RICARDO RAMOS, LT, National Oceanic and Atmospheric Administration, Corps of Commissioned Officers, Boulder, Colorado 80303
JAMES PETERSON, Climate Monitoring and Diagnostics Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado 80303
The National Oceanic and Atmospheric Administration (NOAA) has had a continuous presence at the South Pole since 1971. NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL), based in Boulder, Colorado, has established and now maintains four baseline observatories in remote locations around the world: Point Barrow, Alaska; Mauna Loa, Hawaii; Cape Matatula, American Samoa; and Amundsen-Scott South Pole Station, Antarctica. CMDL conducts research related to atmospheric constituents that are capable of forcing change in the climate of Earth through modification of the atmospheric radiative environment, and those that may cause depletion of the global ozone layer. CMDL accomplishes this goal primarily through long-term measurements of key atmospheric species such as carbon dioxide (CO2), carbon monoxide, methane, nitrous oxide, surface and stratospheric ozone, halogenated compounds including CFC replacements, aerosols, and solar and infrared radiation at the baseline observatories and through cooperative measurements at other sites spanning the globe. Through these measurements, CMDL documents global changes in those species important for climate forcing and depletion of the ozone layer, identifying sources, sinks, and interannual variability. Mark Boland, LT, NOAA Corps (Officer-In-Charge) and Glen McConville (Electronics Technician) operated the CMDL program at South Pole during the 1996-1997 season.
Special conditions at the South Pole make it an ideal location for monitoring the composition and behavior of the atmosphere.
A brief summary of the CMDL program during the 1996-1997 season follows.
Carbon dioxide is measured continuously using a nondispersive infrared analyzer. Atmospheric CO2 concentrations continue to increase globally. The long-term record from South Pole, presented in figure 1, shows a growth rate of approximately 1.4 parts per million per year (Hofmann, Peterson, and Rosson 1996).
We are using two electron-capture gas chromatographs to make continuous measurements of various halocompounds, and as a complement to this, steel flasks are pressurized with outside ambient air and are then sent to Boulder for analysis.
Our research has shown that the rate of growth of chloro-fluorocarbons (CFCs) is decreasing and that their concentrations should reach maximum levels in the stratosphere within the next several years (see figure 2). It is anticipated that the ozone layer will then begin a slow recovery, which, barring any noncompliance with the Montreal Protocol, will be readily detectable by the year 2050 (Hofmann 1996).
Surface ozone is measured using the Dasibi ozone monitor. Stratospheric ozone is measured using two different instruments. The Dobson spectrophotometer measures total column ozone, and high-altitude balloons are used to determine the atmospheric ozone profile. Ozone measurements at the South Pole go back to 1961 when the first Dobson spectrophotometer measurements were made and, thus, provide an ongoing 35-year record.
Figure 3 shows the ozonesonde profile from the 8 October 1997 flight as compared to a preantarctic-ozone-hole profile from 7 August 1997. This profile clearly shows the near total destruction of ozone in the 14- to 20-kilometer altitude region of the stratosphere. This depletion is typical of the losses seen during the springtime over Antarctica, when nearly two-thirds of the ozone is lost.
We have 10 separate instruments for measuring solar and thermal radiation. They include pyrheliometers, pyranometers, and pyrgeometers.
Three different instruments are measuring aerosol particles and concentrations.
The nephelometer measures the scattering part of the extinction coefficient due to particles. First, air is pulled into the instrument through a filter that removes all the aerosol particles. Scattered light intensity is measured and recorded as the background. Then ambient air is introduced into the instrument, and the intensity of the scattered light is measured again. Simple subtraction then yields the contribution due to aerosols. This cycle is performed at four wavelengths of light (450, 550, 700, and 850 nanometers) to give a size dis tribution. Particle sizes measured range from 0.1 to 1.0 micrometers.
The Pollack Condensation Nuclei Counter uses light attenuation by cloud formation due to particle growth [from adiabatic expansion of condensation nuclei (CN)] in supersaturated air to measure CN. The CN are typically 0.001 to 0.1 micrometers in radius. These particles are also called "Aitken nuclei."
The TSI CNC also measures Aitken nuclei. It uses a laser diode light source and a single-particle counting optical detector to count individual particles approximately 0.014 micrometers and larger that have been grown onto alcohol droplets.
Bordering the Clean Air Sector is our 23-meter-high meteorological walk-up tower. Located on the tower, we have an anemometer, for determining wind speed and direction; three aspirated and one nonaspirated thermometers; and a hygrometer, for measuring frost-point. Located inside the Clean Air Facility are two barometers.
Data from all of the instruments are transferred electronically to the CMDL offices in Boulder. This data transfer is performed daily, weekly, or monthly depending on the instrument. Most of the instrument data-acquisition systems have programs that automatically "zip" the data files, which can then be FTPed to Boulder for postprocessing and analysis.
In addition to the CMDL-sponsored research, six cooperative research projects are conducted at the South Pole for various universities and other government agencies. These projects include isotopic composition for atmospheric CO2, CO2 flask sampling, oxygen and nitrogen flask sampling, snow sampling for hydrogen peroxide, measuring the distribution of specific and anthropogenic radionuclides in surface air (filter sampling), and quantifying the production rate of radiocarbon by galactic cosmic rays.
This program has been operated in cooperation with, and through support from, the National Science Foundation for more than 25 years.
Hofmann, D.J. 1996. Recovery of antarctic ozone hole. Nature, 384, 222-223.
Hofmann, D.J., J.T. Peterson, and R.M. Rosson (Eds.). 1996. Climate Monitoring and Diagnostics Laboratory, No. 23, Summary Report 1994-95. Boulder, Colorado: NOAA/ERL, U.S. Department of Commerce.