biological activities and nutrient distribution are beyond the scope of this report. Beyond biological considerations, the variations in large scale nutrient distributions are used as tracers to infer general ocean circulation.

• There are several minor oceanic constituents that have recently become of interest as scientists attempt to answer climate change and global warming questions. For example, knowing the distribution and changes in distribution of co₂ and n₂0 are important to understanding the carbon cycle and human impacts from burning fossil fuel. Even very minor ocean trace elements such as strontium and uranium that have been embedded in marine corals over millenia are used to detect changing environmental conditions in the distant past, giving a perspective for the observed changes that have occurred in the recent decades.

WMO's Global Atmospheric Watch : The GAW program is the principal permanent operational program for monitoring the evolution of the chemical composition of the atmosphere on global and local scales.

WCRP's Stratospheric Processes and their Role in Climate : The SPARC project will make ground-based and vertical profile measurements of physical parameters in the stratosphere as well as aerosols and chemical species of fundamental importance to determine stratospheric change.

IGBP's International Global Atmospheric Chemistry Program : The IGAC makes measurements of chemical processes in the troposphere, particularly those related to the oxidizing capacity of the atmosphere.

WMO's International Global Aerosol Program : IGAP will make observations of the optical properties related to aerosols to determine the impact of aerosols on climate.

The Carbon Dioxide Information Analysis Center (CDIAC) has archives containing greenhouse gas data and operates as a World Data Center for Atmospheric Trace Gases. (See Appendix A for details on contacting CDIAC.)